sip over sctp

SIP over SCTP

1 Introduction...............................................................................................................................................2 2 Test Bed....................................................................................................................................................3

2.1 lksctp project......................................................................................................................................3 2.2 Dissipate Library................................................................................................................................4

3 SCTP as Transport for SIP: tests ..............................................................................................................5 3.1 Performance of Sip Call Setup using SCTP ......................................................................................5

3.1.1 Advantages over UDP .................................................................................................................5 3.1.2 Advantages over TCP .................................................................................................................6 3.1.3 SIP over SCTP ............................................................................................................................8

3.2 Interaction of a Sip transaction between various protocols .............................................................10 3.3 Open Issues ......................................................................................................................................12

6 SCTP as Signaling Transport Protocols..................................................................................................13 7 The implementation ................................................................................................................................14 8 Installation instructions...........................................................................................................................17 9 User Interface..........................................................................................................................................19 10 Test User Interface ................................................................................................................................24 11 References .............................................................................................................................................26

1 Introduction With this work we want to obtain experimental results showing SCTP’s real benefits. We will compare SCTP with already existing transport protocol and will analyze which real gains SCTP brings. At present there aren’t SIP implementation use SCTP as transport. So we have developed a new SIP client that can to run over all type of transport protocol: UDP, TCP, SCTP.

2 Test Bed Hardware Only two computers form the Test Bed: One is a desktop : Pentium IV, 260 MB ram, and two 3com Ethernet card 10/100 The other is a portable: Pentium III, 260 MB ram, and one PCMCIA Ethernet card 10 Mb The two computers are connected in net and in Internet through a Digicom Switch10/100 O.S. and Softwares Linux Red Hat 7.3 distribution, with KDE as graphic desktop. Kernel 2.5.67 with “lksctp project” dissipate library KPhone

2.1 lksctp project lksctp goal is to coordinate the continuing development of the SCTP kernel reference code, and to help disseminate information about SCTP. The SCTP kernel reference code is primarily developed at Motorola, but many people around the world help out. The reference code is completely Open Source and follows the current development of the Linux kernel. LKSCTP is the Linux kernel implementation of SCTP, it will be included in kernel 2.6 with following features • Message oriented, reliable transport protocol • Direct support for multi-homing • Runs on top of Internet Protocol (IPV4,6) • Connection-oriented data delivery • Congestion Control • In addition to TCP features: – Message Framing – Ordered and Unordered Message Delivery

– Multi-streaming – Multi-homing • Accepted in Kernel 2.5.33 • http://lksctp.sourceforge.net

2.2 Dissipate Library libdissipate is a library for developping applications based on the SIP signalling protocol defined in RFC3261. It can make and accept calls using SIP over UDP.

It is released under the GNU GPL license, with a provision that you can link it with Qt. The code has been tested on Linux and Solaris, but other OSs may also work.

We are modifying these library, like that be now further on support the SIP Use On UDP, also the use of SIP On TCP and SCTP. For the support of SCTP we have used a mapping of the Stream Control Transmission Protocol (SCTP) into a sockets API as referenced in [6]. In particular we have preferred the support a UDP-style interface: “This set of semantics is similar to that defined for connectionless protocols, such as UDP. It is more efficient than a TCP-like connection-oriented interface in terms of exploring the new features of SCTP”[6]

3 SCTP as Transport for SIP: tests For testing the working of the Sip Client, SCTP Kphone, on transport protocol SCTP, we are reporting to as specified in the draft “SCTP as a transport for SIP” [1]. Principally we want evaluate:

1) the possible advantage of SCTP over TCP (HOL blocking avoidance): the results of simulation are correct, or are they due to that implementation of stack SCTP ?

what are the advantages of a lightweight mechanism to perform transaction identification (mapping of SIP transaction into streams?)

