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Adoption

Adoption is a process whereby a person assumes the parenting of another, usually a child, from that person's biological or legal parent or parents. Legal adoptions permanently transfer all rights and responsibilities, along with filiation, from the biological parents to the adoptive parents.

Unlike guardianship or other systems designed for the care of the young, adoption is intended to effect a permanent change in status and as such requires societal recognition, either through legal or religious sanction. Historically, some societies have enacted specific laws governing adoption, while others used less formal means (notably contracts that specified inheritance rights and parental responsibilities without an accompanying transfer of filiation). Modern systems of adoption, arising in the 20th century, tend to be governed by comprehensive statutes and regulations.

Antiquity
While the modern form of adoption emerged in the United States, forms of the practice appeared throughout history. The Code of Hammurabi, for example, details the rights of adopters and the responsibilities of adopted individuals at length. The practice of adoption in ancient Rome is well-documented in the Codex Justinianus.
 * Adoption for the well-born

Markedly different from the modern period, ancient adoption practices put emphasis on the political and economic interests of the adopter, providing a legal tool that strengthened political ties between wealthy families and created male heirs to manage estates. The use of adoption by the aristocracy is well-documented: many of Rome's emperors were adopted sons. Adrogation was a kind of Roman adoption in which the person adopted consented to be adopted by another.

Infant adoption during Antiquity appears rare. Abandoned children were often picked up for slavery and composed a significant percentage of the Empire's slave supply. Roman legal records indicate that foundlings were occasionally taken in by families and raised as a son or daughter. Although not normally adopted under Roman Law, the children, called alumni, were reared in an arrangement similar to guardianship, being considered the property of the father who abandoned them.

Other ancient civilizations, notably India and China, used some form of adoption as well. Evidence suggests the goal of this practice was to ensure the continuity of cultural and religious practices; in contrast to the Western idea of extending family lines. In ancient India, secondary sonship, clearly denounced by the Rigveda, continued, in a limited and highly ritualistic form, so that an adopter might have the necessary funerary rites performed by a son. China had a similar idea of adoption with males adopted solely to perform the duties of ancestor worship.

The practice of adopting the children of family members and close friends was common among the cultures of Polynesia including Hawaii where the custom was referred to as hānai.

Middle ages to modern period

 * Adoption and commoners

The nobility of the Germanic, Celtic, and Slavic cultures that dominated Europe after the decline of the Roman Empire denounced the practice of adoption. In medieval society, bloodlines were paramount; a ruling dynasty lacking a "natural-born" heir apparent was replaced, a stark contrast to Roman traditions. The evolution of European law reflects this aversion to adoption. English common law, for instance, did not permit adoption since it contradicted the customary rules of inheritance. In the same vein, France's Napoleonic Code made adoption difficult, requiring adopters to be over the age of 50, sterile, older than the adopted person by at least 15 years, and to have fostered the adoptee for at least six years. Some adoptions continued to occur, however, but became informal, based on ad hoc contracts. For example, in the year 737, in a charter from the town of Lucca, three adoptees were made heirs to an estate. Like other contemporary arrangements, the agreement stressed the responsibility of the adopted rather than adopter, focusing on the fact that, under the contract, the adoptive father was meant to be cared for in his old age; an idea that is similar to the conceptions of adoption under Roman law.

Europe's cultural makeover marked a period of significant innovation for adoption. Without support from the nobility, the practice gradually shifted toward abandoned children. Abandonment levels rose with the fall of the empire and many of the foundlings were left on the doorstep of the Church. Initially, the clergy reacted by drafting rules to govern the exposing, selling, and rearing of abandoned children. The Church's innovation, however, was the practice of oblation, whereby children were dedicated to lay life within monastic institutions and reared within a monastery. This created the first system in European history in which abandoned children did not have legal, social, or moral disadvantages. As a result, many of Europe's abandoned and orphaned children became alumni of the Church, which in turn took the role of adopter. Oblation marks the beginning of a shift toward institutionalization, eventually bringing about the establishment of the foundling hospital and orphanage.

As the idea of institutional care gained acceptance, formal rules appeared about how to place children into families: boys could become apprenticed to an artisan and girls might be married off under the institution's authority. Institutions informally adopted out children as well, a mechanism treated as a way to obtain cheap labor, demonstrated by the fact that when the adopted died their bodies were returned by the family to the institution for burial.

This system of apprenticeship and informal adoption extended into the 19th century, today seen as a transitional phase for adoption history. Under the direction of social welfare activists, orphan asylums began to promote adoptions based on sentiment rather than work; children were placed out under agreements to provide care for them as family members instead of under contracts for apprenticeship. The growth of this model is believed to have contributed to the enactment of the first modern adoption law in 1851 by the Commonwealth of Massachusetts, unique in that it codified the ideal of the "best interests of the child". Despite its intent, though, in practice, the system operated much the same as earlier incarnations. The experience of the Boston Female Asylum (BFA) is a good example, which had up to 30% of its charges adopted out by 1888. Officials of the BFA noted that, although the asylum promoted otherwise, adoptive parents did not distinguish between indenture and adoption: "We believe," the asylum officials said, "that often, when children of a younger age are taken to be adopted, the adoption is only another name for service."

Modern period

 * Adopting to create a family

The next stage of adoption's evolution fell to the emerging nation of the United States. Rapid immigration and the American Civil War resulted in unprecedented overcrowding of orphanages and foundling homes in the mid-nineteenth century. Charles Loring Brace, a Protestant minister, became appalled by the legions of homeless waifs roaming the streets of New York City. Brace considered the abandoned youth, particularly Catholics, to be the most dangerous element challenging the city's order.

His solution was outlined in The Best Method of Disposing of Our Pauper and Vagrant Children (1859), which started the Orphan Train movement. The orphan trains eventually shipped an estimated 200,000 children from the urban centers of the East to the nation's rural regions. The children were generally indentured, rather than adopted, to families who took them in. As in times past, some children were raised as members of the family while others were used as farm laborers and household servants. The sheer size of the displacement—the largest migration of children in history—and the degree of exploitation that occurred, gave rise to new agencies and a series of laws that promoted adoption arrangements rather than indenture. The hallmark of the period is Minnesota's adoption law of 1917, which mandated investigation of all placements and limited record access to those involved in the adoption.

During the same period, the Progressive movement swept the United States with a critical goal of ending the prevailing orphanage system. The culmination of such efforts came with the First White House Conference on the Care of Dependent Children called by President Theodore Roosevelt in 1909, where it was declared that the nuclear family represented "the highest and finest product of civilization" and was best able to serve as primary caretaker for the abandoned and orphaned. As late as 1923, only two percent of children without parental care were in adoptive homes, with the balance in foster arrangements and orphanages. Less than forty years later, nearly one-third were in adoptive homes.

Nevertheless, the popularity of eugenic ideas in America put up obstacles to the growth of adoption. There were grave concerns about the genetic quality of illegitimate and indigent children, perhaps best exemplified by the influential writings of Henry H. Goddard, who protested against adopting children of unknown origin, saying,

"Now it happens that some people are interested in the welfare and high development of the human race; but leaving aside those exceptional people, all fathers and mothers are interested in the welfare of their own families. The dearest thing to the parental heart is to have the children marry well and rear a noble family. How short-sighted it is then for such a family to take into its midst a child whose pedigree is absolutely unknown; or, where, if it were partially known, the probabilities are strong that it would show poor and diseased stock, and that if a marriage should take place between that individual and any member of the family the offspring would be degenerates." The period 1945 to 1974, the baby scoop era, saw rapid growth and acceptance of adoption as a means to build a family. Illegitimate births rose three-fold after World War II, as sexual mores changed. Simultaneously, the scientific community began to stress the dominance of nurture over genetics, chipping away at eugenic stigmas. In this environment, adoption became the obvious solution for both unwed people and infertile couples.

Taken together, these trends resulted in a new American model for adoption. Following its Roman predecessor, Americans severed the rights of the original parents while making adopters the new parents in the eyes of the law. Two innovations were added: 1) adoption was meant to ensure the "best interests of the child", the seeds of this idea can be traced to the first American adoption law in Massachusetts, and 2) adoption became infused with secrecy, eventually resulting in the sealing of adoption and original birth records by 1945. The origin of the move toward secrecy began with Charles Loring Brace, who introduced it to prevent children from the Orphan Trains from returning to or being reclaimed by their parents. Brace feared the impact of the parents' poverty, in general, and Catholic religion, in particular, on the youth. This tradition of secrecy was carried on by the later Progressive reformers when drafting of American laws.

The number of adoptions in the United States peaked in 1970. It is uncertain what caused the subsequent decline. Likely contributing factors in the 1960s and 1970s include a decline in the fertility rate, associated with the introduction of the pill, the completion of legalization of artificial birth control methods, the introduction of federal funding to make family planning services available to the young and low-income, and the legalization of abortion. In addition, the years of the late 1960s and early 1970s saw a dramatic change in society's view of illegitimacy and in the legal rights of those born outside of wedlock. In response, family preservation efforts grew so that few children born out of wedlock today are adopted. Ironically, adoption is far more visible and discussed in society today, yet it is less common.

The American model of adoption eventually proliferated globally. England and Wales established their first formal adoption law in 1926. The Netherlands passed its law in 1956. Sweden made adoptees full members of the family in 1959. West Germany enacted its first laws in 1977. Additionally, the Asian powers opened their orphanage systems to adoption, influenced as they were by Western ideas following colonial rule and military occupation. In France, local public institutions accredit candidates for adoption, who can then contact orphanages abroad or ask for the support of NGOs. The system does not involve fees, but gives considerable power to social workers whose decisions may restrict adoption to "standard" families (middle-age, medium to high income, heterosexual, Caucasian).

