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Country Border Roaming Issue

Viewing 15 posts - 1 through 15 (of 37 total)
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  • #51636 Reply
    jean
    Guest

    Hi guys,

    Good day. Our network has been facing this problem since quite some time ago. Subs are complaining that they MS will roaming to neighbouring country’s network without knowing it. I am from RF planning and is there any way to slove or at least minimize the problem from RF point of view??

    There was a theory that if the my RxLev is 30dB higher than neighbouring country’s network RxLev, it will force the MS to roam into my network. Its call “saturation”. How true is this remark??

    Million thanks.

    #51637 Reply
    Outcast
    Guest

    Hi. If your bts signal higher it will work. Are you sure about signal straight in all state line?
    And one more solution is to restrict roaming in such netwoks, if ypu have roaming ageements.

    #51638 Reply
    paraHO
    Guest

    jean why not put neighbouring country networks in SIM FPLMN (Forbidden List) and update.

    As Outcast said – If you don’t have international roaming agreement the other networks don’t get paid, so may not carry traffic from your subs by barring them.

    Only comment I make about BTS signal higher, your network could get subs from roaming networks at borderand you not get paid and may need to bar.

    #51639 Reply
    Pix
    Guest

    To avoid sending your subs to foreign network, i guess you could decrease your RXLEV ACCESS MIN to the minimal value.

    I assume that could work ? As long as your BTS provides a sufficient RXLEV.

    The MS will temporary and repeatedy try to join it home network if available (i.e. rxlev(home) > RXLEV ACCESS MIN)

    The timer is about 30 minutes, if not mistaken (it’s an internal MS timer)

    Regarding forbidding network… it can be applied only on new SIM’s, yeah ? You can’t update an SIM card through the Um interface, can you ?

    #51640 Reply
    Pan
    Guest

    Dear Jean!
    This is not true, because, if there are at least one suitable cell in the neighbouring country’s network and MS was registered in this network, then MS will don’t attempts to select its Home network. The Home PLMN searching timer is active only when MS was registered in HPLMN country.
    You must to improve the coverage of your network (by any means) to avoid MS to camp on cell that belongs to foreign network.
    To ParaHO:
    In GSM SIM the VPLMN is added in Forbidden PLMN List only if “Plmn not allowed” message is recieved by an MS in responce to on Loc_Upd request from a VPLMN. No another way to doing this. Perhaps there is capability to update this list by HPLMN operator via OTA in UMTS SIM.

    #51641 Reply
    jean
    Guest

    Thanks guys.. its has been a great help. I will keep your answers as my reference. Thanks again

    #51642 Reply
    paraHO
    Guest

    Pix, my friend, rarely do I find you mistaken and I think you are correct here too:

    “The timer is about 30 minutes, if not mistaken (it’s an internal MS timer)”

    See GSM 02.11 version 7.0.1 Release 1998 (ETSI TS 100 921 V7.0.1 (1999-07))

    3.2.2.5 Timer for return to HPLMN
    If the MS in Automatic Mode has selected and registered on a VPLMN of its home country, it shall make periodic attempts to return to its HPLMN.

    The interval between attempts shall be stored in the SIM. Only the service provider shall be able to set the timer value. The timer shall have a value between 6 minutes and 8 hours, with a step size of 6 minutes. One value shall be designated to indicate that no periodic attempts shall be made.

    In the absence of a permitted value in the SIM, or the SIM is phase 1 and therefore does not contain the datafield, then a default value of 30 minutes, shall be used by the MS.

    NOTE: Use of values less than 30 minutes may result in excessive ME battery drain.

    #51643 Reply
    paraHO
    Guest

    Pan, you said

    “To ParaHO:
    In GSM SIM the VPLMN is added in Forbidden PLMN List only if “Plmn not allowed” message is recieved by an MS in responce to on Loc_Upd request from a VPLMN. No another way to doing this. Perhaps there is capability to update this list by HPLMN operator via OTA in UMTS SIM.”

