Configuring Tandem Switching in a VoFR Environment [Gateway Protocols]

Document ID: 14039

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Configure
      Network Diagram
      Configurations
Verify
Troubleshoot
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Related Information

Introduction

This document provides a sample configuration for the Tandem Switch feature in Voice over Frame Relay (VoFR).

Tandem switching allows the route of calls to a hub location prior to the reach of the final destination, where you can also modify the dial plan and destination pattern. This feature bypasses the traditional tandem PBX switching and avoids use of the valuable PBX trunk lines and multiple voice encodings. Tandem switching helps you plan a large network because the hub can be the central location through which all calls go, and a full-mesh topology is not necessary. Tandem switching also simplifies the troubleshoot stages of a call because the call easily breaks down into more call legs with tandem switching. If you use tandem switching, you can avoid creation of full-mesh, which can be costly. Tandem switching also helps with troubleshooting and call management.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

To implement this configuration, you need these software and hardware versions:

A Cisco 3640, Cisco 2610, and Cisco 3810 that all run Cisco IOS® Software Release 12.0 or later.
A hub and spoke, with Cisco 3640 as the hub and Cisco 2610 and Cisco 3810 as the spokes.
A VoFR connection between the Cisco 2600 and the Cisco 3640, and one between the Cisco 3640 and the Cisco 3810.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command

Conventions

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

Configure

In this section, you are presented with the information to configure the features described in this document.

Note: To find additional information on the commands used in this document, use the Command Lookup Tool ( registered customers only) .

Network Diagram

This document uses this network setup:

Configurations

This document uses these configurations:

Cisco 2600
Cisco 3640
Cisco 3810

Cisco 2600

2611# show run
Building configuration...
 
Current configuration:
!
version 12.0
service timestamps debug datetime msec
!

!--- This command puts all debug entries with a timestamp
!--- in milliseconds (msec). This is very important because the handshake 
!--- of telephony signaling transpires in msec. 

 
!
hostname 2611
!
logging buffered 50000 debugging

!--- This command logs the debug output into the buffer 
!--- (RAM) of the router so that the output can be played back for review. 
!--- RAM is limited within the router. If you use a 
!--- large buffer, the buffer reduces useable RAM for the router to
!--- operate. 


 
!
ip subnet-zero
no ip domain-lookup
!
voice-port 1/0/0
!         
voice-port 1/0/1
!
voice-port 1/1/0
!
voice-port 1/1/1
!
dial-peer voice 1 pots
 destination-pattern 1...
 port 1/0/0
!
dial-peer voice 2 pots
 destination-pattern 2...
 port 1/0/1
!
dial-peer voice 10 vofr
 destination-pattern 4...
 session target Serial0/0 101 dtmf-relay
 no vad
!

!--- Enable no voice activity detection (VAD) to avoid any possible
!--- clippings in the voice, since you cannot save a lot of bandwidth
!--- in switched calls. Enable dtmf-relay so that the digits are 
!--- passed out of band, and not in the audio path.

!
dial-peer voice 20 vofr
 destination-pattern 5...
 session target Serial0/0 101
 dtmf-relay no vad
!
!
interface Ethernet0/0
!
interface Serial0/0
 no ip address
 no ip directed-broadcast
 encapsulation frame-relay
 no ip mroute-cache
 cdp enable
 frame-relay traffic-shaping
!

!--- Enable traffic-shaping on the main serial 
!--- interface of each router.

!
interface Serial 0/0.1 point-to-point
 ip address 191.10.10.2 255.255.255.252
 frame-relay interface-dlci 101
  class Tandem
  vofr cisco
!

!--- On the frame-relay subinterface for connectivity to the 
!--- 3640, add the correct frame-relay map-class and
!--- vofr cisco.


!         
map-class frame-relay Tandem
 no frame-relay adaptive-shaping 
 frame-relay cir 384000
 frame-relay bc 3840
 frame-relay be 0
 frame-relay mincir 384000
 frame-relay fair-queue
 frame-relay voice bandwidth 256000
 frame-relay fragment 500
!

!--- The map-class above displays all correct parameters for 
!--- CIR=384k circuit. Packets larger than 500 bytes are fragmented. 
!--- Note: Only data packets are fragmented 
!--- with FRF.12 fragmentation.

!
!
line con 0
 transport input none
line aux 0
line vty 0 4
 login
!
end
 
2611#

Cisco 3640

3640# show run
Building configuration...
 
Current configuration:
!
version 12.0
service timestamps debug datetime msec
!
hostname 3640
logging buffered 50000 debugging
enable password ww
!
ip subnet-zero
no ip domain-lookup
!
voice-port 1/0/0
!
voice-port 1/0/1
!
voice-port 2/0/0
 timeouts call-disconnect 0
!
voice-port 2/0/1
 timeouts call-disconnect 0
!
voice-port 2/1/0
 timeouts call-disconnect 0
!
voice-port 2/1/1
 timeouts call-disconnect 0
!
dial-peer voice 100 vofr
 destination-pattern 4...
 session target Serial0/0 100
 dtmf-relay
 no vad
!
dial-peer voice 200 vofr
 destination-pattern 5...
 session target Serial0/0 100
 dtmf-relay
 no vad
!

