Bri Port Assignments

In the Integrated Services Digital Network (ISDN), there are two levels of service: the Basic Rate Interface (BRI), intended for the home and small enterprise, and the Primary Rate Interface (PRI), for larger users. Both rates include a number of B-channels and a D-channel. Each B-channel carries data, voice, and other services. The D-channel carries control and signaling information.

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The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate Interface user can have up to 128 Kbps service. The Primary Rate Interface consists of 23 B-channels and one 64 Kpbs D-channel in the United States or 30 B-channels and 1 D-channel in Europe.

For more information, see ISDN. For comparison with other Internet connection services, see The speed of....


ISDN Voice Interface Cards (VICs) such as VIC-2BRI-S/T-TE connect directly to Public Switched Telephone Networks (PSTNs), Private Branch Exchanges (PBX), and Private Access Branch Exchanges (PABX), supporting both on-premise and off-premise connections.



There are no specific requirements for this document.

Components Used

The document discusses the following ISDN BRI VICs:





For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Product Numbers

Product Number Description
VIC-2BRI-S/T-TE Two-port ISDN BRI VIC, S/T interface, Terminal Equipment (TE)
VIC-2BRI-NT/TE Two-port ISDN BRI VIC, S/T interface, Network Termination (NT) or TE
VIC2-2BRI-NT/TE Two-port ISDN BRI VIC, S/T interface, NT or TE


This table lists the features that are supported on ISDN BRI VICs:

Feature Description
Voice Ports Two ISDN BRI, total of four B channels, therefore four voice calls per VIC.
ISDN Interface ISDN BRI S/T RJ-45
ConnectionsVIC-2BRI-S/T-TE—Provides TE ISDN interface. Connects to the telco central office switch or a PBX that provides NT. You cannot connect ISDN phones or faxes to this VIC (it would require NT implementation). VIC-2BRI-NT/TE—Provides TE or NT. VIC2-2BRI-NT/TE—Provides TE or NT. Connects as network side or user side to PBX or key system as off-premises connections (ISDN voice BRI). Supports patent-pending flexible Layer 2 (L2) and Layer 3 (L3) configurations.
ISDN Switch Types Supports all Cisco IOS® Software ISDN BRI switch types.

The VIC2-2BRI-NT/TE cards are new generation VICs that are a hardware refresh of the older cards of the similar functionality, with resolved manufacture component issues. New functionality is also introduced on these BRI cards (which reduces the number of Stock Keeping Units (SKUs) required).

The VIC2-2BRI-NT/TE is supported on NM-HD-1V, NM-HD-2V, and NM-HD-2VE, where as the VIC-2BRI-S/T-TE and VIC-2BRI-NT/TE are currently supported on NM-1V/2V.

Features not Supported

This is a list of the features that are not supported on ISDN BRI VICs:

  • ISDN supplementary services

  • Data calls on the B channels

  • Group 4 fax (ISDN digital fax)

  • Calls on the ISDN D channel

  • When you use the VIC-2BRI-S/T-TE with a NM-1V, you are only able to place two calls. The second BRI port is shut down.

  • When you use the VIC-2BRI-S/T-TE with a NM-2V, you can place four calls. If you have another VIC in the second slot, the second BRI port on the VIC-2BRI-S/T-TE is shut down.

  • The ISDN BRI VICs are only supported for connectivity to another switching system (for example: a PBX or to the PSTN). Connectivity to ISDN BRI phones is not supported.


The ISDN parameters are configured similar to a data ISDN BRI interface.

Note: The isdn incoming-voice modem command is required to route the voice call to the digital signal processor (DSP) on the Voice Network Module. For additional information on this command, refer to isdn incoming-voice modem.

For the configuration of voice features in Cisco IOS Software, refer to Voice over IP for the Cisco 3600 Series.

Note: In Cisco IOS Software, issue the voice-port <slot>/<VIC slot>/<unit> global configuration command in order to configure the voice port parameters.

The commands used to configure VoIP on Cisco routers are very similar on all of the router platforms shown in this table.

For configuration of voice features in Catalyst OS (CatOS) on a Catalyst 4000, refer to Configuring the Voice Interfaces.

