The document discusses network protocols and protocol layering. It describes the seven layers of the OSI model and four layers of the TCP/IP model. It explains the functions of each layer, including physical addressing at layer 2, logical addressing and routing at layer 3, transport functions like segmentation and error checking at layer 4, and application functions at layer 7. Common protocols are assigned to each layer, such as IP, TCP, UDP, HTTP, and FTP. Protocol layering allows dividing network designs into functional layers and assigning protocols to perform each layer's tasks.

1. Chapter four
Protocols

2. Network Protocols
 A protocol is a set of rules that governs data communications
 Is a language spoken between computers to exchange information
 Is a formal description of message formats and the rules that two computers
must follow in order to exchange those messages.
 A protocol defines what is communicated, how it is communicated, and
when it is communicated
 To request any service or exchange any information between 2 devices there
must be an agreed set of commands and data formats
 Example: The HTTP protocol defines the format for communication between
web browsers and web servers

3. Cont...
• For instance, for one computer to send a message to another computer, the first computer
must perform the following general steps
 break the data into small sections called packets
 add addressing information to the packets identifying the source and destination
computers
 deliver the data to the network interface card for transmission over the network
• The receiving computer must perform the same steps, but in reverse order
 accept the data from the NIC
 remove transmitting information that was added by the transmitting computer
 reassemble the packets of data into the original message
• The key elements of a protocol are syntax, semantics, and timing
 syntax: refers to the structure or format of the data
 Semantics: refers to the meaning of each section of bits
 Timing: refers to when data should be sent and how fast they can be sent

4. Protocol layering
• Protocol layering is a common technique to simplify networking designs by
dividing them into functional layers, and assigning protocols to perform each
layer's task
• Specify how networks are implemented
• For example, it is common to separate the functions of data delivery and
connection management into separate layers
• Thus, one protocol is designed to perform data delivery, and another protocol,
layered above the first, performs connection management
• The data delivery protocol is fairly simple and knows nothing of connection
management
• The connection management protocol is also fairly simple, since it doesn't need
to concern itself with data delivery

5. Cont...
• The most important layered protocol designs are:
• One famous model is the Open Systems Interconnection (OSI) reference
model
• Another famous model is TCP/IP model

6. OSI and TCP/IP Layers Correspondence

7. Cont.…
Sending system Receiving system
6
5
4
3
2
1
7 Application
Presentation
Session
Transport
Network
Data Link
Physical
6
5
4
3
2
1
7 Application
Presentation
Session
Transport
Network
Data Link
Physical

8. Layer 7: The Application Layer
• The application layer running on the sending system (COMPUTER) is
responsible for the actual request to be made
• This could be any type of networking request—a web request using a web
browser (HTTP), an e-mail delivery request using SMTP, or a file system request
using FTP protocols
• It represents the interface between the end-user and the network.
• Concerned with providing network service to applications like
• Email
• File transfer
• Web services
• Application layer protocols are:- HTTP, FTP, SMTP, SNMP, NFS

9. Layer 6: The Presentation Layer
• After the request is made, the application layer passes the data down to the
presentation layer
• The Presentation Layer handles data format for networked communications.
• This is done by converting data into a generic format that could be understood
by both sides.
• Performs three major functionalities:-
• Translation
• Data compression
• Encryption

10. Layer 5: The Session Layer
• Controls the connections between multiple computers
• The session layer manages the dialog between computers
• It does this by establishing, managing, and terminating
communications between two computers
• So it performs:
• Session management
• Authentication and
• Authorization
• On layers 5-7 the data package is in the form of data stream

11. Layer 4: The Transport Layer
• The transport layer handles transport functions such as reliable and unreliable
delivery of the data. For reliable transport protocols, the transport layer works
hard to ensure reliable delivery of data to its destinations.
• On the sending system, the transport layer is responsible for breaking the data
into smaller packets, so that if retransmission is required, only the packets
missing will be sent. Missing packets are determined by the fact that the
transport layer receives acknowledgments (ACKs) from the remote system, when
the remote system receives the packets.
• The transport layer is responsible for
• Segmentation
• Flow control
• Error correction
• Protocols:
• Transmission Control Protocol (TCP) – Connection Oriented
• User Datagram Protocol (UDP) – Connectionless.