!--- The above two dial peers allow calls for the destination of 
!--- 4xxx and 5xxx to route to next hop via data-link connection
!--- identifier (DLCI) 100 (to the 3810).
!--- Note: You do not need to specify the serial subinterface.


!
Dial-peer voice 101 vofr
 destination-pattern 1...
 session target Serial0/0 101
 dtmf-relay
 no vad
!
dial-peer voice 201 vofr
 destination-pattern 2...
 session target Serial0/0 101
 dtmf-relay
 no vad
!

!--- The above two dial peers allow calls for the destination 
!--- 1xxx and 2xxx to route to next hop via DLCI 101 (to the 2600). 
!--- Note: You do not need to specify the serial subinterface.


!
Interface Ethernet0/0
 ip address 172.16.173.20 255.255.255.192
!         
interface Serial0/0
 no ip address
 no ip directed-broadcast
 encapsulation frame-relay
 no ip mroute-cache
 cdp enable
 frame-relay traffic-shaping
!
interface Serial0/0.1 point-to-point
 ip address 191.10.10.1 255.255.255.252
 frame-relay interface-dlci 101
  class Tandem
  vofr cisco

!--- This is the serial interface that connects 3640 to 2600.
 

Interface Serial0/0.2 point-to-point
 Ip address 190.10.10.1 255.255.255.252
 frame-relay interface-dlci 100
  class Tandem
  vofr cisco
!

!--- This is the serial interface that connects 3640 to 3810.


router eigrp 100
 network 10.0.0.0
 no auto-summary
!
map-class frame-relay Tandem
 no frame-relay adaptive-shaping 
 frame-relay cir 384000
 frame-relay BC 3840
 frame-relay be 0
 frame-relay mincir 384000
 frame-relay voice bandwidth 256000
 frame-relay fragment 500
!
line con 0
 transport input none
line aux 0
 speed 38400
line vty 0 4
 password WW
 login
!
end
 
3640#

Cisco 3810

Building configuration...
 
Current configuration:
!
version 12.0
no service pad
service timestamps debug datetime msec
!
hostname 3810
!
logging buffered 50000 debugging
!
network-clock base-rate 56k
ip subnet-zero
!      
controller T1 0
-snip-
!
interface Ethernet0
 ip address 172.16.173.34 255.255.255.192
!
interface Serial0
!
interface Serial1
 no ip address
 no ip directed-broadcast
 encapsulation frame-relay
 clockrate 1300000
 cdp enable
 frame-relay traffic-shaping
!
Interface Serial1.1 point-to-point
 ip address 190.10.10.2 255.255.255.252
 frame-relay interface-dlci 100
  class Tandem
  vofr cisco
 
!
interface Switch0
-snip-
!
map-class frame-relay Tandem
 no frame-relay adaptive-shaping
 frame-relay cir 384000
 frame-relay BC 3840
 frame-relay be 0
 frame-relay mincir 384000
 frame-relay voice bandwidth 256000
 frame-relay fragment 500
!         
line con 0
 transport input none
line aux 0
line 2 3
line vty 0 4
 login
!
!
voice-port 1/1
 timeouts call-disconnect 0
!
voice-port 1/2
 timeouts call-disconnect 0
!
voice-port 1/3
 timeouts call-disconnect 0
!
voice-port 1/4
 timeouts call-disconnect 0
!
voice-port 1/5
 timeouts call-disconnect 0
!         
!
dial-peer voice 1 pots
 forward-digits all
 destination-pattern 5...
 port 1/2
!
dial-peer voice 2 pots
 forward-digits all
 destination-pattern 4...
 port 1/4
!
!
dial-peer voice 20 vofr
 destination-pattern 1...
 session target Serial1 100
 dtmf-relay
 no vad
!
dial-peer voice 30 vofr
 destination-pattern 2...
 session target Serial1 100
 dtmf-relay
 no vad
!

!--- A call that originates from the 3810 is first dispatched 
!--- to the 3640 that acts as the tandem switching router. The
!--- call then matches dial peer tags 101 and 201. The call then
!--- routes to the final destination, 2611. 


end
 
3810#

Verify

There is currently no verification procedure available for this configuration.

Troubleshoot

There is currently no specific troubleshooting information available for this configuration.

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Related Information

Troubleshooting Tandem Switch VoFR Configurations
Voice Technology Support
Voice and Unified Communications Product Support
Recommended Reading: Troubleshooting Cisco IP Telephony
Technical Support - Cisco Systems

Updated: Feb 02, 2006

Document ID: 14039

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