LAN=Local Area Network; WAN=Wide Area Network, Internet=worldwide connected collection of other networks, Byte, Bit, Analog and Digital signals.
Modulation and Demodulation in a MODEM.
Parallel and Serial communication.-
Communication switching is usually implemented via circuit switching or packet switching. In PS, pieces of your data may travel by multiple paths to its destination.
Bus topology: Two terminations, everyone in between. Ring and Bus are both vulnerable to single breaks.
Star topology: one hub. Fed Ex uses Memphis for its hub. Robust because a broken link only disables one client.
Bus Arbitration - there are two commonly used methods.-
Collision detection. If a transmitter hears someone else transmitting at same time, it waits a short random interval and retries.-
Token passing. System must grab a 'token' ("permission slip") which is circulating. Lost tokens must be restored.
Network Technologies. Ethernet can be star or bus-organized. Stars are usually with 10BaseT, buses as coaxial, e. g. 10Base2 (BNC).
ARCnet uses star or bus.
IBM Token Ring is a hybrid of star and ring.
Bridge: connects two networks using the same technology; passes only appropriate traffic to the other network (i. e. traffic addressed to nodes in the other network.) Bridges help improve performance by reducing collisions.
Router: can connect networks of different technologies. Routers (unlike bridges) have their own network addresses. Routers ignore all traffic unless it is addressed to the router.
Gateways: include routers and other gadgets called application gateways. Example: e-mail gateway.
Comm subsystems come in two flavors: point to point, and broadcast.
Broadcast Channel designs. Static and dynamic allocation methods. Static is mostly used in realtime systems when each component must be guaranteed a specific timing; but much channel capacity gets unused.
Dynamic allocation means any computer with something to say, says it. Bus arbitration (central, e. g. token; or decentralized, e. g. collision detection) is required.