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Location Update

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Manoj Singh
Location Update

Hello All,
Can someone plz let me know how exactly the Location update works in SS7 Network ? Please note i am interested in core network only..... means MSC onwards....
Please share the Traces and Messages that is used during Location Update.

Hoping your quick reply......


The UpdateLocation message is

The UpdateLocation message is sent from VLR to HLR when a mobile subscriber moves between VLRs. If you move from VLR1 to VLR2 this is what happens:

VLR2 ------ UpdateLocation ----------> HLR
HLR ------- CancelLocation -----------> VLR1
HLR ------- InsertSubscriberData --> VLR2

Manoj Singh
Location Update

I know if a subscriber moves from MSC/VLR1 to MSC/VLR2, then in Region2, the call flow will be like this :
VLR2---->Update Location----->HLR
HLR ------- >CancelLocation --------> VLR1
HLR -------> InsertSubscriberData --> VLR2

I have few questions :
1)What is the parameter present in Update location message sent by VLR2 to HLR ?
2) How the HLR will came to know the requesting subscriber was in VLR1 earlier ?
3)When Subs moves from one VLR to another VLR then do it have any parameter/info that he can use for requesting Update Location.
4)In case if Subc moves from one Region to another where different HLR is used then how the Location updates works there ?
5) Can i have complete trace that indicates location update procedure.

1- There could be many

1- There could be many parameters available in UpdateLocation request, many of which are optional:
UpdateLocationArg ::= SEQUENCE {
imsi IMSI,
msc-Number [1] ISDN-AddressString,
vlr-Number ISDN-AddressString,
lmsi [10] LMSI OPTIONAL,
extensionContainer ExtensionContainer OPTIONAL,
... ,
vlr-Capability [6] VLR-Capability OPTIONAL,
informPreviousNetworkEntity [11] NULL OPTIONAL,
cs-LCS-NotSupportedByUE [12] NULL OPTIONAL,
v-gmlc-Address [2] GSN-Address OPTIONAL,
add-info [13] ADD-Info OPTIONAL,
pagingArea [14] PagingArea OPTIONAL,
skipSubscriberDataUpdate [15] NULL OPTIONAL
-- The skipSubscriberDataUpdate parameter in the UpdateLocationArg and the ADD-Info
-- structures

The most important parameters which are mandatory and are always available are:

  1. IMSI: Is the IMSI of subscriber who has entered VLR2
  2. VLR: Is the ISDN of VLR2
  3. MSC: Is the ISDN of MSC connected to VLR

Note that VLR and MSC numbers are usually the same.

2- HLR knows that the subsriber is currently in VLR1 (because once the subsriber entered VLR1, VLR1 sent an UpdateLocation to HLR). After subscriber moves to VLR2, an UpdateLocation message is sent to HLR, which changes the current VLR of subscriber to VLR2.

3- Not a clear question to me

4- Note that the HLR with which subscriber communicates will never change. Even if you move to another region (which is called roaming), the visited VLR will contact your home HLR.