LECTURE 4 NETWORK PROTOCOLS AND COMMNICATION

Question 1

What is message encoding?

Answer 1

Encoding is the process of converting information into another, acceptable form, for transmission. Decoding reverses this process in order to interpret the information.
Messages sent across the network are first converted into bits by the sending host. Each bit is encoded into a pattern of sounds, light waves, or electrical impulses depending on the network media over which the bits are transmitted. The destination host receives and decodes the signals in order to interpret the message.

Question 2

What is message formatting and encapsulation

Answer 2

A letter writer uses an accepted format to ensure that the letter is delivered and understood by the recipient. In the same way, a message that is sent over a computer network follows specific format rules for it to be delivered and processed. Just as a letter is encapsulated in an envelope for delivery, so too are computer messages encapsulated. Each computer message is encapsulated in a specific format, called a frame, before it is sent over the network. A frame acts like an envelope; it provides the address of the intended destination and the address of the source host.

 As application data is passed down the
protocol stack, information is added at each level. This is known as the encapsulation
process.

Question 3

Discuss message size

Answer 3

when a long message is sent from one host to another over a network, it is necessary to break the message into smaller pieces. The rules that govern the size of the pieces, or frames, communicated across the network are very strict. They can also be different, depending on the channel used. Frames that are too long or too short are not delivered.

Question 4

What is segmenting?

Answer 4

The size restrictions of frames require the source host to break a long message into individual pieces that meet both the minimum and maximum size requirements. This is known as segmenting

Question 5

Discuss message timing

Answer 5

Determines when to send messages how fast or slow etc. Involves:
• Access Method
• Flow Control
• Response Timeout

Question 6

Discuss access method

Answer 6

Access method determines when someone is able to send a message. These timing rules are based on the environment. Hosts on a network need an access method to know when to begin sending messages and how to respond when errors occur.

Question 7

Discuss Flow Control

Answer 7

In network communication, a sending host can transmit messages at a faster rate than the destination host can receive and process. Source and destination hosts use flow control to negotiate correct timing for successful communication.

Question 8

Discuss response timeout

Answer 8

Hosts on the network also have rules that specify how long to wait for responses and what action to take if a response timeout occurs.

Question 9

Discuss the different message delivery options

Answer 9

A one-to-one delivery option is referred to as a unicast, meaning that there is only a single destination for the message.

When a host needs to send messages using a one-to-many delivery option, it is referred to as a multicast. Multicasting is the delivery of the same message to a group of host destinations simultaneously.

If all hosts on the network need to receive the message at the same time, a broadcast is used. Broadcasting represents a one-to-all message delivery option. Additionally, hosts have requirements for acknowledged versus unacknowledged messages

Question 10

Discuss the correlation between protocols and layers

Answer 10

 Protocol suites are implemented by hosts and networking devices in software, hardware or both.
 The protocols are viewed in terms of layers, with each higher level
service depending on the
functionality defined by the protocols shown in the lower levels.

Question 11

What is a network protocol?

Answer 11

Networking protocols define a common format and set of rules for exchanging messages
between devices.

Question 12

Using an example explain protocol interaction

Answer 12

Communication between a web server and web client is an example of an interaction between several protocols:
• HTTP - an application protocol that governs the
way a web server and a web client interact.
• TCP - transport protocol that manages the
individual conversations.
• IP – encapsulates the TCP segments into packets, assigns addresses, and delivers to the destination host.
• Ethernet - allows communication over a data link and the physical transmission of data on the
network media.

Question 13

What is a protocol suite?

Answer 13

A protocol suite is a set of protocols that work together to provide
comprehensive network
communication services eg TCPI/IP

The TCP/IP protocol suite is an open standard, the protocols are freely
available, and any vendor is able to implement these protocols on their
hardware or in their software.

Question 14

What is APRANET?

Answer 14

 Advanced Research Projects Agency Network (ARPANET) was the
predecessor to today’s Internet.
• ARPANET was funded by the U.S. Department of Defense for use by
universities and research
laboratories.

Question 15

Map different protocols to the various layers

Answer 15

*see doc for pic

Question 16

Describe the TCP/IP Communication process

Answer 16

The webserver prepares the Hypertext Markup Language (HTML) page. The HTTP application layer protocol sends the data to the transport layer.
• The transport layer breaks the data into
segments and identifies each.
• Next the IP source and destination addresses are added, creating an IP Packet.
• The Ethernet information is then added
creating the Ethernet Frame, or data link frame.
• This frame is delivered to the nearest router along the path towards the web client. Each router adds new data link
information before forwarding the packet.

