1、INTERNATIONAL TELECOMMUNICATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU PUBLIC DATA NETWORKS: INTERFACES X.30 (03/93) SUPPORT OF X.21, X.21 bis AND X.20 bis BASED DATA TERMINAL EQUIPMENTS (DTEs) BY AN INTEGRATED SERVICES DIGITAL NETWORK (ISDN) ITU-T Recommendation X.30 (Previous
2、ly “CCIlT Recommendation”) CCITT RCMN*X.30 (REVUL) 93 BI 4862593 0583004 226 FOREWORD The IT Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The IT-T is responsible for studying technical, operating and tariff questions and issuin
3、g Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on the
4、se topics. IT-T Recommendation X.30 was revised by the IT-T Study Group VII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (IT), the CCITT ceased to exist as of 28 February 1993. In
5、its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the t
6、ext to references containing the acronyms CCIT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 In this Recommendation, the expression “Administration
7、” is used for conciseness to indicate bob a telecommunication adminisuation and a recognized operating agency. O IT 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without
8、 permission in writing from the ITU. E . CONTENTS Reference configurations 1.1 Customer access configuration 1.2 Network configuration 1.3 Interworking situation . Terminal adaption functions 2.1 2.2 Terminal adaption functions for DTEs conforming to X.l user class of service 7 2.3 Terminal adaption
9、 functions for DEs conforming to X.l user class of service 19 . 2.4 Terminal adaption functions for DTEs conforming to X.l user classes of service 1.2. 14. 15. 16. 17 and 18 Test loops 3.1 Test loop reference configuration 3.2 Test loop characteristics 3.4 Coding of activatioddeactivation control me
10、ssage Terminal adaption functions for DTEs conforming to X.l user classes of service 3 to 6 . 3.3 Loop activatioddeactivation mechanism . Annex A . SDL diagrams . A.1 General . A.2 Some remarks about the formal description . Appendix I - Universal terminai adaptor 1.1 User rate identification 1.3 Lo
11、ss of aiignmenthecovery . 1.4 Ready for data alignment Appendix II - Inslot identification of intermediate bit rate 11.1 Identifkation of intermediate rate . 11.2 Restitution of the intermediate rate 11.3 User rate identification Page 2 2 2 3 4 5 23 24 27 31 31 32 32 32 33 33 33 41 41 41 42 43 43 43
12、 43 I Recommendation X.30 (OW3) 1 CCITT RECMNsX.30 (REVUL) 93 4862593 0583006 OT9 Recommendation X.301) SUPPORT OF X.21, X.21 bis AND X.20 bis BASED DATA SERVICES DIGITAL NETWORK (ISDN) (Malaga-Torremolinos, 1984; amended at Melbourne, 1988 and Helsinki, 1993) TERMINAL EQUIPMENTS (DTEs) BY AN INTEGR
13、ATED The CCITT, considering (a) that the Integrated Services Digitai Network (ISDN) will offer the universal interfaces to connect subscxiber terminals according to the reference configurations described in Recommendation 1.41 1; (b) that during the evolution of ISDN, however, there will exist for a
14、 considerable period DTEs conforming to Recommendations X.21, X.21 bis and X.20 bis which have to be connected to the ISDN, (Cl that the D-channel signalling protocol is described in Recommendations 1.430, Q.920, Q.921, Q.930 and Q.931; (d) that the X.21 bis DTEs are an evolution of V-Series DTEs, w
15、hich also provide interworking capability with X.21 DTEs over PDN services, and which use the network provided signal element timing and may have specific ail control features to comply with the x.21 ailing protoco2); (e) that the X.20 bis based DTEs are an evolution of V-Series DTEs, which are oper
16、ating in the asynchronous mode and which may have cal control features to comply with the X.20 calling protocol, unanimously declares 1) classes of service 3 to 7 and 19 to the ISDN operating in accordance with circuit-switched or leased circuit services; 2) of service 1,2, 14, 15, 16, 17 and 18; 3)
17、 4) that the scope of this Recommendation covers the connection of X.21 and X.21 bis based terminals of user that the scope of this Recommendation also covers the connection of X.20 bis based terminals of user classes that the reference configurations of clause 1 shall apply; that the terminal adapt
18、or (TA) functions to support X.21, X.21 bis andor X.20 bis based DTEs including: - rate adaption functions, - cai1 establishment functions, - mapping functions, - ready for data alignment, shall be performed as outlined in clause 2; 5) that the scope of this Recommendation covers the rate adaption r
