Protocols
Chapter Four

The key features of a protocol
In the context of data networking, a protocol is a formal set of
rules and conventions that governs how computers exchange
information over a network medium.
The peer layers communicate by means of formatted blocks of data
that obey a set of rules or conventions known as a protocol. The
key features of protocol are:
Syntax – data block format
Semantics - control information & error handling
Timing - speed matching & sequencing

Types of Communication Models
There are two basic protocol models used in data communications
and computer networks.
I. TCP/IP model and
II. OSI reference model

I.TCP/IP Protocol Suite
TCP/IP stands for Transmission Control Protocol/
Internet Protocol.
It was developed by the Internet Engineering Task
Force(IETF) prior to the OSI model.
Therefore, the layers in the TCP/IP protocol suite do not
match exactly with those in the OSI model.
The TCP/IP protocol suite is defined as four software
layers built upon the hardware.

Layers in the TCP/IP Protocol Suite

Network Access Layer
At the bottom of the TCP/IP model, the Network Access
layer implements the data exchange between the host
and the network.
The equivalent of the Data Link and Physical layers of the
OSI model, the Network Access layer oversees hardware
addressing and defines protocols for the physical
transmission of data.
The reason TCP/IP became so popular is because there
were no set of physical layer specifications, so it could
run on any existing or future physical network.

Internet Layer
The Internet layer corresponds to the OSI’s Network layer,
designating the protocols relating to the logical
transmission of packets over the entire network.
It takes care of the addressing of hosts by giving them an
IP (Internet Protocol) address and handles the routing of
packets among multiple networks.

Host-to-Host/Transport layer
The Host-to-Host layer parallels the functions of the
OSI’s Transport layer, defining protocols for setting up
the level of transmission service for applications.
It tackles issues like creating reliable end-to-end
communication and ensuring the error-free delivery of
data.
It handles packet sequencing and maintains data
integrity.

Process/Application layer
These processes integrate the various activities and
duties spanning the focus of the OSI’s corresponding
top three layers (Application, Presentation, and
Session).
Controls user-interface specifications.
A vast array of protocols join forces at the TCP/IP
model’s Application layer.

TCP/IP Protocol Suite

II. The OSI Model
It was developed by the International Organization for
Standardization (ISO).
It was first introduced in the late 1970s.
It is a model for a computer protocol architecture and as
a framework for developing protocol standards.
An ISO standard that covers all aspects of network
communications is the Open Systems Interconnection (OSI)
model.
It comprises seven layers.

Summary of OSI Layers

TCP/IP and OSI Model

OSI and TCP/IP similarities
Both have layers.
Both have application layers, though they include very
different services.
Both have comparable transport and network layers.
Both assume packets are switched. This means that
individual packets may take different paths to reach the
same destination. This is contrasted with circuit-switched
networks where all the packets take the same path.

OSI and TCP/IP Differences
TCP/IP combines the application, presentation and session
layer issues into its application layer.
TCP/IP combines the OSI data link and physical layers into the
network access layer.
TCP/IP appears simpler because it has fewer layers.
TCP/IP protocols are the standards around which the Internet
developed, so the TCP/IP model gains credibility just because of
its protocols.
In contrast, networks are not usually built on the OSI protocol,
even though the OSI model is used as a guide.

Overview of familiar Protocols

Simple Network Management Protocol (SNMP)
Simple Network Management Protocol (SNMP) collects
and manipulates valuable network information.
 It gathers data by polling the devices on the network
from a network management station (NMS) and alert to
administrator.
This protocol can also stand as a watchdog over the
network, quickly notifying managers of any sudden turn
of events.

