Chapter 3 - Protocols And Models

Question 1

What is the Structure of a Network/Communication System?

Answer 1

• Message Source
• Channel
• Message Destination

Question 2

Rules Within a Communication System

Answer 2

Encoding
   - the language being used between devices
Formatting
   - the structure of the communication
Message Size
   - limited to allow for effectiveness 
Timing
   - controls the flow of the data and timeout period
Delivery
   - unicast, multicast or broadcast

Question 3

What Are Protocols and Their Services?

Answer 3

A formal description of a set of rules and conventions that govern particular aspects of how devices on a network communicate. Their services include:

• Device Addressing
• Data Format
• Reliability and Flow Control
• Data Sequencing
• Application Interface

Question 4

What Are the Layers of Protocols?

Answer 4

Application Layer: DNS, DHCP, SMTP, POP3, IMAP, FTP, HTTP

Transport Layer: TCP, UDP

Internet Layer: IP, NAT, ICMP, OSPF, EIGRP, BGP

Network Access Layer: ARP, ETHERNET, WLAN

Question 5

What Are the Functions of the Main Network Protocols?

Answer 5

HTTP: governs the way that a web server and a web client interact, providing an application interface

TCP: divides the HTTP messages into segments and provides reliability, flow control and sequencing

IP: encapsulates the segments into packets, assigns the appropriate addresses and selects the best path to the destination host

ETHERNET: takes the IP packets and formats them to be transmitted over the network media, providing error detection

Question 6

What Are the International Standards Organisations?

Answer 6

• Internet Society (ISOC)
• Internet Architecture Board (IAB)
• Internet Engineering Task Force (IETF)
• Internet Research Task Force (IRTF)
• ICANN
• IANA
• IEEE
• ISO

Question 7

What Types of Reference Models are Available?

Answer 7

• Open Systems Interconnection (OSI): the most widely used inter-network reference model
• TCP/IP: a protocol based model that describes the functions that occur at each layer of the TCP/IP suite

Question 8

How Does the Encapsulation Process Occur?

Answer 8

1. Application - data is generated here
2. Transport - a TCP header is added to the segment
3. Internet - an IP header is added to the packet for end-to-end connectivity
4. Network Access - a physical address and error check function are added to the frame

Question 9

How Does the De-Encapsulation Process Occur?

Answer 9

1. Network Access - frame is rebuilt, physical address is checked and removed, error check performed
2. Internet - packet is examined, logical address is checked
3. Transport - segment is examined, header is checked and then deleted
4. Application - data recovered is handed to the required protocol

Question 10

What is the Difference Between a Physical and Logical Address?

Answer 10

A Physical address is used for local delivery only and doesn’t provide network identity (e.g. MAC addresses)

A Logical address is used for end-to-end delivery and provides network identity (e.g. source/destination IP addresses)