1、 Page I E Recommendation T/S 49-15 (by correspondence, May 1987) ISDN, SIGNALLING SYSTEM IN PRIVATE NETWORK Recommendation proposed by Working Group T/WG 1 1 “Signalling, Protocols and Switching” (SPS) Text of the Recomrnendation revised adopted by “Telecomritriications” Comrnission : “The conferenc
2、e of European Postal and Telecommunication Administrations, consideririg - the ISDN User-Network Interface specifications as defined in CCITT Recommendations : - 1.430 i and 1.431 2 on layer 1 - 4.920 3/1.440 4 and 4.921 5/1.441 6 on data link layer (layer 2) - 4.930 7/1.450 SI and 4.931 9/1.451 lo
3、on layer 3, - that, in order to armonize the digital access signalling within Europe, CEPT reduced the number of options which currently exist within these CCITT Recommendations, and adapted Recommendations T/S 46-20 i i (layer 2) and T/S 46-30 12 (layer 3), - that integrated services private branch
4、 exchanges (ISPBXs) will be some of the potential users of the digital facilities, integration between communication and ofice automation, and between data and voice is expected to start in the business area” where ISPBXs are generally used, O recommends to the members that - the Digital Interface a
5、s specified in CCITT Recommendation 1.430 i, 1.431 2, 4.920 3/1.440, 4.921 5/1.441 a, Q.930/1.450 SI, 4.93 1 9/1.451 lo and the enhancements, options and system parameters as outlined in CEPT Recommendation T/S 46-20 li and T/S 46-30 E121 should be the basis for ISDN signalling between ISPBXs over l
6、eased lines, and between the ISPBX and the ISPBX extension, - adaptations to the Private Network and the ISPBX to ISPBX environment containing multi-link connections, as outlined in Recommendations T/S 49-15 to T/S 49-50 should be used when developping and introducing private network ISDN Signalling
7、. The scope is described below.” O Edition of August 15, 1987 CEPT T/S*49-15*E 87 m 232b414 0008988 5 m T/S 49-15 E Page 2 1. INTRODUCTION The Recommendations for ISDN signalling in a Private Network are contained in the T/S 49-series (T/S 49-15 to T/S 49-50) and are based on the CCITT Recommendatio
8、n texts and/or on the 1986 version of the CEFT Recommendations T/S 46-20 i 11 and T/S 46-30 12. In Table 1 (T/S 49-15) thecross references between existing Public User Network Recommendations and Private Network Recommendations are indicated. PRIVATE NETWORKS PUBLIC NETWORK Rec. Nr. T/S 49-15 T/S 49
9、-16 T/S 49-20 T/S 49-30 T/S 49-36 T/S 49-40 T/S 49-50: Title I CEPT ISDN Signalling system in Private Networks Scope I - PROTOCOLS AND PROCEDURES ACROSS THE ISPBX-ISPBX INTERFACE Layer 1: Physical characteristics Layer 2: Data link Layer 3: Leased line (ISPBX-ISPBX) interface - T/S 46-20 1 11 T/S 46
10、-30 12 PROTOCOLS AND PROCEDURES ACROSS THE EXTENSION INTERFACE ISPBX Layer 1: Physical characteristics Layer 2 : Data link Layer 3 : Extension-ISPBX interface T/S 46-20 1 11 T/S 46-30 i21 CCITr - 1.430 i/ 1.431 2 1.440 4/ 1.441 6 4.920 Pl/ 4.921 5 1.450 SI/ 1.451 lo Q.930 7l/ Q.931 9 1.430 i/ 1,431
11、2 1.440 4/ 1,441 a 4.920 Pl/ 4.921 5 1.450 SI/ 1.451 lo Q.930 i711 Q.931 9 Table 1 (T/S 49-15). 2. LAY-OUT OF THE PRIVATE NETWORK SIGNALLING RECOMMENDTIONS 2.1. ISDN signalling system across the ISPBX-ISPBX interface These Recommendations (T/S 49- 16, T/S 49-20 and T/S 49-30) includes specific Priva
