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CUSTOMER_CODE SMUDE DIVISION_CODE SMUDE EVENT_CODE APR2016 ASSESSMENT_CODE BCA4010_APR2016 QUESTION_TYPE DESCRIPTIVE_QUESTION QUESTION_ID 4096 QUESTION_TEXT Explain the Data Link Layer functions and service primitives used. SCHEME OF EVALUATION The services of the data link layer are: ● Unacknowledged Connectionless Service - Brief Explanation (2 Marks) ● Acknowledged Connectionless Service – Brief explanation (2 Marks) ● Connection – oriented Service – Brief explanation (2 Marks) The service primitives used by the data link layer are: ● Request – used by the network layer to ask the data link layer to do something ● Indication – usedto indicate to the network layer that an event has happened ● Response – used on the receiving side by the network layer to reply to a previous indication. ● Confirm – provide a way for data link layer on the requesting side to learn whether the request was successfully carried out and if not, why. (1 x 4 = 4 Marks) QUESTION_T DESCRIPTIVE_QUESTION YPE QUESTION_ID 72443 QUESTION_T Explain the HDLC (High Level Data Link Control Protocol) along with frame EXT formats. SCHEME OF EVALUATION a. HDLC Frame Format. Bits:1 3 1 3 b. An Information Frame c. A supervisory Frame d. An Unnumbered Frame (4 Marks) HDLC frames can be transmitted over synchronous or asynchronous links. Beginning and ending of each frame is identified using a frame delimiter 01111110. It consists of 3 different frames: 1. I frames: This frame has the control field as shown in fig (b) and are used to transport user data from the network layer. Seq define the sequence number; P/F defines Poll/Final field. It is called Poll when used by the primary station to obtain a response from a secondary station, and Final when used by the secondary station to indicate a response or the end of transmission. Next field gives a number that the source machine is expecting from the destination machine in a two way communication system. (2 Marks) 2. Supervisory Frames: This frame has the control field as shown in fig (c). These frames are used for flow and error control whenever piggybacking is impossible or inappropriate. The various Types defined in the frame are: a. Receive ready b. Reject c. Receiver not ready d. Selective reject (2 Marks) 3. U Frames: This frame has the control field as shown in fig (d). Are used for link management. They are used to exchange session management and control information between connected devices. (2 Marks) QUESTION_TYPE DESCRIPTIVE_QUESTION QUESTION_ID 72446 QUESTION_TEXT Explain two operational modes of IPSec in detail. SCHEME OF EVALUATION Lpsec Operates In One Of The Following Two Modes: Transport Mode: In This Mode, Ipsec Protects What Is Delivered From The Transport Layer To The Network Layer. I.E. The Transport Mode Protects The Network Layer Payload, The Payload To Be Encapsulated In The Network Layer. This Mode Does Not Protect The IP Header, I.E. It Protects Only The Packet From The Transport Layer (The Lp Layer Payload). In This Mode, The Ipsec Header And Trailer Are Added To The Information Coming From The Transport Layer. The IP Header Is Added Later. (3marks) This Mode Is Normally Used When We Need Host-To-Host Protection Of Data. The Sending Host Uses Ipsec To Authenticate And/Or Encrypt The Payload Delivered From The Transport Layer. The Receiving Host Uses Ipsec To Check The Authentication And/Or Decrypt The IP Packet And Deliver It To The Transport Layer. (2mark) Tunnel Mode: Tunneling Or Encapsulation Is A Common Technique In Packet-Switched Networks. It Consists Of Wrapping A Packet In A New One. That Is, A New Header Is Attached To The Original Packet. The Entire Original Packet Becomes The Payload Of The New One. In This Mode, Ipsec Protects The Entire IP Packet. It Takes An IP Packet Including The Header, Applies Ipsec Security Methods To The Entire Packet, And Then Adds A New IP Header. (3marks) Tunneling Requires Intermediate Processing Of The Original Packet While Enroute. The Destination Specified In The Outer Header, Usually An Ipsec Firewall Or Router, Receives The Tunneled Packet, Extracts The Original Packet, And Sends It To The Ultimate Destination. (2 marks) QUESTION_TYPE DESCRIPTIVE_QUESTION QUESTION_ID 72447 QUESTION_TEXT Explain the four layers of TCP/IP protocol 2.5 each 1. Application layer SCHEME OF EVALUATION 2. Transport layer 3. Internet work layer 4. Network interface layer QUESTION_TYPE DESCRIPTIVE_QUESTION QUESTION_ID 116175 QUESTION_TEXT Explain the layers of OSI model in brief. The OSI Model is composed of seven ordered layers: • Layer 1 – The Physical Layer • Layer 2 – The Data Link Layer • Layer 3 – The Network Layer • Layer 4 – The Transport Layer • Layer 5 – The Session Layer • Layer 6 – The Presentation Layer • Layer 7 – The Application Layer SCHEME OF EVALUATION (6 marks) (2 marks) (2 marks) QUESTION_TYPE DESCRIPTIVE_QUESTION QUESTION_ID 116176 QUESTION_TEXT Explain with the waveforms the three major problems from which a transmission line suffers. Transmission lines suffer from three major problems: 1. Attenuation distortion 2. Delay distortion 3. ● SCHEME OF EVALUATION ● ● Noise Attenuation distortion: It is the loss of energy as the signal propagates outward. The amount of energy depends on the frequency. The signal attenuates as it propagates. If the attenuation is too much, the receiver may not be able to detect the signal at all, or the signal may fall below the noise level. (1 marks) For reliable communication, the attenuation and delay over the range of frequencies of transmission should be constant. Fig: Signals loose power at it travels time (2marks) Delay distortion: The second transmission impairment is delay distortion. Communication lines have distributed inductance and capacitance, which distort the amplitude of signals and also delay the signals at different frequencies by different amounts. It is caused by the fact that different Fourier components travel at different speed. Fig; Delay distortion (2marks) ● ● It is due to velocity of propagation the frequency varies. Thus, various frequency components of a signal arrive at the receiver at different times. (1mark) Dispersion: Signals tend to spread as they travel, with the amount of spreading dependent on the frequency. (1mark) Noise: Noise is a third impairment. It can be define as unwanted energy from sources other than the transmitter. Thermal noise is caused by the random motion of the electrons in a wire and is unavoidable. Fig: Signal (2marks) Fig: Noise (1mark)