[SIPForum-discussion] SIP using TCP or UDP?

[Prasad MNR]

Hi,
The following is a quote from the book "Understanding Sip" by Alan B.
Johnston.

"UDP provides the simplest transport for user agents and servers and allows
them to operate without transport layer state. however UDP offers no
congestion control. A series of lost packets on a heavily loaded IP link can
cause retransmissions, which in turn produce more lost packets and can push
the link into congestion collapse. Also UDP may only be used for SIP when
the message (and its response) is known to be less than the MTU size of the
ip network. For simple SIP message, this is not a problem. however for large
messages containing multiple message bodies and large header fields, this
can be a problem. In this case, TCP must be used, since SIP does not
support fragmentation at the SIP layer."

I think answers Madan's question and also explains why Raman has suggested
to use UDP if its a local network. I may be wrong at this point of time as I
have just started the journey of learning SIP.

Regards,
Prasad MNR

On 1/15/07, raman kumar <ramank24 at gmail.com> wrote:
>
> Razual has explained the right reson. To use the power of UDP
> connectionaless protocol the
> timer mechanism is inbuilt in the sip
>
> On 14/01/07, Rezaul Kabir <rezaulkabir at gmail.com> wrote:
> > I have not heard any such restrictions on the size of packet. But UDP
> > is used by default and if you closely look at RTC 3261 Section
> > 13.3.1.4 you will notice that it talks about a timer to retransmit
> > packets and similar example is available in the rfc in several areas.
> > This behavior of retransmission clearly indicates that it is desirable
> > to use non-reliable transport such as UDP to send the packets.
> > According to RFC3263 Section 4.1 is the Sip Uri does not specify any
> > transport then UDP should be selected. Also by RFC2543 UDP is
> > mandatory if no transport is defined and for good interpretability.
> > TCP should only be used if one is thinking of using SIPS/TLS OR the
> > Sip Uri specifies TCP as transport.
> >
> >
> > ----
> > Rezaul Kabir
> >
> >
> > On 1/13/07, madan kumar <mada2k at gmail.com> wrote:
> > > i far as i know udp is used when the packet size is less than 1200
> bytes
> > and
> > > TCP is used when it exceeds 1200 bytes ..... do any of u have a
> > explanation
> > > for this
> > >
> > >
> > > On 1/10/07, raman kumar <ramank24 at gmail.com> wrote:
> > > > when using the sip at the back-end use the UDP
> > > > When using in the local premises use TCP
> > > >
> > > >
> > > >
> > > > On 26/12/06, Ramachandran <rgunasekaran at velankani.com> wrote:
> > > > > Dear all,
> > > > >
> > > > >
> > > > >
> > > > >  I am not very sure about the following,
> > > > >
> > > > >
> > > > >
> > > > > What is ideal transport protocol for SIP with IMS deployment?
> > > > >
> > > > > When to use SIP using UDP?
> > > > >
> > > > >
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Ram
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
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> >
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