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.

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
via G.711 Gateway Group GWG1 PSP

Carrier 2 Media G.729A w/Fax
via T.38 IPTG1 PSP

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>

G.729 Pass-Thru with G.711 to T.38 Fallback for Fax Codec Entries

 

Configuration

Value
G711-DEFAULTG729A-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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