1、 Ts49-20 Page E 1 (old reference T/CS 49-20 E) Recommendation T/S 49-20 (Copenhagen 1987) ISDN ISPBX-ISPBX INTERFACE LAYER 2 SPECIFICATION APPLICATION OF CEPT RECOMMENDATION T/S 46-20 Recommendation proposed by Working Group T/WG “Signallitig. protocols and Switching” (SPS) Text of the Recomrneiidat
2、iori adopted by the “Telecommitiications“ Commission: “The European Conference of Postal and Telecommunications Administrations, considering - that CCITT Recommendations Q.920/1.440 i and Q.921/1.441 2 define the ISDN User-Network Interface - that in CEPT Recommendation T/S 46-20 3 the number of opt
3、ions which exist in the CCITT Recommendations - that Recommendation T/S 49-15 4 describes the scope of the ISDN Signalling System in Private Networks, Layer 2 in a Public Network, 4.920 and 4.921, are reduced, O reconmends that European Administrations and Industry who wish to provide or to develop
4、ISDN services in a Private Network within Europe, apply to layer 2 CEPT Recommendation T/S 46-20 as approved by the T Commission (June 1987) in accordance with the application specification as defined below.” Edition of February 10, 1988 CEPT T/S*49-20*E 87 m 232b434 0008998 8 m TIS 49-20 E Page 2 1
5、. INTRODUCTION This Recommendation is intended to provide an application text necessary to ensure harmonization of the ISPBX-ISPBX interface layer 2 while maintaining maximum commonality and compatibility with the user-network interface layer 2 as defined in Recommendation T/S 46-20. It reflects the
6、 following facts given or required at the ISPBX-ISPBX interface: - The ISPBX-ISPBX interface uses the reference configuration shown in Recommendation T/S 49-15 4, - Requirements for conventional leased lines, including on site wiring, are as described in Recommenda- - ISPBX-ISPBX signalling at layer
7、 2 requires a “master” and a “slave” function to be applied to the ends - Only non-automatic Terminal Endpoint Identifiers (TEI) are used for ISPBX-ISPBX interconnection. - The use of broadcast data link connection services and optional TE1 management procedures is for Figure 1. tion T/S 49-15 4, se
8、ction 4 scenario 1. Other scenarios are for further study. of the D-channel. These terms substitute the T/S 46-20 E terms “network side” and “user side”. further study. References 11 CCITT Recommendation 4.920 (1.440). ISDN user-network inteiface data link layer-general aspects. 2 CCITT Recommendati
9、on 4.921 (1.441). ISDN user-network interface data link layer specijcation. 3 CEPT Recommendation T/S 46-20 E (June 1987). ISDN user-network inteuface data link layer spec- cation. 4 CEPT Recommendation T/S 49-1 5 E (June 1987). ISDN signalling system in private networks-scope. 2. GENERAL This Recom
10、mendation describes an application of the layer 2 protocol specified in Recommendation T/S 46-20 E for the ISPBX-to-ISPBX interconnection according to Recommendation T/S 49-1 5 E, section 4, scenario 1. 3. ISPBX-TO-ISPBX LAYER 2 CONFIGURATION 3.1. General Figure 1 (T/S 49-20) replaces Figures 6/Q.92
11、0 and 7/Q.920 in Recommendation T/S 46-20 and depicts the interconnection of TSPBXs. In particular it shows the point-to-point nature of both layer I and layer 2. ISPBX -1 / * ISPBX I Layer 3 b Layer 1 Layer 1 Physical connection *- * Data link connection Figure 1 (TIS 49-20). Point-to-point data li
12、nk connection. Edition off, li), ,368 3.2. 3.3. 3.3.1. 3.3.2. 3.3.3. 3.3.4. CEPT T/S*49-20*E 7 232b414 0008999 T W _ TIS 49-20 E Page 3 Designation of master and slave data link layer entities Recommendation T/S 46-20 E uses the terms “network” and “user” to distinguish asymmetric functions at the t
13、wo ends of a data link entity. In private networks these terms are considered to be inappropriate. Therefore for private network applications the “network” end is to be termed “master” and the “user” end to be “slave”. The master is considered to be in all appropriate respects the T/S 46-20 E networ
14、k end of the data link and the slave the user end. It is important to note that these definitions apply to all data link entities of one access and not to the ISPBX as a whole. In order to support the private network arrangements identified in Recommendation T/S 49-15 E an ISPBX shall be capable to
15、provide both, master and slave functions on different accesses. Depending on the configuration it may occur that one ISPBX simultaneously acts as master and slave on different accesses (see Figure 2 (T/S 49-20). An ISPBX which does not provide master and slave functions imposes constraints on privat
16、e network arrangements. The assignment of the master or slave has to occur on initialization or reinitialization of the access and the designation must have been decided at the time of configuration of the access. This assignment of master/slave functions at layer 2 does not preclude definitions of
17、master/slave functions in other layers. I I I I Figure 2 TIS 49-20. Example of ISPBX interconnection. Functional model of the layer 2 The congurations for ISPBX interconnection are described in Recommendation T/S 49-15 E, Figure 2 (T/S 49-15). With regard to layer 1, these configurations are point-t
