COMP247 Data Communications Assignment 1: Subnetting and Applications

This document presents the solution to a Data Communications assignment (COMP247) from 2019. The assignment focuses on subnetting and the network layer, with the first question requiring the conversion of CIDR notation to dotted-decimal subnet masks and calculating the maximum number of hosts for various network configurations. It also involves checking the legality of subnet masks. The second question delves into two application protocols: Electronic File Transfer, utilizing FTP, and Electronic Mail, using SMTP, POP, and IMAP. The solution provides detailed explanations, supporting arguments, and references in IEEE style to justify the answers. The assignment covers key concepts in networking, including IP addressing, subnetting, and application-layer protocols, providing a comprehensive understanding of data communication principles.

Running head: DATA COMMUNICATION 1
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DATA COMMUNICATION 2
Question 1
a. CIDR which is the short form of Classless Inter-Domain routing is always a
representation of the network bits of the IP address, the number which is always
preceded by the / is the CIDR number. This notation is majorly used due it its
conciseness.
i. /21=255.255.248.0 which if represented if the binary notation is
11111111.11111111.11111000.00000000 since it contains 21 on bits
hence /21
ii. /13=255.248.0.0 since it has 14 on bits in its binary formation.
iii. /29=255.255.255.248 since it has 29 on bits in its binary formation
b.
i. /19
𝐻 = 2𝑛 − 2
Where H=Number of hosts, n=Number of host bits. Since this is /19 the network
bits are 19, leaving 13 bits for the Hosts. But of the host's bits, 2 are subtracted,
that is subnet address and the broadcast address since they cannot be assigned to
host, therefore,
𝐻 = 213 − 2
𝐻 = 8192 − 2
𝐻 = 8190
ii. /30
𝐻 = 22 − 2
𝐻 = 4 − 2

DATA COMMUNICATION 3
𝐻 = 2
iii. /23
𝐻 = 29 − 2
𝐻 = 512 − 2
𝐻 = 510
c. To check for subnet mask legality, we consider legal subnets to be those that
contain all their 1’s in some consecutive order or all their 0’s are in consecutive
order. Anything else is not a legal subnet.
i. 255.255.224.0, when converted to binary notation, is
11111111.11111111.11100000.00000000. This meets the legality check
and its slash notation is /19
ii. 255.128.0.0, when converted to the binary notation, is
11111111.10000000.00000000.00000000. Again, meets the legality
check and its slash notation is /9
iii. 255.252.255.0, when converted to binary notation, is
11111111.11111100.11111111.00000000. This one violates the legality
check criteria hence not a legal subnet since 1’s appear after we have
bot some 0’s
iv. 255.255.255.254, when converted to binary notation, is
11111111.11111111.11111111.11111110. This meets the legality check
since all the 1’s are clearly consecutive. The slash equivalent of this is
/31

DATA COMMUNICATION 4
Question 2
In this section, the two application discussed is Electronic File Transfer and Electronic
Mail.
i. Electronic File Transfer
The electronic file transfer application makes good use of the FTP (File
Transfer Protocol) protocol.
The FTP is majorly used to electronically transfer file data from a local system
to a remote one and vice versa [1]. This is possible because the FTP normally
opens 2 connections, that is data and control connections between the systems
involved. The primary use of data connection is a transfer of data while the
control part is used for sending and receiving instructions [2].
FTP is above the TCP transport layer. The TCP is chosen to ensure there is
reliable file transfer when the connection is established. This ensure no corrupted
files get transfere and if error occurs, a request for tretransmission is initiated by
TCP protocol.
FTP uses the client server architecture. This architecture ensures speedy
transfer of files from clients to server which have better processing capabilities
ii. Electronic Mail
The e-mail application makes use of the SMTP (Simple Mail Transfer
Protocol), for sending of emails while the POP or IMAP protocols used for
retrieval of emails from the mail server. But generally, the main protocol is SMTP.

DATA COMMUNICATION 5
SMTP is in the application layer of TCP/IP stack [3]. It allows clients to open
a connection to the SMTP server and use the connection to send mail. The SMTP
by default is listening for a connection and gets instated by the SMTP connection.
Once the connection is fully established, the client sends the mail successfully
almost instantaneously. [4].
SMTP operated aove the TCP of the transport layer
SMTP again is based on client-server architecture since most of the email request
will be initiated by the client and send over to the server to response. This ensure
faster processing and security of emails.

DATA COMMUNICATION 6
References
[1] L. DeNardis, Protocol Politics : The Globalization of Internet Governance. Cambridge, MA:
The MIT Press, 2009.
[2] “Large File Transfer Software: A Buyer’s Guide,” Streaming Media, vol. 47, no. 4, pp. 58–
60, Mar. 2019.
[3] V. G. Cerf, “The Upper Layers of the Internet,” Commun. ACM, vol. 61, no. 11, pp. 5–5,
Nov. 2018.
[4] C. S. Yoo, “Protocol Layering and Internet Policy,” Univ. Pa. Law Rev., vol. 161, no. 6, pp.
1707–1771, May 2013.