1. Abid Afsar TNS Assignment II Student Number: 2823134
Assignment Cover Sheet
Student name: Abid Afsar
Student number: 2823134
Faculty: Computing Science
Course: TNS Stage/year: 1
Subject:
Study Mode: Full time Yes Part-time
Lecturer Name: Faheem Bukhatwa
Assignment Title: TNS
No. of pages: 20
Disk included? Yes No No
Additional (ie. number of pieces submitted, size of assignment, A2,
Information: A3 etc)
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2. Abid Afsar TNS Assignment II Student Number: 2823134
Date due: 23/12/2011
Date submitted: 23/12/2011
Plagiarism disclaimer:
I understand that plagiarism is a serious offence and have read and understood
the college policy on plagiarism. I also understand that I may receive a mark of
zero if I have not identified and properly attributed sources which have been used,
referred to, or have in any way influenced the preparation of this assignment, or if I
have knowingly allowed others to plagiarise my work in this way.
I hereby certify that this assignment is my own work, based on my personal study
and/or research, and that I have acknowledged all material and sources used in its
preparation. I also certify that the assignment has not previously been submitted
for assessment and that I have not copied in part or whole or otherwise plagiarised
the work of anyone else, including other students.
Signed: _______ ______________ Date:
___23/12/2011___________________
Please note: Students MUST retain a hard / soft copy of ALL assignments as well as a receipt issued and
signed by a member of Faculty as proof of submission.
(1) Compare the ATM protocol’s architecture and associated
layers, to those of the ISO-OSI reference model. Your answer or
diagram should show the layers in each protocol stack.
Answer:
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3. Abid Afsar TNS Assignment II Student Number: 2823134
• International organization for standardization (ISO) also referred
as Open system interconnection (OSI) reference model has the
following seven layers,
i. Application layer
ii. Presentation layer
iii. Session layer
iv. Transport layer
v. Network layer
vi. Data link layer
vii. Physical layer
In comparison to OSI reference model, asynchronous transfer mode
(ATM) has the following three layers
i. ATM Adaptation layer
ii. ATM layer
iii. Physical layer
• The OSI model is used for the transmission over unreliable
medium, while ATM model works with reliable transmission
medium, and it also accommodate a mechanism for error
detection and correction.
• In term of reliability ATM is currently the most reliable mode
of transmission in comparison to OSI model.
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4. Abid Afsar TNS Assignment II Student Number: 2823134
• ATM model corresponds to functionality physical and portion
data layer of OSI model.
• Diagrammatically the concept is represented as
Figure 1: Comparison Diagram of ATM and OSI Architecture
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5. Abid Afsar TNS Assignment II Student Number: 2823134
• OSI lowest layers are related to ATM, and diagrammatically it is
represented as,
Figure 2: Relation of OSI and ATM
(2) Show with the help of a diagram the flow of cells in a real
Communication from end to end, up and down the layers in the
ATM Model. Show two intermediate switches in the diagram.
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6. Abid Afsar TNS Assignment II Student Number: 2823134
Answer:
• In term of sending user information, ATM protocol architecture
is similar to TCP/IP protocol suit. ATM works same like
TCP/IP to forward user information form one machine to
another in the form of packets.
• In regards to routing or switching and control is completely
different because it fully connection- oriented which it establish
in form of virtual connection
• First a unique virtual connection is established which have their
VCI number
• Next communication begin and signalling standard agreement
take place and then data transmission start from one user
machine to another and exactly an original data order
• Finally, on completion of transmission connection is terminated
• ATM network mange data in specific order to manage the
quality of services in a most sophisticated manner
• On higher level it uses user plan and control plan for data
• Diagrammatically the concept is visualised as,
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7. Abid Afsar TNS Assignment II Student Number: 2823134
Figure 3: End- to-End Communication an ATM network
(3) Describe in details the ATM Cell structure.
Answer:
• An ATM use a fixed cell also called packet which is
composed of 5 bytes of header and 48 bytes of payload. All
data in ATM network is switched and multiplexed in the form
of ATM cell.
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8. Abid Afsar TNS Assignment II Student Number: 2823134
• In diagrammatic form it is represented as
ATM Cell
Figure 4: ATM Cell
• ATM cell header can have the following two header format
that is UNI (User to Network Interface) and NNI (Network-
to-Network Interface). The UNI is interface is between
network device and end user while NNI is between network
to network device or between the two back bone networks
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9. Abid Afsar TNS Assignment II Student Number: 2823134
• Diagrammatically the concept of UNI and NNI is illustrated
as,
Figure 5: UNI and NNI interface format
• The above diagram can be explained as, in ATM cell header
fields the first one is GFC( generic flow control) it provides
local function, the second one is VPI(virtual path identifier)
it is a unique identification number for every virtual path,
third one is VCI (virtual channel number) it is a unique
identification number of every virtual circuit, fourth one is
Payload type identify that weather it contain user data or
control data, fifth one is CLP(congestion lost priority) it
identify that if a cell shows congestion it should be
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10. Abid Afsar TNS Assignment II Student Number: 2823134
discarded or it show the status of congestion in the network
and sixth one is HEC(header error control) it provided
information in relation to any error encountered
• Multiplexing is also in important feature of ATM cell, it
multiplex different forms of data such voice, video and text.
