MTP Signaling Analysis and Process

Basic Concept Of MTP Signaling

• SP: Signaling Point

• STP: Signaling Transfer Point

Direct Connection Networking

Quasi- direct connection networking

Difference between Tandem Exchange & STP

 

A and B have no signaling relation. The destination of A is a tandem exchange and it does not  know where is B. Only tandem exchange knows the location of A and B.

 

A and B are in the same signaling network and they know location of each other. STP is just signaling transfer channel. The connection mode is quasi-direct connection.

SS7 Overall Organization Structure

Three Kinds of Basic Signaling Unit Format

Service Information Octet SIO

SI: Service indication

D  C  B  A

0  0  0  0    Signaling network management   SNM

0  0  0  1    Signaling network test SNT

0  0  1  0  spare

0  0  1  1    Signaling connection control part   SCCP

0  1  0  0    Telephone user part TUP

0  1  0  1    ISDN user part ISUP

0  1  1  0    data user part which is related to  calling and circuit DUP

0  1  1  1  data user part capability   registration and withdraw DUP

1  0  0  0 

   ……               spare

1  1  1  1

SSF: Sub-service field

D   C  B  A

0   0   0  0    International network

0   1   0  0    International spare network

1   0   0  0    National network

1   1   0  0    National Spare network

 Universal message assignment flag format

There are four important type of flags：

-Class A, For MTP to manage message；

-Class B, For TUP；

-Class C, For ISUP (circuit related) message；

-Class D, For SCCP message.

Signaling information field SIF 

MTP management message (Class A)

TUP message (Class B)

ISUP message (Class C)

SCCP message (Class D)

MTP Structure

Signaling data link layer – MTP Layer 1

-64Kbit/s bi-directional transparent channel

-Exchange function, It connects SS7 signaling terminal with trunk equipment by                    semi-permanent connection mode

Signaling Link Layer – MTP Layer 2
 

-SU delimiting & alignment

-Error detection

-Error correction

-Initial alignment

-Signaling link error ratio monitor

-Flow control

 

MTP 2 message format

 

Signaling link assignment procedure

Signaling network function – MTP3

-Two functions

-Signaling Message Handling

-Signaling Network Management

-Main MTP3 message

-Link test message SLTM/SLTA

-Transfer inhibit and transfer permission TFP/TFA

-Changeover and changed-back message  COO/COA，  CBD/CBA，ECO/ECA

-Management inhibit and release inhibit  LIN/LIA、LUN/LUA

 

-Signaling link test Message

-When link is normal, signaling link will send SLTM message every minute. After SLTM is received, the destination SP will send back SLTA message. The value and number of test codes in SLTA should be equal to that in SLTM

-If SLTA can not be received within 6s, it can not enter service activation state.

 

 

-Link change over

-Time control changeover

In event of failure as shown, SP1 will start up time control changeover timer. When time out, link 2 will transfer service of link 1.

 

-Link change back

-When failure is recovered, SP1 and SP2 starts change-back procedure

-SP1 starts time control change-back timer. When time out, change-back is over

-Signaling link management inhibit

-Under following conditions management inhibition cannot be carried out:

-inhibition will make destination SP unreachable;

-link congestion.

 

-Signaling link inhibition release

 

-Transfer prohibited procedure

     -When link 1 failure induces failure from STP1 to SP2, STP1 sends TFP to SP1 

-Transfer Allowed procedure 

      -When link1 failure recovery makes route from STP1 to SP2 available, STP1 sends TFA to SP1

 

-Forced Routing

                                        

Service transfer by STP1

 

  -Controlled rerouting 

       -When link1 failure recovery makes route from STP1 to SP2 available, STP1 sends TFA to SP1

             

SP1 receives TFA and recovers former routing