In the international Signalling System No. 7 network, it should be possible
to identify signalling links/routes with a limited SIF length handling
capability and prevent overlength messages being transmitted over them
by
administrative action based on the exchange of operational data. However,
with some national networks due to the rapid change in status of SP/STP
.PP
implementation level (e.g.,\ 62 to 272\ SIF capability) and the number
of SP/STPs in the network, this administrative action and data exchange
may not be
adequate. In this situation, a mechanism based on the following MTP activities
may be more appropriate.
.RT
.LP
i)
Detection of a link with 272 SIF capability may be achieved by coding
the \*QD\*U\ bit of LSSUs sent during alignment as\ 1 (with 62\ octet SIF
links it would be\ 0). On receipt of this LSSU, a Blue Book SP/STP would mark
the link/route as having 272\ SIF capability. A Red Book SP/STP would ignore
the coding of the \*QD\*U\ bit and treat the LSSU in the normal manner.
.LP
ii)
When a Blue Book SP/STP receives a message for onward
routing, it will check if the message (SIF) is greater than 62\ octets.
If the SIF is greater than 62\ octets, it will verify that the link/route
can handle a message of this length. Should the link/route not have the
SIF length
capability, the message will be discarded and an indication sent to the
message origin. A Red Book SP/STP should not receive a message with an
SIF\ >\ 62\ octets.
.LP
iii)
If the message originator is a local MTP User, an MTP
PAUSE
primitive will be returned by the MTP in response to an overlength message
(see \(sc\ 8). Should the originator be at a remote\ SP, a TFA coded to
indicate
that only 62\ octet SIF messages can be transferred will be returned by
the MTP in response to an overlength message (see Q.704\ \(sc\ 15).
.PP
In national networks using an SIF compatibility mechanism, the two spare
bits in the TFA (see Q.704\ \(sc\ 15.8.2) may be coded as an SIF compatibility
indicator as follows:
.LP
bit
B\ A
.LP
0\ 0
Allow 62 octet SIFs/Prohibit 272, X and Y octet SIFs
.LP
0\ 1
Allow 62 and 272 octet SIFs/Prohibit X\ and
Y\ octet\ SIFs
.LP
1\ 0
Allow 62, 272 and X octet SIFs Prohibit Y octet SIFs.
.LP
1\ 1
Allow 62, 272, X and Y octet SIFs.
.PP
\fINote\fR \ \(em\ 272 < X < Y octets, the values of X and Y are for further
study.
.sp 1P
.LP
7.3
\fIYellow Book to Blue Book Interworking\fR
.sp 9p
.RT
.PP
The changes between Yellow and Blue Books have taken place in two stages:
Yellow to Red and Red to Blue. Therefore, to achieve interworking
between Yellow and Blue Book implementations, the actions specified in
\(sc\(sc\ 7.1 and\ 7.2 should be applied. In \(sc\ 7.1 Red Book SP/STP
should be read as Blue Book SP/STP and in \(sc\ 7.2 Red Book SP/STP should
be read as Yellow\ Book\ SP/STP.
.PP
There is one change from the Red Book in the Blue Book that will have an
additional impact on interworking with the Yellow Book, and that is the
deletion of the blocking procedure. This means that while a Yellow Book
implementation can block a signalling link, a Blue Book node can neither
inhibit nor block the link in the opposite direction.
.bp
.RT
.sp 2P
.LP
\fB8\fR \fBPrimitives and Parameters of the Message Transfer Part\fR
.sp 1P
.RT
.PP
The primitives and parameters are shown in Table 1/Q.701.
.RT
.ce
\fBH.T. [T2.701]\fR
.ce
TABLE\ 1/Q.701
.ce
\fBMessage transfer part service primitives\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) sw(48p) | cw(72p) , c | c | ^ .
Primitives Parameters
Generic Name Specific Name
_
.T&
lw(48p) | lw(48p) | lw(72p) .
MTP\(hyTRANSFER Request Indication {
OPC (see Q.704 \(sc 2.2)
DPC (see Q.704 \(sc 2.2)
SLS (see Q.704 \(sc 2.2) (Note 1)
SIO (see Q.704 \(sc 14.2)
User data (see Q.703 \(sc 2.3.8)
}
_
.T&
lw(48p) | lw(48p) | lw(72p) .
MTP\(hyPAUSE (Stop) Indication Affected DPC
_
.T&
lw(48p) | lw(48p) | lw(72p) .