Adoption is today practiced globally. The table below provides a snapshot of Western adoption rates. Adoption in the United States still occurs at rates nearly three times those of its peers even though the number of children awaiting adoption has held steady in recent years, between 100,000 and 125,000 during the period 2009 to 2018.

Forms of adoption
Contemporary adoption practices can be open or closed.
 * Open adoption allows identifying information to be communicated between adoptive and biological parents and, perhaps, interaction between kin and the adopted person. Open adoption can be an informal arrangement subject to termination by adoptive parents who have sole custody over the child. In some jurisdictions, the biological and adoptive parents may enter into a legally enforceable and binding agreement concerning visitation, exchange of information, or other interaction regarding the child. As of February 2009, 24 U.S. states allowed legally enforceable open adoption contract agreements to be included in the adoption finalization.
 * The practice of closed adoption (also called confidential or secret adoption), which has not been the norm for most of modern history, seals all identifying information, maintaining it as secret and preventing disclosure of the adoptive parents', biological kin's, and adoptees' identities. Nevertheless, closed adoption may allow the transmittal of non-identifying information such as medical history and religious and ethnic background. Today, as a result of safe haven laws passed by some U.S. states, secret adoption is seeing renewed influence. In so-called "safe-haven" states, infants can be left anonymously at hospitals, fire departments, or police stations within a few days of birth, a practice criticized by some adoption advocacy organizations as being retrograde and dangerous.

How adoptions originate

Adoptions can occur between related or unrelated individuals. Historically, most adoptions occurred within a family. The most recent data from the U.S. indicates that about half of adoptions are currently between related individuals. A common example of this is a "step-parent adoption", where the new partner of a parent legally adopts a child from the parent's previous relationship. Intra-family adoption can also occur through surrender, as a result of parental death, or when the child cannot otherwise be cared for and a family member agrees to take over.

Adoption is not always a voluntary process. In some countries, for example in the U.K., one of the main origins of children being placed for adoption is that they have been removed from the birth home, often by a government body such as the local authority. There are a number of reasons why children are removed including abuse and neglect, which can have a lasting impact on the adoptee. Social workers in many cases will be notified of a safeguarding concern in relation to a child and will make enquiries into the child's well-being. Social workers will often seek means of keeping a child together with the birth family, for example, by providing additional support to the family before considering removal of a child. A court of law will often then make decisions regarding the child's future, for example, whether they can return to the birth family, enter into foster care or be adopted.

Infertility is the main reason parents seek to adopt children they are not related to. One study shows this accounted for 80% of unrelated infant adoptions and half of adoptions through foster care. Estimates suggest that 11–24% of Americans who cannot conceive or carry to term attempt to build a family through adoption, and that the overall rate of never-married American women who adopt is about 1.4%. Other reasons people adopt are numerous although not well documented. These may include wanting to cement a new family following divorce or death of one parent, compassion motivated by religious or philosophical conviction, to avoid contributing to overpopulation out of the belief that it is more responsible to care for otherwise parent-less children than to reproduce, to ensure that inheritable diseases (e.g., Tay–Sachs disease) are not passed on, and health concerns relating to pregnancy and childbirth. Although there are a range of reasons, the most recent study of experiences of women who adopt suggests they are most likely to be 40–44 years of age, to be currently married, to have impaired fertility, and to be childless.

Unrelated adoptions may occur through the following mechanisms:
 * Private domestic adoptions: under this arrangement, charities and for-profit organizations act as intermediaries, bringing together prospective adoptive parents with families who want to place a child, all parties being residents of the same country. Alternatively, prospective adoptive parents sometimes avoid intermediaries and connect with women directly, often with a written contract; this is not permitted in some jurisdictions. Private domestic adoption accounts for a significant portion of all adoptions; in the United States, for example, nearly 45% of adoptions are estimated to have been arranged privately.
 * Foster care adoption: this is a type of domestic adoption where a child is initially placed in public care. Many times the foster parents take on the adoption when the children become legally free. Its importance as an avenue for adoption varies by country. Of the 127,500 adoptions in the U.S. in 2000, about 51,000 or 40% were through the foster care system.
 * International adoption: this involves the placing of a child for adoption outside that child's country of birth. This can occur through public or private agencies. In some countries, such as Sweden, these adoptions account for the majority of cases (see above table). The U.S. example, however, indicates there is wide variation by country since adoptions from abroad account for less than 15% of its cases. More than 60,000 Russian children have been adopted in the United States since 1992, and a similar number of Chinese children were adopted from 1995 to 2005. The laws of different countries vary in their willingness to allow international adoptions. Recognizing the difficulties and challenges associated with international adoption, and in an effort to protect those involved from the corruption and exploitation which sometimes accompanies it, the Hague Conference on Private International Law developed the Hague Adoption Convention, which came into force on 1 May 1995 and has been ratified by 105 countries as of February 2024.
 * Embryo adoption: based on the donation of embryos remaining after one couple's in vitro fertilization treatments have been completed; embryos are given to another individual or couple, followed by the placement of those embryos into the recipient woman's uterus, to facilitate pregnancy and childbirth. In the United States, embryo adoption is governed by property law rather than by the court systems, in contrast to traditional adoption.
 * Common law adoption: this is an adoption that has not been recognized beforehand by the courts, but where a parent, without resorting to any formal legal process, leaves his or her children with a friend or relative for an extended period of time. At the end of a designated term of (voluntary) co-habitation, as witnessed by the public, the adoption is then considered binding, in some courts of law, even though not initially sanctioned by the court. The particular terms of a common-law adoption are defined by each legal jurisdiction. For example, the U.S. state of California recognizes common law relationships after co-habitation of 2 years. The practice is called "private fostering" in Britain.

Disruption and dissolution
Although adoption is often described as forming a "forever" family, the relationship can be ended at any time. The legal termination of an adoption is called disruption. In U.S. terminology, adoptions are disrupted if they are ended before being finalized, and they are dissolved if the relationship is ended afterwards. It may also be called a failed adoption. After legal finalization, the disruption process is usually initiated by adoptive parents via a court petition and is analogous to divorce proceedings. It is a legal avenue unique to adoptive parents as disruption/dissolution does not apply to biological kin, although biological family members are sometimes disowned or abandoned.

Ad hoc studies performed in the U.S., however, suggest that between 10 and 25 percent of adoptions through the child welfare system (e.g., excluding babies adopted from other countries or step-parents adopting their stepchildren) disrupt before they are legally finalized and from 1 to 10 percent are dissolved after legal finalization. The wide range of values reflects the paucity of information on the subject and demographic factors such as age; it is known that teenagers are more prone to having their adoptions disrupted than young children.

Adoption by same-sex couples
Joint adoption by same-sex couples is legal in 34 countries as of March 2022, and additionally in various sub-national territories. Adoption may also be in the form of step-child adoption (6 additional countries), wherein one partner in a same-sex couple adopts the child of the other. Most countries that have same-sex marriage allow joint adoption by those couples, the exceptions being Ecuador (no adoption by same-sex couples), Taiwan (step-child adoption only) and Mexico (in one third of states with same-sex marriage). A few countries with civil unions or lesser marriage rights nonetheless allow step- or joint adoption.In 2019, the ACS enhanced its approach to measuring same-sex couple households, explicitly distinguishing between same-sex and opposite-sex spouses or partners.

Same-sex parents, according to the ACS, were predominantly female. Notably, 22.5% of female same-sex couple households had children under 18, in contrast to 6.6% of male same-sex couple households. In homes with children, neither male nor female same-sex couples were more likely to have biological children, but male same-sex couples were more likely to adopt children and less likely to have stepchildren.

Parenting
The biological relationship between a parent and child is important, and the separation of the two has led to concerns about adoption. The traditional view of adoptive parenting received empirical support from a Princeton University study of 6,000 adoptive, step, and foster families in the United States and South Africa from 1968 to 1985; the study indicated that food expenditures in households with mothers of non-biological children (when controlled for income, household size, hours worked, age, etc.) were significantly less for adoptees, step-children, and foster children, causing the researchers to speculate that people are less interested in sustaining the genetic lines of others. This theory is supported in another more qualitative study wherein adoptive relationships marked by sameness in likes, personality, and appearance, were associated with both adult adoptees and adoptive parents reporting being happier with the adoption.

Other studies provide evidence that adoptive relationships can form along other lines. A study evaluating the level of parental investment indicates strength in adoptive families, suggesting that parents who adopt invest more time in their children than other parents, and concludes "...adoptive parents enrich their children's lives to compensate for the lack of biological ties and the extra challenges of adoption." Another recent study found that adoptive families invested more heavily in their adopted children, for example, by providing further education and financial support. Noting that adoptees seemed to be more likely to experience problems such as drug addiction, the study speculated that adoptive parents might invest more in adoptees not because they favor them, but because they are more likely than genetic children to need the help.

Psychologists' findings regarding the importance of early mother-infant bonding created some concern about whether parents who adopt older infants or toddlers after birth have missed some crucial period for the child's development. However, research on The Mental and Social Life of Babies suggested that the "parent-infant system", rather than a bond between biologically related individuals, is an evolved fit between innate behavior patterns of all human infants and equally evolved responses of human adults to those infant behaviors. Thus nature "ensures some initial flexibility with respect to the particular adults who take on the parental role."

