1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#) these are not specified in this Recommendation.In case the signalling link test (SLT) is applied while the signalling link is in service the signalling link testmessage is sent at regular intervals T2 (
2、see 5.5). The testing of a signalling link is performed independently from eachend.The ability to send a signalling test acknowledgement message, defined below, must always be provided at asignalling point.The signalling point initiating the tests transmits a signalling link test message on the sign
3、alling link to be tested.This message includes a test pattern which is chosen at the discretion of the end initiating the test. After receiving asignalling link test message, a signalling point responds with a signalling link test acknowledgement message on thesignalling link identified by the SLS c
4、ontained in the signalling link test message. The test pattern included in thesignalling link test acknowledgement message is identical to the test pattern received.The signalling link test will be considered successful only if the received signalling link test acknowledgementmessage fulfills the fo
5、llowing criteria:2 Fascicle VI.7 - Rec. Q.707a) the SLC identifies the physical signalling link on which the SLTA was received.b) the OPC identifies the signalling point at the other end of the link.c) the test pattern is correct.In the case when the criteria given above are not met or a signalling
6、link test acknowledgement message is notreceived on the link being tested within T1 (see 5.5) after the signalling link test message has been sent, the test isconsidered to have failed and is repeated once. In the case when also the repeated test fails, the following actions have tobe taken:- SLT ap
7、plied on activation/restoration, the link is put out of service, restoration is attempted and amanagement system must be informed.- SLT applied periodically, for further study.The formats and codes of signalling link test and signalling link test acknowledgement messages used forsignalling link test
8、ing are specified in 5.4.3 Fault locationFault location operations, employing particular manual or automatic internal test equipment are left to thediscretion of the individual signalling points.Tests requiring provision of messages are for further study. See 3.4 Signalling network monitoringIn orde
9、r to obtain information on the status of the signalling network, monitoring of the signalling activity mustbe provided (for example measures of the signalling load on the signalling data link). The specification of such meansand procedures is contained in Recommendations Q.791 and Q.795.5 Formats an
10、d codes of signalling network testing and maintenance messages5.1 GeneralThe signalling network testing and maintenance messages are carried on the signalling channel in messagesignal units, the format of which is descripted in Recommendation Q.703, 2. As indicated in Recommendation Q.704, 14.2.1, t
11、hese messages are distinguished by the configuration 0001 of the service indicator (SI). The Sub Service Field(SSF) of signalling network testing and maintenance messages is used in accordance with Recommendation Q.704, 14.2.2.The Signalling Information Field (SIF) consists of an integral number of
12、octets and contains the label, theheading code and one or more signals and indications.5.2 LabelFor signalling network testing and maintenance messages, the label has the same structure as the label ofsignalling network management messages (see Recommendation Q.704, 15.2).5.3 Heading code H0The head
13、ing code H0 is the 4-bit field following the label and identifies the message group. The differentheading codes are allocated as follows:0000 Spare0001 Test messagesThe remaining codes are spare.Fascicle VI.7 - Rec. Q.707 35.4 Signalling link test messagesThe format of the signalling link test messa
14、ges is shown in Figure 1/Q.707.The signalling link test messages, are made up of the following fields:- Label: (32 bits), see 5.2- Heading code H0: (4 bits)- Heading code H1: (4 bits)- Spare bits: (4 bits)- Length indicator: (4 bits)- Test pattern: (n 8 bits, 1 n 15).In the label, the signalling lin
15、k code identifies the signalling link on which the test message is sent.The heading code H1 contains signal codes as follows:bits DCBA0 0 0 1 signalling link test message (SLTM)0 0 1 0 signalling link test acknowledgement message (SLTA)The length indicator gives the number of octets which the test p
16、attern comprises.The test pattern is an integral number of octets and is chosen at the discretion of the originating point.5.5 Time-out values and tolerancesQ.707 Timer RangeT1 (see 2.2) 4-12 sSupervision timer for signalling link testacknowledgement message (equal or greater than T6 of Q.703)T2 (se
17、e 2.2) 30-90 sInterval timer for sending signalling linktest messages6 State transition diagramsThe state transition diagram is intended to show precisely the behaviour of the signalling system under normaland abnormal conditions as viewed from a remote location. It must be emphasized that the funct
18、ional partitioning shownin the following diagram is used only to facilitate understanding of the system behaviour and is not intended to specifythe functional partitioning to be adopted in a practical implementation of the signalling system.4 Fascicle VI.7 - Rec. Q.707Fascicle VI.7 - Rec. Q.707 56 Fascicle VI.7 - Rec. Q.707References1 CCITT Recommendation Lining up an international point-to-point leased circuit, Vol. IV, Rec. M.1050.2 CCITT Recommendation Organization of international telephone-type circuits used for data transmission,Vol. VIII, Rec. V.51.3 Ibid., 5.
