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Ibn Battuta

Abū Abd Allāh Muḥammad ibn Abd Allāh Al-Lawātī (24 February 1304 – 1368/1369), commonly known as Ibn Battuta, was a Maghrebi traveller, explorer and scholar. Over a period of thirty years from 1325 to 1354, Ibn Battuta visited most of North Africa, the Middle East, East Africa, Central Asia, South Asia, Southeast Asia, China, the Iberian Peninsula, and West Africa. Near the end of his life, he dictated an account of his journeys, titled A Gift to Those Who Contemplate the Wonders of Cities and the Marvels of Travelling, but commonly known as The Rihla.

Ibn Battuta travelled more than any other explorer in pre-modern history, totalling around 117,000 km, surpassing Zheng He with about 50,000 km and Marco Polo with 24,000 km. There have been doubts over the historicity of some of Ibn Battuta's travels, particularly as they reach farther East.

Name
Ibn Battuta is a patronymic literally meaning "son of the duckling". His most common full name is given as Abu Abdullah Muhammad ibn Battuta. In his travelogue, the Rihla, he gives his full name as Shams al-Din Abu’Abdallah Muhammad ibn’Abdallah ibn Muhammad ibn Ibrahim ibn Muhammad ibn Yusuf Lawati al-Tanji ibn Battuta.

Early life

All that is known about Ibn Battuta's life comes from the autobiographical information included in the account of his travels, which records that he was of Berber descent, born into a family of Islamic legal scholars (known as qadis in the Muslim traditions of Morocco) in Tangier on 24 February 1304, during the reign of the Marinid dynasty. His family belonged to a Berber tribe known as the Lawata. As a young man, he would have studied at a Sunni Maliki madhhab (Islamic jurisprudence school), the dominant form of education in North Africa at that time. Maliki Muslims requested that Ibn Battuta serve as their religious judge, as he was from an area where it was practised.

First pilgrimage
On 2 Rajab in the Muslim year 725 Anno Hegirae (14 June 1325 Anno Domini on the Christian calendar), at the age of twenty-one, Ibn Battuta set off from his home town on a hajj, or pilgrimage, to Mecca, a journey that would ordinarily take sixteen months. He was eager to learn more about far-away lands and craved adventure. He would not return to Morocco again for 24 years.

"I set out alone, having neither fellow-traveller in whose companionship I might find cheer, nor caravan whose part I might join, but swayed by an overmastering impulse within me and a desire long-cherished in my bosom to visit these illustrious sanctuaries. So I braced my resolution to quit my dear ones, female and male, and forsook my home as birds forsake their nests. My parents being yet in the bonds of life, it weighed sorely upon me to part from them, and both they and I were afflicted with sorrow at this separation."

He travelled to Mecca overland, following the North African coast across the sultanates of Abd al-Wadid and Hafsid. The route took him through Tlemcen, Béjaïa, and then Tunis, where he stayed for two months. For safety, Ibn Battuta usually joined a caravan to reduce the risk of being robbed. He took a bride in the town of Sfax, but soon left her due to a dispute with the father. That was the first in a series of marriages that would feature in his travels.

In the early spring of 1326, after a journey of over 3500 km, Ibn Battuta arrived at the port of Alexandria, at the time part of the Bahri Mamluk empire. He met two ascetic pious men in Alexandria. One was Sheikh Burhanuddin, who is supposed to have foretold the destiny of Ibn Battuta as a world traveller and told him, "It seems to me that you are fond of foreign travel. You must visit my brother Fariduddin in India, Rukonuddin in Sind, and Burhanuddin in China. Convey my greetings to them." Another pious man, Sheikh Murshidi, interpreted the meaning of a dream of Ibn Battuta as being that he was meant to be a world traveller.

He spent several weeks visiting sites in the area, and then headed inland to Cairo, the capital of the Mamluk Sultanate. After spending about a month in Cairo, he embarked on the first of many detours within the relative safety of Mamluk territory. Of the three usual routes to Mecca, Ibn Battuta chose the least-travelled, which involved a journey up the Nile valley, then east to the Red Sea port of ʿAydhab. Upon approaching the town, however, a local rebellion forced him to turn back.

Ibn Battuta returned to Cairo and took a second side trip, this time to Mamluk-controlled Damascus. During his first trip he had encountered a holy man who prophesied that he would only reach Mecca by travelling through Syria. The diversion held an added advantage; because of the holy places that lay along the way, including Hebron, Jerusalem, and Bethlehem, the Mamluk authorities kept the route safe for pilgrims. Without this help many travellers would be robbed and murdered.

After spending the Muslim month of Ramadan, during August, in Damascus, he joined a caravan travelling the 1300 km south to Medina, site of the Mosque of the Islamic prophet Muhammad. After four days in the town, he journeyed on to Mecca while visiting holy sites along the way; upon his arrival to Mecca he completed his first pilgrimage, in November, and he took the honorific status of El-Hajji. Rather than returning home, Ibn Battuta decided to continue travelling, choosing as his next destination the Ilkhanate, a Mongol Khanate, to the northeast.

Iraq and Iran
On 17 November 1326, following a month spent in Mecca, Ibn Battuta joined a large caravan of pilgrims returning to Iraq across the Arabian Peninsula. The group headed north to Medina and then, travelling at night, turned northeast across the Najd plateau to Najaf, on a journey that lasted about two weeks. In Najaf, he visited the mausoleum of Ali, the Fourth Caliph.

Then, instead of continuing to Baghdad with the caravan, Ibn Battuta started a six-month detour that took him into Iran. From Najaf, he journeyed to Wasit, then followed the river Tigris south to Basra. His next destination was the town of Isfahan across the Zagros Mountains in Iran. He then headed south to Shiraz, a large, flourishing city spared the destruction wrought by Mongol invaders on many more northerly towns. Finally, he returned across the mountains to Baghdad, arriving there in June 1327. Parts of the city were still ruined from the damage inflicted by Hulagu Khan's invading army in 1258.

In Baghdad, he found Abu Sa'id, the last Mongol ruler of the unified Ilkhanate, leaving the city and heading north with a large retinue. Ibn Battuta joined the royal caravan for a while, then turned north on the Silk Road to Tabriz, the first major city in the region to open its gates to the Mongols and by then an important trading centre as most of its nearby rivals had been razed by the Mongol invaders.

Ibn Battuta left again for Baghdad, probably in July, but first took an excursion northwards along the river Tigris. He visited Mosul, where he was the guest of the Ilkhanate governor, and then the towns of Cizre (Jazirat ibn 'Umar) and Mardin in modern-day Turkey. At a hermitage on a mountain near Sinjar, he met a Kurdish mystic who gave him some silver coins. Once back in Mosul, he joined a "feeder" caravan of pilgrims heading south to Baghdad, where they would meet up with the main caravan that crossed the Arabian Desert to Mecca. Ill with diarrhoea, he arrived in the city weak and exhausted for his second hajj.

Arabia
Ibn Battuta remained in Mecca for some time (the Rihla suggests about three years, from September 1327 until autumn 1330). Problems with chronology, however, lead commentators to suggest that he may have left after the 1328 hajj.

After the hajj in either 1328 or 1330, he made his way to the port of Jeddah on the Red Sea coast. From there he followed the coast in a series of boats (known as a jalbah, these were small craft made of wooden planks sewn together, lacking an established phrase) making slow progress against the prevailing south-easterly winds. Once in Yemen he visited Zabīd and later the highland town of Ta'izz, where he met the Rasulid dynasty king (Malik) Mujahid Nur al-Din Ali. Ibn Battuta also mentions visiting Sana'a, but whether he actually did so is doubtful. In all likelihood, he went directly from Ta'izz to the important trading port of Aden, arriving around the beginning of 1329 or 1331.

Somalia
From Aden, Ibn Battuta embarked on a ship heading for Zeila on the coast of Somalia. He then moved on to Cape Guardafui further down the Somali seaboard, spending about a week in each location. Later he would visit Mogadishu, the then pre-eminent city of the "Land of the Berbers" (بلد البربر Balad al-Barbar, the medieval Arabic term for the Horn of Africa).

When Ibn Battuta arrived in 1332, Mogadishu stood at the zenith of its prosperity. He described it as "an exceedingly large city" with many rich merchants, noted for its high-quality fabric that was exported to other countries, including Egypt. Battuta added that the city was ruled by a Somali Sultan, Abu Bakr ibn Shaikh 'Umar. He noted that Sultan Abu Bakr had dark skin complexion and spoke in his native tongue (Somali), but was also fluent in Arabic. The Sultan also had a retinue of wazirs (ministers), legal experts, commanders, royal eunuchs, and other officials at his beck and call.

Swahili coast
Ibn Battuta continued by ship south to the Swahili coast, a region then known in Arabic as the Bilad al-Zanj ("Land of the Zanj") with an overnight stop at the island town of Mombasa. Although relatively small at the time, Mombasa would become important in the following century. After a journey along the coast, Ibn Battuta next arrived in the island town of Kilwa in present-day Tanzania, which had become an important transit centre of the gold trade. He described the city as "one of the finest and most beautifully built towns; all the buildings are of wood, and the houses are roofed with dīs reeds".

Ibn Battuta recorded his visit to the Kilwa Sultanate in 1330, and commented favourably on the humility and religion of its ruler, Sultan al-Hasan ibn Sulaiman, a descendant of the legendary Ali ibn al-Hassan Shirazi. He further wrote that the authority of the Sultan extended from Malindi in the north to Inhambane in the south and was particularly impressed by the planning of the city, believing it to be the reason for Kilwa's success along the coast. During this period, he described the construction of the Palace of Husuni Kubwa and a significant extension to the Great Mosque of Kilwa, which was made of coral stones and was the largest mosque of its kind. With a change in the monsoon winds, Ibn Battuta sailed back to Arabia, first to Oman and the Strait of Hormuz then on to Mecca for the hajj of 1330 (or 1332).

Anatolia

After his third pilgrimage to Mecca, Ibn Battuta decided to seek employment with the Sultan of Delhi, Muhammad bin Tughluq. In the autumn of 1330 (or 1332), he set off for the Seljuk controlled territory of Anatolia to take an overland route to India. He crossed the Red Sea and the Eastern Desert to reach the Nile valley and then headed north to Cairo. From there he crossed the Sinai Peninsula to Palestine and then travelled north again through some of the towns that he had visited in 1326. From the Syrian port of Latakia, a Genoese ship took him (and his companions) to Alanya on the southern coast of modern-day Turkey.

