Telephone Network PSTN – Public Switched Telephone Network –Worlds public circuit switched voice assemblage. –Similar to how the Internet is the assemblage of the Worlds 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
PBX – Private Branch Exchange Almost every corporation has one. Handles internal switching. –You dont 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 weve 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 COs serve up to 100,000 customers. Searcys CO
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 - POP POP – Point of Presence Where are they at?
Telephone Network - Connectivity Weve 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 youve started giving out IDs NANPA –North American Numbering Plan Association –Designed by AT &T in 1947 –In charge of managing phone numbers
NANPA Evolution – pg. 42 Phone numbers: –Area Code – 3 digits –Exchange Code – 3 digits –Subscriber Code – 4 digits Area codes: –Dont start with 1 or 0 –1-800, 0 for operator, 1 to dial long distance –Other area codes arent 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://telcodata.us/ http://www.nanpa.com – Available numbers in your area code, cool maps.http://www.nanpa.com
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 Terms Intrastate, IntraLATA –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?