3.1 Performance of Sip Call Setup using SCTP We want to evaluate, mainly two aspect:

- The delay of "Call Setup" to consider the middle delay of "Call Setup" - Evaluate, through a middle number of calls for seconds, the average delays of the "call setup"

3.1.1 Advantages over UDP To do.

3.1.2 Advantages over TCP To do

SYN

SYN

SYN

ACK INVITE

6 Secondi Only after this gap

INVITE is sent

Figure 3-1 delay in TCP initialisation

To do

1,5 secondi

1:500 (INVITE)

1:500 (INVITE)

ack 500

Figure 3-2 slow retransmission in TCP

To do

1,5 secondi

1:500(sessione 1:INVITE)

500:1000 (sessione 2:INVITE)

ack 500

ack 1


Figure 3-3 Fast Retrasmit in TCP

To do


500:1000 (sessione 2:INVITE)

ack 1


Figure 3-4 TCP Head of line blocking effects

3.1.3 SIP over SCTP 3.1.3.1 Multistreaming To do

INVITE TSN=6, Stream Id=3, Stream Seq=0


100 TRYING TSN=4, Stream Id=3, Stream Seq=0

SACK TSN=4, GapAckBlock:TSN=6

INVITE of session combine to stream 3 Is delivered at ULP nevertheless the loss INVITE in stream 2


PROXY-SERVER PROXY SERVER

Figure 3-5 SIP with multistreaming SCTP

To do

180 RINGING TSN=4, Stream Id=2, Stream Seq=1

100 TRYING TSN=3, Stream Id=2, Stream Seq=0

200 OK TSN=5, Stream Id=2, Stream Seq=2


Only now 200 OK is delivered, together 180 RINGING 180 RINGING TSN=4, Stream Id=2, Stream Seq=1

Figure 3-6 Final before provisional response

3.1.3.2 Unordered delivery To do

INVITE TSN=6, Stream Id=0 Unordered


100 TRYING TSN=4, Stream Id=0 Unordered


INVITE is delivered instantly though if the

previous was lost


Figure 3-7 SIP messages sent with unordered delivery

To do

CANCEL TSN=6, Stream Id=0 Unordered


481 TSN=4, Stream Id=0 Unordered




Figure 3-8 Problem CANCEL arrives before an INVITE

I have just read your document. One comment about Figure 3-8. I pointed out that problem in an old paper, but then I solved it in RFC 3261. Now proxies wait for the 100 Trying before sending the CANCEL. Therefore, you can remove that figure from the document, since it is not a problem anymore. (GONZALO MAIL del 30-05-2003)

3.2 Interaction of a Sip transaction between various protocols In literature on the SCTP use for SIP, two are the main conclusions: ??In the communication between User Agent and Proxy is worthwhile to use a not connected

transport protocol as UDP ??In the Proxy to Proxy communication is worthwhile to use a connected protocol as TCP

This conclusions derived by the comparison of the various scenarios, every one examined separately. Would be opportune studying what are the problems that can spring in the integration between the various backgrounds. In a scenario as in the following figure, they can there be three types of messages loss in the UDP link that influence in the SCTP link. We are supposing that Proxy as Stateless Sip Proxy. User Agent User Agent PROXY PROXY

UDP UDP SCTP

1) The loss of a 180 Ringing in the first UDP link

INVITE INVITE

INVITE

INVITE INVITE

INVITE

180 RING 180 RINGING

180 RINGING 0,5 sec

2) The loss of a BYE in the last link UDP

BYE BYE BYE

BYE BYE

200 Ok

200 Ok 0,5 sec

BYE

200 Ok 200 Ok

3) The loss of an ACK, in the last link UDP

200 OK 200 OK

200 OK

ACK 200 OK

0,5 sec

200 OK

ACK

200 OK

ACK

These are all situations of messages loss in the UDP link. Besides, it’s necessary considering that SIP retransmissions can happen also without the loss of messages, but simply for expiring of timeout. In every case there are SIP on UDP retransmissions uselessly propagate also on the SCTP link, not completely removing the problem of the congestion in these links. Then we suppose that a better solution is the use of SCTP in every link. We want test the difference between the first scenario and the following.

User Agent User Agent PROXY PROXY

SCTP SCTP SCTP

3.3 Open Issues 1 - If we are in a full SIP over SCTP scenario: after the startup of a session between two SIP client, is it possible make a directly SCTP association between two end point? What will happen to the various servers (if they are statefull) bound to that association? 2 - Isn’t better a mapping of Session (dialog) into Stream, respect a mapping of SIP Transaction into Streams??? 3 - I don’t consider it is possible imagine a situation in which every Statefull Server SIP have an association with all the other Server SIP… so if is required change a path, is this possible? 4 - Are there problem in the interaction between link SIP over TCP and link SIP over SCTP??? 5 - …

