SDCCH dimensioning for HR environment

Hi
I have problem in understanding how Timing alingnment is done on the abis interface for the Trau frames in UPLINK ,and DOWNLINK direction,for different codec scheme frames(FR,HR,AMR).Can anybody send me a trace of trau frames on abis interface .
with warm regards..
Victor

Half rate
Hello all
Why we use Half rate tech. although it has disadvantage .
in our network we use HR we are going to disable it to know what is the effect of HR on our network.

hello zeus,

ghost rach will trigger allocation of an SDCCH at the BSC side.

the following msg will be sent over abis:
channel required
channel activation
channel activation acknoledge
immediate assignment command

and finally, on the air interface : immediate assignment command, from BTS to the MS (on AGCH).

Ghost RACH increases AGCH load and increase the number of SDCCH allocated by BSC (after the channel required, the BSC books a SDCCH channel)

So ghost rach can also lead to SDCCH congestion.

NO impact on PCH.

Regards.

From the same place ghost are originating from… nobody really knows 🙂

It could be one of the following:
BTS internal equipments generating electromagnetic disturbances
External radars (army for instance)
External electromagnetic devices (alarms systems, remote controls…)
Other network operators (from other countries)
Atmospheric disturbances, and so on…

Favorite answer : generated by the BTS itself…

What is POC ?

so you’re measuring a high SDCCH failure rate on “all” cells, during each hour of a day, every day of a week ?

Is it related to the amount of traffic in your network ? (for instance, during the night, there is no traffic, so you don’t see sdcch failure, do you ?)

If the failures happen all the time, even when there is no traffic, you might be getting some country wide interference (another operator ?).. or possibly some problem with other sites collocated on the same pole (did you co-locate your gsm900 sites with dcs1800 sites ?)

If the failures only happen when TCH traffic is occurring, then you can investigate parameters settings (i’m thinking about timers and repetition of RACH…)

Just giving some leads, about BSS side. I’ve got no knowledge about NSS side.

Regards,
Pix

Hi there,

The power control will not affect your SDCCH assignment success.

Exactly, how much is your “SDCCH ASSIGNMENT FAILURE RATE” ? (in average for your GSM1800 cells)

Regarding other answers, i’ll have to study which timers are used during this phase. To simplify the problem:

your BSC is getting a “CHANNEL REQUIRED”, then sends a “CHANNEL ACTIVATION” to the BTS, then receives a “CHANNEL ACTIVATION ACKNOLEDGMENT”.

Next step : the BSC is sending the IMMEDIATE ASSIGNMENT COMMAND, directly to the MS.

It is at that point that you measure a failure : the MS doesn’t answer the assignment command, or, if it does receive it, it is the BTS that doesn’t receive the SABM from the MS.

If messages are not received, it means either the BTS or the MS stop listening… so there might be a timer expiry. Check T3122 / T3120 / T3101… those are the timers that are quite obvious, but there might be additional timers somewhere… I’ll look for it when i have more time. But i think you can quickly find your answer about timers in the 3GPP documentation.

Check 3GPP TS 04.08 “mobile radio interface layer 3 specifications”, especially the chapter 3.3 “RR connection establishment”.

How can we reduce PCH load, if on complete network how or for a single sector too?