broadband

• baseband: single communication channel per physical connection: typically low frequency
• broadband: carrier waves in a given spectrum can carry many logical channels
• example of broadband: your cable tv
• multiplexing: placing several channels of data into a broadband cable
• mux and demux: your cable tv channel selector is a demux
• fdm: frequency division mux, tdm: time division mux
• stdm: statistical time division mux (requires buffer)
• muxing overhead: guardband

• dial up circuit switching: pstn: physical circuit made and held for session
• circuit switching: leased line
• packet switching: datagram: path for each packet
• virtual circuit: paths assigned and re-assigned on packet boundaries but pre-determined for session

• we inherited these from the telephone industry
• 1 or 2 pairs of 20-24 gauge copper wires: insulated
• twisted and shielded for em isolation
• mutual capacitance: subject to internal and external em interference
• cheap and easy to install and connect: pstn: most buildings are prewired for datacom
• normally the endpoint connection: local loop to subscriber, network connection to desktop: limited use as backbone
• utp: unshielded, stp: shielded: shielding reduces external attenuation
• telephone: 56kbps, t1: 1.54/2 mbps: 10baset ethernet: 10 mbps, adsl: 6 mbps, fast ethernet: 100 mbps
• switched connection: leased line: conditioning of leased lines
• t1 and isdn technology
• repeater spacing: current range is 100 meters for 10baseT
• repeater spacing: outside limit of 5 miles for dial-up voice grade central office loop
• tradeoffs: distance vs bandwidth vs error rates
• stp higher bandwidth than utp
• new specifications: adsl high speed internet access

• we inherited these from the cable tv industry
• copper wiring coaxially arranged for better em isolation
• higher bandwidth and lower attenuation noise than stp, cp
• distance limit: 10 miles
• common ethernet or token ring backbone for lan
• bandwidth: 5 mbps-500 mbps in most specifications
• common specifications include ethernet, arcnet, token ring
• 10base5: ethernet: 10 mbps backbone/desktop, 500 meters, max connectors=100
• 10base2: thin ethernet: 200 meters, 30 connectors
• new: cable modem for high speed access to internet

• glass or plastic core surrounded by cladding and protective material
• led=cheaper and more robust: injection laser diode: higher bandwidth
• technology progression: bouncing off walls to axial component only in thin pipe
• wavelengths: 850, 1350, 1550 nm (visible is 400-700)
• multimode step index - multimode graded index - single mode
• reliability: not subject to em attenuation
• security: not subject to wire tap
• expensive to buy, install, add nodes
• t3, ibm token ring, fddi, t3, sonet: specify fiber optic
• typical bandwidth: 100 mbps - 2 gbp
• very low error ratesL distances in hundreds of miles: very light: good for wan backbones and trunks

• trunks for long distance phone service or extension of lan backbone across campus
• line of sight, bad weather, health effects at high power?
• carrier wave: 20-40 mbps
• repeater spacing = 30 miles, curvature of the earth: repeters are expensive

• geosync orbit: 22,300 miles above equator: 3 satellites needed to cover the earth
• 4 degree separation means 360/4 = 90 satellites possible above equator: full so inclined orbits with "tracking" dishes
• dl/ul = downlin/uplink = 4/6 gHz and 12/14 gHz
• dish size: smaller for higher freq and closer satellites
• vsat = very small aperture terminal: small dish for higher freq
• bandwidth: phone service: 50 mbps per transponder: 6 t1 lines or 500 64 kbps lines (atnt think)
• propagation delay: round trip delay = .48 seconds: problem
• to lease a transponder or partial transponder bandwidth contact: hughes telecom, comsat, atnt, tridom, gte spacenet, or scientific atlanta
• [yahoo list of satellite telecom vendors]
• [hughes telecom satellite 101]
• new directions: leo and meo: project iridium