He then journeyed westwards along the coast to the port of Antalya. In the town he met members of one of the semi-religious fityan associations. These were a feature of most Anatolian towns in the 13th and 14th centuries. The members were young artisans and had at their head a leader with the title of Akhil. The associations specialised in welcoming travellers. Ibn Battuta was very impressed with the hospitality that he received and would later stay in their hospices in more than 25 towns in Anatolia. From Antalya Ibn Battuta headed inland to Eğirdir which was the capital of the Hamidids. He spent Ramadan (June 1331 or May 1333) in the city.

From this point his itinerary across Anatolia in the Rihla becomes confused. Ibn Battuta describes travelling westwards from Eğirdir to Milas and then skipping 420 km eastward past Eğirdir to Konya. He then continues travelling in an easterly direction, reaching Erzurum from where he skips 1160 km back to Birgi which lies north of Milas. Historians believe that Ibn Battuta visited a number of towns in central Anatolia, but not in the order in which he describes.

When Ibn Battuta arrived in Iznik, it had just been conquered by Orhan, Sultan of the nascent Ottoman Empire. Orhan was away and his wife was in command of the nearby stationed soldiers, Ibn Battuta gave this account of Orhan's wife: "A pious and excellent woman. She treated me honourably, gave me hospitality and sent gifts."

Ibn Battuta's account of Orhan: ""

Ibn Battuta had also visited Bursa which at the time was the capital of the Ottoman Beylik, he described Bursa as "a great and important city with fine bazaars and wide streets, surrounded on all sides with gardens and running springs".

He also visited the Beylik of Aydin. Ibn Battuta stated that the ruler of the Beylik of Aydin had twenty Greek slaves at the entrance of his palace and Ibn Battuta was given a Greek slave as a gift. His visit to Anatolia was the first time in his travels he acquired a servant; the ruler of Aydin gifted him his first slave. Later, he purchased a young Greek girl for 40 dinars in Ephesus, was gifted another slave in İzmir by the Sultan, and purchased a second girl in Balikesir. The conspicuous evidence of his wealth and prestige continued to grow.

Central Asia
From Sinope he took a sea route to the Crimean Peninsula, arriving in the Golden Horde realm. He went to the port town of Azov, where he met with the emir of the Khan, then to the large and rich city of Majar. He left Majar to meet with Uzbeg Khan's travelling court (Orda), which was at the time near Mount Beshtau. From there he made a journey to Bolghar, which became the northernmost point he reached, and noted its unusually short nights in summer (by the standards of the subtropics). Then he returned to the Khan's court and with it moved to Astrakhan.

Ibn Battuta recorded that while in Bolghar he wanted to travel further north into the land of darkness. The land is snow-covered throughout (northern Siberia) and the only means of transport is dog-drawn sled. There lived a mysterious people who were reluctant to show themselves. They traded with southern people in a peculiar way. Southern merchants brought various goods and placed them in an open area on the snow in the night, then returned to their tents. Next morning they came to the place again and found their merchandise taken by the mysterious people, but in exchange they found fur-skins which could be used for making valuable coats, jackets, and other winter garments. The trade was done between merchants and the mysterious people without seeing each other. As Ibn Battuta was not a merchant and saw no benefit of going there he abandoned the travel to this land of darkness.

When they reached Astrakhan, Öz Beg Khan had just given permission for one of his pregnant wives, Princess Bayalun, a daughter of Byzantine emperor Andronikos III Palaiologos, to return to her home city of Constantinople to give birth. Ibn Battuta talked his way into this expedition, which would be his first beyond the boundaries of the Islamic world.

Arriving in Constantinople towards the end of 1332 (or 1334), he met the Byzantine emperor Andronikos III Palaiologos. He visited the great church of Hagia Sophia and spoke with an Eastern Orthodox priest about his travels in the city of Jerusalem. After a month in the city, Ibn Battuta returned to Astrakhan, then arrived in the capital city Sarai al-Jadid and reported the accounts of his travels to Sultan Öz Beg Khan (r. 1313–1341). Then he continued past the Caspian and Aral Seas to Bukhara and Samarkand, the latter of which he praised as "one of the grandest and finest cities, and the most perfect of them". Here he visited the court of another Mongol khan, Tarmashirin (r. 1331–1334) of the Chagatai Khanate. He also noted the ruined state of the city walls, a result of the Mongol invasion in 1220 and subsequent infighting. From there, he journeyed south to Afghanistan, then crossed into India via the mountain passes of the Hindu Kush. In the Rihla, he mentions these mountains and the history of the range in slave trading. He wrote,

"After this I proceeded to the city of Barwan, in the road to which is a high mountain, covered with snow and exceedingly cold; they call it the Hindu Kush, that is Hindu-slayer, because most of the slaves brought thither from India die on account of the intenseness of the cold."

Ibn Battuta and his party reached the Indus River on 12 September 1333. From there, he made his way to Delhi and became acquainted with the sultan, Muhammad bin Tughluq.

Indian subcontinent

Muhammad bin Tughluq was renowned as the wealthiest man in the Muslim world at that time. He patronized various scholars, Sufis, qadis, viziers, and other functionaries in order to consolidate his rule. On the strength of his years of study in Mecca, Ibn Battuta was appointed a qadi, or judge, by the sultan. However, he found it difficult to enforce Islamic law beyond the sultan's court in Delhi, due to lack of Islamic appeal in India.

It is uncertain by which route Ibn Battuta entered the Indian subcontinent but it is known that he was kidnapped and robbed by rebels on his journey to the Indian coast. He may have entered via the Khyber Pass and Peshawar, or further south. He crossed the Sutlej river near the city of Pakpattan, in modern-day Pakistan, where he paid obeisance at the shrine of Baba Farid, before crossing southwest into Rajput country. From the Rajput kingdom of Sarsatti, Battuta visited Hansi in India, describing it as "among the most beautiful cities, the best constructed and the most populated; it is surrounded with a strong wall, and its founder is said to be one of the great non-Muslim kings, called Tara". Upon his arrival in Sindh, Ibn Battuta mentions the Indian rhinoceros that lived on the banks of the Indus.

The Sultan was erratic even by the standards of the time and for six years Ibn Battuta veered between living the high life of a trusted subordinate and falling under suspicion of treason for a variety of offences. His plan to leave on the pretext of taking another hajj was stymied by the Sultan. The opportunity for Battuta to leave Delhi finally arose in 1341 when an embassy arrived from the Yuan dynasty of China asking for permission to rebuild a Himalayan Buddhist temple popular with Chinese pilgrims.

Ibn Battuta was given charge of the embassy but en route to the coast at the start of the journey to China, he and his large retinue were attacked by a group of bandits. Separated from his companions, he was robbed, kidnapped, and nearly lost his life. Despite this setback, within ten days he had caught up with his group and continued on to Khambhat in the Indian state of Gujarat. From there, they sailed to Calicut (now known as Kozhikode), where Portuguese explorer Vasco da Gama would land two centuries later. While in Calicut, Battuta was the guest of the ruling Zamorin. While Ibn Battuta visited a mosque on shore, a storm arose and one of the ships of his expedition sank. The other ship then sailed without him only to be seized by a local Sumatran king a few months later.

Afraid to return to Delhi and be seen as a failure, he stayed for a time in southern India under the protection of Jamal-ud-Din, ruler of the small but powerful Nawayath sultanate on the banks of the Sharavathi river next to the Arabian Sea. This area is today known as Hosapattana and lies in the Honnavar Taluk of Uttara Kannada. Following the overthrow of the sultanate, Ibn Battuta had no choice but to leave India. Although determined to continue his journey to China, he first took a detour to visit the Maldive Islands where he worked as a judge.

He spent nine months on the islands, much longer than he had intended. When he arrived at the capital, Malé, Ibn Battuta did not plan to stay. However, the leaders of the formerly Buddhist nation that had recently converted to Islam were looking for a chief judge, someone who knew Arabic and the Qur'an. To convince him to stay they gave him pearls, gold jewellery, and slaves, while at the same time making it impossible for him to leave by ship. Compelled into staying, he became a chief judge and married into the royal family of Omar I.

Ibn Battuta took on his duties as a judge with keenness and strived to transform local practices to conform to a stricter application of Muslim law. He commanded that men who did not attend Friday prayer be publicly whipped, and that robbers' right hand be cut off. He forbade women from being topless in public, which had previously been the custom. However, these and other strict judgments began to antagonize the island nation's rulers, and involved him in power struggles and political intrigues. Ibn Battuta resigned from his job as chief qadi, although in all likelihood it was inevitable that he would have been dismissed.

Throughout his travels, Ibn Battuta kept close company with women, usually taking a wife whenever he stopped for any length of time at one place, and then divorcing her when he moved on. While in the Maldives, Ibn Battuta took four wives. In his Travels he wrote that in the Maldives the effect of small dowries and female non-mobility combined to, in effect, make a marriage a convenient temporary arrangement for visiting male travellers and sailors.

From the Maldives, he carried on to Sri Lanka and visited Sri Pada and Tenavaram temple. Ibn Battuta's ship almost sank on embarking from Sri Lanka, only for the vessel that came to his rescue to suffer an attack by pirates. Stranded onshore, he worked his way back to the Madurai kingdom in India. Here he spent some time in the court of the short-lived Madurai Sultanate under Ghiyas-ud-Din Muhammad Damghani, from where he returned to the Maldives and boarded a Chinese junk, still intending to reach China and take up his ambassadorial post.

He reached the port of Chittagong in modern-day Bangladesh intending to travel to Sylhet to meet Shah Jalal, who became so renowned that Ibn Battuta, then in Chittagong, made a one-month journey through the mountains of Kamaru near Sylhet to meet him. On his way to Sylhet, Ibn Battuta was greeted by several of Shah Jalal's disciples who had come to assist him on his journey many days before he had arrived. At the meeting in 1345 CE, Ibn Battuta noted that Shah Jalal was tall and lean, fair in complexion and lived by the mosque in a cave, where his only item of value was a goat he kept for milk, butter, and yogurt. He observed that the companions of the Shah Jalal were foreign and known for their strength and bravery. He also mentions that many people would visit the Shah to seek guidance. Ibn Battuta went further north into Assam, then turned around and continued with his original plan.

