SCCP Introduction - Revision history

Monica at 09:19, 27 October 2017

2017-10-27T09:19:44Z

Monica: /* SCCP GTT */

2017-10-27T09:18:43Z

‎SCCP GTT

Monica at 09:18, 27 October 2017

2017-10-27T09:18:23Z

Monica: /* SCCP GTT Configuration */

2017-10-27T09:17:11Z

‎SCCP GTT Configuration

Monica: /* SCCP GTT Configuration */

2017-10-27T09:16:45Z

‎SCCP GTT Configuration

Monica at 09:16, 27 October 2017

2017-10-27T09:16:11Z

Monica: /* SCCP GTT */

2017-10-27T09:14:52Z

‎SCCP GTT

Liviu: Created page with "SCCP stands for Signalling Connection Control Part. SCCP represents a layer 4 protocol from SS7 signaling stack. It runs over a SS7 layer 3 protocol like MTP3 or M3UA. It pro..."

2017-10-26T11:23:19Z

Created page with "SCCP stands for Signalling Connection Control Part. SCCP represents a layer 4 protocol from SS7 signaling stack. It runs over a SS7 layer 3 protocol like MTP3 or M3UA. It pro..."

New page

SCCP stands for Signalling Connection Control Part.

SCCP represents a layer 4 protocol from SS7 signaling stack.
It runs over a SS7 layer 3 protocol like MTP3 or M3UA.
It provides:
* extended routing
* flow control
* segmentation

==SCCP in YATE==

The SCCP implementation in YATE can be found in ysig library, the configuration
samples in ysigchan.conf.sample.

An SCCP YATE instance is an "on demand" component. Basically this means that if you configure a SCCP section in ysigchan.conf but you do not reference it from a SCCP application (TCAP or GTT) the SCCP component will not be created.

===SCCP components===

The SCCP implementation is divided in three components:

====SCCP====
This represents the main component who is responsible for:
*message coding/decoding.
*segmentation.
*flow-control
*protocol logic.

====SCCP GTT====
This represents the part of SCCP that is responsible with the translation of Global Titles. 
Mainly this component will emit a sccp.route message each time a each time a GT needs to be translated.

====SCCP management====
This part of SCCP protocol offers a way to monitor the state of remote SCCP's and their applications. 
Each time a remote SCCP state will change the SCCP management will emit a sccp.update message to inform all concerned parties about the state change. The informations are mainly used by GTT.

===SCCP Messages===
====Data messages====
* UDT. This is the simplest SCCP message. It is used to transfer data, between two SCCP endpoints, that does not require segmentation.
* XUDT. This message is like UDT but extended. It is used to transfer segmented data or other SCCP parameters like HopCounter.
* LUDT. This message is used to transfer long data. Usually is used over a SIGTRAN connection.

NOTE: In SCCP a message requires segmentation if the route to the destination contains a MTP2 link. The MTP2 link can transport a maximum of 272 octets including the MTP2 and MTP3 headers.

====Management Messages====

All Management messages have 3 important parameters: Affected Point Code, Affected SSN and status. 
This is the list of management messages:
* SSA: Subsystem Allowed: This message is sent to inform a remote SCCP that the specified subsystem can receive messages.
* SSP: Subsystem Prohibited: This message is sent to inform a remote SCCP that the specified subsystem can not receive messages anymore.
* SST: Subsystem Status Test: This message is sent to a remote SCCP to find if the status of the specified subsystem has changed.

All the above messages are quite used in SCCP. But are some messages that are not so used:
* SOR: Subsystem Out of service Request. This message is sent to a remote SCCP to inform it that the specified subsystem requests to go OutOfService.
* SOG: Subsystem Out of service Grant. This message is sent to a remote SCCP as a response to a SOR request.

==SCCP usage scenarios==

SCCP can be used in multiple scenarios, but this are the most known:

===[[STP SCCP configuration|SCCP in STP]]===

SCCP can be used in a STP. 
This scenario is used to take advantage of the SCCP extended routing. 
Basically we will find a combination of SCCP and GTT. 

===[[SEP SCCP configuration|SCCP in SEP]]===

In a SEP the SCCP role is to deliver the received messages to the SCPP applications above him(TCAP).

===[[SCCP decoder]]===
This is a special non-standard feature of YATE. 
The SCCP can be used as a SCCP message decoder. This case can be found if it is used with M3UA-GW. 
YATE M3UA-GW has the ability to route messages to ASPs based on SCCP GT or/and SSN, in this way the SCCP is used to decode the SCCP message for M3UA-GW so that the gateway can look for the routing parameters. 

