1、CCITT RECMN*Gm79b 92 4062591 0574730 5b0 INTERNATIONAL TELECOMMUNICATION UNION CCITT TH E INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE GENERAL ASPECTS OF DIGITAL TRANSMISSION SYSTEMS; TERMINAL EQUIPM ENTS G.796 (09/92) CHARACTERISTICS OF A 64 kbWs 2048 kbis ACCESS PORTS CROSS-CONNECT
2、 EQUIPMENT WITH Recommendation G.796 CCITT RECMN*G.796 92 m 48b2593 0574733 4TY m INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL. TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE GENERAL ASPECTS OF DIGITAL TRANSMISSION SYSTEMS; TERMINAL EQUIPMENTS G.796 (09/92) CHARACTERISTICS OF A 64 k
3、bitls 2048 kbis ACCESS PORTS CROSS-CONNECT EQUIPMENT WITH Recommendation G.796 Geneva, 1992 The CC (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union 0. CCIT is responsible for studying techniCa, operating and tariff q
4、uestions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plaary Assembly of CC which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendatons by the
5、,members of CCm between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988). Recommendation G.796 was prepared by Study Group XV and was approved under the Resolution No. 2 procedure on the 1st of September 1992. In this Recommendation, the expression
6、 “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized private operating agency. . O ITU 1992 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, el or mechanical, including photocopying a
7、nd microfilm, without permission in Writing ftom the ITU. CCITT RECNN*G.796 92 = 4862573 0574733 277 Recommendation 6.7% CHARACTERISTICS OF A fi4 kbiffs CROSS-CONNECT EQUIPMENT WlTH 2048 kbis ACCESS PORTS scope This Recommendation gives the characteristics of a synchronous mss-connect equipment to b
8、e used in a synchronized digital network and which cross-connects time slots at 64 kbit/s or n x 64 kbit/s frodto any 2048 kbit/s access port. 1 1. General characteristics Capacity This parameter depends mainly on the network architechire. It can change with time. Increasing an equipment should not
9、disturb the existing data traffic. 1.2 Access ports transporting synchronous 64 kbit/s and n x 64 kbit/s signals to be cross-connected (see 0 3). Access ports of a cross-connect equipment are input and output ports used to terminate 2048 kbit/s signals 1.3 Timing signal 1.3.1 Control of timing signa
10、l It should be possible to derive the intemal Ming signal from the following: a) b) c) from an intenial oscillator. The frequency accuracy of signals in items a) and b) above will normally be f 1 x 10-11. To take into account possible frequency deviations on these signals occurring due to failure in
11、 the synchronous network, the design of timing derivation circuits should assume a frequency accuracy off 1 ppm. one from a number of external source(s) at 2048 kHz; one from a number of 2048 kbit/s signal(s); Note - Ihe provision of timing signal outputs available for the purpose of synchronizing o
12、ther equipments, is an option that might be required depending upon national synchronization arrangements. 1.3.2 Timing performance mode, the local clock requirements of 8 2.2.3 of Recommendation G.812 should be met. The timing performance of the internal clock should comply with Recommendation G.81
13、2. In the holdover Note -For other timing performance options, refer to $ 6.3 below. 1.4 Blocking factor For the mandatory functions in 8 2.1 below, the blocking factor should be zero for cross-connect equipment of size up to 256 access ports of 2048 kbit/s; a zero blocking factor for the case of gr
14、eater than 256 access ports is desirable. For the optional functions in $ 2.2, the blocking factor should be as low as possible; the maximum value is under study. See Notes in $8 2.1 and 2.2 below. Recommendation 6.796 (09/92) 1 CCITT RECMNUG-796 92 m 4Bb2591 0574734 103 m 2.1 MandatoryfMctionS a) C
15、ross-cnnectioli of 64 kbit/s and n x 64 kbids signals, according to the TS order given in 96 5.2 of Recommendation G.704 and 2.2.3 of Recommendation G.735, bidirectional. The equipment shall maintain octet sequence integrity of the signais being cross-connected; Note I - The need to deal with n x 64
16、 kbit/s signals according to 6 5.2 of Recommendation G.704 and 6 x 64 kbit/s (384 kbit/s) signals according to 8 2.2.3 of Recommendatian G.735, should be taken into account in the design of the equipment architecture to minimi7.e any impact on deiay and blocking factor. Note 2 - For some n x 64 kbit
17、/s applications it is necessary to maintain octet sequence integrity Within the same frame. b) Management; These should include control functions and provision of maintenance information. 2.2 Optional functions a) Cross-connection of 64 kbit/s and n x 64 kbit/s signais, unidirectional. The equipment