Southeast Asia
In 1345, Ibn Battuta traveled to Samudra Pasai Sultanate (called "al-Jawa") in present-day Aceh, Northern Sumatra, after 40 days voyage from Sunur Kawan. He notes in his travel log that the ruler of Samudra Pasai was a pious Muslim named Sultan Al-Malik Al-Zahir Jamal-ad-Din, who performed his religious duties with utmost zeal and often waged campaigns against animists in the region. The island of Sumatra, according to Ibn Battuta, was rich in camphor, areca nut, cloves, and tin.

The madh'hab he observed was Imam Al-Shafi‘i, whose customs were similar to those he had previously seen in coastal India, especially among the Mappila Muslims, who were also followers of Imam Al-Shafi‘i. At that time Samudra Pasai marked the end of Dar al-Islam, because no territory east of this was ruled by a Muslim. Here he stayed for about two weeks in the wooden walled town as a guest of the sultan, and then the sultan provided him with supplies and sent him on his way on one of his own junks to China.

Ibn Battuta first sailed for 21 days to a place called "Mul Jawa" (island of Java or Majapahit Java) which was a center of a Hindu empire. The empire spanned 2 months of travel, and ruled over the country of Qaqula and Qamara. He arrived at the walled city named Qaqula/Kakula, and observed that the city had war junks for pirate raiding and collecting tolls and that elephants were employed for various purposes. He met the ruler of Mul Jawa and stayed as a guest for three days.

Ibn Battuta then sailed to a state called Kaylukari in the land of Tawalisi, where he met Urduja, a local princess. Urduja was a brave warrior, and her people were opponents of the Yuan dynasty. She was described as an "idolater", but could write the phrase Bismillah in Islamic calligraphy. The locations of Kaylukari and Tawalisi are disputed. Kaylukari might referred to Po Klong Garai in Champa (now southern Vietnam), and Urduja might be an aristocrat of Champa or Dai Viet. Filipinos widely believe that Kaylukari was in present-day Pangasinan Province of the Philippines. Their opposition to the Mongols might indicate 2 possible locations: Japan and Java (Majapahit). In modern times, Urduja has been featured in Filipino textbooks and films as a national heroine. Numerous other locations have been proposed, ranging from Java to somewhere in Guangdong Province, China. However, Sir Henry Yule and William Henry Scott consider both Tawalisi and Urduja to be entirely fictitious. (See Tawalisi for details.) From Kaylukari, Ibn Battuta finally reached Quanzhou in Fujian Province, China.

China

In the year 1345, Ibn Battuta arrived at Quanzhou in China's Fujian province, then under the rule of the Mongol-led Yuan dynasty. One of the first things he noted was that Muslims referred to the city as "Zaitun" (meaning olive), but Ibn Battuta could not find any olives anywhere. He mentioned local artists and their mastery in making portraits of newly arrived foreigners; these were for security purposes. Ibn Battuta praised the craftsmen and their silk and porcelain; as well as fruits such as plums and watermelons and the advantages of paper money.

He described the manufacturing process of large ships in the city of Quanzhou. He also mentioned Chinese cuisine and its usage of animals such as frogs, pigs, and even dogs which were sold in the markets, and noted that the chickens in China were larger than those in the west. Scholars however have pointed out numerous errors given in Ibn Battuta's account of China, for example confusing the Yellow River with the Grand Canal and other waterways, as well as believing that porcelain was made from coal.

In Quanzhou, Ibn Battuta was welcomed by the head of the local Muslim merchants (possibly a fānzhǎng or "Leader of Foreigners" ) and Sheikh al-Islam (Imam), who came to meet him with flags, drums, trumpets, and musicians. Ibn Battuta noted that the Muslim populace lived within a separate portion in the city where they had their own mosques, bazaars, and hospitals. In Quanzhou, he met two prominent Iranians, Burhan al-Din of Kazerun and Sharif al-Din from Tabriz (both of whom were influential figures noted in the Yuan History as "A-mi-li-ding" and "Sai-fu-ding", respectively). While in Quanzhou he ascended the "Mount of the Hermit" and briefly visited a well-known Taoist monk in a cave.

He then travelled south along the Chinese coast to Guangzhou, where he lodged for two weeks with one of the city's wealthy merchants.

From Guangzhou he went north to Quanzhou and then proceeded to the city of Fuzhou, where he took up residence with Zahir al-Din and met Kawam al-Din and a fellow countryman named Al-Bushri of Ceuta, who had become a wealthy merchant in China. Al-Bushri accompanied Ibn Battuta northwards to Hangzhou and paid for the gifts that Ibn Battuta would present to the Emperor Huizong of Yuan.

Ibn Battuta said that Hangzhou was one of the largest cities he had ever seen, and he noted its charm, describing that the city sat on a beautiful lake surrounded by gentle green hills. He mentions the city's Muslim quarter and resided as a guest with a family of Egyptian origin. During his stay at Hangzhou he was particularly impressed by the large number of well-crafted and well-painted Chinese wooden ships, with coloured sails and silk awnings, assembling in the canals. Later he attended a banquet of the Yuan administrator of the city named Qurtai, who according to Ibn Battuta, was very fond of the skills of local Chinese conjurers. Ibn Battuta also mentions locals who worshipped a solar deity.

He described floating through the Grand Canal on a boat watching crop fields, orchids, merchants in black silk, and women in flowered silk and priests also in silk. In Beijing, Ibn Battuta referred to himself as the long-lost ambassador from the Delhi Sultanate and was invited to the Yuan imperial court of Emperor Huizong (who according to Ibn Battuta was worshipped by some people in China). Ibn Batutta noted that the palace of Khanbaliq was made of wood and that the ruler's "head wife" (Empress Qi) held processions in her honour.

Ibn Battuta also wrote he had heard of "the rampart of Yajuj and Majuj" that was "sixty days' travel" from the city of Zeitun (Quanzhou); Hamilton Alexander Rosskeen Gibb notes that Ibn Battuta believed that the Great Wall of China was built by Dhul-Qarnayn to contain Gog and Magog as mentioned in the Quran. However, Ibn Battuta, who asked about the wall in China, could find no one who had either seen it or knew of anyone who had seen it.

Ibn Battuta travelled from Beijing to Hangzhou, and then proceeded to Fuzhou. Upon his return to Quanzhou, he soon boarded a Chinese junk owned by the Sultan of Samudera Pasai Sultanate heading for Southeast Asia, whereupon Ibn Battuta was unfairly charged a hefty sum by the crew and lost much of what he had collected during his stay in China.

Battuta claimed that the Emperor Huizong of Yuan had interred with him in his grave six slave soldiers and four girl slaves. Silver, gold, weapons, and carpets were put into the grave.

Return
After returning to Quanzhou in 1346, Ibn Battuta began his journey back to Morocco. In Kozhikode, he once again considered throwing himself at the mercy of Muhammad bin Tughluq in Delhi, but thought better of it and decided to carry on to Mecca. On his way to Basra he passed through the Strait of Hormuz, where he learned that Abu Sa'id, last ruler of the Ilkhanate Dynasty had died in Iran. Abu Sa'id's territories had subsequently collapsed due to a fierce civil war between the Iranians and Mongols.

In 1348, Ibn Battuta arrived in Damascus with the intention of retracing the route of his first hajj. He then learned that his father had died 15 years earlier and death became the dominant theme for the next year or so. The Black Death had struck and he stopped in Homs as the plague spread through Syria, Palestine, and Arabia. He heard of terrible death tolls in Gaza, but returned to Damascus that July where the death toll had reached 2,400 victims each day. When he stopped in Gaza he found it was depopulated, and in Egypt he stayed at Abu Sir. Reportedly deaths in Cairo had reached levels of 1,100 each day. He made hajj to Mecca then he decided to return to Morocco, nearly a quarter of a century after leaving home. On the way he made one last detour to Sardinia, then in 1349, returned to Tangier by way of Fez, only to discover that his mother had also died a few months before.

Spain and North Africa

After a few days in Tangier, Ibn Battuta set out for a trip to the Muslim-controlled territory of al-Andalus on the Iberian Peninsula. King Alfonso XI of Castile and León had threatened to attack Gibraltar, so in 1350, Ibn Battuta joined a group of Muslims leaving Tangier with the intention of defending the port. By the time he arrived, the Black Death had killed Alfonso and the threat of invasion had receded, so he turned the trip into a sight-seeing tour ending up in Granada.

After his departure from al-Andalus he decided to travel through Morocco. On his return home, he stopped for a while in Marrakech, which was almost a ghost town following the recent plague and the transfer of the capital to Fez.

Mali and Timbuktu

In the autumn of 1351, Ibn Battuta left Fez and made his way to the town of Sijilmasa on the northern edge of the Sahara in present-day Morocco. There he bought a number of camels and stayed for four months. He set out again with a caravan in February 1352 and after 25 days arrived at the dry salt lake bed of Taghaza with its salt mines. All of the local buildings were made from slabs of salt by the slaves of the Masufa tribe, who cut the salt in thick slabs for transport by camel. Taghaza was a commercial centre and awash with Malian gold, though Ibn Battuta did not form a favourable impression of the place, recording that it was plagued by flies and the water was brackish.

After a ten-day stay in Taghaza, the caravan set out for the oasis of Tasarahla (probably Bir al-Ksaib) where it stopped for three days in preparation for the last and most difficult leg of the journey across the vast desert. From Tasarahla, a Masufa scout was sent ahead to the oasis town of Oualata, where he arranged for water to be transported a distance of four days travel where it would meet the thirsty caravan. Oualata was the southern terminus of the trans-Saharan trade route and had recently become part of the Mali Empire. Altogether, the caravan took two months to cross the 1600 km of desert from Sijilmasa. From there, Ibn Battuta travelled southwest along a river he believed to be the Nile (it was actually the river Niger), until he reached the capital of the Mali Empire. There he met Mansa Suleyman, king since 1341. Ibn Battuta disapproved of the fact that female slaves, servants, and even the daughters of the sultan went about exposing parts of their bodies not befitting a Muslim. He wrote in his Rihla that black Africans were characterised by "ill manners" and "contempt for white men", and that he "was long astonished at their feeble intellect and their respect for mean things." He left the capital in February accompanied by a local Malian merchant and journeyed overland by camel to Timbuktu. Though in the next two centuries it would become the most important city in the region, at that time it was a small city and relatively unimportant. It was during this journey that Ibn Battuta first encountered a hippopotamus. The animals were feared by the local boatmen and hunted with lances to which strong cords were attached. After a short stay in Timbuktu, Ibn Battuta journeyed down the Niger to Gao in a canoe carved from a single tree. At the time Gao was an important commercial center.

