VGW - Basic Configurations

Basic Voice Gateway Configurations

     Here are the basic configurations I typically use when setting up a voice router. This will help in setting up a voice T1/E1 circuit for H.323 or SIP trunked routers.

Card Type and Clocking
     Before you can configure the card, you'll need to tell the router what card type is configured (T1 or E1), and where it is located.
     The network-clock commands allow voice cards to access the clock on the backplane.  Since these cards don't have DSPs built in on them, they have to use the clock provided by the DSPs on the motherboard. This is opposed to something like a T1 on an NM-HDV where the card has it's own DSPs and doesn't need to use the backplane clocking.

     For VWICs plugged into the chassis they will not operate without network-clock-participate. The TDM backplane can only do one clocking at a time, and the network-clock-select chooses which of the clocks it will sync with the TDM backplane. This proves problematic when you have two separate carrier circuits with different clocking.

  card type e1 0 1
  card type t1 1 1
  network-clock-participate wic 1
  network-clock-select 1 E1 0/1/0


ISDN Switch-Type
     Want to configure a VWIC card so that a PRI can be setup? You better enter the isdn switch-type command first. Without it you won't be able to fully configure the controller or see any serial interfaces. The switch-type can be applied globally or at the Serial interface level which overrides the global setting.

  isdn switch-type primary-ni

Other ISDN switch type ptions are primary-4ess, primary-5ess, primary-dms100, primary-dpnss, primary-net5, primary-ni, primary-ntt, primary-qsig, and primary-ts014.


Voice Card
     Configure a voice card for local and/or CUCM (SCCP) DSP resource sharing. Voice-card 0 points to the default chassis voice-card.
     If you do not have enough DSPs on the chassis for a PRI and you have a module (eg. NM-HDV2) with DSPs, you can use the dspfarm command under the voice card where the additional DSPs are located and make them available for sharing with the chassis. Typically this is not the case and we set “no dspfarm” under Voice-card 0 to prevent DSP sharing within the router.
     If you want to configure hardware conferencing (CFB), transcoding (XCD), or media termination points (MTP) you need to enable “dsp services dspfarm”. That command makes the DSP’s for CFB, XCD, and MTP available to be controlled by the Skinny (SCCP) application that runs on the router.

voice-card 0
   no dspfarm
   dsp services dspfarm


Voice Service VOIP
     To specify which protocols the router can communicate with or allow, configure voice service voip.

  Voice service voip
     allow-connections h323 to h323
     allow-connections h323 to sip
     allow-connections sip to h323
     allow-connections sip to sip
     allow-connections  [SIP | MGCP | H323]
     [SIP | H323]


Voice Class Codec
     These commands specify what codec preferences are allowed and in what order. You apply this group of codecs to specific dial-peers. If no voice-class group of codecs are assigned to a dial-peer, the dial-peer by default utilizes the G.729 Codec. This will bring some hurt when you’re trying to figure out why your T.38 fax isn’t working over SIP!!

  Voice-class codec 1
    codec preference 1 g711ulaw
    codec preference 2 g729br8
    codec preference 3 g729r8


Voice Class H323
     When setting up redundant dial-peers for sending calls from an H.323 gateway to a Pub and Subs there is a default timeout value before the router will check to see if the fallback CUCM servers are available. Unfortunately that default value is 15 seconds which is WAY too long. If you leave the default value, then the router will never check the fallback CUCM servers, which sucks in the cases where the primary is unreachable. Modify the time to something shorter than 10 seconds.
     If your H225 establish time is more than 10 seconds, the Q.931 timer will expire and send a call disconnect message. Three seconds is a good time to set so that failover to redundant dial-peers doesn’t take too long. The allowed range is 0 to 30 with a default of 15 seconds. If you enter 0, the H.225 TCP timer is disabled.

  voice class h323 1
     h225 timeout  tcp  establish 3


Controllers T1/E1
     The controllers are your PRI circuits. You will need to configure these based on the information provided by the carrier or that you requested from the carrier. Also specify the amount of ports or timeslots available as well as the DESCRIPTION with circuit numbers and provider!

  controller E1 0/0/0
    framing CRC4
    linecode HDB3
    pri-group timeslots 1-3,16
    description Partial E1

  controller T1 0/0/1
    framing esf
    linecode b8zs
    cablelength long 0db
    pri-group timeslots 1-24
    description Qwest LongDist #2 CID DS1-55556666

  controller T1 0/0/2
    framing esf
    linecode b8zs
    cablelength long 0db
    pri-group timeslots 1-24
    description ATT Local #2 CID 55HCFS000555-000PT


Serial Interface
     To configure your PRI you will need to setup your serial interfaces with the correct information. Make sure to verify this information (e.g. isdn switch-type primary-ni or primary-dms100, and encapsulation type) with the carrier. Settings at the Serial level have a higher precedence than the global settings.
     The isdn incoming-voice voice command configures the interface to send all incoming calls to the DSP for processing as a voice call and is required.
     The isdn bchan-number-order command changes the order in which bearer channels are utilized.


interface Serial0/1/0:15
 no ip address
 encapsulation hdlc
 isdn switch-type primary-net5
 isdn incoming-voice voice
 no cdp enable

interface Serial0/0/1:23
 no ip address
 encapsulation hdlc
 isdn switch-type primary-dms100
 isdn incoming-voice voice
 no cdp enable







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