1. Data Communication Network Models
Behrouz A. Forouzan
Data Communication - Network Models

2. Data Communication - Network Models
LAYERED TASKS
Each layer at the sending site uses the services of the layer immediately below it
Data Communication - Network Models

3. Data Communication - Network Models
LAYERED TASKS
The layered model Introduced before 1990 was OSI model.
The TCPIIP model became the dominant commercial architecture because it was used extensively in the Internet
Data Communication - Network Models

4. Data Communication - Network Models
THE OSI MODEL
Layer 7
Layer 6
Layer 5
Layer 4
Layer 3
Layer 2
Layer 1
Data Communication - Network Models

5. Data Communication - Network Models
THE OSI MODEL
Within a single machine, each layer calls upon the services of the layer just below it.
Between machines, layer x on one machine communicates with layer x on another machine (agreed-upon series of rules)
Data Communication - Network Models

6. Data Communication - Network Models
THE OSI MODEL
intermediate nodes usually involve only the first three layers of the OSI model
Data Communication - Network Models

7. Data Communication - Network Models
THE OSI MODEL
Data Communication - Network Models

8. Data Communication - Network Models
THE OSI MODEL
Encapsulation: the data portion of a packet at level N - 1 carries the whole packet (data and header and maybe trailer) from level N.
Layer N – 1 Encapsulate Layer N Packet
Data Communication - Network Models

9. OSI Layers Physical Layer
coordinates to carry a bit stream (signal transfer) over a physical medium
mechanical and electrical specifications and procedures and functions of the interface and transmission medium
Data Communication - Network Models

10. OSI Layers Physical Layer
Physical characteristics
interfaces and medium
Bits coding
how Os and I s are changed to signals
Data rate
number of bits sent each second
Clock Synchronization
The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level
Data Communication - Network Models

11. OSI Layers Physical Layer
Line configuration
connection of devices to the media
Point-to-point or multipoint connection
Physical topology
Bus, star, mesh, ring, hybrid
Transmission mode
simplex, half-duplex, or full-duplex
Data Communication - Network Models

12. OSI Layers Data Link Layer
responsible for moving error-free frames from one hop (node) to the next.
Data Communication - Network Models

13. OSI Layers Data Link Layer
Framing
divides stream of bits received from network layer into units called frames
Physical addressing
adds address to the frame to define the sender and/or receiver of the frame.
If the frame destination is a system outside the sender's network, the receiver address is the address of the device that connects the network
Flow control
to avoid overwhelming the receiver (if sender speed is more than receiver)
Data Communication - Network Models

14. OSI Layers Data Link Layer
Error control
detect and retransmit damaged or lost frames
Mechanism to recognize duplicate frames
achieved through a trailer added to end of frame
Access control
When two or more devices are connected to the same link, mechanism is necessary to determine which device has control over the link at a time
Data Communication - Network Models

15. OSI Layers Data Link Layer
Note that the frames exchanged in every link between source and destination have different values in the headers and trailers
The source and Destination address is different in every link
The values of the trailers can also be different if error checking includes the header of the frame
Data Communication - Network Models

16. OSI Layers Data Link Layer
Data Communication - Network Models

17. OSI Layers Network Layer
Data Link Layer:
delivery of the packet between two systems on the same network (links),
Network Layer:
responsible for the source-to-destination delivery of a packet
Data Communication - Network Models

18. OSI Layers Network Layer
Logical addressing
includes logical addresses of sender and receiver which don’t change in every hop through path opposite to physical address in data link layer which changes in every hop
Routing
Intermediate nodes route or switch the packets to their final destination based on logical address
Data Communication - Network Models

19. OSI Layers Network Layer
Data Communication - Network Models

20. OSI Layers Transport Layer
responsible for delivery of entire message not just packet
Network Layer:
source-to-destination delivery of individual packets, it does not recognize any relationship between those packets. I
Transport layer:
ensures that the whole message arrives intact and in-order, overseeing both error control and flow control at the source-to-destination level
Data Communication - Network Models

21. OSI Layers Transport Layer
Data Communication - Network Models

22. OSI Layers Transport Layer
Service-point addressing
Computers often run several programs at same time.
The network address gets each packet to the correct computer;
the transport address gets entire message to the correct process on that computer.
Segmentation and reassembly
A message is divided into transmittable segments, with each segment containing a sequence number
Sequence numbers enable to reassemble the message correctly upon arriving at the destination and to identify and replace lost packets
Flow control
Flow control at this layer is performed end to end rather than across a single link in data link layer
Data Communication - Network Models

