SIP Early Offer vs Delayed Offer

The most visited page in my blog is CUCM SIP Trunk to ITSP connection. From time to time my readers and students ask me to explain what the difference between the Early Offer and Delayed Offer in the SIP signaling is. Let's say your ITSP want you to use SIP signaling with Early Offer in the SIP Trunk. How can you be sure, that your SIP trunk really works in Early Offer mode?

Firmware Upgrade for Cisco IP Phones (CUCM)

Good morning!

I wanted to write this post long ago, however I was extremely busy and did not get around to take the required screenshots. And when preparing for the next course, I had to upgrade the firmware on our lab phones. So it became possible to write about what needs to be done on CUCM to update / change firmware. The procedure is quite simple.

About troubleshooting poor voice quality issue when calling from Cisco Jabber clients

Good morning!

A couple of weeks ago, I was troubleshooting a problem with poor voice quality when calling from Cisco Jabber software clients. The customer's VoIP network covered several offices in different cities, CUCM 8.6 and СUP 8.6 were used. In general, there were about 1,500 users in their enterprise telephone network, and more than a thousand of them did not have Cisco hardware phones and called each other using Cisco Jabber.

The problem was that when calling from Cisco Jabber, users complained about poor voice quality, namely, interruption of speech, gaps, etc, while words and phrases were sometimes completely unintelligible. Moreover, the problem was present even when making calls within the LAN! Usually, this phenomenon is associated with network problems - a large percentage of voice packet losses. And the reason for the loss of voice packets could be a high jitter value, incorrectly configured queues on routers, insufficient bandwidth, enabled VAD, and the wrong choice of codec.

Cisco IP Phone Background Images (CUCM)

Good evening, colleagues!

Today I'd like to tell you about how to install and change the background images of Cisco IP phones. This process is very well described in the phone Administration Guides, but I would still like to make some generalization for the most commonly used phone models and show the process itself using the example of installing a background image for the Cisco 7965 phone on the CUCM server.

Cisco 7911 Phone Bug When Updating Its Firmware

Good afternoon, 

At the CIPT1 course I am currently teaching in Almaty, one of the participants asked me to help with a problem, related to the Cisco 7911 phone. The phone refused to accept new software (the TFTP server had SCCP 9.2.3 firmware, CUCME v7.0 was used as the TFTP server). There was a message there on phone display, saying "Upgrading" along with the MAC address of the phone. The student brought the second 7911 phone and it also behaved exactly the same way as the first one. 

How to register SIP third-party phones on Cisco Call Manager Express (CUCME)

Good day! :)

After another business trip to the branch, I can’t sleep in the morning :( - a 3-hour time difference affects, and I decided not to waste time and write a new post. It will tell you how to register a third-party SIP phone on Call Manager Express (hereinafter referred to as CUCME As you know, at present, many manufacturers produce phones that operate using the SIP protocol, and therefore you can find a wide variety of them: both software and hardware.