After spending a month in Gao, Ibn Battuta set off with a large caravan for the oasis of Takedda. On his journey across the desert, he received a message from the Sultan of Morocco commanding him to return home. He set off for Sijilmasa in September 1353, accompanying a large caravan transporting 600 female slaves, and arrived back in Morocco early in 1354.

Ibn Battuta's itinerary gives scholars a glimpse as to when Islam first began to spread into the heart of west Africa.

Works
After returning home from his travels in 1354, and at the suggestion of the Marinid ruler of Morocco, Abu Inan Faris, Ibn Battuta dictated an account in Arabic of his journeys to Ibn Juzayy, a scholar whom he had previously met in Granada. The account is the only source for Ibn Battuta's adventures. The full title of the manuscript may be translated as A Masterpiece to Those Who Contemplate the Wonders of Cities and the Marvels of Travelling (تحفة النظار في غرائب الأمصار وعجائب الأسفار, Tuḥfat an-Nuẓẓār fī Gharāʾib al-Amṣār wa ʿAjāʾib al-Asfār). However, it is often simply referred to as TheTravels (الرحلة, Rihla), in reference to a standard form of Arabic literature.

There is no indication that Ibn Battuta made any notes or had any journal during his twenty-nine years of travelling. When he came to dictate an account of his experiences he had to rely on memory and manuscripts produced by earlier travellers. Ibn Juzayy did not acknowledge his sources and presented some of the earlier descriptions as Ibn Battuta's own observations. When describing Damascus, Mecca, Medina, and some other places in the Middle East, he clearly copied passages from the account by the Andalusian Ibn Jubayr which had been written more than 150 years earlier. Similarly, most of Ibn Juzayy's descriptions of places in Palestine were copied from an account by the 13th-century traveller Muhammad al-Abdari.

Scholars do not believe that Ibn Battuta visited all the places he described and argue that in order to provide a comprehensive description of places in the Muslim world, he relied on hearsay evidence and made use of accounts by earlier travellers. For example, it is considered very unlikely that Ibn Battuta made a trip up the Volga River from New Sarai to visit Bolghar and there are serious doubts about a number of other journeys such as his trip to Sana'a in Yemen, his journey from Balkh to Bistam in Khorasan, and his trip around Anatolia.

Ibn Battuta's claim that a Maghrebian called "Abu'l Barakat the Berber" converted the Maldives to Islam is contradicted by an entirely different story which says that the Maldives were converted to Islam after miracles were performed by a Tabrizi named Maulana Shaikh Yusuf Shams-ud-din according to the Tarikh, the official history of the Maldives.

Some scholars have also questioned whether he really visited China. Ibn Battuta may have plagiarized entire sections of his descriptions of China lifted from works by other authors like "Masalik al-absar fi mamalik al-amsar" by Shihab al-Umari, Sulaiman al-Tajir, and possibly from Al Juwayni, Rashid al din, and an Alexander romance. Furthermore, Ibn Battuta's description and Marco Polo's writings share extremely similar sections and themes, with some of the same commentary, e.g. it is unlikely that the 3rd Caliph Uthman ibn Affan had someone with the identical name in China who was encountered by Ibn Battuta.

However, even if the Rihla is not fully based on what its author personally witnessed, it provides an important account of much of the 14th-century world. Concubines were used by Ibn Battuta such as in Delhi. He wedded several women, divorced at least some of them, and in Damascus, Malabar, Delhi, Bukhara, and the Maldives had children by them or by concubines. Ibn Battuta insulted Greeks as "enemies of Allah", drunkards and "swine eaters", while at the same time in Ephesus he purchased and used a Greek girl who was one of his many slave girls in his "harem" through Byzantium, Khorasan, Africa, and Palestine. It was two decades before he again returned to find out what happened to one of his wives and child in Damascus.

Ibn Battuta often experienced culture shock in regions he visited where the local customs of recently converted peoples did not fit in with his orthodox Muslim background. Among the Turks and Mongols, he remarked that on seeing a Turkic couple in a bazaar one might assume that the man was the woman's servant when he was in fact her husband. He also felt that dress customs in the Maldives, and some sub-Saharan regions in Africa were too revealing.

Little is known about Ibn Battuta's life after completion of his Rihla in 1355. He was appointed a judge in Morocco and died in 1368 or 1369.

Ibn Battuta's work was unknown outside the Muslim world until the beginning of the 19th century, when the German traveller-explorer Ulrich Jasper Seetzen (1767–1811) acquired a collection of manuscripts in the Middle East, among which was a 94-page volume containing an abridged version of Ibn Juzayy's text. Three extracts were published in 1818 by the German orientalist Johann Kosegarten. A fourth extract was published the following year. French scholars were alerted to the initial publication by a lengthy review published in the Journal de Savants by the orientalist Silvestre de Sacy.

Three copies of another abridged manuscript were acquired by the Swiss traveller Johann Burckhardt and bequeathed to the University of Cambridge. He gave a brief overview of their content in a book published posthumously in 1819. The Arabic text was translated into English by the orientalist Samuel Lee and published in London in 1829.

In the 1830s, during the French occupation of Algeria, the Bibliothèque Nationale (BNF) in Paris acquired five manuscripts of Ibn Battuta's travels, in which two were complete. One manuscript containing just the second part of the work is dated 1356 and is believed to be Ibn Juzayy's autograph. The BNF manuscripts were used in 1843 by the Irish-French orientalist Baron de Slane to produce a translation into French of Ibn Battuta's visit to the Sudan. They were also studied by the French scholars Charles Defrémery and Beniamino Sanguinetti. Beginning in 1853 they published a series of four volumes containing a critical edition of the Arabic text together with a translation into French. In their introduction Defrémery and Sanguinetti praised Lee's annotations but were critical of his translation which they claimed lacked precision, even in straightforward passages.

In 1929, exactly a century after the publication of Lee's translation, the historian and orientalist Hamilton Gibb published an English translation of selected portions of Defrémery and Sanguinetti's Arabic text. Gibb had proposed to the Hakluyt Society in 1922 that he should prepare an annotated translation of the entire Rihla into English. His intention was to divide the translated text into four volumes, each volume corresponding to one of the volumes published by Defrémery and Sanguinetti. The first volume was not published until 1958. Gibb died in 1971, having completed the first three volumes. The fourth volume was prepared by Charles Beckingham and published in 1994. Defrémery and Sanguinetti's printed text has now been translated into number of other languages.

Historicity
German Islamic studies scholar Ralph Elger views Battuta's travel account as an important literary work but doubts the historicity of much of its content, which he suspects to be a work of fiction compiled and inspired from other contemporary travel reports. Various other scholars have raised similar doubts.

In 1987, Ross E. Dunn similarly expressed doubts that any evidence would be found to support the narrative of the Rihla, but in 2010, Tim Mackintosh-Smith completed a multi-volume field study in dozens of the locales mentioned in the Rihla, in which he reports on previously unknown manuscripts of Islamic law kept in the archives of Al-Azhar University in Cairo that were copied by Ibn Battuta in Damascus in 1326, corroborating the date in the Rihla of his sojourn in Syria.

Present-day cultural references

The largest themed mall in Dubai, UAE, the Ibn Battuta Mall is named for him and features both areas designed to recreate the exotic lands he visited on his travels and statuary tableaus depicting scenes from his life history.

A giant semblance of Battuta, alongside two others from the history of Arab exploration, the geographer and historian Al Bakri and the navigator and cartographer Ibn Majid, is displayed at the Mobility pavilion at Expo 2020 in Dubai in a section of the exhibition designed by Weta Workshop.

Tangier Ibn Battouta Airport is an international airport located in his hometown of Tangier, Morocco.

title: Ibn Battuta


text:
ISDN

Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work on the standard began in 1980 at Bell Labs and was formally standardized in 1988 in the CCITT "Red Book". By the time the standard was released, newer networking systems with much greater speeds were available, and ISDN saw relatively little uptake in the wider market. One estimate suggests ISDN use peaked at a worldwide total of 25 million subscribers at a time when 1.3 billion analog lines were in use. ISDN has largely been replaced with digital subscriber line (DSL) systems of much higher performance.

Prior to ISDN, the telephone system consisted of digital links like T1/E1 on the long-distance lines between telephone company offices and analog signals on copper telephone wires to the customers, the "last mile". At the time, the network was viewed as a way to transport voice, with some special services available for data using additional equipment like modems or by providing a T1 on the customer's location. What became ISDN started as an effort to digitize the last mile, originally under the name "Public Switched Digital Capacity" (PSDC). This would allow call routing to be completed in an all-digital system, while also offering a separate data line. The Basic Rate Interface, or BRI, is the standard last-mile connection in the ISDN system, offering two 64 kbit/s "bearer" lines and a single 16 kbit/s "data" channel for commands and data.

Although ISDN was successful in a few countries such as Germany, on a global scale the system was largely ignored and garnered the industry nickname "innovation subscribers didn't need." It found a use for a time for small-office digital connection, using the voice lines for data at 64 kbit/s, sometimes "bonded" to 128 kbit/s, but the introduction of 56 kbit/s modems undercut its value in many roles. It also found use in videoconference systems, where the direct end-to-end connection was desirable. The H.320 standard was designed around its 64 kbit/s data rate. The underlying ISDN concepts found wider use as a replacement for the T1/E1 lines it was originally intended to extend, roughly doubling the performance of those lines.

Digital lines
Since its introduction in 1881, the twisted pair copper line has been installed for telephone use worldwide, with well over a billion individual connections installed by the year 2000. Over the first half of the 20th century, the connection of these lines to form calls was increasingly automated, culminating in the crossbar switches that had largely replaced earlier concepts by the 1950s.

