CS2302 – COMPUTER NETWORKS
TWO MARKS
UNIT-II-
Medium access – CSMA – Ethernet – Token
ring – FDDI - Wireless LAN – Bridges andSwitches
1. What are the functions of MAC?
MAC
sub layer resolves the contention for the shared media. It contains
synchronization, flag, flow and error control specifications necessary to move
information from one place to another, as well as the physical address of the
next station to receive and route a packet.
2. What are the functions of LLC?
The IEEE project
802 models take the structure of an HDLC frame and divides it into 2 sets of
functions. One set contains the end user portion of the HDLC frame – the
logical address, control information, and data. These functions are handled by
the IEEE 802.2 logical link control (LLC) protocol.
3. What is Ethernet?
Ethernet
is a multiple-access network, meaning that a set of nodes send and receive
frames over a shared link.
4. Define the term carrier sense in CSMA/CD?
All
the nodes can distinguish between idle and a busy-link and “collision detect”
means that a node listens as it transmits and can therefore detect when a frame
it is transmitting has interfered (collided) with a frame transmitted by
another node.
5. Define Repeater?
A
repeater is a device that forwards digital signals, much like an amplifier
forwards analog signals. However, no more than four repeaters may be positioned
between any pairs of hosts, meaning that an Ethernet has a total reach of only
2,500m.
6. Define collision detection?
In
Ethernet, all these hosts are competing for access to the same link, and as a
consequence, they are said to be in the same collision detection.
7. Why Ethernet is said to be a I-persistent
protocol?
An
adaptor with a frame to send transmits with probability ‘1 ‘whenever a busy
line goes idle.
8. What is exponential back off?
Once
an adaptor has detected a collision and stopped its transmission, it waits a
certain amount of time and tries again. Each time it tries to transmit but
fails, the adaptor doubles the amount of time it waits before trying again.
This strategy of doubling the delay interval between each transmission attempt
is a general technique known as exponential back off.
9. What is token holding time (THT)?
It
defines that how much data a given node is allowed to transmit each time it
possesses the token or equivalently, how long a given node is allowed to hold
the token.
10. What are the two classes of traffic in FDDI?
·
Synchronous
·
Asynchronous
11. What are the four prominent wireless technologies?
·
Bluetooth
·
Wi-Fi(formally known as 802.11)
·
WiMAX(802.16)
·
Third generation or 3G cellular wireless.
12. Define Bluetooth?
Bluetooth
fills the niche of very short-range communication between mobile phones, PDAs,
notebook computers, and other personal or peripheral devices. For example,
Bluetooth can be used to connect mobile phones to a headset, or a notebook
computer to a printer.
13. What are the four steps involves in scanning?
1.
The node sends a Probe frame.
2.
All APs within reach reply with a Probe Response frame.
3.
The node selects one of the access points, and sends
that AP an Association Request frame.
4.
The AP replies with an Association Response frame.
14. Explain the term handoff?
If
the phone is involved in a call at the time , the call must be transferred to
the new base station in what is called a hand off.
15. Define satphones?
Satphones
use communication satellites as base stations, communicating on frequency bands
that have been reserved internationally for satellite use.
16. How to mediate access to a shared link?
Ethernet,token
ring, and several wireless protocols. Ethernet and token ring media access
protocols have no central arbitrator of access. Media access in wireless
networks is made more complicated by the fact that some nodes may be hidden
from each other due to range limitations of radio transmission.
17. Define Aggregation points?
It
collects and processes the data they receive from neighboring nodes, and then
transmit the processed data. By processing the data incrementally, instead of
forwarding all the raw data to the base station, the amount of traffic in the
network is reduced.
18. Define Beacons?
Beacon
to determine their own absolute locations based on GPS or manual configuration.
The majority of nodes can then derive their absolute location by combining an
estimate of their position relative to the beacons with the absolute location
information provided by the beacons.
19. What is the use of Switch?
It
is used to forward the packets between shared media LANs such as Ethernet. Such
switches are sometimes known by the obvious name of LAN switches.
20. Explain Bridge?
It
is a collection of LANs connected by one or more bridges is usually said to
form an extended LAN. In their simplest variants, bridges simply accept LAN
frames on their inputs and forward them out on all other outputs.
21. What is Spanning tree?
It
is for the bridges to select the ports over which they will forward frames.
22. What are the three pieces of information in the configuration
messages?
1.
The ID for the bridge that is sending the message.
2.
The ID for what the sending bridge believes to the root
bridge.
3.
The distance, measured in hops, from the sending bridge
to the root bridge.
23. What is broadcast?
Broadcast
is simple – each bridge forwards a frame with a destination broadcast address
out on each active (selected) port other than the one on which the frame was
received.
24. What is multicast?
It
can be implemented with each host deciding for itself whether or not to accept the message.
25. How does a given bridge learn whether it should forward a multicast
frame over a given port?
It
learns exactly the same way that a bridge learns whether it should forward a
unicast frame over a particular port- by observing the source addresses that it
receives over that port.
26. What are the limitations of bridges?
·
scale
·
heterogeneity
27. Write
short notes on CRC.(NOV/DEC 2007)
The third and most powerful of the redundancy
checking techniques is the cyclic redundancy checks (CRC) CRC is based on
binary division. Here a sequence of redundant bits, called the CRC remainder is
appended to the end of data unit.
28. Define HDLC.(NOV/DEC 2007)
It is a bit-oriented data link protocol
designed to support both half-duplex and full duplex communication over point
to point and midpoint links.
29. List the types of stations is HDLC.
HDLC differentiates between 3 types of
stations.
a) Primary
b) Secondary
c) Combined
30.Give
the examples of common packet mode multiple access protocols for wired
multi-drop networks are:
- CSMA/CD (used in Ethernet and IEEE 802.3) (NOV/DEC 2007)
- Token bus (IEEE 802.4)
- Token ring (IEEE 802.5)
- Token passing (used in FDDI)
31. Define HUB.
- HUB is a repeater which is a OSI model device. Hubs are common connection point for devices in a network and are commonly used to connect segment of a LAN.
ALSO READ ..!
UNIT I NOTES
UNIT II NOTES
UNIT III NOTES
UNIT IV NOTES
UNIT V NOTES
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