1). How do we achieve a data rate of 56 kbps in 23 channels using a DS-1 format?

3). Recently, a new scanner was announced that provided 1200dpi resolution and

over 1 billion colors.

(a). How much memory in bytes would it take to store a bit map of an 8- by

10-in monochrome picture at 1200 dpi with a 10-bit gray scale?

(1200 x 1200) dpi=1,440,000 bytes, 8-by 10-in. x 1,440,000 x 10

(b). Suppose that the colors are represented as a combination of three colors-red,

blue, green-each with n bits to represent its intensity. What is the least value

of n that will provide over 1 billion colors?

Red=10bits + blue=10bits + green=10bits= 2^30

(c). How long would it take to send a color representation of an 8-by 10-in.

picture at 1200 dpi over a T-1 line (1.544 Mbps)?

8-by 10-in. x (1200 x 1200) dpi x 30 /(1.544Mbps)=

223,8341,968.9bps/3600second=621,761hours

4). Phototypesetters often print black-and-white material at a resolution of 2400 dots

per linear inch. Suppose that you want to send a 7-by 11-in. page of material generated

by your PC to be printed by such a typesetter.

(a). If you store it, uncompressed, as pixels in your PC, how much memory do you

need in bytes?

7-by 11-in. = 77 squares inch; 2400 x 2400 dots per linear inch; bits,

5,760,000 = 443,520,000 bytes = 55,440,000

(b). Suppose you have a modem that transmits at 19,200 bps. How long would it

take you to send the file to the typesetter?

Time = bits / line speed 443,520,000 divide 19,200 bps = 23,100 divide 3600 sec.= 6.42 hours

5). Assume that you are to design a TDM carrier, say T-489, to support 30 voice channels

using 6-bits samples and a structure similar to T-1, Determine the bit rate required.

N: number of hops between two given stations

L: message length, in bits

B: data rate, in bps, on all links

P: packet size, in bits

H: overhead (header), in bits per packet

S: call setup time (circuit-switched or virtual circuit), in seconds

D: propagation delay per hop, in seconds

(a). N=4, L=3200, B=9600, P=1024, H=16, S=0.2, D=0.001, compute the end-to –end

delay for circuit switching. Assume that there is no node delay.

Of bit arrive data rate on links

delay + overhead bits per

packet divide data rate on links

2). Consider a packet-switched network of N nodes, connected by the following topologies:

(a). Star: one central node with no attached station; all other nodes attach to the central

node.

Each connection has one hop

©. Fully connected: each node is directly connected to all other nodes. For each case,

give the average number of hops between stations.

Have two hops

3). Flow control mechanisms are used at both levels 2 and 3 of X.25. Are both necessary, or is this

redundant? Explain.

The layer two-flow circuit regulated total flow of data between DTE and DCE.

The layer three flow control regulated flow ower a single virtual circuit.

4). In X.25, the virtual-circuit number used by one station of two communicating stations is

different from the virtual-circuit number used by the other station. Why would this be so?

After all, it is the same full-duplex virtual circuit.

The virtual circuit number only has local signacited ( no global management of number).

1). Instead of LLC, could HDLC be used as a data link control protocol for a LAN? If not,

what is lacking?

LLC described early chapter of HDLC is addressing of source or destination.