As telephone use surged in the post-WWII era, the problem of connecting the massive number of lines became an area of significant study. Bell Labs' seminal work on digital encoding of voice led to the use of 64 kbit/s as a standard for voice lines (or 56 kbit/s in some systems). In 1962, Robert Aaron of Bell introduced the T1 system, which carried 1.544 Mbit/s of data on a pair of twisted pair lines over a distance of about one mile. This was used in the Bell network to carry traffic between local switch offices, with 24 voice lines at 64 kbit/s and a separate 8 kbit/s line for signaling commands like connecting or hanging up a call. This could be extended over long distances using repeaters in the lines. T1 used a very simple encoding scheme, alternate mark inversion (AMI), which reached only a few percent of the theoretical capacity of the line but was appropriate for 1960s electronics.

By the late 1970s,T1 lines and their faster counterparts, along with all-digital switching systems, had replaced the earlier analog systems for most of the western world, leaving only the customer's equipment and their local end office using analog systems. Digitizing this "last mile" was increasingly seen as the next problem that needed to be solved. However, these connections now represented over 99% of the total telephony network, as the upstream links had increasingly been aggregated into a smaller number of much higher performance systems, especially after the introduction of fiber optic lines. If the system was to become all-digital, a new standard would be needed that was appropriate for the existing customer lines, which might be miles long and of widely varying quality.

Standardization
Around 1978, Ralph Wyndrum, Barry Bossick and Joe Lechleider of Bell Labs began one such effort to develop a last-mile solution. They studied a number of derivatives of the T1's AMI concept and concluded that a customer-side line could reliably carry about 160 kbit/s of data over a distance of 4 to 5 miles. That would be enough to carry two voice-quality lines at 64 kbit/s as well as a separate 16 kbit/s line for data. At the time, modems were normally 300 bit/s and 1200 bit/s would not become common until the early 1980s and the 2400 bit/s standard would not be completed until 1984. In this market, 16 kbit/s represented a significant advance in performance in addition to being a separate channel that coexists with voice channels.

A key problem was that the customer might only have a single twisted pair line to the location of the handset, so the solution used in T1 with separate upstream and downstream connections was not universally available. With analog connections, the solution was to use echo cancellation, but at the much higher bandwidth of the new concept, this would not be so simple. A debate broke out between teams worldwide about the best solution to this problem; some promoted newer versions of echo cancellation, while others preferred the "ping pong" concept where the direction of data would rapidly switch the line from send to receive at such a high rate it would not be noticeable to the user. John Cioffi had recently demonstrated echo cancellation would work at these speeds, and further suggested that they should consider moving directly to 1.5 Mbit/s performance using this concept. The suggestion was literally laughed off the table (His boss told him to "sit down and shut up") but the echo cancellation concept that was taken up by Joe Lechleider eventually came to win the debate.

Meanwhile, the debate over the encoding scheme itself was also ongoing. As the new standard was to be international, this was even more contentious as several regional digital standards had emerged in the 1960s and 70s and merging them was not going to be easy. To further confuse issues, in 1984 the Bell System was broken up and the US center for development moved to the American National Standards Institute (ANSI) T1D1.3 committee. Thomas Starr of the newly formed Ameritech led this effort and eventually convinced the ANSI group to select the 2B1Q standard proposed by Peter Adams of British Telecom. This standard used an 80 kHz base frequency and encoded two bits per baud to produce the 160 kbit/s base rate. Ultimately Japan selected a different standard, and Germany selected one with three levels instead of four, but all of these could interchange with the ANSI standard.

From an economic perspective, the European Commission sought to liberalize and regulate ISDN across the European Economic Community. The Council of the European Communities adopted Council Recommendation 86/659/EEC in December 1986 for its coordinated introduction within the framework of CEPT. ETSI (the European Telecommunications Standards Institute) was created by CEPT in 1988 and would develop the framework.

Rollout
With digital-quality voice made possible by ISDN, offering two separate lines and continuous data connectivity, there was an initial global expectation of high customer demand for such systems in both the home and office environments. This expectation was met with varying degrees of success across different regions.

In the United States, many changes in the market led to the introduction of ISDN being tepid. During the lengthy standardization process, new concepts rendered the system largely superfluous. In the office, multi-line digital switches like the Meridian Norstar took over telephone lines while local area networks like Ethernet provided performance around 10 Mbit/s which had become the baseline for inter-computer connections in offices. ISDN offered no real advantages in the voice role and was far from competitive in data. Additionally, modems had continued improving, introducing 9600 bit/s systems in the late 1980s and 14.4 kbit/s in 1991, which significantly eroded ISDN's value proposition for the home customer.

Conversely, in Europe, ISDN found fertile ground for deployment, driven by regulatory support, infrastructural needs, and the absence of comparable high-speed communication technologies at the time. The technology was widely embraced for its ability to digitalize the "last mile" of telecommunications, significantly enhancing the quality and efficiency of voice, data, and video transmission over traditional analog systems.

Meanwhile, Lechleider had proposed using ISDN's echo cancellation and 2B1Q encoding on existing T1 connections so that the distance between repeaters could be doubled to about 2 miles. Another standards war broke out, but in 1991 Lechleider's 1.6 Mbit/s "High-Speed Digital Subscriber Line" eventually won this process as well, after Starr drove it through the ANSI T1E1.4 group. A similar standard emerged in Europe to replace their E1 lines, increasing the sampling range from 80 to 100 kHz to achieve 2.048 Mbit/s. By the mid-1990s, these Primary Rate Interface (PRI) lines had largely replaced T1 and E1 between telephone company offices.

Replacement by ADSL
Lechleider also believed this higher-speed standard would be much more attractive to customers than ISDN had proven. Unfortunately, at these speeds, the systems suffered from a type of crosstalk known as "NEXT", for "near-end crosstalk". This made longer connections on customer lines difficult. Lechleider noted that NEXT only occurred when similar frequencies were being used, and could be diminished if one of the directions used a different carrier rate, but doing so would reduce the potential bandwidth of that channel. Lechleider suggested that most consumer use would be asymmetric anyway, and that providing a high-speed channel towards the user and a lower speed return would be suitable for many uses.

This work in the early 1990s eventually led to the ADSL concept, which emerged in 1995. An early supporter of the concept was Alcatel, who jumped on ADSL while many other companies were still devoted to ISDN. Krish Prabu stated that "Alcatel will have to invest one billion dollars in ADSL before it makes a profit, but it is worth it." They introduced the first DSL Access Multiplexers (DSLAM), the large multi-modem systems used at the telephony offices, and later introduced customer ADSL modems under the Thomson brand. Alcatel remained the primary vendor of ADSL systems for well over a decade.

ADSL quickly replaced ISDN as the customer-facing solution for last-mile connectivity. ISDN has largely disappeared on the customer side, remaining in use only in niche roles like dedicated teleconferencing systems and similar legacy systems.

Design
Integrated services refers to ISDN's ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of what were expected to be most people's complete communications needs (apart from broadband Internet access and entertainment television) at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. It also refers to integrated switching and transmission in that telephone switching and carrier wave transmission are integrated rather than separate as in earlier technology.

Configurations
In ISDN, there are two types of channels, B (for "bearer") and D (for "data"). B channels are used for data (which may include voice), and D channels are intended for signaling and control (but can also be used for data).

There are two ISDN implementations. Basic Rate Interface (BRI), also called basic rate access (BRA) — consists of two B channels, each with bandwidth of 64 kbit/s, and one D channel with a bandwidth of 16 kbit/s. Together these three channels can be designated as 2B+D. Primary Rate Interface (PRI), also called primary rate access (PRA) in Europe — contains a greater number of B channels and a D channel with a bandwidth of 64 kbit/s. The number of B channels for PRI varies according to the nation: in North America and Japan it is 23B+1D, with an aggregate bit rate of 1.544 Mbit/s (T1); in Europe, India and Australia it is 30B+2D, with an aggregate bit rate of 2.048 Mbit/s (E1). Broadband Integrated Services Digital Network (BISDN) is another ISDN implementation and it is able to manage different types of services at the same time. It is primarily used within network backbones and employs ATM.

Another alternative ISDN configuration can be used in which the B channels of an ISDN BRI line are bonded to provide a total duplex bandwidth of 128 kbit/s. This precludes use of the line for voice calls while the internet connection is in use. The B channels of several BRIs can be bonded, a typical use is a 384K videoconferencing channel.

Using bipolar with eight-zero substitution encoding technique, call data is transmitted over the data (B) channels, with the signaling (D) channels used for call setup and management. Once a call is set up, there is a simple 64 kbit/s synchronous bidirectional data channel (actually implemented as two simplex channels, one in each direction) between the end parties, lasting until the call is terminated. There can be as many calls as there are bearer channels, to the same or different end-points. Bearer channels may also be multiplexed into what may be considered single, higher-bandwidth channels via a process called B channel BONDING, or via use of Multi-Link PPP "bundling" or by using an H0, H11, or H12 channel on a PRI.

The D channel can also be used for sending and receiving X.25 data packets, and connection to X.25 packet network, this is specified in X.31. In practice, X.31 was only commercially implemented in the UK, France, Japan and Germany.

Reference points
A set of reference points are defined in the ISDN standard to refer to certain points between the telco and the end-user equipment.

 * R – defines the point between non-ISDN terminal equipment, terminal equipment 2 (TE2), and a terminal adapter (TA) which provides translation to and from such a device
 * S – defines the point between ISDN terminal equipment, terminal equipment 1 (TE1), or a TA and a Network Termination Type 2 (NT2) device
 * T – defines the point between the NT2 and network termination 1 (NT1) devices.

Most NT-1 devices can perform the functions of the NT2 as well, and so the S and T reference points are generally collapsed into the S/T reference point.

In North America, the NT1 device is considered customer premises equipment (CPE) and must be maintained by the customer, thus, the U interface is provided to the customer. In other locations, the NT1 device is maintained by the telco, and the S/T interface is provided to the customer. In India, service providers provide U interface and an NT1 may be supplied by Service provider as part of service offering.

Basic Rate Interface

The entry level interface to ISDN is the Basic Rate Interface (BRI), a 128 kbit/s service delivered over a pair of standard telephone copper wires. The 144 kbit/s overall payload rate is divided into two 64 kbit/s bearer channels ('B' channels) and one 16 kbit/s signaling channel ('D' channel or data channel). This is sometimes referred to as 2B+D.

