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

Voice

Voice

Voice

Voice

Sound Barrier

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

Telephone Network - Demarc

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

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 http://wandel.ca/homepage/pbx.html With VOIP, your computer can do all this in software.

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

Telephone Hiearchy Ring Topology Star Topology Hybrid

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

Telephone Network - CO

Telephone Network – Pedestal Box

Telephone Network – Wiring Closet

Telephone Network – Patch Panel

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

Telephone Network – LATA Areas

Telephone Network – After Divestiture

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

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

NANPA Map

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.

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

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

LATA Map

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.

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?