assignment06x - NOVA Student Web

rabidwestvirginiaΔίκτυα και Επικοινωνίες

26 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

86 εμφανίσεις

Assignment #





Define local area network?

A local area network (LAN) is a group of microcomputers located


same general area. A LAN covers a clearly defined small area, such as one floor
or work area, a single building, or a group of buildings.


What are the distinguished features of LAN?

The distinguishing features of LAN are:

The small confined area in w
hich it operates

Very high speed transmissions

They operate outside the government
communication environment, because their circuits do not
cross public thoroughfares (roads) and, therefore, do not
require licensing or regulatory approvals to ope


What are the two reasons for developing LANs?

The two basic reasons for developing a LAN are information sharing
and resource sharing. Information sharing refers to business needs that
require users to access the same data files, exchange
information via e
mail, or search the internet for information. Resource sharing refers to one
computer sharing a hardware device (e.g., a printer
) or

software package
with other computers

on the network. The main benefit of resource sharing
is cost saving
s whereas the main benefit of information sharing is improved
decision making

8. Describe at least three types of servers.

A LAN can have many different types of dedicated servers,
such as mail servers, database servers, and

web servers. Three other
common types are file servers, print servers, and remote
access servers

File servers allow many users to share the same set of files on a
common, shared disk drive. The hard disk volume can be of any size, li
only by the size of the disk users, shared only among authorized users, or
restricted to only one user.

Print server handle print requests on the LAN. By offloading the
management of printing from the main LAN file server or database se
print servers help reduce the load on them and increase network efficiency.

access servers (RASs) enable users to dial into and out of
the LAN by telephone. A RAS lets users dial into the LAN and perform all the
same functions a
s though move only small amounts of information and do
not require high speed beyond the limited capabilities of regular voice
grade telephone lines.

9. What is a NIC? What is a hub?

The network interface card (NIC) is used to connect the
to the network cable and is one part of the physical layer connecti
among the computers in the network.

Network hubs act as junction boxes, permitting new computers to
be connected to the networks as easily as plugging a power

cord into an
electrical socket, and provide an easy way to connect network cables. Hubs
also act as repeaters or amplifiers. Hubs are sometimes also called
concentrators, multi station access units, or transceivers.

11. What type of cables are

commonly used in LANs?

Unshielded twisted pair (UTP) is one of the leading LAN cabling

14. What does NOS do? What are the major software parts of NOS?

The network operating system (NOS) is the software that controls
the network. Every NOS provides two sets of software: one that runs on the
network server(s) and one that runs on the network client(s).

The server version of the NOS provides the sof
tware that performs
the functions associated with the data link, network, and application layers
and usually the computer’s own operating system. The client version of the
NOS provides the software that performs the functions associated with the
data link
and the network layers, and must interact with the application
software and the computer’s own operating system.

17. What is Ethernet? How does it work?

Ethernet is a layer 2 protocol, which means it operates at
e data link layer.
Ethernet is the most commonly used LAN in the world,
accounting for almost 70 percent of all LANs. Ethernet uses a bus topology
and a contention
based technique media access technique called Carrier
Sense Multiple Access with Collision D
etection (CSMA/CD).

18. How does logical topology differ from a physical topology?

A logical topology is how the network works conceptually, much
like a logical data flow diagram (DFD) or logical entity relation diagram
(ERD) in system an
alysis and design or database design. A physical topology
is how the network is physically installed, much like a physical DFD or
physical ERD.

19. Briefly describe how CSMA/CD works.

Carrier Sense Multiple Access (CSMA) with Collision D
(CD), like all contention
based techniques, is very simple concept: wait until
the circuit is free and then transmit.

Computers wait until no other devices
are transmitting, and then transmit their data. As long as no other
computer attempts to tr
ansmit at the same time, everything is fine.
However, it is possible that two computers located some distance from one
another can

to the circuit, find it empty, and begin to simultaneously.
This simultaneous transmission is called a
collision. The
two messages
collide and destroy each other.

