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MINISTRY OF SCIENCE AND TECHNOLOGY
DEPARTMENT OF TECHNICAL AND VOCATIONAL EDUCATION
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Final Examination B. Tech Year 2 for EcE (2006)
Computer Communication Network
time: 12:30 ~
Answer Any Five Questions
1(a) Describe the advantages of ISDN.
1(b) Describe different channel types of ISDN. And also explain each channel.
2(a) Discuss about Teleservices.
2(b) Explain Link Access Protocol
D Channel (
3(a) What is Token Ring? And explain about Token Ring Network using Figures.
3(b) Write short note the followings:
The Token Frame (ii) The Data Frame
4(a) What are connectors?
4(b)Briefly explain Network Interface Cards.
5(a) Describe Brid
ge Standards and explain Transparent Bridge.
5(b) Briefly explain Random Access versus Token Passing Protocols.
6(a) Draw IEEE 802.3 frame (1) with an IEEE 802.1q header (2) adds 4 bytes to the
6(b) Explain (1) Stop
ocol (2) Sliding Window Flow
integrated services digital network (ISDN) represent the overhaul
and redesign of our conventional telephone network from an analog system to
end digital network. Th
capable of transmitting voice and data communications over a single
telephone line using in expensive and conventional twisted
The advantage ISDN offers over other services is that separate connections
are not need for these different transmissions. Thus, instead of having a
for voice communications, a second telephone line
computer dial up connections
and a coaxial cable link for video
communications, a single ISDN connection will
support all of these
transmissions. ISDN also provides a cost
effective strategy for internet
working. Instead of paying for dedicated leased lines, remote sites can
interconnect with other sites via dialup links.
ISDN defines several different chan
nel types, which provides a logical
separation of user data from signaling and control information.
The B channel is a 64 kbps clear channel used to transmit computer data,
ce and digitized video. B channel transmissions are either circuit
switched. Data also can be exchanged via frame relay or through a
dedicated leased line arrangement. Since ISDN uses a separate channel (the D
channel) for signaling information 1
00% of the bandwidth allocated for an
ISDN B channel is used for data transmission.
The D channel is either a 16 kbps or 64 kbps channel depending on the
specific service level provided. It is used to carry signal and control
for circuit switched user data. The D channel also can be used to
switched user data( provided that no signal or control
information is needed), data from security alarm signals of remote sensing
device that detect fire or instructors, and
low speed information required from
telemetry services such as meter reading.
The H channel is used for transmitting user data at higher transmission
rates than B channel provides. Four H channels are defined: H 0, H 10, H 11,
and H 12. H 0 co
mprises six B channels for a total capacity of 384 kbps.
Example of applications that might use an H channel include video
conferencing, high speed fax or high speed packet
switched data, and high
supports a se
veral teleservices, including capability for 64
Group IV fax, teletext, and videotex. Teletext and videotex are electronic
information utilities that use computers or standard television sets equipped
with adapters to display information. Teletext is
system; videotex is a two
system. Teletext5 broadcasts data as part of a
on signal; videotex use cable television or telephone lines to transmit
data. typical applications available from
these services include information
l, electronic transactions
al messaging, computing, and
Clearly, many of these applications are now available via the
World Wide Web. However, teletext and videotex services have
been available in countries su
as France, Canada, and
Great Britain since
the early 1980s. Futhermore, trials of these two services were conducted in the
United States during the 1983
1984 time periods. Example
s include Videotron
Ridder Newspapers in southeastern Florida, K
Publishing in Chicago, and Gateway by Times Mirror Videotex Services in
Southern California in 1984.
ISDN versus Regular Phone Service
An ISDN telephone can be used to call
someone whose phone service is
provided by the analog
plain old telephone system. The reverse is also
true. However, we will not be able
to achieve high
quality connect sessions
because only one part of the connection is digital; the other is analog. Thus
there will not be any improvement in line performanc
e. As for any differences
in telephones, ISDN telephone sets have many more built
in functions and
capabilities than conventional analog phones. Aside from that both types of
phoned function similarly, with one excepti
B and H Channels
series: I.430 (BRI) and I.431 (PRI)
0 (BRI) and I.431 (PRI)
Link Access Protocol
D Channel (LAP
beginning or ending of the frame.
Provides addressing information. The service access point identifier
2 protocol provides servi
ce to layer 3. Specific
services. For example SAPI = 16 is for X.25 packet
data transmissions. The command/response bit specifics whether the frame is
a command or response. The extended address
bit specifies the beginning and
nding of the address field. If EA is 0
, then another byte
information follows. An EA of 1 implies that the
current byte is the last byte
or the address. Thus, given a two
address, EA = 0 in the higher
byte and EA = 1 in the lower
r byte. The terminal endpoint identifier
represents the spe
cific address or ID assigned to each ISDN terminal
equipment connected to an ISDN network via an S/T interface.
2 control information
and user data. The
protocol discriminator id
entifies the specific layer
3 protocol. The length byte
specifics the length
of the CRV field, which is either one or two bytes. The
call reference value is the number assigned to each call. Once a
completed, this number can be reassigned to a new call. Message type
identifies specific message related to circuit
example, during call setup, the message CONNECT indicates that the
receiving terminal equipment end node
has accepted a call by the initiating
TE. When a call has been completed, the message RELEASE COMPLETE is
sent to indicate that the channel
HAS BEEN TORN DOWN.
