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SAAL-NNI Signalling ATM adaptation layer for network to network interfaces

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SAAL-NNI (Signalling ATM Adaptation Layer for Network to Network Interfaces) is a protocol used in Asynchronous Transfer Mode (ATM) networks to facilitate the exchange of control information between different network entities. It operates at the ATM adaptation layer and is specifically designed for Network to Network Interfaces (NNI) within the ATM network.

The NNI represents the point of interconnection between two different ATM networks, typically owned and operated by different service providers. SAAL-NNI provides the necessary signaling capabilities to establish, maintain, and release ATM connections across these network boundaries. It enables the exchange of control information related to call setup, routing, and other network management functions.

Let's delve into the details of SAAL-NNI and how it functions:

  1. ATM Adaptation Layer (AAL): SAAL-NNI operates at the ATM adaptation layer, which is responsible for adapting various types of user traffic (such as voice, video, and data) into ATM cells. The AAL provides a specific set of rules for segmenting and reassembling higher-level data into ATM cells.
  2. Signaling: Signaling in SAAL-NNI refers to the exchange of control messages between two NNI endpoints. These messages convey information required for call setup, connection maintenance, and tear-down procedures. The signaling protocol used in SAAL-NNI is known as the Common Signaling Protocol (CSP).
  3. Common Signaling Protocol (CSP): CSP is the protocol used by SAAL-NNI to carry out the signaling functions. It defines the format and content of signaling messages exchanged between NNI endpoints. CSP includes various message types, such as Call Establishment Request (CER), Call Establishment Confirm (CEC), Call Release Request (CRR), and Call Release Confirm (CRC), among others.
  4. Call Setup: When a user initiates a call across the NNI, SAAL-NNI facilitates the call setup process. The originating NNI endpoint sends a Call Establishment Request (CER) message to the destination NNI endpoint. This message contains information about the requested connection, including the destination address, traffic parameters, and any required QoS (Quality of Service) guarantees.
  5. Call Establishment: Upon receiving the CER message, the destination NNI endpoint processes the request and checks for availability of network resources. If the resources are available, it sends a Call Establishment Confirm (CEC) message back to the originating NNI endpoint, indicating successful call setup. The CEC message includes the connection identifier and other relevant parameters.
  6. Connection Maintenance: SAAL-NNI also handles the tasks related to connection maintenance. It ensures that the established connection remains active and performs any necessary actions in response to changes in network conditions. This includes monitoring the connection status, adjusting QoS parameters, and handling congestion control.
  7. Call Release: When a call needs to be terminated, either due to user action or network conditions, SAAL-NNI facilitates the call release process. The originating NNI endpoint sends a Call Release Request (CRR) message to the destination NNI endpoint, indicating the intent to release the connection. The destination NNI endpoint responds with a Call Release Confirm (CRC) message, acknowledging the release.

SAAL-NNI provides a standardized and interoperable signaling mechanism for network entities across different ATM networks. It ensures that control information is exchanged accurately and efficiently, enabling seamless communication and management of ATM connections at the NNI level.