Yankai Xing
email: yankai.xing@ec-nantes.fr

Elkhatib Kamal
email: elkhatib.ibrahim@ec-nantes.fr

Bogdan Marinescu
email: bogdan.marinescu@ec-nantes.fr

Florent Xavier
email: florent.xavier@rte-france.com

Robust H ∞ Dynamic Output-feedback Control of Power Oscillation Damped via VSC-HVDC Transmission Systems

Keywords: Power system oscillations, HVDC, damping controller, inter-area modes, robustness

This paper addresses the problem of a particular case of high-voltage direct current transmission inserted into a meshed AC grid, which has an inter-area oscillation mode with a higher frequency than the normal mode. The classic Power Oscillation Damping (POD) controller failure to deal with this situation and the other changing operation point cases . Moreover, Non-Minimum Phase Zeros (NMPZs) were systematically put into evidence. Combined with the system uncertainties, they present a serious challange for the control. A same reducedorder model of High-Voltage Direct Current line (HVDC) and adjacent AC area as former research is used for control design in this paper. Based on the reference model, using the LMI optimization method, a Dynamic Output Feedback Controller (DOFC) is proposed to provide modulation of active and reactive power to damp the inter-area oscillations, enhance the damping of the other modes, eliminate some impacts of NMPZs in the system and achieve robustness against variation of the operation point. The linearization and nonlinear models of the system are studied to establish and verify the method. The efficiency and robustness of the proposed controller were tested on the same actual benchmark of 19 generators connected through the mesh AC grid.

I. INTRODUCTION

As mentioned in past research [START_REF] Xing | Power oscillations damping controller for hvdc inserted in meshed ac grids[END_REF] and [START_REF] Xing | Robust Research of Power Oscillations Damping Controller for HVDC Inserted in Meshed AC Grids[END_REF], the inter-area modes which were analyzed and controlled were the ones at around 0.2 Hz in Europe. For HVDC line inserted into a mesh AC grid (such as the recent interconnection reinforcement in Europe) (for example, the France-Spain and France-Italy links), the inter-area control can be controlled by the highvoltage direct current converter. The mode may be at a higher frequency of about 1 Hz. The classic vector POD controller( see, e.g., [START_REF] Lee | IEEE recommended practice for excitation system models for power system stability studies (ieee std 421.5[END_REF]) is tested in paper [START_REF] Xing | Power oscillations damping controller for hvdc inserted in meshed ac grids[END_REF], [START_REF] Xing | Robust Research of Power Oscillations Damping Controller for HVDC Inserted in Meshed AC Grids[END_REF] as not satisfying to deal with this complex topology with NMPZs in the system.

In addition, in many applications, modeling errors and system uncertainties in plant models are inevitable. For preciseness, a design technique must accommodate these errors and uncertainties to be practically feasible. Thus, robust control has grown, in the last past years, as one of the most important areas in modern control design since the pioneering works [START_REF] Doyle | Statespace solutions to standard H 2 and H∞ control problems[END_REF].

Moreover, the Linear Matrix Inequality (LMI) methodologies, which are computationally simple and numerically reliable for solving convex optimization problems [START_REF] Boyd | Linear matrix inequalities in systems and control theory[END_REF], moreover, its effective tools for robust controller design of linear uncertain systems. Recently, some attempts have been made to design robust dynamic output feedback controllers [START_REF] Kanev | Robust outputfeedback controller design via local BMI optimization[END_REF], either for norm-bounded uncertainty or polytopic uncertainty.

A large amount of research has been carried out on the development of the dynamic output feedback controllers according to Lyapunov theory via LMI approaches, e.g. [START_REF] Agulhari | LMI relaxations for reduced-order robust H∞ control of continuous-time uncertain linear systems[END_REF]. Most of these methods present an iterative algorithm in which a set of LMIs are iteratively repeated until some certain termination criteria are met. In addition, since Linear Parameter Varying (LPV) systems are also an important class of systems from a theoretical and practical point of view, there has been much progress in the field of gain-scheduled H ∞ control of polytopic LPV systems using parameter-dependent Lyapunov method [START_REF] Kamal | Robust nonlinear control of wind energy conversion systems[END_REF], [START_REF] Kamal | Robust fault tolerant control of DFIG wind energy systems with unknown inputs[END_REF]. In addition, a robust controller which is effective under different operating conditions is required.

Based on the same Bode plot-based reduced-order control model, sufficient conditions are derived for robust stabilization in the sense of Lyapunov asymptotic stability and are formulated in the format of LMIs to obtain gains for a H ∞ -type controller (Dynamic Output-feedback Controller (DOFC)) based on the reference model. Investigations with nonlinear model of the system were done to settle and validate the approach. The efficiency and robustness of the proposed controller are tested and compared with each others.

This paper is organised as follows. Section II introduces the problem formulation, main difficulties and modeling. LMIbased design of robust dynamic output feedback controller is given in section III, section IV shows validation of nominal cases and robust tests. Finally, Section V concludes the paper.

II. MAIN DIFFICULTIES AND MODELING A. Main difficulties

Firstly, highly meshed grid present inter-area modes at higher frequencies which are less spread and at high frequencies. It should be noted for the regulators to not disturb the NMPZs brings much more difficulties for a controller. The existence of the NMPZs depends on the topology of the power grid [START_REF] Xing | Power oscillations damping controller for hvdc inserted in meshed ac grids[END_REF]. This may cause the controller to fail to improve the damping of the mode. In previous work [START_REF] Xing | Power oscillations damping controller for hvdc inserted in meshed ac grids[END_REF], this phenomenon has been verified on the results. Also, modeling errors and system uncertainties in plant models are inevitable. This is the third task to be solved in this paper.

B. Test system

The past research used test system is recalled here. It contains 19 generators and one HVDC line. After eigenanalysis, the modes which we concerned are list in Table I. To capture the dynamics mentioned above in frequencies close to the modes to be damped, and to maintain consistency with former research, the same control model is used to design the controllers. (see [START_REF] Xing | Power oscillations damping controller for hvdc inserted in meshed ac grids[END_REF], [START_REF] Xing | Robust Research of Power Oscillations Damping Controller for HVDC Inserted in Meshed AC Grids[END_REF])

C. Control model

To design the mentioned controller based on the staterepresent model and focus on the interested dynamics, the simple reduced control model is not sufficient. To capture the dynamics mentioned above in frequencies close to the modes to be damped, two strategies are possible. First consists in starting from a full model of the power system and reduce it at a reasonable scale (about 10 state variables) for control by preserving dynamics of interest. This is very difficult for large-scale system and led us to a second approach based on aggregation of a transfer model around the modes of interest (see details in our former work [START_REF] Xing | Robust Research of Power Oscillations Damping Controller for HVDC Inserted in Meshed AC Grids[END_REF]). Another significant control aspect is selection of the input signal for the designed controller. According [START_REF] Belhocine | Input signal and model structure analysis for the hvdc link pod control[END_REF], to rate the candidates input signals, residues of the corresponding open-loop transfer functions are systematically computed. The terminal difference of angles, ∆θ = θ 1 -θ 2 , has the high residue is selected as control signal to provide power modulation as illustrated in Fig. 2.

D. Classic POD and its limitations

The structure of the classic IEEE HVDC POD controller [START_REF] Lee | IEEE recommended practice for excitation system models for power system stability studies (ieee std 421.5[END_REF] contains a gain K, a wash-out filter and n phase lead-lag blocks. It is defined by the transfer function given by [START_REF] Xing | Power oscillations damping controller for hvdc inserted in meshed ac grids[END_REF]. In this case, K = 2.5614, T 1 = 0.4746, T 2 = 0.0688, T w = 1 and n = 2. Its tuning of parameters of our test system are detailed in [START_REF] Xing | Power oscillations damping controller for hvdc inserted in meshed ac grids[END_REF].

H P OD (s) = K T w s 1 + T w s 1 + T 1 s 1 + T 2 s n (1)
When a target damping of 10% was fixed for mode 2, the tuning methodology mentioned above yields: K = 2.5614, T 1 = 0.4746, T 2 = 0.0688, T w = 1 and n = 2. However, the real damping of this mode is only about 6% as reported in Table II. Further more, it can be observed that the damping of mode 4 is decreased by this controller. Moreover, the classic IEEE damping controller design synthesis [START_REF] Lee | IEEE recommended practice for excitation system models for power system stability studies (ieee std 421.5[END_REF] is simple but tends to lack of robustness. Its phase compensation is settled down for a specific grid situation which may not be suitable for changed phase of residue of the mode.

