ETSI ETS 300 008 ed.1 (1991-12)

SLOVENSKI STANDARD
PSIST ETS 300 008:1996
01-november-1996
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Integrated Services Digital Network (ISDN); Signalling System No.7; Message Transfer
Part (MTP) to support international interconnection
Ta slovenski standard je istoveten z: ETS 300 008 E1
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
PSIST ETS 300 008:1996 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

PSIST ETS 300 008:1996
PSIST ETS 300 008:1996
EUROPEAN ETS 300 008
TELECOMMUNICATION December 1991
STANDARD
Source: ETSI TC-SPS Reference: T/S 43-01
ICS: 33.080
ISDN, SS7
Key words:
Integrated Services Digital Network (ISDN);
CCITT Signalling System No. 7
Message Transfer Part (MTP) to support international
interconnection
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - secretariat@etsi.fr
X.400: Internet:
Tel.: +33 92 94 42 00 - Fax: +33 93 65 47 16
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1991. All rights reserved.
New presentation - see History box

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Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Symbols and abbreviations .7
4 Exceptions to CCITT Recommendations Q.701 to Q.708 .8
4.1 National options .8
4.2 Signalling data links .8
4.3 Timer values .8
4.3.1 CCITT Recommendation Q.703.8
4.3.2 CCITT Recommendation Q.704.8
4.4 Signalling link management.9
4.5 Procedures to prevent unauthorised use of a signalling transfer point.9
4.6 Network Indicator.9
4.7 Signalling Point (SP) restart.9
4.8 User flow control .14
5 Modifications to texts taken from the CCITT Blue Book (1988).15
5.1 Interworking between SPs to the CEPT Recommendation T/S 43-01 and this ETS.15
5.2 Changes to CCITT Recommendation Q.701, § 7.2.4.15
5.3 Changes to CCITT Recommendation Q.701, § 7.2.7.15
5.4 Changes to CCITT Recommendation Q.701, § 8.5.16
5.5 Changes to CCITT Recommendation Q.703, § 8.16
5.6 Change to CCITT Recommendation Q.704, § 3.6.2.2 .17
5.7 Change to CCITT Recommendation Q.704, § 5.6.2 .17
5.8 Change to CCITT Recommendation Q.704, § 6.3 .18
5.9 Change to CCITT Recommendation Q.704, § 11.2.3.1 .18
6 Specific requirements.18
6.1 Signalling link loading .18
6.1.1 Basic definition .18
6.1.2 Maximum signalling link load during normal operation .19
6.1.3 Minimum signalling link load handling capability .19
6.1.4 Message length influence.19
6.1.5 Graphic representation.19
History.21

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Foreword
This European Telecommunication Standard (ETS) has been produced by the Signalling Protocols and
Switching (SPS) Technical Committee of the European Telecommunications Standards Institute (ETSI),
as working document T/S 43-01), and was adopted having passed through the ETSI standards approval
procedure.
This ETS is based on CCITT Recommendations Q.701 to Q.708 as given in the CCITT Blue Book, 1988.
The requirements of these CCITT Recommendations shall apply unless modified by the statements
provided in Clauses 4 and 5 of this ETS and, in addition, shall include the specific requirements contained
in Clause 6.
The CEPT Recommendation for the Message Transfer Part (MTP), see CEPT T/S 43-01, April 1987, may
continue to be used for the early introduction of services e.g. GSM, GAP Phase 2 and the ISDN MOU.
Where CEPT Recommendation T/S 43-01 does not already conform with the CCITT Blue Book MTP, the
appropriate sections of CCITT Recommendation Q.701 together with the additions contained in this ETS
shall resolve any interworking problems between this ETS and CEPT Recommendation T/S 43-01.
CCITT Recommendations Q.709 [9] and Q.791 apply as appropriate, unmodified, since they have no
impact on interworking and are considered for guidance only.

