7Telephone 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 networksPOTS – Plain Old Telephone ServiceAnalog, full duplex, dial tone, subscriber dials2 wires for communication (Tip and Ring)Voice travels over a 48 V DC source provided by the Telco.Local Loop2 to 25 miles of 19 AWG unshilded twisted pairDemarc or point of presenceLine in the sand
12PBX – 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 featuresCall forwarding.Call holding.Caller IDWith VOIP, your computer can do all this in software.
13Telephone NetworkThe Telephone Network must implement areas in Connectivity:Provide power to the phone when picked upAnnounce when ringingThe first signal we’ve talked aboutAddress resolution / Call routingHow is this signal passed? In band or out of band? When you press a key, what do you hear?Provide a guaranteed QOS
20Telephone Network Terms Exchange AreaLocal vs long distanceLEC – Local Exchange CarrierILEC – Incumbent LECCLECBOC – Bell Operating CompanyRBOCTrunks – fiber optical10 to 1TIE linesLATA – Local access and transport areaIXC – Inter-exchange CarrierCarry inter-LATA traffic
23Telephone Network - POP POP – Point of PresenceWhere are they at?
24Telephone Network - Connectivity We’ve covered:TerminalsAccessConnectivityHow 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’sNANPANorth American Numbering Plan AssociationDesigned by AT &T in 1947In charge of managing phone numbers
26NANPA Evolution – pg. 42 Phone numbers: Area codes: Area Code – 3 digitsExchange Code – 3 digitsSubscriber Code – 4 digitsArea codes:Don’t start with 1 or 01-800, 0 for operator, 1 to dial long distanceOther area codes aren’t available, 411, 211,311,911Around 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.
27NANPA 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.
28LATA – 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 codesIf you live in Dallas, it now might cost more to call Houston than Los Angeles
30LATA Terms Intrastate, IntraLATA Intrastate, InterLATA Ought to be a local callBut, they can still charge “local” tariffsIntrastate, InterLATASame state, different LATAInterstate, InterLATADifferent state, different LATAInterstate, IntraLATADifferent state, same LATADoes this ever occur?Telephone billing is confusing.
31ConclusionIn 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?