1

CS 2060 HIGH SPEED NETWORKS

YEAR / SEMESTER: IV / VII

2 MARK QUESTIONS

UNIT I

HIGH SPEED NETWORKS

1. Differentiate Frame relay and X.25 packet-switching service The Difference between X.25 and Frame Relay are:

i. Call control signaling is carried on a separate logical connection from user data. Thus, intermediate nodes need not maintain state

tables or process messages relating to call control on an individual per-

connection basis.

ii. Multiplexing and switching of logical connections takes place at layer2 instead of layer3, eliminating one entire layer of processing.

iii. There is no hop-by-hop flow control and error control. End- to-end control and error control are the responsibility of a higher layer, if they

are employed at all

2. What is jitter? The packets between a given source and destination may vary in

length, may take different routes, may be subject to varying delays in the

switches they encounter, the overall packet delay can vary substantially. This

phenomenon, called JITTER may not be desirable for some application; for

example in real-time applications including telephone voice and real-time

video

3. List out some of the control functions of LAPF core. The control functions of LAPF (Link Access Procedure/Protocol for

Frame Relay are:

i. Frame delimiting, alignment and transparency ii. Frame multiplexing/demultiplexing using the address field

iii. Detection of transmission errors iv. Congestion control functions

4. What is called a cell in ATM? In ATM, the information flow on each logical connection is organized

into fixed size packets called cells

5. What are the planes in protocol reference model? The Planes in protocol reference models are: i. User plane

ii. Control plane iii. Management plane

6. What are the advantages of virtual paths? The advantage of the Virtual Paths is: i. Simplified network architecture

ii. Increased network performance and reliability iii. Reduced processing and short connection setup time iv. Enhanced network services

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7. What is VPI? The Virtual path identifier constitutes a routing field for the network.

It is 8 bits at the user-network interface and 12 bits at the network-network

interface. The latter allows support for an expanded number of VPCs internal

to the network, to include those supporting subscribers and those required for

network management

8. What is CLP? The cell loss priority bit is used to provide guidance to the network in

the event of congestion. A value of 0 indicates a cell of relatively higher

priority, which should not be discarded unless no other alternative is available.

A value of 1 indicates that this cell is subject to discard within the network

9. What are the services of ATM? The ATM services are:

i. Real time services: i. Constant Bit Rate (CBR)

ii. Real Time Variable Bit Rate (rt-VBR) ii. Non Real time services:

i. Non Real Time Variable Bit Rate (nrt-VBR) ii. Available Bit Rate (ABR)

iii. Unspecified Bit Rate (UBR) iv. Guaranteed Frame Rate (GFR)

10. What is Frame Relay network? A form of packet switching based on the variable length link layer frames.

There is no network layer. Many of the basic functions have been streamlined and

eliminated to provide great throughput

11. What is the message types needed for Frame relay call control? The message types needed for Frame Relay Call Control is: i. SETUP

ii. CONNECT iii. RELEASE iv. RELEASE COMPLETE

12. What are the AAL services? The Services offered by the ATM Adaptation Layer is:

i. Handling of transmission errors ii. Segmentation and reassembly, to enable larger blocks of data to be

carried in the information field of ATM cells

iii. Handling of lost and misplaced cell conditions iv. Flow control and timing control

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13. What are the applications of AAL? The applications of AAL is:

i. Circuit emulation ii. VBR voice and video

iii. General data services iv. IP over ATM v. Multiprotocol encapsulation over ATM

vi. LAN emulation

14. What is SNP? The sequence Number Protection field is an error code for detection

and possibly correction on the sequence number field. It consists of a 3 bit

cyclic redundancy check, calculated over the 4 bit SN field, and a parity bit.

The parity bit is set so that the parity of the 8 bit SAR header is even

15. Differentiate bridge and layer2 switch.

Bridge Layer2Switch

i. Frame handling alone in software

ii. Analyze & forward one frame at handle at a time

iii. Store and forward

i. Frame handling in hardware

ii. Multiple data paths & can multiple frames at a time

iii. Can do cut through

16. What are the benefits of 10 Gbps Ethernet over ATM? The benefits of 10Gbps Ethernet over ATM is: i. No expensive, bandwidth consuming conversion between Ethernet

packets and ATM cells

ii. Network is Ethernet end to end

iii. IP plus Ethernet offers QoS and traffic policing capabilities approach that of ATM

iv. Wide variety of standard optical interfaces for 10Gbps Ethernet

17. What is the purpose of Fiber channel? Fiber channel is designed to combine the best features of both

technologies the simplicity and speed of channel communication with the

flexibility and interconnectivity that characterize protocol based network

communication.

