1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION S ECTO R OF ITU G.181 (03/93) GENERAL CHARACTERISTICS OF INTERNATIONAL TELEPHONE CONNECTIONS AND INTERNATIONAL TELEPHONE CIRCUITS CHARACTERISTICS OF 1 + 1 TYPE RESTORATION SYSTEMS FOR USE ON DIGITAL TRANSMISSION LINKS IT-T
2、 Recommendation GA 81 (Previously ?CCITT Recommendation?) ITU-T RECMN*G.LBL (REV*L) 93 akl YBb259L 0582238 368 FOmWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operat
3、ing and tariff questions and issuing 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 IT-T Study Groups which, in their tu
4、rn, produce Recommendations on these topics. ITU-T Recommendation G.181 was revised by the ITU-T Study Group XV (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 (ITU), the CCITT ceased
5、 to exist as of 28 February 1993. In 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 Recommendat
6、ion, no change has been made in the text to references containing the acronyms “CCITT, 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 telecommunicati
7、on administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, inc
8、luding photocopying and microfilm, without permission in writing from the ITU. - ITU-T RECMN*G-383 (REV*:L) 93 = 4862593 0582239 2T4 = CONTENTS Page 1 General . 1 2 Object of Recommendation 1 3 Equipment specifications . 1 3.1 Interfaces 1 3.2 Operational aspects . 1 Recommendation 6.181 (03/93) i I
9、TU-T RECMN*G-383 (REV*3) 93 4862573 0582240 TLb = Transmission restoration functions are often implemented in the modern telecommunication network to improve the the maintenance operations easier. I availability and quality of services, by minimizing the effects or potential effects of a transmissio
10、n failure, and to make Recommendation 6.181 i 2 Object of Recommendation CHARACTERISTICS OF 1 + 1 TYPE RESTORATION SYSTEMS FOR USE ON DIGITAL TRANSMISSION LINKS I I l l This Recommendation does not cover the restoration systems fully embedded in transmission systems. The hierarchical level at interf
11、ace T is 2048 kbit/s. (Melbmrne, 1988; amelided at Helsinki, 1993) I Equipment specifications 3 Equipment H and RSE (see Figure 1) may be of the regenerative or non-regenerative type. 1 General 3.1 Interfaces 1 3.1.1 Transmission path interfaces (T) For H and RSE equipment of the regenerative type t
12、he interfaces shall be as specified in Recommendation G.703. The intrinsic output jitter should he not greater than 0.05 U (measurement filter bandwidth 20 Hz to 100 IrHz). The terminology and general principles of transmission restoration are described in Recommendation M.495. The functional organi
13、zation for automatic transmission restoration is described in Recommendation M.496. Recommendation G.181 (03/93) 1 I This Recommendation specifies the characteristics of equipment for 1 + 1 type transmission restoration systems (protection link switching) for digital transmission links (see Recommen
14、dation G.701). The general arrangement of a system of this type is shown in Figure 1. It uses hybrid on the send side, splitting the input path into two output paths. On the receive side the two paths are supervised and are connected further by a switch automatically controlled by the received signa
15、ls. The switch may additionally be operated manually or by some kind of remote procedure. The two transmission directions are handled independently. This Reconmiendation refers to the equipment labelled as H (hybrid) RSE (restoration switching equipment) and RSCE (restoration switching control equip
16、ment). Interface characteristics for H and RSE equipment of the non-regenerative type are at present not covered by this Recommendation. 3.1.2 Control interface (X) The control intefiace X is not at present standardized by CCITT. However in the future it may be specified as a Q interface see Recomme
17、ndation G.773). 3.2 Operational aspects 3.2.1 For H and RSE equipment of the regenerative type the jitter transfer gain should be not greater than 0.5 dB. Transfer of the switched signals The transfer characteristics for H and RSE equipment of the non-regenerative type are at present not covered by
18、this Recommendation. 3.2.2 Response Switching between the two paths occurs only on the receive side, as indicated in Figure 1. H Hybrid RSE Restoration switching equipment RSCE Restoration switching control equipment T Transmission interface X Control interface NOTES 1 2 not covered by this Recommen
19、dation. The two digital links can be in the same cable or follow different routes. The interface between the RSCE and the local manual control is not standardized and it is FIGURE UG.181 1 + 1 transmission restoration system One of the two paths may be the path with the primary right, e.g. path II/I
20、I. If this path fails the switch is operated to path III/III. After restoration of path IVII the switch will automatically be set back to this path. If the two paths have the same right the switch will remain in the last position even after restoration of a failed path. This is the preferred method.
21、 NOTE 1 - Paths II/I and IIIIIII have the same performance under normal planning conditions of transmission routes and systems. The “method of the same right” reduces the frequency of switching and resynchronization by a factor of 2. Switching to a failed path must be avoided. The RSCE should operat
22、e the switch: - automatically according to the criteria expressed by Tables 1 and 2, based on AIS reception and loss of incoming signal or (as an option) on transmission quality (see Note 2); manually on command from the local manual control; under a request coming from interface X. - - NOTE 2 - As
23、an option the switching can be based on transmission quality as defined in Recommendation G.821 and by agreement between Administrations, In this case the transmitted signals need to have a standard frame structure in accordance with Recommendation G.704 which for 2048 kbit/s should also include the
24、 CRC4 option. It is recommended that the time required for the above response actions, that is the “confirmation time” plus the “restoration transfer time” should be less than 10 ms for terrestrial routes and 500 ms for satellite routes. 2 Recommendation 6.181 (03/93) TABLE UG.181 Response criteria
25、for the hybrid H at the transmit side Fault condition Consequent action (signal at Ii and III) No signal at I AIS AIS receive at I AIS Failure of power supply, system failure a The equipment may not be able to send AIS; this depends on the nature of the failure. AIS (if possible “) TABLE 2/G. 18 1 S
26、witching criterion for the RSE at the receive side Remark Consequence action Condition Received signal II and III I (SeeNote) I Signaiat I Received signal at II Switch to II Signal at IV AIS or no signal at III Received signal at III Switch to III Signal at IV AIS or no signal at II AIS at II and II
27、I Switch to II or III The switching equipment sends AIS at IV Switch to II No signul at II and III AIS at II and no signal at III Received AIS is through- connected Received AIS is AIS at III and no signal at II Correct signal rit II Bad quality at III Switch to III Switch to II through-connected Co
28、rrect signal at IV Correct signal ut III Switch to IIi Idem Bad quality at II Bad quality at II Switch to II Bad quality at IV Option AIS or no signal at III Bad quality at III Switch to III Idem AIS or no signal at II Bad quality at III (See Note) Bad quality at IV Bad quality at II Failure of power supply system failure The switching equipment sends AIS (if possible) at IV KOTE - Switch to paths IVII or III/III if both paths have the same right. Switch to the path with the primary right if the other method is used (see 3.2.2).