Question 17

Describe TCP/IP communications from the clients perspective

Answer 17

 When receiving the data link frames from
the web server, the client processes and
removes each protocol header in the
opposite order it was added:
• First the Ethernet header is removed
• Then the IP header
• Then the Transport layer header
• Finally the HTTP information is processed and
sent to the client’s web browser

Question 18

What are the benefits of open standards and who provides them?

Answer 18

Open standards encourage interoperability, competition, and innovation.
 Standards organizations are usually vendor-neutral, non-profit organizations
established to develop and promote the concept of open standards

Question 19

Give examples of internet standards organizations

Answer 19

 Internet Society (ISOC)
 Internet Architecture Board (IAB)
 Internet Engineering Task Force (IETF)
 Internet Research Task Force (IRTF)

Question 20

Give examples of electronics and communications standard organizations

Answer 20

 Institute of Electrical and Electronics Engineers
(IEEE)
 Electronic Industries Alliance (EIA)
 Telecommunications Industry Association (TIA)

Question 21

What are the benefits of using a layered model?

Answer 21

• Assisting in protocol design since protocols at each layer have defined functions.
• Fostering competition because products from different vendors can work together.
• Preventing technology changes in one layer from affecting other layers.
• Providing a common language to describe networking functions and
capabilities.

Question 22

Describe each layer of the OSI Model

Answer 22

 Application - contains protocols used for process-to-process communications.
 Presentation - provides for common representation of the data.
 Session - provides services to the presentation layer to
organize its dialogue and to manage data exchange.
 Transport - defines services to segment, transfer, and reassemble the data.
 Network - provides services to exchange the individual pieces of data over the network between identified end devices.
 Data Link - provides methods for exchanging data frames between devices over a common media.
 Physical - describes the mechanical, electrical, functional, and procedural means to transmit bits across physical connections.

Question 23

Describe each layer of the TCP/IP Model

Answer 23

Application- Represents data to the user, plus encoding and dialog control
Transport- Supports communication between various devices across diverse networks
Internet - Determines the best path through a network
Network Access- Controls the hardware devices and media that make up the network

Question 24

How does the OSI model map onto the TCP/IP model?

Answer 24

*See doc for pic

Question 25

What are the names of the PDUs of different layers

Answer 25

• Data - application layer PDU
• Segment – Transport layer PDU
• Packet – Network layer PDU
• Frame – Data Link Layer PDU
• Bits – Physical Layer PDU

Question 26

Give examples of the encapsulation process

Answer 26

 The encapsulation process works from top to bottom:
• Data is divided into segments.
• The TCP segment is encapsulated in the IP Packet.
• The IP packet is encapsulated in the
Ethernet Frame

Question 27

What is the de-encapsulation process?

Answer 27

 De-encapsulation is the process used by a receiving device to
remove one or more of the protocol headers.
 The de-encapsulation process works from bottom to top.
• The data is de-encapsulated as it
moves up the stack toward the end-user application.

Question 28

What is the purpose of the network layer source and destination addresses?

Answer 28

• Responsible for delivering the IP packet from the original source to the final destination.

Question 29

What is the purpose of the data link addresses ?

Answer 29

 The purpose of the data link address is to deliver the data link frame from one network interface to
another network interface on the same network.
• As the IP packet travels from source to destination it is encapsulated in a new
data link frame when it is forwarded by each router.

Question 30

What are the parts of an IP address?

Answer 30

 The network layer addresses, or IP addresses, indicate the original source and final
destination.
• Network portion – The left-most part of the
address indicates which network the IP address
is a member of.
• Host portion – The remaining part of the address identifies a specific device on the network.

Question 31

What is the difference in addressing when devices are on the same network and on a remote network?

Answer 31

IP
Same- IP addresses,
indicate the original source and final
destination.
Remote- the
source and destination IP
addresses represent hosts on different networks.

DATA-LINK
Same-The data link frame which uses MAC
addressing, is sent directly to the receiving
device
Remote-The data link frame cannot be sent
directly to the remote destination host. Therefore the frame is sent to the default gateway (nearest router
interface). The router removes the received
Layer 2 information and adds new data link information before
forwarding out the exit interface.

Question 32

 Explain the role of protocols and standards organizations in facilitating
interoperability in network communications.

Answer 32

Most protocols are created by a standards organization such as the IETF or IEEE. Since these protocols are uniform different devices or systems form different vendors are able to readily connect and exchange information with each other