Beyond the foundational issues, the unique questions posed for adoptive parents are varied. They include how to respond to stereotypes, answering questions about heritage, and how best to maintain connections with biological kin when in an open adoption. One author suggests a common question adoptive parents have is: "Will we love the child even though he/she is not our biological child?" A specific concern for many parents is accommodating an adoptee in the classroom. Familiar lessons like "draw your family tree" or "trace your eye color back through your parents and grandparents to see where your genes come from" could be hurtful to children who were adopted and do not know this biological information. Numerous suggestions have been made to substitute new lessons, e.g., focusing on "family orchards".

Adopting older children presents other parenting issues. Some children from foster care have histories of maltreatment, such as physical and psychological neglect, physical abuse, and sexual abuse, and are at risk of developing psychiatric problems. Such children are at risk of developing a disorganized attachment. Studies by Cicchetti et al. (1990, 1995) found that 80% of abused and maltreated infants in their sample exhibited disorganized attachment styles. Disorganized attachment is associated with a number of developmental problems, including dissociative symptoms, as well as depressive, anxious, and acting-out symptoms. "Attachment is an active process—it can be secure or insecure, maladaptive or productive." In the U.K., some adoptions fail because the adoptive parents do not get sufficient support to deal with difficult, traumatized children. This is a false economy as local authority care for these children is extremely expensive.

Concerning developmental milestones, studies from the Colorado Adoption Project examined genetic influences on adoptee maturation, concluding that cognitive abilities of adoptees reflect those of their adoptive parents in early childhood but show little similarity by adolescence, resembling instead those of their biological parents and to the same extent as peers in non-adoptive families.

Similar mechanisms appear to be at work in the physical development of adoptees. Danish and American researchers conducting studies on the genetic contribution to body mass index found correlations between an adoptee's weight class and his biological parents' BMI while finding no relationship with the adoptive family environment. Moreover, about one-half of inter-individual differences were due to individual non-shared influences.

These differences in development appear to play out in the way young adoptees deal with major life events. In the case of parental divorce, adoptees have been found to respond differently from children who have not been adopted. While the general population experienced more behavioral problems, substance use, lower school achievement, and impaired social competence after parental divorce, the adoptee population appeared to be unaffected in terms of their outside relationships, specifically in their school or social abilities.

Recent research has shown that adoptive parenting may have impacts on adoptive children, it has been shown that warm adoptive parenting reduces internalizing and externalizing problems of the adoptive children over time. Another study shows that warm adoptive parenting at 27 months predicted lower levels of child externalizing problems at ages 6 and 7.

Effects on the original parents
Several factors affect the decision to release or raise the child. White adolescents tend to give up their babies to non-relatives, whereas black adolescents are more likely to receive support from their own community in raising the child and also in the form of informal adoption by relatives. Studies by Leynes and by Festinger and Young, Berkman, and Rehr found that, for pregnant adolescents, the decision to release the child for adoption depended on the attitude toward adoption held by the adolescent's mother. Another study found that pregnant adolescents whose mothers had a higher level of education were more likely to release their babies for adoption. Research suggests that women who choose to release their babies for adoption are more likely to be younger, enrolled in school, and have lived in a two-parent household at age 10, than those who kept and raised their babies.

There is limited research on the consequences of adoption for the original parents, and the findings have been mixed. One study found that those who released their babies for adoption were less comfortable with their decision than those who kept their babies. However, levels of comfort over both groups were high, and those who released their child were similar to those who kept their child in ratings of life satisfaction, relationship satisfaction, and positive future outlook for schooling, employment, finances, and marriage. Subsequent research found that adolescent mothers who chose to release their babies for adoption were more likely to experience feelings of sorrow and regret over their decision than those who kept their babies. However, these feelings decreased significantly from one year after birth to the end of the second year.

More recent research found that in a sample of mothers who had released their children for adoption four to 12 years prior, every participant had frequent thoughts of their lost child. For most, thoughts were both negative and positive in that they produced both feelings of sadness and joy. Those who experienced the greatest portion of positive thoughts were those who had open, rather than closed or time-limited mediated, adoptions.

In another study that compared mothers who released their children to those who raised them, mothers who released their children were more likely to delay their next pregnancy, to delay marriage, and to complete job training. However, both groups reached lower levels of education than their peers who were never pregnant. Another study found similar consequences for choosing to release a child for adoption. Adolescent mothers who released their children were more likely to reach a higher level of education and to be employed than those who kept their children. They also waited longer before having their next child. Most of the research that exists on adoption effects on the birth parents was conducted with samples of adolescents, or with women who were adolescents when carrying their babies—little data exists for birth parents from other populations. Furthermore, there is a lack of longitudinal data that may elucidate long-term social and psychological consequences for birth parents who choose to place their children for adoption.

Development of adoptees
Previous research on adoption has led to assumptions that indicate that there is a heightened risk in terms of psychological development and social relationships for adoptees. Yet, such assumptions have been clarified as flawed due to methodological failures. But more recent studies have been supportive in indicating more accurate information and results about the similarities, differences and overall lifestyles of adoptees. Adoptees are four times more likely to attempt suicide than other people.

Evidence about the development of adoptees can be supported in newer studies. It can be said that adoptees, in some respect, tend to develop differently from the general population. This can be seen in many aspects of life, but usually can be found as a greater risk around the time of adolescence. For example, it has been found that many adoptees experience difficulty in establishing a sense of identity.

Identity
There are many ways in which the concept of identity can be defined. It is true in all cases that identity construction is an ongoing process of development, change and maintenance of identifying with the self. Research has shown that adolescence is a time of identity progression rather than regression. One's identity tends to lack stability in the beginning years of life but gains a more stable sense in later periods of childhood and adolescence. Typically associated with a time of experimentation, there are endless factors that go into the construction of one's identity. As well as being many factors, there are many types of identities one can associate with. Some categories of identity include gender, sexuality, class, racial and religious, etc. For transracial and international adoptees, tension is generally found in the categories of racial, ethnic and national identification. Because of this, the strength and functionality of family relationships play a huge role in its development and outcome of identity construction. Transracial and transnational adoptees tend to develop feelings of a lack of acceptance because of such racial, ethnic, and cultural differences. Therefore, exposing transracial and transnational adoptees to their "cultures of origin" is important in order to better develop a sense of identity and appreciation for cultural diversity. Identity construction and reconstruction for transnational adoptees the instant they are adopted. For example, based upon specific laws and regulations of the United States, the Child Citizen Act of 2000 makes sure to grant immediate U.S. citizenship to adoptees.

Identity is defined both by what one is and what one is not. Adoptees born into one family lose an identity and then borrow one from the adopting family. The formation of identity is a complicated process and there are many factors that affect its outcome. From a perspective of looking at issues in adoption circumstances, the people involved and affected by adoption (the biological parent, the adoptive parent and the adoptee) can be known as the "triad members and state". Adoption may threaten triad members' sense of identity. Triad members often express feelings related to confused identity and identity crises because of differences between the triad relationships. Adoption, for some, precludes a complete or integrated sense of self. Triad members may experience themselves as incomplete, deficient, or unfinished. They state that they lack feelings of well-being, integration, or solidity associated with a fully developed identity.

Influences
Family plays a vital role in identity formation. This is not only true in childhood but also in adolescence. Identity (gender/sexual/ethnic/religious/family) is still forming during adolescence and family holds a vital key to this. The research seems to be unanimous; a stable, secure, loving, honest and supportive family in which all members feel safe to explore their identity is necessary for the formation of a sound identity. Transracial and International adoptions are some factors that play a significant role in the identity construction of adoptees. Many tensions arise from relationships built between the adoptee(s) and their family. These include being "different" from the parent(s), developing a positive racial identity, and dealing with racial/ethnic discrimination. It has been found that multicultural and transnational youth tend to identify with their parents origin of culture and ethnicity rather than their residing location, yet it is sometimes hard to balance an identity between the two because school environments tend to lack diversity and acknowledgment regarding such topics. These tensions also tend to create questions for the adoptee, as well as the family, to contemplate. Some common questions include what will happen if the family is more naïve to the ways of socially constructed life? Will tensions arise if this is the case? What if the very people that are supposed to be modeling a sound identity are in fact riddled with insecurities? Ginni Snodgrass answers these questions in the following way. The secrecy in an adoptive family and the denial that the adoptive family is different builds dysfunction into it. "... social workers and insecure adoptive parents have structured a family relationship that is based on dishonesty, evasions and exploitation. To believe that good relationships will develop on such a foundation is psychologically unsound" (Lawrence). Secrecy erects barriers to forming a healthy identity.

The research says that the dysfunction, untruths and evasiveness that can be present in adoptive families not only makes identity formation impossible, but also directly works against it. What effect on identity formation is present if the adoptee knows they are adopted but has no information about their biological parents? Silverstein and Kaplan's research states that adoptees lacking medical, genetic, religious, and historical information are plagued by questions such as "Who am I?" "Why was I born?" "What is my purpose?" This lack of identity may lead adoptees, particularly in adolescent years, to seek out ways to belong in a more extreme fashion than many of their non-adopted peers. Adolescent adoptees are overrepresented among those who join sub-cultures, run away, become pregnant, or totally reject their families.

Concerning developmental milestones, studies from the Colorado Adoption Project examined genetic influences on adoptee maturation, concluding that cognitive abilities of adoptees reflect those of their adoptive parents in early childhood but show little similarity by adolescence, resembling instead those of their biological parents and to the same extent as peers in non-adoptive families.

