Communication

Communication

1. Basics

   • Serial Communication
     • Sends each bit sequentially along a wire or channel.
     • Cheaper to set up.
     • Reliable over longer distances.
     • Slower.
   • Parallel Communication
     • Send multiple bits simultaneously over multiple wires and channels.
     • Only reliable over short distances,
     • Faster
   • Synchronous transmission
     • Both sending and receiving devices use an external clock signal to indicate when to send/receive a bit.
     • Fast and reliable.
   • Asynchronous transmission
     • Does not use an external clock, and relies on timing signals within the transmission to synchronise the sender and receivers own clocks.
     • Slower

2. Measurements

   • Baud rate
     • A physical property of a transmission medium (copper, fibreoptic)
     • Number of signal changes per second that the medium can handle without losing data.
   • Bit rate
     • How many bits that can be transmitted per second,
     • Can be higher than the baud rate as more than one bit can be encoded into each signal.
   • Bandwidth
     • The width of a range of frequencies, measured in Hz.
     • Bit rate of a system is directly proportional to its bandwidth
   • Latency
     • Time between the first bit being sent and being received.

3. Topologies

   • Many networks are set up with a physical star topology but a logical bus topology.
   • Computers on the network see all others as if they are all directly connected, and use bus protocols

4. Networks

   • Client-server networks
     • Most computers are designated "clients" and one or more are "servers"
     • Clients request services from the servers.
     • Easier to initially set up
     • Easier to maintain.
   • Peer to peer networks
     • All computers have equal status.
     • All computers request services from and provide services to other computers
     • Difficult to maintain, as all computers on the network need updating if a change is made.