[Users] Re: [Serusers] Scalability in presence notification

Klaus Darilion klaus.mailinglists at pernau.at
Fri Sep 9 10:28:39 CEST 2005

Vincent Luba wrote:
> Hi,
> I need some advices about a design issue. I'm trying to figure out how 
> to manage my presence information notifications, using RFC 3856.
> I have a situation in which end-to-end presence management wouldn't be 
> suitable.
> Still I'm wondering if server based presence management is a good idea. 
> My thought is that it present a scalability issue.

The overall number of messages sent/received will be lower when using 
serverbased presence. Imagine a SIP client with modem connectin and 50 
users on its buddylist:

end2end: 50xNOTIFY to the SIP proxy + 50xNOTIFY to the SIP clients
         + 50 responses (200 ok)     + 50 responses

server based: 1xPUBLISH             + 50xNOTIFY to the SIP clients
              +1 responses (200 ok)  + 50 responses

This will lower the traffic on the SIP proxy and on the UAC side.

But of course, a presence server needs CPU power and has to store the 
presence locally in a database. Thus, as you see, this is a trade of.

simple server and high network traffic
complicated server and low traffic and centralized features (buddy list...)

Additionally, you also have to consider SIP implementations. There are 
not thousands of SIP clients which supports all presence modes. Some 
clients supports end2end, some clients support server based. The same 
with SIP proxies.

Conlusion. Get some clients and implement both scenarios and find the 
one which fits your needs.


> The point is that having the presence server would have to handle every 
> single SUBSCRIBE & PUBLISH request then sends NOTIFY to every watchers.
> Is it an efficient way to handle presence in a network with hundreds 
> online users, everyone having tens of contact on their list.
> Thank you for your comments
> Luba Vincent
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