Characteristics of networks, LANs and WANs, protocols and standards

Overview

Recall questions on what makes a network, bandwidth and latency, protocols and standards, common internet protocols, error handling, open standards, LANs and WANs, the internet as a WAN, and wired and wireless LANs.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What actually makes a set of computers a network?

   Model answer

   Two or more computing devices connected together, by cable or wirelessly, so they can exchange data and share resources such as files, printers, storage, an internet connection or processing power. The connection alone is not enough: the devices must also follow a common set of rules (protocols) for how data is formatted, addressed, transmitted and acknowledged, otherwise the signals arriving mean nothing to the receiver.

2. 2

   Describe the benefits and the drawbacks of networking an organisation's computers rather than leaving them standalone.

   Model answer

   Benefits: hardware and software can be shared (one printer, one shared storage array, site licences); files are held centrally so everyone works on the same version and one backup covers everyone; user accounts, permissions and software updates are managed centrally; communication is possible (email, messaging, voice over IP); one internet connection serves all machines. Drawbacks: cabling, switches, servers and installation cost money; the network needs skilled administration; central components are single points of failure so one failed switch or server can stop many users; malware that reaches one machine can spread to others; a single security breach can expose the whole organisation's data.

3. 3

   What is the difference between the bandwidth and the latency of a network link?

   Model answer

   Bandwidth is the maximum rate at which data can be carried, measured in bits per second - how much can flow per second. Latency is the delay between data being sent and arriving, measured in milliseconds - how long the first bit takes to get there. They are independent: a satellite link can have very high bandwidth and very high latency, while a short copper link can have low bandwidth and very low latency. Throughput is the rate actually achieved in practice, which is always less than or equal to the bandwidth because of protocol overheads, contention and retransmissions.

4. 4

   Define a protocol, and say what a protocol has to specify.

   Model answer

   A protocol is an agreed set of rules governing communication between devices. It must specify the format of a message (which fields appear, in what order, how long each is); how devices are addressed; the order in which messages are exchanged and what response each message requires; how the start and end of a message are recognised; timing and transmission speed; how errors are detected and what happens when one is found; and how the receiver acknowledges what it has received.

5. 5

   What is the difference between a protocol and a standard?

   Model answer

   A protocol is a specific set of rules for a specific kind of communication, such as HTTP for requesting web pages. A standard is a published, agreed specification that manufacturers and software developers implement so that independently made products work together; a standard may define a protocol, but it may equally define a physical connector, a voltage, a wireless frequency, a character encoding or a file format. Protocols are normally published as standards, but standards cover more ground than protocols do.

6. 6

   A student says standards are just bureaucracy. Say concretely what goes wrong when two devices communicate with no agreed standard.

   Model answer

   They may not physically connect at all, because connectors, voltages or radio frequencies differ. If they do connect, the receiver cannot tell where one message ends and the next begins, so the data stream is meaningless. Bits may be interpreted in the opposite order, so numbers come out wrong. Text may be decoded with a different character encoding, so it appears as nonsense. With no rule about who may transmit and when, both devices talk at once and the signals collide. With no common addressing scheme, data cannot be directed to the right machine or the right application. With no agreed error detection, corrupted data is accepted silently as if it were correct. With no agreed acknowledgement, the sender never learns whether anything arrived. The practical result is that only equipment from a single manufacturer works together, so customers are locked to one vendor and separate networks cannot be joined.

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