Hypertext Transfer Protocol (HTTP)
 It’s used to manage communications between web
browsers and web servers and opens the right resource
when you click a link, wherever that resource may actually
reside.
Your browser can understand what you need when you
enter a Uniform Resource Locator (URL), which we usually
refer to as a web address,e.g. http://www.google.com/
Web
browser
E.g.
Chrome
Web server
E.g. google
Internet protocols
E.g. http
Facilitate communication

Hypertext Transfer Protocol Secure (HTTPS)
Hypertext Transfer Protocol Secure (HTTPS) is also
known as Secure Hypertext Transfer Protocol. It uses
Secure Sockets Layer (SSL).
Sometimes you’ll see it referred to as SHTTP or S-HTTP,
which were slightly different protocols, but since
Microsoft supported HTTPS, it became the de facto
standard for securing web communication.

Domain Name Service (DNS)
An IP address identifies hosts on a network and the
Internet as well, but DNS was designed to make things
easier.
DNS allows users to use a domain name to specify an IP
address.
DNS resolves hostnames—specifically, Internet names,
such as www.amu.edu.et to Ip addresses like 10.145.8.10

DNS…
DNS resolves domain names to IP addresses and vice
versa
DNS Server 10.144.5.30
www.amu.edu.et

DNS…
The very last section of the domain is called its top-
level domain (TLD) name

Dynamic Host Configuration Protocol (DHCP)
Dynamic Host Configuration Protocol (DHCP) assigns IP
addresses to hosts dynamically.
It allows for easier administration and works well in small
to very large network environments.
Many types of hard wares can be used as a DHCP server,
including a Cisco router.
A DHCP address conflict occurs when two hosts use the
same IP address.

Simple Mail Transfer Protocol (SMTP)
Governs the transmission of mail messages and attachments.
SMTP is used in the case of outgoing messages.
More powerful protocols such as POP3 and IMAP4 are needed
and available to manage incoming messages.
POP3(Post Office Protocol version 3) is the older protocol
whereas IMAP4(Internet Mail Access Protocol version 4) is the
more advanced protocol.

It allows a user on a remote machine to access the
resources of another machine.
Telnet is not secure because everything is by using plain
text.
Due to lack of encryption telnet is outdated technology.
It is largely used in local area networks, but not in the
internet.
SSH(Secure Shell) is the better alternative for Telnet as it
protects data from being attacked or stolen when
transferred over a network.
Telnet

File Transfer Protocol (FTP)
File Transfer Protocol (FTP)actually lets users to transfer files.
Users must be subjected to an authentication login that’s
usually secured with passwords and usernames.
FTP’s functions are limited to listing and manipulating
directories, typing file contents, and copying files between
hosts.
Not a secure protocol since a data being transferred is not
encrypted(i.e. plain text).
A more secured transfer protocol should be used; that is
Secure FTP(SFTP).

Trivial File Transfer Protocol (TFTP)
TFTP is a very simple file transfer protocol.
It is mainly used to transfer files within a local area network,
but not used to transfer files over the internet due to security
issues.
TFTP doesn’t offer the abundance of functions that FTP does
because it has no directory-browsing abilities, meaning that it
can only send and receive files.
 There’s no authentication as with FTP, so it’s even more
insecure, and few sites support it because of the inherent
security risks.

TCP(Transmission Control Protocol)
TCP takes large blocks of information from an application
and breaks them into segments.
It numbers and sequences each segment to keep the order
of the segments.
After these segments are sent on the transmitting host, TCP
waits for an acknowledgment of the receiving end’s.
It is a reliable protocol, in which it provides a guaranteed
delivery.
Retransmits any segments that aren’t acknowledged.
It is Connection oriented means that a virtual connection is
established before any user data is transferred.

TCP…
 TCP can also recognize duplicate messages and will discard
them appropriately.
 If the sending computer is transmitting too fast for the
receiving computer, TCP can employ flow control
mechanisms to slow data transfer.
All these characteristics makes TCP an end-to-end reliable
transport layer protocol.

User Datagram Protocol (UDP)
User Datagram Protocol (UDP)is basically the scaled-down
model of TCP, which is why UDP is sometimes referred to as a
thin protocol.
A thin protocol doesn’t take up a lot of room—or in this
case, require much bandwidth on a network.
UDP does not sequence the segments and does not care
about the order in which the segments arrive at the
destination.
UDP just sends the segments off and forgets about them.

