1、National Standard of Canada CAN/CSA-Z24 3.52-88 ( IS0 74 78-1 98 7) (Reaffirmed 2004) Infermation Processing Systems-Data Communication-Multilink Procedures Prepared by Canadian Standards Association Approved by Standards Council of Canada ISSN 031 7-5669 Published in December 1988 by Canadian Stand
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17、 National Standard of Canada is a standard which CSA I N T E R N AT IO N A 1 - Les normes nationales du Canada sont publikes en versions fransaise et anglaise. Although the intended primary application of this Standard is stated in its Scope, it is imporfant to note that it remains the responsibilit
18、y of the users to judge its suitability for their particular purpose. Contents Contents Technical Committee on Telecommunications and Information Exchange Between Systems iv Preface vi 0. Introduction 7 I. Scope and field of application 1 2. Definitions and parameters I 3. Muftilink frame format 3 4
19、. Transmitter operation 3 5. Receiver operation 6 6. Initializing the MLP 8 7. Resetting the MLP 8 Annex-Examples of multilink resetting procedures 10 Information Processing Systems-Data Communication-Multilink Procedures December 1988 iti Technical Committee Technical Committee on Telecommunication
20、s and Information Exchange Between Systems R.1. Prince P.G. Bowie D.W. Branton A. Collins S. J. Crossman P. Dagher G.P. Dallaire T. Davies E. Despres R. Dexter J.A. Field G. Gothe K. Knightson A. Lee V.C. MacDonald W.A. McCrum 0. Monkewich B.A. Ruptash Bell-Northern Research, Ottawa, Ontario Bell Ca
21、nada, Ottawa, Ontario IBM Canada Ltd., Markham, Ontario The Canadian Bankers Association, Toronto, Ontario Telecom Canada, Ottawa, Ontario Teleglobe Canada, Montreal , Quebec Department of Communications-Canada, Ottawa, Ontario Be I I-N ort he rn Research , Ottawa, Ontario Trans port Can ad a , Otta
22、wa, Ontario Standards Council of Canada, Ottawa, Ontario University of Waterloo, Waterloo, Ontario CN C P Telecom m u n icat i o ns, Toronto, Ontario Bell-Northern Research, Ottawa, Ontario Microtel Pacific Research, Ottawa, Ontario Ottawa, Ontario Department of Corn mu n ications-Canada, Ottawa, On
23、tario Department of Corn mu n ications-Canada, Ottawa, Ontario Datapoint Canada, W i Ilowdale, Ontario Chairman Associate Associate Associate Associate Associate Associate Associate Associate iv cAN/CsA-Z243.52-88 (IS0 7478-1987) December 1988 Technical Committee D.A. Sheppard F.Y. Shum P.V. Bates P
24、rotocols Standards (b) provide an explanation of circumstances surrounding the actual field condition; and (c) be phrased where possible to permit a specific “yes” or ,no answer. sample copy, write to CSA Marketing or telephone (476) 747-4019. Requests for interpretation should Interpretations are p
25、ublished in CSA Information Update. For subscription details and a free cAN/Cy-Z243.52-88 (IS0 7478-1987) December 1988 INTERNATIONAL STANDARD IS0 7478 : 1987 (E) Information processing systems - Data communication - Multilink procedures 0 Introduction Multilink procedures reference the layers of th
26、e IS0 Open Systems Interconnection (OS11 reference modef; specifically the physical, data link, and network layers. The multilink pro- cedures (MLP) reside in the data link layer. Multilink procedures provide the means for accepting data units from the network layer, scheduling data units for transm
27、ission and retransmission over a group of parallel data links, and reordering the received data units prior to delivering them to the network layer. Multilink procedures provide the following general features : a) multiple connections between data stations; achieve economy and reliability of service
28、 by providing b) permit addition and deletion of connections without interrupting the service provided by the multiple connec- tions; cl tions through load sharing; optimize bandwidth utilization of a group of connec- dl tion(s) fails; achieve graceful degradation of service when a connec- el iogica
29、l data link appearance.to the network layer; and provide each multiple connection group with a single f) data units prior to delivering them to the network layer. provide, when required, resequencing of the received 1 Scope and field of application This International Standard specifies multilink pro
30、cedures where a multiplicity of parallel data links at the data link layer are used to provide a variable bandwidth data link between network layer entities. The multilink procedures (MLP) exist as a new upper sublayer of the data link layer, operating between the network layer and a multiplicity of
31、 single data link protocol functions (SLPs) in the data link layer (see figure 1). This International Standard does not specify the way in which the SLPs indicate to the MLP that the transmission of a rnultilink frame has successfully been completed. These rnultilink procedures do not preclude the u
32、se of different single link procedures, each with differing delay characteristics and/or line speeds to form one multilink group. When the procedures defined by this International Standard are to be used on one or more parallel data links, both ends of the data link must know that these procedures a
