Yes, but this depends on your deployment setup and policies. Obviously, you cannot support all features with all UAs. Three-way conferencing for example. There's no guarantee that REFER and NOTIFYs work for three random UAs from different vendors. There are still too many bugs around. So, you need to say: If you have this and that UA, you will probably not get three-way conferencing. Not much difference from saying: If you have this and that UA, you may experience service outages.

There are several ways of creating server-side redundancy and scalability. Unfortunately, none are trivial. There are three I have heard have been successfully used in large-scale setups:
1. Cacheless usrloc with a mysql cluster as back-end DB combined with implementation of the Path header (to find the registrar of a given UA). No replication across servers
2. Multiple SER registrars, each with a standalone, local DB and where SIP is used to replicate registrations. By storing replications from a peer in a location_peer1 table and then lookup using this table, you can route INVITEs to the registrar being able to pinhole the NAT in front of a given UA
3. Each SER is connected to a single mysql DB cluster as in #1, but since usrloc also is in memory (cacheless usrloc is not used), replication is done between the SER servers and save_memory() is used to store the location only in memory (the registrar updates the cluster with save())

Each of these three can be combined with either:
a. call-id sticky front-end load balancer (commercial or modified LVS)
b. DNS SRV
c. Linux HA creating two and two peers

Only b) combined with either 1) or 3) or 2+c) can give geographic, client and server-side redundancy and scalability.

Scalability and redundancy is sort of a pet project of mine... I would like to see a simple, clear-documented and code-supported setup that satisfies most common requirements. Currently I'm leaning against #2 (which actually can be implemented in vanilla SER 0.9.x, but would be easier and better with built-in support). I'm thinking about a setup where two and two servers are peers to eachother using Linux HA. Both servers would have one active SER instance and one inactive ready for taking over for the peer.

I have posted this overview to:
http://www.iptel.org/drupal/failover_redundancy_and_scalability_overview

See also:
http://www.iptel.org/drupal/ser/wishlist

g-)
G.Jacobsen wrote:

Samuel,

Do you happen to know what percentage of UAs out there are really "Compliant" UAs ?

My impression so far regarding SRV DNS records is that they are theoretically a nice feature but unfortunately almost useless since one needs to cater for those non-compliant UAs anyway. I would love to be convinced of the contrary.

Can anyone supply real usage figures regarding compliant/non-compliant UAS ?

TIA

Gerry

-----Original Message-----
From: serusers-bounces@lists.iptel.org [mailto:serusers-bounces@lists.iptel.org]On Behalf Of samuel
Sent: Donnerstag, 6. Juli 2006 14:52
To: Ritesh Jalan
Cc: seruser List
Subject: [Bulk] Re: [Serusers] Global Failover Server

Look at RFC 3623.
Cofigure two SRV entries in your DNS, one pointing to the UAS SERver and another to the UK server. "Compliant" UAs will try to contact the other proxy upon failure of their current one.

Samuel.

2006/7/5, Ritesh Jalan <ritesh.j@net4.in>:

Hi All

Pls. guide me how can we implement failover on SIP Server located globally, Like one server in USA another in UK.

Ritesh Jalan
Mobile: 91-9818616329
MSN: ritesh_jalan@hotmail.com

_______________________________________________
Serusers mailing list
Serusers@lists.iptel.org
http://lists.iptel.org/mailman/listinfo/serusers
_______________________________________________
Serusers mailing list
Serusers@lists.iptel.org
http://lists.iptel.org/mailman/listinfo/serusers
  