Similar mechanisms appear to be at work in the physical development of adoptees. Danish and American researchers conducting studies on the genetic contribution to body mass index found correlations between an adoptee's weight class and his biological parents' BMI while finding no relationship with the adoptive family environment. Moreover, about one-half of inter-individual differences were due to individual non-shared influences.

These differences in development appear to play out in the way young adoptees deal with major life events. In the case of parental divorce, adoptees have been found to respond differently from children who have not been adopted. While the general population experienced more behavioral problems, substance use, lower school achievement, and impaired social competence after parental divorce, the adoptee population appeared to be unaffected in terms of their outside relationships, specifically in their school or social abilities.

The adoptee population does, however, seem to be more at risk for certain behavioral issues. Researchers from the University of Minnesota studied adolescents who had been adopted and found that adoptees were twice as likely as non-adopted people to develop oppositional defiant disorder (ODD) and attention deficit hyperactivity disorder (ADHD), with an 8% rate in the general population. Suicide risks were also significantly greater than the general population. Swedish researchers found both international and domestic adoptees undertook suicide at much higher rates than non-adopted peers; with international adoptees and female international adoptees, in particular, at highest risk.

Nevertheless, work on adult adoptees has found that the additional risks faced by adoptees are largely confined to adolescence. Young adult adoptees were shown to be alike with adults from biological families and scored better than adults raised in alternative family types including single parent and step-families. Moreover, while adult adoptees showed more variability than their non-adopted peers on a range of psychosocial measures, adult adoptees exhibited more similarities than differences with adults who had not been adopted. There have been many cases of remediation or the reversibility of early trauma. For example, in one of the earliest studies conducted, Professor Goldfarb in England concluded that some children adjust well socially and emotionally despite their negative experiences of institutional deprivation in early childhood. Other researchers also found that prolonged institutionalization does not necessarily lead to emotional problems or character defects in all children. This suggests that there will always be some children who fare well, who are resilient, regardless of their experiences in early childhood. Furthermore, much of the research on psychological outcomes for adoptees draws from clinical populations. This suggests that conclusions such that adoptees are more likely to have behavioral problems such as ODD and ADHD may be biased. Since the proportion of adoptees that seek mental health treatment is small, psychological outcomes for adoptees compared to those for the general population are more similar than some researchers propose.

While adoption studies have shown that by adulthood the personalities of adopted siblings are little or no more similar than random pairs of strangers, the parenting style of adoptive parents may still play a role in the outcome of their adoptive children. Research has suggested that adoptive parents can have impacts on adoptees as well, several recent studies have shown that warm adoptive parenting can reduce behavioral problems of adopted children over time.

Mental health
Adopted children are more likely to experience psychological and behavioral problems than non-adopted peers. Children who were older than four at the time of their adoption experience more psychological problems than those who were younger.

According to study in the UK, adopted children can have mental health problems that do not improve even four years after their adoption. Children with multiple adverse childhood experiences are more likely to have mental health problems. The study suggests that to identify and tread mental health problems early, care professionals and the adopting parents need detailed biographical information about the child's life. Another study in the UK suggests that adopted children are more likely to suffer from post-traumatic stress (PTS) than the general population. Their PTS symptoms depend on the type of adverse experiences they went through and knowledge of their history offers an option for tailored support.

Adoptees of LGBT parents
There is evidence that shows the adoptees of LGBT families and those in heterosexual families have no significant differences in development. One of the main arguments used against same-sex adoption is that a child needs a mother and a father in the home to develop properly. However, a 2013 study of predictors for psychological outcomes of adoptees showed that family type (hetero, gay, lesbian) does not affect the child's adjustment; rather the preparedness of the adoptive parent(s), and health of relationship to partner, and other contextual factors predicted later adjustment in early placed adoptees. Along with this, a 2009 study showed again that sexual orientation of parents does not affect externalizing and internalized problems, but family functioning and income can affect adjustment, especially for older adoptees.

Late discovery adoptees
Late Discovery Adoption is a term used to describe the situation where an adopted individual first discovers that they are adopted at a later age than is universally considered to be appropriate, often well into adulthood. Adopted individuals who discover their adoption status at a later age are referred to as Late Discovery Adoptees (LDAs). Failure of the adoptive parent(s) to disclose adoption status to a child is an outdated adoption practice that was once fairly common for adoptees born in the 1930s, 1940s and 1950s. Since the 1970s, it has been socially unacceptable to keep the truth from adopted individuals regarding their genetic origins. The discovery of the deception regarding true parentage and that one is, in fact, a Late Discovery Adoptee can add "layers of trauma, loss, betrayal, identity confusion, and disorganization upon learning the truth."

Public perception of adoption
In Western culture, many see that the common image of a family being that of a heterosexual couple with biological children. This idea places alternative family forms outside the norm. As a consequence – research indicates – disparaging views of adoptive families exist, along with doubts concerning the strength of their family bonds.

The most recent adoption attitudes survey completed by the Evan Donaldson Institute provides further evidence of this stigma. Nearly one-third of the surveyed population believed adoptees are less-well adjusted, more prone to medical issues, and predisposed to drug and alcohol problems. Additionally, 40–45% thought adoptees were more likely to have behavior problems and trouble at school. In contrast, the same study indicated adoptive parents were viewed favorably, with nearly 90% describing them as "lucky, advantaged, and unselfish".

The majority of people state that their primary source of information about adoption comes from friends and family and the news media. Nevertheless, most people report the media provides them a favorable view of adoption; 72% indicated receiving positive impressions. There is, however, still substantial criticism of the media's adoption coverage. Some adoption blogs, for example, criticized Meet the Robinsons for using outdated orphanage imagery as did advocacy non-profit The Evan B. Donaldson Adoption Institute.

The stigmas associated with adoption are amplified for children in foster care. Negative perceptions result in the belief that such children are so troubled it would be impossible to adopt them and create "normal" families. A 2004 report from the Pew Commission on Children in Foster Care has shown that the number of children waiting in foster care doubled since the 1980s and now remains steady at about a half-million a year."

Attitude toward Adoption Questionnaire (ATAQ): this questionnaire was first developed by Abdollahzadeh, Chaloyi and Mahmoudi(2019). Preliminary Edition: This questionnaire has 23 items based on the Likert scale of 1 (totally Disagree), up to 5 (Totally Agree) being obtained after refining the items designed to construct the present tool and per-study study. The analysis of item and initial psychometric analyses indicate that there are two factors in it. Items 3-10-11-12-14-15-16-17-19-20-21 are reversed and the rest are graded positively. The results of exploratory factor analysis by main components with varimax rotation indicated two components of attitude toward adoption being named respectively cognitive as the aspects of attitude toward adoption and behavioral-emotional aspects of attitude toward adoption. These two components explained 43.25% of the variance of the total sample. Cronbach's alpha coefficient was used to measure the reliability of the questionnaire. Cronbach's alpha coefficient was 0.709 for the whole questionnaire, 0.71 for the first component, and 0.713 for the second one. In addition, there was a significant positive relationship between desired social tendencies and the cognitive aspect of attitude toward adoption as well as the behavioral -emotional aspects of attitude toward adoption (P ≤ 0.01).

Forced adoption
Family preservation is the emphasis that, if possible, mothers and children should be kept together. In the U.S., this was clearly illustrated by the shift in policy of the New York Foundling Home, an adoption-institution that is among the country's oldest and one that had pioneered sealed records. It established three new principles including "to prevent placements of children...", reflecting the belief that children would be better served by staying with their biological families, a striking shift in policy that remains in force today. In addition, groups such as Origins USA (founded in 1997) started to actively speak about family preservation and the rights of mothers. The intellectual tone of these reform movements was influenced by the publishing of The Primal Wound by Nancy Verrier. "Primal wound" is described as the "devastation which the infant feels because of separation from its birth mother. It is the deep and consequential feeling of abandonment which the baby adoptee feels after the adoption and which may continue for the rest of his life."

Forced adoption has also been enforced with the rationale of child welfare. The children of unwed or single mothers are commonly the target of such forced adoption. This was prominent during baby scoop era in the 1950s through the 1970s in the anglosphere. The children of parents in poverty have also been targeted for forced adoption under the rational of child welfare. This was often the case for Verdingkinder or "contract children" in Switzerland between the 1850s through the middle of the twentieth century.

Forced assimilation
Removing children of ethnic minorities from their families to be adopted by those of the dominant ethnic group has been used as a method of forced assimilation. Forced adoption based on ethnicity occurred during World War II. In German-occupied Poland, it is estimated that 200,000 Polish children with purportedly Aryan traits were removed from their families and given to German or Austrian couples, and only 25,000 returned to their families after the war. The Stolen Generation of Aboriginal people in Australia were affected by similar policies, as were Native Americans in the United States and First Nations of Canada. These practices have become significant social and political issues in recent years, and in many cases the policies have changed. The United States, for example, now has the 1978 Indian Child Welfare Act, which allows the tribe and family of a Native American child to be involved in adoption decisions, with preference being given to adoption within the child's tribe. While forced assimilation usually revolves around ethnicity, assimilating children of political minorities has also occurred. In Spain under Francisco Franco's 1939–1975 dictatorship the newborns of some left-wing opponents of the regime, or unmarried or poor couples, were removed from their mothers and adopted. New mothers were frequently told their babies had died suddenly after birth and the hospital had taken care of their burials, when in fact they were given or sold to another family. It is believed that up to 300,000 babies were involved. These system—which allegedly involved doctors, nurses, nuns and priests—outlived Franco's death in 1975 and carried on as an illegal baby trafficking network until 1987 when a new law regulating adoption was introduced.