19、equirements which are caused by the connection of existing terminals to the ISDN usednetwork interface, but does not cover the requirements on bit rate conversion caused by the inter-operation of terminals with different bit rates (ISDN-CSPDN interworking). This Recommendation is also included in th
20、e Recommendations of the I-Series under the number 1.461. 1 *) See Recommendation V.110. i Recommendation X.30 (03/93) 1 CCITT RECNN*X.30 (REVS31 93 c3 q862593 0583007 T35 H 1 Reference configurations Figures 1-1 and 1-2 show examples of possible configurations and are included simply as an aid to 2
21、 describing the TA functions. 1.1 Customer access configuration For the connection of X.21, X.21 bis or X.20 bis based DTEs to the ISDN, Figure 1-1 shows a possible reference configuration. 1.2 Network configuration The specification of terminal adaption functions takes account of the network config
22、uration and the end-to-end connection types shown in Figure 1-2 in which the associated terminal equipment TE1 and TE2 may be involved. The TA functions for this scenario are described in 2. Tlie terminals TE1 and TE2 are physically and logically connected to the ISDN where the call is handled. The
23、TA performs the necessary rate adaption, the signalling conversion from the X.21 signailing to the Q.931 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 interconnection by using In
24、terworking Functions (IWF). X.21M.21 bisM.20 bis T X.21M.21 bisM.20 bis TA i u TO71 641 0-93/D01 TA Terminai adaptor NT Network termination ET Exchange termination NOTES 1 2 For ISDN reference configurations, see Recommendation 1.430. The ISDN signalling protocol is described in Recommendations Q.92
25、1 and 4.931. FIGURE 1-1B.30 Customer access configuration example 2 Recommendation X.30 (03/93) / ISDN , I i / I I I I I S, T I I / I S, , / H-l-Ei -/- x.211 S. T x.21 bid X.20 bis T x.211 X.21 bid X.20 bis i TO716420-931002 Circuit switched daia network or public mtched telephone newrk / .pH Some A
26、dministrations may provide separate TAS either for each Recommendation X.1 user class of service or for a group of user classes of service. Other Administrations may provide a universal TA for all user classes of service 3 to 7 or 15, or 1,2,14, 15, 16,17 and 18. 4 Recommendation X.30 (03/93) 2.1 2.
27、1.1 2.1.1.1 Octet O Odd frames - Even frames - Octet 1 Terminai adaption functions for DTEs conforming to X.1 user classes of service 3 to 6 00000000 1 El E2 E3 E4 E5 E6 E7 1 P1 P2 P3 P4 P5 P6 SQ Rate adaption functions General approach Octet 3 Octet 4 The rate adaption functions within the TA are s
28、uown in Figure 2- 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 kbits. 1 Q5 Q6 Q7 Q8 R1 R2 SR 1 R3 R4 R5 R6 R7 R8 SP TA I I X.2 1 M.2 1 bis step 1 Step 2 T0716430-9YD03 FIGURE 2-1E.30 2.1.1.
29、2 First step of rate adaption (RA1) of X.1 rates to the intermediate rates of 8/16 kbit/s 2.1.1.2.1 Frame sructure The conversion of the X.1 rates for user classes 3,4 and 5 to 8 kbit/s, and for user class of service 6 to 16 kbit/s, shall be implemented by means of the 40 bit frame structure shown i
30、n Figure 2-2. Bit number 1 2345678 Octet 2 FIGURE 2-uX.30 Figure 2-2 shows that, in addition to the basic frame, a two frame multiframe is employed. In odd frames, octet O contains ail zeros, whilst in even frames octet O consists of a one foilowed by seven E bits (see 2.1.1.2.4). The order of bit t
31、ransmission of the 40 bit frame is from left-to-right and from top-to-bottom. Recommendation X.30 (03/93) 5 CCITT RECMN*X-30 (REV%L) 73 B1 4862573 058LOLL 466 M 2.1.1.2.2 Frame synchronization The 17 bit frame alignment pattern consists of all 8 bits (set to zero) of octet O in odd frames and bit 1
32、(set to 1) of the followitig consecutive 9 octets of the 80 bit long multiframe (see also 2.1.1.4.2). The fust bit of octet O alternates between one and zero in consecutive frames and therefore provides a multiframe synchronization bit. 2.1.1.2.3 Status bits SP, SQ, SR and X The bits SP, SQ, SR and
33、X are used to convey channel associated status information. The mapping of the information on circuit C of the X.21 interface to the 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 associated with the bit groups P, Q and R. To assure pro
34、per and secure operation the mapping scheme has to be consistent with Recommendations X.21 and 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 and SR of the bit groups P, Q and R are evaluated by sampl
