Lecture 5 Intersystem Operation

1
Lecture 5 Intersystem Operation
2
Basic AMPS

• Gives air interface between tower and mobile
  phone
• Does not provide capability to deliver roaming
  between different service providers
• Why?
• Business arrangement between providers
• Validate the user

3
Initial solutions

• Clearing house database
• Special number (two numbers) system
• Call forwarding by forcing the user to punch
  special numbers whenever the user moves to new
  locations

4
IS-41

• Telecommunications Industry Association (TIA)
  produced a Interim Standard 41.
• IS-41 is open air communications interface
  between a pair of service (AMPS) providers
• IS-41 is a seven layer protocol conforming to the
  OSI model
• Layer 7 and layers 1 thro 4 are used

5
IS-41 reference model
VLR
VLR
EIR
MSC
AC
HLR
BS
CSS
MSC
PSTN
ISDN
AC Authentication center BS Base Station CSS
- User
MSC mobile switching center PSTN public
switched tele. Net VLR visitor location register
EIR Equipment identity register HLR Home
location register ISDN integ. services digital
net
6
Elements of the model

• Two databases (VLR and HLR)
• Though we have functionally different elements,
  they may be in the same location
• Connection between two systems (or MSC) is
  established by two separate lines called
• Voice trunks (transport of user info)
• Data link (signaling)

7
Registration of a user while visiting a new Base
Prior MSC
Prior VLR
Base
HLR
VLR
MSC
Reg. info
store
Reg. notification
store
Reg. notification
Reg. Notification ack
Reg. Notification ack
Reg. cancellation
Remove user
Reg. Cancellation ack
8
Registration of a user while visiting a new Base
Prior MSC
Prior VLR
Base
HLR
VLR
MSC
Reg. cancellation
Remove user
Authenticate user
Reg. Cancellation ack.
Authentication info
User profile?
User profile info
Store profile
9
Call Setup to a roaming subscriber
Home MSC
HLR
VLR
MSC
Base
User
Receive Call
Location request
Route request
Route request
Route info
Route info
Location info
Call setup request (use temp. phone )
Page command
PAGE
Detect MIN
AMPS call setup protocol