33、re to be used before the first multilink frame is sent. This could be achieved by a prior agreement that all communications on this data link will use these procedures, or by one of the SLPs negotiating the use of these procedures, or by some other means. The method by which both ends achieve a comm
34、on understanding as to the use or non-use of these muhilink procedures is not defined in this International Standard. 2 Definitions and parameters 2.1 MLP reset confirmation bit (Cl : The MLP reset confirmation bit is used in repty to the R bit set to 1 to confirm that all of the MLP state variables
35、 have been reset. The C bit set to 0 is used in normal communication; Le., no reset request has been activated. The C bit set to 1 is used to reply to the multilink frame with the R bit set to 1, and indicates that the MLP state variable reset process has been completed. In this C = 1 case, the mult
36、ilink frame is used without a data unit field . 2.2 to transfer data over one or more SLPs which form a group. muftilink procedures (MCP) : The protocols employed 2.3 the multilink sequence number assigned to a multiiink frame. muitilink send sequence number MN(S)I : Value of NOTE - The number assig
37、ned lies in the range of 0 to 4095 inclusive and is used to resequence, when resequencing is required, and to detect missing or duplicate multilink frames at the receiving multilink procedure data station (MLP) before data units are delivered to the network layer. 2.4 lost multilink frame timer (MT1
38、J : During law traffic periods, the expiration of this timer provides the means to determine that the muhilink frame with MN(S) equal to MWR) is losf. 2.5 group busy timer (MT2J : Optional. the receiving MLP, the expiration of this timer provides the means to determine that a “blocked“ condition exi
39、sts because buffers were exhausted before resequencing could be accomplished. 2.6 MLP reset confirmation timer (MT3) : Timer MT3 is used to provide a means of identifying that the multilink frame with the C bit set to 1 that is expected following the 1 IS0 7478 : 1987 (E) Physical layer Data link la
40、yer Network layer Communi- cations rnedi? 1 I Single link interface 1 -l+l Element 1 I Element 2 I 1 I 1 I I 4- I I I I 1 I I I MLP 1 +-r 1 Element 1 I I I 0 e e Element N I I I I Multiple single I k Multilink interface I I line interface Key SLP = single link procedure MLP = multilink procedure Fig
41、ure 1 - Multilink functional organization transmission of the multilink frame with the R bit set to 1 has not been received. 2.7 multilink receive state variable MWRII : Denotes the MN(S1 of the next in-sequence multilink frame to be transferred to the network layer. NOTE - The MV(R) identifies the
42、lower edge of the receive window. 2.8 multilink send state variable MV(S)I : Denotes the next in-sequence MN(S) to be assigned to a multilink frame to be sent over this multilink group. 2.9 rnultilink frame acknowledgment state variable MV(T)I : Denotes the MN(S1 of the oldest multilink frame awaiti
43、ng an indication of acknowledgment from the local SLP. NOTE - The MWT) identifies the lower edge of the transmit window. 2.10 rnultilink window size (MW) : For a given direction of transmission, both the transmitting MLP and the receiving MLP shall use the same value of MW. f I I I I I I I I I I 1 1
44、 NOTE - The transmit window contains the sequence numbers MWTI to MV(T) + MW - 1 inclusive. The receive window contains the sequence numbers MWR) to MV(R)+ MW - 1 inclusive. 2.11 receive MLP window guard (MX) : The range of sequence numbers of fixed size, of higher value than those in the receive wi
45、ndow, that, if received as MN(S1, indicates that any muftilink frames in the range MWR) to MN(S1-received - MW that have not been received have been lost. 2.12 range of abnormal multilink frames (MZ) : The range of sequence numbers in which MN(S) should not be received during normal operation. NOTE
46、- Multilink frames received in range MZ should be discarded. 2.13 number of SLP retransmission attempts (N) : The number of times that a single link procedure data station ISLPI attempts retransmission of a multilink frame before notifying the MLP of the situation. NOTE - Subsequent SLP action shoul
47、d be dependent upon SLP design. Subsequent hlLP action shoutd involve assigning the multilink frame to the same or one or more other SLPs for transmission. 1) MW is a system parameter which can never exceed 4095 - MX. Factors which will affect the value of parameter MW include, but are not limited t
48、o, link transmission and propagation delays, the number of links, the range of multilink frame lengths, and single link parameters (N retransmission attempts, response times, and outstanding number of unacknowledged I frames). 2 IS0 7478 : 1987 (E) 2.14 MLP reset request bit (R) : The MLP reset requ
49、est bit is used to request a reset of the MLP state variables. The R bit set to 0 is used in normal communication; i.e., no request for a multilink reset. The R bit set to 1 is used to request the reset of the receiving MLP state variables. In the R = 1 case, the multilink frame data unit field does not contain higher layer information, but may contain an optional Cause Field that incorporates the reason for the reset. NOTE - For the DTE-DCE X.25 interface application”, a Cause Field of 8 bits is specified. The encoding of that %bit field is a subject for further study. 2.
