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Activity report – SIPit 19

SIPit 19 took place Oct 16-20, 2006 at the University of New Hampshire InterOperability Laboratory ( There were 140 attendees from 73 companies visiting from 16 countries present. There were 79 teams and 90 distinct implementations.

The University of New Hampshire InterOperability Laboratory did a spectacular job of providing a rock-solid network for us to test on. (For those who haven’t been to a SIPit, it is a particularly intense network torturing environment). Kudos to UNH-IOL. (Editors note: UNH-IOL has become a SIP Forum Full Member.

The majority of the spec-arguments during testing centered around how to handle early media and early dialogs. There was also a non-trivial subset of the implementers that were confused about whether REGISTER and PUBLISH create dialogs (much of this confusion seems to come from the presence of to-tags in the 200 OK responses to REGISTER in the examples in 3261). There were a number of interesting questions about edge cases that were forwarded to the appropriate IETF lists separately.

We tried something different for collecting data for this report at this SIPit. We utilized a web-based automated survey tool. As a result, we collected information on more questions than we usually do, so this report is a bit long. A side-effect is that the accuracy of the information is probably a little lower. Almost all of what’s below is self-reported, and its unavoidable that for any given question an implementer or two didn’t understand, or didn’t know the answer. So, with an appropriate level of respect for errors in sampling, here’s what we found:


The roles represented (some implementations act in more than one role):

Endpoint 36
Proxy/registrar 19
Standalone proxy 8
Redirect server 4
Gateway 4
Automaton UA (voicemail, conference, etc.) 15
B2BUA/sbc 17
User Agent w/signaling but no media 6
Test/monitoring tool 8

General SIP compliance

Implementations using each transport for SIP messages:

UDP 100%
TCP 82%
TLS (server auth only) 45%
TLS (server or mutual auth) 36%

Proper use of DNS for SIP continues to rise

Full RFC3263 use of DNS 59%
SRV only 14%
A records only 15%
no DNS support 12%

Support for various items

Correctly reassembled fragmented UDP70%

ENUM 32%
rport 65%
multiplexing SIP/STUN 30%
RFC4320 fixes 25%
Identity 14%
connect-reuse 30%
SIP over multicast 10%
SIP over IPv6 30%

14 of the implementations claimed support for outbound. Interoperability around this draft was fairly low, but the implementers are aggressively improving it.

15 implementations claimed support for some version of GRUU. Nothing worked together before code changes at the event. By the end a few teams were getting scenarios to work.

Only 3 implementations were attempting to support the consent framework.


The endpoints implemented these methods:

INVITE and ACK 100%
BYE 100%
INFO 74%

The endpoints implemented these extensions:

RFC3891: replaces 67%
RFC4028: session-timer 63%
RFC3327: path 17%
RFC3840: pref 11%
RFC3841: caller-prefs 4%
RFC3323: privacy 26%
RFC4538: target-dialog 6%
RFC4488: norefersub 7%
RFC3262: 100rel 56%
RFC3994: indication of message composition 3%
sipping-cc-transfer 44%

NAT traversal

When asked about STUN support, the client implementations replied:

I do not implement STUN as a client 59%
I implement all of the client requirements of RFC3489 13%
I implement some, but not all, of the client requirements of RFC3489 7%
I implement all the client requirements of draft-ietf-behave-rfc3489bis 6%
I implement some, but not all, of the client requirements of draft-ietf-behave-rfc3498bis 6%
Other 9%

25% of endpoints still do not use symmetric RTP.

There were only a couple of TURN client implementations. We had several STUN servers and 2 TURN servers. There were only 3 ICE implementations, and only one of those was at the current version. Interoperability was reasonably high, but not seamless. The issues with interoperability were all implementation problems.


I asked the endpoint implementations to characterize their handling of S/MIME:

I break if someone sends me S/MIME 15%
I pretend S/MIME doesn’t exist if it shows up 22%
I don’t pay attention to S/MIME but will proxy it or hand it to my application 35%
I pay attention to S/MIME I receive but don’t send any 7%
I don’t pay attention to S/MIME I receive but I do send some 2%
I try to do something useful with S/MIME I receive and send 4%
Other 15%

I asked the same question about multipart mime support:

I break if someone sends me multipart/mime 7%
I pretend multipart/mime doesn’t exist if someone sends it to me 20%
I ignore multipart/mime but will proxy it or hand it to my application if it shows up 19%
I try to do something useful with multipart/mime I receive but I never send it 15%
I ignore multipart/mime that I receive but I try to do something useful with multipart/mime I send 4%
I try to do something useful with multipart/mime I send and receive 22%
Other 13%

48% of the endpoint implementations claimed to correctly handle merged requests.


