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All drawings appearing in this Fascicle have been done in Autocad.
Recommendation Q.707
TESTING AND MAINTENANCE
1 General
In order to realize the performance requirements described in
Recommendation Q.706, means and procedures for signalling network testing and
maintenance are required in addition to the means defined in Recommendations
Q.703 and Q.704.
2 Testing
2.1 Signalling data link test
As defined in Recommendation Q.702, S 1, the signalling data link is a
bidirectional transmission path for signalling. Testing and maintenance functions
can be initiated independently at either end.
The signalling data link and the constituent parts of the digital and
analogue versions are described in Recommendation Q.702, S 1.
They must be tested before being put into service to ensure that they meet
the requirements of Recommendation Q.702, S 3.
Since interruptions of the signalling data link will affect many
transactions, they must be treated with the utmost care. Appropriate special
measures should be taken to prevent unauthorized maintenance access which could
result in interruptions to service. These special measures may include marking or
flagging the equipment and indications on distribution frames or test bays where
access is possible (see Recommendation M.1050 [1]).
The signal unit error rate monitor and the alignment error rate monitor
described in Recommendation Q.703, S 10, also provide means for detecting
deterioration of a signalling data link.
Further studies are required with reference to Recommendation V.51 [2].
2.2 Signalling link test
As defined in Recommendation Q.703, S 1.1.1 and illustrated in Figure
1/Q.701, the signalling link comprises a signalling data link with signalling
link functions at either end.
In the following, an on-line signalling link test procedure is specified
which involves communication between the two ends of the concerned signalling
link. This procedure is to be used when a signalling link is activated or
restored (see Recommendation Q.704, S 12). The signalling link becomes available
only if the test is successful. This procedure is intended for use while the
signalling link is in service. In addition, local failure detection procedures
should be performed at either end; 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 test message is sent at regular intervals
T2 (see S 5.5). The testing of a signalling link is performed independently from
each end.
The ability to send a signalling test acknowledgement message, defined
below, must always be provided at a signalling point.
The signalling point initiating the tests transmits a signalling link test
message on the signalling link to be tested. This message includes a test pattern
which is chosen at the discretion of the end initiating the test. After receiving
a signalling link test message, a signalling point responds with a signalling
link test acknowledgement message on the signalling link identified by the SLS
contained in the signalling link test message. The test pattern included in the
signalling link test acknowledgement message is identical to the test pattern
received.
Fascicle VI.7 - Rec. Q.707 PAGE1
The signalling link test will be considered successful only if the
received signalling link test acknowledgement message fulfills the following
criteria:
a) 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 link
test acknowledgement message is not received on the link being tested within T1
(see S 5.5) after the signalling link test message has been sent, the test is
considered to have failed and is repeated once. In the case when also the
repeated test fails, the following actions have to be taken:
- SLT applied on activation/restoration, the link is put out of service,
restoration is attempted and a management 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 for signalling link testing are specified in S 5.4.
3 Fault location
Fault location operations, employing particular manual or automatic
internal test equipment are left to the discretion of the individual signalling
points.
Tests requiring provision of messages are for further study. See [3].
4 Signalling network monitoring
In order to obtain information on the status of the signalling network,
monitoring of the signalling activity must be provided (for example measures of
the signalling load on the signalling data link). The specification of such means
and procedures is contained in Recommendations Q.791 and Q.795.
5 Formats and codes of signalling network testing and
maintenance messages
5.1 General
The signalling network testing and maintenance messages are carried on the
signalling channel in message signal units, the format of which is described in
Recommendation Q.703, S 2. As indicated in Recommendation Q.704, S 14.2.1, these
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, S 14.2.2.
The Signalling Information Field (SIF) consists of an integral number of
octets and contains the label, the heading code and one or more signals and
indications.
5.2 Label
For signalling network testing and maintenance messages, the label has the
same structure as the label of signalling network management messages (see
Recommendation Q.704, S 15.2).
5.3 Heading code H0
The heading code H0 is the 4-bit field following the label and identifies
the message group. The different heading codes are allocated as follows:
0000 Spare
0001 Test messages
The remaining codes are spare.
5.4 Signalling link test messages
The format of the signalling link test messages is shown in Figure
1/Q.707.
Figure 1/Q.707 - CCITT 35550
The signalling link test messages, are made up of the following fields:
- Label: (32 bits), see S 5.2
- Heading code H0: (4 bits)
- Heading code H1: (4 bits)
- Spare bits: (4 bits)
- Length indicator: (4 bits)
- Test pattern: (n x 8 bits, 1 n 15).
In the label, the signalling link code identifies the signalling link on
which the test message is sent.
The heading code H1 contains signal codes as follows:
bi D C B A
ts
PAGE1 Fascicle VI.7 - Rec. Q.707
0 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 pattern
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 tolerances
Q.707 Timer Range
T1 (see S 2.2) 4-12 s
Supervision timer for signalling (equal or greater than T6 of
link test acknowledgement message Q.703)
T2 (see S 2.2) 30-90 s
Interval timer for sending
signalling link test messages
6 State transition diagrams
The state transition diagram is intended to show precisely the behaviour
of the signalling system under normal and abnormal conditions as viewed from a
remote location. It must be emphasized that the functional partitioning shown in
the following diagram is used only to facilitate understanding of the system
behaviour and is not intended to specify the functional partitioning to be
adopted in a practical implementation of the signalling system.
FIGURE 2/Q.707 (feuillet 1 sur 2) - T1109700-88
Figure 2/Q.707 (feuillet 1 sur 2) - T1109710-88
References
[1] CCITT Recommendation Lining up an international point-to-point leased
circuit, Vol. IV, Rec. M.1050.
[2] CCITT Recommendation Organization of the maintenance of international
Fascicle VI.7 - Rec. Q.707 PAGE1
telephone-type circuits used for data transmission, Vol. VIII, Rec. V.51.
[3] Ibid., S 5.
PAGE1 Fascicle VI.7 - Rec. Q.707