COMP247 Data Communications

This document provides answers to questions related to subnetting and the network layer, as well as applications, protocols, and layering in data communications. It discusses subnet masks, maximum number of hosts, legal subnet addresses, and their corresponding slash notation. It also explains the domain name system (DNS) and its application, as well as IP telephony (VoIP) and its protocols.

Running head: COMP247 DATA COMMUNICATIONS
COMP247 Data Communications
Name of the Student
Name of the University
Author’s Note

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COMP247 DATA COMMUNICATIONS
Answer to Question 1: Subnetting and the network layer
a. The equivalent subnet mask for the following slash notation in dotted decimal
notation is as follows:
i. /21 –
= 255.255.248.0
ii. /13 –
= 255.248.0.0
iii. /29 –
= 255.255.255.248
b. The maximum number of hosts that can be addressed on the following networks are
given below:
i. /19 – 255.255.224.0
= 8192 – 2
=8190 hosts
ii. /30 – 255.255.255.252
= 4 – 2
= 2 hosts
iii. /23 – 255.255.254.0
= 512 – 2
= 510 hosts
c. Checking legal subnet address and its corresponding slash notation form are given
below:
i. 255.255.224.0 –
Binary form - 11111111.11111111.11100000.00000000
Notation - /19

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COMP247 DATA COMMUNICATIONS
ii. 255.128.0.0 –
Binary form – 11111111.10000000.00000000.00000000
Notation - /9
iii. 255.252.255.0 –
Binary form – 11111111.11111100. 11111111.00000000
Notation - invalid
iv. 255.255.255.254 –
Binary form - 11111111.11111111.11111111.11111110
Notation - /31
Answer to Question 2: Applications, Protocols and Layering
Domain name system (DNS) –
A. It is used for mapping the IP address with the URL that is used for identifying a
website. WWW is used as application layer protocol for translating the domain.
B. Client server model is utilized for enabling communication based on the UDP
protocol. It works using the port 53 and is a transport layer protocol for defining the
route of the message. The meaning, syntax and rules and defined and configures the
DNS to respond against the messages sent from the server or clients.
C. The DNS server responds to the internal and external domain and UDP protocol is
used for sending the message in the transport layer.
D. The messages are sent and received using the UDP protocol and it has the advantage
over TCP protocol that is UDP protocol is much faster than TCP and thus less time is
needed for resolving DNS query (Hu et al. 2016). It has the support for multiple client
as no connection state is needed and for improving security extra layers of protection

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COMP247 DATA COMMUNICATIONS
can be enforced. The DNS request can fit with the UDP segment due to its smaller
segment size.
E. DNS uses the client server architecture for transmission of data packets.
F. DNS finds its application for naming website and resolution of address and used for
the translation of domain name using IP address using the DNS server.
There are various network of DNS and it itself is not able to translate all the domain
and for this it needs to ask different servers for getting the correct IP address for the
URL.
IT Telephony (VoIP) –
A. The IP Telephony uses the TCP/IP protocol and the application layer uses the NTP
(Network time protocol), RTP (Real time transport protocol), and RTCP (Real time
transport control protocol).
B. The NTP enables timing for ensuring that signals are transmitted and received within
proper timeframe for assuring quality. The RTP is used for providing end to end
network transport functions and RTCP is used for monitoring delays in voice signal
delivery and providing minimal functions for controlling and ensuring packet
delivery.
C. The application layer protocol uses UDP protocol in the transport layer.
D. The transport layer uses the UDP protocol for delivering the voice packets since it is a
real time application and it is important to deliver the voice packets to the receiver
immediately (Roy 2016). Thus UDP is favourite for providing transport layer in VoIP
network.
E. Peer to peer architecture is used by the VoIP protocol.
F. Since no central servers are needed in IP telephony and there is a need for the two
agents to communicate directly with one another the peer to peer architecture is

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COMP247 DATA COMMUNICATIONS
selected. There is also need of real time response and thus structured P2P architecture
is used for the development of the IP telephony framework.
Bibliography
Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D. and Hoffman, P.,
2016. Specification for dns over transport layer security (tls) (No. RFC 7858).
Roy, R.R., 2016. Handbook on Session Initiation Protocol: Networked Multimedia
Communications for IP Telephony. CRC Press.