Early Media enable/disable

[Alan Couto]

Hello friends,

About Early Media:

Early Media allows the sending of media from the called party or an application server to the caller, even before
the call is accepted. The most common reasons for using Early Media include the following:
• The called device might want to establish an Early Media RTP path to reduce the effects of audio cut-through
delay (clipping) for calls experiencing long signaling delays or to provide a network-based voice message
to the caller.

Question: There's any way to check if Early Media is enabled or not at the router?  Aditionally, there's any command to enable/disable Early Media?

Thanks,

Alan.

[Jaime Valencia]

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube_sip/configuration/xe-3s/cube-sip-xe-3s-book/do-to-eo.html

[Rolando Valenzuela]

Jaime article is better ;) I didnt know there was one with all together.

Rolando Valenzuela.

[Alan Couto]

Hello Jaime,

The config is about early offer only.

As I took a look at other topics early offer is different from early media.

In an Early Offer, the session initiator (calling device) sends its capabilities (for example, codecs supported) in the SDP contained in the initial Invite (thus allowing the called device to choose its preferred codec for the session).

In Early Media,the media channel is setup before the call is established. This can be used to reduce the effects of audio cut-through delay or to provide a network-based voice message to the caller.

In most sip calls, Media is established after the calling party receives a 200 OK. With Early media, Media is established in 183 with SDP, much before 200 OK is sent. This allow providers to play announcement or MOH or whatever they choose to play before sending 200 OK.

Also this document..

http://www.cisco.com/c/en/us/td/docs/routers/asr1000/configuration/guide/sbcu/2_xe/sbcu_2_xe_book/sbc_ear.html

[Ayodeji Okanlawon]

Hi Alan,

I am assuming you are familiar with the sip protocol. This is important in understanding early media.

Another good use of early media is a case where you call an IVR system. However your call shouldnt be charged until you speak to an operator/agent. However before the agent answers the call there are several announcements etc. We use early media for this too with SIP

Depending on what call control system you are using..CUCM typically uses PRACK for early media.

Usually in your sip setup or signalling you will get a 183 session progress with SDP and the person sending you this can force early media by inserting the following header in its 183 session progress response "rel1xx require"

Here is an excerpt from one of my docs..

Use of Early Media
While the PSTN provides inband progress information to signal early media (such as a ring tone or a busy signal), the same thing does not occur for SIP. The originating party includes Session Description Protocol (SDP) information, such as codec usage, IP address, and port number, in the outgoing INVITE message. In response, the terminating party sends its codec, IP address, and port number in a 183 Session Progress message to indicate possible early media.

The 183 Session Progress response indicates that the message body contains information about the media session. Both 180 Alerting and 183 Session Progress messages may contain SDP, which allows an early media session to be established prior to the call being answered.

When early media needs to be delivered to SIP endpoints prior to connection, Cisco Unified Communications Manager always sends a 183 Session Progress message with SDP. Although Cisco Unified Communications Manager does not generate a 180 Alerting message with SDP, it does support the 180 Alerting message with SDP when it receives one.

The SIP Profile Configuration window contains a Disable Early Media on 180 check box. Check the check box to play local ringback on the called phone and connect the media upon receipt of the 200OK response. See the SIP Profile Configuration Settings section of the Cisco Unified Communications Manager Administration Guide.

[Alan Couto]

Hi aokanlawon!

Nice to talk to you again. There's no CUCM see below the elements:

phone at NGN -> SIP Server (not cisco) SIP->SIP Cisco router E1 ISDN-> E1 ISDN Traditional PBX -> phone

Client asks about Early Media with 183 Session Progress.

So, there's any way to force/enable early media at Cisco router? (IOS XE, 4451-X).

[Ayodeji Okanlawon]

By default it should support early media. Otherwise you can try this commands..

voice service voip
sip
rel1xx supported 100rel
rel1xx require 100rel