18. List some of the requirements of Wireless LAN. The requirement of Wireless LAN is:

i. Throughput ii. Number of nodes

iii. Connection to backbone LAN iv. Service area v. Handoff/roaming

vi. Dynamic configuration

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19. What are the IEEE 802.11 services? The IEEE 802.11 services are: i. Association

ii. Reassociation iii. Disassociation iv. Authentication v. Privacy

20. What are the physical Medias defined in 802.11? The physical medias defined in 802.11 is i. Direct sequence spread spectrum operating in the 2.4 GHz ISM band,

at data rates of 1 Mbps and 2 Mbps

ii. Frequency hopping spread spectrum (FHSS) operating in the 2.4GHz ISM band at data rates of 1Mbps and 2Mbps

iii. Infrared at 1 Mbps and 2 Mbps operating at a wavelength between 850 and 950nm

21. Define: Cell lose ratio It defines the fraction of cells lost during the transmission

22. Define: Cell transfer delay It is the average time needed for a cell to travel from source to destination.

23. Define: Cell delay variation tolerance It is a measure of the variation in cell transmission time.

24. Define: Sustainable cell rate. The SCR is the average cell rate over a long time interval. The actual cell rate

may be lower or higher than this value, but the average should be equal to or

less than SCR.

25. Define: peak cell rate The Peak cell rate(PCR) defines the senders maximum cell rate. The users cell

rate can sometime reach this pack as long as the cell delivered in error.

26. What is the purpose of pay load type field in ATM cell format? It is 3 bit information. It indicates type of data in the information field. The

first bit indicates whether it is user data or network management data, second

bit indicate whether it experience congestion or not, third bit indicate SDU

type.

27. What is the purpose of cell lose priority bit in ATM cell format? It provides guidance to the network in the event of congestion. A value of 0

indicates a cell of relatively higher priority which should not be discarded

unless no other alternatives is available. A value of 1 indicates that this cell is

subject to discard with in the network.

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28. Define: cell sequence integrity It is the characteristic of virtual channel that can be used for call control(i.e

signaling channel)

29. What are the two types of sub layer used in ATM adaptation layer? Convergence layer, and Segmentation layer.

30 Compare packet switching(X.25) and frame relay network.

(AU:Nov/Dec. 2007)

Packet Switching(X.25) Frame-relay network

Hop by hop flow and error control. Ene-to end flow and error control

Multiplexing & switching done in layer3 Multiplexing and switching operation are

carried out in layer 2

In band signaling. Common channel signaling

Data rate-64Kbps. Data rate -2mbps

31. What is the need for AAL? (AU:Nov/Dec 2007) The use of ATM creates the need for an adaptation layer to support

information transfer protocol but not based on ATM. Example PCM voice,

LAPF.

32. What are the data link control functions that are provide by LAPF core? (AU:may/june 2008)

Frame delimiting, alignment and transparency.

Frame multiplexing.

Detection of transmission errors.

Congestion control functions

Inspection of frame that it is neither too long nor too short.

33. What are the uses of wireless LAN? (AU:may/june 2008)

It saves the cost of installation of LAN cabling and cases the task of

location and other modification to network structure.

It provides an effective and more attractive alternative in stock

exchanging, warehouses etc.

34. Distinguish between frame relay and ATM. (AU:may/june 2009)

Frame relay ATM

Variable cell size. Fixed cell size

2Mbps speed 10-100 Mbps speed

Less efficient Compared to Frame relay,

ATM is more efficient

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35. What is the difference between class A and class B service offered by ATM? (AU:may/june 2009)

Class A Class B

Constant bit rate. Variable bit rate

ATM adaptation layer. ATM adaptation layer protocol

used in AAL2

36. Define: minimum cell rate It is the minimum cell rate acceptable that a sender guaranteed to send.

37. Define: cell error ratio. It is the fraction of the cell delivered in error.

38 Define: Collision domain.

The maximum distance that data can travel between two station is called

collision domain in Ethernet.

39. Define: Ffabric in fiber channel communication. The fiber channel communication network consists of one or more switching

elements, which are collectively called as fabrics.

1.21. What is meant by meta signaling channel?

This channel is used to set up a virtual channel that can be used for call control

(i.e signaling channel)

40. What is meant by ad hoc networking? An Ad hoc network is a peer-to peer network (no centralized server) set uop

temporarily to meet some immediate need.

41. Draw IEEE 802.3 MAC frame format.

Preamble SFD Destinatio

n address

Source

address

PDU Data &

padding

CRC

42. What do you mean by common channel signaling and in channel signaling? Common channel signaling: The dates and control signals of a user are

transmitted on separate channel. The control signals of all the users are passed

through a signal common channel.

In channel signaling: The data and control signals of a user are transmitted on

same channel. There are two types

Inband signaling.

Out of band signaling.

43. Compare inband signaling and out of band signaling. Inband signaling: if data and control signals traveling in same channel have

same frequency then it is inband signaling.

Out of band signaling:If data and control signals traveling in same channel

with different frequencies then it is called out-of band signaling.

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UNIT II

CONGESTION AND TRAFFIC MANAGEMENT

1. Difference between multiserver queue and multiple single server.

Multiserver queues Multiple single sever queues

1.It has less waiting time 1. Waiting time is more since there are

many single servers.

2.It has infinite populations and infinite

queue size

2.Population and queue size is less and

have significant impact on performance

2. Define: Kendall's notation The notation is given by X/Y/N where

i. X refers to the distribution of inter arrival times ii. Y refers to the distribution of service times iii. N refers to the number of server

3. Define: Mean residence time Residence times is defined as the average time that an item spends in a system,

waiting and being served and it is referred as Tr.