Commercialized adoption
Adoption is usually managed by judges, bureaucrats and social workers. Profiting from giving or receiving orphans has incentivized abusive practices.

Baby farming
Baby farming is the practice of accepting custody of a child in return for payment. This was most common in Victorian Britain. Illegitimacy and its attendant social stigma were usually the impetus for a mother's decision to give her child to a baby farmer. Baby 'farmers' would sometimes neglect or murder the babies to keep costs down.

Child harvesting
Child harvesting is the practice of rearing human children to be sold, typically for adoption. Poor mothers have used street clinics, known as "baby factories", to deliver babies to be adopted by richer women for payment. While this can be voluntary, baby factories have also coerced or abducted women into such facilities to be raped in order to sell their babies for adoption. Organized rings in Nairobi are known to abduct the children of homeless mothers sleeping on the street. During the One Child Policy in China, when women were only allowed to have one child, local governments would often allow the woman to give birth and then they would take the baby away. Child traffickers, often paid by the government, would sell the children to orphanages that would arrange international adoptions worth tens of thousands of dollars, turning a profit for the government.

Official records
Adoption practices have changed significantly over the course of the 20th century, with each new movement labeled, in some way, as reform. Beginning in the 1970s, efforts to improve adoption became associated with opening records and encouraging family preservation. These ideas arose from suggestions that the secrecy inherent in modern adoption may influence the process of forming an identity, create confusion regarding genealogy, and provide little in the way of medical history.

Open records: After a legal adoption in the United States, an adopted person's original birth certificate is usually amended and replaced with a new post-adoption birth certificate. The names of any birth parents listed on the original birth certificate are replaced on an amended certificate with the names of the adoptive parents, making it appear that the child was born to the adoptive parents. Beginning in the late 1930s and continuing through the 1970s, state laws allowed for the sealing of original birth certificates after an adoption and, except in some states, made the original birth certificate unavailable to the adopted person even at the age of majority.

Adopted people have long sought to undo these laws so that they can obtain their own original birth certificates. Movements to unseal original birth certificates and other adoption records for adopted people proliferated in the 1970s along with increased acceptance of illegitimacy. In the United States, Jean Paton founded Orphan Voyage in 1954, and Florence Fisher founded the Adoptees' Liberty Movement Association (ALMA) in 1971, calling sealed records "an affront to human dignity". While in 1975, Emma May Vilardi created the first mutual-consent registry, the International Soundex Reunion Registry (ISRR), allowing those separated by adoption to locate one another. and Lee Campbell and other birthmothers established CUB (Concerned United Birthparents). Similar ideas were taking hold globally with grass-roots organizations like Parent Finders in Canada and Jigsaw in Australia. In 1975, England and Wales opened records on moral grounds.

By 1979, representatives of 32 organizations from 33 states, Canada and Mexico gathered in Washington, DC, to establish the American Adoption Congress (AAC) passing a unanimous resolution: "Open Records complete with all identifying information for all members of the adoption triad, birthparents, adoptive parents and adoptee at the adoptee's age of majority (18 or 19, depending on state) or earlier if all members of the triad agree." Later years saw the evolution of more militant organizations such as Bastard Nation (founded in 1996), groups that helped overturn sealed records in Alabama, Delaware, New Hampshire, Oregon, Tennessee, and Maine. A coalition of New York and national adoptee rights activists successfully worked to overturn a restrictive 83-year-old law in 2019, and adult adopted people born in New York, as well as their descendants, today have the right to request and obtain their own original birth certificates. As of 2021, ten states in the United States recognize the right of adult adopted people to obtain their own original birth certificates, including Alabama, Alaska, Colorado, Connecticut, Kansas, Maine, New Hampshire, New York, Oregon and Rhode Island. Connecticut in 2021 became the tenth state to restore an adopted person's right to request and obtain their original birth certificates.

Language of adoption
The language of adoption is changing and evolving, and since the 1970s has been a controversial issue tied closely to adoption reform efforts. The controversy arises over the use of terms which, while designed to be more appealing or less offensive to some persons affected by adoption, may simultaneously cause offense or insult to others. This controversy illustrates the problems in adoption, as well as the fact that coining new words and phrases to describe ancient social practices will not necessarily alter the feelings and experiences of those affected by them. Two of the contrasting sets of terms are commonly referred to as "positive adoption language" (PAL) (sometimes called "respectful adoption language" (RAL)), and "honest adoption language" (HAL).

Positive adoptive language (PAL)
In the 1970s, as adoption search and support organizations developed, there were challenges to the language in common use at the time. As books like Adoption Triangle by Sorosky, Pannor and Baran were published, and support groups formed like CUB (Concerned United Birthparents), a major shift from "natural parent" to "birthparent" occurred. Along with the change in times and social attitudes came additional examination of the language used in adoption.

Social workers and other professionals in the field of adoption began changing terms of use to reflect what was being expressed by the parties involved. In 1979, Marietta Spencer wrote "The Terminology of Adoption" for The Child Welfare League of America (CWLA), which was the basis for her later work "Constructive Adoption Terminology". This influenced Pat Johnston's "Positive Adoption Language" (PAL) and "Respectful Adoption Language" (RAL). The terms contained in "Positive Adoption Language" include the terms "birth mother" (to replace the terms "natural mother" and "real mother"), and "placing" (to replace the term "surrender"). These kinds of recommendations encouraged people to be more aware of their use of adoption terminology.

Honest adoption language (HAL)
"Honest Adoption Language" refers to a set of terms that proponents say reflect the point of view that: (1) family relationships (social, emotional, psychological or physical) that existed prior to the legal adoption often continue past this point or endure in some form despite long periods of separation, and that (2) mothers who have "voluntarily surrendered" children to adoption (as opposed to involuntary terminations through court-authorized child-welfare proceedings) seldom view it as a choice that was freely made, but instead describe scenarios of powerlessness, lack of resources, and overall lack of choice. It also reflects the point of view that the term "birth mother" is derogatory in implying that the woman has ceased being a mother after the physical act of giving birth. Proponents of HAL liken this to the mother being treated as a "breeder" or "incubator". Terms included in HAL include terms that were used before PAL, including "natural mother", "first mother", and "surrendered for adoption".

Inclusive adoption language
There are supporters of various lists, developed over many decades, and there are persons who find them lacking, created to support an agenda, or furthering division. All terminology can be used to demean or diminish, uplift or embrace. In addressing the linguistic problem of naming, Edna Andrews says that using "inclusive" and "neutral" language is based upon the concept that "language represents thought, and may even control thought."

Advocates of inclusive language defend it as inoffensive-language usage whose goal is multi-fold:

 * 1) The rights, opportunities, and freedoms of certain people are restricted because they are reduced to stereotypes.
 * 2) Stereotyping is mostly implicit, unconscious, and facilitated by the availability of pejorative labels and terms.
 * 3) Rendering the labels and terms socially unacceptable, people then must consciously think about how they describe someone unlike themselves.
 * 4) When labeling is a conscious activity, the described person's individual merits become apparent, rather than his or her stereotype.

A common problem is that terms chosen by an identity group, as acceptable descriptors of themselves, can be used in negative ways by detractors. This compromises the integrity of the language and turns what was intended to be positive into negative or vice versa, thus often devaluing acceptability, meaning and use.

Language at its best honors the self-referencing choices of the persons involved, uses inclusive terms and phrases, and is sensitive to the feelings of the primary parties. Language evolves with social attitudes and experiences.

Reunion
Estimates for the extent of search behavior by adoptees have proven elusive; studies show significant variation. In part, the problem stems from the small adoptee population which makes random surveying difficult, if not impossible.

Nevertheless, some indication of the level of search interest by adoptees can be gleaned from the case of England and Wales which opened adoptees' birth records in 1975. The U.K. Office for National Statistics has projected that 33% of all adoptees would eventually request a copy of their original birth records, exceeding original forecasts made in 1975 when it was believed that only a small fraction of the adoptee population would request their records. The projection is known to underestimate the true search rate, however, since many adoptees of the era get their birth records by other means.

The research literature states adoptees give four reasons for desiring reunion: 1) they wish for a more complete genealogy, 2) they are curious about events leading to their conception, birth, and relinquishment, 3) they hope to pass on information to their children, and 4) they have a need for a detailed biological background, including medical information. It is speculated by adoption researchers, however, that the reasons given are incomplete: although such information could be communicated by a third-party, interviews with adoptees, who sought reunion, found they expressed a need to actually meet biological relations.

It appears the desire for reunion is linked to the adoptee's interaction with and acceptance within the community. Internally focused theories suggest some adoptees possess ambiguities in their sense of self, impairing their ability to present a consistent identity. Reunion helps resolve the lack of self-knowledge.

Externally focused theories, in contrast, suggest that reunion is a way for adoptees to overcome social stigma. First proposed by Goffman, the theory has four parts: 1) adoptees perceive the absence of biological ties as distinguishing their adoptive family from others, 2) this understanding is strengthened by experiences where non-adoptees suggest adoptive ties are weaker than blood ties, 3) together, these factors engender, in some adoptees, a sense of social exclusion, and 4) these adoptees react by searching for a blood tie that reinforces their membership in the community. The externally focused rationale for reunion suggests adoptees may be well adjusted and happy within their adoptive families, but will search as an attempt to resolve experiences of social stigma.

