160 people from 16 countries attended SIPit 18 with 73 different SIP  
implementations.

A short summary of some of the capabilities of those implementations  
follows:

UDP 					73
TCP 					53
TLS 					30
SCTP 					6
SRTP 					10 (7 use sdes)
rport 					36
GRUU 					5
outbound 				2
connect-reuse 			6
IPv6 					19
Full 3263 				25
3263 no naptr (SRV on) 	13
A only 					22
IP only (no DNS) 			9
Session timer 			38
Prack 					32 (9 non-trivial users)
Update 					25
NIT fixes (4320) 			7
Out of Dialog Refer 		3
Dialog package 			8
Turn 					3
XCAP 					4 (2 servers)

Generally, the level of interoperability was very high.

Very few of the attendees were aware of GRUU, but there were some  
implementations to test
(and they interoperated). The big surprise was the number of SIP over  
SCTP implementations
testing at this event.

There was significant testing of TLS and SRTP. TLS interoperability  
is solidifying.
SRTP interoperability was poor (key exchange is not working)

There were several common implementation errors and questions. Below are
rough descriptions of each (in no particular order). I'll send more  
detailed messages
when I'm back online in a couple of weeks.

- Several UAs were doing 3263 lookups but ignoring the port from the  
SRV record,
   always sending to 5060

- Many UAs are gratuitously putting ports in URIs when the  
appropriate thing to do
   would be to only place a domain name. This particularly caused  
error when the
   port retrieved from SRV was placed explicitly in the RURI of the  
message sent

- There was non-trivial testing of RPID at this event. There was  
disagreement around
   where <activities> was legal or had meaning.

- More than one implementation still has ACK-200 vs ACK-non200  
confused. In particular,
   more than one implementation used the branch parameter from an  
INVITE in the ACK-200.
   There was also some confusion leading to reusing the INVITE branch  
parameter in PRACKs

- Those testing IPv6 made different assumptions about enclosing  
literal v6 addresses in Vias
    in []. By the end of the event, most implementations were  
accepting either. Its about 50/50
    on what gets sent.

- The SIP over SCTP implementers point out a need for clarification  
around using the 1 to many
    vs 1 to 1 mode.

- Several implementations (including a few mature ones) are still  
having case-insensitivity related
   interop problems. I saw arguments over "Digest" vs "DIGEST", and  
case sensitivity around
   mime-types.

- There were many questions about record-routing when changing  
transports, and where the
    double-record-routing technique we've been suggesting people use  
is documented.

- Implementers are looking for better guidance for solving the issue  
we identified with discarding
   transactions state on an ACK-200. We need to get more guidance  
into current bugzilla report
   and/or issue a draft on this soon.

- There were a few XCAP tests at this event. Interoperability was  
mixed. Very little "just worked",
    but after agreements were made about URI paths and versions of  
schemas most tests were
    successful.

- Several UAs still miss that request-merging and handling  
multiple-200s (or multiple 183s) is even
   a concern.

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