MTP\(hyRESUME (Start) Indication Affected DPC
_
.T&
lw(48p) | lw(48p) | lw(72p) .
MTP\(hySTATUS Indication
Affected DPC Cause (Note 2)
.TE
.LP
\fINote\ 1\fR
\ \(em\ The MTP users should take into account that this parameter is used for load sharing by the MTP, therefore, the SLS values should be distributed as equally as possible. The MTP guarantees (to a high degree of probability) an
in\(hysequence delivery of messages which contain the same SLS code.
.LP
\fINote\ 2\fR
\ \(em\ The Cause parameter has, at present, two values:
.LP
i)
\fISignalling network congested (level)\fR
.LP
This parameter value is included if national options with congestion
priorities and multiple signalling link states without congestion priorities as in Recommendation\ Q.704 are implemented.
.LP
ii)
\fIRemote User unavailable.\fR
.nr PS 9
.RT
.ad r
\fBTable 1/Q.701 [T2.701], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
8.1
\fITransfer\fR
.sp 9p
.RT
.PP
The primitive
\*QMTP\(hyTRANSFER\*U
is used between level 4 and
level 3 (SMH) to provide the MTP message transfer service.
.RT
.sp 1P
.LP
8.2
\fIPause\fR
.sp 9p
.RT
.PP
The primitive
\*QMTP\(hyPAUSE\*U
indicates to the \*QUsers\*U the
total inability of providing the MTP service to the specified destination.
.RT
.sp 1P
.LP
8.3
\fIResume\fR
.sp 9p
.RT
.PP
The primitive
\*QMTP\(hyRESUME\*U
indicates to the \*QUser\*U the
total ability of providing the MTP service to the specified destination.
.PP
This primitive corresponds to the destination accessible state as
defined in Recommendations\ Q.704.
.bp
.RT
.sp 1P
.LP
8.4
\fIStatus\fR
.sp 9p
.RT
.PP
The primitive
\*QMTP\(hySTATUS\*U
indicates to the \*QUsers\*U the
partial
inability of providing the MTP service specified destination. The primitive
is also used to indicate to a User that a remote corresponding User is
unavailable (see Q.704\ \(sc\ 11.2.7).
.PP
In the case of national option with congestion priorities or multiple signalling
link congestion states without priorities as in Recommendation\ Q.704 are
implemented, this \*QMTP\(hySTATUS\*U primitive is also used to indicate
a change of congestion level.
.PP
This primitive corresponds to the destination congested/User Part
unavailable state as defined in Recommendation\ Q.704.
.RT
.sp 1P
.LP
8.5
\fIRestart\fR
.sp 9p
.RT
.PP
The MTP indicates to the \*QUsers\*U at the restarting SP that the MTP
is commencing or ending the signalling point restart procedure (see
Recommendation\ Q.704, \(sc\ 9).
.PP
The indication may have the following qualifiers:
.RT
.LP
i)
Begin
.LP
ii)
End
.PP
The qualifier \*QBegin\*U indicates to the \*QUsers\*U that all
destinations should be marked as accessible (but that the resumption of
signalling traffic must await the reception of MTP\(hyRESUME primitive or MTP
restart indication \*QEnd\*U).
.PP
The qualifier \*QEnd\*U indicates to the \*QUsers\*U that signalling traffic
may be restarted, taking into account any MTP\(hyPAUSE primitives previously
received.
.PP
The means of conveying the MTP restart indication to the MTP \*QUsers\*U,
is for further study.
.RT
.sp 2P
.LP
\fBRecommendation\ Q.702\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSIGNALLING\ DATA\ LINK\fR
.EF '% Fascicle\ VI.7\ \(em\ Rec.\ Q.702''
.OF '''Fascicle\ VI.7\ \(em\ Rec.\ Q.702 %'
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.PP
1.1
A \fIsignalling data link\fR | is a bidirectional transmission path for
signalling, comprising two \fIdata channels\fR operating together in opposite
directions at the same data rate. It constitutes the lowest functional
level
(level\ 1) in the Signalling System No.\ 7 functional hierarchy.
.sp 9p
.RT
.PP
1.2
Functional configuration of a signalling data link is shown in
Figure\ 1/Q.702.
.PP
The terms \fItransmission channel\fR | and \fItransmission link\fR | are
used in Signalling System No.\ 7 instead of transfer channel and transfer
link used in Signalling System No.\ 6.
