SDCCH Mean Holding Time

What is the value measured ??

Hi Rala,

The average BSC value is 4.5 to 5s. It means that within this BSC, some cell might actually have up to 8 or 9 seconds SDCCH MHT. Can you confirm ?

If that’s the case, you should check the split of SDCCH causes : do you see a lot of SMS ? SMS requires more time to be transmitted than a call setup.

Do you measure a lot of SDCCH drop ? When the radiolink between MS and BTS is broken, the time to detect a SDCCH drop is about 9 seconds.
During these 9 seconds, the SDCCH is still active. Therefore, if you see a lot of drops, it can also cause a long MHT.

Typical cell value ranges from 3 seconds to 5 seconds (and more if there are a lot of SMS’s)

Regards,
Pix

No i don’t think so… reducing the LA size will decrease the Paging load, and increase the amount of location updates. But the LU duration is about 3 or 4 seconds (AFAIK), and that’s already your average. Mathematically, it doesn’t make sense 🙂

Location Area should be as big as your Paging capacity allows.

Really, have a look cell per cell (what’s max MHT per cell ?) and split the sdcch cause. The location area is probably not the problem, that’s why I didn’t include it in my previous post.

Rala,

PCH load and SDCCH load… it’s not related, theoretically. Those are two distinct physical channels, carrying data from different processes (Paging : broadcasted DL “ping” of a subscriber, SDCCH : dedicated channel for call setup, LU, SMS, etc.).

I can imagine that if the BTS has an overloaded CPU, because it’s trying to manage too many pagings, it might delay all processes including the SDCCH phase.

any other idea why ??

One more thing that I see after split the LAC is the Location update in the cell that have the SDCCH MHT decreased is very high.

How long time the location update use the SDCCH channel when compare to the others(MOC, MTC)? Is it shorter?
(If it is shorter it might be the cause of the SDCCH MHT decreasing.)

Regards,

Dear Pix,
In your point of view,
if the LU requires SDCCH = 3 s.,
how about the call set up?

I try to find out these time from TEMS, the time from “Immediate Assignment request” to “Immediate Assignment complete” of call set up and LU is about 2 s..

Regards,

Rala,

This is not SDCCH DURATION !!

SDCCH duration starts at IMMEDIATE ASGNMENT COMMAND and finishes when the SDCCH is released (switch to TCH, end of location update request, end of SMS, drop, etc…)