Gateway Protocols

Document ID: 22303

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Background Information
      Requirements of VoFR with Cisco IOS Routers
Configure
      Network Diagram
      Configurations
Verify
Troubleshoot
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Related Information

Introduction

This document explains the basics to understand, configure, and troubleshoot Cisco proprietary Voice over Frame Relay (VoFR). It is a best practice to run VoFR links; however, you are able to run VoFR over High-Level Data Link Control (HDLC) links if you can configure Frame Relay switching on one gateway and back-to-back Frame Relay to simulate a Frame Relay cloud. As long as you can terminate voice calls between two or more Frame Relay connected routers, and your network does not have a Cisco CallManager or IP phone to route calls to, VoFR is an efficient and easy way to accomplish voice routing over the internet. This document focuses on a hub and spoke topology for VoFR; there is a single PVC shared for voice and data between the hub and each spoke.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on these hardware versions:

• 3700 gateway

• 3600 gateway

• 2600 gateway

• MC3810 gateway

Note: In this particular example, a 3640 and two 2610 gateways have been used. The voice or data T1 is connected either to a PBX at a customer branch or to an external public switched telephone network (PSTN) connection from the customer's service provider. In addition, at least four phones with RJ-11 connections to the end gateways are also needed.

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, see the Cisco Technical Tips Conventions.

Background Information

Requirements of VoFR with Cisco IOS Routers

There are several pointers to keep in mind when you configure VoFR on Cisco IOS® Software platforms.

Please note that to configure vofr cisco under the Frame Relay interface-dlci section of the configuration will take down the PVC momentarily, until the far end Permanent Virtual Circuit (PVC) is also configured for vofr cisco. The recommended approach to configure vofr cisco on a live Frame Relay network is to have remote access, not over the Frame Relay connection, but to both the hub and remote routers. This will reduce the amount of time the Frame Relay network is down. If this is not feasible, another approach is to configure the remote routers first with the help of Telnet over the Frame Relay network. You will configure vofr cisco on the remote router and then IP connectivity will be lost. You can then configure vofr cisco on the hub router and IP connectivity will be restored. Note that the traffic shaping parameters on a given PVC must be identical in both locations.

Furthermore, you need to keep two main issues in mind regarding traffic shaping with VoFR.

• The PVCs configured for VoFR must have a minimum guaranteed Committed Information Rate (CIR) for traffic shaping to be valid. If the CIR is not guaranteed and available 100 percent of usage time, the router Frame Relay traffic shaping cannot guarantee excellent voice quality at all times.

• You must enable Frame Relay traffic shaping on the main physical interface and add map classes to each individual subinterface. Please note that if you enable traffic shaping on the main interface only, and do not add a specific map class to all subinterfaces, those PVCs will be automatically shaped down to 56k CIR. As part of the map class, you must apply fragmentation of data packets (FRF.12) in order to minimize delay and choppiness in the voice quality. For more information, refer to Frame Relay Traffic Shaping for VoIP and VoFR and VoFR Encapsulation and Fragmentation.

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 the network setup shown in the diagram below.

Configurations

The configurations here consist of basic dial plans. In this example, a single PVC is shared for data and voice between the hub and each remote. The Cisco 3640 contains a digital voice card connected to a PBX, and the Cisco 2611 and Cisco 2610 each contain two analog FXS ports connected to phones.

• The minimum Cisco IOS support for VoFR is 12.07T; latest 12.1 or 12.2 mainline is recommended for stability and extra features.

• The Cisco 3640 hub has two Frame-Relay PVCs, one to each Cisco 2600 remote router.

• Each PVC size is 256k, the mincir is the same as the CIR, and the fragment size for optimal voice quality is 320 bytes.

• Each VoFR call with a default of g729r8 requires 10 kbps.

• The same map class is applied to both PVCs on the Cisco 3640, in this case, only because the PVC size is identical. Individual map classes may be applied to each PVC if the CIR is different for each.

