4.9 communication and networking

**a set of rules **defining how devices will communicate

• standards for physical connections and cabling • bit rate or baud rate • data format • transmission a/synchronous • error checking procedures

data is sent one bit at a time over one communication line

the usb (universal serial bus)

a ribbon of several smaller cables used primarily for connecting internal components

several bits are sent simultaneously along separate lines, only reliable over short distances

• serial connectors (USB) much smaller + cheaper than parallel connectors • a PC has several USB ports for connecting peripherals

requires less wires: lower cost, less difficult to manage when setting up the system no risk of crosstalk/skew over long distances, as only one bit is transmitted at a time — less chance of errors, no limiting factor on transmission speed, no limiting factor on cable length (for skew)

• bits transmitted across parallel links travel at diff speeds • in synchronous data transmission, results in data falling out of sync with clock signal, data not read correctly

• over long distances • higher transmission speeds • in extreme cases can lead to bits from different pulses overlapping, causing data corruption

• when comm lines tightly packed, signals from one line can ‘leak’ into another, causing data corruption • worse with higher transmission speeds

• clock signal times when signals are sent • signals, sent at regular intervals, received in same order that they were sent • suitable for transmitting info in real-time systems

• no clock signal • start and stop bits used to indicate duration of byte transmission • each byte sent separately the moment it is available, doesn’t wait for clock signal • also has a parity bit

start the receiver clock; synchronise the clock in the transmitter to the receiver clock;

allows next bit to be recognised; provides time for receiver to process the received data;

• relatively slow owing to the increased num of bits being sent • cheap and effective form of serial transmission well suited to low-speed connections

baud rate x no. of bits per signal

physical: the architecture of the connections (between devices on the network); logical: how the packets flow around a network;

• connects clients to a single cable called a backbone • terminator placed at either end of the backbone • no need for a central hub, server connected to back bone like a client

a node broadcasts data (to the entire network); all nodes on the network receive the data; a node examines the received data to check if it is the intended recipient; only one node can transmit data at a time;

• no central hub, reducing chance of network failure + decreasing cost of installation • inexpensive to install as min length of cable is required

• packets sent through shared backbone, every client on network can see packets not intended for them • backbone used for communication by multiple clients, risk of collisions • backbone failure = entire network failure

• packets sent directly to recipient, over a cable connected only to the recipient. other clients can’t see • easy to add/remove clients • each cable has just one device comming over it, eliminating collisions • failure of one cable does not affect entire network performance

• central hub failure = all comms over the network are stopped • expensive to install due to amount of cables