Networking Sample Questions

praveensagar4u.blogspot.com
Question Bank

1. Which of the following protocols are examples of TCP/IP transport layer protocols?
a. Ethernet
b. HTTP
c. IP
d. UDP
e. SMTP
f. TCP

2. Which of the following protocols are examples of TCP/IP network access layer protocols?
a. Ethernet
b. HTTP
c. IP
d. UDP
e. SMTP
f. TCP
g. PPP

3. The process of HTTP asking TCP to send some data and make sure that it is received correctly is an example of what?
a. Same-layer interaction
b. Adjacent-layer interaction
c. The OSI model
d. All the other answers are correct.

4. The process of TCP on one computer marking a segment as segment 1, and the receiving computer then acknowledging the receipt of segment 1, is an example of what?
a. Data encapsulation
b. Same-layer interaction
c. Adjacent-layer interaction
d. The OSI model
e. None of these answers are correct.

5. The process of a web server adding a TCP header to a web page, followed by adding an IP header, and then a data link header and trailer is an example of what?
a. Data encapsulation
b. Same-layer interaction
c. The OSI model
d. All of these answers are correct.

6. Which of the following terms is used specifically to identify the entity that is created when encapsulating data inside data link layer headers and trailers?
a. Data
b. Chunk
c. Segment
d. Frame
e. Packet
f. None of these—there is no encapsulation by the data link layer.

7. Which OSI layer defines the functions of logical network-wide addressing and routing?
a. Layer 1
b. Layer 2
c. Layer 3
d. Layer 4
e. Layer 5
f. Layer 6
g. Layer 7

8. Which OSI layer defines the standards for cabling and connectors?
a. Layer 1
b. Layer 2
c. Layer 3
d. Layer 4
e. Layer 5
f. Layer 6
g. Layer 7

9. Which OSI layer defines the standards for data formats and encryption?
a. Layer 1
b. Layer 2
c. Layer 3
d. Layer 4
e. Layer 5
f. Layer 6
g. Layer 7

10. Which of the following terms are not valid terms for the names of the seven OSI layers?
a. Application
b. Data link
c. Transmission
d. Presentation
e. Internet
f. Session

Fill In The Blanks:

1. Number of links to connect n nodes in a mesh topology is = _______.

2. Mesh Topology is _______ flexible and has a ________ expandability

3. In BUS topology, at each end of the bus is a ____________, which absorbs any signal, removing it from the bus. 

4. In BUS topology, One can easily add any new node or delete any node with-out affecting other nodes; this makes this topology easily _____________. 

5. _________ and ______________ will force a maximum length of shared medium which can be used in BUS topology. 

6. The two alternatives for the operation of the central node in STAR topology are:

__________ and ___________. 

7. In Ring Topology, the links are _____________; that is, data are transmitted in __________ direction only and all are oriented in the same way

8. In Ring Topology, Repeater works in 3 modes: ____________, _____________ and ______________.

9. ___________ topology can be considered as an extension to BUS topology.

10. ______________ is suitable for use in star and ring topologies

11. Coaxial cable is suitable for use in __________ topology.

Solutions:

1. n(n-1)/2

2. not, poor

3. terminator

4. expandable.

5. Delay, signal unbalancing

6. repeater, switch

7. unidirectional, one

8. Listen, Transmit, By-Pass

9. Tree

10. Twisted pair

11. BUS

Short Answer Questions:

Q-1.  List out the advantages and drawbacks of bus topology.

Ans: Advantages:

i) Easy to implement 

ii) It is very cost effective because only a single segment required

iii) It is very flexible

iv) Moderate reliability.

v) Can add new station or delete any station easily (scalable)

Disadvantages:

i) Required suitable medium access control technique.

ii) Maximum cable length restriction  imposed due to delay and signal

unbalancing problem.

Q-2.  List out the advantages and drawbacks of ring topology.

Ans: Advantages:

i) Data insertion, data reception and  data removal can be provided by repeater

ii) It can provide multicast addressing.

iii) Point-to-point links to its adjacent nodes (moderate cost)

Disadvantages:

i) The repeater introduces a delay

ii) The topology fails if any link disconnects or a node fails.

iii) Direct link not provided

iv) It provides complex management

Q-3.  Why star topology is commonly preferred?

Ans: It gives high reliability, more flexible and higher bandwidth. Since there is a central control point, the control of network is easy and priority can be given to selected nodes.

Q-4. Is there any relationship between transmission media and topology?