12、te Network requirements. The layer 3 protocols and procedures are the most important to be adapted to the Private Network environment. Also layers 1 and 2 need to be adapted to make them compatible with both Private and Public Network. Recommendations T/S 49-16 (layer i), T/S 49-20 (data link layer)
13、 and T/S 49-30 (layer 3) are drafted as self- contained specifications for a digital Private Network signalling system in line with the already existing CCITT Recommendations 1.430 l/I.431 2, CEPT Recommendations T/S 46-20 li and T/S 46-30 12 for Public Networks. Incorporation of the Private Network
14、 aspects into the existing Public Network Recommendations was not possible due to the urgent need to obtain results and the amount of work for redrafting and verifying. In the future it may be possible to have only one Recommendation, covering both Private and Public Networks. For this reason each R
15、ecommendation contains an introduction describing which adaptations were necessary to take into account the Private Network environment, 2.2. ISDN Signalling System across the Extension-ISBPX interface Recommendations (T/S 49-36, T/S 49-40 and T/S 49-50) are as far as possible identical to the User-
16、Network interface. They refer to the same basic call control procedures and describe adaptations to existing Recommenda- tions necessary for a Private Network environment. O *- -Edition of August 15, 1987 CEPT T/S*49-35*E 87 2326434 0008989 7 W TIS 49-15 E Page 3 3. FIELD OF APPLICATIONS Recommendat
17、ions T/S 49-16 to T/S 49-50 define the ISDN signalling protocols and procedures across the ISPBX-ISPBX interface. The interface concerned is at the Q reference point (see Note). The reference configurations for the interface is given in Figure 1 (T/S 49-15). Recommendation T/S 49-36 to 49-50 define
18、the ISDN signalling protocols and procedures across the extension-ISPBX interface. The interface concerned is at the S reference point as defined in CCITT Recommendation 1.411 13. The reference configuration is given in Figure 1 (T/S 49-15). Further study is, however, required. T Q 7- LEASED LINE t-
19、 W,: ISPBX r *: Line transmission equipment PEL: Public Exchange Line Figure 1 (T/S 49-15). Private Network reference configuration (further study is required). Note. CCITT Recommendation 1.411 13 indicates a reference model of the user-to-network access of the ISDN. A T reference point functions as
20、 a demarcation point between the ISDN and the “user” whereby “user” indicates all equipment in the subscribers domain, including the terminals, i.e. OS1 endsystems. Between an S and a T reference point, an NT, may exist. This is a functional block which provides Layer 2 and/or Layer 3 protocol handl
21、ing, multiplexing and switching. A typical representative of an NT, is an ISPBX (Integrated Services Private Branch Exchange), but also a gateway of an LAN connected to the ISDN at the T reference point would be an example of NT,. Figure 1 (T/S 49-15) shows the interconnection scenario of ISPBXs wit
22、hin the ISDN environment. In order to adequately describe such scenario it is useful to enhance the User-Network Reference Configuration by such ISPBX-ISPBX Reference Configuration. A new reference point is introduced, Q, which designates the endpoints of a private circuit at each of the two ISPBXs.
