# Assignment #2

Δίκτυα και Επικοινωνίες

24 Οκτ 2013 (πριν από 5 χρόνια και 3 μήνες)

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Assignment 2:

1.

Consider an organization (a University, for example) with a network address of 137.207.0.0.

Another way to write this network address (or net ID for short) is 137.207.0.0/16.

The 16 is the
number of relevant bits (16 bits in this case
because it is a class B address).

Let's say that this network decides to use multi
-
level subnetting.

Assume there are various
departments, each of which has its own wide area network (WAN).

a.

If there are exactly 8 departments, and it is unlikely that any

more departments will be
added in the future, how many bits in the address should be used for subnetting between
these departments at the highest level?

What should be the subnet mask used in this
case?

Write 137.207.138.167 in CIDR notation, taking thi
s subnetting scheme into account.

b.

Assume, at a lower level in the network, the subnet mask to be used is 255.255.255.224.

What subnet ID would the router at this level determine from the address
137.207.234.107?

Solution:

(a)

3 bits (since 2 raised to the po
wer 3 is 8).

The subnet mask in this case should be 255.255.224.0.

137.207.138.167/19 is the
correct CIDR notation for the address.

(b)

In Decimal: In Binary:

137.207.234.107

10001001 11001111 11101010 01101011

&

255.255.255.224 & 11111111
11111111 11111111 11100000

----------------------------

------------------------------------------------------------

137.207.234.96

10001001 11001111 11101010 01100000

2.

Sixteen
-
bit messages are transmitted using a Hamming code. How many check bits

are needed
to

ensure that the receiver can detect and correct single b
it errors? Show the bit pattern
transmitted for the

message 1101001100110101. Assume that even parity is used in the
Hamming code.

Solution:

Parity bits are needed at positions 1, 2,

4, 8, and 16, so messages that do not extend beyond bit
31 (including the parity bits) fit. Thus, five parity bits are sufficient. The bit pattern transmitted is
011010110011001110101