Multiplexing improve overall efficiency and also improve
the performance of overall resources, diagrammatically it is
illustrated as
Figure 6: ATM Cell Multiplexing
(4) Describe the address fields used for ATM addressing. Use a
diagram to show the fields.
Answer:
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11. Abid Afsar TNS Assignment II Student Number: 2823134
• ATM address use virtual circuit and it is 20 bytes in length
and the ATM has three distinct formats, in general term it is
represented as
Figure 7: ATM address Format
• The parts of an ATM address can be defined as, the first part
is the ATM switch identifier it composed of 13 bytes, and
identifies the switch position in network. The main three
addressing scheme viewing location of switch differently.
The second one is adapter MAC address hold 6 bytes. It
shows the particular adapter type in the ATM network and the
MAC address operation is similar like in Ethernet or token
ring. The third one is selector (SE) hold a space of 1 byte, and
it chooses a logical connection end point on physical ATM
adapter.
• The three addressing schemes use in ATM networks are
i. Data Country/region Code (DCC)
ii. International Code Designator (ICD)
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12. Abid Afsar TNS Assignment II Student Number: 2823134
iii. E.164
The three different format of ATM address is
diagrammatically illustrated as
Figure 9: ATM Distinct Address Format
(5) Describe the structure of the ATM Adaptation layer AAL5 and
the services provided by each.
Answer:
• The AAL layer provide interface to the upper layer of the
ATM reference model
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13. Abid Afsar TNS Assignment II Student Number: 2823134
• It further sub divide into two sub layers that is segmentation
and reassembling, and convergence
• The basic duty of ALL layer is the format conversion
• The ALL received 48 bytes payload from higher level layer
and a header of 5 bytes from ATM layer
• ALL have four different types that are AAL 1, ALL 2/3, ALL
4 and AAL 5.
• These different types of ALL’s can also be distinguished by
connection oriented or connectionless mechanism. The ALL
1, 2,5 are pulley connection oriented while ALL ¾ is partly
connection oriented and AAL ¾ is partly connectionless as
well.
• Diagrammatically it is represented as
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14. Abid Afsar TNS Assignment II Student Number: 2823134
(6) What are Partial Packet Discard (PPD) and Early Packet
Discard (EPD)?
Answer: these are the ATM cell discard techniques and segments
large size packets into a series of bursts at ATM and ALL 5 cells.
This phenomenon is very useful at ATM over IP (AIP) and ATM
over LAN emulation (LANE) networks. These techniques closely
work with traffic policy and also look on to QoS as well. When the
cells of a large packet are dropped due to some reason and some of
the fragmented packets are also discard and will be send for
transmission. The discarding or dropping of fragmented packets are
call partial packet discard (PED). And when cells are fragmented
portion of a large packet, and are known in advance that the buffer
space is not sufficient to accommodate the entire packet, and then
there is no need to send some of its cells. It is better to discard the
entire packet and will be retransmitted this whole phenomena is
called early packet discard (EPD)
(7) Discuss in details four traffic control mechanisms used in the
ATM Model.
Answer: the ATM network should always be capable to recover
from any sort of potential errors, weather a human or machine error
such as intermittent or accidental and so on. The following control
mechanism are widely used in ATM traffic management arena
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15. Abid Afsar TNS Assignment II Student Number: 2823134
1. Network Recourse Management: This is always a priority of
network management to achieve good quality and efficiency,
and meet the user quality of service requirements. There is no
perfect standard for network resource is available until today.
The core problem is the statistical behaviour of the ATM
networks because several cells were entered into the buffer from
different sources and also due multiplexing as well.
2. Connection Admission Control: it is the initial call setup
procedure, and to establish a virtual channel or path that is
acceptable to the network. It will make sure that the new
connection will not devalue the other connection already in
place and the quality of other channel is not affected.
3. Usage Parameter Control and Network parameter Control
(UPC/NPC): These two techniques doing different function at
network interface. The UPC is functioning on user network
interface while NPC functioning on network node interface. the
main purpose of UPC and NPC is to secure the network
resources from intentional and malicious attack. It will also
check the validity of VPI/VCI entries, monitor traffic volume for
the agreed traffic parameter and standards and guarantee that all
traffic obeying the specified criteria, and check the accepted
traffic volume on each access link.
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16. Abid Afsar TNS Assignment II Student Number: 2823134
4. Priority Control: An ATM cell have the priority cell loss bit in
the header. And the information is classed according to their
priority and at least an ATM cell has two distinguished classes.
5. Traffic Shaping: It is a form of alerts given at the time when
there is a speedy traffic on an access link, these alerts are given
to slow their peak cell rate, limit the cell delay by appropriately
organising the cells in time.
6. Congestion Control: is a state of a network in which the traffic
overload or overflow on the network, everything jammed , and
no new network connection can be established, the
unguaranteed quality of service network is not able to add or
remove network connection. These problem can be solved by
using the above mechanism such as connection admission, and
UPC and NPC.
