This profile specifies T.38 data rate management type.

To View and Edit T38

On the SBC main screen, go to Configuration > Profile Management > Category: Media Profiles > Packet Service Profile > T38.

Select the desired Packet Service Profile from the drop-down list to view its respective T38 parameters.

The T38 window is displayed.

Profile Management - Media Profiles - Packet Service Profile - T38

The following fields are displayed:

T38 Parameters

Parameter

Description

Data Rate Management Type

• type1LocalGenerationOfTcf – Type 1 data rate management requires that the Training Check Frame (TCF) training signal be generated locally by the receiving gateway. Data rate management is performed by the emitting gateway based on training results from both PSTN connections. Type 1 is used for TCP implementations and is optional for use with UDP implementations.
• type2TransferOfTcf (default) – Type 2 data rate management requires that the TCF be transferred from the sending gateway to the receiving gateway rather than having the receiving gateway generate it locally. Speed selection is done by the gateways in the same way as they would on a regular PSTN connection. Data rate management type 2 requires the use of UDP and is not recommended for use with TCP.

Low Speed Number of Redundant Packets

For low-speed fax relay, specifies the number of redundant IFP messages sent in a UDP for fax transmission. Possible values are 0, 1, and 2.

The default value is 1.

Max Bit Rate

Use this object to select the T.38 Maximum Bit Rate which controls and manipulates bits 11, 12, 13, and 14 in the DIS command received by the SBC from either the TDM circuit interface or the T.38 packet interface• 2.4 Kbps.

  • 2.4Kbits_s – For modem type ITU-T V.27ter fallback mode.
  • 4.8Kbits_s – For modem type ITU-T V.27ter.
  • 9.6Kbits_s – For modem types ITU-T V.27ter and V.29.
  • 14.4Kbits_s – (default) For modem types ITU-T V.27ter, V.29, and V.17. Use this setting to constrain the type of modem modulation schemes.

(See T.38 Max Bit Rate Handling for Non-Direct Handling Calls topic below for additional details)

Number of Redundant Packets

For high-speed fax relay, specifies the number of redundant Internet Facsimile Protocol (IFP) messages sent in a User Datagram Packet (UDP) for fax transmission. Possible values are 0, 1, or 2.

The default value is 1.

Protocol Version

Specifies the T38 Protocol Version to be used. Options are:

  • 0 (default)
  • 3 (Used for SG3 (Super G3) call)

Make the required changes and click Save at the right hand bottom of the panel to save the changes made.

 

T.38 Max Bit Rate Handling for Non-Direct Media Calls

SBC Core Behavior

For T.38 version=0, the SBC supports four bit rates: 2.4 Kbps, 4.8 Kbps, 9.6 Kbps and 14.4 Kbps.

The SBC normalizes the T.38 bit rate that it receives in the SDP from the peers.

  • If the bit rate received in the SDP is one of these four values, the SBC selects the minimum of route-configured bit rate and peer's bit rate.
  • However, if the bit rate received in the SDP is not one of these four values, the SBC selects one of these four bit rates that is lower than the peer's bit rate.
    Consequently, the SBC uses the minimum value of: route-configured bit rate and peer's bit rate after normalization.
    Examples:
    • If peer is requesting 14.4 Kbps and the route is configured with 14.4 Kbps, the SBC uses 14.4 Kbps.
    • If peer is requesting 14.4 Kbps and the route is configured with 9.6 Kbps, the SBC uses 9.6 Kbps.
    • If peer is requesting 10 Kbps and the route is configured for 14.4 Kbps, the SBC uses 9.6 Kbps.
    • If peer is requesting 7.2 Kbps and the route is configured for 9.6 Kbps, the SBC uses 4. 8 Kbps.
    • If peer is requesting 7.2 Kbps and the route is configured for 2.4 Kbps, the SBC uses 2.4 Kbps.

External PSX Provisioning

Another configuration related to T.38 Max Bit Rate handling for non-Direct Media calls is the PSX "Use Max Bit Rate Only" object, with the following considerations:

  • The PSX PSP flag "Use Max Bit Rate Only" does not impact the logic explained above for bit rate selection based on a peer's value plus the SBC supported/configured values.
  • If "Use Max Bit Rate Only" flag is disabled, the SBC will further adjust/reduce the bit rate (computed above) based on the T38FaxMaxBuffer, T38FaxMaxDatagram and T38FaxUdpEC attributes. Thus, enabling this flag only prevents the SBC from further reducing the bit rate using these attributes.


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