    You make go point Pan. However, I not think it follows that in SIM EF PLMNsel that all roaming networks will be listed there also. So when MS attempts to Loc_Upd request to VPLMN – no roaming agreement for MCC/MNC, barred message is sent and VPLMN MCC/MNC is updated to the FPLMN.

    You make good point about which OTA and USIM and I agree with you. The old GSM SIMs used type of silicon that only allow for Masked ROM and OTA was directed toward SMS using GSM SIM specific alphabet. So direct updating of EF PLMNsel didn’t happen as far as I know. USIMs use latest silicon and use flash technology allowing for instance OTA updates to many memory areas in (a) USIM module or (b) GSM module.

    #51644 Reply
    pix
    Guest

    paraHO,

    i’ve heard about this timer on this forum, few months ago :)) thanks for finding the 3GPP.

    paraHO, Pan,

    it looks like, as Pan said, the periodical attempt for returingin in HPLMN is done only if MS is in the home country. If Ms is attached on a VPLMN from another country, it’ss not try to return back home.

    So, it is like this :
    .. The MS on the border measures both HPLMN and VPLMN.

    .. Because HPLMN is the favourite PLMN, as long as RxLev(home) > RXLEV ACCESS MIN, the MS is camping on HPLMN.

    .. Only if the coverage of HPLMN is lost (RxLev < RXLEV ACCESS MIN), the MS will try to reselect a cell from a VPLMN (and in your case, a VPLMN from another operator). .. When a MS is on the VPLMN from another country, it doesn't try to return to HPLMN. .. Barring the neighbor network at MSC level is probably a bit tough : there are probably roaming agreements. And it'll penalyse travellers... --> Is this correct ?

    Then two solutions :
    1- ensure good coverage level and set RXLEV ACCESS MIN to -110dBm
    2- tell your subscribers to manually select your network, so they won’t try to go to the VPLMN by themselves. (on my phone, if a change of PLMN occurs, MS asks me to choose the new PLMN)

    –> Agree ? Any additional solutions ?

    #51645 Reply
    paraHO
    Guest

    Pix

    “If Ms is attached on a VPLMN from another country, it’ss not try to return back home.”

    1) Unless of course the mobile switches off and then on then it will check for HPLMN
    2) or as this a border case with neighbour VPLMN what happens with handover. MS usually detect 7 (one cammped and 6 neighbours). If MS moving toward HPLMN from VPLMN then MS likely to detect HPLMN cells.
    3) Or the MS timer wont impact for non-registered or even registered MCC/MNC in EF PLMNsel being barred..

    You give good suggestion to set the backstop to -110dBm. What if VPLMN neighbours do the same? Will you get ping-pong?

    You also say tell subs to manually select. This good idea too, but subs get angry if they have constantly manually select, particularly if manually select is permanently required where they “live” or “work” because the subs are near the border of VPLMN.

    I can see alot of MS battery drain going on and re-charging needed.

    In border cases – either operators agree roaming agreement costs or they create a regional IMSIs/TMSIs database where MSC bars calls for subs on or near border VPLMN networks.

    It would be useful if jean says how many subs involved with his problem?

    #51646 Reply
    pix
    Guest

    paraho,

    1) ok
    2) not ok : the cells that are neighbors in idle mode are described in the system information message. The MS cannot reselect a BCCH that’s not in the SI2 (or SI5 ? i always mistake). If the MS is in VPLMN, it’ll stay there, until rxlev(vPLMN) goes below RXLEV ACCESS MIN(vPLMN)
    3) out of my competency : i don’t understand 🙂

    ping-pong : no. as long as the RXLEV(hPLMN) above the RXLEV ACCESS MIN, it will not try to find another PLMN. It doesn’t even measure the vPLMN.

    One more question : if a BCCH in the SI2 is the same as the BCCH of a vPLMN cell, can the cell mistakenly reselect the other vPLMN neighbor cell ? I would say “no”.. but i’m not sure. Any idea ?

