# Exploring the Layers of the SS7 Stack

The Signaling System No. 7 (SS7) is a globally used set of telephony signaling protocols that enables call setup, routing, billing, and information exchange between telephone networks.

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## SS7 Layers

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1761577064599/0843674c-80a0-4b28-82c7-032cac7891d0.png align="center")

The SS7 protocol suite is organized into a stack, structured in levels, similar to the OSI model:

**MTP Level 1 (Physical Layer)**

This is the physical and electrical connection for the network, handling the delivery of signaling messages via the transmission medium.

**MTP Level 2 (Link Layer)**

Ensures error checking and message sequence control by detecting and correcting errors in the transmission of signaling information.

**MTP Level 3 (Network Layer)**

Provides message routing between exchanges and manages message distribution, ensuring the integrity of signaling message transfer.

**SCCP (Signaling Connection Control Part)**

Adds enhanced routing capabilities and supports connection-oriented and connectionless network services, facilitating a variety of telecommunications services beyond basic call control.

**TCAP (Transaction Capabilities Application Part)**

Enables the deployment of non-circuit-related queries and transactions, supporting features like number translation, roaming, and database queries.

**ISUP (ISDN User Part)**

Handles the setup and tear down of voice and data calls over the public switched telephone network (PSTN).

**MAP (Mobile Application Part)**

Utilized in mobile networks for functions such as roaming, location updating, handovers, and short message service (SMS) delivery.

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1761577134085/f2cc790c-c37f-4f9a-98da-d0249f2dd152.png align="center")

The SS7 stack is essential for communication between network elements in telecommunications networks, supporting efficient and robust call processing and management.

# Thoughts4U

Do you know the difference between Voice, Data, and Signaling?

* **<mark>Data </mark>** \- The Internet uses <mark>data packets</mark> flowing through Routers and ASs. This is a digital network and is called a **<mark>PACKET SWITCH (PS) network.</mark>**
    
* **<mark>Voice </mark>** \- The voice is older than the data, the old version uses ANALOG circuits to transfer the voice end-to-end, this is called a **<mark>CIRCUIT SWITCH (CS)</mark>** network. This type of network requires some intelligence in the network - NGIN (Next Generation Intelligence Networks)
    
* **<mark>Signaling </mark>** \-SS7 - SigTran - SIP
    

[Telecom Security](https://www.telco-sec.com/)