III. ROBUST H ∞ DYNAMIC OUTPUT-FEEDBACK CONTROL BASED ON REFERENCE MODEL

To overcome these difficulties mentioned above, and from experiences of solving convex optimization problems via LMIs [START_REF] Kamal | Fuzzy Observer-Based Fault Tolerant Control Against Sensor Faults for Proton Exchange Membrane Fuel Cells[END_REF]- [START_REF] Kamal | An intelligent maximum power extraction algorithm for hybrid wind-diesel-storage system[END_REF], the Robust H ∞ Dynamic Output-feedback Controller (DOFC) Based on Reference Model strategy is proposed.

A. Selection of reference model

The reference model is chosen as having the desired output, that is horizontally shifting the poles to left until getting the desired damping (over 10%). In this case, the state space of the reference model can be given as the following:

ẋr (t) = A r x r (t) + B r u r (t) y r = C r x r (t) (2)
The selection of reference model is significant for the effectiveness of this controller. In general, this reference model is chosen as having the desired output, that is horizontally shifting the poles to left until getting the desired damping (over 10%). More addition, in order to eliminate the impact of unstable zeros, unstable zeros in reference model are placed to left plane but closed to virtual axis (decrease the control difficulty). In the meanwhile, the other stable zeros keep the Now, consider linear time-invariant continuous system is given by:

ẋ(t) = Ax(t) + Bu(t) y(t) = Cx(t) (3)
where x(t) ∈ n×1 , y(t) ∈ g×1 and u(t) ∈ m×1 are the state vector, output vector and the control input, respectively, C ∈ g×n is the system output matrix, A ∈ n×n and B ∈ n×m , are the system and input matrice, respectively.

The structure of Robust H ∞ Dynamic Output-feedback Controller (DOFC) Based on Reference Model strategy is given in Fig. 2. Consider the class of linear time-invariant continuous-time control system and reference system given in (3) and (2), respectively. The dynamic output feedback controller is given by.

ẋc (t) = A c x c (t) + B c u c (t), y c = C c x c (t) (4)
where A c , B c and C c are controller matrices to be designed. Applying the reference model ( 2) and the dynamic output feedback controller (4) to the system (3). From Fig. 2, it can be seen that:

u = u r -u c = u r -y c = u r -C c x c u c = y = Cx (5)
From ( 3), ( 2) and ( 4) , the augmented of the control system is given by:

Ẋ(t) = ĀX(t) + Bu r , Y (t) = CX(t) (6)
where

Ā =   A 0 -BC c 0 A r 0 B c C 0 A c   , B =   B B r 0   , C =   -C C r 0   T , X(t) =   x x r x c   T B.

Stability Analysis of the Proposed Robust H ∞ DOFC design

The main results for the global asymptotic stability of the system (6) are given Theorem 2:

Theorem 2: The system ( 6) is robustly stabilizable with the dynamic output-feedback controller given in (4), if there exist positive definite symmetric matrices Q, Z ∈ (n+nr)×(n+nr) and full matrices A, B, C ∈ (n+nr)×(n+nr) and scalar γ, such that the following LMI is satisfied,

min γ (7) subject to         φ 1 + φ T 1 A T + A 0 0 A r B B r Q -C T C T r * φ 2 + φ T 2 Z 0 B r + B -C T C T r * * -γI 0 * * 0 -γI         ≤ 0 ( 8
)
Q I I Z ≥ 0 ( 9
)
where

φ 1 = A 0 0 A r Q + -B C 0 , φ 2 = Z A 0 0 A r + B BC 0 T , N = (I -ZQ)M -T , Ā = A -Z A 0 0 A r Q -N B c C 0 T Q -Z BC c 0 M T A c = N -1 ĀM -T , C c = CM -T , B c = N -1 B,
Proof. Bound real lemma [START_REF] Zhou | Robust and Optimal Control[END_REF] if there are exists a (n + n r ) -dimensional controller making ||P || ∞ ≤ γ if and only if there exits symmetry matrix W ∈ 2(n+nr)×2(n+nr) satisfying

  ĀT W + W Ā W B CT BT W -γI 0 C 0 -γI   ≤ 0, W ≥ 0 (10)
Inequality ( 10) is a BMI when the controller is unknown. Here we will use the variables substitution method proposed in [START_REF] Scherer | Multiobjective output-feedback control via LMI optimization[END_REF] to linearize it. Partition W and W -1 as

W = Z N N T , W -1 = Q M M T ( 11
)
where Q and Z are (n + n r )X(n + n r ) symmetry matrices, M and N are (n + n r )X(n + n r ) full matrices, stands for unknown matrix. Set

1 = Q I M T 0 , 2 = I Z 0 N T (12)
From W W -1 = I , we can infer

2 W Ā = 2 Ā 1 ( 13
)
So that,

2 Ā 1 = I 0 Z N   A 0 -BC c C A r 0 B c C 0 A c   Q I M T 0 =   A 0 0 A r Q + -BB c 0 M T A 0 0 A r Q 1 Q 2   (14)
T

1 W B = T 2 B 1 = I 0 Z N   B B r 0   =     B B r Z B B r     (15) then, T 1 C = -C C r C Q I M T 0 T     Q -C T C T r -C T r C T r     (16) where,
Q 1 = Z A 0 0 A r Q + N B c C 0 Q + Z -BC c 0 M T + N A c M T , Q 2 = Z A 0 0 A r + N B c C 0 (17) Thus, Â = Z A 0 0 A r Q + N B c C 0 Q + Z -BC c 0 M T +N A c M T , B = N B k , Ĉ = C k M T (18)
Therefore, [START_REF] Belhocine | Input signal and model structure analysis for the hvdc link pod control[END_REF] are equivalent to (8) and ( 9) in the Theorem 2.

IV. VALIDATION TESTS In this section, the DOFC based on reference model strategy depicted in section III are validated in the case of the problem of damping inter-area oscillations via power modulation of a VSC-HVDC link integrated in a power AC grid in two cases linearized and nonlinear systems. For all tests, the response to the short-circuit at the node connected to generator 918 (which is closed to most participated generator 911 of mode 2) is studied which excites the modes of interest. (Table I).

Notice that, to evaluate the effective of the controllers, some key point should be mentioned: The several swing in the beginning mainly contains the dynamic performance of controllers; the oscillation in the end before settling down can be seen as interested mode in the system (1Hz).

A. Validation on the linearized system

In this subsection, the controller is tested on the linear approximation of the system in Matlab. The step response of the difference of angles ∆θ in nominal case is shown in Figure 3. From this linearized system closed-loop results, it can be seen that, for the modes damping, the DOFC POD gives a good performance compared to classic POD strategy.

B. Validation on the nonlinear system

The controllers are now tested on the nonlinear model of the system in Eurostag. Not only nominal case is considered but also robust cases as given in the following tests. The non-linear system closed-loop responses shown in Fig. 4. The linearization after applying PODs is done to calculate the damping shown in Table II.

1) Nominal case: Comparison between controllers of nominal case is shown in Figure 4.

From Fig. 4, it can be seen that, for at the least damped mode, the DOFC POD performs the best in the swings in the end of the curve where the mode is the most observable. Notice that, several swings in the beginning are due to the dynamic transient of the system. From Table II, the DOFC POD improve each modes over 10%. The classic POD improves a little the mode 2, but disturbs mode 4. 2) Robust cases: In order to analyze system uncertainties, the changing operation point situations are studied in this part.

The uncertainty analysis is proceeding in several cases listed here:

1) Inverse the power flow direction and the value of the active power on HVDC lines (from +800M W to -200M W ); 2) Increase the load on the nodes connected the most participating generator in the critical mode 2 (increase 30%); 3) Tripping the generators closed to the most participation machine; 4) Tripping lines closed to the most participating generator to the critical mode 2. Comparisons between controllers of robust cases are shown in Figure 5, 6, 7, 8.

For reverse power flow case, the performance of DOFC POD is good in the beginning. Closed loop with classic POD is even worse than open-loop.

For increased load case and tripping generator cases, it is obviously, the most advantage controller is DOFC POD.

In tripping lines case, The classic POD has the same performance with DOFC POD for damping the modes but worse dynamic response in the beginning.

From these tests one can conclude that, for damping of the interested modes, the performance of DOFC is Considerable. For same level of damping, robustness is improved with proposed DOFC POD strategy.