12. TCP and UDP
• TCP is a connection-oriented protocol
• TCP provides the functions:
• Dividing a chunk of data into segments
• Reassembly segments into the original chunk
• Error checking and flow control through a virtual link that it
establishes and finally terminates.
• Offering a reliable data delivery service
• Examples include FTP and Email

13. UDP (User Datagram Protocol)
UDP (User Datagram Protocol): unreliable, connectionless protocol that not error
checks or offers any flow control.
Is faster than TCP because no feedback in UDP
Examples: online streaming movies , Voice over IP, game

14. Layer 3: The Network Layer
• The network layer is responsible for managing and routing of packets by using
information stored in a routing table
• The routing table is a list of available paths that are stored in memory on the
routers
• In front of the segments a network header is places, telling the sender's IP
address and the destination IP address.
• This header remains constant and will be just read and not changed by the
equipment's during the communication.
• The network layer is responsible for working with
• Logical addressing
• Routing
• Path determination

15. Cont.….
Which path should traffic take through networks is decided at this layer
Address - where something is
Route - how to get there
Only two devices which are directly connected by the same “wire” can
exchange data directly
Devices not on the same network must communicate via intermediate system
Router is an intermediate system
The network layer determines the best way to transfer data. It manages
device addressing and tracks the location of devices.
Hardware:
• The router operates at this layer.

16. Layer 2: The Data Link Layer
• The data link layer is responsible for physical addressing
• MAC addressing of the sender and receiver for each packet to form a frame
• Data unit used at data link layer is called a frame
• Is responsible for error correction functions

17. Layer 1: The Physical Layer
• The bottom layer of the OSI hierarchy is concerned only with moving bits of data
onto and off the network medium
• Responsible for converting the data frame to a pattern of signals that will be
used to send the data across the communication medium.
• On the receiving system, the signals will be converted to frame by the data link
layer and then passed up to the network layer for further processing
• Cable, connectors, repeaters, transmitters, receivers, are associated with physical
layer

18. TCP/IP Model
 Is a standard that defines how to establish and maintain a network
conversation via which application programs can exchange data
TCP/IP is a set of protocols developed to allow cooperating computers
to share resources across a network
TCP works with the Internet Protocol (IP), which defines how
computers send packets of data to each other.

19. Layer of Models

20. Cont.…
Application layer: concerned with
• Representation
• Encoding
• Dialogue control
• Transport layer: concerned with
• Reliabil and unreliable
• Flow control
• Error correction
• Internet layer: concerned with
• Logical addressing
• Best path determination
• Network access layer
• Concerned with physical addressing
• Transmission of data across media

21. OSI and TCP/IP
OSI and TCP/IP - similarities
• Both have layers
• Both assume packets are switched (called packet switched), i.e. that packets could
take different paths to reach to the same destination. Circuit switched is a case in
which all packets take the same path
• Both should be known by network professionals
OSI and TCP/IP - differences
• TCP/IP combines session, presentation and application layers into a single
layer
• TCP/IP combines physical and data link layer into a single layer
• TCP/IP is the standard in which the internet has grown

22. Categorizing protocols
• Application protocols work in
• Application layer
• Presentation layer
• Session layer
• Transport protocols work in
• Transport layer
• Network protocols work in
• Network layer
• Data link layer
• Physical layer

23. Application layer protocols
• Hypertext Transfer Protocol (HTTP)
• Used for exchanging files (text, graphic images, sound, video, and other
multimedia files) on the World Wide Web.
• File Transfer Protocol (FTP)
• Used for transferring files from one computer to another
• Simple Mail Transfer (SMTP)
• Used for transferring e-mail across the Internet.
• Network File System (NFS)
• Used to transfer files from one computer to another
• Simple Network Management Protocol (SNMP)
• Used to manage a network

24. Transport protocols
• Transmission Control Protocol (TCP)
• Enables two hosts to establish a connection and exchange streams of data. It
guarantees delivery of data and also guarantees that individual units of data
(called packets) will be delivered in the same order in which they were sent
• User datagram protocol (UDP)
• The other transport layer protocol, provides datagram delivery service. UDP
does not verify connections between receiving and sending hosts. Because
UDP eliminates the processes of establishing and verifying connections,
applications that send small amounts of data use UDP rather than TCP.

25. Network protocol
• Internet Protocol (IP)
• Specifies the format of packets and the addressing scheme.
• Most networks combine IP with a Transport Control Protocol (TCP), which
establishes a virtual connection between a destination and a source.
• IP by itself is something like the postal system.
• It allows you to address a package and drop it in the system, but there’s no direct
link between you and the recipient
• Address Resolution Protocol (ARP)
• The Address Resolution Protocol (ARP) conceptually exists between the data-link
and Internet layers. ARP assists IP in directing datagrams to the appropriate
receiving host by mapping Ethernet addresses (48 bits long) to known IP addresses
(32 bits long).
• Ethernet
• The most common local area network (LAN) protocol
• X.25
• Common wide area network (WAN) protocol