Mobile Computing – Personal Communication Services (PCS)
- PCS (Personal Communication 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.
(MS-Mobile Station, BS-Base Station, MSC-Mobile Switching Center)
3) Cellular Telephony
AMPS (analog) – Advanced Mobile Phone System
DAMPS – Digital AMPS
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.
- Based on routable address, a trunk is set up.