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Network Hardware
Local Area Networks
• LANs consist of Transmission media and network nodes.
• The network nodes fall into two major classes:
• Data terminal equipment (DTE)—Devices that are either
the source or the destination of data frames. DTEs are typically
devices such as PCs, workstations, file servers, or print servers.
• Data communication equipment (DCE)—Intermediate
network devices that receive and forward frames across the
network. DCEs may be either standalone devices such as
repeaters, hubs, switches, and routers, or communications
interface units such as network interface cards (NIC) and modems.
Network Interface Cards
• A network interface card (NIC) is a device that connects a
client computer, server, printer or other component to a
network.
• The NIC provides two important services:
- it connects a computer physically to the network.
- it converts information on the computer to ( and from)
electrical signals of appropriate shape and transmission speed
for your network.
Network Interface Cards
• NICs can be an expansion card (the most popular
implementation) or built in to the motherboard of the
computer.
• The NIC connects to the network via a small receptacle called
a port.
- For wired networks, you insert the network cable
into this port.
- For wireless networks, the port includes a transmitter/
receiver that sends/receives radio signals.
Network Interface Cards
• All NIC on your network must conform to a common physical
and data link level protocol in order for their electrical signals
to be compatible (and therefore to exchange information
successfully).
• For example, if you are running a 10BaseT Ethernet network,
then all of your computers, printers, and servers must contain
10BaseT Ethernet network interfaces.
• Some NICs accommodate more than one physical or data link
protocol—for example, combinations of 10BaseT and
100BaseTX protocols (most network interfaces automatically
sense the appropriate speed).
Network Interface Cards
A NIC typically has at least two LEDs that indicate certain
conditions:
• Link light—This LED indicates whether a network connection exists
between the card and the network.
•Activity light—This LED indicates network activity. Under normal
conditions, the light should flicker sporadically and often. Constant
flickering may indicate a very busy network or a problem
somewhere on the network that is worth investigating.
• Speed light—This LED indicates that the interface is connected at a
certain speed.
Network Interface Cards
• Each NIC is associated with a unique address called its media access
control (MAC) address.
• The MAC address helps route information within your local area
network and is used by interconnecting devices such as switches.
• On Ethernet networks, each NIC receives a unique MAC address
when it is manufactured. When the network interface is installed
into a slot or onto the motherboard of a computer or printer, the
interface MAC address becomes the address for the computer or
printer.
• The MAC address is just one of several network addresses assigned
to each network computer, server, or peripheral. Another network
address is the device's Internet (IP) address. This address helps route
information between networks, and is used by interconnecting
devices called routers.
Hubs
• If the network includes more than two computers or peripherals 
You should use a hub or a switch on your Ethernet LAN network.
• The basic function of a hub is to take data from one of the
connected devices , optionally amplifies signal, and forward it
to all the other ports on the hub.
• This method of operation is inefficient because, in most cases,
the data is intended for only one of the connected devices.
• Hubs are also called concentrators or repeaters.
• Hub can be passive hub or active hub (regenerates the
signal before it forwards it ).
• Hub are used on 10BaseT and 100BaseTX Ethernet
networks.
Hubs
• A hub does not perform any processing on the data that it
forwards, nor does it perform any error checking.
• Hubs come in various sizes, the most common being 12-port
or 24-port.
• In a more complex network, many hubs can be
interconnected.
• In addition to ports for connecting computers, hub has a port
designated as an uplink port that enables the hub to be
connected to another hub to create larger networks.
Hubs
• Like network interfaces, hubs must be compatible with the
physical and data link protocol that you use. For example, if
you are running a 10BaseT Ethernet network, then all hub
connections to this network must also use this protocol.
Repeaters
• Repeater
• Simplest connectivity device regenerating signals
• Operates at Physical layer
• Has no means to interpret data  cannot direct data to their destination.
• It cannot improve or correct a bad or erroneous signal; it merely repeat it
• Limited scope
• One input port, one output port
• Receives and repeats single data stream
• Hub is a repeater with more than one output port
• Suitable only for bus topology networks
• Extend network inexpensively
• Rarely used on modern networks
• Limitations; other devices decreasing costs
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Bridges
• Connects two network segments
• Analyze incoming frames and decide where to send
• Based on frame’s MAC address
• Operate at Data Link layer
• Bridges look like repeaters, single input port and single
output port
• They differ from repeaters in that they can interpret physical
addressing information
• Advantages over repeaters and hubs
• Protocol independence
• Add length beyond maximum segments limits
• Improve network performance because they can be
programmed to filter out certain types of frames ( e.g. broadcast
frame)
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Figure 6-15 A bridge’s use of a filtering database
• Disadvantage compared to repeaters and hubs
• Longer to transmit data
• Filtering database (forwarding table)
• Used in decision making
• Filter or forward
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Bridges (cont’d.)