.FE
1.3
A digital signalling data link is made up of digital
\fItransmission channels\fR and digital switches or their terminating
equipment providing an interface to signalling terminals. The digital
transmission channels may be derived from a digital multiplex signal at
1544, 2048 or 8448\ kbit/s having a frame structure as defined in
Recommendation\ G.704\ [1], or from digital multiplex streams having a frame
structure specified for data circuits (Recommendations\ X.50\ [4], X.51\ [5],
X.50 | fIbis\fR \ [6], X.51 | fIbis\fR \ [7]).
.PP
1.4
An analogue signalling data link is made up of voice\(hyfrequency
analogue transmission channels either 4\ kHz or 3\ kHz spaced, and modems.
.PP
1.5
Signalling System No.\ 7 is capable of operating over both
terrestrial and satellite \fItransmission links\fR .
.bp
.LP
.rs
.sp 40P
.ad r
\fBFigure 1/Q.702, p.21\fR
.sp 1P
.RT
.ad b
.RT
.PP
1.6
The operational signalling data link shall be exclusively
dedicated to the use of a Signalling System No.\ 7 signalling link between
two signalling points. No other information should be carried by the same
channel together with the signalling information.
.PP
1.7
Equipment such as echo suppressors, digital pads, or A/\(*m law
convertors attached to the transmission link must be disabled in order to
assure full duplex operation and bit integrity of the transmitted data stream.
.PP
1.8
64\(hykbit/s digital signalling channels entering a digital
exchange via a multiplex structure shall be switchable as semi\(hypermanent
channels in the exchange.
.bp
.LP
\fB2\fR \fBSignalling bit rate\fR
.sp 1P
.RT
.sp 2P
.LP
2.1
\fIGeneral\fR
.sp 1P
.RT
.PP
2.1.1
The standard bit rate on a digital bearer will be 64 kbit/s.
.sp 9p
.RT
.PP
2.1.2
Lower bit rates may be adopted for each application, taking into
account the User Part requirements and the capability of available transmission
links.
.PP
2.1.3
The minimum signalling bit rate for telephone call control
applications will be 4.8\ kbit/s. For other applications such as network
management, bit rates lower than 4.8\ kbit/s can also be used.
.sp 2P
.LP
2.2
\fIUse of bit rates lower than 64 kbit/s\fR
.sp 1P
.RT
.PP
2.2.1
For national telephone call control applications, use of
Signalling System No.\ 7 at bit rates lower than 64\ kbit/s shall take account
of the requirement to minimize the answer signal delay when in\(hyband line
signalling systems are involved (Recommendation\ Q.27\ [8]).
.sp 9p
.RT
.PP
2.2.2
Signalling System No. 7 can be used for direct international
application at bit rates lower than 64\ kbit/s between countries which
have no in\(hyband line signalling systems in their national extension
networks (see
\(sc\ 2.1.3).
.PP
2.2.3
The possible use of Signalling System No.\ 7 at bit rates lower
than 64\ kbit/s between countries which have in\(hyband line signalling systems
in their national extension networks is for further study.
.sp 2P
.LP
\fB3\fR \fBError characteristics and availability\fR
.sp 1P
.RT
.PP
Error characteristics and availability requirements will conform to relevant
Recommendations (for example, Recommendation\ G.821\ [9] on digital
circuits). No additional characteristics or requirements will be specified
in this Recommendation.
.RT
.sp 2P
.LP
\fB4\fR \fBInterface specification points\fR
.sp 1P
.RT
.PP
4.1
Interface requirements may be specified at one of three points, A, B or
C in Figure\ 2/Q.702. The appropriate point depends on the nature of
transmission links used and the approach toward the implementation of interface
equipment adopted by each Administration.
.sp 9p
.RT
.PP
4.2
For the international application, interface requirements at
either Point\ B or Point\ C will apply.
.PP
4.3
Interface requirements for an international digital signalling
data link will be specified at Point\ C in accordance with the specific
multiplex structure used (see \(sc\ 5.)
.PP
4.4
Interface requirements for an international analogue signalling
data link will be specified at Point\ B on a single channel basis, and
thus are independent of multiplex equipment used. (See \(sc\ 6.)
.PP
4.5
Interface at Point A may or may not appear in particular
implementations, as each Administration may adopt different approaches
towards the implementation of interface equipment. If it does appear in
implementations, then the interface requirements specified in
