1) Overview

mobile_computing_pcs


  • PCS (Personal┬áCommunication Services) is a general term for a variety of voice, data & multimedia services. (GSM is a kind of PCS system)
  • Such a Personal Communication Service can be accessed at any time, place or form (They are mobile/portable/ubiquitous).
  • PCS lays the foundation architecture. GSM & GPRS build upon & extend the PCS architecture to achieve new functionality.

2) Architecture

pcs_architecture

(MS-Mobile Station, BS-Base Station, MSC-Mobile Switching Center)


3) Cellular Telephony

AMPS (analog) – Advanced Mobile Phone System
DAMPS – Digital AMPS

pcs_cellular_telephony_networks

4) Mobility Management

  • It is a measure of the performance of the PCS system.
  • Uses the database registers HLR & VLR for home & visitor location respectively.

Handoff - when you switch between two Base Stations but you are in the same area(say, within Delhi).

If the old and new Base Stations are a part of the same MSC, it is called inter-BS or Inter-cell.
If the old & new BS are from different MSC’s, it is inter-system or inter-MSC handoff.

Methods of Handoff Detection :

MCHO – MS monitors signal from BS continuously & initiates handoff when criteria is met.
MAHO – MS monitors signal when asked to do so by the network.
NCHO – BS monitors signal from MS.


Roaming- When you move from one area to another.(say, from Delhi to Harayana).

a) Registration Steps:

  • VLR informs HLR about current user location.
  • HLR sends acknowledgement (including the MS profile stored in HLR) to VLR
  • VLR informs MS of succesful registration (Welcome to Harayana!)
  • HLR sends de-registration msg to old VLR
  • Old VLR acknowledges de-registration.

b) Call Delivery Steps:

  • Query to get routable address passes from the PSTN to HLR to VLR.
  • The VLR returns the routable address from VLR to HLR to PSTN.
  • ┬áBased on routable address, a trunk is set up.

SEE ALSO Fundamentals Of Computer Networks