Question1: The objective of this question is to
(a) describe the general concepts of TCP/IP protocols and
(b) apply channel capacity theories.
(a) Consider the sending of a UDP segment to its peer entity. The UDP segment consists of 1200 bytes UDP dataplus 8bytes ofheader. Thesegment is encapsulated into anIP datagram that hasan additional 20 bytes of header.TheIPdatagram is in turn encapsulated intoLANframes. EachLAN frame allows apayload of 500 bytes anda header of 26 bytes. Thus,a fragmentation is needed at datalink layer.
(i) Sketch a diagram to show the layering and fragmentation process.
(ii) How many bits, including headers, are delivered to the destination?
(iii) What is the total percentageoverhead of headers?
(b) Comparethewhitenoisepower densitylevels in closed rooms inLondon and Sydney in January, with averagetemperatures of 5oC and24 oC respectively.
(c) Considera communication channel with 10 MHzbandwidth.
(i) If one wishes to transmit at adata rate of150 Mbps, what is the minimum signal- to-noise ratio in dBrequired to accomplish this?
(ii) If thenoise poweris 8 x10-6 Watt, what isits signal power in Watt?
Question2: The objective of this question is to comparedigital encoding and modulation techniques.
(a) Consider thebinarybitsequence,1111000000 00 10 00 0 1.
(i) Draw the wave form for Manchester encoding.
(ii) Draw thewaveform forHDB3encoding.
(iii) What arethe strengths and weaknesses of HDB3 encoding?
(b) Figure shows the constellation diagram of a modulation technique.
(i) Identify the modulation technique. Explain.
(ii) How manybits can berepresented per signal elementin this modulation technique?
(iii) Given the baud rate of4800bauds, how manybits persecondcan the modem achieve?
(iv) Ingeneral, using QAM, do the same bits always correspond to the sameanalog signal?Explain.
Question3: The objective of this question is to (a) distinguish asynchronous and synchronous transmissions and (b) apply error detection techniques to communications.
(a) Consider the transmission of 16 characters overa10 kbps communication line. Each characterconsistsof 7information bits and oneparitybit.
(i) Calculate the effective data rate of the transmission for Asynchronous transmission usingonestart bit and 1.5 stop bits for eachcharacter.
(ii) Calculate the effective data rate of the transmission for synchronous transmission.
Assume that the data can be accommodated in one data frame with 48 bits overhead.
(b) Consider a transmission system using Cyclic Redundancy Check(CRC) technique with agenerator polynomial 1010111 to generatea Frame Check Sequence(FCS).
(i) If the data to be transmitted is 1 11 1 1010 11, compute the FCS using Modulo 2 arithmetic.
(ii) What is the transmitted frame?
(c) What arethe strengthsofthe CRC technique?
Question 4: The objective of this question is to (a) apply flow/error control techniques to practical problems and (b)describe HDLC protocols.
(a) Three nodes, A, B, C are connected by two full duplex links from A to B andfrom Bto C as shown in Figure. The distance AB is 4000 km and BC is 1000 km. Frames generated byA aresent to C throughB. The propagation delay is 5us/km for both links. All data frames are 1000 bits long. ACK frames are separate frames of negligible length. Between A and B, a sliding window protocol with window sizeof 3 is used. Between B and C, a stop-and-wait protocol is used. Assume that thereareno errors in transmission.If the data rate between A and B is 100 kbps, determine the minimum transmitted data raterequired between B and C so that the buffers of B are not flooded.
(b) Consider HDLC protocol.
(i) Apply the bit stuffing rule to the following data string and obtain theoutputstring:
01111001 10111110 11111101 00000010 (leftto right)
(ii) What happens at the receiver if the transmitted sequence is received without errors?
(iii) What happens at the receiver if the transmitted sequence is received with a single bit error in the16th transmitted bit?