Current configuration:
!
version 12.1
service timestamps debug datetime msec
!
hostname 3640
logging buffered 50000 debugging
enable password ww
!
ip subnet-zero
no ip domain-lookup
!
controller t1 2/0
framing esf
linecode b8zs 
ds0-group 1 timeslots 1-4 type e&m-winkstart
! 
interface Ethernet0/0
 ip address 172.16.173.20 255.255.255.192
!         
!
interface Serial0/1
 no ip address
 no ip directed-broadcast
 encapsulation frame-relay
 clockrate 1300000
 frame-relay traffic-shaping

!--- This CLI enables traffic shaping and must be applied 
!--- for map-classes to take effect.

!
interface Serial 0/1.1 point-to-point
 description Connection to Remote 2611
 ip address 192.168.10.1 255.255.255.252
 frame-relay interface-dlci 100
  vofr cisco

!--- This CLI enables VoFR and may take down the PVC until  
!--- both sides are configured and reset properly.

  class map_vofr
!
interface Serial 0/1.2 point-to-point
description Connection to Remote 2610
ip address 192.168.20.1 255.255.255.252
frame-relay interface-dlci 200 
vofr cisco
class map_vofr
! 
map-class frame-relay map_vofr
 no frame-relay adaptive-shaping
 frame-relay cir 256000
 frame-relay bc 2560

!--- For optimal voice quality, this value should be 1/100 
!--- of CIR.

 frame-relay be 0

!--- For optimal voice quality, always set to 0 to eliminate
!--- the PVC from bursting.

 frame-relay mincir 256000
 frame-relay fair-queue
 frame-relay voice bandwidth 20000

!--- voice bandwidth in bps is total BW for maximum number 
!--- of simultaneous calls per PVC

 frame-relay fragment 320

!--- For optimal voice quality, the fragment size is 
!--- calculated as 80 bytes per 64k CIR

!
voice-port 2/0:1
!
dial-peer voice 1 pots
destination-pattern 12..
prefix 12
port 2/0:1
!
dial-peer voice 2 pots
destination-pattern 14..
prefix 14
port 2/0:1
! 
dial-peer voice 100 vofr
destination-pattern 5...
session target serial0/1 100
no vad
dtmf-relay 
!
dial-peer voice 200 vofr
destination-pattern 6...
session target serial0/1 200
no vad
dtmf-relay 
!
line con 0
 transport input none
line aux 0
 speed 38400
line vty 0 4
 password ww
 login
!
end
!
!
 

Current configuration:
!
version 12.1
service timestamps debug datetime msec 
! 
hostname 2611
!
logging buffered 50000 debugging
!
ip subnet-zero
no ip domain-lookup 

interface Ethernet0/0
!
interface Serial0/0
description Connection to Hub 3640
bandwidth 512000
no ip address
no ip directed-broadcast
encapsulation frame-relay
frame-relay traffic-shaping
!
interface Serial 0/0.1 point-to-point
ip address 192.168.10.2 255.255.255.252
frame-relay interface-dlci 100
vofr cisco
class map_vofr
!
! 
map-class frame-relay map_vofr
no frame-relay adaptive-shaping
frame-relay cir 256000
frame-relay bc 2560
frame-relay be 0
frame-relay mincir 256000
frame-relay fair-queue
frame-relay voice bandwidth 22000
frame-relay fragment 320
!
! 
voice-port 1/0/0
! 
voice-port 1/0/1
!
dial-peer voice 1 pots
destination-pattern 5...
port 1/0/0
!
dial-peer voice 2 pots
destination-pattern 5...
port 1/0/1
!
dial-peer voice 10 vofr
destination-pattern 12..
session target Serial0/0 100
no vad
dtmf-relay
! 
! 
line con 0
transport input none
line aux 0
line vty 0 4
login
!
end
! 
 

