University of California, San Diego

ECE 128A

Homework Set #1: Solutions

Homework Problems (from textbook):
P1.1 How many hosts can one have on the Internet if each one needs a distinct IP address?
Solution:
232, as IP addresses have 32 bits.
P1.2 If the addresses were allocated arbitrarily, how many entries should a routing table
have?
Solution:
232, an entry for each possible destination.
P1.3 Imagine that all routers have 16 ports. In the best allocation of addresses, what is the
size of the routing table required in each router?
Solution:
In the best allocation, the first 4 bits (16 possible values) of the IP address determine
the port. Therefore, the routing table has 16 entries.
P1.4 Assume that a host A in Berkeley sends a stream of packets to a host B in Boston.
Assume also that all links operate at 100Mbps and that it takes 130ms for the first
acknowledgment to come back after A sends the first packet. Say that A sends one
packet of 1KByte and then waits for an acknowledgment before sending the next packet,
and so on. What is the long-term average bit rate of the connection? Assume now
that A sends N packets before it waits for the first acknowledgment, and that A sends
the next packet every time an acknowledgement is received. Express the long-term
average bit rate of the connection as a function of N . [Note: 1Mbps = 106 bits per
second; 1ms = 1 millisecond = 10-3 second.]
Solution:
In the first case the long term average bit-rate is B1 = 1 kByte=0:13s = 61; 538 bps.