Some adoptees reject the idea of reunion. It is unclear, though, what differentiates adoptees who search from those who do not. One paper summarizes the research, stating, "...attempts to draw distinctions between the searcher and non-searcher are no more conclusive or generalizable than attempts to substantiate ... differences between adoptees and nonadoptees."

In sum, reunions can bring a variety of issues for adoptees and parents. Nevertheless, most reunion results appear to be positive. In the largest study to date (based on the responses of 1,007 adoptees and relinquishing parents), 90% responded that reunion was a beneficial experience. This does not, however, imply ongoing relationships were formed between adoptee and parent nor that this was the goal.

Cultural variations
Attitudes and laws regarding adoption vary greatly. Whereas all cultures make arrangements whereby children whose birth parents are unavailable to rear them can be brought up by others, not all cultures have the concept of adoption, that is treating unrelated children as equivalent to biological children of the adoptive parents. Under Islamic Law, for example, adopted children must keep their original surname to be identified with blood relations, and, traditionally, women wear a hijab in the presence of males in their adoptive households. In Egypt, these cultural distinctions have led to making adoption illegal opting instead for a system of foster care.

Homecoming Day
In some countries, such as the United States, "Homecoming Day" is the day when an adoptee is officially united with their new adoptive family.

title: Adoption


text:
Synchronous optical networking

Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission rates data can also be transferred via an electrical interface. The method was developed to replace the plesiochronous digital hierarchy (PDH) system for transporting large amounts of telephone calls and data traffic over the same fiber without the problems of synchronization.

SONET and SDH, which are essentially the same, were originally designed to transport circuit mode communications (e.g., DS1, DS3) from a variety of different sources, but they were primarily designed to support real-time, uncompressed, circuit-switched voice encoded in PCM format. The primary difficulty in doing this prior to SONET/SDH was that the synchronization sources of these various circuits were different. This meant that each circuit was actually operating at a slightly different rate and with different phase. SONET/SDH allowed for the simultaneous transport of many different circuits of differing origin within a single framing protocol. SONET/SDH is not a complete communications protocol in itself, but a transport protocol (not a 'transport' in the OSI Model sense).

Due to SONET/SDH's essential protocol neutrality and transport-oriented features, SONET/SDH was the choice for transporting the fixed length Asynchronous Transfer Mode (ATM) frames also known as cells. It quickly evolved mapping structures and concatenated payload containers to transport ATM connections. In other words, for ATM (and eventually other protocols such as Ethernet), the internal complex structure previously used to transport circuit-oriented connections was removed and replaced with a large and concatenated frame (such as STS-3c) into which ATM cells, IP packets, or Ethernet frames are placed.

Both SDH and SONET are widely used today: SONET in the United States and Canada, and SDH in the rest of the world. Although the SONET standards were developed before SDH, it is considered a variation of SDH because of SDH's greater worldwide market penetration. SONET is subdivided into four sublayers with some factor such as the path, line, section and physical layer.

The SDH standard was originally defined by the European Telecommunications Standards Institute (ETSI), and is formalised as International Telecommunication Union (ITU) standards G.707, G.783, G.784, and G.803. The SONET standard was defined by Telcordia and American National Standards Institute (ANSI) standard T1.105. which define the set of transmission formats and transmission rates in the range above 51.840 Mbit/s.

Difference from PDH
SDH differs from Plesiochronous Digital Hierarchy (PDH) in that the exact rates that are used to transport the data on SONET/SDH are tightly synchronized across the entire network, using atomic clocks. This synchronization system allows entire inter-country networks to operate synchronously, greatly reducing the amount of buffering required between elements in the network. Both SONET and SDH can be used to encapsulate earlier digital transmission standards, such as the PDH standard, or they can be used to directly support either Asynchronous Transfer Mode (ATM) or so-called packet over SONET/SDH (POS) networking. Therefore, it is inaccurate to think of SDH or SONET as communications protocols in and of themselves; they are generic, all-purpose transport containers for moving both voice and data. The basic format of a SONET/SDH signal allows it to carry many different services in its virtual container (VC), because it is bandwidth-flexible.

Protocol overview
SONET and SDH often use different terms to describe identical features or functions. This can cause confusion and exaggerate their differences. With a few exceptions, SDH can be thought of as a superset of SONET.

SONET is a set of transport containers that allow for delivery of a variety of protocols, including traditional telephony, ATM, Ethernet, and TCP/IP traffic. SONET therefore is not in itself a native communications protocol and should not be confused as being necessarily connection-oriented in the way that term is usually used.

The protocol is a heavily multiplexed structure, with the header interleaved between the data in a complex way. This permits the encapsulated data to have its own frame rate and be able to "float around" relative to the SDH/SONET frame structure and rate. This interleaving permits a very low latency for the encapsulated data. Data passing through equipment can be delayed by at most 32 microseconds (μs), compared to a frame rate of 125 μs; many competing protocols buffer the data during such transits for at least one frame or packet before sending it on. Extra padding is allowed for the multiplexed data to move within the overall framing, as the data is clocked at a different rate than the frame rate. The protocol is made more complex by the decision to permit this padding at most levels of the multiplexing structure, but it improves all-around performance.

Basic transmission unit
The basic unit of framing in SDH is a STM-1 (Synchronous Transport Module, level 1), which operates at 155.520 megabits per second (Mbit/s). SONET refers to this basic unit as an STS-3c (Synchronous Transport Signal 3, concatenated). When the STS-3c is carried over OC-3, it is often colloquially referred to as OC-3c, but this is not an official designation within the SONET standard as there is no physical layer (i.e. optical) difference between an STS-3c and 3 STS-1s carried within an OC-3.

SONET offers an additional basic unit of transmission, the STS-1 (Synchronous Transport Signal 1) or OC-1, operating at 51.84 Mbit/s—exactly one third of an STM-1/STS-3c/OC-3c carrier. This speed is dictated by the bandwidth requirements for PCM-encoded telephonic voice signals: at this rate, an STS-1/OC-1 circuit can carry the bandwidth equivalent of a standard DS-3 channel, which can carry 672 64-kbit/s voice channels. In SONET, the STS-3c signal is composed of three multiplexed STS-1 signals; the STS-3c may be carried on an OC-3 signal. Some manufacturers also support the SDH equivalent of the STS-1/OC-1, known as STM-0.

Framing
In packet-oriented data transmission, such as Ethernet, a packet frame usually consists of a header and a payload. The header is transmitted first, followed by the payload (and possibly a trailer, such as a CRC). In synchronous optical networking, this is modified slightly. The header is termed the overhead, and instead of being transmitted before the payload, is interleaved with it during transmission. Part of the overhead is transmitted, then part of the payload, then the next part of the overhead, then the next part of the payload, until the entire frame has been transmitted.

In the case of an STS-1, the frame is 810 octets in size, while the STM-1/STS-3c frame is 2,430 octets in size. For STS-1, the frame is transmitted as three octets of overhead, followed by 87 octets of payload. This is repeated nine times, until 810 octets have been transmitted, taking 125 μs. In the case of an STS-3c/STM-1, which operates three times faster than an STS-1, nine octets of overhead are transmitted, followed by 261 octets of payload. This is also repeated nine times until 2,430 octets have been transmitted, also taking 125 μs. For both SONET and SDH, this is often represented by displaying the frame graphically: as a block of 90 columns and nine rows for STS-1, and 270 columns and nine rows for STM1/STS-3c. This representation aligns all the overhead columns, so the overhead appears as a contiguous block, as does the payload.

The internal structure of the overhead and payload within the frame differs slightly between SONET and SDH, and different terms are used in the standards to describe these structures. Their standards are extremely similar in implementation, making it easy to interoperate between SDH and SONET at any given bandwidth.

In practice, the terms STS-1 and OC-1 are sometimes used interchangeably, though the OC designation refers to the signal in its optical form. It is therefore incorrect to say that an OC-3 contains 3 OC-1s: an OC-3 can be said to contain 3 STS-1s.

SDH frame

The Synchronous Transport Module, level 1 (STM-1) frame is the basic transmission format for SDH—the first level of the synchronous digital hierarchy. The STM-1 frame is transmitted in exactly 125 μs, therefore, there are 8,000 frames per second on a 155.52 Mbit/s OC-3 fiber-optic circuit. The STM-1 frame consists of overhead and pointers plus information payload. The first nine columns of each frame make up the section overhead and administrative unit pointers, and the last 261 columns make up the information payload. The pointers (H1, H2, H3 bytes) identify administrative units (AU) within the information payload. Thus, an OC-3 circuit can carry 150.336 Mbit/s of payload, after accounting for the overhead.

Carried within the information payload, which has its own frame structure of nine rows and 261 columns, are administrative units identified by pointers. Also within the administrative unit are one or more virtual containers (VCs). VCs contain path overhead and VC payload. The first column is for path overhead; it is followed by the payload container, which can itself carry other containers. Administrative units can have any phase alignment within the STM frame, and this alignment is indicated by the pointer in row four.

The section overhead (SOH) of a STM-1 signal is divided into two parts: the regenerator section overhead (RSOH) and the multiplex section overhead (MSOH). The overheads contain information from the transmission system itself, which is used for a wide range of management functions, such as monitoring transmission quality, detecting failures, managing alarms, data communication channels, service channels, etc.

The STM frame is continuous and is transmitted in a serial fashion: byte-by-byte, row-by-row.

