1、O * O O - CEPT T/S*Yb-YO*E 87 Page 1 (old reference: T/CS 46-40 E) Recommendation T/S 46-40 (Copenhagen 1987) SUPPORT OF X.21, X.216is AND X.2Obis BASED DATA TERMINAL EQUIPMENTS (DTEs) BY AN INTEGRATED SERVICES DIGITAL, NETWORK (ISDN): SYNCHRONOUS AND ASYNCHRONOUS TERMINAL ADAPTATION FUNCTION Recomm
2、endation proposed by Working Group T/WG 11 “Signalling, Protocols and Switching” (SPS) Text of the Recommendation adopted by the “Telecommuriications” Commission: “The European Conference of Postal and Telecommunications Administrations, considering (a) that the Integrated Services Digital Network (
3、ISDN) will offer the universal interfaces to connect subscriber (b) that during the evolution of ISDN, however, there will exist for a considerable period DTEs conforming to (c) that D-channel signalling protocol is described in Recommendations T/S 46-20 and T/S 46-30, (d) that the X.2lbis DTEs are
4、an evolution of V-series DTEs, which also provide interworking capability with X.21 DTEs over PDN services, and which use the network provided signal element timing and may have specific call control features to comply with the X.21 calling protocol (2), (e) that the X.20bis based DTEs are an evolut
5、ion of V-series DTEs, which are operating in the asynchronous mode and which may have call control features to comply with the X.20 calling protocol, terminals according to the reference configurations described in Recommendation 1.41 1, Recommendations X.21, X.2lbis and X.20bis which have to be con
6、nected to the ISDN, unnnimoiisly recommel-tds (I) that the scope of the Recommendation covers the connection of X.2lbis based terminals of user classes of service 3 to 7 and 30 to the ISDN operating in accordance with circuit-switched or leased circuit services, (2) that the scope of this Recommenda
7、tion also covers the connection of X.20bi.s based Terminals of CCITT user classes of service 1, (2), 40 to 44 to the ISDN operating in accordance with circuit-switched or leased circuit services, (3) that the reference configurations of paragraph 1. of the Recommendations shall apply, (4) the termin
8、al adaptator (TA) fiinctions to support X.21, X.2lbis and X.20bis based DTEs including: - bit rate adaptation functions - call establishment functions - mapping functions - ready for data alignment shall be performed as outlined in paragraph 2., (5) that the scope of this Recommendation only covers
9、the bit rate conversion, which is caused by the connection of existing t$rminals to the ISDN user/network interface, but does not cover the requirements on bit rate conversion caused by the inter-operation of terminals with different bit rates (ISDN/CSPN interworking), (6) that this Recommendation d
10、oes not specify a particular implementation but recommends how the functions must be implemented when they are supported by a particular Terminal Adaptator equipment.” Edition of Febriiary 29, 1988 CEPT T/S*4b-40*E 7 2326414 OOOb9 TIS 46-40 E Page 2 CONTENTS 1 . REFERENCECONFIGURATIONS 1.1. Customer
11、 access configuration . 1.2. Network configuration . 2 . TERMINAL ADAPTATION FUNCTIONS . 2.1. 2.2. 2.3. 2.4. Adaptation functions for DTEk conforming to X.l user classes of service 3 to 6 Adaptation functions for DTEh conforming to X.l user classes of service 7 Adaptation functions for DTEs conformi
12、ng to X.l user classes of service 30 Adaptation functions for DTEk conforming to X.l user classes of service 1, 2, 40 to 44 . 3 . TESTLOOPS ANNEXES Annex A List and definition of interchange circuits . Annex B Ready for data alignment procedures . Annex C Messages used at the S-interface . Annex E S
