Knowledge Share – the blog (and some voip issues)

People tend to communicate only about their problems in the IT world, something is not working, you email colleague, post on forums and open cases. But if something goes well, no one gets to know. In fact, many of the people that are asking a lot of questions, don’t take the time to get back and grade/update/feedback the answering person. That should not be our IT environment; we should share good things and bad things. Have you ever asked yourselves why? Is it job security? Stressed schedule? Human nature? Cultural patterns? Whatever the reason may be, it’s not a good thing imho. This is why I decided to start a blog, in which I intend to share some of my daily work and some knowledge I have collected during my years in the industry. Only good things I hope, but I’ll share the path it took to get there. Hopefully, others will join and do the same. Enough with that, let’s get down to business, my first entry is dedicated to a customer complain I had to take care of just recently, after deploying a Cisco VoIP solution, where one of the locations had a complaint: “Since changing to the new phone system (Call Manager 6.1) we are getting low volume and echo on our phones”. Audio quality, one of my less favorite issues, why? Because it’s subjective, you can’t just tell someone that the quality is good or that the handset was tested and proved to be fine. No scientific way that can prove it (unless you can afford running PESQ test every time something like that comes up). My first question was with regards to the difference between external and internal calls, to which I got reply that it is not a problem with internal calls. Anything that goes over VoIP is fine; going over the PSTN is not so good. They get low volume even when setting the phone to its maximum volume. The local gateway is a 28xx using FXO lines to the PSTN. My first line of action was to increase the incoming volume from those FXO lines; echo (which is my second problem) is sometimes caused by maximizing the volume so that is an option as well. On voice ports, in a Cisco voice gateway, one can control the incoming volume by changing the ‘input gain’ value to a negative one. That value is set to 0 by default and will increase the volume when set to negative. Ranges are -6 to 14. Here is what I did to implement the changes: Initial input gain value verification (in bold): Voice-GW#sh voice port 0/1/0 Foreign Exchange Office 0/1/0 Slot is 0, Sub-unit is 1, Port is 0 Type of VoicePort is FXO Operation State is DORMANT Administrative State is UP No Interface Down Failure Description is *** Line number XXX *** Noise Regeneration is enabled Non Linear Processing is enabled Non Linear Mute is disabled Non Linear Threshold is -21 dB Music On Hold Threshold is Set to -38 dBm In Gain is Set to 0 dB Out Attenuation is Set to 3 dB Echo Cancellation is enabled Echo Cancellation NLP mute is disabled … Value Change: Voice-GW #conf t Enter configuration commands, one per line. End with CNTL/Z. Voice-GW (config)#voice-p 0/1/0 Voice-GW (config-voiceport)#input gain -5 Change verification: Voice-GW #sh voice port 0/1/0 … In Gain is Set to -5 dB … That specific voice gateway had four FXO ports, so I made sure to apply the changes to all of them. Now comes the time to verify the effectiveness of the solution. Did it work? Since it’s night time I have no one to verify it with, so that will have to wait to next time. Later …