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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 

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 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
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s 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
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's Codec Entry. The fax portion of the call will require transcoding between G.711 and T.38 by
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.

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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