13、ystem parameters (Timers value) Appendix A Flow control (between asynchronous DTEs TAS) . Appendix B Network independent clocking Annex D Operating sequences 5 5 18 18 24 26 27 29 45 52 55 56 58 . Edition of February 29. 1988 CEPT T/SP4b-YO*E 87 2326414 O008870 4 TIS 46-40 E Page 3 1. REFERENCE CONF
14、IGURATIONS Figures 1 (T/S 46-40) and 2 (T/S 46-40) show examples of possible configurations and are included simply as an aid to describing the TA functions. 1.1. Customer access configuration Fr the connection of X.21, X.2lbis and X.20bis based DTEs to the ISDN, Figure 1 (T/S 46-40) shows a possibl
15、e reference configuration. X.21 lX.21 bis/X.2Qbis U TA : Terminal adaptor NT : Network termination LT : Line termination Note. The D-channel signalling protocol may operate in a point-to-multipoint fashion as described in Recommendation Figure 1 (TIS 46-40). T/S 46-30. 1.2. Network configuration The
16、 specification of terminal adaptation functions takes account of the network configuration and the end-to-end connection types shown in Figure 2 (T/S 46-40) in which the associated terminal equipment TE1 and TE2 may be involved. The TA functions are described in section 2. Edition of February 29, 19
17、88 CEPT T/S*4b-40*E 87 m 2326414 0008871 b m TIS 46-40 E Page 4 TE1 IU: Interworking unit Circuit switched/ data Aedrk or public switched telephone network Qblic - Figure 2 (T/S 46-40). The terminals TE1 and TE2 are physically and logically connected to the ISDN where the call is handled. The TA per
18、forms the necessary bit rate adaptation, the signalling conversion from X.21 signalling to the D-channel signalling and vice versa (X.21 mapping) and ready for data alignment. Interworking with dedicated networks, e.g. a CSPDN, will be provided on the basis of trunk lines interconnexion by using the
19、 interworking unit (IU). The following principles shall apply : i) The non-voice services within the ISDN should basically not diverge from what is being developed in Series X Recommendations. This refers to the various aspects concerning quality of service, user facilities, call progress signals (s
20、ee the Series X Recommendations, e.g. X.2 and X.96). However, existing features would be enhanced and additional features would also be developed if account were taken of the new ISDN customer capabilities (e.g. multi-terminal arrangements, user rate at 64 kbit/s, simulta- neous multi-media access a
21、s well as the possible solution of compatibility checking). ii) Integration of X.21 based services into the ISDN is applicable to user classes of service 3 to 7 and 30. Integrations of X.20bis based services into the ISDN is applicable to user classes of service 1, (2), 40 to 44. iii) Terminal TE1 a
22、nd TE2 connected to an ISDN are using the ISDN numbering scheme. 1.3. Interworking situation Bearing in mind that this Recommendation defines the functions performed by X.21 terminal adaptors (TA X.21), X.2lbis terminal adaptors (TA X.2lbis) and X.20bis terminal adaptors (TA X.20bis), the following
23、case of interworking between these terminal adaptors and between these terminal adaptors and DTEs connected to CSPDN and PSTN may appear: Edition of Febrgry.23. lys8 CEPT T/S*46-40*E 87 2326434 0008872 8 2. 2.1. 2.1.1. 2.1.1.1, TIS 46-40 E Page 5 (a) For user class (1) TA X.21 (2) TA X.21 (3) TA X.2
24、lbis (4) TA X.21 (5) TA X.21 (6) TA X.2lbis (7) TA X.21 (8) TA X.2lbis (9) TA X.2lbis 3f service 3 to 7: TA X.21 TA X.2lbis TA X.2lbis DTE X.21 DTE X.21bis DTE X.21 V-series DTE V-series DTE DTE X.2lbis (b) For user class of service 30: (10) TA X.21 TA X.21 (11) TA X.2lbis TA X.2lbis (12) TA X.21 TA
25、 X.2lbis (13) TA X.21 TE1 (S-interface) (14) TA X.2lbis TE1 (S-interface) (15) TA X.20bis TA X.20bis (16) TA X.20bis DTE X.20bis (17) TA X.20bis V-series DTE (c) For user classes of service 1, 2, 40 to 44: Note 1. This Recommendation is intended to cover all TA-functions necessary to allow interwork