Transport overhead
The transport overhead is used for signaling and measuring transmission error rates, and is composed as follows:

 * Section overhead: Called regenerator section overhead (RSOH) in SDH terminology: 27 octets containing information about the frame structure required by the terminal equipment.
 * Line overhead: Called multiplex section overhead (MSOH) in SDH: 45 octets containing information about error correction and Automatic Protection Switching messages (e.g., alarms and maintenance messages) as may be required within the network. The error correction is included for STM-16 and above.
 * Administrative unit (AU) pointer: Points to the location of the J1 byte in the payload (the first byte in the virtual container).

Path virtual envelope
Data transmitted from end to end is referred to as path data. It is composed of two components:
 * Payload overhead (POH): 9 octets used for end-to-end signaling and error measurement.
 * Payload: User data (774 bytes for STM-0/STS-1, or 2,430 octets for STM-1/STS-3c)

For STS-1, the payload is referred to as the synchronous payload envelope (SPE), which in turn has 18 stuffing bytes, leading to the STS-1 payload capacity of 756 bytes.

The STS-1 payload is designed to carry a full PDH DS3 frame. When the DS3 enters a SONET network, path overhead is added, and that SONET network element (NE) is said to be a path generator and terminator. The SONET NE is line terminating if it processes the line overhead. Note that wherever the line or path is terminated, the section is terminated also. SONET regenerators terminate the section, but not the paths or line.

An STS-1 payload can also be subdivided into seven virtual tributary groups (VTGs). Each VTG can then be subdivided into four VT1.5 signals, each of which can carry a PDH DS1 signal. A VTG may instead be subdivided into three VT2 signals, each of which can carry a PDH E1 signal. The SDH equivalent of a VTG is a TUG-2; VT1.5 is equivalent to VC-11, and VT2 is equivalent to VC-12.

Three STS-1 signals may be multiplexed by time-division multiplexing to form the next level of the SONET hierarchy, the OC-3 (STS-3), running at 155.52 Mbit/s. The signal is multiplexed by interleaving the bytes of the three STS-1 frames to form the STS-3 frame, containing 2,430 bytes and transmitted in 125 μs.

Higher-speed circuits are formed by successively aggregating multiples of slower circuits, their speed always being immediately apparent from their designation. For example, four STS-3 or AU4 signals can be aggregated to form a 622.08 Mbit/s signal designated OC-12 or STM-4.

The highest rate commonly deployed is the OC-768 or STM-256 circuit, which operates at rate of just under 38.5 Gbit/s. Where fiber exhaustion is a concern, multiple SONET signals can be transported over multiple wavelengths on a single fiber pair by means of wavelength-division multiplexing, including dense wavelength-division multiplexing (DWDM) and coarse wavelength-division multiplexing (CWDM). DWDM circuits are the basis for all modern submarine communications cable systems and other long-haul circuits.

SONET/SDH and relationship to 10 Gigabit Ethernet
Another type of high-speed data networking circuit is 10 Gigabit Ethernet (10GbE). The Gigabit Ethernet Alliance created two 10 Gigabit Ethernet variants: a local area variant (LAN PHY) with a line rate of 10.3125 Gbit/s, and a wide area variant (WAN PHY) with the same line rate as OC-192/STM-64 (9,953,280 kbit/s). The WAN PHY variant encapsulates Ethernet data using a lightweight SDH/SONET frame, so as to be compatible at a low level with equipment designed to carry SDH/SONET signals, whereas the LAN PHY variant encapsulates Ethernet data using 64B/66B line coding.

However, 10 Gigabit Ethernet does not explicitly provide any interoperability at the bitstream level with other SDH/SONET systems. This differs from WDM system transponders, including both coarse and dense wavelength-division multiplexing systems (CWDM and DWDM) that currently support OC-192 SONET signals, which can normally support thin-SONET–framed 10 Gigabit Ethernet.

SONET/SDH data rates
User throughput must not deduct path overhead from the payload bandwidth, but path-overhead bandwidth is variable based on the types of cross-connects built across the optical system.

Note that the data-rate progression starts at 155 Mbit/s and increases by multiples of four. The only exception is OC-24, which is standardized in ANSI T1.105, but not a SDH standard rate in ITU-T G.707. Other rates, such as OC-9, OC-18, OC-36, OC-96, and OC-1536, are defined but not commonly deployed; most are considered orphaned rates.

Physical layer
The physical layer refers to the first layer in the OSI networking model. The ATM and SDH layers are the regenerator section level, digital line level, transmission path level, virtual path level, and virtual channel level. The physical layer is modeled on three major entities: transmission path, digital line and the regenerator section. The regenerator section refers to the section and photonic layers. The photonic layer is the lowest SONET layer and it is responsible for transmitting the bits to the physical medium. The section layer is responsible for generating the proper STS-N frames which are to be transmitted across the physical medium. It deals with issues such as proper framing, error monitoring, section maintenance, and orderwire. The line layer ensures reliable transport of the payload and overhead generated by the path layer. It provides synchronization and multiplexing for multiple paths. It modifies overhead bits relating to quality control. The path layer is SONET's highest level layer. It takes data to be transmitted and transforms them into signals required by the line layer, and adds or modifies the path overhead bits for performance monitoring and protection switching.

Overall functionality
Network management systems are used to configure and monitor SDH and SONET equipment either locally or remotely.

The systems consist of three essential parts, covered later in more detail:
 * Software running on a 'network management system terminal' e.g. workstation, dumb terminal or laptop housed in an exchange/ central office.
 * Transport of network management data between the 'network management system terminal' and the SONET/ SDH equipment e.g. using TL1/ Q3 protocols.
 * Transport of network management data between SDH/ SONET equipment using 'dedicated embedded data communication channels' (DCCs) within the section and line overhead.

The main functions of network management thereby include:
 * Network and network-element provisioning
 * In order to allocate bandwidth throughout a network, each network element must be configured. Although this can be done locally, through a craft interface, it is normally done through a network management system (sitting at a higher layer) that in turn operates through the SONET/SDH network management network.

 * Software upgrade
 * Network-element software upgrades are done mostly through the SONET/SDH management network in modern equipment.

 * Performance management
 * Network elements have a very large set of standards for performance management. The performance-management criteria allow not only monitoring the health of individual network elements, but isolating and identifying most network defects or outages. Higher-layer network monitoring and management software allows the proper filtering and troubleshooting of network-wide performance management, so that defects and outages can be quickly identified and resolved.

Consider the three parts defined above:

Network management system terminal

 * Local Craft interface
 * Local "craftspersons" (telephone network engineers) can access a SDH/ SONET network element on a "craft port" and issue commands through a dumb terminal or terminal emulation program running on a laptop. This interface can also be attached to a console server, allowing for remote out-of-band management and logging.

This will often consist of software running on a Workstation covering a number of SDH/SONET network elements
 * Network management system (sitting at a higher layer)

TL1/ Q3 Protocols
SONET equipment is often managed with the TL1 protocol. TL1 is a telecom language for managing and reconfiguring SONET network elements. The command language used by a SONET network element, such as TL1, must be carried by other management protocols, such as SNMP, CORBA, or XML. SDH has been mainly managed using the Q3 interface protocol suite defined in ITU recommendations Q.811 and Q.812. With the convergence of SONET and SDH on switching matrix and network elements architecture, newer implementations have also offered TL1.
 * TL1
 * Q3

Most SONET NEs have a limited number of management interfaces defined:

 * TL1 Electrical interface
 * The electrical interface, often a 50-ohm coaxial cable, sends SONET TL1 commands from a local management network physically housed in the central office where the SONET network element is located. This is for local management of that network element and, possibly, remote management of other SONET network elements.

Dedicated embedded data communication channels (DCCs)

 * SONET and SDH have dedicated data communication channels (DCCs) within the section and line overhead for management traffic. Generally, section overhead (regenerator section in SDH) is used. According to ITU-T G.7712, there are three modes used for management:
 * IP-only stack, using PPP as data-link
 * OSI-only stack, using LAP-D as data-link
 * Dual (IP+OSI) stack using PPP or LAP-D with tunneling functions to communicate between stacks.

To handle all of the possible management channels and signals, most modern network elements contain a router for the network commands and underlying (data) protocols.

Equipment
With advances in SONET and SDH chipsets, the traditional categories of network elements are no longer distinct. Nevertheless, as network architectures have remained relatively constant, even newer equipment (including multi-service provisioning platforms) can be examined in light of the architectures they will support. Thus, there is value in viewing new, as well as traditional, equipment in terms of the older categories.

Regenerator
Traditional regenerators terminate the section overhead, but not the line or path. Regenerators extend long-haul routes in a way similar to most regenerators, by converting an optical signal that has already traveled a long distance into electrical format and then retransmitting a regenerated high-power signal.

Since the late 1990s, regenerators have been largely replaced by optical amplifiers. Also, some of the functionality of regenerators has been absorbed by the transponders of wavelength-division multiplexing systems.

STS multiplexer and demultiplexer
STS multiplexer and demultiplexer provide the interface between an electrical tributary network and the optical network.

Add-drop multiplexer
Add-drop multiplexers (ADMs) are the most common type of network elements. Traditional ADMs were designed to support one of the network architectures, though new generation systems can often support several architectures, sometimes simultaneously. ADMs traditionally have a high-speed side (where the full line rate signal is supported), and a low-speed side, which can consist of electrical as well as optical interfaces. The low-speed side takes in low-speed signals, which are multiplexed by the network element and sent out from the high-speed side, or vice versa.

Digital cross connect system
Recent digital cross connect systems (DCSs or DXCs) support numerous high-speed signals, and allow for cross-connection of DS1s, DS3s and even STS-3s/12c and so on, from any input to any output. Advanced DCSs can support numerous subtending rings simultaneously.

