Local calls within the same exchange are routed through the main distribution frame and copper cables directly connecting the users. Local calls between different exchanges are routed from one exchange's main distribution frame through a digital distribution frame and onto the other exchange's main distribution frame. Transit calls between different transit exchanges are routed from one exchange through optical fiber links to other transit exchanges until reaching the destination exchange. International calls between gateway exchanges are routed from one local exchange through transit exchanges and international gateway exchanges connected by submarine cables or satellites.

1. 1

2. PTCL Call Setup
Between Different
Exchanges

3. 3
Local Call Setup within the Same Local
Exchange
MDF LE
User A
User B
DP DC
Distribution
Point
Distribution
Cabinet
Main
Distribution
Frame
Copper
Cable
Local
Exchange

4. 4
Local Call Setup between Different Local
Exchanges
MDF LE DDF
DDFL.E.MDF
Digital
Distribution
Frame
User A
User
B

5. 5
Transit Call Setup between Different
Transit Exchanges
LE
LE
DDF
TE
DDF
Transit
Exchange
(TE)
Optical Fibre
Optical Fibre
TE
TE
DDF
LE
DDF
LE
User A
User B
Transit
Exchange
(TE)

6. 6
International Call Setup between
Gateway Exchanges
LE
LE
DDF
TE
DDF
TE
Optical Fibre
Optical Fibre
TE
TE
DDF
LE
DDF
LE
User A
User B
IGE
DDF
IGE
IGE
IGE
DDF
Submarine
(OF) Cable
Int. Gateway
Ex. (IGE)
Satellite

7. 7
Prepared by:
Tayyab Sher
Contac:
+923017252598
International Islamic University
Islamabad
Supervised by:
Engr. Khalid Sarwar
Contact:
+923135003545
PTCL Satellite Town
Rawalpindi