WHat is prack message in SIP

[Pointbreak]

Team,

WHat is prack message in SIP

[Vivek Batra · Accepted solution]

It is provisional acknowledgement. As name says, it is used to acknowledge SIP provisional responses like 180 Ringing, 183 Session Progress etc.

When you use SIP on UDP, by default provisional responses are sent unreliability (does not re-transmit). Lets assume if 180 Ringing is lost over the network, caller will not get RBT and suddenly will listen the word 'Hello'. To avoid this, '100rel' extension is used during call setup which indicates called party to send provisional response reliably and keep re-transmitting until PRACK message is received or timeout happens.

Refer RFC 3262 for more details.

- Vivek

[Pointbreak]

Thanks for your response.

ms-client-diagnostics: 51004; reason="Action initiated by user"

above is a trace part from the calling party in the "cancel" message. The outbound call was rejected by the server end; then why this is initiated by Calling party.

[Ayodeji Okanlawon]

In addition to what Vivek has said, PRACK is also used for early media. In SIP media flows at when we get or send 200 OK, however there are scenarios where we need media to flow before that.

A typical example is when the called party wants to play announcement. In scenarios like this we will use prack to send media either in 180 or 183 progress messages.

[Pointbreak]

Hi,

Where are UDP and TCP ports used in SIP environment

Among INVITE, BYE, ACK, CANCEL, INFO, UPDATE, REFER, NOTIFY, BENOTIFY, OPTIONS.

[Ayodeji Okanlawon]

Every protocol needs a transport mechanism. SIP uses UDP, TCP, and SCTP for transport.

In each of your sip Methods, (everything in CAPS) you can see what transport protocol by looking at the via header.

Examples:

This INVITE uses TCP as the transport protocol

INVITE sip:1598@10.100.24.171:5060 SIP/2.0
 Via: SIP/2.0/TCP 10.100.42.141:5060;branch=z9hG4bK66a0972f72e00

In this example, the INVITE uses UDP

INVITE sip:208774@10.100.40.100:5060 SIP/2.0
Via: SIP/2.0/UDP 10.100.140.14:5060;branch=z9hG4bK39e90e56b5e1ea

This OPTIONS ping uses UDP

Sent:
OPTIONS sip:02079501251@10.106.33.24:5070;transport=udp SIP/2.0
Via: SIP/2.0/UDP 10.105.40.200:5060;branch=z9hG4bK10D683B1078

This BYE uses UDP

BYE sip:0189@10.100.140.20:5060 SIP/2.0
Via: SIP/2.0/UDP 10.100.10.14:5060;branch=z9hG4bK39e90b13e4c448

[Pointbreak]

Sir,'

Thanks for your mail.

At the invite message, I can seen in both TCP and UDP 5060 port is used. COuld you please explain that sir!

[Ayodeji Okanlawon]

You can't have both tcp and udp in the same Invite. Please share the INVITE trace 

[Pointbreak]

Hi,

Not in the same INVITE. From the above i am asking ,is 5060 TCP or UDP port?

[Ayodeji Okanlawon]

5060 is for SIP. That is the port that SIP protocol uses. This can run on either UDP or TCP.

[Kevin Monteiro · Accepted solution]

Hi Manzoor,

Here is a excellent document for your understand about PRACK:

http://www.cisco.com/c/en/us/support/docs/voice/session-initiation-protocol-sip/116086-configure-cube-cucm-sip-00.html

Hope this helps.

Rate the post accordingly.

-Regards,

Kevin Monteiro

[Ayodeji Okanlawon]

Kevin, (+5)

Great document thanks for sharing it.