Routers
A router directs, or routes, network messages across one or more networks. A router
determines the best path a message should take to its destination based on the address of
the destination.
Routers are also used to control broadcast storms on a network. Network nodes often
do not know the address of a workstation or node to which it wants to send data, so it
sends a broadcast message to the network addressed to no specific node, but to all nodes
at the same time. When too many workstations broadcast too many messages to the
whole network, the result is abroadcaststorm. A router helps prevent broadcast storms by
routing messages only to certain segments of the network.Gateways
A gateway, which is usually a combination of hardware and software, enables two
networks using different transmission protocols to communicate with one another. Gate-
ways are used in a number of situations involving the conversion of the characteristics on
one network to another, including architecture, protocols, and language.
Three different types of gateways exist: Address gateway Connects networks using different addressing schemes,
directory structures, and file management techniques, such as a Microsoft
network to a Novell NetWare network.
Protocol gateway Connects networks that use different protocols. This is
the most common gateway. An example of a protocol gateway is a router
that interconnects a LAN to the Internet.
Format gateway Connects networks using different data format schemes, for
example, one using the American Standard Code for Information Interchange
(ASCII) and another using Extended Binary-Coded Decimal Interchange Code
(EBCDIC). This type of gateway is used to connect a PC to a mainframe computer.Network Interface Cards (NICs)
The most basic of network connectivity devices is the network interface card (NIC), also
called a network adapter. A NIC, which is pronounced as “nick,” is the device that is in-
stalled in every PC or peripheral device to attach it to the network cabling and to connect
it to the network operating system and protocols. The primary purpose of the NIC is to
transmit and receive data to and from other NICs.
Here are some of the major characteristics of a NIC: MAC (Media Access Control) address Each NIC is physically encoded with
a unique identifying address when it is manufactured. A NIC’s MAC address
is used to identify it on the network.Chapter 20: Networks and Communications^523