18、o-point. Figure 3 (T/S 49-20) depicts the structure of layer 2 and details Figure 10/Q.920 in Recommendation T/S 46-20 E. It includes functional blocks as follows: One or more data link entity/entities (DLE). One layer management entity (LME). One connection management entity (CME) for each DLE. One
19、 layer 2 multiplexing function, if more than one DLE exists. Edition of February 10, 1988 CEPT T/S*49-20*E 87 TIS 49-20 E Page 4 2326414 0007000 O I i w Layer 1 L- I Layer 3 Layer 2 Figure 3 (T/S 49-20). Structure of layer 2 for ISPBX interconnection. 3.4. Links required for peer-to-peer user inform
20、ation transfer (support of layer 3) The information transfer between peer-to-peer layer 3 entities is based on one or more point-to-point data link connections. Broadcast data link services are not provided to layer 3 entities in ISPBXs. 3.5. Links required for peer-to-peer layer management informat
21、ion transfer Two layer management concepts may be used: i) Either all layer management functions are performed locally, or ii) peer-to-peer layer management entities communicate for the support of layer management functions. However, the use of this function is for further study (see Appendix). If a
22、ll layer management functions are performed locally, no links for peer-to-peer management information transfer are required. 4. SERVICES PROVIDED TO LAYER 3 For the support of layer 3, only the acknowledged information transfer service is required i.e., layer 3 passes information to layer 2 by means
23、 of the DL-DATA-REQUEST primitive but layer 3 shall never use the DL-UNIT DATA-REQUEST primitive. There is no requirement to provide the U1 frame and the broadcast link for the support of layer 3. This implies in particular that the layer 3 SETUP message issued by the ISPBX is conveyed by an I frame
24、 via a point-to-point link. Edition of February 10, 1988 CEPT T/S*49-20*E 7 M 2326434 O009003 2 M 5. 6. 7. 7.1. 7.1. 7.1.2. 7.1.3. 7.2. 8. 8.1. 8.2. TIS 49-20 E Page 5 SERVICES REQUIRED FROM THE PHYSICAL LAYER (LAYER 1) The services provided by layer 1 at the D-channel connection endpoint within the
25、 physical layer service access point are described in detail in Recommendation T/GSI 04-02/1 E and their applicability to ISPBX interconnection in Recommendation T/S 49-16 E (Note). The procedural means which allow layer 2 to interact with layer 1 accross the layer 2/layer 1 boundary are described i
26、n Recommendation T/S 46-20 E. Recommendation T/S 49-16 E, Part I, paragraph 3.3. specifies the subset of primitives recognized in Recommendation T/S 46-20 E which is used in case of the primary rate access for ISPBX interconnection. Note. The current Recommendation T/S 49-16 E specifies the primary
27、rate access, the basis access is for further study. LAYER 2 FRAME REPERTOIRE A data link layer entity which identifies valid frames (for the definition and treatment of invalid frames see Recommendation T/S 46-20 E, 4.921, paragraph 2.9.) as undefined takes action in accordance with Recommandation T
28、/S 46-20 E (see 4.921, paragraph 5.8.5.). Undefined frames are those whose control field contains encodings not identified in Recommendation TIS 46-20 E, Table 5/Q.921. No peer-to-peer connection management procedures are defined for ISPBX interconnection, therefore XID frames (they support the appl
29、ication “connection management”, see Recommendation TIS 46-20 E, Table 5/Q.921) shall be discarded and no action shall be taken as a result of that frame. With regard to the application “unacknowledged and multiple frame acknowledged information transfer” (see Recommendation T/S 46-20 E, Table 574.9
30、2 1) the full frame repertoire identified in Recommendation T/S 46-20 E or, as an implementation option, a subset whereby U1 frames are discarded or treated as undefined, may be supported. If the full repertoire is supported, the content of the I field contained in the U1 frame shall be delivered to
31、 layer 3, otherwise no action shall be taken as a result of that U1 frame. Nofe. Those data link layer entities which discard U1 frames do not coinply with Recommendation T/S 46-20 E since they do not provide the unacknowledged information transfer service as specified in Recommendations T/S 46-20 E
32、 and CCITT 4.920 and 4.921 (November 1986 version). INTERCONNECTION ARRANGEMENTS Single TE1 configuration The single TE1 configuration provides the minimum layer 2 services to layer 3. It is identified by the TE1 value to O. No other TEIs are permitted in this configuration. The characteristics of t
33、he single TE1 configuration are summarized in the following: Provision of only one point-to-point data link connection within each SAP between layer 3 entities for acknowledged information transfer of layer 3 message units. The TE1 = O will be assigned independently at each end according to paragrap
