The Network Edge

• End systems OR Hosts = DESKTOP COMPUTERS (pcs, macs, linux boxes), SERVERS (web, email servers), MOBILE DEVICES (laptops, smartphones, tablets)

• HOSTS ————> CLIENTS & SERVERS.

• Access Network —> the network that physically connects an end system to the first router (edge router) on a path from the end system to any other distant end system.

• 2 most prevalent types of broadband residential access are:
  DSL (Digital Subscriber Line)
  & a Cable.

• Can obtain DSL from the same telephone company (telco) that provides its wired local phone access.

• The home’s DSL modem takes digital data and translates it to high frequency tones for transmission over telephone wires to the central office, the analog signals from many such houses are translated back into digital format at the DSLAM.

• Both data and telephone signals are carried and encoded at different frequencies.
  high speed downstream (50kHz to 1 MHz)
  medium speed upstream (4kHZ to 50kHz)
  ordinary two-way telephone channel (0-4kHz)

• Splitter → separates the data and telephone signals arriving to the home and forwards the data signal to DSL modem

• DSLAM → separates data and phone signal and sends data into the internet.

• CABLE INTERNET ACCESS uses the cable television company’s existing television infra.

• Fiber optics ——> neighborhood level junctions ——→ coaxial cable ——> individual houses [hybrid fiber coax]

• @ cable head end, Cable Modem Termination System (CMTS) similar to DSLAM, turning analog signal sent from cable modems in many downstream homes back into digital format.

• It is a shared broadcast medium.

FTTH (Fiber to the Home) provide an optical fiber path from the CO directly to the home.

PHYSICAL MEDIA: -

• Examples → twisted pair copper wire, coaxial cable, multimode fiber optic cable, terrestrial radio spectrum, satellite radio spectrum.

• 2 categories ——> Guided media [waves are guided along a solid medium] & Unguided media [waves propagate in the atmosphere and in outer space]

• TWISTED PAIR COPPER WIRE —> least expensive and most commonly used guided transmission medium, used by telephone networks.

• consists of 2 insulated copper wires, twisted together to reduce electrical interference from similar pairs close by.

• Unshielded Twisted Pair (UTP) used for LANs. Data rates - 10Mbps to 10Gbps. [depends on thickness of the wire & distance between transmitter and receiver.

• FIBER OPTICS —→ thin, flexible medium that conducts pulses of light, with each pulse representing a bit. They are immune to electromagnetic interference, have a very low signal attenuation up to 100kms and are very hard to tap. Preferred for the long-haul guided transmission medium for overseas links.

• TERRESTRIAL RADIO CHANNELS —> carry signals in the electromagnetic spectrum. They are an attractive medium because they require no physical wire to be installed, penetrate walls, provide connectivity to mobile user, can carry signals to long distances. mainly depends on the propagation environment and the distance over which a signal is to be carried.

• 3 groups: those that operate over short distances (1-2m), those that operate in local areas (up to few 100m), & those who operate in wide area (tens of kms).

• SATELLITE RADIO CHANNELS ——> it links two or more earth-based microwave transmitter/receiver, known as ground stations. receives transmissions on one frequency band, regenerates the signal using a repeater and transmits the signal on another frequency.

• 2 types: geostationary satellites & low earth orbiting (LEO).