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Discovering computer networks: hands on in the Open Networking Lab
Discovering computer networks: hands on in the Open Networking Lab

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8.4 Summary of Session 8

In this session you have seen how the traceroute command can be used diagnostically to locate routers that are not forwarding packets. You also saw that traceroute gives an indication of the latency of routers, although the latency indicated by traceroute can be misleading.

You also saw how the collision avoidance of Wi-Fi enables a Wi-Fi radio channel to be shared in an orderly way among multiple users (even among users who are on different Wi-Fi networks but whose networks use the same channel and are within range of each other). The access method was shown to be dependent on delays of varying lengths, and on busy radio channels users are likely to suffer longer delays than on little-used channels.

Finally you saw that enterprise networking, although sharing many of its basic networking principles with home networking, makes use of more complex equipment, which is configured using specialised techniques, and extensively uses subnetworking (or subnetting) for network management, security and robustness.

New terms

In this session you have met the following terms.

Table _unit5.2.1

backing off

In Wi-Fi, backing off is a procedure for randomly allocating access to a radio channel to a single device out of all the ones waiting to transmit data. When a radio channel has been unused for a set length of time (the ‘check period’), devices with data to transmit count down from a random number. This is backing off. The first device to reach zero gains access to the radio channel.

check period

A fixed length of time for which a radio channel must be unused before backing off begins.

contention window

The period of time during which contending devices count down from a random number in order to determine which one will gain access to the radio channel. It’s the stage during which backing off occurs.

enterprise network

A network used in large-scale businesses and organisations. Enterprise networks use powerful, dedicated hardware, such as separate switches, routers, firewalls and DHCP servers, rather than a single device that does all this as would be found in a home network.

listen before transmit

A protocol (carrier-sense multiple access with collision avoidance, or CSMA/CA) to ensure that only one device at a time transmits data on a radio channel. The protocol governs all devices within range of each other that use the same radio channel, irrespective of whether the devices belong to the same network.

multiple access

Allowing many users to use the same medium.

round-trip time (RTT)

The time it takes a packet of data to reach a destination and be returned.


An online clock that other devices consult to find the current date and time.

time to live (TTL)

The maximum number of hops an IP packet can make before it is discarded.


A diagnostic tool for locating blockages on the route of an IP packet.