The Telephone Network
Chapter 3
Basic Call Processing
Call
Request
Call
Accepted
Conversation
Starts
TALKING
Time
Call
Termination
Global Telephone Network
Local
Exchg
sw
Digital
Loop
Carrier
Satellite
Global Telephone
Network
Radio
Links
United States
Microwave
Trunk
832
Local Exchange
(Exchange
Switch)
Trunk
Relay Tower
Trunk
Local Exchange
(Exchange
Switch)
DLC
(Digital Loop
Carrier)
Twisted
Pair
860-832-2321
Main
Switch
Telephone
RJ-11
(Telephone
Socket)
860-832-2941
Fax
860-832-2321
Undersea Fiber
v
v
International
Exchange
Across the oceasn
v
Main Exchange
860
T1/Twisted Pair
v
v
International
Exchange
Exchange
Local
Switch
Exchange
Tandem
Sw
Int.
Exchg
SW
Germany
Network Basics

Components




Technology: type of the circuit established on the trunk



Analog: FDM
Digital: TDM, T-Carriers
Basic Switching technology


Trunk: connection between central offices
Local Office/Switch: Receives and route call requests; connected to the
customer
Tandem Office/Switch: Receives and routes call requests; connected to
another office
Digital (TDM based) / Analog
Routing: can be Intra or Inter-company


To a customer on the same switch
To another tandem switch
T-Carrier Trunks
Basic Call Routing
Tandem
Office
The local switch
can route the
request three
different ways:
Customer
(Intra/Inter Company)
Shared
Trunk
Exchange Switch
214-403-4433
Local
Office
Local
Office
Customer
Tandem
Switch
Customer
Local
Switch
Definitions

Tandem Switch


Trunk




Local Exchange Carrier
ILEC



Local Access Transport Area
161 LATA have been defined covering the US, 1981
Different companies can have point of present (POP) in different LATAs
LEC


Connection between two offices - a trunk is often shared between multiple
users
LATA


An intermediary switch connected to another switch
Incumbent Local Exchange Carrier
Refers to 7 RBOCs companies
CLEC

Competitive Local Exchange Carrier
More Definitions

Telco


FG-D




short form for telephone company. Sometimes it means a local
telephone company, such as a Bell operating company or an
independent local telephone company.
Featured Group D - A protocol which defines interconnection rules
between a local exchange carrier (LEC) and an inter-exchange
carrier (IEC) such as MCI or Sprint.
Also known as equal access because it guarantees that all carriers
are processed equally.
It is also referred to the trunk connection
Inter-exchange carrier (IEC or IXC)


A telephone company that provides connections between local
exchanges in different geographic areas.
They're commonly referred to as "long-distance carriers." IXCs
include AT&T, MCI, Sprint, and others.
Inter-Company Routing
Tandem
Switch
Tandem
Long Distance
DLC: Digital Loop Carrier –
multiplexing channels
Shared
Trunk
POT: Plane OLD Telephone/
Or Point of Termination
End office
Switch
All wires belong to ILEC
ILEC
CLEC
DLC
POT
u
Long Distance Routing
Different LATA/Diff. Company
Trunk
ILEC
DLC
u
Toll/
Tandem
SW
Featured
Group D Trunk
IXC
LD SW
Tandem
Long
Distance
Network
Inter-exchange
Long Distance
SW
IXC
LD SW
Local
Office
IXC: Inter Exchange Carrier –
must have a point of presence
in LATA
IMT
(DS3/SONET)
IMT: Inter Machine Trunks
provided by IXC
Long Distance Routing
Different LATA/Diff. Company
Trunk
ILEC
DLC
u
Toll/
Tandem
SW
Featured
Group D Trunk
IXC
LD SW
Tandem
Int/LD
Distance
Network
Inter-exchange
Long Distance
SW
IXC
LD SW
Local
Office
IXC: Inter Exchange Carrier –
must have a point of presence
in LATA
IMT
(DS3/SONET)
IMT: Inter Machine Trunks
provided by IXC
Long Distance Calls


A +1 indicates that the call is going to
the tandem switch – long distance call
Sometimes a code is used to indicate
the long distance company:


1323 +1 +area code +local number  MCI
Avoided due to equal access law  using
they use Featured Group D Trunks
Featured Group D (FG-D)

The FG-D protocol defines
interconnection rules between a local
exchange carrier (LEC) and an interexchange carrier (IEC) such as MCI or
Sprint.
Long Distance (international) Calls
IMT
Inter-exchange Office
Inter-exchange Office
Tandem Office
Tandem Office
Local Office
Local Office
DLC
DLC
POT
Inter Machine Trunks
POT
Putting it all together….
Overseas
Switch
POP
POP
Switch
Switch
Switch
POP
POP
Switch
POP
Routing is a
major issue!
POP
Switched access provided by LEC (DS3)
Inter Machine Trunks provided by IXC (DS3/SONET)
Inter Machine Trunks connecting switches (DS3/SONET)
Some interesting stuff!
24 hour period - calls per minute recorded at an IXC switch
2,000
1,800
Calls per minute
1,600
1,400
1,200
1,000
800
600
400
200
0
0:00
2:00
4:00
6:00
8:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
Busy hour - calls per minute recorded at an IXC switch
2,000
Calls per minute
1,800
1,600
1,400
1,200
1,000
800
600
400
200
0
10:30
10:45
11:00
11:15
11:30