18、 shall maintain octet sequence integrity of the signals being cross-connected, Note - For some applications it is necessary to maintain octet sequence integrity within the same frame. b) Cross-connection of channel associated signalling bits, a, b, c, d, in time slot 16 corresponding to the 64 kbit/
19、s time slot cross-connection. The equipment shall maintain a, b, c, d bits integrity; Distribution of 64 and n x 64 kbit/s signals on a broadcast basis; c) d) Cross-connectiOn of n x 64 kbit/s signals which are not according to the time slot order given in 18 5.2 of Rmmmendation G.704 or 2.2.3 of Re
20、commendatim G.735 or those where the formats differ between input and output ports, bidirectional and unidirectional. The equipment shall maintain octet sequence integrity of the signals being cross-connected; Note I - The need to deal with n x 64 kbit/s signals with different formats should be take
21、n into account in the design of the equipment architecture to minimize any impact on delay and blocking factor. Note 2 - FW some appiications it is necessary to maintain octet kquence integrity within the same frame. The following optionai functions are under study: e) - cfos-coection Of Sub 64 kbit
22、/S cbannels; - CToss-connection of 64 and n x 64 kbit/s signals on a point-to-multint bsis. 3 Interfaces 3.1 2048 kbus inteflaces 3.1.1 Physical inteace According to 8 6 of Recommendation G.703. 2 Recommendation 6.7% (W92) 3.1.2 Frame structure Refer to QQ 2.3 of Rmmmendation G.704 and 5 of Recommen
23、dation G.704 for basic frame structure and for characteristics of frame structure carrying channels at various bit rates in 2048 kbit/s. Bit 1 of the frame should be used in accordance with Q 2.2.3 of Recommendation G.704, i.e. for a CRC check bit procedure. Refer to 8 2.2.3 of Recommendation G.735
24、for time slot order of 384 kbids sound programme signals contained in a 2048 kbit/s fiame. Depending on the application, some 2048 kbit/s access frames could contain channel associated or common channel signalling. 3.2 Synchronization intequce ut 2048 k.Hz The physical and electricai characteristics
25、 of the synchronization interface shall be according to 8 10 of Recommendation G.703. 3.3 3.4 4 4.1 4.2 4.3 4.4 5 Znter$ace with TMN Under study. Local operator interface According to Recommendation M.3010, F interface. Frame aiignment and CRC prdures An illustration of the procedure is given in Fig
26、ure UG.706. Loss offme alignment Refer to Q 4.1.1 of Recommendation G.706. Recovery offame alignment Refer to 6 4.1.2 of Recommendation G.706. CRC multiframe alignment in time slot O Refer to 6 4.2 of Recommendation G.706. CRC bit monitoring Refer to 6 4.3 of Recommendation G.706. Defect or failure
27、conditions and performance monitoring figure UG.796 gives the location and definition of the reference points used in the specification of defect or failure conditions, performance monitoring and consequent actions. Recommendation 6.7% (09/92) 3 *. , CCITT RECMNtG.796 92 = 4862591 057473b Tb U Al re
28、ference point A2 reference point E1 reference paint 82 reference point 0.704 frame logical signai at receiver part of 2048 kbiis access port. G.704 frame logical signal at transmitter part of 2048 kbiis access port. 64 kbit/s data channels derived from signals at Al reference point before cross-conn
29、exion. 64 kbis data channels derived from signals at 81 reference point after crossconnection. Receiver part of a 2048 kbis access port exduding the adaptatien of the G.703 signal to the G.704 frame logical signai. Transmitter part of a 2048 kbis accessport exduding the adaptation of the G.704 a fra
30、me logical signal to the G.703 signal. X Cross connection function. Note -Al and A2 (respectiveiy Bi and B2) are related to the same 2048 kbit/s 8ccess port. FIGURE 1/G.7% Reference madel for a cross-connect 5.1 Defect or fairure conditions at the AI reference point and consequent actwns at the BI a
31、nd A2 reference points 5.1.1 Defect or failure conditions The equipment should detect the following conditions: 5.1.1.1 Failure of power supply 5.1.1.2 Loss of incoming signals at 2048 kbMs A loss of signai (LOS) defect condition is determined by the absence of signai transitions of either positive
32、or negative polarity over a period of 255 Contiguous pulse positions, sbg With the last dpt of a pulse. A LOS defect condition is deemed to be terminated on the detection of an average pulse density of at least 12.5% over a period of 255 contiguous pulse positions starhg with the receipt of a pulse.