V. CONCLUSION

The problem of power oscillations damping control of a VSC-HVDC was addressed in the particular context where the link is inserted in a meshed AC grid. The only information of the residues of the modes to be damped is not sufficient in this case and a dynamic control model which captures not only the modes to be damped but also the other dynamics which might be excited by the closed-loop is proposed. Moreover, information from this model was used in a reference model, in order to counteract the effects of non-minimum phase zeros. In addition, realistic situations of power grids motivated us to improve robustness against typical variations of the grid and un-modeled dynamics. This allowed us to provide better robustness, i.e., maintain the damping properties not only in the nominal case but also in case of disturbances (short-circuits) and usual grid variation (line /generator trips, modification of operation point, etc). The control was validated on a realistic case in simulation with a professional grid dedicated software (Eurostag). The resulting control can be easily implemented in state-space in real-word of grid applications.

Fig. 1 .

 1 Fig. 1. Step response of reference model.

Fig. 2 .

 2 Fig. 2. Controller structure.

Fig. 3 .

 3 Fig. 3. Comparision of linearized model.

Fig. 4 .

 4 Fig. 4. Nominal case.

Fig. 5 .

 5 Fig. 5. Reverse power flow case.

Fig. 6 .

 6 Fig. 6. Increase load case.

Fig. 7 .

 7 Fig. 7. Tripping generator case.

Fig. 8 .

 8 Fig. 8. Tripping lines case.

TABLE II

 II

		COMPARISON OF DAMPING
			ξ	ξ
	No.	ξ without POD (%)	with classic	with DOFC
			POD (%)	POD (%)
	1	19.5	30.5	23.3
	2	4.5	6.1	12.6
	3	10.1	12.0	10.8
	4	8.3	8.1	10.6
	5	10.1	12.4	14.1


T Clausen

Internet Engineering Task Force (IETF) U. Herberg Request for Comments: 6622 Fujitsu Laboratories of America Category: Standards Track

This document describes general and flexible TLVs for representing cryptographic Integrity Check Values (ICVs) (i.e., digital signatures or Message Authentication Codes (MACs)) as well as timestamps, using the generalized Mobile Ad Hoc Network (MANET) packet/message format defined in RFC 5444. It defines two Packet TLVs, two Message TLVs, and two Address Block TLVs for affixing ICVs and timestamps to a packet, a message, and an address, respectively.

Introduction

This document specifies o Two TLVs for carrying Integrity Check Values (ICVs) and timestamps in packets, messages, and address blocks as defined by [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

o A generic framework for ICVs, accounting (for Message TLVs) for mutable message header fields (<msg-hop-limit> and <msg-hop-count>), where these fields are present in messages.

This document sets up IANA registries for recording code points for hash-function and ICV calculation, respectively.

Moreover, in Section 12, this document defines the following:

o One common method for generating ICVs as a cryptographic function, calculated over the hash value of the content.

Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

This document uses the terminology and notation defined in [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

In particular, the following TLV fields from [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] are used in this specification: <msg-hop-limit> is the hop limit of a message, as specified in Section 5.2 of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

<msg-hop-count> is the hop count of a message, as specified in Section 5.2 of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

<length> is the length of a TLV in octets, as specified in Section 5.4.1 of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

Applicability Statement

MANET routing protocols using the format defined in [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] are accorded the ability to carry additional information in control messages and packets, through the inclusion of TLVs. Information so included MAY be used by a MANET routing protocol, or by an extension of a MANET routing protocol, according to its specification.

Herberg & Clausen Standards Track [Page 3]

This document specifies how to include an ICV for a packet, a message, and addresses in address blocks within a message, by way of such TLVs. This document also specifies a) how to treat "mutable" fields, specifically the <msg-hop-count> and <msg-hop-limit> fields, if present in the message header when calculating ICVs, such that the resulting ICV can be correctly verified by any recipient, and b) how to include this ICV.

This document describes a generic framework for creating ICVs, and how to include these ICVs in TLVs. In Section 12, an example method for calculating such ICVs is given, using a cryptographic function over the hash value of the content.

Security Architecture

Basic MANET routing protocol specifications are often "oblivious to security"; however, they have a clause allowing a control message to be rejected as "badly formed" or "insecure" prior to the message being processed or forwarded. MANET routing protocols such as the Neighborhood Discovery Protocol (NHDP) [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and the Optimized Link State Routing Protocol version 2 [START_REF] Clausen | The Optimized Link State Routing Protocol version 2[END_REF] recognize external reasons (such as failure to verify an ICV) for rejecting a message that would be considered "invalid for processing". This architecture is a result of the observation that with respect to security in MANETs, "one size rarely fits all" and that MANET routing protocol deployment domains have varying security requirements ranging from "unbreakable" to "virtually none". The virtue of this approach is that MANET routing protocol specifications (and implementations) can remain "generic", with extensions providing proper security mechanisms specific to a deployment domain.

The MANET routing protocol "security architecture", in which this specification situates itself, can therefore be summarized as follows:

o Security-oblivious MANET routing protocol specifications, with a clause allowing an extension to reject a message (prior to processing/forwarding) as "badly formed" or "insecure".

o MANET routing protocol security extensions, rejecting messages as "badly formed" or "insecure", as appropriate for a given security requirement specific to a deployment domain.

o Code points and an exchange format for information, necessary for specification of such MANET routing protocol security extensions.

Herberg & Clausen Standards Track [Page 4]

This document addresses the last of the issues listed above by specifying a common exchange format for cryptographic ICVs, making reservations from within the Packet TLV, Message TLV, and Address Block TLV registries of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF], to be used (and shared) among MANET routing protocol security extensions.

For the specific decomposition of an ICV into a cryptographic function over a hash value (specified in Section 12), this document establishes two IANA registries for code points for hash functions and cryptographic functions adhering to [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

With respect to [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF], this document is o Intended to be used in the non-normative, but intended, mode of use described in Appendix B of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

o A specific example of the Security Considerations section of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] (the authentication part).

Overview and Functioning

This document specifies a syntactical representation of securityrelated information for use with [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] addresses, messages, and packets, and also establishes IANA registrations of TLV types and type extension registries for these TLV types.

Moreover, this document provides guidelines for how MANET routing protocols and MANET routing protocol extensions using this specification should treat ICV and Timestamp TLVs, and mutable fields in messages. This specification does not represent a stand-alone protocol; MANET routing protocols and MANET routing protocol extensions, using this specification, MUST provide instructions as to how to handle packets, messages, and addresses with security information, associated as specified in this document.

This document assigns TLV types from the registries defined for Packet, Message, and Address Block TLVs in [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF]. When a TLV type is assigned from one of these registries, a registry for type extensions for that TLV type is created by IANA. This document utilizes these type extension registries so created, in order to specify internal structure (and accompanying processing) of the <value> field of a TLV.

For example, and as defined in this document, an ICV TLV with type extension = 0 specifies that the <value> field has no pre-defined internal structure but is simply a sequence of octets. An ICV TLV with type extension = 1 specifies that the <value> field has a pre-defined internal structure and defines its interpretation.

Herberg & Clausen Standards Track [Page 5]

(Specifically, the <value> field consists of a cryptographic operation over a hash value, with fields indicating which hash function and cryptographic operation have been used; this is specified in Section 12.)

Other documents can request assignments for other type extensions; if they do so, they MUST specify their internal structure (if any) and interpretation.

General ICV TLV Structure

The value of the ICV TLV is <value> := <ICV-value> where <ICV-value> is a field, of <length> octets, which contains the information to be interpreted by the ICV verification process, as specified by the type extension.

Note that this does not stipulate how to calculate the <ICV-value> nor the internal structure thereof, if any; such information MUST be specified by way of the type extension for the ICV TLV type. See Section 13. This document specifies two such type extensions --one for ICVs without pre-defined structures, and one for ICVs constructed by way of a cryptographic operation over a hash value.

General Timestamp TLV Structure

The value of the Timestamp TLV is <value> := <time-value> where <time-value> is an unsigned integer field, of length <length>, which contains the timestamp.

Note that this does not stipulate how to calculate the <time-value> nor the internal structure thereof, if any; such information MUST be specified by way of the type extension for the TIMESTAMP TLV type. See Section 13.

Herberg & Clausen Standards Track [Page 6]

A timestamp is essentially "freshness information". As such, its setting and interpretation are to be determined by the MANET routing protocol, or MANET routing protocol extension, that uses the timestamp and can, for example, correspond to a UNIX timestamp, GPS timestamp, or a simple sequence number.

Packet TLVs

Two Packet TLVs are defined: one for including the cryptographic ICV of a packet and one for including the timestamp indicating the time at which the cryptographic ICV was calculated.

Packet ICV TLV

A Packet ICV TLV is an example of an ICV TLV as described in Section 6.

The following considerations apply:

o Because packets as defined in [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] are never forwarded by routers, no special considerations are required regarding mutable fields (e.g., <msg-hop-count> and <msg-hop-limit>), if present, when calculating the ICV.

o Any Packet ICV TLVs already present in the Packet TLV block MUST be removed before calculating the ICV, and the Packet TLV block size MUST be recalculated accordingly. Removed ICV TLVs MUST be restored after having calculated the ICV value.

