7-layer protocol hierarchy

1. Consider two hosts, A and B, connected by a single link of rate R bps. Suppose that the
   two hosts are separated by m meters, and suppose the propagation speed along the link
   is s meters/sec. Host A is to send a packet of size L bits to Host B.
   (a) Express the propagation delay, ?௣௥௢௣, in terms of m and s.
   (b) Determine the transmission time of the packet, ?௧௥௔௡௦,, in terms of L and R.
   (c) Ignoring processing and queuing delays, obtain an expression for the end-to-end
   delay.
   (d) Suppose Host A begins to transmit the packet at time t = 0. At time t = ?௧௥௔௡௦, where
   is the last bit of the packet?
   (e) Suppose ?௣௥௢௣ is greater than ?௧௥௔௡௦. At time t = ?௧௥௔௡௦s, where is the first bit of the
   packet?
   (f) Suppose ?௣௥௢௣ is less than ?௧௥௔௡௦. At time t = ?௧௥௔௡௦, where is the first bit of the
   packet?
   (g) Suppose s = 2.5×108
   meters/sec, L = 100 bits, and R = 28 kbps. Find the distance m so
   that ?௣௥௢௣=?௧௥௔௡௦.
2. A computer system has a 7-layer protocol hierarchy. Applications generate messages of
   length 500 bytes. At the data link layer, a 30-byte header and 4-byte trailer are added. At
   the remaining 6 layers, a 20-byte header is added. What fraction of the network
   bandwidth is filled with headers?
3. In traditional telephone systems, local loop (i.e., between a telephone set and its
   nearest telephone switch) link bandwidth is about 3KHz.
   (a) What are the maximum achievable baud rates and data rates (assume noiseless
   channel) if BPSK and 64-QAM are used?
   (b) If the signal-to-noise ratio imposed by the system between two remote telephone
   sets is about 30dB, what is the maximum achievable data rate?
   (c) In a few sentences, please explain how to improve data rate. Answer the following questions of OSI reference model:
   (a) Which layer is responsible for converting data packets from the Data Link layer into
   electrical signals?
   (b) At which layer is routing implemented, enabling connections and path selection
   between two end systems?
   (c) Which layer defines how data is formatted, presented, encoded, and converted for
   use on the network?
   (d) Which layer is responsible for creating, managing and terminating sessions between
   applications?
   (e) Which layer provides logical addressing that routers will use for path determination?
   (f) Which layer specifies voltage, wire speed, and moves bits between devices?
   (g) Which layer combines bits into bytes and bytes into frames, uses MAC addressing,
   and provide error detection?

Sample Solution