Problem SD congestion -> High location Area updates

[kyokuman]

Hi Guys,

I have question regarding Location Area Update in 2G.

When MS entering in new cell with different LAC, it initiates LA update through Channel Request.
If there is SD congestion at this moment, BSC sends IMM Assignment REJECT.

MS will wait T3122 (generally 10s), and tries again.

However, it can try max 4 attempts (max retransmission parameter)

If no success, Location Area update is terminated.

What happens next ? When MS will try again the LAC update?

Thanks for your help !

[zlobster]

Hi Guys,

I have question regarding Location Area Update in 2G.

When MS entering in new cell with different LAC, it initiates LA update through Channel Request.
If there is SD congestion at this moment, BSC sends IMM Assignment REJECT.

MS will wait T3122 (generally 10s), and tries again.

However, it can try max 4 attempts (max retransmission parameter)

If no success, Location Area update is terminated.

What happens next ? When MS will try again the LAC update?

Thanks for your help !

MS will continue trying LAU untill:

-it finds a better cell from different LA or
-its battery dies :lol

BTW, I think the max. retran. rate is for the max. number of RACH requests the MS shall send if no IMMEDIATE_ASSIGNMENT is received (being even a REJECT).

GSM 04.08 - 3.3.1.1: request for resources by the MS
GSM 04.08 - 10.5.2.17
GSM 05.08 - 6.6.2 : cell reselection
GSM 12.20 - 5.2.8.7: max number of retransmisions

[kyokuman]

Hi,

Thanks for answer !!1

However, If Max Retrans is reached, How the MS can keep initiating Location Update ?

MS requests LA update through Channel request, isnt it ?

[leteo]

Hi Guys,

I have question regarding Location Area Update in 2G.

When MS entering in new cell with different LAC, it initiates LA update through Channel Request.
If there is SD congestion at this moment, BSC sends IMM Assignment REJECT.

MS will wait T3122 (generally 10s), and tries again.

However, it can try max 4 attempts (max retransmission parameter)

If no success, Location Area update is terminated.

What happens next ? When MS will try again the LAC update?

Thanks for your help !

It will come back to Idle mode and try again.
Refer to this doc :lol :handshake

[zlobster]

The max_retran is the max number of RACH (channel requests), not the maximum number of retries for successful LA update.

Something like this:
MS------RACH------> BTS
MS<........................ BTS
MS------RACH------> BTS
MS<........................ BTS
MS------RACH------> BTS
MS<........................ BTS
MS------RACH------> BTS
MS<........................ BTS

now max_retran expires, e.g. the MS cannot hear the IMMEDIATE ASSIGNMENT from the network.

[kyokuman]

Ok, I see now.

But how long MS is waiting before re-seding RACH?

[zlobster]

Ok, I see now.

But how long MS is waiting before re-seding RACH?

T3101 - GSM 04.08

It will wait T3101 seconds...

[kyokuman]

Hi,

Thats strange, because for me

T3101 is a timer for the BSC waiting for an Establish Indication message after sending an Immediate Assignment message. If T3101 expires before the BSC receives an Establish Indication message, the BSS releases the seized SDCCH.

[mohyedeen_alkousy]

you have two scenarios
1. if the cell have congestion in SDCCH and the BSC cannot assign SDCCH for the MS, in that case the BSC will send immediate assignment reject to MS and the MS will wait for some time (T3122 wait indication timer)
before MS tries again and this scenario will repeat itself.

2.if the cell have quality problems that prevent mobile from receiving the immediate assignment command or prevent the BTS from receiving the channel request then the mobile will tries channel request again (according to the parameter maximum retransmission usually 4 times) after that the mobile station will make cell reselection immediatly to another cell and tried channel request again.

[kyokuman]

Thanks everybody, but my question was :

What is the time between 2 consecutive restranmissions ?


And the answer is not T3101 but Tx-integer !


You agree?

[mohyedeen_alkousy]

it's not fixed time its random to avoid RACH collisions

[kyokuman]

So, WHAT decides to send RACH retransmission and WHEN ?

[kyokuman]

"
After initiating the immediate assignment procedure, the MS always listens to the BCCH and the corresponding CCCH. If the MS does not receive the Immediate Assignment Command message or Immediate Assignment Extended message, it resends the Channel Request message at a specified interval. When the number of times that the Channel Request message is resent exceeds MSMAXRETRAN, the immediate assignment procedure fails. "


What means this "specified interval" ?:(:handshake

[zlobster]

Hi,

Thats strange, because for me

T3101 is a timer for the BSC waiting for an Establish Indication message after sending an Immediate Assignment message. If T3101 expires before the BSC receives an Establish Indication message, the BSS releases the seized SDCCH.

Yep, my bad... :mad:

It's really the time BSS waits for seizure of the SDCCH after it has been granted to the MS...

AFAIK... The MS will try the next RACH attempt at random. This is made in order to avoid re-occurring conflicts from 2 (EDIT: or more) different MS trying to access the system simultaneously (ALOHA method).

[kyokuman]

Thanks to All !

I believe I have all info I needed ! :handshake:D:victory:;)

[zlobster]

Ahh, glad we were able to help you! :victory:

Too bad most of the ppl doesn't ever read the other ppl's signatures... :rolleyes:

The road to Forbidden City (http://www.finetopix.com/forbidden-city/) is long and treacherous. But it begins with small rep. :victory:

[cuzmulder]

Hi,
scenario #3:
do you know happens when PGCH from network is received at MS but response from MS not received at BTS because unbalanced radio link? Will MS tries channel request again until reach maximum retransmission limit and then stop?

Thank you for answer!


you have two scenarios
1. if the cell have congestion in SDCCH and the BSC cannot assign SDCCH for the MS, in that case the BSC will send immediate assignment reject to MS and the MS will wait for some time (T3122 wait indication timer)
before MS tries again and this scenario will repeat itself.

2.if the cell have quality problems that prevent mobile from receiving the immediate assignment command or prevent the BTS from receiving the channel request then the mobile will tries channel request again (according to the parameter maximum retransmission usually 4 times) after that the mobile station will make cell reselection immediatly to another cell and tried channel request again.