Cisco – Upgrading ASA and ASDM on a ASA5510

Cisco does a fantastic job obscuring this information for some reason. To answer your specific questions:

1. System Version 7.1.5.34900-7 is actually CUCM Version 7.1(5b)SU4. You'll need to download System Version 7.1.5.35901-1 or higher, to get the OS and Application fixes that are found in CUCM Version 7.1(5b)SU6a.
2. I wouldn't go so far as to say that there is always a 1-to-1 relationship between the two formats (CUCM Version vs System Version). However, in my experience, when Cisco releases a new System Version, they also increment the CUCM version number.
3. In older versions of CUCM, there was a much greater disconnect between "OS Fixes" and "CUCM Fixes", which would give you the disparity that Michael Luo describes in the page you linked. However in recent times (post version 7.1 days), all of the recommendations that I have received from Cisco TAC, seem to indicate that the higher the number, the better, period.

The only exceptions that I have encountered, are unreleased "Engineering Special" versions; special releases that are usually only distributed by TAC to fix a very specific and uncommon bug. In the event that you are on an "Unreleased ES" version, you should contact TAC for upgrade support anyway, as there may be undocumented bugs related to upgrading from that version to a normal, mainline release.

The longer answer is that we can piece together a good picture using information from the two sources you linked. They are actually my two "go to" locations for deciphering this information.

First, according to the page you linked from Michael Luo over at UC Corner, we get a picture of how Cisco is structuring the CUCM/Unity Connection/Presence/UCCX build numbers:

On each sub-version, there are also "build-numbers". e.g. 6.1.2.1000, 6.1.2.2000, etc. Build-number is the most confusing part.

Generally speaking, build numbers should increase in 1000, such as 6.1.2.1000, 6.1.2.2000, etc.

CUCM is built on Linux OS. Whenever Cisco release an OS security patch, they'll increase the build number by 1000. This is called PSIRT patch.

Remember CUCM is an application running on Linux. OS patch does not contain any CUCM bug fixes. Any bug fixes would be in ES (Engineering Special). ES versions would be indentified by the last three digits in build numbers (e.g. 6.1.2.1112)

Secondly, from the CUCM Software Compatability Matrix PDF, (sourced from Cisco Support documentation here), we can find a rough guide of what CUCM Version Number matches which System Version number. This has always in my experience proved to be an accurate guide.

For example:

CUCM Version    |    System Version
-----------------------------------
9.1(1a)         |    9.1.1.20000-5
9.1(1)          |    9.1.1.10000-11
9.0(1)          |    9.0.1.10000-37
8.6(2a)SU3      |    8.6.2.23900-10
8.6(2a)SU2      |    8.6.2.22900-9

One thing to add to the things collected is the licensed features (show activation-key detail)

This all depends on the asa model and running version. Some parts will be in the config, others in flash files, and yet others in "private" flash files. The quickest and most complete procedure would be to swap the compact flash. Keep in mind the activation key is stored there as well, so get that from the new system before the swap.

For example, my ASA has webvpn configuration components that aren't in the running config, or visible flash filesystem.

For all models, you'll have to open the case to get the CF. ASA5505, it's along the edge of the board, visible from the outside, but not removable until the cover is lifted. ASA5510/20/... the CF is on a board near the external CF.