Technical data

Brocade ServerIron ADX Advanced Server Load Balancing Guide 11

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SIP SLB over UDP

SIP server health monitoring

There are two types of SIP servers of particular importance: SIP proxy servers and SIP registrar

servers. The ServerIron ADX supports advanced UDP Layer-7 application health checks for both

server types.

ServerIron ADX switches can be enabled to send REGISTER or OPTION messages to SIP servers to

track their health. When an error-free response status (default is 200 OK) is received, then the

ServerIron ADX marks the SIP server as being available, and starts assigning new SIP sessions to

the available servers.

The switches can also be configured to send health-monitoring messages at user-defined

frequency and retrial attempts. By default, 200 OK is considered a valid response code. Optionally,

you can configure the switch to accept other response codes that indicate a healthy and available

server.

SIP messages with specific SIP methods are switched to the appropriate SIP server. As an example,

distributed among SIP proxy servers.

SIP SLB over UDP

SIP server load balancing over UDP is available in stateless SLB mode and stateful SLB mode. SIP

SLB over UDP features the following elements in both stateless and stateful modes:

• Persistence parameter can be extended: The persistence parameter can be extended to other

key header fields, such as the VIA header. This applies to both SIP stateful and SIP stateless

modes.

• Support for fragmented UDP support: Applies to both SIP stateful and SIP stateless modes

• TCP SIP requests result in a TCP reset packet: According to RFC 3261, this will force the sender

to retry the request using UDP. This applies to both SIP stateful and stateless modes.

The following elements are supported in stateful SLB mode only:

• SIP stateful support: Server selection is based on round-robin persistence on a user-configured

key header, such as Call-ID, and corresponding SIP sessions are created for this purpose.

• Server initiated SIP requests handling: Sessions are created so that subsequent transactions

with the same persistence parameter are directed to the same real server. This applies to SIP

stateful mode only. This enables the ServerIron ADX to load balance the back-to-back user

agent (B2BUA) SIP servers.

• A SIP session created in ServerIron ADX with multiple barrel processors are synchronized to all

barrel processors (BPs).

• Redundancy support: SIP stateful supports both hot standby HA and symmetric active-standby

HA configuration by synchronizing SIP sessions to peer box. Symmetric Active-Active HA

configuration is not recommended.

• A SIP session created in ServerIron ADX with multiple barrel processors are synchronized to all

barrel processors (BPs).

Configuring SIP SLB over UDP (Stateless SLB mode)

The following sections discuss SIP over UDP.