Ans: Yes, medium should be selected based on the topology. For example, for bus topology coaxial cable medium is suitable, and for ring/star topology twisted-pair or optical fiber can be used.

Fill In The Blanks:

1. The basic question which has to be answered by the medium-access control techniques is “How Goes ________”?

2. In _______________ technique, each node gets a chance to access the medium by rotation.

3. The key issues involved in MAC protocol are - Where and ______ the control is exercised.

4. ‘Where’ refers to whether the control is exercised in a _____________ or ______________ manner.

5. The _______________ techniques can be broadly  categorized into three types; Round-Robin, Reservation and___________.

6. ______________ is an example of centralized control and ______________ is an example of distributed control

Version 2 CSE IIT, Kharagpur 7. In Polling technique, if there is  no data, usually a ______________ message is sent back. 

8. In pure ALOHA, channel utilization, expressed as throughput S, in terms of the offered load G is given by _________ 

9. In slotted ALOHA, a maximum throughput of ________ percent at 100 percent of offered load can be achieved, while it is ______ percentage for pure ALOHA. 

10. _________________ is abbreviated as CSMA/CD and is also known as  .__________

11. To achieve stability in CSMA/CD back off scheme, a technique known as ______________ is used

Solutions:

1. Next

2. token passing

3. How

4. centralized, distributed

5. asynchronous, Contention

6. Polling, token passing

7. poll reject

8. S=Ge-2G

9. 37, 18

10. Carrier Sensed Multiple Access with Collision Detection, Listen-While-Talk .

11. binary exponential back off

Short Answer Questions:

Q-1. In what situations contention based MAC protocols are suitable?

Ans:    Contention based MAC protocols are suitable for bursty nature of traffic under light to moderate load. These techniques are always decentralized, simple and easy to implement.

Q-2.  What is vulnerable period? How it affects the performance in MAC protocols?

Ans: The total period of time when collision may occur for a packet is called vulnerable period. Let, all packets have a fixed duration  λ. Then vulnerable period is 2λ in pure ALOHA scheme and  λ in slotted ALOHA scheme. If vulnerable period is long, probability of the occurrence collision increases leading to reduction in throughput.

Q-3.  How throughput is improved in slotted ALOHA over pure ALOHA?

 Ans: In pure ALOHA vulnerable period is 2λ. 

So, S/G = e-2G  or throughput S = G e-2G , where G is the total number of packets. 

Maximum value of G = 0.5 or maximum throughput Smax = 1/2e.

In slotted ALOHA, vulnerable period is λ    and S/G = e-G  or throughput S = G e-G . Here,

maximum value of G is 1 and maximum throughput Smax = 1/e.

Q-4. What is the parameter ‘a’? How does it affect the performance of the CSMA protocol?

Ans:  The efficiency of CSMA scheme  depends on propagation delay, which is represented by a parameter ‘a’ as defined below.

                            propagation delay

                     a = --------------------------------

                            packet transmission time 

 Smaller the value of propagation delay, lower is the vulnerable period and higher is the efficiency. If propagation delay is zero, collision cannot occur in CSMA scheme. But in practice, there is some delay and depending on the value of  ‘a’ collision occurs.

Q-5.   How performance is improved in CSMA/CD protocol compared to CSMA protocol?

Ans: In CSMA scheme, a station monitors the channel before sending a packet. Whenever a collision is detected, it does not stop transmission leading to some wastage of time. On the other hand, in CSMA/CD scheme, whenever a station detects a collision, it sends a jamming signal by which other station comes to know that a collision occurs. As a result, wastage of time is reduced leading to improvement in performance. 

Fill In The Blanks :

1. The  802.2 standard describes the ____________, which is the upper part of the data link layer. 

2. LLC offers three types services: Unreliable datagram service, ________________ and _______________.

3. IEEE 802 bundle also includes a MAN standard IEEE 802.6 which is also known as ______________.

4. 100Base-T2 means _______________________________

5. 100 Mbps, baseband, long wavelength over optical fiber cable will be abbreviated as ________________

6. Ethernet uses __________ encoding

Answers:

1. LLC (logical link layer)

2. Acknowledged datagram service, Reliable connection oriental service

3. Distributed Queue Dual Bus (DQDB)

4. 100 Mbps, baseband, over two twisted-pair cables

5. 1000Base F

6. Bi-phase Manchester

Short question Answers

Q-1 What are the goals in mind of IEEE 802 committee?

