Technical data

ServerIron ADX Advanced Server Load Balancing Guide 17

53-1002435-03

Configuring SIP SLB

Syntax: show sip server

Use this command to display real server-related information.

SIP Stateful sample configuration

SIP SLB over TCP

Like HTTP, SIP follows a request-and-response model. However, SIP transactions are independent

of the underlying transport layer protocol. For example, some transactions run over UDP

connections, some get transported over TCP connections, and some use a combination of TCP and

UDP interchangeably, depending on the size of the data.

Generally most SIP deployments are observed over UDP transport. However, some service

providers use TCP instead of UDP to offer advanced SIP-based voice and video services. The

primary reason for this method is to avoid the fragmentation experienced over UDP connections

and to use the congestion avoidance mechanism of TCP.

In most cases, TCP and UDP are used interchangeably, depending on the data length. Support for

TCP in addition to UDP is provided for seamless deployment of advanced SIP services. This

implementation is based on RFC 3261.

Connection handling with SIP requests initiated by client

When a SIP client initiates a call using TCP, it either uses a separate TCP connection for each call or

groups multiple calls together over a single TCP connection.

When a ServerIron ADX receives these calls over a single or multiple TCP connections, it load

balances them among back-end proxy servers. The call persistence is maintained using the SIP

Call-ID.

For the server-side connection, the ServerIron ADX uses either a single or multiple TCP connections

with or without using source Network Address Translation (NAT) of the client IP address.

Client side: No connection reuse

Figure 6 shows that each SIP call uses a separate TCP connection. Each request has its unique

Call-ID. ServerIron ADX load balances these requests among back-end SIP proxy servers.

ServerIronADX# show sip server

Avail. SIP sessions = 0 Total SIP sessions = 500000

Server State - 0: disabled, 1:enabled, 2:failed, 3:test, 4:suspect, 5:grace_dn,

6:active

Real Server St CurrConn TotConn CurrSess PeakConn

r31 6 28723 344489 28723 91687

r32 6 28722 344505 28722 91632

r33 6 28722 344549 28722 91951

r34 6 28722 344596 28722 91566

r35 6 28723 344702 28723 91870