The solution to this is to listen while transmitting, better known as
collision detection (CD). If the NIC detects any signal other than its own, it
presumes that a collision has occurred, and s
ends a jamming signal. All
computers stop transmitting and wait for the circuit to become free before
trying to retransmit. The problem is that the computers which caused the
collision could attempt to retransmit at the same time. To prevent this,
each com
puter waits a random amount of time after the colliding message
disappears before attempting to retransmit.

20. Why should CSMA/CD networks be built so that no more than 50
percent of their capacity is dedicated to actual network traffic?

/CD networks should be built so that no more than 50 percent
of their capacity is dedicated to actual network traffic, because their
performance seriously degrades at greater than 50 percent traffic loading.
The remaining 50 percent of the capacity should
be reserved for:

Message traffic peaks

Packet collision handling

Error correction and retransmission

Handshaking routines

Addresses (destination and source)

Message type (control and information)

Error checking bits

21. Explain the term 100Base
T, 100Base
F, 1000Base
T, 10 GbE, and
10/100 Ethernet.

T: An Ethernet LAN standard that runs at 100 million bps and
uses unshielded twisted
pair wires


T: An Ethernet LAN standard that runs at 1 billion bps and
uses unshielded twisted

pair wires.

F: An Ethernet LAN standard that runs at 1billion bps and
uses fiber
optic cable

10GbE: An Ethernet which runs at 10

Gbps and uses unshielded
pair wires.

10/100Mbps: An Ethernet, which is a hybrid that uses either 10Base
or 100Base

22. How does switched Ethernet differ from traditional Ethernet?

Switched Ethernet provides individual de
dicated ports to each node
connected to it physically and processes packets based on this unique port.
Traditional Ethernet whether 10Base2, 10Base5 or a 10BaseT HUB
processes packets based on the entire LAN segment to which a node is
physically connected.

Switched Ethernet has considerably better. Switched
Ethernet has considerably better performance than traditional Ethernet
because computers do not have to share circuits with other computers.

23. How do layer
2 Ethernet switches know where to send the pa
ckets they
? Describe how switches gather and use this knowledge.

2 switches operate on the destination MAC address of each
packet processed to determine which port to pass on each packet presented
for transmission.

2 switches learn and store in memory in the form of a
forwarding table, the specific port location of each MAC address for every
device connected to any of its ports.

24. What are the primary advantages and disadvantages of switched

he primary advantages of switched Ethernet are it dramatically
improves network performance over HUB base networking, eliminates
bottlenecks and can operate at 10/100/1000 Mbps depending on the specific
type of switches used.

The primary disadv
antages of switched Ethernet are switches cost
more than HUBs and the cost increases linearly when moving from 10Mbps
up through 1000Mbps switches.

31. Describe four ways to improve network performance on the server.


tune the network o
perating system settings


Upgrade to a faster computer

Increase the server’s memory

Upgrade to a faster network interface card

Increase the server’s memory

32. Describe four ways to improve network performance on the circuit.

Upgrade to a
faster circuit

Add another circuit

Change protocols

Segment the network

33. Why does network segmentation improve LAN performance?

If there is more traffic on a LAN than the network circuit and media
access protocol can handle. The solution i
s, divide the LAN into several
smaller segments. Breaking a network into smaller parts is called network
segmentation. By carefully identifying how much each computer contributes
to the demand on the server, and carefully spreading those computers to
rent network segments, the network bottleneck can often be broken.

35. Compare and contrast cut through, store and forward, and fragment

Cut through switching, the switch begins transmitting before it has
received the entire pa
cket. The advantage of this is low latency and results in
a very fast network.

Cut through switching can only be used when the
incoming data circuit has the same data rate as the outgoing circuit.

Store and forward switching does not begin tran
smitting the outgoing
packet until it has received the entire incoming packet and has checked to
make sure it contains no errors. It provides higher latency and thus results in
a slower network. Circuit speeds may be different.

Fragment free sw
itching reads the first 64 byte segment (contains the
header). It performs error check, if it is okay then starts transmitting.

Part 2(supply screen shots)

Screen shot of shared folder

Screen shot of shared printer