26、ing as listed above. Currently, this Recommendation covers all TA-functions necessary to allow interworking between DTEs connected to ISDN and to CSPDN with the following exceptions: 1. for X.21bis and X.20bis only, the call set-up procedure with direct call has been explicitly covered, but other in
27、terface arrangements of X.2lbis and X.20bis are not precluded, 2. for X.llbis, the half-duplex mode of operating is not specified. This applies to all the cases listed above, where at least one X.2lbis terminal is involved. Alignment with the functions provided by the interworking units may be neces
28、sary when the relevant Recommendations are available. Note 2. With the interworking cases 1-17 mentioned above, the functions provided by TA X.2lbis, TA X.20bis and the functions provided by TA V-110 should be compatible. TERMINAL ADAPTATION FUNCTIONS The adaption functions to support X.21, X.2lbis
29、and X.20bis based DTEs can be subdivided into three areas, namely: - bit rate adaption function; - X.21 mapping functions and related call control functions; - ready for data alignment. Some Administrations may provide separate TAS either for each Recommendation X. 1 user class of service or for a g
30、roup of user classes of service. Other Administrations may provide a universal TA for all user classes of service 3 to 7 or 30 or 1, (2), 40 to 44. Within the Recommendation only such functions are described which refer to single rate TAS. Adaption functions for DTEs conforming to X.l user classes o
31、f service 3 to 6 Bit rate adaption jinctions General approach The bit rate adaption functions within the TA are shown in Figure 3 (T/S 46-40). The function RA1 adapts the X.l user rate to the next higher rate expressed by 2k times 8 kbit/s (where k = O or 1). RA2 performs a second conversion to 64 k
32、bit/s. Edition of February 29, 1988 CEPT T/S*4b-YO*E 87 2326434 0008873 T TIS 46-40 E Page 6 TA . 64 kbitls II kbitls II I X.21lX.21bis I Step Step 2 Figure 3 (T/S 46-40). 2.1.1.2. First step of rate adaption (RA1) of X.l rates to the intermediate rates of 8/16 kbit/s 2.1.1.2.1, Frame structure The
33、conversion of the X. 1 rates for user classes 3,4 and 5 to 8 kbit/s, and for user class 6 to 16 kbit/s, shall be implemented by means of the 40 bit frame structure shown in Figure 4 (T/S 46-40). Bit number Il 2 3 4 5 6 7 8 Octet O Odd frames Even frames 00000000 1 El E2 E3 E4 E5 E6 E7 I Octet i I 1
34、P1 P2 P3 P4 P5 P6 SQ Octet 2 1 P7 P8 Ql 42 43 44 X Octet 3 1 Q5 Q6 47 Q8 R1 R2 SR I Octet 4 I 1 R3 R4 R5 R6 R7 R8 SP Note. Spare bit X is reserved for future use and shall be set to O (see CCIT Recommendation 1.463/V.110). Figure 4 (T/S 46-40). Figure 4 (T/S 46-40) shows that in addition to the basi
35、c frame, a two-multiframe is employed. In odd frames, octet O contains all zeros, whilst in even frames octet O consists of a one followed by seven E bits (see paragraph 2.1.1.2.4.). The order of bit transmission of the 40 bit frame is from left to right and from top to bottom. The 17 bit frame alig
36、nment pattern consists of all 8 bits (set to zero) of octet O in odd frames and bit 1 (set to 1) of the following consecutive 9 octets of the 80 bit long multiframe (see also paragraph 2.1.1.4.2.). The first bit of octet O alternates between one and zero in consecutive frames and therefore provides
37、a multiframe synchronization bit. The bits SP, SQ and SR are used to convey channel associated status information. The mapping of the information on circuit C of the X.21 interface to S bits and the circuit I in the distant interface should be done in such a way that the SP, SQ and SR bits are assoc
