- This topic has 15 replies, 1 voice, and was last updated 9 years, 11 months ago by pix.
24th March 2010 at 22:45 #61686Fresh OptGuest
What causes subscriber to be unreachable if I know that subscriber it is located to a cell. After second attempt the subscriber can be reachable. It happens very often. Is it related to paging? If yes, what’s the solution?
Fresh Opt25th March 2010 at 05:04 #61687AliAsgherGuest
Please check whether paging discards are present on the cell.25th March 2010 at 08:28 #61688ipxGuest
the subscriber can only be reached after the 2nd attempt ?
this particular MS only or all MS in the cell ?
all the time, or just once in a while ?
does the MS make a call setup or a location update before you attempt to reach it for the 2nd time ?
what is the delay between the two call attempts ?
can you increase this duration ?
how did you detect this problem, could you please describe the method ?
If a Paging is discarded due to congestion, it is going to be repeated by the MSC. In other terms : if the MSC doesn’t get a Paging Response before a certain timer, it will repeat the Paging 1 or 2 times.
The subscriber is said to be “unreachable”, and it can mean two things :
1/ the first paging is always lost (incl. the repeatitions) and the 2nd paging is always successful. But I don’t think so. Too weird.
2/ the IMSI is not present in the VLR, therefore the MSC doesn’t send the 1st paging : it directly respond to the calling party, saying ‘called party unreachable’. But why would this IMSI becomes attached at the second attempt ?
Well, i must admit, i need more inputs from fresh opt…
pix25th March 2010 at 08:59 #61689AliAsgherGuest
In case paging discards are high on the cell, there is probability that the page is not sent (1st time and repeatition both). I was just assuming this case. Whereas on following attempts may be the page was transmitted and call was through.
Also I don’t think it is possible that the case described (1st time unsuccessful and second time successful) is happening all the time. It must be happening some of the time. Thatswhy I suspected paging getting lost due to high PCH congestion.
I have observed two such cases where
1) In a high rise building MS was reselecting many cells and was continuously doing Location updates. Overshooting of too distant cells was the cause and even sometimes the MS was going into emergency calls.
2) In case MS sends a channel request, then in the time when the channel request is sent and the status of the MS is not registered as dedicated mode, if a page is sent for the MS it will be lost as MS will not respond and also the network does not know that MS is in dedicated mode.25th March 2010 at 10:46 #61690Fresh OptGuest
we were both in the same Location Area. I don’t know were we in the same cell, but we were close to each other. The second MS did some calls, after a while I called him, couldn’t succeed (message: “Subscriber is unreachable..”). After the second try I could call him and it was OK. The place is urban area, very “busy” cells. It not happened only to me, we received many subscriber complaints, that was the reason I posted this issue. It’s strange! Most of cells in the area are not congested, paging load is around 59%. Is it related to paging or some other issues (in NSS for example)?
Fresh Opt25th March 2010 at 11:51 #61691SHELDONGuest
Hi Fresh Opt,
As Pix and AliAsgher pointed out, it MIGHT be a paging problem. You say your paging load is 59%, but what percentage of your pages are discarded?
Also, are all the complaints/experienced coming from the same location? If yes, then it can also be caused by a faulty BCCH TRX (transmitting corrupted paging msgs).
The problem can also be coming from somewhere else, eg the core network, IN, etc. Check the MSC-VLR/HLR signalling to make sure everything’s ok.
SHELDON25th March 2010 at 20:39 #61692Fresh OptGuest
Thanks to you all. I’ll be focusing on paging. And I was thinking to remove some cells from the LAC in order to reduce loading. It’s a city with 2 BSCs and 1 LAC, 190 cells. How can I check paging congestion and discarding? Any counter (vendor Alcatel rel. B9)?
Fresh Opt25th March 2010 at 22:53 #61693pixGuest
do you have a RNO around ?
there are few indicators to check the paging load.26th March 2010 at 09:12 #61694Fresh OptGuest
Yes, we have RNO. I can see paging load but not paging congestion.
And loading is 59%.
Fresh Opt26th March 2010 at 10:02 #61695GuruGuest
There is a chance of getting ” not reachable” if the MS is located in a LAC boundary.14th April 2010 at 20:58 #61696Fresh OptGuest
I found that subscribers which are connected to GPRS can’t be paged. How is it possible that, it shouldn’t. Any suggestions?
Regards,15th April 2010 at 07:46 #61697Fresh OptGuest
Anyone? Could GPRS cause paging discards?15th April 2010 at 09:44 #61698SHELDONGuest
Hi Fresh Opt,
I would say GPRS CAN lead to paging discards, but in my opinion, the effect of GPRS on paging discards will be minimal. I say CAN because if you’re using combined procedures for both CS and PS paging, then it’s possible some CS pages will be discarded when the paging queue is full (due to many PS pages). I hope we’re on the same page regarding ‘paging discards’.
The ability or otherwise to page subscribers connected to GPRS depends on several factors.
1. Your GPRS network operation mode( mode III is required to be able to have concurrent PS and CS connections)
2. MS capabilities (CLASS A and B MSs can engage in both PS and CS connections at the same time)
3. The MS’s GPRS MM state
Let me elaborate a little on 3: For an ordinary MS which is GPRS ‘connected’, the ability or otherwise to page it depends on the current MM state. If the MS is engaging in packet transfer(READY state), then it can’t monitor the paging channel, thus it can’t respond to pages. However, if the MS is in standby or Idle state, it can respond to pages.
SHELDON15th April 2010 at 12:02 #61699Fresh OptGuest
as I find out subscribers connected to GPRS they often use GPS navigation with Google map. So, for sure it’s the case under 3 you described. We use network operation mode II. Do you think is normal in these conditions we have?
Thank you for your answers.
Fresh Opt17th November 2011 at 08:40 #61700ArifGuest
Hi Fresh Opt,
We have the identical problem in our network as well. We have Gs interface, i.e. MTC can be done during upload or download state.
Is the problem of yours solved? Please share the info.