1.2 The Network Edge
Last updated
Last updated
Host
Clients
Tend to be desktop and mobile PCs, smartphones, and so on
Servers
Tend to be more powerful machines that store and distribute Web pages, stream video, relay e-mail and so on
Most of the servers reside in large data centers
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.
Home Access: DSL, Cable, FTTH, Dial-Up, and Satellite
Two most prevalent types of broadband residential access: digital subscriber line (DSL) and cable
DSLAM: digital subscriber line access multiplexer
Hybrid fiber coax (HFC): both fiber and coaxial cable are employed
Fiber to the home (FTTH)
Optical network terminator (ONT)
Access in the Enterprise (and the Home): Ethernet and WiFi
Local area network (LAN)
Ethernet
Wireless LAN
Access based on IEEE 802.11 technology, more colloquially known as WiFi
Wide-Area Wireless Access: 3G and LTE
Unlike WiFi, a user need only be within a few tens of kilometers (as opposed to a few tens of meters) of the base station
E.x. HFC uses a combo of fiber cable and coaxial cable. DSL and Ethernet use copper wire. Mobile access networks use the radio spectrum.
For each transmitter-receiver pair, the bit is sent by propagating electromagnetic waves or optical pulses across a physical medium.
Can take many shapes and forms and does not have to be of the same type for each transmitter-receiver pair along the path
E.x. twisted-pair copper wire, coaxial cable, multimode fiber-optic cable, terrestrial radio spectrum, and satellite radio spectrum
Categories
guided media: the waves are guided along a solid medium, such as a fiber-optic cable, a twisted-pair copper wire, or a coaxial cable
unguided media: the waves propagate in the atmosphere and in outer space, such as in a wireless LAN or a digital satellite channel
Cost of physical link is relatively minor compared with other networking costs
Twisted-Paire Copper Wire
Unshielded twisted pair (UTP)
Rate: 10 Mbps to 10 Gbps
Dominant solution for high-speed LAN networking
Coaxial Cable
Can be used as a guided shared medium
A number of end systems can be connected directly to the cable, with each of the end systems receiving whatever is sent by the other end systems
Fiber Optics
Thin, flexible medium that conducts pulses of light, with each pulse representing a bit
Preferred for oversea links
Terrestrial Radio Channels
Radio channels carry signals in the electromagnetic spectrum.
Classified: short distance, local areas, span from ten to a few hundred meters, wide area, spanning tens of kilometers
Satellite Radio Channels
Links two or more Earth-based microwave transmitter/receivers, known as ground stations. The satellite receives transmissions on on frequency band, regenerates the signal using a repeater, and transmits the signal on another frequency.
geostationary satellites
low-earth orbiting (LEO) satellites