38、iated with the bit groups P, Q and R. To assure proper and secure operation the mapping scheme has to be consistent with CCITT Recommendations X.21 an X.24. The mechanism for mapping is as follows: - in all cases where X.21-byte timing interchange circuit B is not provided, the status bits SP, SQ an
39、d SR of the bit groups P, Q and R are evaluated by sampling the C-lead in the middle of the 8th bit of the respective preceding bit group. On the other hand, the conditions of the status bits SP, SQ and SR are adopted by the I-lead beginning with the transition of the respective 8th bit if a bit gro
40、up P, Q and R to the 1st bit of the consecutive bit group on the R-lead (see Figure 5/X.30); 2.1.1.2.2. Frame synchronization 2.1.1.2.3. Status bits SP, SQ, SR Edition of February 29, 1988 TIS 46-40 E Page 7 - in the case where X.21-byte timing interchange circuit B is provided for character alignme
41、nt, the circuit C is sampled together with the bit 8 of the preceding character and the circuit 1 is changing its state at the boundaries between old and new characters at the circuit R. This operation is dened in Recommenda- tion X.24. Note 1. According to Recommendation X.21 the provision of the 8
42、 bit timing interchange circuit B is not mandatory. Note 2. The status bits may be used to transfer, during the data transfer phase, information for half-duplex operation, between TA X.21/TA X.2lbis and TA X.2lbis (Le. mapping of the condition of the C-lead of the TA X.21, of the 105 lead of the TA
43、X.216is, to the condition on the 109 lead of the remote TA X.llbis, and mapping of the condition of the 105 lead of the TA X.2lbis to the condition of the I-lead on the remote TA X.21). The E bits provide the additional signalling capacity for the conveyance of information relating to user rate. The
44、 coding of these bits is shown in Table 1 (T/S 46-40). 2.1.1.2.4. Additional signalling capacity (E bit) (Note 1) 4,800 xxx 9,600 xxx X X: Indicates spare bits which are reserved for future use and should be set to 1. Table 1 (T/S 46-40). Note 1. For the 600 bit/s rate E7 is coded to enable the 8 x
45、40 bit multiframe synchronization. To this aim, E7 in those 40 bit frames which terminate a multiframe are set to zero (see paragraph 2.1.1.2.6. and Figure 6a (T/S 46-40). Note 2. Different user rates with the same coding are distinct by different intermediate rates. Note 3. The coding if the user r
46、ates provide also for user rates specified for the TA recommended in CCITT Recommenda- tion 1.463p.110. Note 4. It should be noted that possible future use of bits E4 and E5 is intended in Recommendation 1.463/V.110. Note 5. Asynchronous rate information must be determined by the use of out-of-band
47、signalling. Synchronous rate information may be determined by the use of El, E2, E3 bits in conjunction with the intermediate rate. 2.1.1.2.5. Data bits Data is conveyed in P, Q and R bits, i.e. 24 bits per frame. 2.1.1.2.6. Repetition strategy For the adaption of user rates 600, 2,400,4,800 bit/s t
48、o the 8 kbit/s intermediate rate and of the 9,600 bit/s user rate to the 16 kbit/s intermediate rate, the sequence of even and odd octet O shall be maintained as defined in Figure 4 (T/S 46-40). In order to achieve both short frame synchonization as well as short transfer delay times a user-bit repe
49、tition method is proposed. Figures 6a (T/S 46-40) and 6b (T/S 46-40) contain a scheme for the adaption of the 600 bit/s user rate and of the 2,400 bit/s rate respectively onto the 8 kbit/s bearer rate. Figures 6c (T/S 46-40) and 6d (T/S 46-40) show the adaption of the 4,800 bit/s user rate to the 8 kbit/s bearer rate and of the 9,600 bit/s user rate to the 16 kbit/s bearer rate. In the case of a 600 bit/s user rate, an explicit multiframe synchronization pattern using bit E7 is provided to ensure preservation of user-octet boundaries and associated status bit. The coding
