INTERNATIONAL TELECOMMUNICATION UNION
COM 11-R 45-E
March 2002
Original: English
TELECOMMUNICATION
STANDARDIZATION SECTOR
STUDY PERIOD 2001 - 2004
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STUDY GROUP 11 - REPORT R 45
SOURCE*:
STUDY GROUP 11
TITLE:
IMPLEMENTORS' GUIDE (03/2002) FOR RECOMMENDATION Q.714
(05/2001)
________
Summary
This implementor's guide contains the modifications to recommendation Q.714 (05/2001) in order
to support an SCCP traffic limitation mechanism where different congestion levels are used for the
connectionless and connection-oriented services. It also corrects some editorial errors in the text.
1
Introduction
1.1
References
[1]
ITU-T Recommendation Q.714 (05/2001): Signalling connection control part procedures.
1.2
Background
This guide includes enhancements to the ITU-T Recommendation Q.714[1] in order to support an
SCCP traffic limitation mechanism where different congestion levels are used for the
connectionless and connection-oriented services. It also corrects some editorial errors in the text. It
is intended to be an additional authoritative source of information for implementors to be read in
conjunction with the Recommendation itself.
1.3
Scope of the guide
This guide records minor enhancements to the Recommendation in the following categories:
•
correction of editorial errors;
•
SCCP traffic limitation mechanism.
* Contact:
Antonio Cañete
L. M. ERICSSON
Tel:
+34 91 339 2460
Fax:
+34 91 339 2906
E-mail: Antonio.canete-Martinez@ece.ericsson.se
Attention: This is not a publication made available to the public, but an internal ITU-T Document intended only for use by the Member States of
the ITU, by ITU-T Sector Members and Associates, and their respective staff and collaborators in their ITU-T related work. It shall not be made
available to, and used by, any other persons or entities without the prior written consent of the ITU-T.
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1.4
Contacts
Rapporteur Q.13/11:
1.5
Dr Pietro Schicker
Swiscom Ltd
Switzerland
+41 1 938 1555
+41 1 938 1557
schicker@scicon.ch
Document History
Version
03/2002
2
Tel:
Fax:
E-mail:
Summary
New Implementors' Guide
Correction of editorial errors
The text of § 5.3.2.1/Q.714 is not aligned with the SDL diagram in Figure C-1/Q.714, where at
reception of a message for an unavailable local subsystem, no SSP message is sent back if the
corresponding forward message was routed on GT.
Correct the second sentence of § 5.3.2.1/Q.714 as follows:
A Subsystem-Prohibited message is sent to the signalling point identified by the OPC in the
MTP-TRANSFER indication primitive, and the MTP-SAP instance if the originating subsystem is
not local and if the forward message has the routing indicator set to "Route on SSN".
3
SCCP traffic limitation mechanism
In the traffic limitation mechanism, the congestion at SCCP is measured and reported to adjacent
nodes by means of the SSC management message.
In the SSC message, a single congestion level is reported, considering SCCP as a whole. However,
SCCP has two services: the connectionless service and the connection-oriented service, for which
the nature of traffic and type of resources needed is different.
In order to balance SCCP connectionless and connection-oriented traffic, separate measurements of
SCCP congestion should be made and reported for the connectionless and connection-oriented
services.
The introduction of such a differentiated congestion handling leads to the following modifications
in the indicated chapters of Q.714, where deleted text is shown in strikethrough format, while added
text is shown underlined, in addition, modifications in the figures are highlighted:
§ 2.6.1 General
Each destination (DPC + MTP-SAP instance) is associated with Restriction Levels for
connectionless (RLcl) and for connection oriented (RLco) services, and RestrictionSubLevels for
connectionless (RSLcl) and connection-oriented (RSLco) which are reported by SCMG (see 5.2.4).
§ 2.6.3 Handling of messages to a congested node:
When a message has to be sent towards a remote SCCP node, the importance of the message is
compared to the restriction level of that remote SCCP node for the service corresponding to the
message to be sent (connectionless or connection-oriented):
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§ 5.2.7 SCCP reports of SCCP and nodal congestion:
This subclause describes procedures related to congestion conditions that are experienced by the
SCCP or node and reported by the SCCP. The SCCP notifies the originating/relay nodes
sending/relaying traffic towards a congested node of the congestion. A time-controlled procedure is
run at the originating/relaying node using two status variables,CLSCL and CLSCO, which indicate the
level of congestion for the connectionless and connection-oriented services at the remote node.