The interface specifies the following network interfaces:
 * The U interface is a two-wire interface between the exchange and a network terminating unit, which is usually the demarcation point in non-North American networks.
 * The T interface is a serial interface between a computing device and a terminal adapter, which is the digital equivalent of a modem.
 * The S interface is a four-wire bus that ISDN consumer devices plug into; the S & T reference points are commonly implemented as a single interface labeled 'S/T' on a Network termination 1 (NT1).
 * The R interface defines the point between a non-ISDN device and a terminal adapter (TA) which provides translation to and from such a device.

BRI-ISDN is very popular in Europe but is much less common in North America. It is also common in Japan — where it is known as INS64.

Primary Rate Interface
The other ISDN access available is the Primary Rate Interface (PRI), which is carried over T-carrier (T1) with 24 time slots (channels) in North America, and over E-carrier (E1) with 32 channels in most other countries. Each channel provides transmission at a 64 kbit/s data rate.

With the E1 carrier, the available channels are divided into 30 bearer (B) channels, one data (D) channel, and one timing and alarm channel. This scheme is often referred to as 30B+2D. In North America, PRI service is delivered via T1 carriers with only one data channel, often referred to as 23B+D, and a total data rate of 1544 kbit/s. Non-Facility Associated Signalling (NFAS) allows two or more PRI circuits to be controlled by a single D channel, which is sometimes called 23B+D + n*24B. D-channel backup allows for a second D channel in case the primary fails. NFAS is commonly used on a Digital Signal 3 (DS3/T3).

PRI-ISDN is popular throughout the world, especially for connecting private branch exchanges to the public switched telephone network (PSTN).

Even though many network professionals use the term ISDN to refer to the lower-bandwidth BRI circuit, in North America BRI is relatively uncommon whilst PRI circuits serving PBXs are commonplace.

Bearer channel
The bearer channel (B) is a standard 64 kbit/s voice channel of 8 bits sampled at 8 kHz with G.711 encoding. B-channels can also be used to carry data, since they are nothing more than digital channels.

Each one of these channels is known as a DS0.

Most B channels can carry a 64kbit/s signal, but some were limited to 56K because they traveled over RBS lines. This was commonplace in the 20th century, but has since become less so.

X.25
X.25 can be carried over the B or D channels of a BRI line, and over the B channels of a PRI line. X.25 over the D channel is used at many point-of-sale (credit card) terminals because it eliminates the modem setup, and because it connects to the central system over a B channel, thereby eliminating the need for modems and making much better use of the central system's telephone lines.

X.25 was also part of an ISDN protocol called "Always On/Dynamic ISDN", or AO/DI. This allowed a user to have a constant multi-link PPP connection to the internet over X.25 on the D channel, and brought up one or two B channels as needed.

Frame Relay
In theory, Frame Relay can operate over the D channel of BRIs and PRIs, but it is seldom, if ever, used.

Telephone industry
ISDN is a core technology in the telephone industry. A telephone network can be thought of as a collection of wires strung between switching systems. The common electrical specification for the signals on these wires is T1 or E1. Between telephone company switches, the signaling is performed via SS7. Normally, a PBX is connected via a T1 with robbed bit signaling to indicate on-hook or off-hook conditions and MF and DTMF tones to encode the destination number. ISDN is much better because messages can be sent much more quickly than by trying to encode numbers as long (100 ms per digit) tone sequences. This results in faster call setup times. Also, a greater number of features are available and fraud is reduced.

In common use, ISDN is often limited to usage to Q.931 and related protocols, which are a set of signaling protocols establishing and breaking circuit-switched connections, and for advanced calling features for the user. Another usage was the deployment of videoconference systems, where a direct end-to-end connection is desirable. ISDN uses the H.320 standard for audio coding and video coding.

ISDN is also used as a smart-network technology intended to add new services to the public switched telephone network (PSTN) by giving users direct access to end-to-end circuit-switched digital services and as a backup or failsafe circuit solution for critical use data circuits.

Video conferencing
One of ISDNs successful use-cases was in the videoconference field, where even small improvements in data rates are useful, but more importantly, its direct end-to-end connection offers lower latency and better reliability than packet-switched networks of the 1990s. The H.320 standard for audio coding and video coding was designed with ISDN in mind, and more specifically its 64 kbit/s basic data rate. including audio codecs such as G.711 (PCM) and G.728 (CELP), and discrete cosine transform (DCT) video codecs such as H.261 and H.263.

Broadcast industry
ISDN is used heavily by the broadcast industry as a reliable way of switching low-latency, high-quality, long-distance audio circuits. In conjunction with an appropriate codec using MPEG or various manufacturers' proprietary algorithms, an ISDN BRI can be used to send stereo bi-directional audio coded at 128 kbit/s with 20 Hz – 20 kHz audio bandwidth, although commonly the G.722 algorithm is used with a single 64 kbit/s B channel to send much lower latency mono audio at the expense of audio quality. Where very high quality audio is required multiple ISDN BRIs can be used in parallel to provide a higher bandwidth circuit switched connection. BBC Radio 3 commonly makes use of three ISDN BRIs to carry 320 kbit/s audio stream for live outside broadcasts. ISDN BRI services are used to link remote studios, sports grounds and outside broadcasts into the main broadcast studio. ISDN via satellite is used by field reporters around the world. It is also common to use ISDN for the return audio links to remote satellite broadcast vehicles.

In many countries, such as the UK and Australia, ISDN has displaced the older technology of equalised analogue landlines, with these circuits being phased out by telecommunications providers. Use of IP-based streaming codecs such as Comrex ACCESS and ipDTL is becoming more widespread in the broadcast sector, using broadband internet to connect remote studios.

Backup lines
Providing a backup line for business's inter-office and internet connectivity was a popular use of the technology.

International deployment
A study of the Germany's Federal Ministry of Education and Research shows the following share of ISDN-channels per 1,000 inhabitants in 2005:
 * Norway 401
 * Denmark 339
 * Germany 333
 * Switzerland 331
 * Japan 240
 * United Kingdom 160
 * Finland 160
 * Sweden 135
 * Italy 105
 * France 85
 * Spain 58
 * United States 47

Australia
Telstra provides the business customer with the ISDN services. There are five types of ISDN services which are ISDN2, ISDN2 Enhanced, ISDN10, ISDN20 and ISDN30. Telstra changed the minimum monthly charge for voice and data calls. In general, there are two group of ISDN service types; The Basic Rate services – ISDN 2 or ISDN 2 Enhanced. Another group of types are the Primary Rate services, ISDN 10/20/30. Telstra announced that the new sales of ISDN product would be unavailable as of 31 January 2018. The final exit date of ISDN service and migration to the new service would be confirmed by 2022.

France
Orange offers ISDN services under their product name Numeris (2 B+D), of which a professional Duo and home Itoo version is available. ISDN is generally known as RNIS in France and has widespread availability. The introduction of ADSL is reducing ISDN use for data transfer and Internet access, although it is still common in more rural and outlying areas, and for applications such as business voice and point-of-sale terminals. In 2023, Numeris services will enter a phase-out process. They will be replaced by VoIP services.

Germany

In Germany, ISDN was very popular with an installed base of 25 million channels (29% of all subscriber lines in Germany as of 2003 and 20% of all ISDN channels worldwide). Due to the success of ISDN, the number of installed analog lines was decreasing. Deutsche Telekom (DTAG) offered both BRI and PRI. Competing phone companies often offered ISDN only and no analog lines. However, these operators generally offered free hardware that also allows the use of POTS equipment, such as NTBAs ("Network Termination for ISDN Basic rate Access": small devices that bridge the two-wire UK0 line to the four-wire S0 bus) with integrated terminal adapters. Because of the widespread availability of ADSL services, ISDN was primarily used for voice and fax traffic.

Until 2007 ISDN (BRI) and ADSL/VDSL were often bundled on the same line, mainly because the combination of DSL with an analog line had no cost advantage over a combined ISDN-DSL line. This practice turned into an issue for the operators when vendors of ISDN technology stopped manufacturing it and spare parts became hard to come by. Since then phone companies started introducing cheaper xDSL-only products using VoIP for telephony, also in an effort to reduce their costs by operating separate data & voice networks.

Since approximately 2010, most German operators have offered more and more VoIP on top of DSL lines and ceased offering ISDN lines. New ISDN lines have been no longer available in Germany since 2018, existing ISDN lines were phased out from 2016 onwards and existing customers were encouraged to move to DSL-based VoIP products. Deutsche Telekom intended to phase-out by 2018 but postponed the date to 2020, other providers like Vodafone estimate to have their phase-out completed by 2022.

Greece
OTE, the incumbent telecommunications operator, offers ISDN BRI (BRA) services in Greece. Following the launch of ADSL in 2003, the importance of ISDN for data transfer began to decrease and is today limited to niche business applications with point-to-point requirements.

India
Bharat Sanchar Nigam Limited, Reliance Communications and Bharti Airtel are the largest communication service providers, and offer both ISDN BRI and PRI services across the country. Reliance Communications and Bharti Airtel uses the DLC technology for providing these services. With the introduction of broadband technology, the load on bandwidth is being absorbed by ADSL. ISDN continues to be an important backup network for point-to-point leased line customers such as banks, e-Seva Centers, Life Insurance Corporation of India, and SBI ATMs.

Japan
On April 19, 1988, Japanese telecommunications company NTT began offering nationwide ISDN services trademarked INS Net 64, and INS Net 1500, a fruition of NTT's independent research and trial from the 1970s of what it referred to the INS (Information Network System).

Previously, in April 1985, Japanese digital telephone exchange hardware made by Fujitsu was used to experimentally deploy the world's first I interface ISDN. The I interface, unlike the older and incompatible Y interface, is what modern ISDN services use today.

Since 2000, NTT's ISDN offering have been known as FLET's ISDN, incorporating the "FLET's" brand that NTT uses for all of its ISP offerings.

In Japan, the number of ISDN subscribers dwindled as alternative technologies such as ADSL, cable Internet access, and fiber to the home gained greater popularity. On November 2, 2010, NTT announced plans to migrate their backend from PSTN to the IP network from around 2020 to around 2025. For this migration, ISDN services will be retired, and fiber optic services are recommended as an alternative.