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1 Scope
The scope of this ETS is the further development of the CCITT Signalling System No. 7 protocols for both
the Integrated Services Digital Network (ISDN) and Public Switched Telephone Network (PSTN) following
the publication of CCITT Recommendations Q.701 to Q.708 [1] to [8].
This ETS is applicable to the international network and is not meant to restrict national networks.
2 Normative references
This ETS incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to, or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies.
[1] CCITT Recommendation Q.701 (1988): "Functional description of the message
transfer part (MTP) of Signalling System No.7".
[2] CCITT Recommendation Q.702 (1988): "Signalling data link".
[3] CCITT Recommendation Q.703 (1988): "Signalling link".
[4] CCITT Recommendation Q.704 (1988): "Signalling network functions and
messages".
[5] CCITT Recommendation Q.705 (1988): "Signalling network structure".
[6] CCITT Recommendation Q.706 (1988): "Message transfer part signalling
performance".
[7] CCITT Recommendation Q.707 (1988): "Testing and maintenance".
[8] CCITT Recommendation Q.708 (1988): "Numbering of international signalling
point codes".
[9] CCITT Recommendation Q.709 (1988): "Hypothetical signalling reference
connection".
[10] CCITT Recommendation Q.791 (1988): "Monitoring and measurements for
Signalling System No.7 networks".
[11] CEPT Recommendation T/S 43-01 (April 1987): "CCITT No.7 Message Transfer
Part (MTP)".
3 Symbols and abbreviations
For the purposes of this ETS, the following abbreviations apply.
DPC Destination Point Code
ISDN Integrated Services Digital Network
LSSU Link Status Signal Unit
MSU Message Signal Unit
MTP Message Transfer Part
PSTN Public Switched Telecommunications Network

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SIF Signalling Information Field
SIO Service Information Field
STP Signalling Transfer Point
SP Signalling Point
TFP transfer-prohibited signal
TRA transfer-restart-allowed signal
UPU User Part Unavailable
4 Exceptions to CCITT Recommendations Q.701 to Q.708
The following exceptions to CCITT Recommendations Q.701 to Q.708 [1] to [8], as specified in the Blue
Book, 1988, shall apply.
4.1 National options
No national options, or remarks, with regard to national options shall apply to this ETS.
4.2 Signalling data links
A standard bit rate of 64 kbit/s on signalling data links shall apply.
If signalling data links are to be provided over an analogue transmission path, any necessary digital to
analogue or analogue to digital conversion shall be on the multiplexed transmission link after interface
point C, as defined in figure 2 of CCITT Recommendation Q.702 [2].
4.3 Timer values
The timer values included in CCITT Recommendations Q.703 [3], Q.704 [4] and Q.707 [7] shall apply,
with the following exceptions.
4.3.1 CCITT Recommendation Q.703
These timers shall not apply: T1 (4,8 kbit/s), T2 low, T2 high, T4n (4,8 kbit/s), T4e (4,8 kbit/s), T6 (4,8
kbit/s) and T7 (4,8 kbit/s).
4.3.2 CCITT Recommendation Q.704
These timers shall not apply: T7, T11, T15, T16 and T24.
Timer values to be modified in CCITT Recommendation Q.704 [4], § 16.8:
- T18 Timer within a signalling point whose MTP restarts, for supervising link and linkset activation as
well as the receipt of routing information. The value is implementation and network dependent.
Criteria to choose T18 are given in CCITT Recommendation Q.704 [4], § 9.2.
- T19 Supervision timer during MTP restart to avoid possible ping-pong of transfer-prohibited signal
(TFP) and traffic-restart-allowed signal (TRA) messages: 67 to 69 seconds.
- T20 Overall MTP restart timer at the signalling point whose MTP restarts: 59 to 61 seconds.
- T21 Overall MTP restart timer at a signalling point adjacent to one whose MTP restarts: 63 to 65
seconds.
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NOTE: The values of the MTP restart timers (T18 to T21) defined above are for use during
normal operation. It might be advantageous for the network operator(s) to define an
alternative value for each timer for use in potential network failures. Such an
emergency might be recognised by an abnormally large number of outages, and it
would be at the discretion of the operator(s) to use the emergency set of timer values
within the network. Thus, the selection of the appropriate timer set is within the
responsibility of the network administration.
4.4 Signalling link management
Of the requirements in CCITT Recommendation Q.704 [4], only the basic signalling link management
functions of § 12.2 shall apply and § 12.3, § 12.4, § 12.5 and § 12.6 shall not apply.
4.5 Procedures to prevent unauthorised use of a signalling transfer point
While CCITT Recommendation Q.705 [5] is intended as a guidance document only, it should be noted
that the optional procedure for the prevention of unauthorised use of a Signalling Transfer Point (STP) as
specified in CCITT Recommendation Q.705 [5], § 8, shall not be essential.
4.6 Network Indicator
Only the value 00 shall be used for the Network Indicator.
4.7 Signalling Point (SP) restart
CCITT Recommendation Q.704 [4], § 9, shall be replaced by the following.
9 MTP restart
9.1 General
When a signalling point is isolated from the network for some time, it cannot be sure that its routing
data are still valid (note that circumstances might cause the management entity to isolate the node,
i.e. make all links unavailable, in order to facilitate recovery from a partial isolation). Thus, problems
could be present when the sending of User traffic is resumed, due to wrong routing data as well as
due to many parallel activities (e.g. link activation, changebacks, etc.) which have to be performed
within the node whose MTP is restarting.
The objective of the MTP restart procedure is to protect both the node whose MTP is restarting, and
the network. This is done by giving the restarting MTP time to activate sufficient links, and to
exchange enough routing data with the network, before User traffic is restarted. Note that in this
context "sufficient" and "enough" mean that potential remaining problems should not cause the
node to fail again.
A central part of the restart procedure is the exchange of network status information between the
restarting MTP and the adjacent nodes. In order for the procedure to make sense, the network
status should not change significantly during this information exchange. As a consequence there is
an overall restart time defined for the node whose MTP is restarting as well as for the adjacent
nodes. During this time, all activities within the node whose MTP is restarting as well as the
adjacent nodes should be completed. This requires that the time available is used in an efficient
way.
As a basis of the restart procedure it is assumed that most of the signalling points within the
network are accessible. Thus, at the beginning of the restart procedure, all concerned routes are
considered to be allowed, and the update of the network status is performed by the exchange of
transfer-prohibited signal (TFP) messages.