Current configuration:
!
version 12.1
service timestamps debug datetime msec 
! 
hostname 2610
!
logging buffered 50000 debugging
!
ip subnet-zero
no ip domain-lookup 

interface Ethernet0/0
!
interface Serial0/0
description Connection to Hub 3640
bandwidth 512000
no ip address
no ip directed-broadcast
encapsulation frame-relay
frame-relay traffic-shaping
!
interface Serial 0/0.1 point-to-point
ip address 192.168.20.2 255.255.255.252
frame-relay interface-dlci 200
vofr cisco
class map_vofr
!
! 
map-class frame-relay map_vofr
no frame-relay adaptive-shaping
frame-relay cir 256000
frame-relay bc 2560
frame-relay be 0
frame-relay mincir 256000
frame-relay fair-queue
frame-relay voice bandwidth 22000
frame-relay fragment 320
!
! 
voice-port 1/0/0
! 
voice-port 1/0/1
!
dial-peer voice 1 pots
destination-pattern 6...
port 1/0/0
!
dial-peer voice 2 pots
destination-pattern 6...
port 1/0/1
!
dial-peer voice 10 vofr
destination-pattern 14..
session target Serial0/0 200
no vad
dtmf-relay
!
! 
line con 0
transport input none
line aux 0
line vty 0 4
login
!
end
! 

Verify

This section provides information you can use to confirm your configuration runs properly.

Certain show commands are supported by the Output Interpreter Tool ( registered customers only) , which allows you to view an analysis of show command output.

• show frame-relay pvc [dlci#]—Check to make sure that traffic shaping is applied to the correct PVCs and that all parameters match that of map-class.

  If you already have traffic over the link, you need to verify these:

  1. The counters for discard eligible (DE) packets, backward explicit congestion notification (BECN), and forward explicit congestion notification (FECN) parameters are at zero at all times. Since adaptive shaping has been turned off and this example is shaping to the true CIR of the circuit, no DE packets or BECN/FECN warning should come from the circuit.

  2. The traffic shaping will only go active when you need to send traffic at or above the CIR. Therefore, it is normal to have shaping inactive listed.

  3. There should be no dropped packets. The dropped packet counter lists lost packets in the circuit, and unless the system exceeds its true CIR, the circuit should, under no conditions, allow to e dropping packets.

  4. Frame Relay traffic shaping drops should be at zero. This counter will increment if traffic shaping is wrong and, as a result, packets are dropped at the router while queuing them to be sent out.

  Note: The only distinguishing factor between data and voice is the fragmented packets. The show frame-relay fragment [dlci#] command indicates the number of packets fragmented: these are solely data packets. Therefore, if some of these packets are dropped, you can estimate that some data packets are lost. However, in all other counts, you should not encounter packet loss since it can be data or voice.

• show interface serial [slot/port]—Make sure there are no output drops and no errors on all counters. Notice that queuing is set to dual fifo, which is the queuing strategy for vofr cisco, with voice on the high queue and all other data on the weighted fair queue.

  2611# show frame pvc 100 PVC Statistics for interface Serial1 (Frame Relay DTE) DLCI = 100, DLCI USAGE = LOCAL, PVC STATUS = DELETED, INTERFACE = Serial0/0.1 input pkts 0 output pkts 0 in bytes 0 out bytes 0 dropped pkts 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 0 out bcast pkts 0 out bcast bytes 0 pvc create time 05:29:55, last time pvc status changed 05:29:05 Service type VoFR-cisco configured voice bandwidth 22000, used voice bandwidth 0 fragment type VoFR-cisco fragment size 320 cir 256000 bc 2560 be 0 limit 320 interval 10 mincir 256000 byte increment 125 BECN response no fragments 0 bytes 0 fragments delayed 0 bytes delayed shaping inactive traffic shaping drops 0 Voice Queuing Stats: 0/100/0 (size/max/dropped) Current fair queue configuration: Discard Dynamic Reserved threshold queue count queue count 64 16 2 Output queue size 0/max total 600/drops 0 2611#show traffic-shape Interface Se3/0:1.1 Access Target Byte Sustain Excess Interval Increment Adapt VC List Rate Limit bits/int bits/int (ms) (bytes) Active 100 256000 320 2560 0 10 320 - - 2611#show frame fragment 100 interface dlci frag-type frag-size in-frag out-frag dropped-frag Serial3/0:1.1 100 VoFR-cisco 320 0 0 0

Troubleshoot

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

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Related Information

• Voice Technology Support
• Voice and IP Communications Product Support
• Recommended Reading: Troubleshooting Cisco IP Telephony
• Technical Support - Cisco Systems