2. Protocol
Protocol is an agreement between the
communication parties on how
communication is to proceed
Rules and conventions used in the
conversation
2
3. Protocol Stack
A list of protocols used by a certain
system, one protocol per layer
3
4. Design Issues for Layers
• Mechanism for identifying senders and
receivers
• Rules for data transfer
• Error control
• Possible loss of sequencing
• Transmission rate
• Length of messages
• Multiplexing
• Route
4
7. OSI Reference Model
• Developed by International Standard
Organization (ISO)
• Called ISO OSI (Open System
Interconnection) reference model
• Has seven layers
Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer 7
10. OSI Model
Itself is not a network architecture
because it does not specify the exact
services and protocols to be used in
each layer.
It just tells what each layer should do.
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13. Interfaces
A layer’s interface tells the process above
it how to access it.
It specifies what the parameters are and
what results to expect. It, too, says
nothing about how the layer works
inside.
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15. OSI Layers - Summary
15
Layers Functions
7. Application Provides electronic mail, file transfers, and other
user services.
6. Presentation Translates data formats, encrypts and decrypts
data.
5. Session Synchronizes communicating users, recovers
from errors, and brackets operations.
4. Transport Determines network, may assemble and
reassemble packets, flow control.
3. Network Determines routes, addressing.
2. Data link Detects or corrects errors, defines frames.
1. Physical Transmits physical data.
17. The Physical Layer
• It transmits bits of information across a link.
• Deals with the problems such as :
– Size and shape of connectors,
– Assignment of functions to pins,
– Conversion of bits to electrical signals,
– Bit-level synchronization.
• several different types of physical layers to exist
within a network
• multiple different types of physical layers to exist
within a node, because each technology requires its
own physical layer.
17
18. The Data Link Layer
• Transmits chunk of information across a
link.
• Creates and recognizes frame boundaries.
• Solves the problems caused by damaged,
lost, and duplicate frames.
• Traffic flow regulation and error handling.
• Controls access to the shared channel in
broadcast networks.
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19. The Network Layer
• Enables any pair of systems in the network to
communicate each other.
• Controls the operation of the subnet.
- how packets are routed from
source to destination.
-how to control traffic congestion.
• Manages network interconnection.
- Addressing
- Packet size
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20. The Transport Layer
• Establishes a reliable communication stream between a pair of
systems.
• Deals with errors that can be introduced by the network layer:
– Lost of packets,
– Duplicated packets,
– Packet reordering,
– Fragmentation and reassembly
• Accepts data from the session layer, split it up into small units if
necessary, pass them to the network layer, and ensure that all the
pieces arrive correctly at the other end.
• May multiplex several network connections.
• True end-to-end layer, from source to destination.
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21. The Session Layer
• Allows users on different machines to
establish sessions between them.
• Provides session services:
– Token management
– Synchronization
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22. The Presentation Layer
• Concerned with the syntax and semantics
of the information transmitted.
• Does encoding and decoding.
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23. The Application Layer
• Contains a variety of protocols that are commonly
needed.
• It is common for multiple applications to be
running concurrently in a node.
• Application:
– File transfer,
– Virtual terminal,
– Web browsing,
– Etc.
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26. • Each layer communicates with its peer layer
through a protocol data unit (PDU).
• When layer n+1 gives information to layer n for
transmission, the information is known as an
SDU, or service data unit.
• As with PDUs, a single-letter prefix is added to
eliminate ambiguity.
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PDUs and SDUs
27. 27
PDUs and SDUs (Cont.)
PSDU
SSDU
Application
Presentation
Session
Transport
Network
Data Link
Physical
TSDU
NSDU
LSDU
PhSDU
Application
Presentation
Session
Transport
Network
Data Link
Physical
APDU
PPDU
SPDU
TPDU
NPDU
LPDU
PhPDU
28. The TCP/IP Reference Model
TCP – Transmission Control Protocol
IP – Internet Protocol
Layers:
• Application layer
• Transport layer
• Internet layer
• Host-to-network layer
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29. TCP/IP
• TCP/IP does not have session or
presentation layers.
• Experience with OSI model has
proven that they are of little use to
most applications.
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30. TCP/IP – Application Layer
• contains all the high-level protocols.
- virtual terminal TELNET
- file transfer FTP
- electronic mail SMTP
- domain name service DNS
- HTTP
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31. TCP/IP – Transport Layer
• same as in the OSI transport layer, it is
designed to allow peer entities on the
source and destination hosts to carry on
a conversation.
• has two protocols: TCP & UDP
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32. TCP
(Transmission Control Protocol)
• connection-oriented
• reliable
• handles flow control
• fragments the incoming byte stream into
discrete messages and passes them to
internet layer.
• the receiving TCP reassembles the
messages into the output stream.
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33. UDP (User Datagram Protocol)
• connectionless
• unreliable
• widely used for one-shot, client-server
type request-reply queries and
applications in which prompt delivery is
more important than accurate delivery.
34. TCP/IP – Internet Layer
• connectionless
• Packet-switching
• defines official packet format
• delivers IP packets where they are
supposed to go.
- Packet routing is clear the major
issue here.
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35. TCP/IP – Host-to-network Layer
This protocol is not defined and varies
from host to host and network to
network, however, TCP/IP protocol says
that the host has to connect to the
network using some protocol.
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