Ans: IEEE 802 committee has few goals in mind, namely

– To promote compatibility

– Implementation with minimum efforts

– Accommodate diverse applications

Q-2.  List the functions performed by the physical layer of 802.3 standard?

Ans.  Functions of physical layer are:

i) Data encoding/decoding (To facilitate synchronization and efficient transfer of signal through the medium).

ii) Collision detection (It detects at the transmit side)

iii) Carrier sensing (Channel access senses a carrier on the channel at both the transmit and receive sides)

iv) Transmit/receive the packets (Frame transmitted to all stations connected to the channel)

v) Topology and medium used (Mediums are co-axial cable, twisted pair and fiber optic cable) 

Q-3.  Why do you require a limit on the minimum size of Ethernet frame?

Ans. To detect collision, it is essential that a sender continue sending a frame and at the same time receives another frame sent by another station. Considering maximum delay with five Ethernet segments in cascade, the size of frame has been found to be 64 bytes such that the above condition is satisfied. 

Q-4.  What are the different types of cabling supported by Ethernet standard?

Ans.  Types of cabling are:

i) 10 BASE 5 - Maximum cable length  is 500 meters using 4” diameter coaxial cable.

ii)  10 BASE 2 - Maximum cable length is 185 meters using 0.25” diameter CATV cable.

iii) 10 BASE T - Maximum cable length  is 100 meters using twisted-pair cable (CAT-3 UTP).

iv) 10 BASE FL - Maximum cable length is 2 Km using multimode fiber optic cable (125/62.5 micrometer).

Fill In The Blanks:

1. Originally, ______________ developed Token Ring network in the ________.

2. A disadvantage of this topology is that it is vulnerable to _________ or _____ failure.

3. Unlike CSMA/CD networks (such as Ethernet), token-passing networks are ________________, which means that it is possible to calculate the maximum time that will pass before any end station will be capable of transmitting.

4. Token Ring frames have two fields that control priority: ___________ and the ___________field.

Version 2 CSE IIT, Kharagpur 5. In Token Ring inside the wire center, _____________ are used to isolate a broken wire or a faulty station.

6. The Mac sublayer in Token BUS consists of four major functions: ____________, the access control machine (ACM), ______________________and  .____________

7. ___________ determines when to place a frame on the bus, and responsible for the maintenance of the logical ring including the error detection and fault recovery.

Answers:

1. IBM, 1970

2. link, station

3. deterministic

4. the priority field, reservation

5. bypass relays

6. the interface machine (IFM), the receiver machine (RxM), the transmit machine (TxM).

7. Access control machine (ACM)

Short question Answers:

Q-1.  What is the advantage of token passing protocol over CSMA/CD protocol?

Ans.     Advantage of token passing protocol over CSMA/CD protocol: 

The CSMA/CD is not a deterministic protocol. A packet may be delivered after many (up to 15) collisions leading to long variable delay. An unfortunate packet may not get delivered at all. This feature makes CSMA/CD protocol unsuitable for real-time applications. On the other hand, token passing protocol is a

deterministic approach, which allows a  packet to be delivered within a known time frame. It also allows priority to be assigned to packets. These are the two key advantages of token passing protocol over CSMA/CD protocol.

Q-2.  What are the drawbacks of token ring topology?

Ans.  Token ring protocol cannot work if a link or a station fails. So, it is vulnerable to link and station failure. 

Q-3.  How the reliability of token ring topology can be improved?

Ans.  Reliability of the ring network can be improved by implementing the ring topology using a wiring concentrator. This allows not only to detect fault, but also to isolate the faulty link/station with the help of a bypass relay. 

Q-4.  What role the active token monitor performs?

Ans. Token ring is maintained with the help  of active token monitor. Any one of the stations has the capability to act as active token monitor, but at a particular instant only one acts as active token monitor. It monitors various error situations such as multiple token, orphan packet, etc, and takes appropriate action to come out of the error situation. 

Fill In The Blanks: 

1. The high speed LANs that have emerged  can be broadly categorized into three types______________, successors of Ethernet and ___________.

2. ATM, fiber channel and the Etherswitches comes under high speed LANs based  on _______________.

3. ______________________ is abbreviated as FDDI.

4. FDDI over copper is referred to as __________________________.

5. The basic topology for FDDI is _____________________.

6. An _____________ provides continuous dual-ring operation if a device on the dual ring fails

7. Each data frame in FDDI carries up to ____________ bytes.

8. FDDI gives fair and equal access to the ring by using a _________ protocol.

9. FDDI implements MAC using three timers namely: ________________,  Token Rotation Timer (TRT) and ___________________

10. Token holding Timer  (THT), which determines .___________________________

11. The frame status (FS) byte is  set by the ____________ and checked by the _______________ station which removes its frame from the ring and generates another token.