• New bridge installation
• Learn network
• Discover destination packet addresses
• Record in filtering database
• Destination node’s MAC address
• Associated port
• All network nodes discovered over time
• Today bridges nearly extinct
• Improved router and switch speed, functionality
• Lowered router and switch cost
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Switches
• Switches are connectivity devices that subdivide network
• Smaller logical pieces, segments
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Operates at Data Link layer (traditional switchesl)
Operate at layers 3 and 4 (advanced and modern switches)
Interpret MAC address information
Switches vary greatly in size and function
Most switches have at least the following omponents
• Internal processor, operating system, memory, several ports
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Figure 6-16 Switches
• Multiport switch advantages over bridge
• Better bandwidth use, more cost-efficient
• Each port acts like a bridge
• Each device effectively receives own dedicated channel
• Ethernet perspective
• Dedicated channel represents collision domain
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Installing a Switch
• Follow manufacturer’s guidelines
• General steps (assume Cat 5 or better UTP)
• Verify switch placement
• Make sure the switch is situated where you are going to keep it
after all the cables are connected
• Turn on switch
• before connecting any cables to the switch’s ports, plug it in
and turn it on. Also, when connecting a node to a switch, the
node should not be turned on.
• Verify lights, self power tests
• The switch’s power light should illuminate. Most switches
perform self-tests when turned on, and blinking lights indicate
that these tests are in progress. Wait until the tests are
completed (as indicated by a steady, green power light).
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Installing a Switch (cont’d.)
• Configure (if necessary)
• If you are using a small, inexpensive switch, you might not
have to configure it and you can skip to next step . However,
you might need to assign an IP address to the switch, change
the administrator password, or set up management functions.
Configuring a switch usually requires connecting it to a PC and
then running a configuration utility from a CD-ROM that came
with the switch. Refer to your switch’s instructions to find out
how to configure it.
• Connect NIC to a switch port (repeat for all nodes)
• Using a straight-through patch cable, connect the node’s NIC to
one of the switch’s ports If you intend to connect this switch to
another connectivity device, do not connect patch cables from
nodes to the uplink port or to the port adjacent to the uplink
port. On most hubs and switches, the uplink port is directly
wired to its adjacent port inside the device.
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Installing a Switch (cont’d.)
• After all nodes connected, turn on nodes
• After all the nodes have been connected to the switch, if you do
not plan to connect the switch to another connectivity device, you
can turn on the nodes. After the nodes connect to the network
through the newly installed switch, check to verify that the switch’s
link and traffic lights for each port act as they should, according to
the switch’s documentation. Then make sure the nodes can
access the network as planned.
• Connect switch to larger network (optional)
• To connect the switch to a larger network, you can insert one end
of a crossover patch cable into the switch’s uplink port, then insert
the other end of the cable into a data port on the other connectivity
device. Alternately, you can insert one end of a straight-through
cable into one of the switch’s data ports, then insert the other end
of the straight-through cable into another device’s data port. If you
are connecting one switch’s uplink port to another switch’s uplink
port, you must use a crossover cable. After connecting the switch
to another device, the switch senses the activity on its uplink port,
evidenced by its blinking traffic light.
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Installing a Switch (cont’d.)
Figure 6-17 Connecting a
workstation to a switch
Figure 6-18 A switch on a small network
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Switching Methods
• Switches differ in how they interpret incoming frames and
determine what to do with the frames
• Four switching modes exist
• Two basic methods discussed
• Cut-Through Mode
• Store-and-Forward Mode
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Cut-Through Mode
• Switch reads frame’s header
• Forwarding decision made before receiving entire packet
• Uses frame header: first 14 bytes contains destination MAC
address
• Cannot verify data integrity using frame check sequence
• Cannot detect corrupt packets 
• may increase the number of errors found on the network by
propagating flawed packets
• Advantage
• Speed
• Disadvantage
• Data buffering (switch flooded with traffic)
• Best use
• Small workgroups in which speed is important
• Low number of devices
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Store-and-Forward Mode
• Switch reads entire data frame into memory
• Checks for accuracy before transmitting information
• Advantage over cut-through mode
• Transmit data more accurately
• Disadvantage over cut-through mode
• More time consuming
• Best use
• Larger LAN environments because they do not propagate
data errors.
• Can transfer data between segments running different
transmission speeds
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Content and Multilayer
Switches
• Layer 3 switch (routing switch)
• Interprets Layer 3 data
• Layer 4 switch
• Interprets Layer 4 data
• Content switch (application switch)
• Interprets Layer 4 through Layer 7 data
• Advantages
• Advanced filtering, statistics keeping, security functions
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Content and Multilayer Switches (cont’d.)
• Disadvantages
• No agreed upon standard
• Layer 3 and Layer 4 switch features vary widely
• Distinguishing between Layer 3 and Layer 4 switch
• Manufacturer dependent
• Higher-layer switches
• Three times Layer 2 switches
• Used in backbone
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