Provides for data integrity via CRC checksums.
A token ring network is a local ar
ea network technology based on a
token passing for media access control. Data frame on a token ring network
are transmitted from note to node, a clockwise or counterclockwise direction,
over a point to point link. A token ring implemented either as a logic
using a physical ring topology.
The Token Frame
At the data link layer, access to the network is control by a
special,”token”frame, which circulates around the ring when all lobes are idle.
A code vi
olation occurs if there is no transition at the midpoint of a bit
signal. The access control field consist of eight bits: three priority bits (P), a
token bit (T), a monitor bit (M) and three reservation bits (R).
The Data Frame
he content of a token ring data frame that the first three field of the
data frame are equivalent to the token frame. A lobe that possesses the free
token and has data to transmit changes the access control field’s token bit to 1
and then arguments the tok
en frame by including a frame control field,
destination and sources address, user data, a CRC checksum and a frame
Connector attach components together several types of connector are
available, serving various purpo
se. Four example connectors are used to (a)
connect network interface cards, such as an Ethernet card to a cable, (b)
connect cable segment (c) terminate a segment. Connector actually connect
the cable to a terminating resisto
r or an array of resistors and
known as terminators. The type of connector is usually a function of cable
type. Connectors are classified by their gender, and they do indeed ‘mate’.
Connectors are also frequently
by their type. Three
common types are DB type, ce
ntronics and DIN. DB connectors serve as an
interface between a computer and a peripheral device such as a printer or
external modern. Several types of DB connector exist and are distinguished by
the number of pins they contain. DIN(Deutsche
m, a G
industrial standard) and ele
to DB type
connectors excepts DIN connectors are circular instead of rectangular and
centronics connector contain ‘teeth’ instead of pins. Other connector type
include coax, V
ber, video, SCSI
Network interfacing cards (NIC) operates at the data link layer.
people think of network interface cards as Ethernet cards, but this not entirely
correct. An Ethernet card is a network interface card used in
Not all network
interface cards are Ethernet cards, through. A
network interface card is known b many names. Some of the more common
ones are LAN adapter, network adapter, networ
Generally, we prefer to ca
ll them NIC.
Two bridge standards have been defined by IEEE. The first is
transparent bridge and is used in IEEE 802.3 and 802.5 networks. The second
is a sourcing routing bridge which was introduced by IBM and is used
exclusively in token ring networks.
frames between LANs and
provide filtering. They allow frame from a node on one network to be
forwarded to a node on another network but discard any frames destined for
the same network from which the frames
originated. Thus bridges keeps local
traffic local but forward traffic destined for a remote network. Since bridge
operates at the data link layer, they check the hardware address of a particular
network interface card to determine whether to forward or di
scount a frame.
A transparent bridge is a “plug and play” unit. Operating in”
promiscuous mode” a transparent bridge captures every frame that is
transmitted on all the networks to which the bridge is connected. The brid
examine every frame it receive and extracts each frame’s source address,
which is then added to a “learned address” table maintained by the bridge.
Eventually, this table contains an entry for each unique source address and the
port on which the frame
Random access protocol defines how a node can access a
communication channel. These protocols employ the philosophy that a node
can transmit whenever it has data to transmit. Random access protocols imply
contention; is a phenomenon in
which more than one entity competes to do
something at the same time.
Token passing protocol LAN is token bus, which is defined in
IEEE 802.4. a token bus network is characterized as a logical ring on a
physical bus. Physically, the network resemble
s a bus topology, but logically
it is arranged as a ring with respect to passing the token from lobe to lobe.
Stop and Wait Flow Control Protocol
An example of a very simple flow control protocol is the stop
col. As inferred by its name, stop and
wait requires the sender to transmit
one frame and then wait for the receiver to acknowledge receipt of this frame.
The acknowledgement sent by the receiver is a basic frame that simply in
form the sender that the rec
eiver is now ready to accept another data frame.
Asender must wait until it receivers an acknowledgement from the receiver
for the frame it transmitted before it is permitted to transmit another frame. If
a receiver withholds an acknowledgement, then the f
low of data between
sender and receiver stops. Although stop and wait is very effective it is also
very impractical for modern networking environments. First as described, stop
and wait uses a simplex transmission; data frames flow in only one direction.
n most data communication environments, data transmission is full duplex.
Second the protocol is ideal when transmitting larger frames. Unfortunately,
larger frames are generally partitioned into smaller data unit to a commended
a receiver’s limited buffer
size. Small frames
also facilitates faster error
detection and reduces the amount of data that require retransmission in event
that an error is detected.
Sliding Window Flow
An enhancement to the stop an wai
t protocol is the sliding window
concept, which improves data flow by having the receiver inform the sender
of its available buffer space. The sliding window concept is implemented by
requiring the sender to sequentially number each data frame it sends and
having the sender and receiver maintain information about the number of
frames they can respectively send or receive. Flow control based on this
concept is called sliding window protocol.
A general example of how the sliding window concept is used
flow control is provided in which show a simplex data transmission from
host A (the sender) to host B (the receiver). We assume a three
field. An explanation of how this concept is implemented follows.
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