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The MTP restart procedure uses the traffic-restart-allowed signal (TRA) message which contains:
- the label, indicating the originating signalling point and the adjacent destination signalling
point;
- the traffic restart allowed signal.
The format and coding of this message appear in CCITT Recommendation Q.704, § 15.
When an adjacent node has finished sending all relevant TFP messages to the node with the
restarting MTP, it finally sends a TRA message which indicates that all relevant routing information
has been transferred. Thus, at the node with the restarting MTP, the number of received TRA
messages is an indication of the completeness of the routing data.
When the restarting MTP has completed all actions or when the overall restart time is over, it sends
TRA messages directly to all of its adjacent nodes accessible via a direct linkset. These messages
indicate that the restart procedure is terminated and User traffic should be started.
9.2 Actions in a signalling point whose MTP is restarting
9.2.1 A signalling point starts the MTP restart procedure when its first link is in service at level 2. The
restarting MTP:
- if it has the transfer function, starts a timer T18;
- starts an overall restart timer T20; and
- continues activating or unblocking all of its signalling links by means of the basic signalling link
management procedures (see CCITT Recommendation Q.704, § 12.2).
NOTE: In order to use the overall restart time in an efficient way, it is preferable to make all
linksets available at nearly the same time, by activating first one link per linkset, and by
applying emergency alignment for at least the first link in each linkset. Because of this
measure, the routing data update can be started for all routes at the very beginning of
the restart procedure.
9.2.2 If the signalling point's restarting MTP has the transfer function, the MTP restart procedure consists
of two phases. Within the first phase, supervised by timer T18, links are activated and the routing
tables within the restarting MTP are updated according to the transfer prohibited and transfer
allowed messages (see CCITT Recommendation Q.704, § 15) received from the adjacent nodes.
In addition, the restarting MTP takes into account any traffic restart allowed messages received
from adjacent nodes. Timer T18 is implementation and network dependent, and is stopped when:
(1) sufficient links and linksets are available to carry the expected signalling traffic; and
(2) enough TRA messages (and therefore routing data) have been received to give a high level of
confidence in the MTP routing tables.
NOTE: In normal circumstances the restarting MTP should wait for TRA messages from all
adjacent nodes. There are, however, other situations where this might not be useful,
e.g. for a long-term equipment failure.
When T18 is stopped or expires, the second phase begins, which includes as a major part a
broadcast of non-preventive transfer prohibited messages (i.e. those TFPs according to CCITT
Recommendation Q.704, § 13.2.2, v), taking into account signalling linksets which are not available
and any TFP and TFA messages received during phase 1.