§ 5.2.7.1
Actions in the congested SCCP node:
When a message arrives at a congested SCCP node, SCCP Routing Control informs SCCP
management (see 2.3.1). SCMG shall return a SCCP/Subsystem-Congested message (SSC) to the
signalling point identified by the OPC in the MTP-routing label of the MTP-TRANSFER indication
primitive and the MTP-SAP from which the message is received. The SCCP/Subsystem-Congested
message shall indicate the SPC of this congested SCCP node in the "affected PC" parameter, SSN
of the SCMG; (1) in the "affected SSN" parameter and a value in the "congestion level" parameter
to indicate the severity of the congestion. Optionally, the affected SCCP service field may indicate
whether the connectionless, connection-oriented or both services are affected. Any reaction towards
a local originator is implementation dependent. The detection of SCCP or nodal congestion is
implementation dependent.
§ 5.2.7.2 Action in a relay or originating node:
When a SCCP/Subsystem-Congested message is received from the congested SCCP, and the
affected signalling point has been marked as "prohibited", no further action is taken. When a
SCCP/Subsystem-Congested message is received from the congested SCCP, and the affected point
code has not been marked as "prohibited", SCCP management shall compare the values of CLSCL
and/or CLSCO associated with the congested SCCP node with the value in the congestion level
parameter indicated in the SCCP/Subsystem-Congested message, depending on the affected SCCP
service indicated. If the CLSCL and/or CLSCO has been marked with a higher congestion level, the
value shall remain unchanged, or else the CLSCL and/or CLSCO shall be updated with the value of the
congestion level parameter of the received SCCP/Subsystem-Congested. If the CLSCL has been
marked with a higher or same level, the timer for connectionless TconCL shall be restarted. If the
CLSCO has been marked with a higher or same level, the timer for connection-oriented TconCO shall
be restarted.
If the TconCL timer expires and the CLSCL has not yet reached zero, the CLSCL shall be decremented
by one and timer TconCL shall be restarted. If the CLSCL is reduced to zero, the timer TconCL is
stopped.
If the TconCO timer expires and the CLSCO has not yet reached zero, the CLSCO shall be decremented
by one and timer TconCO shall be restarted. If the CLSCO is reduced to zero, the timer TconCO is
stopped.
Whenever a remote SCCP is marked as accessible (MTP-RESUME, SSA, indication of the end of
MTP-restart received), the congestion levels CLSCL and CLSCO stored by SCCP may be changed
(network dependent).
The SCMG shall initiate the procedure of 5.2.8 when the values of CLSCL or CLSCO change.
The congestion levels CLSCL and CLSCO are within the range 0 through 8, with 0 indicating that no
congestion is present.
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§ 5.2.8 Inter- and Intra- SCMG congestion reports procedure:
3)
CLSCL and CLSCO, SCCP congestion levels due to receipt of the congestion level parameter
of SSC message for each affected SP and SSN=1 (5.2.7).
The above values are used as inputs to compute the values of the following variables:
a)
RLCL and RLCO, SCRC traffic restriction levels for each affected SP.
b)
RSLCL and RSLCO, restriction sublevels per RL for each affected SP.
c)
RIL, restricted importance level parameter reported to SCCP users for each affected SP. As
an implementation option, SCCP users subscribed to the connectionless service can be
informed of a RIL related to RLCL. The same applies for SCCP connection-oriented users
and RLCO.
If there is any change in RLCL, RLCO, RSLCL or RSLCO, SCRC is informed of the new values.
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Determine
restriction
Importance
present ?
No
Yes
Valid
value ?
Yes
Priority in
SIO ?
No
Reduce
importance to
permitted
maximum
ConnectionOriented?
No
Yes
Derive
importance value
from
priority
Assign
default
importance
Yes
No
Importance
< RLCL ?
Importance
< RLCO ?
Yes
No
No
No
Importance
= RLCL ?
No
Importance
= RLCO ?
