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    Network Elements

    A network element is a load-balanced group of RADIUS servers that provides authentication, authorization, and accounting (AAA) services for mobile subscribers accessing an access point name (APN).

    When a mobile subscriber attempts to get access to an APN, the broadband gateway sends an Access-Request message to one of the RADIUS servers in the network element the APN is configured to use for authentication. Similarly, accounting messages for the mobile subscriber go to the network element the APN is configured to use for accounting.

    Network elements for authentication and accounting are specified in the AAA profile that is applied to the APN.

    Load Balancing Within Network Elements

    To facilitate the large number of mobile subscriber sessions requiring AAA services, the broadband gateway distributes the RADIUS messages across the servers in the network element, using one of the following load-balancing algorithms:

    • Direct (default)—Causes all requests to go to the first server listed in the network element configuration; if that server cannot handle additional requests, they go to the next server in the list.
    • Round-robin—Sends the first request to the first server listed in the network element configuration, the second request to the second server in the list, and so on.

    Server Priority

    Within a network element, a RADIUS server can be assigned a priority of 1 or 2. The broadband gateway distributes RADIUS messages only to the priority 1 servers, using the configured load-balancing algorithm. If all the priority 1 servers should fail, then the broadband gateway starts using the priority 2 servers.

    Dead Server Detection

    To determine whether a RADIUS server in a network element has failed, the broadband gateway keeps track of how often requests sent to a server time out and must be retransmitted. If requests need to be retransmitted a given number of times over a given interval, the broadband gateway marks the server as “dead,” then starts sending requests to the next available server in the network element (to a priority 1 server if one is available, or a priority 2 server if no priority 1 servers are available).

    At the same time, the broadband gateway starts a timer (the revert-interval) for the server. After this timer expires, the broadband gateway marks the dead server alive again, and once again includes it in the rotation for sending RADIUS messages.

    Maximum Pending Requests for a Network Element

    You can specify the maximum number of requests that can be queued to the network element. When the pending request queue is full, any additional requests are dropped. If the number of pending requests reaches 80 percent of the maximum, an SNMP trap is generated.

    Published: 2011-11-23