Telecommunications Systems  Midterm Results Hi = 90Lo = 42 Average = Stan. Deviation = A > 85B > 67 C > 55D > 45

Term Paper Tips  remember to probe further  any statements not ‘common knowledge’ should be cited in the body of your paper  don’t get too ‘bubbly’  Suggested format for Web citations: address/Path/Filename (plus author, article name, & date if available) VERIFY YOU’VE PROVIDED ENOUGH INFO FOR THE INSTRUCTOR TO TRACK DOWN WEB ARTICLES! Sometimes the format above is not enough if article found via a search engine!!!

Homework  Term Paper due 12 April 2000  Readings: [13] “Backbone Trunking: An Analysis of Switching & Multiplexing Options over Fiber” [14] “Building the Brave New World”

VoIP being hyped today!  One reason: It’s cheaper than POTS. Will likely remain this way... ... but the Price Gap will close:  Internet Carrying Capacity decreases as voice traffic increases (network becones less effective at hauling traffic)  Priorities & RSVP-like services need implementing (installing these will cost money)  Voice traffic must be more expensive that data traffic (else priorities & reservations abused)  FCC Action? Universal Service & Access Charges  Long term value lies in integration of voice and data

The Telephone System  Despite 1996 Telecommunications Act, a two-tier system largely remains  LEC’s mainly restricted to Intra-LATA traffic  Can move Inter-LATA if FCC laundry list is met  As of December ’99, only Bell Atlantic is FCC approved  IXC’s mainly move Inter-LATA traffic  Can now move Intra-LATA traffic  Intra-LATA Competition is now mainly limited to large cities & large customers  Arriving agonizingly slowly elsewhere

POTS Connectivity  Small Cities have a CO Big Cities have CO’s  Hierarchical system, add High Usage Direct Lines between CO’s Tandem (Trunk-to-Trunk) Switches  Minimum of two physically separate routes out of all switches desired  Best compromise of cost & reliability

POTS  Items in a typical phone: microphone & speaker hybrid dialing circuitry (DTMF) on/off hook switch ring circuitry  Items in a typical CO: crosspoint switch hybrids A/D & D/A converters echo cancelers TDM

The phone system...  Parts are 4 wire (headset and long haul)  4 wire = two unidirectional signals  Parts are 2 wire (local loop)  2 wire = one bi-directional signal  Parts are analog (phone & local loop)  About 80% of U.S. Local Loops are copper all-the-way  Parts are digital (long haul, many CO switches, some local loops)  About 20% of U.S. Local Loops use Digital Loop Carriers

POTS Connectivity Phone CO Fiber Optic Trunk Copper Local Loop Copper Local Loop 4 Wire 2 Wire ‘4 Wire’ Analog Digital TDM 64 Kbps

The phone system...  4Wire to 2 Wire Conversion at Central Office Hybrids can cause some problems  Singing (Cure: Attenuation)  Echoes (Cure: Echo Canceler)  Analog to Digital Conversion points also cause some problems  CO Switch filters on analog voice lines, necessary to prevent voice distortion, limit modem data speeds to about 33 Kbps  Trend is to an all-digital system  U.S. long haul POTS voice circuits use digital Time Division Multiplexing