23、 The private circuit may consist of a dedicated physical medium or may be represented by a temporary or permanent connection through the ISDN. In the case an ISDN intervenes further study is needed. 4. LEASED LINES The channel structures of the leased lines used at the Q reference point as in Figure
24、 1 (T/S 49-15) for connecting two ISPBXs may differ in the future from the conventional physical leased line structure. In Recommendations T/S 49-15 to 49-50 the signalling over leased lines will take account of three evolving scenarios: Scenario 1 -Figure 2 (T/S 49-15) ISPBX private network using d
25、edicated leased lines. This scenario shows the present situation where Private Networks are established by leased lines. This means that: - the private accesses are physically separated from the public access; - there may be ISPBXs which have no direct public access (e.g. ISPBX B). Edition of August
26、 15, 1987 CEPT T/S*49-35*E 7 2326434 OOO990 3 TIS 49-15 E Page 4 ISDN x 3qjT ISPBX l I Figure 2 (T/S 49-15). ISPBX private network using dedicated leased lines. Scenarios 2 and 3 are not studied in detail yet. The result of the studies is in the Annex to this Recommen- dation. It is assumed that in
27、the future all three scenarios can exist at the same time, due to different customer requirements. So a common solution should be adopted for all three scenarios (further study is required - see Note). The Private Network Recommendations (T/S 49-16 to 49-50) only cover scenario 1. Scenarios 2 and 3
28、are for further study. Especially the study of scenario 3 which will require close coordination with public network Study Groups. Furthermore, depending on the actual access capability and on transmission considerations, three possibili- ties are under consideration: - use a multiplicity of basis ch
29、annel structures; - use a primary rate channel structure; - use more primary rate channel structures. The basic channel structure (layer 1) using the D-channel protocol for signalling between ISPBXs is for further study (see draft Recommendations T/S 46-16). Note. To adopt a common solution, two imm
30、ediate requirements that need to be added to the D-channel protocols to facilitate this common approach are identified: 1. A message for use between ISPBXs that can be used in either direction and will pass transparently through both Transit PBXs and the Public ISDN. 2. An “ISPBX Information Element
31、” that can be transported between ISPBXs within any appropriate message. 5. TERMS AND DEFINITIONS A basic vocabulary of terms can be found in CCITT Recommendations G.701 and 1.112. In addition definitions of terms as used in the Private Network environment are given below. 5.1. The term “USER” Refer
32、ring to CCITT Recommendation 1.411 13, the term USER represents everything which is, as seen from the network (= ISDN) beyond the T reference point. E.g. in the CCITT sense a ISPBX is a “user”. It is left open whether or not in some cases the user equipment (NT,s and TES) or even the operating human
33、 beings or application processes above the equipment are addressed. In the traditional Telephony USER is clearly the human being operating or using some technical equipment, O mostly terminal equipment. - - Edition of August 15, 1987 CEPT T/S*49-15*E 87 m 2326434 0008993 5 TIS 49-15 E Page 5 Since i
34、n data communications the philosophy of layered models has arisen, USER often designates a given layer using the services of the layer(s) below. In other contexts, USER is also used in the same sense as in the traditional telephony. In the context of ISPBXs and Private Networks the term USER is reta
35、ined in the CCITT sense. This requires further definitions in the PBX environment which are illustrated in Figure 3 (T/S 49-15). T I M -I I-. ISDN Private Network EXTENSION ISPBX terminology Figure 3 (T/S 49-15). Private Network terminology. 5.2. Other definitions of terms (for further study). 6. EX
36、AMPLE OF PROCEDURE FOR A SIMPLE CIRCUIT SWITCHED CALL This section, which contains examples of sequences of messages, is provided as an Appendix for informa- tion. For implementation requirements Recommendation T/S 49-30 applies. Edition of August 15, 1987 F CEPT T/S*49-15*E 87 m 2326434 0008992 7 m