4. List some of the common distributions made. The Common distributions made are:

i. G, general distribution of inter arrival times or service times ii. GI, general distribution of inter arrival times with restriction that

inter arrival times are independent

iii. M, negative exponential distribution iv. D, deterministic arrivals or fixed length service

5. Why Queuing Analysis is used? The Queuing Analysis is used for:

i. Option 1: Will wait and see what happens ii. Option 2: Analyst may take the position impossible to project

future demand and degree of certainty

iii. Option 3: Use of an Analytic model iv. Option 4: Use of Simulation model

6. List some of the model characteristics. The characteristics are

i. Item population ii. Queue size

iii. Dispatching discipline

7. List the assumption made on input and output. The assumptions made on input are,

i. Arrival time ii. Service time

iii. Number of servers

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The assumptions made on output are,

Items waiting Waiting time Items queued Residence time

8. What is the objective of congestion control? The objective of congestion control is to maintain the number of packets

within the network below the level at which performance falls off dramatically.

9. Differentiate between implicit congestion and explicit congestion.

Implicit congestion Explicit congestion

1.It deals with discard and delay 1.It deals with binary rate and credit

2.Mainly used for connectionless or

datagram configurations such as IP based

internet

2.It takes place in two direction forward

and backward

10. Define: Backpressure Backpressure is a method which can be applied in a logical connection used

for connection oriented network and X.25 based packet network in which traffic

generation can be reduced.

11. Define: Choke packet. Choke packet is control packet generated at a congested node and transmitted

back to a source node to restrict traffic flow.

Eg: ICMP (Internet Control Message Protocol) and Source quench.

12. List the congestion control mechanism in packet switching networks. The Congestion Control Mechanism in Packet Switching networks are:

i. Send a control packet from congested node to some or al source nodes

ii. Rely on routing information iii. Make use of an end-to-end probe packet iv. Allow a packet switching nodes to add congestion information to

packets as they go by

13. List the objectives of frame relay congestion control. The objectives of Frame Relay Congestion Control are:

i. Minimize frame discard ii. Create minimal network additional traffic

iii. Maintain, with high probability and minimum variance iv. Be simple to implement v. Distribute network resource fairly among users

14. What is Discard Strategy? Discard Strategy deals with the most fundamental response to congestion;

when congestion becomes severe enough, the network is forced to discard frames.

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15. What is Congestion Avoidance? Congestion Avoidance is used at onset of congestion to minimize the effect on

the network. Explicit signaling mechanism from the network that will trigger the

congestion avoidance

16. What is Congestion recovery? Congestion recovery procedures are used to prevent network collapse in the

face of severe congestion. These procedure are typically initiated when the network

begun to drop frames due to congestion.

Eg. LAPF , TCP

17. What is committed information rate (CIR)? Committed information rate is a rate, in bits per second that the network agrees

to support for a particular frame-mode connection. It is vulnerable to discard in the

event of congestion.

18. Define BECN. Backward explicit congestion notification (BECN) notifies the user that

congestion avoidance procedures should be initiated where applicable for traffic in

the opposite direction of the received frame. It indicates that frames user transmits on

this logical connection may encounter congested resources.

19. Define FECN. Forward explicit congestion notification (FECN) notifies the user that

congestion avoidance procedures should be initiated where applicable for traffic in the

same direction of the received frame. It indicates that frames user transmits on this

logical connection, has encountered congested resources.

20. What is network response and user response? Network response is necessary for frame handler to monitor its queuing

behavior. Here the choice is based on end user.

User response is determined by the receipt of BECN or FECN .The simplest

procedure is to use BECN because other one is complex.

21. Write the Littles formula and explain its uses. (AU:Nov/Dec 2007) (AU:may/june 2008)

Littles formula for single server is = Ts

Littles formula for multiserver is

= Ts N

It is used to deduce the average at any given value.

22. Compare multi server and multiple single server queues. (AU:Nov/Dec 2007)

Multiple single server queue Multiserver queue

Congestion statistics for this model are in Congestion statistics for this model is in

two cases case of M/M/N

M/MI

M/DI

Probability can be Probability of number of items in the

Zero system is greater than or equal to number

Ratio less than I of servers.

Ratio close to I

Ratio greater than I

23. What are the drawbacks of Backpressure? (AU:may/june 2009)

It can be used only in connection oriented network that allows hop by hop

flow control. Neither frame relay nor ATM has any capability for restricting flow on

hop by hop basis.

24. What are the causes for congestion? (AU:may/june 2009)

The causes for congestion are:

Limitation in queue size.

Load exceeds the network capability.

25. When queue will be formed in a network? Queue is formed if the service required by a user is not available immediately.

That is, if the current demand for a particular service exceeds the capacity of service

provider then queue will be formed.

26. What are the characteristics of queue process? The characteristics of queuing process are

Arrival pattern of data from user

Service pattern of server

Queue discipline

System capacity

Number of servers.

