The current resolution of the issue of SRV usage in stateless proxies is documented in:
http://www.jdrosen.net/papers/draft-ietf-sip-srv-03.txt It recommends a hash of message inputs for the random number generation, and also discusses ordering of the DNS results. Note that this won't work if DNS configurations change mid-transaction. -Jonathan R. [EMAIL PROTECTED] wrote: > > > Vikram, > > Using invariants like call-ID is what has been suggested. > This has problems when servers fail or recover in the > middle of a transaction. DNS SRV usage in stateless proxies > is an open issue due to these reasons. You can have a look > at issue #220 (slide 39) in this presentation on bis-05 > open issues: > > http://www.jdrosen.net/sip/sip_bis_open_dec01.ppt > > -Binu > > > > > > Vikram Varma <[EMAIL PROTECTED]> on 12/12/2001 01:26:13 AM > > To: K Binu/HSSBLR > cc: "'[EMAIL PROTECTED] '" > <[EMAIL PROTECTED]> > > Subject: RE: [Sip-implementors] retransmissions in a stateless proxy > > > > > Binu, > I am not sure what you mean by the second paragraph. > When you do a DNS query, you get a list of IP addresses corresponding to > that domain. As you have mentioned, there may be a weighting factor. > Are you saying that the stateless proxy should have an algorithm based on > nonvariables within the dialog, such as CallID, to choose which IP from the > list the message should be sent to? i.e. > if algorithm(CallID) = 5, choose the 5th one on the list? > This is probably a good method, however, it will not work when the DNS > records are changed. (I dont know how often that will happen, but it > probably will). > Thanks > Vikram > > > > -----Original Message----- > From: [EMAIL PROTECTED] > To: Ansar Kassim Pillai > Cc: [EMAIL PROTECTED] > Sent: 12/3/2001 8:42 PM > Subject: Re: [Sip-implementors] retransmissions in a stateless proxy > > > > > Ansar, > > A domain that has a stateful proxy server farm is not > likely to implement a round robin DNS mechanism where > a lookup returns a different IP for each query. > The right way to implement DNS based load balancing > is to use the load balancing mechanism in DNS SRV records. > In such setups, when the stateless proxy performs a query > for the next hop server, it might get multiple IP addresses > for the server with equal priority. The records will contain > a weight field that indicates the preference to be given to > the record when a random selection is made. > > In this case, the proxy must make a random selection from > the alternatives such that the probability of an address > getting selected depends on its weight. Here, the stateless > proxy should not use a truly random number to decide on the > selection. Instead, it should choose a number generated > from message elements like the call-ID and sequence number, > which are invariant in retransmissions or transactions. > This will ensure that for messages in the same transaction > the same proxy is selected from the SRV results. > > For more information on SRV records and the mechanism used > for selecting SRV entries, refer RFC 2782. > > -Binu > > > _______________________________________________ > Sip-implementors mailing list > [EMAIL PROTECTED] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > -- Jonathan D. Rosenberg, Ph.D. 72 Eagle Rock Avenue Chief Scientist First Floor dynamicsoft East Hanover, NJ 07936 [EMAIL PROTECTED] FAX: (973) 952-5050 http://www.jdrosen.net PH: (973) 952-5000 http://www.dynamicsoft.com _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