The rationale for removing any Packet ICV TLV already present prior to calculating the ICV is that several ICVs may be added to the same packet, e.g., using different ICV functions.

Packet TIMESTAMP TLV

A Packet TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 7. If a packet contains a TIMESTAMP TLV and an ICV TLV, the TIMESTAMP TLV SHOULD be added to the packet before any ICV TLV, in order that it be included in the calculation of the ICV. Two Message TLVs are defined: one for including the cryptographic ICV of a message and one for including the timestamp indicating the time at which the cryptographic ICV was calculated.

Message ICV TLV

A Message ICV TLV is an example of an ICV TLV as described in Section 6. When determining the <ICV-value> for a message, the following considerations MUST be applied:

o The fields <msg-hop-limit> and <msg-hop-count>, if present, MUST both be assumed to have the value 0 (zero) when calculating the ICV.

o Any Message ICV TLVs already present in the Message TLV block MUST be removed before calculating the ICV, and the message size as well as the Message TLV block size MUST be recalculated accordingly. Removed ICV TLVs MUST be restored after having calculated the ICV value.

The rationale for removing any Message ICV TLV already present prior to calculating the ICV is that several ICVs may be added to the same message, e.g., using different ICV functions.

Message TIMESTAMP TLV

A Message TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 7. If a message contains a TIMESTAMP TLV and an ICV TLV, the TIMESTAMP TLV SHOULD be added to the message before the ICV TLV, in order that it be included in the calculation of the ICV.

Address Block TLVs

Two Address Block TLVs are defined: one for associating a cryptographic ICV to an address and one for including the timestamp indicating the time at which the cryptographic ICV was calculated. in the verification process of the ICV. When determining the <ICV-value> for an address, the following consideration MUST be applied:

o If other TLV values are concatenated with the address for calculating the ICV, these TLVs MUST NOT be Address Block ICV TLVs already associated with the address.

The rationale for not concatenating the address with any ICV TLV values already associated with the address when calculating the ICV is that several ICVs may be added to the same address, e.g., using different ICV functions.

Address Block TIMESTAMP TLV

An Address Block TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 7. If both a TIMESTAMP TLV and an ICV TLV are associated with an address, the TIMESTAMP TLV <value> MUST be covered when calculating the value of the ICV to be contained in the ICV TLV value (i.e., concatenated with the associated address and any other values as described in Section 10.1).

ICV: Basic

The basic ICV, represented by way of an ICV TLV with type extension = 0, is a simple bit-field containing the cryptographic ICV. This assumes that the mechanism stipulating how ICVs are calculated and verified is established outside of this specification, e.g., by way of administrative configuration or external out-of-band signaling. Thus, the <ICV-value>, when using type extension = 0, is <ICV-value> := <ICV-data> where <ICV-data> is an unsigned integer field, of length <length>, which contains the cryptographic ICV.

12. ICV: Cryptographic Function over a Hash Value One common way of calculating an ICV is applying a cryptographic function over a hash value of the content. This decomposition is specified in this section, using a type extension = 1 in the ICV TLVs. The following data structure allows representation of a cryptographic ICV, including specification of the appropriate hash function and cryptographic function used for calculating the ICV:

<ICV-value> := <hash-function> <cryptographic-function> <key-id-length> <key-id> <ICV-data> where <hash-function> is an 8-bit unsigned integer field specifying the hash function.

<cryptographic-function> is an 8-bit unsigned integer field specifying the cryptographic function.

<key-id-length> is an 8-bit unsigned integer field specifying the length of the <key-id> field in number of octets. The value 0x00 is reserved for using a pre-installed, shared key.

<key-id> is a field specifying the key identifier of the key that was used to calculate the ICV of the message, which allows unique identification of different keys with the same originator. It is the responsibility of each key originator to make sure that actively used keys that it issues have distinct key identifiers.

If <key-id-length> equals 0x00, the <key-id> field is not contained in the TLV, and a pre-installed, shared key is used.

<ICV-data> is an unsigned integer field, whose length is <length> -3 -<key-id-length>, and which contains the cryptographic ICV.

The version of this TLV, specified in this section, assumes that calculating the ICV can be decomposed into

ICV-value = cryptographic-function(hash-function(content))

The hash function and the cryptographic function correspond to the entries in two IANA registries, which are set up by this specification and are described in Section 13. The rationale for separating the hash function and the cryptographic function into two octets instead of having all combinations in a single octet --possibly as a TLV type extension --is that adding further hash functions or cryptographic functions in the future may lead to a non-contiguous number space.

The rationale for not including a field that lists parameters of the cryptographic ICV in the TLV is that, before being able to validate a cryptographic ICV, routers have to exchange or acquire keys (e.g., public keys). Any additional parameters can be provided together with the keys in that bootstrap process. It is therefore not necessary, and would even entail an extra overhead, to transmit the parameters within every message. One implicitly available parameter is the length of the ICV, which is <length> -3 -<key-id-length>, and which depends on the choice of the cryptographic function.

Considerations for Calculating the ICV

The considerations listed in the following subsections MUST be applied when calculating the ICV for Packet, Message, and Address ICV TLVs, respectively.

12.2.1. Packet ICV TLV When determining the <ICV-value> for a packet, the ICV is calculated over the fields <hash-function>, <cryptographic-function>, <key-id-length>, and --if present --<key-id> (in that order), concatenated with the entire packet, including the packet header, all Packet TLVs (other than Packet ICV TLVs), and all included Messages and their message headers, in accordance with Section 8.1.

Message ICV TLV

When determining the <ICV-value> for a message, the ICV is calculated over the fields <hash-function>, <cryptographic-function>, <key-id-length>, and --if present --<key-id> (in that order), concatenated with the entire message. The considerations in Section 9.1 MUST be applied.

Address Block ICV TLV

When determining the <ICV-value> for an address, the ICV is calculated over the fields <hash-function>, <cryptographic-function>, <key-id-length>, and --if present --<key-id> (in that order), concatenated with the address, and concatenated with any other values --for example, any other address block TLV <value> that is

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associated with that address. A MANET routing protocol or MANET routing protocol extension using Address Block ICV TLVs MUST specify how to include any such concatenated attribute of the address in the verification process of the ICV. The considerations in Section 10.1 MUST be applied.

Example of a Message Including an ICV

The sample message depicted in Figure 1 is derived from Appendix D of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF]. The message contains an ICV Message TLV, with the value representing an ICV that is 16 octets long of the whole message, and a key identifier that is 4 octets long. The type extension of the Message TLV is 1, for the specific decomposition of an ICV into a cryptographic function over a hash value, as specified in Section 12. o Two Packet TLV types, which have been allocated from the 0-223 range of the "Packet TLV Types" repository of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF], as specified in Table 1.

o Two Message TLV types, which have been allocated from the 0-127 range of the "Message TLV Types" repository of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF], as specified in Table 2.

o Two Address Block TLV types, which have been allocated from the 0-127 range of the "Address Block TLV Types" repository of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF], as specified in Table 3.

This specification created the following: o A type extension registry for each of these TLV types with initial values as listed in Tables 1, 2, and 3.

IANA has assigned the same numerical value to the Packet TLV, Message TLV, and Address Block TLV types with the same name.

The following terms are used as defined in [START_REF] Narten | Guidelines for Writing an IANA Considerations Section in RFCs[END_REF]: "Namespace", "Registration", and "Designated Expert".

The following policy is used as defined in [START_REF] Narten | Guidelines for Writing an IANA Considerations Section in RFCs[END_REF]: "Expert Review".

Expert Review: Evaluation Guidelines

For TLV type extensions registries where an Expert Review is required, the Designated Expert SHOULD take the same general recommendations into consideration as those specified by [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

For the Timestamp TLV, the same type extensions for all Packet, Message, and Address Block TLVs SHOULD be numbered identically. In addition, a MANET routing protocol or MANET routing protocol extension that uses this specification MUST specify how to use the framework, and the TLVs presented in this document. In addition, the protection that the MANET routing protocol or MANET routing protocol extensions attain by using this framework MUST be described.

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As an example, a MANET routing protocol that uses this component to reject "badly formed" or "insecure" messages if a control message does not contain a valid ICV SHOULD indicate the security assumption that if the ICV is valid, the message is considered valid. It also SHOULD indicate the security issues that are counteracted by this measure (e.g., link or identity spoofing) as well as the issues that are not counteracted (e.g., compromised keys).