27. What is meant by congestion avoidance? It is the procedure used at beginning stage of congestion to minimize its effort.

28. What is meant by implicit congestion signaling? (AU: Nov/Dec 2010) When network congestion occurs, packets get discard and acknowledgement

will be delayed. As a result, source understands that there is congestion implicitly.

Here, users are notified about congestion indirectly.

29. Define: Committed burst size(Bc)

This is the maximum number of bits in a predefined period of time that the

network is committed to transfer without discarding any frames.

30. Define: Committed information rate(CIR) CIR is a rate in bps that a network agrees to support for a particular frame

mode connection. Any data transmitted in excess of CIR is vulnerable to discard in

event of congestion. CIR is less than access rate.

31. Defin: Access rate. For every connection in frame relay network, an access rate (bps) is defined.

The access rate actually depends on bandwidth of channel connecting user to network.

32. Define: Excess burst rate (Be). This is the maximum number of bits in excess of Bc that a user can send

during a predefined period of time. The network is committed to transfer these bits if there is no congestion. Frames with Be have lower probability to transfer than frames with Bc.

33. What is meant by explicit congestion signaling? In this method, congestion is indicated directly by a notification. The

notification may be in backward or forward direction.

34. What do you mean by choke packet? Choke packet is a control packet generated at a congested node and

transmitted back to a source node to restrict traffic flow. A choke packet is the ICMP

(internet control message protocol) source quench packet.

35. Write Kendalls notation. A convenient notation called kendall notation, have been developed for

summarizing the principle assumption that are made in developing a queuing model.

The notation is given as ( a / b / c) : (d / e)

Here a distribution of inter arrival time b- distribution of service time.

c number of server

d maximum number allowed items in system e queuing discipline used.

36. Define: Coefficient of variation The ratio of standard deviation of service time and mean service time is called

coefficient of variation.

37. List the different congestion techniques.

Discard strategy.

Congestion avoidance (Explicit signaling)

Congestion recover ( implicit signaling)

38. What do you mean by traffic control management?

If user does not respond to congestion notices, then frame relay network has to

discard frames. This method is called traffic control management.

39. List the mechanisms used for congestion control in packet switching network. Mechanisms used are:

Congestion node sends a control packet called choke packet to source nodes.

As a result, it will limit the transmission.

Depending on routing algorithm, routing decision may influence the rate at

which new packets are produced.

Timestamp is added in header of packet and it measures the delay between

two particular points.

Congestion notification information is added to packet, to inform about

congestion to source and destination.

UNIT-III

TCP & ATM Congestion Control

1. List the various retransmission strategies in the implementation of TCP. The various retransmission strategies are as follows:

i. First-only ii. Batch iii. Individual

2. What is meant by self-clocking? TCP automatically senses the network bottleneck and regulates its flow

accordingly. This has been referred to as TCPs self-clocking behavior.

3. What is meant by binary exponential back off? Binary Exponential Back off is a simple technique for implementing

RTO back off is to multiply the RTO for a segment by a constant value for

each retransmission:

RTO=q X RTO The above equation causes RTO to grow exponentially with each

retransmission. The most commonly used value of q is 2. With this value, the

technique is referred to as exponential back off.

4. What do you mean by window-limited mode? In window-limited mode, a TCP source is governed by the TCP flow

and congestion control mechanism. When a TCP connection is set up and a

VC is assigned, ABR will typically allocate a relatively high rate to the source,

only reducing that rate when congestion occurs. Thus, for a time TCP can send

as much data as it can.

5. What do you mean by rate-limited mode? In rate-limited mode TCP is prepared to send segments continuously,

and congestion may occur. The ABR mechanism exerts a back pressure on

TCP sources that can reduce the transmission of TCP segments.

6. What is meant by source traffic descriptor? The source characteristics of an ATM flow are captured in source

traffic descriptor, which includes the following:

i. Peak cell rate(PCR) ii. Sustainable cell rate(SCR) iii. Maximum burst size(MBS) iv. Maximum frame size(MFS)

7. What are the characteristic captured by the ATM Traffic Descriptor? The characteristics of an ATM flow over an ATM connection are

captured in a connection traffic descriptor, which includes the following:

i. Source traffic descriptor ii. Cell delay variation tolerance(CVDT) iii. Conformance definition

8. Define: peak cell rate The peak cell rate defines an upper bound on the traffic that can be

submitted by a source on an ATM connection. The PCR is defined in terms of

the variable T, the minimum spacing between cells, so that the PCR=1/T.The

PCR descriptor is mandatory for CBR and VBR services.

9. Define: sustainable cell rate The sustainable cell rate defines an upper bound on the average rate of

an ATM connection, calculated over a time scale that is large relative to T.

SCR is needed to specify a VBR source. It enables the network to allocate

resources efficiently among a number of VBR sources without dedicating the

resources required to support a constant PCR rate.

10. Define: Maximum burst size The maximum burst size is the maximum number of cells that can be

sent continuously at the peak cell rate. If the cells are presented to the network

in clumps equal to the MBS, then the idle gap between clumps must be

sufficient so that the overall rate does not exceed the SCR.