Platform Support

Cisco IOS Support 1 1751, 17603 2600 2600XM/2650XM 36204, 3640 2 3660 2 2691, 3725, 3745 VG200
VIC-2BRI-S/T-TE 2-Port ISDN BRI VIC, S/T interface, TE Not Supported 12.0(2)XD, 12.0(3)T, 12.0XK, 12.1(1), 12.1(1)T, 12.2(1), 12.2(2)T,12.2(2)XT, 12.2(11)YT, 12.3(1) All Cisco IOS Software Versions  12.0(7)XK, 12.1(1)T, 12.1(5)YB, 12.1(5)YD, 12.2(1), 12.2(2)T, 12.2(2)XT, 12.2(11)YT, 12.2(15)ZJ, 12.3(1), 12.3(2)T All Versions All Cisco IOS Software Versions
VIC-2BRI-NT-TE 2-Port ISDN BRI VIC, S/T interface, NT, TE All Versions 12.1(3)XI, 12.1(5)T,12.1(5)YB, 12.1(5)YD, 12.2(1), 12.2(2)T, 12.2(2)XT, 12.2(11)YT, 12.3(1) 12.2(8)T1,12.2(11)T, 12.2(11)YT, 12.2(12), 12.2(15)ZJ, 12.3(1), 12.3(2)T 12.1(3)XI, 12.1(5)T, 12.1(5)YB, 12.1(5)YD, 12.2(1), 12.2(2)T, 12.2(2)XT, 12.2(11)YT, 12.2(15)ZJ, 12.3(1) 12.1(3)XI, 12.1(5)T, 12.1(5)YB, 12.1(5)YD, 12.2(1), 12.2(2)T, 12.2(2)XT, 12.2(11)YT, 12.2(15)ZJ, 12.3(1) 12.2(11)YT, 12.2(13)T, 12.2(15)ZJ, 12.3(1), 12.3(2)T, 12.3(4)XD 12.1(5)T, 12.2(1), 12.2(2)T, 12.3(1)
VIC2-2BRI-NT-TE 2-Port ISDN BRI VIC, S/T interface, NT, TE 12.2(15)ZL, 12.3(2)XA, 12.3(2)XC, 12.3(2)XE, 12.3(4)T, 12.3(5) Not Supported 12.2(15)ZJ, 12.3(4)T 12.2(15)ZJ, 12.3(4)T (Not supported for Cisco 3620.4) 12.2(15)ZJ, 12.3(4)T 12.2(15)ZJ, 12.3(4)T, 12.3(4)XD Not Supported

1 Voice requires a Cisco IOS Software Voice feature set on the 1700 series router, and a Cisco IOS Software Plus feature set on the 2600/3600 series router.

2 Voice is not supported on the 3631 router.

3Cisco 1750 router platforms do not support the BRI VICs.

4Cisco 3620 series routers do not support the VIC2-2BRI-NT-TE cards.

Known Issues

Some of the known issues with the BRI VICs are discussed in this section.

When the BRI voice interfaces are configured, this error message is received:

%C542-1-INSUFFICIENT_DSPS: VNM(1), cannot support all voice channels on VICs.

This is because the VIC-2BRI-S/T-TE can have more B channels than the Voice Network Module can handle. The NM-1V can handle two voice calls (has two DSPs). The NM-2V can handle four voice calls (four DSPs). For more information on this, refer to the error message %C542-1-INSUFFICIENT_DSPS (registered customers only) in the Error Message Decoder (registered customers only)

Another known problem is due to Cisco bug ID CSCdv00152 (registered customers only) .

The compand-type a-law command does not exist on the CLI for a BRI port.

This bug restricted the use of the to North America, as it resulted in the wrong compand decoding being applied and caused distorted voice. It was introduced in Cisco IOS Software Releases12.2(2) and 12.2(3)T, and corrected in the 12.2(5) and 12.2(8)T releases.


One of the applications of the BRI VICs is shown in this example. Observe that the BRI VIC can be directly connected to the PSTN or the ISDN PBX.

Note: The Cisco IOS software releases provided are typically the minimum version required to support the platform, module, or feature in question. To find out a complete list of Cisco IOS Software releases a feature, module, interface card, or chassis is supported in, refer to the Software Advisor (registered customers only) tool.

Note: Refer to the Command Lookup Tool (registered customers only) for more information on the commands given in this document.

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