Paging and Location Update
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Transcript of Paging and Location Update
Paging and Location Update
By: Abidullah Zarghoon
Some Terms:• MSC/VLR - Mobile Switching Center / Visitor
Location Register
• HLR - Home Location Register
• PLMN - Public Land Mobile Network
• TMSI – Temporary Mobile Subscriber Identity
• LA - Location Area
• LAI - Location Area Identity
• LAC - Location Area Code
• LU – Location Update
• MS - The Mobile Station
• BSS - The Base Station Subsystem
• NSS - The Network Switching Subsystem
• OSS - The Operation Support Subsystem
Overview• A GSM or UMTS network, like all cellular networks, is
basically a radio network of individual cells, known
as base stations.
• Each base station covers a small geographical
area which is part of a uniquely identified location
area.
Location Area• A location area is a set of base stations that are
grouped together to optimize signaling
• Location Area is a group of cells and the subscriber
is paged in this area.
• One or more base station controllers are used to
serve each Location Area but by a single MSC.
• Each Location Area has a unique Location Area
Identity number.
Location Area Update• The mobile station also performs location updating,
in order to indicate its current location, when it
moves to a new Location Area or a different Public
Land Mobile Network (PLMN). This location updating
message is sent to the new MSC/VLR, which gives
the location information to the subscriber's HLR. If
the mobile station is authorized in the new
MSC/VLR, the subscriber's HLR cancels the
registration of the mobile station with the old
MSC/VLR.
Location Update Procedure
• The location update procedure allows a mobile
device to inform the cellular network, whenever it
moves from one location area to the next.
• Mobiles are responsible for detecting location area
codes.
• When mobile finds that location area code is
different from its last update, it performs another
update by sending to the network, a location
update request, together with its previous location
and TMSI (Temporary Mobile Subscriber Identity)
Periodic Location Update• A location updating is also performed periodically.
If after the updating time period, the mobile station
has not registered, it is then deregistered.
• Each mobile is required to regularly report its
location at a set time interval using a periodic
location update.
Random Location Update• Whenever a mobile moves from one location area
to the next while not on a call, a random location
update is required.
• This is also required of a stationary mobile that
reselects coverage from a cell in a different
location area, because of signal fade.
Continued… • When a subscriber is paged in an attempt to deliver
a call or SMS and the subscriber does not reply to
that page then the subscriber is marked as absent
in both the Mobile Switching Center / Visitor
Location Register (MSC/VLR) and the Home
Location Register (HLR) (Mobile not reachable flag
MNRF is set). The next time the mobile performs a
location update the HLR is updated and the mobile
not reachable flag is cleared.
Paging• Paging is the one-to-one communication between
the mobile and the base station
• Paging is a procedure the network uses to find out a
subscriber’s location before actual call
establishment.
• Paging is used to alert the mobile station of an
incoming call.
• Paging is initiated by the NSS (Network Subsystem)
and is based on the Location Registration
information the Mobile Subscriber has supplied
when performing the Location Update.
Paging Strategies• Location Area Splitting in Paging Areas
o Mobile registers only when entering the Location Area; it doesn’t register
when moving between Paging Areas of one Location Area.
o For an incoming call, paging messages are broadcasted in the Paging
Areas according to a sequence determined by different strategies.
Location Area Splitting in Paging Areas
Paging Strategies• Multilayer Location Areas:
o Each mobile is assigned to a given group, and each group is assigned
one or several layers of Location Areas.
o Location Update traffic is distributed over all the cells.
o Multilayer Las solves the problem where Location Update traffic is mainly
concentrated in the cells of the Location Area border.
Multilayer Location Areas:
Differences between Paging and Location Update
• Mobility Management
based on pure Pagingo If a call arrives, terminal is
paged in all cells of the mobile
network
o Location update is not
required
o As paging must be executed
in all cells of the network for
each arriving call/SMS/data-
packet
• high signaling overhead
• high delay in
call/SMS/data-packet
delivery
• Mobility Management
based on pure Location
Update:o Each time the user crosses cell
boundaries a location update
is triggered
o Paging is not required
o As location updates must be
initialized whenever crossing
cell boundaries
• high signaling and
database update
overhead
• high power consumption in
the terminals
• Location Update• Paging
Some Definitions• TMSI:
o The Temporary Mobile Subscriber Identity (TMSI) is a temporary identification number that is used in the GSM network instead of the IMSI
to ensure the privacy of the mobile subscriber
• LAIo A Location Area Identity (LAI) is a globally unique number.
• LACo A Location Area Code (LAC) is only unique in a particular network
• Cell: o Cell is the basic service area: one BTS covers one cell. Each cell is given a
Cell Global Identity (CGI), a number that uniquely identifies the cell.
• MSC/VLR Service Area:o The area covered by one MSC is called the MSC/VLR service area.
• PLMNo The area covered by one network operator is called PLMN. A PLMN can
contain one or more MSCs.
o A network that is established and operated by an administration or by
a recognized operating agency (ROA) for the specific purpose of
providing land mobile telecommunications services to the public
References:• Advances in Network Management
o By Jianguo Ding – 2009