Norway
On April 19, 1988, Norwegian telecommunications company Telenor began offering nationwide ISDN services trademarked INS Net 64, and INS Net 1500, a fruition of NTT's independent research and trial from the 1970s of what it referred to the INS (Information Network System).

United Kingdom
In the United Kingdom, British Telecom (BT) provides ISDN2e (BRI) as well as ISDN30 (PRI). Until April 2006, they also offered services named Home Highway and Business Highway, which were BRI ISDN-based services that offered integrated analogue connectivity as well as ISDN. Later versions of the Highway products also included built-in USB sockets for direct computer access. Home Highway was bought by many home users, usually for Internet connection, although not as fast as ADSL, because it was available before ADSL and in places where ADSL does not reach.

In early 2015, BT announced their intention to retire the UK's ISDN infrastructure by 2025.

United States and Canada
ISDN-BRI never gained popularity as a general use telephone access technology in Canada and the US, and remains a niche product. The service was seen as "a solution in search of a problem", and the extensive array of options and features were difficult for customers to understand and use. ISDN has long been known by derogatory backronyms highlighting these issues, such as It Still Does Nothing, Innovations Subscribers Don't Need, and I Still Don't kNow, or, from the supposed standpoint of telephone companies, I Smell Dollars Now.

Although various minimum bandwidths have been used in definitions of Broadband Internet access, ranging up from 64 kbit/s up to 1.0 Mbit/s, the 2006 OECD report is typical by defining broadband as having download data transfer rates equal to or faster than 256 kbit/s, while the United States FCC, as of 2008, defines broadband as anything above 768 kbit/s. Once the term "broadband" came to be associated with data rates incoming to the customer at 256 kbit/s or more, and alternatives like ADSL grew in popularity, the consumer market for BRI did not develop. Its only remaining advantage is that, while ADSL has a functional distance limitation and can use ADSL loop extenders, BRI has a greater limit and can use repeaters. As such, BRI may be acceptable for customers who are too remote for ADSL. Widespread use of BRI is further stymied by some small North American CLECs such as CenturyTel having given up on it and not providing Internet access using it. However, AT&T in most states (especially the former SBC/SWB territory) will still install an ISDN BRI line anywhere a normal analog line can be placed and the monthly charge is roughly $55.

ISDN-BRI is currently primarily used in industries with specialized and very specific needs. High-end videoconferencing hardware can bond up to 8 B-channels together (using a BRI circuit for every 2 channels) to provide digital, circuit-switched video connections to almost anywhere in the world. This is very expensive, and is being replaced by IP-based conferencing, but where cost concern is less of an issue than predictable quality and where a QoS-enabled IP does not exist, BRI is the preferred choice.

Most modern non-VoIP PBXs use ISDN-PRI circuits. These are connected via T1 lines with the central office switch, replacing older analog two-way and direct inward dialing (DID) trunks. PRI is capable of delivering Calling Line Identification (CLID) in both directions so that the telephone number of an extension, rather than a company's main number, can be sent. It is still commonly used in recording studios and some radio programs, when a voice-over actor or host is in one studio conducting remote work, but the director and producer are in a studio at another location. The ISDN protocol delivers channelized, not-over-the-Internet service, powerful call setup and routing features, faster setup and tear down, superior audio fidelity as compared to plain old telephone service (POTS), lower delay and, at higher densities, lower cost.

In 2013, Verizon announced it would no longer take orders for ISDN service in the Northeastern United States.

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

title: ISDN


text:
Genomic imprinting

Genomic imprinting is an epigenetic phenomenon that causes genes to be expressed or not, depending on whether they are inherited from the female or male parent. Genes can also be partially imprinted. Partial imprinting occurs when alleles from both parents are differently expressed rather than complete expression and complete suppression of one parent's allele. Forms of genomic imprinting have been demonstrated in fungi, plants and animals. In 2014, there were about 150 imprinted genes known in mice and about half that in humans. As of 2019, 260 imprinted genes have been reported in mice and 228 in humans.

Genomic imprinting is an inheritance process independent of the classical Mendelian inheritance. It is an epigenetic process that involves DNA methylation and histone methylation without altering the genetic sequence. These epigenetic marks are established ("imprinted") in the germline (sperm or egg cells) of the parents and are maintained through mitotic cell divisions in the somatic cells of an organism.

Appropriate imprinting of certain genes is important for normal development. Human diseases involving genomic imprinting include Angelman, Prader–Willi, and Beckwith–Wiedemann syndromes. Methylation defects have also been associated with male infertility.

Overview
In diploid organisms (like humans), the somatic cells possess two copies of the genome, one inherited from the male and one from the female. Each autosomal gene is therefore represented by two copies, or alleles, with one copy inherited from each parent at fertilization. The expressed allele is dependent upon its parental origin. For example, the gene encoding insulin-like growth factor 2 (IGF2/Igf2) is only expressed from the allele inherited from the male. Although imprinting accounts for a small proportion of mammalian genes, they play an important role in embryogenesis particularly in the formation of visceral structures and the nervous system.

The term "imprinting" was first used to describe events in the insect Pseudococcus nipae. In Pseudococcids (mealybugs) (Hemiptera, Coccoidea) both the male and female develop from a fertilised egg. In females, all chromosomes remain euchromatic and functional. In embryos destined to become males, one haploid set of chromosomes becomes heterochromatinised after the sixth cleavage division and remains so in most tissues; males are thus functionally haploid.

Imprinted genes in mammals
That imprinting might be a feature of mammalian development was suggested in breeding experiments in mice carrying reciprocal chromosomal translocations. Nucleus transplantation experiments in mouse zygotes in the early 1980s confirmed that normal development requires the contribution of both the maternal and paternal genomes. The vast majority of mouse embryos derived from parthenogenesis (called parthenogenones, with two maternal or egg genomes) and androgenesis (called androgenones, with two paternal or sperm genomes) die at or before the blastocyst/implantation stage. In the rare instances that they develop to postimplantation stages, gynogenetic embryos show better embryonic development relative to placental development, while for androgenones, the reverse is true. Nevertheless, for the latter, only a few have been described (in a 1984 paper). Nevertheless, in 2018 genome editing allowed for bipaternal and viable bimaternal  mouse and even (in 2022) parthenogenesis, still this is far from full reimprinting. Finally in March 2023 viable bipaternal embryos were created.

No naturally occurring cases of parthenogenesis exist in mammals because of imprinted genes. However, in 2004, experimental manipulation by Japanese researchers of a paternal methylation imprint controlling the Igf2 gene led to the birth of a mouse (named Kaguya) with two maternal sets of chromosomes, though it is not a true parthenogenone since cells from two different female mice were used. The researchers were able to succeed by using one egg from an immature parent, thus reducing maternal imprinting, and modifying it to express the gene Igf2, which is normally only expressed by the paternal copy of the gene.

Parthenogenetic/gynogenetic embryos have twice the normal expression level of maternally derived genes, and lack expression of paternally expressed genes, while the reverse is true for androgenetic embryos. It is now known that there are at least 80 imprinted genes in humans and mice, many of which are involved in embryonic and placental growth and development. Hybrid offspring of two species may exhibit unusual growth due to the novel combination of imprinted genes.

Various methods have been used to identify imprinted genes. In swine, Bischoff et al. compared transcriptional profiles using DNA microarrays to survey differentially expressed genes between parthenotes (2 maternal genomes) and control fetuses (1 maternal, 1 paternal genome). An intriguing study surveying the transcriptome of murine brain tissues revealed over 1300 imprinted gene loci (approximately 10-fold more than previously reported) by RNA-sequencing from F1 hybrids resulting from reciprocal crosses. The result however has been challenged by others who claimed that this is an overestimation by an order of magnitude due to flawed statistical analysis.

In domesticated livestock, single-nucleotide polymorphisms in imprinted genes influencing foetal growth and development have been shown to be associated with economically important production traits in cattle, sheep and pigs.

Genetic mapping of imprinted genes
At the same time as the generation of the gynogenetic and androgenetic embryos discussed above, mouse embryos were also being generated that contained only small regions that were derived from either a paternal or maternal source. The generation of a series of such uniparental disomies, which together span the entire genome, allowed the creation of an imprinting map. Those regions which when inherited from a single parent result in a discernible phenotype contain imprinted gene(s). Further research showed that within these regions there were often numerous imprinted genes. Around 80% of imprinted genes are found in clusters such as these, called imprinted domains, suggesting a level of co-ordinated control. More recently, genome-wide screens to identify imprinted genes have used differential expression of mRNAs from control fetuses and parthenogenetic or androgenetic fetuses hybridized to gene expression profiling microarrays, allele-specific gene expression using SNP genotyping microarrays, transcriptome sequencing, and in silico prediction pipelines.

Imprinting mechanisms
Imprinting is a dynamic process. It must be possible to erase and re-establish imprints through each generation so that genes that are imprinted in an adult may still be expressed in that adult's offspring. (For example, the maternal genes that control insulin production will be imprinted in a male but will be expressed in any of the male's offspring that inherit these genes.) The nature of imprinting must therefore be epigenetic rather than DNA sequence dependent. In germline cells the imprint is erased and then re-established according to the sex of the individual, i.e. in the developing sperm (during spermatogenesis), a paternal imprint is established, whereas in developing oocytes (oogenesis), a maternal imprint is established. This process of erasure and reprogramming is necessary such that the germ cell imprinting status is relevant to the sex of the individual. In both plants and mammals there are two major mechanisms that are involved in establishing the imprint; these are DNA methylation and histone modifications.

Recently, a new study has suggested a novel inheritable imprinting mechanism in humans that would be specific of placental tissue and that is independent of DNA methylation (the main and classical mechanism for genomic imprinting). This was observed in humans, but not in mice, suggesting development after the evolutionary divergence of humans and mice, ~80 Mya. Among the hypothetical explanations for this novel phenomenon, two possible mechanisms have been proposed: either a histone modification that confers imprinting at novel placental-specific imprinted loci or, alternatively, a recruitment of DNMTs to these loci by a specific and unknown transcription factor that would be expressed during early trophoblast differentiation.

Regulation
The grouping of imprinted genes within clusters allows them to share common regulatory elements, such as non-coding RNAs and differentially methylated regions (DMRs). When these regulatory elements control the imprinting of one or more genes, they are known as imprinting control regions (ICR). The expression of non-coding RNAs, such as antisense Igf2r RNA (Air) on mouse chromosome 17 and KCNQ1OT1 on human chromosome 11p15.5, have been shown to be essential for the imprinting of genes in their corresponding regions.