Figure

  Figure 1: Example Message with ICV

  10.1. Address Block ICV TLVAn Address Block ICV TLV is an example of an ICV TLV as described in Section 6. The ICV is calculated over the address, concatenated with any other values --for example, any other Address Block TLV <value> fields --associated with that address. A MANET routing protocol or MANET routing protocol extension using Address Block ICV TLVs MUST specify how to include any such concatenated attribute of the address

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Table 5 :

 5 Address Block TLV Type Registrations IANA has made allocations from the "Address Block TLV Types" namespace of[START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] for the Packet TLVs specified in Table3.IANA has created a new registry for hash functions that can be used when creating an ICV, as specified in Section 12 of this document. The initial assignments and allocation policies are specified in Table4.IANA has created a new registry for the cryptographic functions, as specified in Section 12 of this document. Initial assignments and allocation policies are specified in Table5. Cryptographic Function Registry14. Security ConsiderationsThis document does not specify a protocol. It provides a syntactical component for cryptographic ICVs of messages and packets, as defined in[START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF]. It can be used to address security issues of a MANET routing protocol or MANET routing protocol extension. As such, it has the same security considerations as[START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF].

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Acknowledgements

The authors would like to thank Bo Berry (Cisco), Alan Cullen (BAE), Justin Dean (NRL), Christopher Dearlove (BAE), Paul Lambert (Marvell), Jerome Milan (Ecole Polytechnique), and Henning Rogge (FGAN) for their constructive comments on the document.

The authors also appreciate the detailed reviews from the Area Directors, in particular Stewart Bryant (Cisco), Stephen Farrell (Trinity College Dublin), and Robert Sparks (Tekelec), as well as Donald Eastlake (Huawei) from the Security Directorate.

May 2012 13.2. Packet TLV Type Registrations IANA has made allocations from the "Packet TLV Types" namespace of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] for the Packet TLVs specified in Table 1. ----------+------+-----------+------------------------------------ ----------+------+-----------+------------------------------------

+-


Ulrich Herberg

Christopher Chris Dearlove

Thomas Heide Clausen

RFC7183: Integrity Protection for the Neighborhood Discovery Protocol (NHDP) and Optimized Link State Routing Protocol Version 2 (OLSRv2

come

This specification updates [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] by defining mandatory-to-implement security mechanisms (for integrity and replay protection). A deployment of these protocols may choose to employ an alternative(s) to these mechanisms; in particular, it may choose to protect packets rather than messages, it may choose to use an alternative Integrity Check Value (ICV) with preferred properties, and/or it may use an alternative timestamp. A deployment may choose to use no such security mechanisms, but this is not recommended.

The mechanisms specified are the use of an ICV for protection of the protocols' control messages and the use of timestamps in those messages to prevent replay attacks. Both use the TLV mechanism specified in [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] to add this information to the messages. These ICV and TIMESTAMP TLVs are defined in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF]. Different ICV TLVs are used for HELLO messages in NHDP and TC (Topology Control) messages in OLSRv2, the former also protecting the source address of the IP datagram that contains the HELLO message. This is because the IP datagram source address is used by NHDP to determine the address of a neighbor interface, and it is not necessarily otherwise contained in the HELLO message, while OLSRv2's TC message is forwarded in a new packet; thus, it has no single IP datagram source address.

The mechanism specified in this document is placed in the packet/ message processing flow as indicated in Figure 1. It exists between the packet parsing/generation function of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF] and the message processing/generation function of NHDP and OLSRv2.

| packet | | +--------------------------------+ | | | RFC 5444 packet | | parsing/generation | | | +--------------------------------+ | | Messages | /|\ Messages with \|/ | added TLVs | | D +--------------------------------+ R /__________________ | | O \ Messages | Mechanism specified in | P (failed check) | this document | | | +--------------------------------+ | | Messages | /|\ Messages (passed check) \|/ | | | +--------------------------------+ | | | NHDP/OLSRv2 message | | processing/generation | | | +--------------------------------+

Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

Additionally, this document uses the terminology and notation of [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF], [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF], [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF], and [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF]. 3. Applicability Statement [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] enable specifications of extensions to recognize additional reasons for rejecting a message as "badly formed and therefore invalid for processing", and mention security (integrity protection) as an explicit example. This document specifies a mechanism that provides this functionality.

Implementations of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] MUST include this mechanism, and deployments of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] SHOULD use this mechanism, except when a different security mechanism is more appropriate.

The applicability of this mechanism is determined by its characteristics, which are that it:

o Specifies a security mechanism that is required to be included in conforming implementations of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF].

o Specifies an association of ICVs with protocol messages, and specifies how to use a missing or invalid ICV as a reason to reject a message as "badly formed and therefore invalid for processing".

o Specifies the implementation of an ICV Message TLV, defined in o Specify which key identifiers are to be used in a MANET in which the routers share more than one secret key. (Such keys will be differentiated using the <key-id> field defined in an ICV TLV in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF].)

o Specify how to distribute cryptographic material (shared secret key(s)).

o Specify how to detect compromised routers with valid keys.

o Specify how to handle (revoke) compromised routers with valid keys.

Protocol Overview and Functioning

The mechanism specified in this document provides the following functionalities for use with messages specified by [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF]:

o Generation of ICV Message TLVs (as defined in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF]) for inclusion in an outgoing message. An implementation of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] MAY use more than one ICV TLV in a message, even with the same type extension, but these ICV TLVs MUST each use different keys or they MUST use a different algorithm to calculate the ICV, e.g., with different hash and/or cryptographic functions when using type extension 1 or 2. An implementation of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] MUST at least be able to generate an ICV TLV using HMAC-SHA-256 and one or more secret keys shared by all routers.

o Generation of TIMESTAMP Message TLVs (as defined in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF]) for inclusion in an outgoing message. An implementation of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] MAY use more than one ICV TLV in a message, but it MUST NOT use the same type extension. An implementation of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] that is able to synchronize the clocks in all routers in the network with sufficient precision MUST at least be able to generate a TIMESTAMP TLV using POSIX time.

o Verification of ICV Message TLVs contained in a message, in order to determine if this message MUST be rejected as "badly formed and therefore invalid for processing" [RFC6130] [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF]. An implementation of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] MUST at least be able to verify an ICV TLV using HMAC/SHA-256 and one or more secret keys shared by all routers.

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o Verification of TIMESTAMP Message TLVs (as defined in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF]) contained in a message, in order to determine if this message MUST be rejected as "badly formed and therefore invalid for processing" [RFC6130] [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF]. An implementation of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] that is able to synchronize the clocks in all routers in the network with sufficient precision MUST at least be able to verify a TIMESTAMP TLV using POSIX time.

ICV Packet TLVs (as defined in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF]) MAY be used by a deployment of the multiplexing process defined in [START_REF] Clausen | Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format[END_REF], either as well as or instead of the protection of the NHDP and OLSRv2 messages. (Note that in the case of NHDP, the packet protection is equally good, and also protects the packet header. In the case of OLSRv2, the packet protection has different properties than the message protection, especially for some forms of ICV. When packets contain more than one message, the packet protection has lower overheads in space and computation time.)

When a router generates a message on a MANET interface, this mechanism:

o Specifies how to calculate an ICV for the message.

o Specifies how to include that ICV using an ICV Message TLV.

[RFC6130] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] allow for the rejection of incoming messages prior to processing by NHDP or OLSRv2. This mechanism, when used, specifies that a message MUST be rejected if the ICV Message TLV is absent, or its value cannot be verified. Note that this means that routers whose implementation of NHDP and/or OLSRv2 does not include this specification will be ignored by routers using this mechanism, and these two sets of routers will, by design, form disjoint MANETs.

(The unsecured MANET will retain some information about the secured MANET, but be unable to use it, not having any recognized symmetric links with the secured MANET.)

Parameters

The following router parameters are specified for use by the two protocols; the first is required only by NHDP, but may be visible to OLSRv2, the second is required only by OLSRv2:

o MAX_HELLO_TIMESTAMP_DIFF -The maximum age that a HELLO message to be validated may have. If the current POSIX time of the router validating the HELLO message, minus the timestamp indicated in the TIMESTAMP TLV of the HELLO message, is greater than MAX_HELLO_TIMESTAMP_DIFF, the HELLO message MUST be silently discarded.

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o MAX_TC_TIMESTAMP_DIFF -The maximum age that a TC message to be validated may have. If the current POSIX time of the router validating the TC message, minus the timestamp indicated in the TIMESTAMP TLV of the TC message, is greater than MAX_TC_TIMESTAMP_DIFF, the TC message MUST be silently discarded.