35、ing 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 of a bit group R, P and Q to the 1st bit of the consecutive bit grou
36、p P, Q and R on the R lead (see Figure 2-3). - In the case where X.21-byte timing interchange circuit B is provided for character alignment, circuit C is sampled together with the bit 8 of the preceding character and circuit I is changing its state at the boundaries between old and new characters at
37、 circuit R. This operation is defined in Reco- mmendation X.24. 2.1.1.2.4 Additional signalling capacity (E bits) The E bits provide the additional signalling capacity for the conveyance of information relating to the user rate. The coding of these bits is shown in Table 2- 1. 2.1.1.2.5 Data bits Da
38、tri 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 600,2400,4800 bids to the 8 kbids intermediate rate and of the 9600 bids user rate to the 16 kbids intermediate rate, the sequence of even and odd octet O shall be maintained as d
39、efined in Figure 2-4. In order to achieve both short frame synchronization as well as short transfer delay times, a user-bit-repetition method is proposed. Figures 2-4a and 24b contain a scheme for the adaption of the 600 bids user rate and of the 2400 bids user rate respectively into the 8 kbids be
40、arer rate. Figures 2-4c and 2-4d show the adaption of the 4800 bids user rate to the 8 kbit/s bearer rate and of the 9600 bids user rate to the 16 kbids bearer rate. In the case of a 600 bids user rate, an explicit frame group synchronization pattern using bit E7 is provided to ensure preservation o
41、f user octet boundaries and associated status bit. The coding for the E7 bit shall be as follows: . . .1110111011101 . where the value O is marking the last 40 bit frame of each 8 x 40 bit frame group which contains three integer user octets. 2.1.1.3 Second step of rate adaption (RA2) As rate adapti
42、on of a single substream (SA6 kbids) to 64 kbids and multiplexing of several substreams to 64 kbids have to be compatible to enable interworking, a common approach is needed for second step rate adaption and for subchannel multiplexing. It is described in Recommendation 1.460. 6 Recommendation X.30
43、(03/93) CCITT RECMN*X.30 (REV*L) 93 W III III III III o I II III I II III - U a s h U n s 6 - O O -I r I I I I I I I I I I I l I I l I I I I- ,-I l I I I I I I I I I I -I - I I I I I I I I I I I 1 I I -I r I I I I I I I I I I I I I l I I -J - I I I I I I I I -,J I- l I I I I I I I h cl a 4862573 058
44、30L2 3T2 1 m 2 Recommendation X.30 (03/93) 7 CCITT RECMN8X.30 (REV*L) 73 U 40bi7571 0581013 239 User rate (bitls) TABLE 2-1K.30 El E2 E3 FA E5 E6 E7 600 2400 4800 9600 1 O O X X X O or 1 (Note 1) 1 1 O X X X X O 1 1 X X X X O 1 1 X X X *x X indicates spare bits which are reserved for future use and
45、should be set to 1. NOTES 1 E7 in those 40 bit frames which terminate a frame group are set to zero (see 2.1.1.2.6 and Figure 2-4a). 2 3 Recommendation V. 110. 4 independent clocking information. 5 information may be determined by the use of El, E2, E3 bit in conjunction with the intermediate rate.
46、For the 600 bitls user rate E7 is coded to enable the 8 x 40 bit frame group synchronization. To this aim, Different user rates with the same coding are distinct by different intermediate rates. The coding of the user rates provides also for user rates specified for the TA recommended in It should b
47、e noted that bits E4 to E6 may be used in Recommendation V.110 for the transport of network Asynchronous rate information must be determined by the use of 4.931 signalling. Synchronous rate 2.1.1.4 For framingheframing and user rate identification the following strategies shall be applied. Framinglr
48、eframing method and user rate identification 2.1.1.4.1 Search for frame alignment The following 17 bit alignment pattern is searched for: 00000000 IXXXXXXX IXXXXXXX IXXXXXXX IXXXXXXX 1xxxxxxx IXXXXXXX 1XXXXXXX 1XXXXXXX 1xxxxxxx No errors shall be tolerated in the defined bit positions (i.e. all bit
49、positions excluding those denoted by “X). To ensure a reliable synchronization, it is suggested that at least two 17 bit alignment patterns in consecutive frames be detected. In the case of X.l user class of service 3 (600 bids), a further search for the frame group synchronization pattern contained hi bit position E7 shall be performed. 2.1.1.4.2 Alignment monitoringlrecovery The monitoring of the alignment shall be a continuous process using the same procedures as for initial detection. Loss of alignment is assumed following the det
