Leg control, in the context of telecommunications and specifically SIP (Session Initiation Protocol), refers to the management and manipulation of information exchanged on a communication leg between two endpoints. It ensures that communication flows correctly and efficiently.
Understanding the Leg Control Model (LCM)
The Leg Control Model (LCM) is the mechanism responsible for governing this information exchange. Here's a breakdown:
- Function: The LCM operates on the SIP information exchanged on a specific communication leg with the destination endpoint. Essentially, it acts as a traffic controller for data packets flowing between endpoints.
- Outgoing LCM (OLCM): This is a specific component within the LCM that focuses on managing the outgoing SIP requests from an Application Server (AS) to a User Equipment (UE).
- Information Control: The OLCM ensures proper management and control over the data packets being sent to the User Equipment (UE). It makes sure the data is correctly formatted and transmitted, allowing for smooth and seamless communication.
How Leg Control Works in Practice
Imagine a phone call placed using SIP. The journey of a SIP message from the AS to the UE can be described as follows:
- Application Server (AS): The AS initiates a request to call the UE.
- Outgoing LCM (OLCM): The OLCM takes charge of that request, ensuring it conforms to the required specifications and standards of SIP communication.
- User Equipment (UE): The UE receives the properly formatted message, allowing it to process the request and participate in the session.
Key Functions of the LCM:
- Session Management: Manages the establishment, maintenance, and termination of communication sessions.
- Media Negotiation: Ensures that the media being exchanged between the endpoints (like audio and video) are compatible.
- Security Control: Enforces security policies for the communication legs.
- Traffic Engineering: Optimizes data flow for efficient and reliable communication.
Summary
In simple terms, leg control, facilitated by the Leg Control Model (LCM) and specifically the Outgoing LCM (OLCM), is a crucial part of the SIP communication process. It allows systems to control and manage the data flowing in a specific leg of a communication, ultimately leading to seamless and efficient communication between endpoints.