The following constraints apply to these parameters:

o MAX_HELLO_TIMESTAMP_DIFF > 0 o MAX_TC_TIMESTAMP_DIFF > 0
However, these bounds are insufficient: MAX_HELLO_TIMESTAMP_DIFF and MAX_TC_TIMESTAMP_DIFF MUST be least as great as the maximum expected "age" of a message (i.e., the time difference between a message has been sent by a router and received by all intended destinations).

For HELLO messages, this needs only cover a single hop, but TC messages may have been forwarded a number of times. In particular, for TC messages, if using jitter as specified in [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] and [START_REF] Clausen | Jitter Considerations in Mobile Ad Hoc Networks (MANETs)[END_REF], the largest contribution the age may be a delay of up to F_MAXJITTER per hop (except the final hop) that the message has traveled. Other factors in the delay of both message types, per hop, may include the link-layer that is used in the MANET, and CPU and memory resources of routers (e.g., queuing delays, and delays for processing ICVs). An implementation MAY set lower and/or upper bounds on these parameters, if so, then these MUST allow values meeting these requirements. An implementation MAY make its value of MAX_TC_TIMESTAMP_DIFF dependent on the number of hops that a TC message has traveled.

The above constraints assume ideal time synchronization of the clock in all routers in the network. The parameters MAX_HELLO_TIMESTAMP_DIFF and MAX_TC_TIMESTAMP_DIFF (and any constraints on them) MAY be increased to allow for expected timing differences between routers (between neighboring routers for MAX_HELLO_TIMESTAMP_DIFF, allowing for greater separation, but usually not per hop, for MAX_TC_TIMESTAMP_DIFF).

Note that excessively large values of these parameters defeats their objectives, so these parameters SHOULD be as large as is required, but not significantly larger.

Using POSIX time allows a resolution of no more than one second. In many MANET use cases, time synchronization much below one second is not possible because of unreliable and high-delay channels, mobility, interrupted communication, and possible resource limitations.

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In addition, when using the default message intervals and validity times as specified in [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF], where the shortest periodic message interval is 2 seconds, repeating the message within a second is actually beneficial rather than harmful (at a small bandwidth cost). Also, the use of [START_REF] Clausen | Jitter Considerations in Mobile Ad Hoc Networks (MANETs)[END_REF] jitter can cause a message to take that long or longer to traverse the MANET, thus even in a perfectly synchronized network, the TC maximum delay would usually be greater than 1 second.

A finer granularity than 1 second, and thus the use of an alternative timestamp, is however RECOMMENDED in cases where, possibly due to fast moving routers, message validity times are below 1 second.

Message Generation and Processing

This section specifies how messages are generated and processed by [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] when using this mechanism.

Message Content

Messages MUST have the content specified in [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF], respectively. In addition, messages that conform to this mechanism MUST contain:

o At least one ICV Message TLV (as specified in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF]), generated according to Section 6.2. Implementations of [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] MUST support the following version of the ICV TLV, but other versions MAY be used instead, or in addition, in a deployment, if more appropriate: * For TC messages: The ICV Value MAY be truncated as specified in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF]; the selection of an appropriate length MAY be administratively configured. A message MAY contain several ICV Message TLVs. ), the additional TLVs specified in Section 6.1 MUST (unless already present) be added to an outgoing message when using this mechanism.

The following processing steps (when using a single timestamp version and a single ICV algorithm) MUST be performed for a cryptographic algorithm that is used for generating an ICV for a message:

1. All ICV TLVs (if any) are temporarily removed from the message. Any temporarily removed ICV TLVs MUST be stored, in order to be reinserted into the message in step 5. The message size and Message TLV Block size are updated accordingly.

2. <msg-hop-count> and <msg-hop-limit>, if present, are temporarily set to 0.

3. A TLV of type TIMESTAMP, as specified in Section 6.1, is added to the Message TLV Block. The message size and Message TLV Block size are updated accordingly.

4. A TLV of type ICV, as specified in Section 6.1, is added to the Message TLV Block. The message size and Message TLV Block size are updated accordingly.

5. All ICV TLVs that were temporary removed in step 1, are restored. The message size and Message TLV Block size are updated accordingly.

6. <msg-hop-count> and <msg-hop-limit>, if present, are restored to their previous values.

An implementation MAY add either alternative TIMESTAMP and/or ICV TLVs or more than one TIMESTAMP and/or ICV TLVs. All TIMESTAMP TLVs MUST be inserted before adding ICV TLVs. On receiving a ... message, a router MUST first check if the message is invalid for processing by this router [START_REF] Clausen | Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)[END_REF] and [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] proceed to give a number of conditions that, each, will lead to a rejection of the message as "badly formed and therefore invalid for processing". When using a single timestamp version, and a single ICV algorithm, add the following conditions to that list, each of which, if true, MUST cause NHDP or OLSRv2 (as appropriate) to consider the message as invalid for processing when using this mechanism:

1. The Message TLV Block of the message does not contain exactly one TIMESTAMP TLV of the selected version. This version specification includes the type extension. (The Message TLV Block may also contain TIMESTAMP TLVs of other versions.)

2. The Message TLV Block does not contain exactly one ICV TLV using the selected algorithm and key identifier. This algorithm specification includes the type extension, and for type extensions 1 and 2, the hash function and cryptographic function.

(The Message TLV Block may also contain ICV TLVs using other algorithms and key identifiers.)

3. Validation of the identified (in step 1) TIMESTAMP TLV in the Message TLV Block of the message fails, as according to Section 6.3.1.

4. Validation of the identified (in step 2) ICV TLV in the Message TLV Block of the message fails, as according to Section 6.3.2.

An implementation MAY check the existence of, and verify, either an alternative TIMESTAMP and/or ICV TLVs or more than one TIMESTAMP and/ or ICV TLVs.

Validating a Message Based on Timestamp

For a TIMESTAMP Message TLV with type extension 1 (POSIX time) identified as described in Section 6.2:

1. If the current POSIX time minus the value of that TIMESTAMP TLV is greater than MAX_HELLO_TIMESTAMP_DIFF (for a HELLO message) or MAX_TC_TIMESTAMP_DIFF (for a TC message), then the message validation fails. For an ICV Message TLV identified as described in Section 6.2:

1. All ICV Message TLVs (including the identified ICV Message TLV) are temporarily removed from the message, and the message size and Message TLV Block size are updated accordingly.

2. The message's <msg-hop-count> and <msg-hop-limit> fields are temporarily set to 0.

3. Calculate the ICV for the parameters specified in the identified ICV Message TLV, as specified in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF].

4. If this ICV differs from the value of <ICV-data> in the ICV Message TLV, then the message validation fails. If the <ICV-data> has been truncated (as specified in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF], the ICV calculated in the previous step MUST be truncated to the TLV length of the ICV Message TLV before comparing it with the <ICV-data>.

5. Otherwise, the message validation succeeds. The message's <msg-hop-count> and <msg-hop-limit> fields are restored to their previous value, and the ICV Message TLVs are returned to the message, whose size is updated accordingly.

Provisioning of Routers

Before a router using this mechanism is able to generate ICVs or validate messages, it MUST acquire the shared secret key(s) to be used by all routers that are to participate in the network. This specification does not define how a router acquires secret keys.

Once a router has acquired suitable key(s), it MAY be configured to use, or not use, this mechanism. Section 23.6 of [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] provides a rationale based on [START_REF] Bellovin | Guidelines for Cryptographic Key Management[END_REF] why no key management is specified for OLSRv2.

Security Considerations

This document specifies a security mechanism for use with NHDP and OLSRv2 that allows for mitigating several security threats. This section briefly summarizes security threats that are mitigated by the mechanism presented in this document.

Identity Spoofing

As only routers possessing the selected shared secret key are able to add a valid ICV TLV to a message, identity spoofing, where an attacker falsely claims an identity of a valid router, is countered. When using one or more shared keys for all routers in the MANET, it is only possible to determine that it is a valid router in the network, not to discern particular routers. Therefore, a malicious router in possession of valid keys (e.g., a compromised router) may still spoof the identity of another router using the same key.

Link Spoofing

Link spoofing, where an attacker falsely represents the existence of a nonexistent link, or otherwise misrepresents a link's state, is countered by the mechanism specified in this document, using the same argument as in Section 8.1.1.

Replay Attack

Replay attacks are partly countered by the mechanism specified in this document, but this depends on synchronized clocks of all routers in the MANET. An attacker that records messages to replay them later can only do so in the selected time interval after the timestamp that is contained in message. As an attacker cannot modify the content of this timestamp (as it is protected by the identity check value), an attacker cannot replay messages after this time. Within this time interval, it is still possible to perform replay attacks; however, the limits on the time interval are specified so that this will have a limited effect on the operation of the protocol.