UDP …
It doesn’t follow segments, check up on them, or even
allow for an acknowledgment of safe arrival.
Because of this, it’s referred to as an unreliable
protocol.
This does not mean that UDP is ineffective, only that it
doesn’t deal with reliability issues at all.
Furthermore, UDP doesn’t create a virtual circuit or
doesn’t contact the destination before delivering
information to it.
Because of this, it’s also considered a connectionless
protocol.

UDP in short
Minimum overhead.
Used to send short messages.
Not reliable as TCP (out of order, missing datagram,
duplicate datagram).
Lack of flow control and error control
Faster and efficient.

Internet Protocol (IP)
The Internet Protocol (IP) is a protocol, or set of rules, for
routing and addressing packets of data so that they can travel
across networks and arrive at the correct destination.
IP is the network layer communications protocol for
relaying datagrams across network boundaries.
Its routing function enables internetworking, and essentially
establishes the Internet.
IP has the task of delivering packets from the source host to
the destination host solely based on the IP addresses in the
packet headers.
Internet Protocol versions: IPv4, IPv6.

Address Resolution Protocol(ARP)
ARP maps 32-bit logical (IP) address to 48-bit physical
address(MAC address).
An Ip address is used to locate a device on a network,
whereas MAC address is what identifies the actual device.
Host or router transmit IP datagram packet containing
logical address obtained from DNS.
Sender knows logical address(IP) of receiver but not its
physical address(MAC) so ARP maps the logical address of
the receiver to physical address it obtains from receiver.
ARP Retrieves the physical address of the receiver.

ARP…
R1 R2 R3
192.168.1.2 192.168.1.4
192.168.1.5
Sends ARP query packet
Contains
Logical address of
sender
(192.168.1.2)
Logical address of
receiver
(192.168.1.5)
Sends ARP response packet
Contains
Logical address of
receiver
(192.168.1.5)
physical address of
receiver
(00:04:ff:ff:ff:d0)
 The receiver sends ARP response packet which contains the logical
(IP) address and physical address of the receiver.
 ARP response packet is unicast directly to the sender whose
physical address is present in the ARP query packet.
Sender Receiver
Intended
receiver

Reverse Address Resolution Protocol (RARP)
RARP is a TCP/IP protocol that allows any host to obtain its IP
address from the server.
RARP perform the following steps to obtain an IP address
from the server.
 The sender broadcast the RARP request to all hosts.
 The RARP request packet contains the physical address
of the sender.
 All the host receiving the RARP request process it, but
the authorized server only replies to the requesting host.

RARP…
R1 R2
R3
192.168.1.4
192.168.1.5
Sender broadcast RARP request
Contains
Physical address of
sender
(00:04:ff:ff:ff:d0)
Sends RARP response packet
Contains
The authorized
RARP server
replies to
requesting host
which contains IP
address for
(192.168.1.2)
RARP maps 48-bit physical address(MAC address) to 32-bit
logical (IP) address.
Sender
Receiver
authorized
RARP server
00:04:ff:ff:ff:d0

Internet Control Message Protocol(ICMP)
Used to report errors with delivery of IP data.
E.g. if particular service or host not reachable or to
check routers are correctly routing .
ICMP uses Ping tool to check host if it is reachable and
how long it takes to reach.
Error reporting, but not error correction.
Two types of messages
Error reporting message
Problems with router or host e.g. destination
unreachable, time exceeded, parameters problem
Query message
Help in getting specific information. e.g. neighbors

Internet Group Management Protocol(IGMP)
IGMP is a protocol that allows several devices to share
one IP address so they can all receive the same data.
IGMP is a network layer protocol used to set up
multicasting on networks that use the Internet Protocol
version 4 (IPv4).
Protocol that manages group membership.
Provides information to multicast routers about the
membership status of hosts.

Thank you!!