What is SS7 – SS7 Tutorial


What is SS7

  • SS7-Signaling System 7
  • GSM Communication Protocol implemented on SS7

SS7 Layers


Message Transfer Part

  • MTP1- Message Transfer Part-1

–MTP1 represents the physical layer, responsible for the connection of SS7 Signaling Points into the transmission network.

  • MTP2- Message Transfer Part-2

MTP 2 ensures exact end-to-end transmission of a message

  • MTP3- Message Transfer Part-3

–MTP3 provides routing functionality to transport messages to the destination.


  • Signaling Connection Control Part

–Network Layer protocol that provides extended Routing, Flow Control, segmentation, Connection orientation and Error Correction facilities in telecommunications networks. SCCP relies on the services of MTP for basic routing and error detection.

–SCCP responsible for GT(Global Title) Routing and Subsystem number (SSN)


  • Transaction Capabilities Application Part

–TCAP facilitate multiple concurrent dialogs between the same sub-systems on the same machines, using Transaction IDs to differentiate these. Similar to TCP multiple sessions on same IP address and port.


  • Mobile Application Part

–Provides an application layer for the different GSM nodes to communicate with each other to provide services to mobile users. MAP is the application-layer protocol used to access the HLR (Home Location Register), VLR (Visitor Location Register), MSC (Mobile Switching Center), SMSC (Short Message Service Center).


  • Intelligent Network Application Part

– Extended form of INAP is Customized Application for Mobile Networks Enhanced Logic (CAMEL). INAP is also application layer protocol to communicate with service control point (SCP).

  • CAMEL Application Part

–A signaling protocol used in the Intelligent Network architecture


  • ISDN (Integrated Services Digital Network) User Part.  ISUP is used to set up telephone calls in the public switched telephone network (PSTN). In SS7 ISUP is only voice related messages/signaling to establish voice calls between 2 voice circuit.

What is Linkset

  • A set of MTP link form a Linkset. Node on each side of a linkset will identify using a point code. Source node define SPC (source point code) and destination node define DPC (destination point code)
  • SLC- Signaling link Selection code. MTP layer define the number of every link within a linkset using SLC.

What is GT Routing

  • There must be a GT for every node in case of GT based routing. Message transfer between neighbor node using point code and SCCP layer check the GT in the routing table for the next hope.


To have brief description check below video