    #51647 Reply
    paraHO
    Guest

    Pix, I like your response but have query…

    “2) not ok : the cells that are neighbors in idle mode are described in the system information message. The MS cannot reselect a BCCH that’s not in the SI2 (or SI5 ? i always mistake). If the MS is in VPLMN, it’ll stay there, until rxlev(vPLMN) goes below RXLEV ACCESS MIN(vPLMN)”

    Isn’t there a problem with that? If jean’s subs were in HPLMN why then would they stray to VPLMN. Surely, the subs will remain in HPLMN using your example?

    3) Pix no worries about this one. What I meant was if MS timer for HPLMN not relevant and the MS simply selected MCC/MNC where there is no roaming agreement then VPLMN/HPLMN could bar access as it wouldn’t get paid, hence FPLMN would be updated.

    Pix you said
    “one more question : if a BCCH in the SI2 is the same as the BCCH of a vPLMN cell, can the cell mistakenly reselect the other vPLMN neighbor cell ? I would say “no”.. but i’m not sure. Any idea ?”

    I would say in SI2 the answer is yes. This is exactly what happens on the South East Coast of England (UK) where MS can detect BCCH of HPLMN and then show same BCCH of VPLMN from operator in France. Its a commercial game operators play to entice revenue… its big business… to get dedicated mode traffic and control using SI5. This example fails with dropped calls due to quality, TA etc etc

    BTW – I have screen prints of MS which is subscriber on the T-Mobile network where T-Mobile coverage get so bad at fringe coverage that MS goes into re-scan and MS show O2 or Vodafone as serving radio coverage. This is in rural area, but can be like border areas. However, as no roaming agreement the MS not make chargeable calls but could use competitive coverage for emergency calls.

    #51648 Reply
    Pan
    Guest

    Dears Pix, ParaHo.
    ParaHo, thank you for your comments. As many heads, as many wits:)
    I have some corrections to your post. The only thing that will force MS to select HPLMN from VPLMN Foreign country is suitable cell absence in VPLMN. Suitable cell definition – see GSM 03.22.
    Now – in order of appearing:
    \\\\\\”1) Unless of course the mobile switches off and then on then it will check for HPLMN”\\\\\
    No, no, no. Since after mobile switch off/on it shall search for Last Registered Network (i.e. VPLMN) – not HPLMN (GSM 03.22).
    2)I agree with Pix (“until rxlev(vPLMN) goes below RXLEV ACCESS MIN(vPLMN)” – the basic but not the only criterion of cell suitability) Only manually selection (if suitable cell available in VPLMN Foreign Country)
    \\\\\”3) Or the MS timer wont impact for non-registered or even registered MCC/MNC in EF PLMNsel being barred”\\\\\
    I don’t understand this sentenses too.
    EF FPLMN (Forbidden PLMNs)and EF PLMNsel (PLMN selector) – are different elementary files on sim. They have different functions.
    EF PLMNsel defines the preferred PLMNs of the user in priority order (user PLMN preferences, as he want) This list have influence on PLMN selection order during PLMN selection procedure (see GSM 3.22 for more details).

    #51649 Reply
    Pan
    Guest

    To Pix:
    “one more question : if a BCCH in the SI2 is the same as the BCCH of a vPLMN cell, can the cell mistakenly reselect the other vPLMN neighbor cell ? I would say “no”.. but i’m not sure. Any idea ?”
    I think, that BSIC (BCC and NCC) must be used for avoiding this problem. As it is said in 03.002:”…care should be taken to ensure that the same NCC is not used in adjacent PLMNs which may use the same BCCH carrier frequencies in neighbouring areas”
    with regards

    #51650 Reply
    Bilal
    Guest

    I think Pan is right about Same BCCH but different BSIC case. A cell is identified by the BCCH-BSIC combination not the BCCH only. MS is idle mode needs to decode the BSIC of neighbor cell at least once in 30 seconds to ensure that it is monitoring the same cell. If BSIC is different then it will be regarded as a new cell and then MS will decode the BCCH SIs to find out that this cell belongs to vPLMN so no reselection to the cell till every hPLMN cell becomes unavailable.

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