34、h 9.1.1.1 ., item i). In addition, an ISPBX may have the capability to perform TE1 assignment upon the receipt of the first frame containing the TE1 = O assigned at the peer side. No peer-to-peer layer management services are supported in this configuration (and in particular no peer-to-peer TE1 man
35、agement procedures are supported). Multiple TE1 configurations Application for such configurations is for further study (see Appendix for guidelines). ELEMENTS FOR LAYER-TO-LAYER COMMUNICATION General The repertoires of primitives used in this application Recommendation for various configurations ar
36、e based on the repertoire of primitives defined in Recommendation TIS 46-20 E, Table 6/Q.921. Primitives for the support of the single TE1 Configuration EI = O) Table 1 (T/S 49-20) depicts the primitives relevant for layer 2 in case of the single TE1 configuration. Edition of February 10, 1988 CEPT
37、T/S*49-20*E ? M 232b4L4 0007002 4 W TIS 49-20 E Page 6 Tvoe I Parameters I I II I Message unit Generic name Priority Message contents Request Indication Response Confirm indicator unit L3 e-r L2 I DL-ESTABLISH I X X X I DL-RELEASE I x I x I - I x I - I - I DL-DATA I MDL-ASSIGN (Note) MDL-REMOVE MDL-
38、ERROR I L2 e-r L1 X X - - - x Layer 3 peer-to- peer message X X - - - X TE1 value, CES I I I I I I X - - - - X TE1 value, CES X X - - X Reason for error - message PH-DATA - - - - PH-ACTIVATE X X PH-DEACTIVATE - X - - - - L3 +-+ L2: Layer 3/data link layer boundary. L2 c-* L1: Data link layer/physica
39、l layer boundary. M +-+ L2: Management entity/data link layer boundary. Note. As opposed by Recommendation T/S 46-20 E these primitives do not imply any peer-to-peer layer 2 management communication. Table 1 (T/S 49-20). Primitives associated with layer 2 in the single TE1 configuration. 9. LAYER MA
40、NAGEMENT SERVICES 9.1. Layer management The Layer Management Entity (LME) (see Figure 3 (T/S 49-20) provides the management of resources that have a layer wide impact. 9.1.1. TEI administration 9.1.1.1. TE1 assignment procedures An interface for ISPBX-to-ISPBX interconnection is member of the non-au
41、tomatic TE1 assignment category (see Recommendation T/S 46-20 E, 4.921 paragraph 5.3.2.) and the TE1 will be entered into the ISPBX equipment, for example, by the user or manufacturer. This implies that no peer-to-peer layer management communication takes place for the purpose of TE1 assignment. Whe
42、n a TE1 has been assigned by the exchange of MDL-ASSIGN primitives the ISPBX establishes an association between the TE1 and a Connection Endpoint Suffix (CES). Each ISPBX may establish the corresponding association: i) independently based on local primitives; or ii) upon the receipt of the first fra
43、me containing the TE1 = O assigned at the peer side. e - Edition of February 10, 1988 CEPT T/S*49-20*E 87 2326414 0009003 b M _- master side + slave side TIS 49-20 E Page 7 1 9.1.2. master side + slave side Commar-2nlresponse bit management The peer-to-peer procedures specified in Recommendation T/S
44、 46-20 E identify a network and user side of the ISDN user-network interface for the purpose of the coding of the C/R bit position contained in the layer 2 address field. In the case of ISPBX interconnection, the network side corresponds to the “master” while the user side corresponds to the “slave”
45、. The assignment of “master” or “slave” has to be established by the configuration of the link. The codings of the C/R bit is shown in Table 2 (T/S 49-20). O 9.2. 9.2.1. 9.2.2. I Command/Response I Direction I C/R value I Table 2 (T/S 49-20). C/R field bit usage. Connection management The Connection
46、 Management Entities (CME) (see Figure 3 (T/S 49-20) provides the management of resources that have an impact on individual connections. Parameters With respect to parameters, an ISPBX layer 2 applies the internal parameter initialization. After completion of TE1 assignment the layer management noti
47、fies the connection management to initialize parameters. The connection management may either initialize the link parameters to the default values (see Recommenda- tion T/S 46-20 E, 4.921 paragraph 5.9. and Table 3 (T/S 46-20) or parameter values which are entered into the ISPBX equipment, for examp
48、le, by the user as agreed with the peer user. However, no peer-to-peer parameter negotiation procedures based on XID frames are currently needed. Error processipig Recommendation T/S 46-20 E, Table II-l/Q.921 defines those error situations in the peer-to-peer proce- dures which will be notified to c
49、onnection management by means of the MDL-ERROR-INDICATION primitive. Edition of February 10, 1988 CEPT T/S*49-20*E 87 m 232b414 0009004 B m TIS 49-20 E Page 8 9.2.2.1. Error processing in the single TE1 configuration Table 3 (T/S 49-20) defines the actions to be taken in a single TE1 configuration consisting of a single link within each supported SAP whereby all the links are identified by the same TE1 value, which is fixed to “O”. The table uses the layout of Table II-l/Q.921 except the actions which are specified in Table 3 (T/
