6 ServerIron ADX Advanced Server Load Balancing Guide
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SIP SLB and Call Persistence using ServerIron ADX
1
Max-Forwards
The Max-Forwards header field must be used with any SIP method to limit the number of proxies or
gateways that can forward the request to the next downstream server.
The Max-Forwards value is an integer in the range 1-255 indicating the remaining number of times
that a request message is allowed to be forwarded. The recommended initial value is 70.
SIP SLB and Call Persistence using ServerIron ADX
Figure 2 shows an overview of a ServerIron SIP Server Load Balancing implementation.
FIGURE 2 ServerIron SIP Server Load Balancing implementation
There are three kinds of SIP servers:
• proxy server
• redirect server, and
• registrar server.
In Figure 2, the ServerIron SIP load balancer (SIP Server Load Balancing) uses the Domain-1 VIP to
load balance SIP requests from Client A (user1) or Client B (user2) among Domain 1 proxy servers
and registrar servers.
The SIP Server Load Balancing uses the Domain-2 VIP to load balance SIP requests from Client A
(user1) or Client B (user2) among Domain 2 proxy servers and registrar servers.
The ServerIron offers support for the following SIP servers in accordance with RFC 3261:
ServerIron
From/To SIP Phone To/From VIP
L2/3
Infrastructure
INVITE F2
SIP
Proxy
Server
INVITE F1
RINGING F4
OK F6
TRYING F3
RINGING F5
OK F7
RINGING F4
OK F6
INVITE F2
TRYING F3
RINGING F5
OK F7
INVITE F1
User 2
User 1
ACK F8
MEDIA RTP
BYE F9
OK F10
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