https://github.com/systemvll/ss7-workbench
Some explanation about how SS7 works
https://github.com/systemvll/ss7-workbench
Last synced: 4 months ago
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Some explanation about how SS7 works
- Host: GitHub
- URL: https://github.com/systemvll/ss7-workbench
- Owner: SystemVll
- Created: 2025-04-26T19:02:52.000Z (about 1 year ago)
- Default Branch: main
- Last Pushed: 2025-04-26T19:05:06.000Z (about 1 year ago)
- Last Synced: 2025-10-09T18:45:13.614Z (8 months ago)
- Size: 2.93 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
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Metadata Files:
- Readme: README.md
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README
# Signaling System 7 (SS7) Network Architecture and Messaging
## Network Architecture
The Signaling System 7 (SS7) network forms the backbone of global telecommunications infrastructure, facilitating communication between various network entities. SS7 is a critical protocol suite that enables phone call setup, text messaging, and other telecommunication services across different carriers and countries.
### Key Components:
1. **Signaling Points (SP)**: Network nodes that originate, terminate, or route signaling messages. These can be further categorized into:
- **Service Switching Points (SSPs)**: Telephone exchanges responsible for call setup, release, and routing
- **Signal Transfer Points (STPs)**: Packet switches that route signaling messages between different network elements
- **Service Control Points (SCPs)**: Databases containing service logic and subscriber information
2. **Signaling Links**: High-speed data links connecting various signaling points in the network, typically categorized as A-links (access), B-links (bridge), C-links (cross), D-links (diagonal), E-links (extended), and F-links (fully associated).
The SS7 network architecture implements redundancy and alternate routing capabilities to ensure high availability and reliability of telecommunication services. When a user initiates a call or sends an SMS, the request traverses through this network, with signaling messages exchanged between various nodes to establish connections and deliver services.
## SS7 Protocol Stack and Packet Structure
The SS7 protocol stack is organized in layers similar to the OSI model, each serving specific functions in the signaling process:
1. **Message Transfer Part (MTP)**: Provides reliable transfer of signaling messages
- MTP Level 1: Physical layer (equivalent to OSI Layer 1)
- MTP Level 2: Data link layer (equivalent to OSI Layer 2)
- MTP Level 3: Network layer (equivalent to OSI Layer 3)
2. **Signaling Connection Control Part (SCCP)**: Provides enhanced routing capabilities beyond MTP
3. **Transaction Capabilities Application Part (TCAP)**: Supports non-circuit related communication between applications
4. **Mobile Application Part (MAP)**: Supports mobile communications, including SMS and roaming
5. **ISDN User Part (ISUP)**: Handles call setup, management, and teardown
The packet structure reflects this layered approach, with different segments handling routing, control, and application-specific information.
## SMS Example using SS7 Protocol
### SMS Transmission Process in SS7 Networks
When a mobile subscriber sends an SMS message, a complex sequence of signaling messages is exchanged across the SS7 network:
1. **Message Submission**: The sending device transmits the SMS to its serving Mobile Switching Center (MSC).
2. **SMSC Routing**: The MSC forwards the message to the Short Message Service Center (SMSC) responsible for storing and forwarding SMS messages.
3. **Recipient Location**: The SMSC queries the Home Location Register (HLR) using MAP operations to determine the current location of the recipient.
4. **Message Delivery**: Once the recipient's location is known, the SMSC forwards the message to the MSC serving the recipient's current area.
5. **Final Delivery**: The serving MSC delivers the SMS to the recipient's device.
Throughout this process, various SS7 protocols work together:
- **MTP** provides reliable transport of signaling messages between network nodes
- **SCCP** adds advanced routing capabilities using point codes and global titles
- **TCAP** manages the transaction between the originating and destination entities
- **MAP** provides the application-level operations specific to mobile services
Each SMS message is encapsulated within this protocol stack, with headers, routing information, and parameters at each layer ensuring proper handling and delivery across the telecommunications network. This sophisticated architecture enables the billions of text messages sent globally every day to reach their intended recipients reliably.