[SIPForum-discussion] Load Balancing in SIP Networks

Chinar Trivedi chinart13 at gmail.com
Sat Oct 19 13:20:16 UTC 2013

Let's us analyze for which all elements in IMS (or any SIP Network for that
matter) load balancing feature is needed (SBC, P-CSCF, I-CSCF, S-CSCF)

1. Is Load Balancing (LB) needed for discovering SBC or a UE hitting DNS to
resolve SBC is needed? As SBC is a Security node in any SIP Network,
typically what is expected from SBC is NAT, Topology hiding, Call Admission
Control, etc.
Having said that, should UE directly be seeing SBC's IP address or should
UE's query hit a LB to select SBC. If DNS feature is needed, should UE's
query be hitting DNS for resolving SBC.
In that case, should LB be acting as DNS or we don't need a LB at all and
DNS itself should be enough for resolving SBC's IP address and SBC Location.

2. Is LBing needed only for the forward path or also the reverse path? What
I understand is LBing is done only in the forward path i.e After every SIP
element, LB will choose the respective SIP device (P/I/S-CSCF) from a pool
of multiple SIP elements in actual Registration/ SIP Call. Typically, in
any SIP Network, the 200 OK Response shouldn't be hitting LB.

If we don't want 200OK or any RESPONSE code messages to hit the SIP
elements, won't the connection break on Layer 3?

3. Most important aspect of LBing in SIP Networks is maintaining
persistence. There are few standard ways of maintaining persistence for
HTTP Protocols like least response time, Back end Server CPU Load etc. But
for SIP networks, will it be done on parameters like Call-ID/IMPU or
multiple parameters should be used. Can we set up multiple rules for LBing
SIP networks?

Let us discuss/analyze. My understanding on above points may be wrong. Feel
free to correct me.

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