(8) Explain in detail how IP over ATM takes place. Your
explanation must discuss: connecting IP to an ATM, addresses and
the transfer of IP data grams.
Answer: ATM network is connection oriented network and it
widely support network protocols such as IP, Framerelay, and
IPv6, IPX, Decnet and so on. An ATM use three types of
connection which are permanent virtual circuit (PVC) and Soft
PVC, and short virtual circuit (SVC). The ATM network is divided
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17. Abid Afsar TNS Assignment II Student Number: 2823134
into logical networks and each logical network has own separate IP
subnet also called logical subnet (LIS). Every system in the LIS has
share the same IP prefix and net mask. In LIS end system
communicant with each other through ATM end-to-end
connection. And in a different LIS’s the communication is take
place through router.
(9) Describe the link state routing algorithm and list its advantages
over distance vector routing algorithm.
Answer:
Link state is a routing protocol such as OSPF and IS-IS used in
packet switch networking in computer communication. The main
concept of the link state routing protocol is that every network node
has to take routing information of the connected neighbours in the
form of a table. Every network node calculates best to the other
concerned destination. The calculated best path is then place in
routing table.
Advantages:
1. Link state algorithm converge fast than distance vector protocol
2. It use multicast to share the network information
3. It support classless routing
4. Link state operate better at large enterprise network
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18. Abid Afsar TNS Assignment II Student Number: 2823134
5. It has small routing table
6. It is capable of scalability
7. It has a low network overhead
8. It has no node limits
9. It use cost for shortest path findings
(10) Compare memory requirement imposed on the receiver node
by selective reject protocol and the go-back-N protocol. Give
examples to support your answers.
Answer:
Go-Back-N protocol manage the transmission time involved at
receiver end, and the transmission time of acknowledgment to come
back at sender end, and are carefully checked for efficiency purpose
and the technique is called pipelining. The sender is obliged to keep
track of frames and their concerned acknowledgment, and also have
to look timeout interval as well. As a result of tracking of each record
the memory requirement for sender is increased. On the other hand
the receiver only receives the frame or acknowledgment which the
receiver need. In situation where frame lost or duplication occurs in
frames or acknowledgments, the receiver discards whole frame, and
call for resend. In memory perspective the receiver only need
memory, when the frame is in right order with no error, lost and
duplication.
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19. Abid Afsar TNS Assignment II Student Number: 2823134
For example: we want to send frames of window size 9, can be shown
in the following figure
Sender End 0 1 2 3 4 5 6 7 8
Ack 0 Ack 1
Receiver End 0 1 2 3 4 5 6 7 8
discard discard discard discard discard discard
Error
Retransmission of the same frames
Sender End 2 3 4 5 6 7 8
Ack 2 Ack 3 Ack 4 Ack 5 Ack 6
Receiver End 2 3 4 5 6 7 8
In the above figure error occur in frame 2 and all the subsequent
frames were also discarded. The sender was not aware of the problem,
and again sends the same copies of the frame because of the timeout
interval expiry. The limitation of go-back-n protocol is the sender
unawareness of the problem, and this makes it inefficient. And
negatively affect the channel usage, memory at sender side, and
bandwidth.
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20. Abid Afsar TNS Assignment II Student Number: 2823134
In contrast selective reject protocol when the problem occur during
delivery of the frames, only particular frames were send back again
by the sender. On the receiver end all frames are not discarded and
only damage frame is acknowledged. In selective reject protocol
receiver side buffer size is increased because of keeping every correct
frame send by the sender. In this technique both sender and receiver
vigilantly watch their time counter, and the receiver have knowledge
that which frame has a problem and need to be re-acknowledge. It
uses NAK (negative acknowledgment) for lost or damaged bit
retransmission.
For example: we want to send frames of window size 9, using
selective reject protocol is shown in the following figure
Sender End 0 1 2 3 4 5 6 7 8
Ack 0 Ack 1
NAk 2
Ack 1 Ack 2 Ack 3 Ack 4
Receiver End 0 1 2 3 4 5 6 7 8
buffered buffered buffered buffered buffere buffered
Error
d
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21. Abid Afsar TNS Assignment II Student Number: 2823134
Selective reject protocol improves the channel usage time and
bandwidth, and also has a positive effect on the overall efficiency of
transmission between sender and receiver.
Bibliography
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22. Abid Afsar TNS Assignment II Student Number: 2823134
[1]. Tanenbaum, Andrew S. Computer Networks. Upper Saddle
River, NJ: Prentice Hall PTR, 1996. Print.
[2]. Händel, Rainer, Manfred N. Huber, Stefan Schröder, and Rainer
Händel. ATM Networks: Concepts, Protocols, Applications.
Wokingham, England: Addison-Wesley Pub., 1994. Print.v
[3]. ATM Addresses." Microsoft TechNet: Resources for IT
Professionals. Web: 23 Dec. 2011
<http://technet.microsoft.com/en-us/library/cc976977.aspx>.
[4]. Clark, Martin P. ATM Networks: Principles and Use. Chichester,
England: Wiley/Teubner, 1996. Print.
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