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Note that timer T18 is determined such that during phase 2 the broadcast of TFP messages may
be completed in normal situations. TRA messages received during phase 2 should be ignored. If
during phase 2 a destination has been declared to be inaccessible by sending of a TFP message,
and afterwards, but still within phase 2, this destination becomes accessible to the restarting MTP
by reception of a TFA message or the availability of a corresponding link, this new accessibility is a
late event and should be treated outside the restart procedure.
The handling of the new accessibility of the said destination before the sending of a TFP referring to
that destination is an implementation dependent matter.
When all TFP messages have been sent, the overall restart timer T20 is stopped and phase 2 is
finished.
Note that preventive TFP messages (i.e. those according to CCITT Recommendation Q.704,
§ 13.2.2, i), except possibly those for highest priority routes, must have been sent before normal
User traffic is carried. This might be done during or after phase 2.
9.2.3 If the restarting MTP has no transfer function, phase 1 (see CCITT Recommendation Q.704,
§ 9.2.2) but not phase 2 is present. In this case, the whole restart time is available for phase 1. The
overall restart timer T20 is stopped when:
(1) sufficient links and linksets are available to carry the expected signalling traffic; and
(2) enough TRA messages (and therefore routing data) have been received to give a high level
of confidence in the MTP routing tables.
9.2.4 When T20 is stopped or expires, the restarting MTP of the signalling point or signalling transfer
point sends traffic restart allowed messages to all adjacent signalling points via corresponding
available direct linksets, and an indication of the end of MTP restart is sent to all local MTP Users
showing each signalling point's accessibility or inaccessibility. The means of doing the latter is
implementation dependent.
In addition, timer T19 is started (see CCITT Recommendation Q.704, § 9.5.2) for all signalling
points to which a TRA message has just been sent. Normal operation is then resumed.
When T20 expires the transmission of TFP messages is stopped. However, preventive TFP
messages (i.e. those according to CCITT Recommendation Q.704, § 13.2.2, i), except possibly
those for highest priority routes, must have been sent before MTP User traffic is restarted.
9.3 Actions in a signalling point X, adjacent to a signalling point Y whose MTP restarts.
9.3.1 A signalling point X considers that the MTP of an inaccessible adjacent signalling point Y is
restarting when:
- the first link in a direct linkset is in the "in service" state at level 2; or
- another route becomes available due either to reception of a corresponding TFA or TRA
message, or by the corresponding linkset becoming available (see CCITT Recommendation
Q.704, § 3.6.2.2).
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9.3.2 When the first link in a direct linkset towards signalling point Y, whose MTP is restarting, is in the "in
service" state at level 2, signalling point X starts a timer T21 and takes account of any TFP and TFA
messages received from signalling point Y. In addition X takes the following action:
- if X has the transfer function, when the direct linkset is available at level 3, X sends any
necessary TFP messages to Y; then
- X sends a traffic restart allowed message to signalling point Y.
If a signalling point, previously declared to be inaccessible, becomes available again before T21 is
stopped or expires, a corresponding TFA message is sent to the signalling point Y whose MTP is
restarting.
If a signalling point becomes prohibited to signalling point X after a TRA message has been sent by
X to Y, X sends a corresponding TFP message to Y.
When a traffic restart allowed message has been received by X from signalling point Y, and a TRA
message has been sent by X to Y, X stops timer T21. Note that preventive TFP messages
according to CCITT Recommendation Q.704, § 13.2.2, i) must be sent before MTP User traffic is
restarted.
NOTE: This includes the case where the MTP of Y is restarting as well as the case that both X
and Y start the adjacent signalling point MTP restart procedure at the new availability
of the interconnecting direct linkset. In the latter case, one side will receive a TRA
message from the other while still sending TFP messages, so that it has not yet sent
its TRA message. The transmission of routing information should be completed before
this TRA message is sent to the adjacent node and timer T21 stopped.
When T21 is stopped or expires, signalling point X sends an MTP-RESUME primitive concerning Y,
and all signalling points made available via Y, to all local MTP Users. If X has the transfer function,
it broadcasts to adjacent available signalling points transfer allowed messages concerning Y and all
signalling points made accessible via Y. Note that preventive TFPs according to CCITT
Recommendation Q.704, § 13.2.2, i) must be sent before MTP User traffic is restarted.
In the abnormal case where transfer prohibited messages are still being sent to Y when T21 expires
(and hence no TRA message has yet been sent to Y), such routing data transmission is stopped
and no TRA message is sent to Y. No
...