Limitations

If no synchronized clocks are available in the MANET, replay attacks cannot be countered by the mechanism provided by this document. An alternative version of the TIMESTAMP TLV defined in [START_REF] Herberg | Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)[END_REF], with a monotonic sequence number, may have some partial value in this case, but will necessitate adding state to record observed message sequence number information.

The mechanism provided by this document does not avoid or detect security attacks by routers possessing the shared secret key that is used to generate integrity check values for messages.

Herberg, et al.

Standards Track [Page 13]

This mechanism relies on an out-of-band protocol or mechanism for distributing the shared secret key(s) (and if an alternative integrity check value is used, any additional cryptographic parameters).

This mechanism does not provide a key management mechanism. Refer to Section 23.6 of [START_REF] Clausen | The Optimized Link State Routing Protocol Version 2[END_REF] for a detailed discussion why the automated key management requirements specified in [START_REF] Bellovin | Guidelines for Cryptographic Key Management[END_REF] do not apply for OLSRv2 and NHDP.

  .......................................12 8. Security Considerations ........................................12 8.1. Mitigated Attacks .........................................13 8.1.1. Identity Spoofing ..................................13 8.1.2. Link Spoofing ......................................13 8.1.3. Replay Attack ......................................13 8.2. Limitations ...............................................13 9. Acknowledgments ................................................14 10. References ....................................................14 10.1. Normative References .....................................14 10.2. Informative References ..................................

Figure 1 :

 1 Figure 1: Relationship with RFC 5444 and NHDP/OLSRv2

Herberg

+ type-extension := 1 *

 1 For HELLO messages: + type-extension := 2 * hash-function := 3 (SHA-256) * cryptographic-function := 3 (HMAC)

  Table of Contents 1. Introduction ....................................................3 2. Terminology .....................................................4 3. Applicability Statement ...

......................................5 4. Protocol Overview and Functioning ...............................6 5. Parameters ......................................................7 6. Message Generation and Processing ...............................9 6.1. Message Content ............................................9 6.2. Message Generation ........................................10 6.3. Message Processing ........................................11 6.3.1. Validating a Message Based on Timestamp ............11 6.3.2. Validating a Message Based on Integrity Check ......12 7. Provisioning of Routers .

Acknowledgments

The authors would like to gratefully acknowledge the following people: Justin Dean (NRL) and Henning Rogge (Frauenhofer FKIE).

Authors' Addresses


Mouhanni
email: hind.mouhanni@gmail.com

Hassan Hamdi

Abdelaziz Bendou

Eric Cavalli

Lhoussine Benzine

Evaluation de l'impact environnemental de la réutilisation des eaux usées épurées en irrigation : analyse ionique des sols

Keywords: usées épurées, irrigation, gazon des golfs, salinité, analyses ioniques, sol

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

De ce fait, l'utilisation des Eaux Usées Epurées (EUE) pour l'irrigation peut contribuer à préserver les ressources en eau de la région De plus, vu la richesse des EUE en éléments fertilisants, cette solution permettra le recyclage de ces éléments et la diminution de l'usage abusif des engrais. Le potentiel actuel des eaux usées traitées par la STEP M'Zar du grand Agadir, susceptible d'être utilisé sans restriction pour l'irrigation (catégorie A normes OMS), peut atteindre 50 000 m 3 /j . Une étude de faisabilité sur la réutilisation des EUE de la STEP de M'Zar a été lancée par la Régie Autonome Multiservices d'Agadir (RAMSA). La superficie totale des espaces verts (public, privé, terrains de golf) est estimée à 878 ha avec un besoin en eau d'irrigation à satisfaire de l'ordre de 8 millions m 3 /an. Avec un débit journalier de 50 000 m 3 /j, les EUE de la STEP de M'zar combleront entièrement ce besoin. Les terrains des golfs occupent à eux seuls 268 ha de la superficie totale des espaces verts d'Agadir (30,5 %), avec une consommation d'eau estimée à 3216000 m 3 /an. Cette étude s'intéresse donc à l'utilisation des EUE pour l'irrigation des golfs. Elle présente la planification, le protocole et les résultats préliminaires des essais qui sont menés pour évaluer les impacts environnementaux de cette utilisation. Une attention particulière est accordée au suivi et à la comparaison des résultats des analyses ioniques des sols des parcelles du gazon irriguées par les EUE et de celles irriguées par les eaux de la nappe phréatique .

MATERIELS ET METHODES

Site expérimental

Les essais in situ sont réalisés sur le site de la STEP de M'zar du grand Agadir où deux zones de terrain ont été aménagées : une pour les essais utilisant les EUE de la STEP pour l'irrigation et l'autre pour l'utilisation des eaux de la nappe phréatique (eau de puits) pour l'irrigation.

Planification des essais

Afin d'étudier la faisabilité et évaluer l'impact de l'utilisation des EUE sur l'irrigation du gazon des golfs, 3 variétés de gazon des golfs à savoir le Penccross (V1),le Ray-grass anglais (V2), et le mélange de 60% du Ray-grass anglais et du 40% du fétuque rouge (V3) ont été utilisées sur 3 parcelles de terrain (P 1 , P 2 , P 3 ). À des fins de comparaison, les mêmes essais sont reproduits dans les mêmes conditions en utilisant les eaux de la nappe phréatique (eau de puits). Chaque parcelle a une dimension de 25 m 2 et est subdivisée en deux parcelles de 12,5 m 2 afin d'assurer une répétition des conditions de chaque essai. La subdivision de chaque parcelle est assurée par la pose d'un isolant en plastique sur une profondeur de 0,5m afin d'empêcher l'infiltration entre les subdivisions. Chaque parcelle contient une couche de 20 cm de sol composé de 75% de la terre végétale et de 25% de sable, ainsi qu'un lysimètre sur ses deux coins opposés. Les lysimètres ont un volume de 1 m 3 et reproduisent les conditions du sol et de la variété de gazon ensemencée dans la parcelle concernée ; ils sont conçus avec une bonne étanchéité permettant la récupération du lixiviat après l'irrigation.

Caractéristiques des sols et des eaux d'irrigation

Les sols des parcelles sont composés de 75 % de terre végétale et 25 % de sable. Les analyses pédologiques des constituants du sol sont présentées dans le tableau 1. La figure 2 montre que les sols irrigués par les eaux de puits ont des concentrations de Na+, Ca++, Mg++ qui sont relativement constantes alors que la concentration du Cl-qui présente des fortes variations. Les concentrations moyennes du sodium, magnésium, calcium et du chlorure sont de 14,9 ; 5,0 ; 7,4 et 62,6 (x 10 3 ) mole/kg respectivement, le SAR est de 3,79. On constate de fortes concentrations en chlorure des sodium : originellement présents dans le substrat ils sont dissous lors de l'irrigation [START_REF] Jalali | Effect of sodium and magnesium on Kinetics of potassium release in some calcareous soils of Western Iran[END_REF].

CONCLUSION

Le suivi de la qualité des sols des parcelles du gazon irriguées par les EUE et les EP nous ont permis de mettre en évidence une augmentation de la salinité des sols. Cette salinisation des sols ne dépend pas seulement de la qualité des eaux d'irrigation mais aussi de la concentration et du type des sels solubles

  Evaluation de l'impact environnemental de la réutilisation des eaux usées épurées en irrigation : analyse ionique des sols Hind Mouhanni, Hassan Hamdi, Abdelaziz Bendou, Eric Cavalli, Lhoussine Benzine To cite this version: Hind Mouhanni, Hassan Hamdi, Abdelaziz Bendou, Eric Cavalli, Lhoussine Benzine. Evaluation de l'impact environnemental de la réutilisation des eaux usées épurées en irrigation : analyse ionique des sols. Environnement, Ingénierie & Développement, 2011, N°59 -Mars 2011, pp.41-46. 10.4267/dechets-sciences-techniques.2930. hal-03172407 1. INTRODUCTION La région d'Agadir est une région agricole qui se caractérise par un climat aride, des ressources en eau très limitées et des sols pauvres en éléments nutritifs. Le secteur agricole est le plus grand consommateur d'eau.

Figure 1 :

 1 Figure 1 : Evolution du pH et de la conductivité électrique dans les sols des parcelles ensemencées par les trois variétés de gazon : (a) V1 ; (b) V2 ; (c) V3 irriguées avec les eaux puits et les eaux épurées.

Figure 2 :

 2 Figure 2 : Evolution du sodium ; calcium ; magnésium ; chlorure et le SAR dans les sols des parcelles ensemencées par trois variétés du gazon : V1 (a) ; V2 (b) ; V3 (c) irrigués avec les eaux épurées et V1 (a') ; V2 (b') ; V3 (c') les eaux de puits.

  du gazon irriguée par les eaux épurées et contient la variété i SPVi : sol du gazon irriguée par les eaux de puit et contient la variété i

Tableau 1 .