Here is how the endpoints said they handled receiving 200 OKs from more than one branch of a forked INVITE:

I send BYEs to all but one branch 54%
I use all of them (perhaps mixing the different media streams locally) 6%
I don’t handle this case gracefully 16%
Other 11%


Here is a sample of how endpoint implementors replied when asked how they handled early media from more than one leg:

  • We allow multiple RTP streams with an affinity to the last one.
  • First Media received is played until 200.
  • The first 183 will be honored in case of the UAC. The rest will be dropped.
  • Allow media from only negotiated address. Ignore media until negotiated (offer-answer exchanged).
  • Listen to most recently started stream.
  • All early media will passed on to the UA.
  • Pick the one who most recently sent me a criticial threshold of media.
  • Play only one media stream and ignore others.
  • The last sdp received override previous one.
  • First 18x message goes through, rest dropped.
  • Open voice only with the first one, but answer all of the 18x.
  • We will use the first recieved.
  • I ignore early media.
  • All get relayed – (all rendered leave final choice to recipient UA).
  • Last early media replaces previous.
  • We update media as the 18x’s come in. 200OK media will be the confirmed media channel.
  • Take the first.

Interestingly, 15% of the endpoints supported DHCP option 120.


This is how the endpoints (that actually handled media) described their use of RTCP:

I fully implement RTCP and use the RTCP from my peers 38%
I send some RTCP, and open a port to receive RTCP, but I ignore any packets I receive 20%
I never send RTCP, but I do open a port for receiving (and ignoring) it 18%
I don’t even open a port for RTCP 24%


There were 12 (roughly 25%) endpoints testing SRTP support. Keying was predominantly SDES. Interoperability is not yet high, but more pairs got something working than at SIPit 18.

There were only 4 endpoints supporting comedia.


There were 22 proxies present.

The proxy implementers characterized their handling of infinite loop prevention this way:

I implement loop detection as per the sip-loop-fix draft 0%
I perform RFC3261 loop detection 45%
I don’t loop detect, but do pay attention to max-forwards 45%
I don’t loop detect or look at max-forwards 10%

I asked proxies “Will you proxy a request with a RURI containing an unknown scheme (such as splork:) when there is a Route header field whose first value is a SIP URI you can resolve?” and got these responses:

Yes 32%
No 68%

Half of the proxies in attendance actively participated in session-timer.

There were 9 implementations (41%) that categorized themselves as proxies that would not forward an unknown method.

Two-thirds of the proxies claimed to properly handle SIPS.

None of the proxies made use of 3840 or 3841 information (capabilities and caller-prefs)


There were 19 registrars.

  • 7 of the registrars (37%) accepted non-sip or sips Contacts in a registration
  • 11 (58%) would accept a REGISTER request that had a multipart-mime body (almost all ignored it)
  • 1 would accept an S/MIME signed or encrypted register

Half of the border-elements (B2BUA/SBC-like implementations) could be configured to forward unknown methods.

75% could be configured to forward unknown SDP lines.

SIP Events

There were 41 SIP Events implementations present.

15 (37%) of them would send unsolicited notifies (there were 2 more things that ONLY sent unsolicited notifies).

They supported these event packages:

refer 29
message-summary 23
presence 14
dialog 12
reg 5
ua-profile (sipping-config-framework) 4
conference 4
reg gruu extension (sipping-gruu-reg-event) 2
certificate/credentials (sip-certs) 2
session-spec-policy (sipping-policy) 1
kpml 1
vx-rtcpxr (sipping-rtcp-summary) 0

Only 4 (10%) supported winfo

4 supported event-list

37% of the implementation supporting SIP Events supported PUBLISH

Of the 14 implementations supporting event presence, there was support for the following document formats:

base PIDF only 12
timed presence 0
prescaps-ext 0

5 implementations supported XCAP

7 supported pres-rules


I asked all the implementations present which P- headers they actively supported. (I suspect many of the respondents who passively let the headers pass or ignore them answered yes, so these numbers, more than any others of the above are probably inflated):

P-Asserted-Identity 28
P-Preferred-Identity 21
P-Called-Party-ID 10
P-Associated-URI 9
P-Access-Network-Info 9
P-Charging-Vector 8
P-Visited-Network-ID 6
P-Charging-Function-Address 5
P-User-Database 4
P-DCS-* (any of the P-DCS headers) 4
P-Media-Authorization 3

That’s it. Please let me know if there are different questions you want to see asked next SIPit.

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