Communication Manager: SIP External FAX is not working with 3rd party right FAX SIP server, outgoing is working fine. "488 Not Acceptable Here"

Doc ID		SOLN268281
Version:		12.0
Status:		Published
Published date:		18 Mar 2021
Created Date:		10 May 2015

Author:

Amol R Kajgikar

Details

CM Release String: vcm-016-03.0.124.0
Publication Date: 04 October 2012

UPDATES:
Update ID Status Type Update description
------------------------------- ------------ ------- ---------------------------
03.0.124.0-20850 activated cold patch 20850 for 03.0.124.0

Session Manager

6.3.8

SBC

SBC-4.2

Problem Clarification

Fax: Incoming FAX is not working with 3rd party right FAX SIP server, outgoing is working fine.

Integration as below

Service Provider SIP trunk --> SBC --> Session Manager --> CM --> Session Manager--> Right FAX Server

Cause

CODEC issue

display ip-codec-set 1 Page 1 of 2

IP Codec Set

Codec Set: 1

    Audio        Silence      Frames   Packet
    Codec        Suppression Per Pkt Size(ms)
1: G.711A            n         2        20
2: G.711MU           n         2        20
3:
4:
5:
6:
7:

IP Codec Set

Allow Direct-IP Multimedia? n

                    Mode                   Redundancy
    FAX             t.38-standard           0             ECM: n<======
    Modem           off                     0
    TDD/TTY         US                      3
    Clear-channel   n                       0

1) When SBC sent invite to CM it send codec G711 and CM passes the same to Session manager.

2) Session manger passed same information to Right FAX.

3) As this is FAX call CM sent reinvite to SBC with T.38 and same sent to Session Manager.

4) Session manager Passed this information to Right Fax.

5) Right fax denied this with error as below,

“488 Not Acceptable Here” till end of the call…..

Solution

From the information that is described in this Article it appears that the Right Fax server is not setup for T.38 properly. Changing the Codec to G711 should be utilized as a temporary fix until the Right Fax server is setup to use T.38. Avaya recommends that T.38 be used for Third party and external Faxing. If G711 is used it is considered a best effort scenario.

With the information below changing ECM to No does not disable T.38, but stops the Error Correction Mode for T.38.

display ip-codec-set 1 Page 1 of 2

IP Codec Set

Codec Set: 1

    Audio        Silence      Frames   Packet
    Codec        Suppression Per Pkt Size(ms)
1: G.711A            n         2        20
2: G.711MU           n         2        20
3:
4:
5:
6:
7:

IP Codec Set

Allow Direct-IP Multimedia? n

                    Mode                   Redundancy
    FAX             t.38-standard           0             ECM: n<=== disable ECM from the codec and its working fine.
    Modem           off                     0
    TDD/TTY         US                      3
    Clear-channel   n                       0

Attachment Description

t38 information

Additional Relevant Phrases

session manager SMGR

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