33、 Note I - The detection of this defect is required only when it does not result in an indication of loss of frame alignment. 5.1.1.3 Loss offrame alignment =. Refer to 8 4.1 above. 4 Recommendation 6.7% (09192) CCITT RECMN*G-776 72 H 4Ab257L 0574737 712 H 5.1.1.4 Loss of multiframe alignmew Refer to
34、 0 5.2 of Recommendation G.732. The dewtion of this defect is required when channel associated signalling is used. 5.1.1.5 Error ratio I x 10-3 Refer to 8 4.1.5 of Recommendation G.736. Note - The detection of this defect is optional. When required, it could be determined by counting either the numb
35、er of errored frame alignment words or the number of errored bits in frame alignment words or by using the CRC4 procedure. 5.1.1.6 Reception of AIS An AIS defect condition is determined when the incoming signal has less than two ZEROS in each of two consecutive diframe periods (512 bits per diframe)
36、. The defect is cleared if each of two consecutive frame periods contains three or more ZEROS or FAS has been found. 5.1.1.7 Defect indicationfrom a remote equipment This is detected on bit 3 TSO WAS. 5.1.1.8 Reception ofAIS in time slot 16 Refer to 0 4.2.4 of Recommendation G.736 and 0 3.2.2 of Rec
37、ommendation 0.162. 5.1,1.9 Other defect or failure conditions E.g. frame slips: under study. 5.1.2 Consequent actions Further to the detection of a defect or a failure condition, appropriate consequent actions should be taken as specified in Table UG.796. The consequent actions should be taken rapid
38、ly as indicated below: - the application of AIS at B 1 reference point should be taken within 3 ms of the detection of the relevant defect or failure condition; - the maximum period between the detection of a defect or a failure condition and the transmission of a defect indication at the A2 referen
39、ce point is a national requirement; a figure of the order of 100 ms is suggested; - the maximum period between the detection of a defect or a failure condition and the generation of any failure information is dependent on the maintenance strategy for the equipment (see 8 7). Recommendation 6.7% (09/
40、92) 5 TABU 1D.796 Defect or failure condition and consequent action for 2048 icbiffs access ports Defect or failure Failure condition at the information Al reference point generated (Note 1) Failure of power supply Loss of incoming signai Loss of frame aiigment I Errorratio 1 x 10-3 (Note 5) receive
41、d ftom remote end bit 3 TSO NFAS I AIS received 1 Loss of mutiframe alinnment Defect indication received frrm remote end bit 6 TS16 FRO AIS received in TS16 Consequent actions Defect indidon I AIS applied at B1 reference point to remote end TS16 bits I Yes (if practicable) Yesbit3TSO WAS yes I yes I
42、 Yes I Yes Yesbit3FO I WAS Yes bit 3 TSO Yes Yes WAS (Note 3) (Note 3) No I No I No No I Yes Yesbit6Ts16 I FRO No I No 1 No I No I Yes Yes bit 6 TS16 FRO Note 1 - For any partiCuisr fail? condition, an action is initiakd - at the level of the equipment (e.g. bell,lamp, phter); or - at the level of t
43、be management of the equipment, refer to 0 7 below. individually, it is possible to classify failure informaton as one of the follobhg: - notappicable; - maintenance event information (MEi); - defd maintenance alarm (DMA); - prompt maintenance aiam (PMA). Note 2- Applicable if TS16 is used for chann
44、el associated signalhg ur channel associated supervisionhnainmance. AIS is applied to the relevant a, b, c. d bits. Nore 3 -According b national requirmients. Note 4 - In onder to enable appqmiate actions at runote end, tbe indication of Teoeptioll of AIS should not Wtransmitted on bit 3 of %O NFAS.
45、 TransmisSion of this infonnafion is under study. Note 5 - The detection of this ddwt condition is optional. . 5.2 5.2.1 Defect or failure conditions Defect or failure conditions and consequent actionsfbr the core of the equipment The equipment huid detect the foiiowhg conditions: 5.2.1.1 Failure of
46、 a connection A connection inside the equipment should be deemed to have failed when the 64 and n x 64 kbit/s path between the Al and A2 reference points of the relevant ports is not available for a period of time greater than 1 second. 5.2.1.2 Loss of synchronization signul(s) The equipment is time
47、d on its own internal oscillator when that is not the nonnai mode of operation. I Failure information generated (Note i) 5.2.1.3 Other defect or failure conditions For further study. I 5.2.2 Consequent actions AIS applied at A2 or B 1 or 42 reference pointt Data TS TS 16 bits ! (Note 2) Defect indic
48、ation to remote end A2 reference point Further to the detection of a defect or a failure condition, appropriate consequent dons Lould be taken as specified in Table 2/G.796. The consequent actions should be taken as soon as possible: the application of AIS at relevant B2 reference points (or B1 or A
49、2) should be taken within 3 ms of the detection of the defect or failure condition when this action is practicable; the maximum period between the detection of a defect or a failure condition and the transmission of defect indications to the remote end is a national requirement; a figure of the order of 100 ms is suggested, the maximum period between the detection of a - degraded performance; - unacceptable performance. Recommendation 6.796 (09192) 7 I CCITT RECMN*G.79b 92 = 48b259L OS74740 Y07 mi Tbe strategy to detemine these quality performance parameters are
