CSP 214 Written Homework 1 Solutions - Fall, 1997

1a) There is a difference, as the RTT between machines both located at
Duke can be as low as sub milliseconds (shown as 0 by the ping
utility). For other RTP sites, RTTs are slightly higher, but still
generally below 5 ms. This most likely is not noticable to typical
applications, so the difference probably isn't significant.

1b) Typical RTTs are between 50-100 ms.

1c) Typical RTTs are between 100-150 ms.

1d) Typical RTTs to Europe depend greatly on which site (and
consequently which path). Some destinations are as close as 100-150ms,
which is comparable to intra-US delays to the west coast. Some paths
are longer 300+ ms.

2) Duke connects directly to NCREN, NCREN has connections through
Sprint, UUNet, Alternet. Note: one wouldn't really consider netcom
(Duke) to be an ISP because it serves only Duke, i.e., the general
public can't buy Internet access through them.

3) 10-20 hops is common for many destinations.

4) For a bit rate of 155Mbps, one bit takes 1/[155Mb/sec] =
6.45X10**-9 sec/bit

5) To download the file via modem,
   10**6 Bytes/sec * 8 Bits/Byte / [28.8*10**3 bits/sec]
   = 2778 seconds
   = 46 min

   Going to school and back would seem to be quicker.

6) 1) application
   2) transport or datalink
   3) transport
   4) data link or transport
   5) network
   6) physical
   7) presentation

7a) Most likely delay sensitive, since the amount of data exchanged
during the operation is small.

7b) Most likely bandwidth, though that depends on the size of the file
and the actual characteristics of the data channel. It turns out in
practice that most files are relatively small (a few K or less), so on
an Ethernet (for example), it may well be that delay is the
significant factor.

7c) Probably delay sensitive, though again it is hard to
generalize. If the directory is large, bandwidth may be the issue.

7d) Delay.

8) With multicast communication, a single packet is delivered to a set
of destinations (more than one). With unicast, a packet is intended
for a single recipient.