 1 Résultats des analyses de la terre végétale et du sable.• Les EUE sont classées C4S1, elles sont très salines (valeur de EC à 25°C égale à 3,15 ds/m).Cependant, elles peuvent être appliquées sur n'importe quel type de sol vu la valeur du SAR< 10. On constate que les EUE ont une charge ionique importante vu leurs teneurs en chlorure, sodium et nitrates, pouvant affecter l'absorption d'autres cations (ex magnésium). En revanche, d'autres éléments minéraux indispensables pour la croissance du gazon dépassent les besoins comme le calcium qui contribue à alimenter le complexe d'échange du sol [3]. La comparaison de l'apport des eaux d'irrigation en éléments majeurs (N, P, K) est rapportée dans le tableau 3. Apport en NPK (kg/ha/an) par les eaux d'irrigation pour un volume de 1314.m 3 /ha/an. Les eaux de la nappe phréatique sont très pauvres en éléments nutritifs par rapport aux teneurs des EUE. Ces dernières sont très riches en azote et en potassium et pauvres en phosphore. Il ressort de ces analyses que les EUE peuvent avoir des effets positifs sur la fertilité du sol et sur le rendement des cultures à condition qu'elles restent conformes aux recommandations OMS pour l'irrigation des cultures (catégories A). Dans tous les cas, on constate des valeurs du pH voisines de la neutralité : entre 7,1 et 8,8 avec une moyenne de 7,9. Le pH du sol est constant dans le temps indépendamment de la variété du gazon et du type d'eau d'irrigation. Par contre, les fluctuations des courbes de la conductivité électrique (EC) présentent une différence de comportement selon le type et la salinité d'eau d'irrigation utilisée. Les sols du gazon irrigués par les eaux de puits présentent des valeurs de la CE qui varient entre 0,46 et 10,4 dS/m avec une moyenne de 4,07 dS/m.

	Paramètres	Unités	Eau puits (EP)	EUE
	Conductivité électrique (E.C) à 25° C	dS/m	7,4	7,1
	Chlorure Cl -	mole/l (x10 -3 )	0,58	3,15
	Potassium K +	mole/l (x10 -3 )	3,61	20,31
	Sodium Na +	mole/l (x10 -3 )	1,32	21,21
	Calcium Ca ++	mole/l (x10 -3 )	1,19	7,35
	Magnésium Mg ++	mole/l (x10 -3 )	1,32	2,71
	Phosphore	mole/l (x10 -3 )	0,01	0,28
	Bicarbonate HCO 3 -	mole/l (x10 -3 )	3,13	5,19
	Sulfate SO 4 --	mole/l (x10 -3 )	0,10	0,88
	Nitrates (N-NO 3 )	mole/l (x10 -3 )	0,08	5,64
	Sodium Adsorption Ratio (SAR)		0,02	6,66
	Les eaux de la nappe et celles épurées peuvent être classées comme eau d'irrigation selon l'USDA (United
	States Department of Agriculture). La classification USDA est basée sur les valeurs de la conductivité

D'après ces résultats, la terre présente une texture limoneuse avec peu d'argile et peu de sable. Elle est assez pauvre en éléments nutritifs majeurs (azote total, phosphore assimilable et potasse échangeable) et en matière organique. En outre, les sables sont très pauvres en tout élément fertilisant. La salinité des deux constituants du sol est très faible. L'alcalinité des sables est plus élevée que celle de la terre végétale. Donc le sol est propre à la culture mais il ne fournit aucun élément nutritif, ce qui impose d'apporter des éléments fertilisants par les eaux d'irrigation ou par d'éventuels amendements. Les eaux utilisées pour l'irrigation des parcelles expérimentales sont de deux types :

• les eaux de la nappe phréatique de la plaine du Souss, pompées à partir des puits de surface de la station.

•

les EUE de la STEP de M'zar du grand Agadir, traitées par le procédé d'épuration par infiltration percolation sur des lits de sable.

Les principales caractéristiques des eaux utilisées pour l'irrigation sont indiquées dans le tableau 2.

Tableau 2 : Résultats du bilan ionique des EUE et EP utilisées pour l'irrigation. électrique (EC) et celle de l'indice SAR (Sodium Adsorption Ratio)

[START_REF] Ayers | la qualité de l'eau en agriculture[END_REF]

:

• Les eaux de la nappe sont classées C2S1, elles peuvent être utilisées sur n'importe quel type de sol. La salinité des eaux (EC = 0,520 ds/m) est proche de la limite pour la croissance du gazon sans appliquer des traitements spéciaux pour la salinité (limite située à EC = 0,750 ds/m).

2.4. Protocole d'irrigation de semences et de suivi

Les parcelles irriguées par les EUE sont éloignées de celles irriguées par les eaux de puits pour éviter toute contamination. Leur irrigation est effectuée par le même système. Il s'agit d'une aspersion par pistolet ayant un débit constant de 828 l/h, ce qui permet la maîtrise du même volume d'eau d'irrigation. Chaque parcelle de 25 m 2 est irriguée trois fois par jour et reçoit au total 90 litres d'eau par jour. Un des objectifs de l'étude vise à comparer la germination de trois variétés du gazon des golfs utilisées dans la région. Il s'agit du Penccross (V1), du Ray-grass anglais (V2), et du mélange de 60% du Ray-grass anglais et du 40% du fétuque rouge (V3). Les trois variétés ont été ensemencées respectivement sur les parcelles (P1, P2 et P3) et irriguées avec les EUE et celles de la nappe pour comparaison. Le suivi a débuté en juin 2007 par une semence des graines qui a été effectuée à la main. Les premiers plants du gazon ont germé après trois jours de semis pour la variété V2 et cinq jours pour les variétés V1 et V3. Les prélèvements des échantillons composites du sol sont effectués tous les 6 jours à partir du premier jour de germination. Ce suivi a duré 60 jours au total résultant en 10 compagnes d'échantillonnage. Pour chaque compagne 6 échantillons du sol sont récoltés pour être analysés. Les échantillons concernent les 20 cm supérieurs du sol de chaque parcelle. Le temps de germination pour les deux qualités d'eaux est le même ce qui prouve que les conditions initiales du sol et du semis sont pareilles pour les différentes parcelles.

3. RESULTATS ET DISCUSSION

Les analyses ioniques des sols irrigués par les deux types d'eau d'irrigation ont porté sur les paramètres suivants : pH, conductivité électrique (EC), sodium, calcium, magnésium, chlorures, ratio d'adsorption du sodium (SAR), sulfates et bicarbonates (figures 1 et 2). moyenne de 22,94 dS/m. La valeur moyenne des concentrations des sels solubles est de 0,016 g/kg pour les trois variétés. Les sels solubles du composé ont diminué de 96 % à cause de la lixiviation par les eaux épurées salines ce qui augmente aussi l'EC des sols et par la suite de la nappe phréatique

[START_REF] Chenini | Optimisation et durabilité du traitement et de la réutilisation des eaux usées en agriculture[END_REF]

.

  L'apport de la salinité aux sols irrigués par les eaux de la nappe est très faible par rapport aux sels existant dans la terre végétale et le sable. Par contre l'utilisation des EUE comme eau d'irrigation s'accompagne d'une augmentation des niveaux de concentration des ions d'une manière plus importante que celles observées dans les sols irrigués par les eaux de puits. Les concentrations moyennes du sodium, magnésium, calcium et du chlorure sont de 80,7 ; 10,4 ; 16,01 ; 14,64 et 187,36 (x10 3 ) mole/kg respectivement et le SAR est de 14,64. L'accumulation des chlorures du sodium est rapider au début de l'irrigation. Elle est due à l'adsorption du chlorure de sodium sur les agrégats du sol. Le suivi des ions Ca++ et Mg++ ne présente aucun changement significatif après l'irrigation par les deux type d'eaux d'irrigation[START_REF] Bazza | Irrigation avec les eaux usées traitées[END_REF].

	Les concentrations moyennes des sulfates et des bicarbonates dans les sols du gazon irrigués par les EUE et les EP sont de 7,06 ; 6,5 et 5,54 ; 6,55 (x10 3 ) mole/kg respectivement. Les concentrations des sulfates et des
	bicarbonates rapportent une constante dans le temps quelque soit le type de gazon et la qualité d'eau
	d'irrigation utilisé, malgré la formation des précipités de carbonate de calcium et de magnésium lors de
	l'irrigation par les EUE [3].