Network infrastructure

Workstations must be electronically interconnected to communicate. The
equipment over which the network traffic (electronic signals) travels
between computers on the network is the network infrastructure.

Network hubs

In a typical office network, a strand of wiring similar to phone cable is run
from each computer to a central location, such as a phone closet, where each
wire is connected to a network hub. The network hub, similar conceptually
to the hub of a wheel, receives signals transmitted by each computer on the
network and sends the signals out to all other computers on the network.
Figure 2-1 illustrates a network with a star-shaped topology (the physical
design of a network). Other network topologies include ring and bus. Home
networks typically use a star topology because it’s the simplest to install and
troubleshoot.

Bridges

A network bridge provides a pathway for network traffic between networks or
segments of networks. A device that connects a wireless network segment to
a wired network segment is a type of network bridge. In larger networks, network
bridges are sometimes used to connect networks on different floors in
the same building or in different buildings. In a wireless home network, the
device that manages the wireless network, the access point, often acts as a
bridge between a wireless segment of the network and a wired segment.
Hubs and switches
Networks transmit data in bundles called packets. Along with the raw information
being transmitted, each packet also contains the network address of
the computer that sent it and the network address of the recipient computer.
Network hubs send packets indiscriminately to all ports of all computers connected
to the hub — which is why you don’t see them much any longer.
A special type of hub called a switched hub examines each packet, determines
the addressee and port, and forwards the packet only to the computer and
port to which it is addressed. Most often, switched hubs are just called
switches. A switch reads the addressee information in each packet and sends
the packet directly to the segment of the network to which the addressee is
connected. Packets that aren’t addressed to a particular network segment are
never transmitted over that segment, and the switch acts as a filter to eliminate
unnecessary network traffic. Switches make more efficient use of the
available transmission bandwidth than standard hubs, and therefore offer
higher aggregate throughput to the devices on the switched network.

Routers

Over a large network and on the Internet, a router is analogous to a superefficient
postal service — it reads the addressee information in each data packet
and communicates with other routers over the network or Internet to determine
the best route for each packet to take. In the home, a home or broadband
router uses a capability called Network Address Translation (NAT) to enable all
the computers on a home network to share a single Internet address on the
cable or DSL network. The home router sits between your broadband modem
and all the computers and networked devices in your house, and directs traffic
to and from devices both within the network and out on the Internet.
So, the local area network in your home connects to the wide area network,
which takes signals out of the home and on to the Internet.