11. Define: Minimum cell rate The minimum cell rate, used with ABR and GFR, defines the

minimum commitment requested of the network; a value of zero can be used.

The goal of both ABR and GFR service is to provide rapid access to unused

network capacity at up to PCR, whenever the capacity is available.

12. Define: Maximum frame size. The maximum frame size is the maximum size of a frame in cells that

can be carried over a GFR connection. This parameter is only relevant for that

GFR service.

13. Define: Cell delay variation tolerance The cell delay variation tolerance is a measure of the amount of

variation in cell delay that is introduced by the network interface (e.g : SDH)

and at the UNI. CDVT represents a bound on the delay variability due to the

slotted nature of ATM, the physical layer overhead, and ATM layer function

such as cell multiplexing.

14. Define: Cell loss ratio. The cell loss ratio is simply the ratio of lost cells to total transmitted

cells on a connection.

15. Define: Traffic policing The GCRA algorithm is referred to as a form of traffic policing.

Traffic policing occurs when a flow of data is regulated so that cells( or frames

or packets) that exceed a certain performance level are discarded or tagged.

16. Define: Traffic shaping Traffic shaping is used to smooth out a traffic flow and reduce cell

clumping. This can result in a fairer allocation of resources and a reduced

average delay time.

17. What is meant by open loop control? Open loop control is an approach where there is no feedback to the

source concerning to the congestion once the connection is established, UPC

may discard or tag as lower priority any cell that exceeds parameters of the

traffic contract.

18. What is meant by closed loop control? The way that allow a number of sources to share the capacity not used

by CBR and VBR but to provide feedback to sources to adjust the load

dynamically and thus avoid cell loss and share the capacity fairly. This is

referred to as closed-loop control because of its use of feedback.

19. List the parameters for the rate of transmission of cells. The rate of transmission of cells from a source on an ABR connection

is characterized by four parameters:

i. Allowed cell rate(ACR) ii. Minimum cell rate(MCR) iii. Peak cell rate(PCR) iv. Initial cell rate(ICR)

20. Define: Fair share. Fair share can be defined as follows:

Fair share = Target rate

Number of connection

21. State the conditions that must be met for a cell to conform. (AU: Nov/Dec 2007)

In case of ATM, the information flow on each logical connection is organized

into fixed size packets called cells.

22. What are the retransmit policies used in TCP traffic control? (AU: Nov/Dec 2007)

The retransmit policies used in TCP traffic control are:

First only.

Batch

Individual.

23. Why congestion control is difficult to implement in TCP? (AU: April/may 2008)

The end system is expected to exercise flow control upon the source and

system at a higher layer. Thus it is difficult to implement in TCP.

24. Define sustainable cell rate. What is the use of SCR? (AU: April/may 2008) The SCR is the average cell rate over a long time interval. the actual cell rate

may be lower or higher than this value, but the average should be equal to or less than

SCR.

25. What is protocol? Give two examples. (AU: May/June2009) a set of rules used to govern the data transfer.

Example: UDP (User datagram protocol, TCP(Transmission control protocol).

26. Give the significance of timer management in networking. (AU: May/June2009)

The value retransmission time out (RTO) have a initial effect on TCPs reaction to congestion. Hence by calculating RTO effectively, congestion can be

avoided. to calculate RTO effectively, the timer management is essential.

27. What are the mechanisms used in ATM traffic control to avoid congestion condition?

Resource management

Connection admission control

Usage parameter control

Traffic shaping.

28. How is RTO useful to control congestion in TCP? The value of RTO (Retransmission time out) has a critical effect on TCPs

reaction to congestion. Hence by calculating RTO effectively, congestion can be

controlled.

29. Define Reactive Congestion control. Whenever a packet discard occur due to severe condition, some control

mechanism is needed to recover from network collapse. this mechanism is known as

reactive congestion control.

30. What is the use of Preventive congestion control? This preventive congestion control mechanism is used to avoid congestion

before it occurs.

31. What is the difference between flow control and congestion control?

Flow control: The transmitter should not overwhelm the receiver so flow

control is performed.

Congestion control: Its aim is to limit the total amount of data entering the

network; to amount of data that network can carry.

32. What is meant by silly window syndrome? if frequently datas are sent as small segment, the response will be speed in

sender side but it cause degradation in performance. This degradation is called silly

window syndrome.

33. What are the mechanisms used in TCP to control congestion? The mechanisms used in TCP to control congestion are:

RTO timer management

Window management.

34. Define Behavior class selector (BCS). Behavior class selector (BCS) enables an ATM network to provide different

service levels among UBR connections by associating each connection with one of a

set of behavior class.

35. What is meant by allowed cell rate (ACR)? The current rate at which source is permitted to send or transmit cell in ABR

mechanism is called allowed cell rate.

36. List the three fields in the TCP header. The three fields in the TCP header are as follows:

Sequence number (SN)

Acknowledgement number (AN)

Window (W)

37. What is meant by closed loop control in ABR mechanism? Closed loop control: ABR has feedback to the source concerning congestion.