===[[SCCP address translation]]===
SCCP can be used as a bridge for two different point code types. For example it can receive messages from point code 1 international and send the message to point code 1 national.

==SCCP Segmentation==

SCCP may segment messages based on message length and SS7 network topology. 
This meens that if a SS7 message exceeds the limit for a TDM link, the message will be segmented by SCCP and in multiple XUDT messages. 
If the topology of the SS7 network is known and the SCCP needs to send a message only over SIGTRAN than it will send it in one or multiple LUDT messages. 

In MTP3 configuration section exists two parameters: route and adjacent. 
Adjacent represents the pointcode of the remote end of the Layer2 links. 
Route can be repeated and represents the destination pointcodes that this linkset knows about. 
When you configure the adjacent and the route parameters you can set the size of the path. This represents the maximum nuber of octets that can be transmited over the route. Default is 272 (TDM maximum size), but if you know that for example you have only M2PA links between local node and the adjacent node than you can specify the size of the route to 4000. 
In this way when SCCP needs to send a message that exceeds the limits of a TDM link, after will obtain the route for the destination of the message will limit the message to worse link message size. 
 

For example lets say that SCCP from SEP1 has a large message to send to SEP. 
The link between STP2 and SEP1 is a M2PA link so it will send a LUDT message to STP2. 

STP2 receives the message and detects that it has to send it to STP2. Link between STP2 and STP1 also M2PA so STP2 will send a LUDT message to STP1. 

STP 1 receives the message and detects that it has to send it to SEP. 
STP1 and SEP are connected with two links. On is M2PA and one is MTP2. 
If size parameter is correctly set than SCCP on STP1 will detect that the maximum size that it can send is 272 and will segment the message and send it in multiple XUDT messages.

@@ Line 35: / Line 35: @@
 This part of SCCP protocol offers a way to monitor the state of remote SCCP's and their applications.<br/>
 Each time a remote SCCP state will change the SCCP management will emit a sccp.update message to inform all concerned parties about the state change. The informations are mainly used by GTT.
 ===SCCP Configuration===
@@ Line 166: / Line 188: @@
   ; sccp: string: The name of the sccp to attach to this GTT
   ;sccp=sccp
 ===Status===

@@ Line 30: / Line 30: @@
 Mainly this component will emit a sccp.route message each time a each time a GT needs to be translated.<br/>
-SCCP implementation in Yate is located in ysig library. The methods declaration is in libs/ysig/yatesig.h and the implementation in libs/ysig/sccp.cpp. Classes name are SS7SCCP, GTT.
+SCCP GTT implementation in Yate is located in ysig library. The methods declaration is in libs/ysig/yatesig.h and the implementation in libs/ysig/sccp.cpp. Classes name are SS7SCCP, GTT.
 ====SCCP management====

@@ Line 28: / Line 28: @@
 ====SCCP GTT====
 This represents the part of SCCP that is responsible with the translation of Global Titles.<br/>
-Mainly this component will emit a sccp.route message each time a each time a GT needs to be translated.
+Mainly this component will emit a sccp.route message each time a each time a GT needs to be translated.<br/>
 SCCP implementation in Yate is located in ysig library. The methods declaration is in libs/ysig/yatesig.h and the implementation in libs/ysig/sccp.cpp. Classes name are SS7SCCP, GTT.
 ===SCCP Configuration===
@@ Line 163: / Line 166: @@
   ; sccp: string: The name of the sccp to attach to this GTT
   ;sccp=sccp
 ===SCCP Messages===

@@ Line 33: / Line 33: @@
 SCCP implementation in Yate is located in ysig library. The methods declaration is in libs/ysig/yatesig.h and the implementation in libs/ysig/sccp.cpp. Classes name are SS7SCCP, GTT.
-===SCCP GTT Configuration===
+===SCCP Configuration===
 From sample ysigchan.conf:

@@ Line 33: / Line 33: @@
 SCCP implementation in Yate is located in ysig library. The methods declaration is in libs/ysig/yatesig.h and the implementation in libs/ysig/sccp.cpp. Classes name are SS7SCCP, GTT.
-=====SCCP GTT Configuration=====
+===SCCP GTT Configuration===
 From sample ysigchan.conf:

@@ Line 163: / Line 163: @@
   ; sccp: string: The name of the sccp to attach to this GTT
   ;sccp=sccp
 ====SCCP management====
@@ Line 208: / Line 187: @@
 * SOR: Subsystem Out of service Request. This message is sent to a remote SCCP to inform it that the specified subsystem requests to go OutOfService.
 * SOG: Subsystem Out of service Grant. This message is sent to a remote SCCP as a response to a SOR request.