1. Telephone Network Hierarchy Analog Sounds
ENGR 475 – Telecommunications
Harding University
Jon White

2. Voice

3. Voice

4. Voice

5. Voice

6. Sound Barrier

7. Telephone Network PSTN – Public Switched Telephone Network
World’s public circuit switched voice assemblage.
Similar to how the Internet is the assemblage of the World’s IP based packet switched networks
POTS – Plain Old Telephone Service
Analog, full duplex, dial tone, subscriber dials
2 wires for communication (Tip and Ring)
Voice travels over a 48 V DC source provided by the Telco.
Local Loop
2 to 25 miles of 19 AWG unshilded twisted pair
Demarc or point of presence
Line in the sand

8. Telephone Network - Demarc

10. Telephone Network Components
Terminals
Phones
Access
Phone lines
Connectivity
Intelligence to let phones use phone lines to call other phones
Switches
PBX – Private Branch Exchanges
Other Features
Call forwarding, re-dial, caller ID, voice mail, protocol conversion

12. PBX – Private Branch Exchange
Almost every corporation has one.
Handles internal switching.
You don’t have to go outside your network when calling someone in your building.
Performs other helpful features
Call forwarding.
Call holding.
Caller ID
With VOIP, your computer can do all this in software.

13. Telephone Network
The Telephone Network must implement areas in Connectivity:
Provide power to the phone when picked up
Announce when ringing
The first signal we’ve talked about
Address resolution / Call routing
How is this signal passed? In band or out of band? When you press a key, what do you hear?
Provide a guaranteed QOS

14. Telephone Hiearchy
Ring Topology
Star Topology
Hybrid

15. Telephone Network Toll Center = Tandem Office
End office = Central Office (CO)
Modern CO’s serve up to 100,000
customers.
Searcy’s CO

16. Telephone Network - CO

17. Telephone Network – Pedestal Box

18. Telephone Network – Wiring Closet

19. Telephone Network – Patch Panel

20. Telephone Network Terms
Exchange Area
Local vs long distance
LEC – Local Exchange Carrier
ILEC – Incumbent LEC
CLEC
BOC – Bell Operating Company
RBOC
Trunks – fiber optical
10 to 1
TIE lines
LATA – Local access and transport area
IXC – Inter-exchange Carrier
Carry inter-LATA traffic

21. Telephone Network – LATA Areas

22. Telephone Network – After Divestiture

23. Telephone Network - POP
POP – Point of Presence
Where are they at?

24. Telephone Network - Connectivity
We’ve covered:
Terminals
Access
Connectivity
How a call gets routed to the proper place.
One of the most difficult parts.
Whole world has to agree.
Hard to change once you’ve started giving out ID’s
NANPA
North American Numbering Plan Association
Designed by AT &T in 1947
In charge of managing phone numbers

25. NANPA Map

26. NANPA Evolution – pg. 42 Phone numbers: Area codes:
Area Code – 3 digits
Exchange Code – 3 digits
Subscriber Code – 4 digits
Area codes:
Don’t start with 1 or 0
1-800, 0 for operator, 1 to dial long distance
Other area codes aren’t available, 411, 211,311,911
Around 6 billion phone numbers are currently available.
How much storage space is required to store 6 billion phone numbers using ASCII representation along with the switch they belong to?
Number portability.

27. NANPA Like IP addresses, we are running out of telephone numbers.
Cell phones, fax, pagers, American Idol, modems
- Your switch and what your phone number tells people.
– Available numbers in your area code, cool maps.

28. LATA – Local Access and Transport Areas
Confusing billing!
Occurred after the 1984 At &T breakup.
Now, there are differences in how long distance your long distance call is.
Often, the LATA boundaries are arbitrary.
LATAs are smaller than area codes
If you live in Dallas, it now might cost more to call Houston than Los Angeles

29. LATA Map

30. LATA Terms Intrastate, IntraLATA Intrastate, InterLATA
Ought to be a local call
But, they can still charge “local” tariffs
Intrastate, InterLATA
Same state, different LATA
Interstate, InterLATA
Different state, different LATA
Interstate, IntraLATA
Different state, same LATA
Does this ever occur?
Telephone billing is confusing.

31. Conclusion
In what ways is the telephone network different than the Internet? In what ways is it the same?
Some of the distinctions in billing are rapidly fading away. Why is that?