Equipment can be
divided into two types :
■ End
user devices—Include computers, printers, scanners, and other devices that
provide services directly to the user.
■ Network
devices—Include all devices that connect the end-user devices to allow them
to communicate.
Repeaters
´ Repeaters are networking devices that exist at Layer
1, (physical layer), of the OSI
reference model.
´ data is
transformed into either electrical or light pulses that pass along the
networking medium. These pulses are called signals.
´ When signals leave a
transmitting station, they are clean and easily recognizable.
´ However, the longer
the cable length, the weaker and more deteriorated the signals become as they
pass along the networking medium.
´ The purpose of a
repeater is to regenerate and retime network signals at the bit level(0,1),
allowing them to travel a longer distance on the medium.
Hubs
´ The purpose of a hub
is to regenerate and retime network signals.
´ The characteristics
of a hub are similar to those of a repeater.
´ A hub is a common connection point for devices in a
network.
´ Hubs commonly connect
segments of a LAN.
´ A hub contains multiple
ports. When a packet arrives at one port, it is copied tocthe other ports so
that all the LAN’s segments can see all the packets.
Hub do broadcast which increase a load on network.
´ Because hubs and
repeaters have similar characteristics, a hub is also called a multiport
repeater.
´ The difference
between a repeater and a hub is the number of cables that connect to the
device.
´ Whereas a repeater
typically has only two ports, a hub generally has
´ from four to 20 or
more ports.
´ Whereas a repeater
receives on one port and repeats on the other, a hub receives on one port and
transmits on all the other ports
´ The following are the
most important properties of hubs:
´
´ Hubs amplify signals.
´ Hubs propagate
signals through the network.
´ Hubs do not require
filtering.
´ Hubs do not require
path determination or switching.
´ Hubs are used as
network-concentration points.
Network Interface Cards
´ Network interface
cards (NICs) are considered Layer 2 devices
´ NIC throughout the world carries a unique
code, called a Media Access Control (MAC) address.
´ This address controls
data communication for the host on the LAN.
´ The NIC controls the
access of the host to the medium.
Bridges
´ A bridge is
a Layer 2(data link layer) device designed to create two or more LAN segments,
each of which is a separate collision domain.
´ In other words, bridges were designed to
create more usable bandwidth. The purpose of a bridge is to filter traffic on a
LAN to keep local traffic local yet allow connectivity to other parts
(segments) of the LAN for traffic that is directed there.
´ Every networking
device has a unique MAC address on the NIC.
´ The bridge keeps
track of which MAC addresses are on each side of the bridge and makes
forwarding decisions based on this MAC address list.
´ Bridges filter
network traffic by looking only at the MAC address. Therefore, they can rapidly
forward traffic representing any network layer protocol.
´ bridges look only at
MAC addresses, they are not concerned with network layer protocols.
´ bridges are concerned only with passing or
not passing frames, based on their destination MAC addresses.
´ Bridges are more
“intelligent” than hubs. That is, they can analyze incoming frames and forward
(or drop) them based on addressing information.
´ Bridges collect and pass packets between two
or more LAN segments.
´ Bridges create more
collision domains, allowing more than one device to transmit simultaneously
without causing a collision.
´ Bridges maintain MAC
address tables.
Layer 2 Switches
´ Layer 2 switches,
also called LAN switches or workgroup switches, often replace shared hubs and
work with existing cable infrastructures to ensure that the switches are
installed with minimal disruption of existing networks.
´ Like bridges,
switches connect LAN segments, use a table of MAC addresses to determine the
segment on which a frame needs to be transmitted, and reduce traffic.
´ Switches operate at
much higher speeds than bridges.
´ Switches are data
link layer devices that, like bridges, let multiple physical LAN segments be
interconnected into single larger networks.
´ Similar to bridges, switches forward and flood
traffic based on MAC addresses.
´ Because switching is
performed in hardware, it is significantly faster than the switching function
performed by a bridge using software.
Routers
´ A router,
is a type of internetworking device that passes data packets between networks
based on Layer 3(network layer) addresses.
´ A router can make decisions regarding the best
path for delivery of data on the network.
´ Layer 3 allows the router to make decisions
based on network addresses instead of individual Layer 2 MAC addresses.
´ Routers also can
connect different Layer 2 technologies, such as Ethernet, Token Ring, and Fiber
Distributed Data Interface (FDDI).
´ Routers also commonly
connect Asynchronous Transfer Mode (ATM) and serial connections.
´ However, because of
their capability to route packets based on Layer 3 information,routers have
become the backbone of the Internet and run the IP protocol.
´ The purpose of a
router is to examine incoming packets (Layer 3 data), choose the best path for
them through the network, and then switch them to the proper outgoing port.
´ Routers are the most
important traffic-regulating devices on large networks.
´ Routers let virtually
any type of computer communicate with any other computer anywhere in the world.