37、 TIS 49-15 E Page 6 Annex Scenarios 2 and 3 for lease lines Scenario 2 - Figure A-1 (T/S 49-15): ISPBX private network using semi-permanent connections. This scenario makes use of semi-permament B-channel connections in public networks and signalling via the D-channel (and the public network signall
38、ing system No. 7). This means that: - the public and private circuits are carried in the same interface structure; - the private circuit semi-permanent connections are controlled by Administrations; - the D-channel carries both public and private network signalling; - there may be ISPBXs which have
39、no direct public access (e.g. ISPBX B). Figure K m ISPBX - - Y -q, c I -. -.- D CHANNEL - - I* I r Y b ISPB?i - - - - -t_:_.L - . - PRNATE NETWORK C u ISDN A-1 (T/S 49-15). ISPBX private network using semi-permanent connections. Edition of August 15, 1987 TIS 49-15 E Page 7 Scenario 3 - Figure A-2 (
40、T/S 49-15): ISPBX connected to the public ISDN only (virtual private network). This scenario shows an ISDN where it is no longer necessary to have dedicated lines/channels between the ISPBXs. Connection will be established on a per call basis and will be capable of supporting all of the requirements
41、 of an ISPBX. This means that: - there are virtual leased lines; - all ISPBXs are connected to the ISDN; - ISPBX-ISPBX signalling is conveyed by means of “User to User” signalling within the ISDN signalling. Figure A-2 (T/S 49-15). U ISPBX C - ISPBX connected to public ISDN only (virtual private net
42、work). Edition of August 15, 1987 CEPT T/S*YS-LS*E 7 W 232b4l14 0008994 O TIS 49-15 E Page 8 Appendix Example of procedure for a simple circuit switched call Figure AP-1 (T/S 49-15) contains some example message flows to show the establishment and clearing of a simple call wholly within the ISDN env
43、ironment. It also contains some example message flows to show what might happen when a simple call encounters a busy destination. The following notes are in relation with this Figure AP-1 (T/S 49-15): Note 1. It is not possible to use CALL PROCEEDING as an end to end carrier of information (e.g. sup
44、plementary service information) as delivery of the message to the calling terminal cannot be guaranteed. This may be because, for example, the expiry of T302 at a transit ISPBX has already caused a CALL PROCEEDING message to be sent in the backwards direction. Note 2. Whether the use of CONNECT ACKn
45、owledge is mandatory or not is left for further study. Note 3. Any ISPBX may terminate the overlapp proceeding state by sending CALL PROCEEDING. Note 4. The expiry of timer T302 may occur at any ISPBX within a private network, or at more than one node. Note 5. This method of link by link clearing de
46、nies the capability of retaining the circuit switched connection whilst negociation for (as yet unspecified) typical ISPBX supplementary services takes place. Note 6. The diagram shows an example of the preferred method of clearing a point to point call (e.g. leased line) using a two message clearin
47、g sequence (RELEASE/RELEASE COMPLETE). Edition of August 15, 1987 CEPT T/S*49-L5*E 87 = 2326434 0008995 2 0.931 EXIEHSION LINE TIS 49-15 E Page 9 ISDB TERMII.AL POINT TO IsD:l PoirJT TO POIJTJ LOCAL uuiripoirrr CATE- GORY G ORIG. 0.931 TWK 0.931 ISPBX LEASED ISPBX LEASED A LINE T LINE IsPBX 0.931 AC
48、CESS EXCE. 0.931 ACCESS CALL PROCEEO . ALERTI1C COtJ1JECTiOB CALL ESTABLISHMENT FROM ISPBX-PE TO ISDN-TE - I I I I ) - CALL, RE. INFO LAST DIGIT NOIE 4 EXPIRY CONHECTION NOTE 2 I CONVERSATIOH ALERTI!JG +- I CLEAR OWN - CALL CLEARDOWN FROM THE ACTIVE STATE DISCOIHECT IIOTE 5 NOTE 6 - CALL ESTABLISHME
49、NT ENCOUNTERING A BUSY ISDN-TE ( TORE E.G. SUSY) fVlTE 5 - - RELEASE BUSY t!TE 6 .- I - BC. RELEASE CO%lPL. * (CAUSE OUSYj Figure AP-1 (T/S 49-15). Procedure for a simple circuit switched call (Example). Edition of August 15, 1987 - CEPT T/S*49-15*E 7 m 2326434 000b 4 m TIS 49-15 E Page 1 O References CCITT Recommendation 1.430. Basic User-Network Interjke-Layer 1 specification (Red Book: Volume III, Fascicule