6 SCTP as Signaling Transport Protocols To do.

7 The implementation

Socket layer SCTP kernel

LK SCTP

ULP level SCTP level IP level

Sendmsg

Recvmsg ULP_queue

packet

inqueue

outqueue

FMS

socket

dissipate

Kphone interface user

SIP application layer

Transport layer

kphone

Kphone skeleton

SipTransaction

SipClient

SipCall

UDPMessage Socket

User interface

Send a request

SCTPMessage Socket

TCPMessage Socket

(1)

(2) (3)

(4)

(5)

Kernel linux (transport level)

SIP layer

Transport layer

(6)

SipTransaction

SipClient

SipCall

UDPMessage Socket

Receive a message

SCTPMessage Socket

TCPMessage Socket

(1)

(2)

(3)

(4) (5)

Kernel linux (transport level)

SIP layer

Transportlayer

(6)

(7)

(8)

8 Installation instructions Linux Red Hat 7.3 distribution

Kernel 2.5.67 - you can download the kernel [here] - you have patch the kernel 2.5.67 with 2.5.67 - lksctp-2_5_67-0_6_9.patch that includes sctp specific changes that didn't go into 2.5.67 [ here] - you have configure your kernel, you can download my .config file [here]

Does it compile, but not load? If so, you likely need new modutils for kernel 2.5 module-init-tools-0.9.11a.tar [here] For the installation read below or README file in the package.

1) you have to install in /sbin: ./configure --prefix=/ make moveold (if installing for the first time). "make moveold" renames the old insmod, modprobe, rmmod and lsmod to insmod.old, modprobe.old, rmmod.old and lsmod.old, and the matching manpages. 2) Now, build it: make make install 3) If running for the first time, you might want to convert your old modules.conf to modprobe.conf: ./generate-modprobe.conf /etc/modprobe.conf 4) You will need to run "depmod" for your new kernel, eg: depmod 2.5.50 6) If you want to hack on the source: aclocal && automake --add-missing --copy && autoconf

lksctp tools tar ball includes user level sctp library and test programs for sctp users and developers -lksctp-tools-2_5_67-0_6_9.tgz [here]

SIP/SCTP tar [here] new If you want receive the source code, please send me an email.

9 User Interface

Figure 9-1 The SCTP version

Figure 9-2 User Identity

Figure 9-3 Choose the transport protocol

Figure 9-4 Start a New Call

Figure 9-5 Receive an Incoming Call

10 Test User Interface

Figure 10-1 Client Side

Figure 10-2 Server Side

11 References

Draft and RFC

[1] J. Rosemberg, H. Schulzrinne, and G. Camarillo, “"The Stream Control Transmission Protocol as a Transport for the Session Initiation Protocol”. draft-ietf-sip-sctp-03.txt

[3] Rosemberg, H. Schulzrinne, et al. “SIP: Session initiation protocol”. Request for Comments

3261 [4] R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer, T. Taylor, I. Rytina, M. Kalla, L.

Zhang and V. Paxsons. Stream control transmission protocol. Request for Comments 2960, Internet Engineering Task Force, October 2000

[5] R. Stewart, L. Ong, I. Arias-Rodriguez, and K. Poon, “Stream Control Transmission Protocol

(SCTP) Implementer's Guide” draft-ietf-tsvwg-sctpimpguide-08.txt [6] R. Stewart, Q. Xie, L. Yarroll, J. Wood, K. Poon, K. Fujita, “Sockets API Extensions for Stream

Control Transmission Protocol (SCTP)” draft-ietf-tsvwg-sctpsocket-06.txt Articles & Presentation

[7] Intro article by Daisy Chang and Jon Grimm (IBM) http://www-124.ibm.com/linux/presentations/lwce2002/Chats/SCTP/SCTP-LWE.pdf

[8] La Monte H.P. Yarroll, Karl Knutson, "Linux Kernel SCTP : The Third Transport” http://lwn.net/2001/features/OLS/pdf/pdf/sctp.pdf

[9] G. Camarillo, H. Schulzrinne, R. Kantola, "A transport protocol for SIP"

[10] G. Camarillo, H. Schulzrinne, R. Kantola, "Signalling transport protocols"

[11] Loreto S., De Marco G., Longo M, De Vito D., 2003 "SCTP as a transport for SIP: a Case Study" http://www.iiis.org/sci2003

sip over sctp

Documents

sip transaction

real gains sctp

performance of sip

transport protocols

arent sip implementation

new sip client

type of transport protocol

existing transport protocol