Yes
Yes
See Q.714
§2.6.3
Is
message to
be restricted
?
See Q.714
§2.6.3
Yes
Is
message to
be restricted
?
Yes
No
No
Result is
'unrestricted'
Yes
Result is
'restricted'
Result is
'unrestricted'
Result is
'restricted'
Key to terms:
RL - Restriction Level
FIGURE C-1/Q.714 (Sheet 12 of 12)
SCCP routing control procedures (SCRC)
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Input is RLm, RSLm,
CLsCL and CLSCO
(and also the affected SP)
Section
5.2.8/Q.714
Process
RLm, RSLm,
CLSCL and CLSCO
No
To derive
RLCL, RSLCL,
RLCO, RSLCO,
and also RIL
RIL
changed
?
Yes
Local
broadcast
of RIL (+Affected Service)
SPCC LBCS
No
RSLCL. RL CL,
RL CO or RLCO
RSL
Changed?
RL
Yes
RLCL. RSL CL,
RLCO and RSLCO
SPCCSCRC
FIGURE D-4/Q.714 (Sheet 4 of 4)
Signalling point congested control (SPCC)
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2
1
2
1
2
1,2
2
1
Idle
Local
broadcast
of RESUME
SPACLBCS
No
LBCS´User
N-PCSTATE
indication
Select
local
sub-system
Yes
Any
(more) allo-wed local
SS?
see Note
Local
broadcast
of PAUSE
SPPCLBCS
2
Local broadcast
of RIL
(+ Affected Service)
SPCCLBCS
1
Local broad-cast of SCCP
accessible
SPACLBCS
Local broadcast
of RIL
(+ Affected Service)
SRCCLBCS
Local broad-cast of SCCP
inaccessible
SPCCLBCS
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Local broadcast (LBCS)
FIGURE D-9/Q.714 (Sheet 2 of 2)
Note: As specified in §5.3.6.1 in Recommendation Q.714, only concerned sub-systems are informed.
Local
broadcast
of STATUS
SPCCLBCS
2
2
Local
broadcast
of RIL
SPCCLBCS
Local broad-cast of SCCP
inaccessible
SPPCLBCS
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Referring to
local conditions.
Can now be 0
Idle
CL Message for
congested
for
SP or node
SCRC  SLCC
C initialised
to 0 at start
C :=C +1
C initialised
to 0 at start
C =8 ?
No
Yes
SCMG
message
SLCC SCLC
C :=0
Changed
CL congestion
level
CO Message for
congested
SP or node
SCRC  SLCC
C :=C +1
No
SSC
congestion
level for
connectionless
C =8 ?
Yes
SCMG
message
SLCC SCLC
Store CL level
for
SSC messages
Changed
CO congestion
level
Store CO level
for
SSC messages
CL Congestion
level
CO Congestion
level
SLCC SCRC
SLCC SCRC
SSC
congestion
level for
Connectionoriented
C :=0
Idle
FIGURE D-12/Q.714 (Sheet 1 of 2)
Local SCCP and nodal congestion control (SLCC)
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Idle or
Active
____
Tconcl
SCMG
message
SSC
____
Tconco
SCLCSRCC
CLscl :=CLscl +1
Affected
service
?
No
CL
CLscl
<= received
cong. level
?
No
CO
CLsco
<= received
cong. level
?
Yes
CLscl
< received
cong. level
?
Yes
No
CLsco
< received
cong. level
?
Yes
No No
Yes
(Re-)start
Tconcl
(Re-)start
Tconco
CLscl >0 ?
Yes
Yes
(Re-)start
Tconcl
No
CL & CO
No
CLscl
<= received
cong. level
?
CLsco :=CLsco +1
Yes
Start Tconcl
CLscl
< received
cong. level
?
CLsco >0 ?
Start Tconco
Section
5.2.8/Q.714
No
Yes
Idle
CLscl :=
received
cong. level
CLsco :=
received
cong. level
CLscl :=
received
cong. level
Section
5.2.8/Q.714
Section
5.2.8/Q.714
Section
5.2.8/Q.714
Section
5.2.8/Q.714
Active
Active
FIGURE D-13/Q.714 (Sheet 1 of 2)
Remote SCCP and nodal congestion control (SRCC)
_________________
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