Monday, 21 September 2015

CUCM SIP Early Offer


By default CUCM uses SIP Delayed Offer. In order to enable Early Offer, use one of the following methods:

  1. MTP is required option should be selected on SIP Trunk. Then trunk will operate in Early Offer mode and will send SDP capabilities of the MTP device in initial INVITE message (IP, UDP Port, Codec Capabilities, etc). The MTP device will be allocated from the Trunk MRGL instead of the calling endpoint MRGL

KEEP REMEMBERING: By default if CUCM fails to allocate MTP, call will resume without MTP. This means that CUCM SIP Trunk will fallback to delayed offer. This service parameter can be changed.

TIP: In early offer, you can change the codec between alaw and ulaw (or G729 Annex-b and w/o Annex-b) using the option "MTP Preferred Originating Codec" under SIP Trunk. This won't overcome region config which should be G711 or G729.

  1. SIP Profile checkbox “Early Offer support for voice and video calls (insert MTP if needed)”.
    1. For calling endpoints that are capable of providing their details such as IP, UDP Port, Supported Codecs, MTP won't be inserted for outgoing call signalling
    2. For calling endpoints that aren't capable of providing their details such as IP, UDP Port, Supported Codecs, MTP will be inserted for outgoing call signaling and CUCM will include MTP details in the SDP of the initial INVITE
      1. MTP will be allocated from calling endpoint MRGL
      2. If failed, MTP will be allocated from outgoing trunk MRGL

Calling Device Type
Outgoing Trunk
MTP Inserted
SIP Phone
Early Offer SIP Trunk
No
New SCCP Phone
Early Offer SIP Trunk
No
Old SCCP Phone
Early Offer SIP Trunk
Yes
Early Offer SIP Trunk
Early Offer SIP Trunk
No
Delayed Offer SIP Trunk
Early Offer SIP Trunk
Yes
Slow Start H323
Early Offer SIP Trunk
Yes
Fast Start H323
Early Offer SIP Trunk
No
MGCP
Early Offer SIP Trunk
No


Method 1 vs. Method 2

  1. SIP Profile method support SRTP and Video calls since it supports MTP codec passthrough. This isn't support in Method-01 since MTP can be either G711 or G729.
  2. Less usage of MTP resources (only if needed)
  3. MTP is inserted from Calling endpoint instead of outgoing SIP trunk

2 comments:

  1. Very nice information and simple way to understand.

    Many Thanks!

    ReplyDelete
  2. Nice info. Easy to understand.

    ReplyDelete