Content deleted Content added
m wiki style fix - head word should be bold, not italics |
include discussion of 'natural' forwarding models, and remove packet-switching references |
||
Line 1:
'''Forwarding''' is the relaying of [[packet|packets]] from one [[network segment]]
to another by [[node (networking)|nodes]]
in a
[[Image:unicast_forwarding.png|frame|A [[unicast]] forwarding pattern, typical of many networking technologies including the overwealming majority of [[Internet]] traffic]]
Line 14:
of delivering a copy to every device on the network.
In practice, broadcast packets are not forwarded everywhere
on a network, but only to devices within a [[broadcast ___domain]]
making ''broadcast'' a relative term.
Less common than broadcasting, but perhaps of greater
utility and theoretical significance is [[multicast|multicasting]],
where a packet is selectively duplicated and copies
delivered to each of a set of recipients.
Networking technologies tend to naturally support certain
forwarding models. For example, fiber optics and copper
cables run directly from one machine to another form natural
unicast media - data transmited at one end is received
by only one machine at the other end. However, as illustrated
in the diagrams, nodes can forward packets to create
multicast or broadcast distributions from naturally
unicast media. Likewise, traditional [[Ethernet]]
([[10BASE5]] and [[10BASE2]], but not the more modern
[[10BASE-T]]) are natural broadcast
media - all the nodes are attached to a single, long
cable and a packet transmited by one device is seen by
every other device attached to the cable. Ethernet
nodes implement unicast by ignoring packets not
directly addessed to them. A wireless network
is naturally multicast - only those devices within
a reception radius of a transmiter can receive
its packets. Wireless nodes ignore packets
addressed to other devices, but require forwarding
to reach nodes outside their reception radius.
At nodes where multiple outgoing links are available, the
choice of which, all, or any to use
a given packet requires a decision
making process that, while simple in concept, is of
sometimes bewildering complexity. Since a forwarding
decision must be made for every packet handled by a
node, the total time required for this can become
a major limiting factor in
Much of the design effort of high-speed [[routers]]
and [[network switch|switch]]es has been focused on making rapid forwarding decisions
for large numbers of packets.
| |||