Technical data

Brocade ServerIron ADX Advanced Server Load Balancing Guide 19

53-1003441-01

SIP SLB over 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.

FIGURE 6 Single TCP connection for each SIP request