In switched digital networks
the switching nodes can operate in three different ways:
Packet switching is favored for computer communication:
The switches on a route establish a
physical circuit between two hosts for the duration of the
communication session. This is how the telephone system
The sending host parcels up data into long
messages which are transferred step by step over each link between
the switches and delivered to the recipient.
As message switching, but the parcels are
short, so that the switching nodes can store numbers of them in
For a packet to get from one host to another through a series
of switches, each switch on the route requires to know where
the packet is going.
The range of network characteristics is wide and
WAN and LAN Characteristics are varied:
It makes good use of the links. Between bursts of data
between one pair of hosts. other hosts may use the same links
Delays due to storing short packets in switches are short
compared with storing long messages.
Switches need less memory/buffer space to hold packets for
forwarding than for messages.
Hardware to implement packet switches is now relatively cheap.
Switches and links may break during a communication session, but
alternative routes be found.
Packet switched networks have been in use for over 15 years.
Early examples are the now decommissioned US ARPANET and the UK
National Physical Laboratory Network.
The PNOs provide international packet switched networks.
National networks now exist with millions of attached
WAN data rates go from 300 bps up to 100s Mbps
Error rates of order 1 in #tex2html_wrap_inline4196#
Delays from 100msecs to Seconds.
Bit serial interfaces.
LAN data rates from 10 kbps to 140Mbps
Error rates of order 1 in #tex2html_wrap_inline4198#
Delays of order msecs.
Frame or byte level interfaces.