Week 3 Overview In Week 3, you will focus on the different types of ...

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Week 3 Overview


In
Week 3
, you will focus on the different types of protocols, the popular protocol suites, and the three
-
way handshake of the
Transmission Control Protocol (TCP).

Let's begin this week by exploring protocols and the categories of
protocols. Remember to refer to additional sources such as the South
University Online Library or the Internet.

Protocols


Generally, the term protocol refers to the set of rules that govern any conversation between two parties or entities. Without

the proper
usage of governing protocols, conversations cannot lead to the desired results. In computer networks, protocols carry data in

the form
of protocol data units (PDUs). The characteristics of each PDU and how it is handled during its journey from s
ource to destination is
specified by the rules of the protocol used.

In this topic, we will concentrate on the protocols that are related to routing data. The routing PDU is called "packet" and
it is directly
related to the network layer of the Open System
s Interconnection (OSI) model.

Managing data units differ depending on the category of the protocol. A protocol can be categorized as:



Nonroutable



Routed



Routing

Here is a quick overview on these categories.

Nonroutable Protocols

Protocols that can transfer data only within the same network segment are called nonroutable protocols. Network Basic Input/O
utput
System (NetBEUI) is a nonroutable protocol.

A router simply drops a NetBEUI packet instead of forwarding it to other networks
.

Routed Protocols

Routed protocols can carry data between network segments spread across a building or the globe. Examples of routed protocols
are
Internet Protocol (IP) and Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX).

You can select
a routed protocol for a network based on the applications that will run on the network. For example, to run any of the
services that are a part of the Transmission Control Protocol/Internet Protocol (TCP/IP) suite, you need to use TCP/IP.

Routing Protocols

Based on the routable protocol used on a network, routers store information about the logical network

the path through which data
traffic will flow in a network. Routers share this information using a routing protocol. Therefore, routing protocols allow r
outers to
advertise and learn about available routes and which routes are the best to reach a destination.

For example, Router A at site 1 is connected to Router B at site 2. Router A has information about site 1 and Router B has in
formation
about site 2.
To enable site 1 to communicate with site 2, Router A should have information about site 2 and Router B should have
information about site 1. This is possible only if both routers run the same routing protocol and share the information about

their
networks
. Examples of routing protocols are Routing Information Protocol (RIP), Open Shortest Path First (OSPF), Interior Gateway
Routing Protocol (IGRP), and Border Gateway Protocol (BGP).

Routing protocols can be classified as distance vector (DV) protocols and
link state protocols.

You may visit the
Webliography

of this course to learn more about routing protocols.

The following facts should be considered before selecting a routing protocol for a network:



Convergence
: This specifies the synchronization of the r
outing tables stored in all routers to the changes caused by a network
change such as a link or device failure on a network. Select routing protocols with low convergence time.



Scalability
: This specifies the capacity of the routing protocol to allow a ne
twork to expand. Select a protocol that allows
scalability with minimum convergence delay and eliminates routing loops.



Bandwidth utilization
: This specifies the amount of bandwidth that is needed for traffic such as the periodic updates of
routing tables

amongst the network's routers. Routing protocols that respond to network changes rather than periodically
updating routing tables consume less network bandwidth.



Resource utilization
: This specifies the amount of memory and CPU speed used by the routing
protocol in a router. Select a
protocol that uses minimum resources.

Popular Protocol Suites


Protocols are organized according to their functions in what is called protocol suites. The protocols of a protocol suite sho
uld effectively
work together
on transmitting data over a network. Therefore, newly designed protocols are prepared with a specific protocol suite in
mind.

The most commonly used protocol suite is the TCP/IP. This suite includes protocols that allow all the Internet networks to
communi
cate. Basically, this protocol suite is the standard by which we can connect to Internet services. There are other protocols
suites such as AppleTalk; however, TCP/IP is the dominating suite in today's networks.

You may visit the
Webliography

of this cours
e to learn more about the TCP/IP protocol suite.

Three
-
Way Handshake of TCP


To talk to your friend, you pick up the phone and dial your friend's number. The phone rings at the other end. Your friend pi
cks up the
receiver and says, "hello." After
receiving the hello sound, you also say "hello" and start talking. After you finish talking, you end the
call by saying "bye," and your friend also says "bye." This process is similar to what TCP does in establishing a session bet
ween a
sender and a receiv
er.

An important concept that is related to the transport layer of the TCP/IP suite is the
three
-
way handshake
. The transport layer
protocols are either connection oriented or connectionless. A connection
-
oriented protocol creates a
three
-
way session

betwe
en two
communicating devices, a sender, and a receiver:



The sender

(client) sends the first special TCP segment. The term segment refers to the PDU of the transport layer. This first
segment carries no application
-
layer data.



The receiver

(server) responds with a second special TCP segment. This second segment also carries no application
-
layer
data.



The sender

responds again with a third special segment. The third segment may carry application
-
layer data.

Once a TCP connection is establi
shed, the two application processes can send data to each other. Assume that two computers A and B
are to communicate. They rely on the three
-
way handshake:

1.

Computer A sends a synchronize (SYN) segment with a sequence number
x
. This is equivalent to dialing the phone number in
the example described at the beginning of this page. After receiving the SYN segment with sequence number
x
, computer B
sends back an acknowledgement (ACK) with sequence number
x+1

and sends another SYN w
ith sequence number
y
. This is
equivalent to your friend picking up the phone and saying "hello."

2.

After receiving SYN, computer A sends back an ACK with sequence number
y+1
. After establishing connection between the
communicating computers, data is transf
erred between them. In reality, the sender usually sends a number of segments prior
to receiving the first ACK. This is determined by the TCP window size (sliding window). The sliding window refers to the numb
er
of unacknowledged segments a sender can send

prior to getting the ACK segment for its first SYN segment. Click
here

to learn
more.

3.

The connection is terminated at the end of data transfer in a process very similar to that of est
ablishing a connection. The only
difference is that four segments are exchanged in the termination process. Computer A sends a finish (FIN) segment with
sequence number
x
. After receiving this segment, computer B returns an acknowledgement with sequence nu
mber
x+1
.
Computer B then sends a FIN segment with sequence number
y

and in response, computer A returns the acknowledgement
FIN with sequence number
y+1
.

Week 3 Summary


This week, you learned about the different types of protocols, the popular
protocol suites, and the three
-
way handshake of the TCP.

In
Week 4
, you will cover network design configurations, IP addressing, network operating systems, and designing the network layout.