Scenario#41 – No Ringback tone from H323 Gateway going to SIP trunk

One of our customer reported an issue with ring back tone when calling their Contact center. I made a test call and observed that as a caller when you call their main Contact center number all you hear is dead silence and then when agent picks up the phone you could hear them talk. There was no ring back tone and no automated messages before an agent picks up the call. The call flow was something like this: PSTN > ISDN30 > H323 Dial-peer > SIP Trunk > 3rd-party Contact Center Equipment First I thought it could be the third-party … Continue reading Scenario#41 – No Ringback tone from H323 Gateway going to SIP trunk

Scenario#32 – SIP Calls drop after 75 minutes

I had an interesting case where SIP calls over a SIP trunk were dropping after like 75 minutes. The duration was not confirmed as sometimes it use to drop even before 75 minutes. I looked into few CCSIP debugs (debug ccsip messages) and found that the ‘BYE’ message was actually coming from our end (Call manager/Gateway). Platform information: CCM: System version: CUBE-10#sh ver Cisco IOS Software, 3800 Software (C3825-ADVIPSERVICESK9-M), Version 12.4(24)T4, RELEASE SOFTWARE (fc2) Technical Support: Copyright (c) 1986-2010 by Cisco Systems, Inc. Compiled Fri 03-Sep-10 09:15 by prod_rel_team ROM: System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1) CUBE-10 … Continue reading Scenario#32 – SIP Calls drop after 75 minutes

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 match ip precedence 3 match ip dscp af31 match access-group name voice-signal ! ip access-list extended voice-signal permit tcp any any range 2000 2002 permit udp any any eq 2427 permit tcp any any eq 2428 permit tcp any any eq 1720 permit tcp any any … Continue reading Applying QoS for Voice Traffic

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