This approach is called closed loop control.

38. What is meant by open loop control in ABR mechanism? Open loop control: If there is no feedback to the source concerning

congestion, then this type of approach is called as open loop control.

39. Define cell insertion time. It is the time taken to insert a single cell on to the network.

40. List the ATM traffic attributes. ATM traffic related attributes falls into four categories. They are

Traffic descriptor.

QoS parameters

Congestion control parameters

Other attributes. It includes behavior class selector and minimum

desired cell rate.

UNIT IV

INTEGRATED AND DIFFERENTIATED SERVICES

1. What are the requirements for inelastic traffic? The requirements for inelastic traffic may include the following and they are

i. Throughput. ii. Delay. iii. Jitter. iv. Packet loss.

2. What are the functions that are provided by ISA to manage congestion and QoS transport?

The functions that are provided by ISA to manage congestion and QoS

transport are

i. Admission control. ii. Routing algorithm. iii. Queuing discipline. iv. Discard policy.

3. What are the principal background functions of ISA? The principal background functions of ISA are

i. Reservation protocol. ii. Admission control. iii. Management agent. iv. Routing protocol.

4. What are the services provided by ISA? Three categories of services are provided by ISA and they are

i. Guaranteed. ii. Controlled load. iii. Best effort.

5. What are the different queuing techniques? The different queuing techniques are:

Fair Queuing (FQ). Processor Sharing (PS). Bit-Round Fair Queuing (BRFQ). Generalized Processor Sharing (GPS). Weighted Fair Queuing (WFQ).

6. Define: RED RED is an approach to congestion management in internets is proactive packet

discard. In this technique , a router discards one or more incoming packets before the

output buffer is completely full, in order to improve the performance of the network.

7. State the design goals of Random Early Detection The design goals of Random Early Detection (RED) are

i. Congestion avoidance. ii. Global Synchronization avoidance. iii. Avoidance of bias against bursty traffic. iv. Bound on average queue length.

8. What are the different types of Traffic? The traffic on network or internet can be classified into two broad categories

i. Elastic Traffic ii. Inelastic Traffic

9. List out the advantages of ISA. The advantage of ISA is:

i. .Many traffic sources can easily and accurately be defined by a token bucket scheme.

ii. The token bucket scheme provides a concise description of the load to be imposed by a flow, enabling the service to determine easily the resource

requirement.

iii. The token bucket scheme provides the input parameters to a policing function.

10. Define: Behavior Aggregate

Behavior Aggregate is a set of packets with the same DS code point crossing a

link in a particular direction.

11. Define Classifier Classifier selects packets based on the DS field

(BA classifier) or on multiple fields within the packet header

(MF classifier).

12. Define: Marking Marking is the process of setting the DS codepoint in a packet. Packets may be

marked on initiation and may be re-marked by an en route DS node.

13. Define Dropping Dropping is the process of discarding packets based on specified rules; also

called policing.

14. Define: Metering Metering is the process of measuring the temporal properties of a packet

stream selected by a classifier. The instantaneous state of that process may affect

marking, shaping and dropping functions.

15. Define: Shaping Shaping is the process of delaying packets within a packet stream to cause it to

conform to some defined traffic profile.

16. What is traffic conditioning? Traffic Conditioning is the control functions performed to enforce rules

specified in a TCA, including metering, marking, shaping and dropping.

17. What is Traffic conditioning Agreement? Traffic Conditioning Agreement is a specifying, classifying rules and traffic

conditioning rules that are to apply to packets selected by the classifier.

18. Draw the format of DS field.

1 2 3 4 5 6 7

19. Draw the format of IPV4.

1 2 3 4 5 6 7

20. What are the elements of Traffic Conditioning function? The elements of Traffic Conditioning function are

i. Classifier ii. Meter iii. Marker iv. Shaper v. Dropper

21. What is elastic traffic? (AU: Nov/Dec2007) Elastic traffic is that which can adjust, over wide changer to changer in delay

and throughput across an internet and still meet the needs of its applications. This is

the traditional type of traffic supported on IP-based internets and is type of traffic for

which internets were designed.

22. What are the key elements of controlled load service? (AU: Nov/Dec2007) The key elements of the controlled load services are:

The service approximates tightly the behavior visible to applications receiving

best-effort service under unloaded conditions.

A very high percentage of transmitted packets will be successfully delivered.

23. What are the drawbacks of FIFO queuing discipline? (AU:April/May2008)

No special treatment for packets with higher priority is provided.

DSCP unused

If small packet is queued behind long packet, then small packet experience

long delay.

24. What is an inelastic traffic? What are the requirements for inelastic traffic? (AU:April/May2008)

It does not easily adapt, if at all, to changes in delay and throughput across the

internet. Example: Real time traffic, its requirements are, throughput, delay, jitter and

packet loss.

25 What is meant by rate control? Give examples. (AU:May/June2009)

The rate of transmission of cells from a source to a network connection can be

controlled by a feedback mechanism is known as rate control.