23. OSI Layers Transport Layer
Connection control
can be connectionless or connection oriented
A connectionless transport layer treats each segment as an independent packet
A connection oriented transport layer makes a connection to destination first before delivering the packets. After all the data are transferred, the connection is terminated
Error control
responsible for error control. However, error control at this layer is performed process-to-process rather than across a single link as in data link layer.
makes sure that the entire message arrives at the receiver without error.
Error correction is usually achieved through retransmission.
Data Communication - Network Models

24. OSI Layers Transport Layer
Data Communication - Network Models

25. OSI Layers Session Layer
The session layer is responsible for dialog control and synchronization
Data Communication - Network Models

26. OSI Layers Session Layer
Dialog control
allows two systems to enter into a dialog
Half-duplex or full-duplex dialog
Synchronization
allows a process to add checkpoints, or synchronization points, to a stream of data
For example, if a system is sending a file of 2000 pages, it is advisable to insert checkpoints after every 100 pages to ensure that each 100-page unit is received and acknowledged independently. In this case, if a crash happens during the transmission of page 523, the only pages that need to be resent after system recovery are pages 501 to 523. Pages previous to 501 need not be resent.
Data Communication - Network Models

27. OSI Layers Presentation Layer
is concerned with the syntax and semantics of the information exchanged between two systems
responsible for translation, compression, and encryption.
Data Communication - Network Models

28. OSI Layers Presentation Layer
Translation
responsible for interoperability between different data encoding methods in different systems
Encryption
transforms the original information to another form
Decryption reverses the original process to transform the message back to its original form
Compression
Data compression reduces the number of bits contained in the information
Data Communication - Network Models

29. OSI Layers Application Layer
responsible for providing services to the user
Mail, File Transfer, Web Browsing, Directory Service
Data Communication - Network Models

30. Data Communication - Network Models
OSI Layers
Data Communication - Network Models

31. Data Communication - Network Models
TCP/IP Model
Physical and Data Link Layers
does not define any specific protocol
supports all the standard and protocols
Internetwork Protocol Layer IP
ARP,RARP, ICMP, and IGMP.
Transport Layer
TCP , UDP and SCTP
Application Layer
combined session, presentation, and application layers in the OSI modeL
Data Communication - Network Models

32. Data Communication - Network Models
TCP/IP Model
Data Communication - Network Models

33. Data Communication - Network Models
ADDRESSING
physical (link) addresses
logical (IP) addresses
port addresses
Specific addresses
Data Communication - Network Models

34. Data Communication - Network Models
ADDRESSING
Relation between addresses and layers
Data Communication - Network Models

35. Data Communication - Network Models
Physical ADDRESSING
The physical address, also known as the link address, is the address of a node as defined by its LAN or WAN
Ethernet uses a 6-byte (48-bit) physical address that is imprinted on the network interface card (NIC).
07:01:02:01 :2C:4B
LocalTalk (Apple), however, has a I-byte dynamic address that changes each time the station comes up
Data Communication - Network Models

36. Data Communication - Network Models
Physical ADDRESSING
Data Communication - Network Models

37. Data Communication - Network Models
Logical Addressing
are necessary for universal communications
independent of underlying physical networks.
Physical addresses are not adequate in an internetwork environment where different networks can have different address formats
Unique in universe
IP Address is Internet Logical Address
The physical addresses will change from hop to hop, but the logical addresses usually remain the same
Data Communication - Network Models

38. Data Communication - Network Models
Logical Addressing
Data Communication - Network Models

39. Data Communication - Network Models
Logical Addressing
in Every hop , routing table in consulted to find next-hop
ARP Protocol is used to translate Logical Address of next-hop to it’s physical Address
Data Communication - Network Models

40. Data Communication - Network Models
Port Address
IP address and physical address are necessary for a data to travel from source to destination
Port address determines which services in destination host should data be delivered
port address is a 16-bit address represented by one decimal number
Data Communication - Network Models

41. Data Communication - Network Models
Port Address
Three process with
A, B and C Addresses
Two Processes with
J and K Addresses
Data Communication - Network Models

42. Data Communication - Network Models
Specific Addresses
Addresses in Application Layer
Address
URL Address in web
Data Communication - Network Models