Scenario#24 – SIP Calls drop after Silence

Came across a complex situation where customer was using this SIP trunk as an alternative to ISDN-30 (if all channels are used or if ISDN goes down). The ISDN-30 link was working fine but they had issues on SIP trunk (how many times I have heard this?) …. their outbound calls over SIP were using a prefix ‘8’ to route calls on SIP trunk to SIP Provider. The Outbound calls were working fine. The inbound calls drop after 8 secs and none of the calling/called party could hear each other. Complete silence.. Call flow was something like this: PSTN (81763)  … Continue reading Scenario#24 – SIP Calls drop after Silence

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. DSP stands for Digital Signal Processor; it is a generic Industry terminology. A PVDM module could be staffed with one or multiple DSPs. PVDM2-8 = 8ch (G), 4ch (H), 4ch (M) PVDM2-16 = 16ch (G), 6ch (H), 8ch (M) PVDM2-32 = 32ch (G), 12ch (H), … Continue reading DSP, PVDM & Media Resources

Scenario#22 – ISDN user busy 0x8091

This was an interesting scenario where incoming calls were getting ‘user busy’ message at the gateway and an engage tone was heard at calling party side. *Aug 18 08:36:53.581: ISDN Se0/0/0:15 Q931: RX <-CALL_PROC pd = 8  callref = 0x8D7E Channel ID i = 0xA9839E Exclusive, Channel 30 *Aug 18 08:36:54.997: ISDN Se0/0/0:15 Q931: RX <- DISCONNECT pd = 8  callref = 0x8D7E Cause i = 0x8091 -User busy It was not just one extension but several extensions which were having the same issue. They were all running fine till yesterday! Something must have happened… I did debug voip ccapi … Continue reading Scenario#22 – ISDN user busy 0x8091

Troubleshooting Ringback Issues H323

Before we dive into troublehsooting let’s keep the following in mind when an ISDN call progress. If A is making a call to B so A is calling party and B is called party. The ISDN messages negotiated between the two would be as follows: A —-> Setup —-> B B —-> Call Proceeding —-> A B —-> Alerting —-> A B —-> Connect —-> A H.225 is a protocol specified by H.323 for call signaling and call setup. H.225 specifies the use and support of Q.931. The messages we usually hear “Number you dial is not recognized” or “The … Continue reading Troubleshooting Ringback Issues H323

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 > NTP server Is there any NTP Server? If there is an IP address mentioned then try to Ping that IP from OS Admin > Services > Ping Most of the time customers add the CUCM IP address as NTP address. This is not correct. Under … Continue reading Scenario#10 – Phones showing Incorrect time

Blocking Incoming Calls using Translation rule

How to block an incoming number on an H323 gateway? For an MGCP gateway this is not possible as CUCM cannot block incoming calls. Configure the following to block calls from 08009782222. Voice translation-rule 400 rule 1 reject /08009782222/ Voice translation-profile BLOCK translate calling 400 dialpeer voice 1 pots incoming called-number . call-block translation-profile incoming BLOCK call-block disconnect-cause incoming call-reject Continue reading Blocking Incoming Calls using Translation rule

H323 Dial Peer made simple

H323 dial peers play an important role in Call routing though a H323 gateway. Understanding dial peers is very crucial for Call routing or any dial plan design. Most of the time people are confused between POTS and VoIP dialpeers and how they should be used. I will try to make the concept as easy as possible to better understand the working of H323 protocol. There are mainly two types of dial peers. The POTS (Plain old Telephony System) and the VoIP dialpeer (Voice over IP). There are two more VoFr and VoATM but they are not widely used and … Continue reading H323 Dial Peer made simple