12. When the frame returns to the sending  station, that station removes the frame from the ring by a process called ___________.

13. The physical layer is divided into two sub layers - _______ and ______

Solutions.

1. based on token passing, based on switching technology.

2. based on switching technology.

3. Fiber Distributed Data Interface

4. Copper-Distributed Data Interface (CDDI).

5. dual counter rotating rings

6. optical bypass switch

7. 4500

8. timed token

9. Token holding Timer (THT), Valid Transmission Timer (VTT)

10. how long a station may continue once it has captured a token

11. destination, source

12. stripping

13. PMD, PHY

Short Questions: 

Q-1.  In what way the MAC protocol of FDDI differs from that of token ring?

Ans:  In the frame format of FDDI protocol, preamble is eight bytes instead of one byte in token ring. Also token has one additional byte. FDDI can have multiple frames simultaneously, which cannot be present in token ring. Here, the access method is timed token passing. Multiple frames can be transmitted after capturing a token.  First, the entire token is captured and then the data frames are introduced, whereas token ring follows token passing protocol and beginning of token  is converted to the header of a frame.  In case of token ring token is released after receiving the acknowledgement (as the data frame returns after circulating the  ring). On the other hand, in case of FDDI, token is released immediately after sending  data frame, which is known as early token release. 

Q-2.  How FDDI offers higher reliability than token ring protocol?

Ans:  Token ring protocol is applicable in a single ring. Disadvantage of this protocol is that, if one segment of wires fails or a node fails, the protocol cannot work. To increase reliability, dual counter ring topology used in FDDI protocol, where there are two rings, called primary ring and secondary ring. In case  of failure of a node or a fiber link, the ring is restored the by wrapping up the primary ring to the secondary ring. Further improvement in reliability can achieve by using  dual ring of trees and  dual homing mechanism. It will provide multiple paths and if one path fails, another path will be available for passing token or data. 

Q-3 What are the functionalities of a Optical Bypass Switch?

Ans: An optical bypass switch provides continuous dual-ring operation if a device on the dual ring fails. This is used both to prevent ring segmentation and to eliminate failed stations from the ring. The optical bypass switch performs this function using optical mirrors that pass light from the ring directly to the DAS (dual-attachment station) device during normal operation. If a failure of the DAS device occurs, such as a power-off, the optical bypass switch will pass the light through itself by using internal mirrors and thereby will maintain the ring's integrity. When using the OB, you will notice a tremendous digression of your network as the packets are sent through the OB unit.

Q-4 What are the functionalities provided by SMT standard?

Ans: The Station Management (SMT) standard provides services that monitor and control a FDDI station.  SMT include facilities for connection management, node configuration, recovery from error condition, and encoding of SMT frames.

Q-5 Describe various fields in frame format of FDDI?

Ans: Let us have a look at the various fields:

SD: The first byte, after the preamble, of the field is the frame’s starting flag. As in

Token ring these bits are replaced in physical layer by the control codes.

FC: it identifies the frame type i.e. token or a data frame.

Address: the next 2 fields are destination and source addresses. Each address consists of

2-6 bytes.

Data: Each data frame carries up to 4500 bytes.

FCS: FDDI uses the standard IEEE four-byte cyclic redundancy check.

ED: this field consists of half a byte in data frame or a full byte in token frame. This

represents end of the Token.

FS: FDDI FS field is similar to that of Token Ring. It is included only in data/Command

frame and consists of one and a half bytes. 

Fill In The Blanks: 

1. Switched Ethernet gives dedicated 10 Mb/s bandwidth on __________ of its ports.

2. In Ethernet (IEEE 802.3) the topology, though physically is _________ but logically is BUS. i.e. the collision domain of all the nodes in a LAN is   ._________

3. In Switched Ethernet, collision domain is separated. Hub is replaced by a  .________

4. There are two techniques used in the implementation of Ethernet switches: _____________ and ________ 

5. IEEE has designed two categories of Fast Ethernet: ____________ and   .__________

6. 100-Base-X itself is divided into two: __________ and __________ 

7. The Gigabit Ethernet Alliance was formed in ___________ by ______ companies.

8. The GMII is the interface between the ________ layer and the ___________ layer.

9. ________, a sublayer of GMII provides a medium-independent means for the PCS to support various serial bit-oriented physical media.

