The example in Tables 1 and 2 is another scenario where fax support is required. In this example we assume that Carrier 1 can support G.729A encoding as well as G.711. In the packet-to-packet control fields of the two PSPs we have selected "conditional" transcoding with no explicit conditions selected. This causes SBC to transcode only if required to match disparate Carrier 1 and Carrier 2 codecs. Since in this case both carriers support G.729A, no transcoding is needed for the initial audio portion of the call. Either SBCs or Carrier 2 may detect the fax tone and initiate a modification of its media stream that agrees with the Fax Tone Treatment setting in the SBC's Codec Entry. The fax portion of the call will require transcoding between G.711 and T.38 by SBC.
Table 1: G.729 Pass Through with G.711 to T.38 Fallback for Fax PSPs
Configuration | Value | |
|---|---|---|
Carrier 1 Media G.711 (or G.729A) w/ Fax | Carrier 2 Media G.729A w/Fax | |
PSP | PSP-Carrier1 | PSP-to-Peer |
Silence Factor | 40 | 40 |
Voice Initial Playout Buffer | 10 | 10 |
TOS | 0 | 184 |
Data Initial Playout Buffer | 50 | 50 |
Codec Entry 1 | G711-DEFAULT | G729A-DEFAULT - FaxViaT38 |
Codec Entry 2 | G729A-DEFAULT - FaxViaG711 | <none> |
Codec Entry 3 | <none> | <none> |
Codec Entry 4 | <none> | <none> |
AAL Payload Size | 47 | 47 |
T.38 No. Redundant Packets | 1 | 1 |
T.38 Low Speed No. Redundant Packets | 1 | 1 |
T.38 Max Bit Rate | 14.4 | 14.4 |
Data Rate Mgt Type | Type 2 | Type 2 |
Honor Remote Precedence | Disabled | Disabled |
P2P Transcode | Conditional | Conditional |
Conditions | <none selected> | <none selected> |
Codecs Allowed This Leg | G.711A, G.711U | G.729, T.38 |
Codecs Allowed Other Leg | <none selected> | <none selected> |
RTCP | <not selected> | <not selected> |
Silence Insertion Descriptor | Take defaults | Take defaults |
Digit Detect Send Enabled | <not selected> | <not selected> |
Table 2: G.729 Pass-Thru with G.711 to T.38 Fallback for Fax Codec Entries
Configuration | Value | ||
|---|---|---|---|
| G711-DEFAULT | G729A-DEFAULT FaxViaG711 | G729A-DEFAULT FaxViaT38 | |
Audio Encoding | G.711 | G.729A | G.729A |
Fax Tone Treatment | <none> | Fallback to G.711 | Fax Relay |
Packet Size | 10 ms | 10 ms | 10 ms |
Fax Treatment Failure Handling | Continue | Continue | Continue |
G.711 Law | Law from other leg | N/A | N/A |
Modem Tone Treatment | None | None | None |
Modem Treatment Failure Handling | Continue | Continue | Continue |
DTMF Relay | None | None | None |
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