Applying QoS for Voice Traffic

QoS is very important for Voice traffic which is delay sensitive. I won’t go into details of QoS over here and will just explain the configuration we normally use on a Voice gateway for QoS. class-map match-any Voice-RTP match ip precedence 5 match ip dscp ef match ip rtp 16384 16383 class-map match-any Voice-Cntl matchContinue reading “Applying QoS for Voice Traffic”

Scenario#27 – RightFax Server not working – MGCP

I had an interesting scenario where customer logged a case with us regarding their RightFax server not working. Those of you who don’t know what is a RightFax server can read about it here. When you dial the fax number from outside, it reaches the gateway and you hear one ringback and then a fastContinue reading “Scenario#27 – RightFax Server not working – MGCP”

DSP, PVDM & Media Resources

The Cisco High-Density Packet Voice Digital Signal Processor (DSP) Module (PVDM2) enables Cisco Integrated Services Routers to provide high-density voice connectivity, conferencing, and transcoding capabilities in Cisco IP Communications solutions. PVDM stands for packet voice DSP module; it is the Cisco product name for the module that provides digital signal processing resources to a system.Continue reading “DSP, PVDM & Media Resources”

Scenario#10 – Phones showing Incorrect time

I don’t remember how many times I came across customers complaining that their phones are either x minutes ahead or x minutes behind the normal time. This is what I do whenever I come across time issues. This is for applicance based Call manager (5.x, 6.x, 7.x, 8.x) Go to OS Admin > Settings >Continue reading “Scenario#10 – Phones showing Incorrect time”

MGCP Call Preservation

MGCP gateway is a Survivable endpoint unlike H323 which is not survivable. What does it mean? It means that an active call through an MGCP gateway will not tear-down and the call will be preserved. As discussed already in another section that an MGCP gateway terminates Layer 2 signalling at the gateway while Backhauling LayerContinue reading “MGCP Call Preservation”

MGCP Gateway Setup

MGCP Configuration Using Trombone Feature: To register an MGCP gateway to call manager, follow these steps: Do a show inventory OR show diag to check the position of E1/T1 Enable the E1/T1 by using command – card type T1 0 0 OR card type T1 0 1 (whatever the case may be) Do show verContinue reading “MGCP Gateway Setup”


In a typical ISDN setup for an Inbound call from PSTN to an IP phone (-SCAC-) CCM  –  GW  – PSTN Setup <——- Call proceeding ——-> Alerting ——-> Connect ——> Gateway and PSTN switch exchange Q921 Layer 2 information. Gateway registers with ISDN switch and terminates Q921 at gateway. A Q931 Setup message arrives. TheContinue reading “MGCP Call Flow – ISDN PRI”

MGCP – How it works?

General: MGCP stands for Media Gateway Control Protocol. It’s a client-server protocol which means that it has  to depend on Media Controller (Call agent) for call routing. In case of Cisco this MC is a CUCM. The Call agent controls the ports of a MGCP gateway. UDP Port 2427  is used for communication between CallContinue reading “MGCP – How it works?”