Example: Available bit rate(ABR)

26. What is label stacking? (AU:May/June2009) Label stacking allows aggregation of more number of label switching paths

into single label switching path.

27. Define delay jitter. The delay jitter is the maximum variation in delay experienced by packets in a

single session.

28. What is meant by best effort service? Flows that are not reserving resources are provided with best effort service.

The network will put best effort to deliver the packet, but if congestion occurs

severely it will discard the packet.

29. What is meant by guaranteed service? Flows that are reserving resources are provided with guaranteed service. The

service provides assured capacity levels.

30. Define global synchronization. Due to packet discard during congestion, many TCP connections entered slow

start at the same time. As a result,the network is unnecessarily under utilized for some

time. The TCP connections which entered into slow start will come out of slow start

at about same time causing congestion again. This phenomenon is called global

synchronization.

31. What are the design goals of RED algorithm? The design goals of RED algorithm are:

Congestion avoidance.

Global synchronization avoidance.

Round on average queue length.

32. Define: Behavior aggregate in per hop behavior A set of packets with the same DS code point crossing a link in a particular

direction behavior aggregate.

33. Define: DS code point. A specified value of 6 bit DS code point portion of the 8 bit DS field in the IP

header which indicate to which class packets belongs and its drop procedure.

34. What is meant by traffic conditioning agreement? An agreement that specify rules that are to apply for packets selected by the

classifier is called traffic conditioning agreement.. Control functions performed in

TCA are metering, marking, shaping and dropping.

35. Define: DS boundary node. DS boundary node is defined as , DS node that connects one DS domain to

the node in another domain.

36. Define DS interior node. A node in DS domain, which is not the boundary node is called DS interior

node.

37. Define: DS node. A router that supports DS policies is called as DS node. A host system that use

DS for application is also called as DS node.

38. What is meant by differentiated service? It does not attempt to view the total traffic demand in integrated service.

It does not reserve network capacity in advance. It provides different level of QoS to different traffic flows.

39. What is meant by integrated services? The integrated service provider-

Views the totally of current traffic demand.

Limits the demand with respect to the current capacity handled by the

network.

Reserve resources with in the domain to provide a particular QoS guaranteed.

UNIT-V

PROTOCOLS FOR QoS SUPPORT

1. What is soft state? A soft state is simply a set of state information at a router that expires

unless regularly refreshed from the entity that requested the state.

2. Define: Channel-changing capability. Enabling the receiver to select one source from among multiple

sources transmitting to a multicast group is known as channel-changing

capability.

3. What are the characteristics of RSVP? The various characteristics of RSVP are

Unicast and multicast Simplex Receiver-initiated reservation Maintaining soft state in the internet Providing different reservation styles Transparent operation through non-RSVP routers Support for IPv4 and IPv6.

4. Define: A session.

A session is a data flow identified by its destination; it reflects the soft

state nature of RSVP operation. A session is defined by destination IP address,

IP protocol identifier, destination port.

5. Define: Flow descriptor. A reservation request issued by a destination end system is called a

flow descriptor and consists of a flowspec and a filter spec.

6. What is reservation attribute? A receiver may specify a resource reservation that is to be shared

among a number of senders (shared) or may specify a resource reservation that

is to be allocated to each sender (distinct).

7. What is sender selection? A receiver may either provide a list of source (explicit) or implicitly

select all sources by providing no filter spec (wild card).

8. Define: Wild-card-filter style The wild-card-filter (WF) style specifies a single resource reservation

to be shared by all senders to this address. Symbolically, this style is

represented in the form WF(*{Q}), where the asterisk represents wild-card

sender selection and Q is the flowspec.

9. Define: Fixed-filter style The fixed-filter (FF) style specifies a distinct reservation for each

sender and provides an explicit list of senders. Symbolically, this style is

represented in the form FF(S1{Q1},S2{Q2}, . . .), where Si is a requested

sender and Qi is the resource request for that sender.

10. Define: Shared-explicit style The shared-explicit (SE) style specifies a single resource reservation to

be shared among an explicit list of senders. Symbolically, this style is

represented in the form SE(S1,S2, . . .{Q}).

11. List the requirements for connection-oriented QoS support. The requirements for connection-oriented QoS support are:

Guarantee affixed amount of capacity for specific applications, such as audio/video conference.

Control latency and jitter and ensure capacity for voice. Provide very specific, guaranted, and quantifiable service

level agreements, or traffic contracts.

Configure varying degrees of QoS for multiple network customers.

12. What is traffic engineering? The ability to define routes dynamically, plan resource commitments

on the basis of known demand, and optimize network utilization is referred

to as traffic engineering.

13. Define: Label switched routers. An MPLS network or internet consisting of a set of nodes, called label

switched router (LSRs), capable of switching and routing packets on the basis

of which a label has been appended to each packet.

14. Draw the MPLS label format.

Bits: 20 3 1 8

Exp = experimental

S = bottom of stack bit

15. What is hop-by-hop routing? In hop-by-hop routing, each LSR independently chooses the next hop

for each FEC. RFC implies that this option makes use of an ordinary routing

protocol, such as OSPF.

