计算机网路课后作业（1）

Chapter 1

r11

The end-to-end delay is L/R1 + L/R2.

r12

A circuit-switched network can guarantee a certain amount of end-to-end bandwidth
for the duration of a call. Most packet-switched networks today (including the
Internet) cannot make any end-to-end guarantees for bandwidth. FDM requires
sophisticated analog hardware to shift signal into appropriate frequency bands.

r16

Fixed:processing delays, transmission delays, propagation delays,
Variable: queuing delays,which are variable.

r19

a) 500 kbps
b) 64 seconds
c) 100kbps; 320 seconds

r23

The five layers in the Internet protocol stack are – from top to bottom – the
application layer, the transport layer, the network layer, the link layer, and the
physical layer.

r24

Application-layer message: data which an application wants to send and passed onto
the transport layer; transport-layer segment: generated by the transport layer and
encapsulates application-layer message with transport layer header; network-layer
datagram: encapsulates transport-layer segment with a network-layer header; linklayer frame: encapsulates network-layer datagram with a link-layer header.

r25

Routers process network, link and physical layers (layers 1 through 3). Link layer switches process link and physical layers (layers 1 through2). Hosts process all five

p8

p25

) 160,000 bits
b) 160,000 bits
c) The bandwidth-delay product of a link is the maximum number of bits that can be in
the link.
d) the width of a bit = length of link / bandwidth-delay product, so 1 bit is 125 meters
long, which is longer than a football field
e) s/R