Differentially methylated regions are generally segments of DNA rich in cytosine and guanine nucleotides, with the cytosine nucleotides methylated on one copy but not on the other. Contrary to expectation, methylation does not necessarily mean silencing; instead, the effect of methylation depends upon the default state of the region.

Functions of imprinted genes
The control of expression of specific genes by genomic imprinting is unique to therian mammals (placental mammals and marsupials) and flowering plants. Imprinting of whole chromosomes has been reported in mealybugs (Genus: Pseudococcus) and a fungus gnat (Sciara). It has also been established that X-chromosome inactivation occurs in an imprinted manner in the extra-embryonic tissues of mice and all tissues in marsupials, where it is always the paternal X-chromosome which is silenced.

The majority of imprinted genes in mammals have been found to have roles in the control of embryonic growth and development, including development of the placenta. Other imprinted genes are involved in post-natal development, with roles affecting suckling and metabolism.

Hypotheses on the origins of imprinting
A widely accepted hypothesis for the evolution of genomic imprinting is the "parental conflict hypothesis". Also known as the kinship theory of genomic imprinting, this hypothesis states that the inequality between parental genomes due to imprinting is a result of the differing interests of each parent in terms of the evolutionary fitness of their genes. The father's genes that encode for imprinting gain greater fitness through the success of the offspring, at the expense of the mother. The mother's evolutionary imperative is often to conserve resources for her own survival while providing sufficient nourishment to current and subsequent litters. Accordingly, paternally expressed genes tend to be growth-promoting whereas maternally expressed genes tend to be growth-limiting. In support of this hypothesis, genomic imprinting has been found in all placental mammals, where post-fertilisation offspring resource consumption at the expense of the mother is high; although it has also been found in oviparous birds where there is relatively little post-fertilisation resource transfer and therefore less parental conflict. A small number of imprinted genes are fast evolving under positive Darwinian selection possibly due to antagonistic co-evolution. The majority of imprinted genes display high levels of micro-synteny conservation and have undergone very few duplications in placental mammalian lineages.

However, our understanding of the molecular mechanisms behind genomic imprinting show that it is the maternal genome that controls much of the imprinting of both its own and the paternally-derived genes in the zygote, making it difficult to explain why the maternal genes would willingly relinquish their dominance to that of the paternally-derived genes in light of the conflict hypothesis.

Another hypothesis proposed is that some imprinted genes act coadaptively to improve both fetal development and maternal provisioning for nutrition and care. In it, a subset of paternally expressed genes are co-expressed in both the placenta and the mother's hypothalamus. This would come about through selective pressure from parent-infant coadaptation to improve infant survival. Paternally expressed 3 (PEG3) is a gene for which this hypothesis may apply.

Others have approached their study of the origins of genomic imprinting from a different side, arguing that natural selection is operating on the role of epigenetic marks as machinery for homologous chromosome recognition during meiosis, rather than on their role in differential expression. This argument centers on the existence of epigenetic effects on chromosomes that do not directly affect gene expression, but do depend on which parent the chromosome originated from. This group of epigenetic changes that depend on the chromosome's parent of origin (including both those that affect gene expression and those that do not) are called parental origin effects, and include phenomena such as paternal X inactivation in the marsupials, nonrandom parental chromatid distribution in the ferns, and even mating type switching in yeast. This diversity in organisms that show parental origin effects has prompted theorists to place the evolutionary origin of genomic imprinting before the last common ancestor of plants and animals, over a billion years ago.

Natural selection for genomic imprinting requires genetic variation in a population. A hypothesis for the origin of this genetic variation states that the host-defense system responsible for silencing foreign DNA elements, such as genes of viral origin, mistakenly silenced genes whose silencing turned out to be beneficial for the organism. There appears to be an over-representation of retrotransposed genes, that is to say genes that are inserted into the genome by viruses, among imprinted genes. It has also been postulated that if the retrotransposed gene is inserted close to another imprinted gene, it may just acquire this imprint.

Imprinted loci phenotypic signatures
Unfortunately, the relationship between the phenotype and genotype of imprinted genes is solely conceptual. The idea is frameworked using two alleles on a single locus and hosts three different possible classes of genotypes. The reciprocal heterozygotes genotype class contributes to understanding how imprinting will impact genotype to phenotype relationship. Reciprocal heterozygotes have a genetically equivalent, but they are phenotypically nonequivalent. Their phenotype may not be dependent on the equivalence of the genotype. This can ultimately increase diversity in genetic classes, expanding flexibility of imprinted genes. This increase will also force a higher degree in testing capabilities and assortment of tests to determine the presences of imprinting.

When a locus is identified as imprinted, two different classes express different alleles. Inherited imprinted genes of offspring are believed to be monoallelic expressions. A single locus will entirely produce one's phenotype although two alleles are inherited. This genotype class is called parental imprinting, as well as dominant imprinting. Phenotypic patterns are variant to possible expressions from paternal and maternal genotypes. Different alleles inherited from different parents will host different phenotypic qualities. One allele will have a larger phenotypic value and the other allele will be silenced. Underdominance of the locus is another possibility of phenotypic expression. Both maternal and paternal phenotypes will have a small value rather than one hosting a large value and silencing the other.

Statistical frameworks and mapping models are used to identify imprinting effects on genes and complex traits. Allelic parent-of-origin influences the vary in phenotype that derive from the imprinting of genotype classes. These models of mapping and identifying imprinting effects include using unordered genotypes to build mapping models. These models will show classic quantitative genetics and the effects of dominance of the imprinted genes.

Disorders associated with imprinting
Imprinting may cause problems in cloning, with clones having DNA that is not methylated in the correct positions. It is possible that this is due to a lack of time for reprogramming to be completely achieved. When a nucleus is added to an egg during somatic cell nuclear transfer, the egg starts dividing in minutes, as compared to the days or months it takes for reprogramming during embryonic development. If time is the responsible factor, it may be possible to delay cell division in clones, giving time for proper reprogramming to occur.

An allele of the "callipyge" (from the Greek for "beautiful buttocks"), or CLPG, gene in sheep produces large buttocks consisting of muscle with very little fat. The large-buttocked phenotype only occurs when the allele is present on the copy of chromosome 18 inherited from a sheep's father and is not on the copy of chromosome 18 inherited from that sheep's mother.

In vitro fertilisation, including ICSI, is associated with an increased risk of imprinting disorders, with an odds ratio of 3.7 (95% confidence interval 1.4 to 9.7).

Male infertility
Epigenetic deregulations at H19 imprinted gene in sperm have been observed associated with male infertility. Indeed, methylation loss at H19 imprinted gene has been observed associated with MTHFR gene promoter hypermethylation in semen samples from infertile males.

Prader-Willi/Angelman
The first imprinted genetic disorders to be described in humans were the reciprocally inherited Prader-Willi syndrome and Angelman syndrome. Both syndromes are associated with loss of the chromosomal region 15q11-13 (band 11 of the long arm of chromosome 15). This region contains the paternally expressed genes SNRPN and NDN and the maternally expressed gene UBE3A.
 * Paternal inheritance of a deletion of this region is associated with Prader-Willi syndrome (characterised by hypotonia, obesity, and hypogonadism).
 * Maternal inheritance of the same deletion is associated with Angelman syndrome (characterised by epilepsy, tremors, and a perpetually smiling facial expression).

DIRAS3 (NOEY2 or ARH1)
DIRAS3 is a paternally expressed and maternally imprinted gene located on chromosome 1 in humans. Reduced DIRAS3 expression is linked to an increased risk of ovarian and breast cancers; in 41% of breast and ovarian cancers the protein encoded by DIRAS3 is not expressed, suggesting that it functions as a tumor suppressor gene. Therefore, if uniparental disomy occurs and a person inherits both chromosomes from the mother, the gene will not be expressed and the individual is put at a greater risk for breast and ovarian cancer.

Other
Other conditions involving imprinting include Beckwith-Wiedemann syndrome, Silver-Russell syndrome, and pseudohypoparathyroidism.

Transient neonatal diabetes mellitus can also involve imprinting.

The "imprinted brain hypothesis" argues that unbalanced imprinting may be a cause of autism and psychosis.

Imprinted genes in other animals
In insects, imprinting affects entire chromosomes. In some insects the entire paternal genome is silenced in male offspring, and thus is involved in sex determination. The imprinting produces effects similar to the mechanisms in other insects that eliminate paternally inherited chromosomes in male offspring, including arrhenotoky.

In social honey bees, the parent of origin and allele-specific genes has been studied from reciprocal crosses to explore the epigenetic mechanisms underlying aggressive behavior.

In placental species, parent-offspring conflict can result in the evolution of strategies, such as genomic imprinting, for embryos to subvert maternal nutrient provisioning. Despite several attempts to find it, genomic imprinting has not been found in the platypus, reptiles, birds, or fish. The absence of genomic imprinting in a placental reptile, the Pseudemoia entrecasteauxii, is interesting as genomic imprinting was thought to be associated with the evolution of viviparity and placental nutrient transport.

Studies in domestic livestock, such as dairy and beef cattle, have implicated imprinted genes (e.g. IGF2) in a range of economic traits, including dairy performance in Holstein-Friesian cattle.

Mouse foraging behavior
Foraging behavior in mice studied is influenced by a sexually dimorphic allele expression implicating a cross-gender imprinting influence that varies throughout the body and may dominate expression and shape a behavior.

Imprinted genes in plants
A similar imprinting phenomenon has also been described in flowering plants (angiosperms). During fertilization of the egg cell, a second, separate fertilization event gives rise to the endosperm, an extraembryonic structure that nourishes the embryo in a manner analogous to the mammalian placenta. Unlike the embryo, the endosperm is often formed from the fusion of two maternal cells with a male gamete. This results in a triploid genome. The 2:1 ratio of maternal to paternal genomes appears to be critical for seed development. Some genes are found to be expressed from both maternal genomes while others are expressed exclusively from the lone paternal copy. It has been suggested that these imprinted genes are responsible for the triploid block effect in flowering plants that prevents hybridization between diploids and autotetraploids. Several computational methods to detect imprinting genes in plants from reciprocal crosses have been proposed.

title: Genomic imprinting