Label Value Exp S Time to live

16. What is explicit routing? In explicit routing, a single LSR, usually the ingress or egress LSR,

specifies some or all of the LSRs in the LSP for a given FEC. There are two

types of explicit routing namely strict explicit routing and loose explicit

routing.

17. Define: Constraint-based routing algorithm. A routing algorithm that takes into account the traffic requirements of

various flows and that takes into account the resources available along various

hops and through various nodes is referred to as a constraint-based routing

algorithm.

18. What is a translator? The translator is a simpler device that produces one or more outgoing

RTP packets for each incoming RTP packet. The translator may change the

format of the data in the packet or use a different lower-level protocol suite to

transfer from one domain to another.

19. What are the fields in RTP fixed header? The fields in RTP header are : Version (2 bits) Padding (1 bit) Extension (1bit) CSRC Count (1 bit) Marker (1 bit) Payload Type (7 bits) Sequence Number (16 bits) Timestamp (32 bits) Synchronization Source Identifier Contributing Source Identifier.

20. What are the functions performed by RTCP?

Quality of Service (QoS) and congestion control Identification Session size estimation and scaling Session control

21. What is meant by soft state in RSVP? RSVP use connectionless approach, each intermediate router maintain state

information about nature of flow, that will be refreshed by end system at

predetermined amount of time. This is called soft state.

22. Why receiver is responsible to initiate reservation in RSVP? Each member (destination) in multicast may require different resources to be

reserved depending on QOS it needs. So it is therefore better for receiver to make

resource reservation.

23. Define: Session in RSVP Once a reservation is made at a router by a particular destination, the router

considers this as a session and allocates resources for the life of that session. Session

is defined by

Session: Destination IP addresses.

IP protocol identifier.

Destination port.

24. Define: Flow specification in RSVP The flow specification of RSVP specifies a desired QOS and is used to set

parameters in a nodes packet scheduler. Flow space is defined by Flow space: Service class

Reserve specification

Traffic specification.

25. Define: Filter specification in RSVP Filter specification in RSVP defines the set of packets or flow, for which a

reservation is requested. Filter space is define by

Filter specification: Source address

UDP / TCP source port.

26. What are the types of reservation style used in RSVP?

Wild card filter reservation style.

Fixed filter reservation style.

Shared explicit reservation style.

27. What do you mean by label merging and frame merging? Label merging: The replacement of multiple incoming labels for a particular

forward equivalent class with a single outgoing label is called label merging.

Frame merging: Label merging, when it is applied to operation over frame

based media, then it is called as frame merging

28. Define label swapping in MPLS. The basic operation of looking up an incoming label to determine the outgoing

label and forwarding is called label swapping.

29. Define Label switched hop in MPLS. The hop between two MPLS nodes on which forwarding is done using label is

called label switched hop.

30. What is meant by ingress edge and egress edge in MPLS domain?

Ingress edge: Label switched router through which packets from internet

router enters into MPLS domain is called ingress edge.

Egress edge LSR: LSR through which packets leaves the MPLS domain is

called egress edge.

31. List the characteristics of MPLS. MPLS characteristic that ensure its popularity are

Connection oriented QOS support.

Traffic Engineering.

Virtual private network (VPN) support.

Multi protocol support.

32. Define: MPLS MPLS (multi protocol label switching) is a mechanism used to speed up IP

packet forwarding process and therefore reduce delay and improve overall throughput

of internet.

33. Define: Label switched router in MPLS An MPLS network consists of a set of nodes called label switched router(LSR)

capable of switching and routing packets on the basis of which a label has been added

to each packets.

34. What is the purpose if time to live field in label format? The value of this field is decremented at each router and the packet is dropped

if the count falls to zero.

35. What is meant by integrated layer processing in RTP? In TCP/IP each layer processed sequentially, whereas in integrated layer

processing, adjacent layers are tightly coupled and they function parallel.

36. What is the function of RTP relays and give its types? A relay operating at a given protocol layer is an intermediate system that acts

as both a destination and a source in a data transfer.

37. What is the function of mixer in RTP? (AU: Nov/Dec 2007)

Mixer: It is a source of synchronization. It receives stream of RTP packets

from one or more sources. Combines these streams and forwards a new RTP

packet stream to one or more destinations.

38. What is wild card filter style? (AU: Nov/Dec 2007) The wild card-filter style specifies a single resource reservation to be shared

by all senders to this address. This style is represented in form WF(*{Q}) where

asterisk represent wild-card sender selection and Qis the flows pet.

39. What is the use of translator in RTP? (AU: April/may 2008) Translator produces one or more outgoing RTP packets for each incoming

packets. It changes the format of the data that suite to transfer from one domain

to another.

40. Mention the protocol used for congestion control. (AU: May/June 2009)

RSVP (Resource reservation protocol.

TCP (transfer control protocol.

41. What is RTP? Discuss with examples. (AU: May/June 2009) RTP is the acronym for Real time protocol. It is a transport level protocol used

for real time distributed application.

Example: Audio and video conferencing.

Interactive simulation.

Remote medical diagnosis.