[SIPForum-discussion] Load Balancing in SIP Networks

Keyur Amin fossil0681 at yahoo.com
Mon Oct 21 17:13:09 UTC 2013


1. You are confusing Load Balancing with DNS. If you are using a SIP Load Balancer, it would sit in front of the your SBCs. The DNS lookup should return Load Balancers' IP address. 
2. Typically, you would want all your new requests to route via the Load Balancer. Responses are not required to route via a Load Balancer. No, it will not break layer 3. 

Keyur Amin



On Monday, October 21, 2013 10:44 AM, Chinar Trivedi <chinart13 at gmail.com> wrote:
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, 

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 

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 

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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