10. Packet Bursting is an extension of ______________. Packet Bursting is "Carrier Extension plus a ____________".

Solutions:

1. each

2. star, common

3. switch

4. store-and-forward, cut-through

5. 100Base-X, 100Base-T4

6. 100Base-TX, 100base-FX.  

7. May 1996, 11

8. MAC, Physical

9. PMA (Physical Medium Attachment)

10. Carrier Extension, burst of packets

Short Questions: 

Q-1. Explain the basic difference between IEEE 802.3 and switched Ethernet, as far as implementation is concerned.

Ans: In Ethernet (IEEE 802.3) the topology, though physically is start but logically is BUS. i.e. the collision domain of all the nodes in a LAN is common. In this situation only one frame can send the frame, if more than one station sends the frame, there is a collision. 

In Switched Ethernet, this collision domain is separated. Hub is replaced by a switch, a device that can recognize the destination address and can route the frame to the port to which the destination station is connected, the rest of the media is not involved in the transmission process. The switch can receive  another frame from another station at the same time and can route this frame to its own final destination.

Q-2. Explain the two techniques for implementing Ethernet switches. 

Ans: There are two techniques used in the implementation of Ethernet switches:  storeand-forward and  cut-through. In the first case, the entire frame is captured at the incoming port, stored in the switch’s memory, and after an address lookup to determine the LAN destination port, forwarded to  the appropriate port. The lookup table is automatically built up. On the other hand,  a cut-through switch begins to transmit the frame to the destination port as soon as it decodes the destination address from the frame header.

Store-and-forward approach provides a greater level of error detection because damaged frames are not forwarded to the destination port. But, it introduces longer delay of about 1.2 msec for forwarding a frame and suffers  from the chance of loosing data due to reliance on buffer memory. The cut-through switches, on the other hand, has reduced latency but has higher switch cost.

Q-3. What are the different categories of Fast Ethernet?

Ans: IEEE has designed two categories of Fast Ethernet: 100Base-X and 100Base-T4. 100Base-X uses two cables between hub and the station while 100Base-T4 uses four. 100-Base-X itself is divided into two: 100Base-TX and 100base-FX.   * 100 BASE-T4: This option is designed to avoid overwriting. It is used for half-duplex communication using four wire-pairs of the existing category 3 UTP cable, which is already available for telephone services in homes/offices. Two of four pairs are bi-directional; other two are

unidirectional. This means that there are 3 pairs to be used for carrying data, in each direction (2 bi-directional and 1 unidirectional). Because 100Mbps data cannot be handled by voicegrade UTP, this specification splits the 100 Mbps flow into three 33.66Mbps flow.

*100 BASE TX: This option uses two category 5 UTP or two shielded (STP) cable to connect a station to hub. One pair is used to carry frames from the hub to the station and other to  carry frames from station to hub. Encoding is 4B/5B to handle 100  Mbps; signaling is NRZ-I. The distance between station and hub should be less than 100 meters.

  *100 BASE FX: This option uses two Fiber optic cables, one carry frames from station to hub and other from hub to station. The encoding is 4B/5B and signaling in NRZ-I. the distance between station and hub should be less than 2000 meters.

Q-4. What are the Objectives of The Gigabit Ethernet Alliance?

Ans: The objectives of the alliance are: 

• supporting extension of existing Ethernet and Fast Ethernet technology in response to demand for higher network bandwidth. 

• developing technical proposals for the inclusion in the standard 

• establishment of inter-operability test procedures and processes 

Q-5. Explain GMII (Gigabit Media Independent Interface) in brief.

Ans: The GMII is the interface between the MAC layer and the Physical layer. It allows any physical layer to be used with the MAC layer. It is an extension of the MII (Media Independent Interface) used in Fast Ethernet. It uses the same management interface as MII. It supports 10, 100 and 1000 Mbps data rates. It provides separate 8-bit wide receive and transmit data paths, so it can support both full-duplex as well as half-duplex operation. 

The GMII provides 2 media status signals: one indicates presence of the carrier, and the other indicates absence of collision. With the GMII, it is possible to connect various media types such as shielded and unshielded twisted pair, and single-mode and multi mode optical fiber, while using the same MAC controller. It has three sub-layers namely: PCS (Physical Coding Sublayer), PMA (Physical Medium Attachment) and PMD (Physical Medium Dependent).

praveensagar4u.blogspot.com