Network architectures
SONET and SDH have a limited number of architectures defined. These architectures allow for efficient bandwidth usage as well as protection (i.e. the ability to transmit traffic even when part of the network has failed), and are fundamental to the worldwide deployment of SONET and SDH for moving digital traffic. Every SDH/SONET connection on the optical physical layer uses two optical fibers, regardless of the transmission speed.

Linear Automatic Protection Switching
Linear Automatic Protection Switching (APS), also known as 1+1, involves four fibers: two working fibers (one in each direction), and two protection fibers. Switching is based on the line state, and may be unidirectional (with each direction switching independently), or bidirectional (where the network elements at each end negotiate so that both directions are generally carried on the same pair of fibers).

Unidirectional path-switched ring
In unidirectional path-switched rings (UPSRs), two redundant (path-level) copies of protected traffic are sent in either direction around a ring. A selector at the egress node determines which copy has the highest quality, and uses that copy, thus coping if one copy deteriorates due to a broken fiber or other failure. UPSRs tend to sit nearer to the edge of a network, and as such are sometimes called collector rings. Because the same data is sent around the ring in both directions, the total capacity of a UPSR is equal to the line rate N of the OC-N ring. For example, in an OC-3 ring with 3 STS-1s used to transport 3 DS-3s from ingress node A to the egress node D, 100 percent of the ring bandwidth (N=3) would be consumed by nodes A and D. Any other nodes on the ring could only act as pass-through nodes. The SDH equivalent of UPSR is subnetwork connection protection (SNCP); SNCP does not impose a ring topology, but may also be used in mesh topologies.

Bidirectional line-switched ring
Bidirectional line-switched ring (BLSR) comes in two varieties: two-fiber BLSR and four-fiber BLSR. BLSRs switch at the line layer. Unlike UPSR, BLSR does not send redundant copies from ingress to egress. Rather, the ring nodes adjacent to the failure reroute the traffic "the long way" around the ring on the protection fibers. BLSRs trade cost and complexity for bandwidth efficiency, as well as the ability to support "extra traffic" that can be pre-empted when a protection switching event occurs. In four-fiber ring, either single node failures, or multiple line failures can be supported, since a failure or maintenance action on one line causes the protection fiber connecting two nodes to be used rather than looping it around the ring.

BLSRs can operate within a metropolitan region or, often, will move traffic between municipalities. Because a BLSR does not send redundant copies from ingress to egress, the total bandwidth that a BLSR can support is not limited to the line rate N of the OC-N ring, and can actually be larger than N depending upon the traffic pattern on the ring. In the best case, all traffic is between adjacent nodes. The worst case is when all traffic on the ring egresses from a single node, i.e., the BLSR is serving as a collector ring. In this case, the bandwidth that the ring can support is equal to the line rate N of the OC-N ring. This is why BLSRs are seldom, if ever, deployed in collector rings, but often deployed in inter-office rings. The SDH equivalent of BLSR is called Multiplex Section-Shared Protection Ring (MS-SPRING).

Synchronization
Clock sources used for synchronization in telecommunications networks are rated by quality, commonly called a stratum. Typically, a network element uses the highest quality stratum available to it, which can be determined by monitoring the synchronization status messages (SSM) of selected clock sources.

Synchronization sources available to a network element are:
 * Local external timing
 * This is generated by an atomic cesium clock or a satellite-derived clock by a device in the same central office as the network element. The interface is often a DS1, with sync-status messages supplied by the clock and placed into the DS1 overhead.

 * Line-derived timing
 * A network element can choose (or be configured) to derive its timing from the line-level, by monitoring the S1 sync-status bytes to ensure quality.

 * Holdover
 * As a last resort, in the absence of higher quality timing, a network element can go into a holdover mode until higher-quality external timing becomes available again. In this mode, the network element uses its own timing circuits as a reference.

Timing loops
A timing loop occurs when network elements in a network are each deriving their timing from other network elements, without any of them being a "master" timing source. This network loop will eventually see its own timing "float away" from any external networks, causing mysterious bit errors—and ultimately, in the worst cases, massive loss of traffic. The source of these kinds of errors can be hard to diagnose. In general, a network that has been properly configured should never find itself in a timing loop, but some classes of silent failures could nevertheless cause this issue.

Next-generation SONET/SDH
SONET/SDH development was originally driven by the need to transport multiple PDH signals—like DS1, E1, DS3, and E3—along with other groups of multiplexed 64 kbit/s pulse-code modulated voice traffic. The ability to transport ATM traffic was another early application. In order to support large ATM bandwidths, concatenation was developed, whereby smaller multiplexing containers (e.g., STS-1) are inversely multiplexed to build up a larger container (e.g., STS-3c) to support large data-oriented pipes.

One problem with traditional concatenation, however, is inflexibility. Depending on the data and voice traffic mix that must be carried, there can be a large amount of unused bandwidth left over, due to the fixed sizes of concatenated containers. For example, fitting a 100 Mbit/s Fast Ethernet connection inside a 155 Mbit/s STS-3c container leads to considerable waste. More important is the need for all intermediate network elements to support newly introduced concatenation sizes. This problem was overcome with the introduction of Virtual Concatenation.

Virtual concatenation (VCAT) allows for a more arbitrary assembly of lower-order multiplexing containers, building larger containers of fairly arbitrary size (e.g., 100 Mbit/s) without the need for intermediate network elements to support this particular form of concatenation. Virtual concatenation leverages the X.86 or Generic Framing Procedure (GFP) protocols in order to map payloads of arbitrary bandwidth into the virtually concatenated container.

The Link Capacity Adjustment Scheme (LCAS) allows for dynamically changing the bandwidth via dynamic virtual concatenation, multiplexing containers based on the short-term bandwidth needs in the network.

The set of next-generation SONET/SDH protocols that enable Ethernet transport is referred to as Ethernet over SONET/SDH (EoS).

End of life and retirement
SONET/SDH was used by internet access providers for large customers, and is no longer competitive in the supply of private circuits. Development has stagnated for the last decade (2020) and both suppliers of equipment and operators of SONET/SDH networks are migrating to other technologies such as OTN and wide area Ethernet.

British Telecom has recently (March 2020) closed down their KiloStream and Mega Stream products which were the last large scale uses of the BT SDH. BT has also ceased new connections to their SDH network which indicates withdrawal of services soon.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Synchronous optical networking


text:
Yorkshire pudding

Yorkshire pudding is a baked pudding made from a batter of eggs, flour, and milk or water. A common English side dish, it is a versatile food that can be served in numerous ways depending on its ingredients, size, and the accompanying components of the meal. As a first course, it can be served with onion gravy. For a main course, it may be served with meat and gravy, and is part of the traditional Sunday roast, but can also be filled with foods such as bangers and mash to make a meal. Sausages can be added to make toad in the hole. In some parts of England, (especially the Midlands) the Yorkshire pudding can be eaten as a dessert, with a sweet sauce called raspberry vinegar. The 18th-century cookery writer Hannah Glasse was the first to use the term "Yorkshire pudding" in print.

Yorkshire puddings are similar to Dutch baby pancakes, and to popovers, an American light roll made from an egg batter.

History

When wheat flour began to come into common use for making cakes and puddings, cooks in northern England (Yorkshire) devised a means of making use of the fat that dropped into the dripping pan to cook a batter pudding while the meat roasted. In 1737, a recipe for "a dripping pudding" was published in Sir Alexander William George Cassey's book The Whole Duty of a Woman:

"Make a good batter as for pancakes; put in a hot toss-pan over the fire with a bit of butter to fry the bottom a little then put the pan and butter under a shoulder of mutton, instead of a dripping pan, keeping frequently shaking it by the handle and it will be light and savoury, and fit to take up when your mutton is enough; then turn it in a dish and serve it hot."

Similar instructions were published during 1747 in the book The Art of Cookery made Plain and Easy by Hannah Glasse, with the name 'Yorkshire pudding'. It was she who renamed the original version, known as Dripping Pudding, which had been cooked in England for centuries, although these puddings were much flatter than the puffy versions made in modern times. William Sitwell suggests that the pudding got the name 'Yorkshire' due to the region's association with coal and the higher temperatures this produced which helped to make the batter crisper.

Originally, the Yorkshire pudding was served as a first course with thick gravy to dull the appetite with the low-cost ingredients so that the diners would not eat so much of the more expensive meat in the next course. Because the rich gravy from the roast meat drippings was used with the first course, the main meat and vegetable course was often served with a parsley or white sauce. In poorer households, the pudding was often served as the only course. Using dripping, a simple meal was made with flour, eggs and milk. This was traditionally eaten with a gravy or sauce, to moisten the pudding.

The Yorkshire pudding is meant to rise. The Royal Society of Chemistry suggested in 2008 that "A Yorkshire pudding isn't a Yorkshire pudding if it is less than 4 in tall".

Baking method
Yorkshire pudding is baked by pouring a batter made from milk, flour and eggs into oiled and preheated baking pans (ramekins or muffin tins in the case of miniature puddings). A basic formula uses 200ml flour and 200ml milk with four eggs (also 200ml). Water produces a lighter, crisper, but less sweet pudding than using milk. They can also be baked in cast-iron frying pans or similar. A 1926 recipe involves covering the pudding with greaseproof paper to steam it and then serving it with jam, butter and sugar.

Yorkshire Pudding Day
National Yorkshire Pudding Day has been celebrated on the first Sunday in February in Britain since 2007. It is celebrated on 13 October in the United States.

title: Yorkshire pudding