1. Data and Computer Communications
Protocols and Architecture By
Ruhul Amin

2. Need For Protocol Architecture
E.g. File transfer
Source must activate comms. Path or inform network of destination
Source must check destination is prepared to receive
File transfer application on source must check destination file management system will accept and store file for his user
May need file format translation
Each problem needs to address separately
Task broken into subtasks
Implemented separately in layers in stack

3. Key Elements of a Protocol
Syntax
Data formats
Signal levels
Semantics
Control information
Error handling
Timing
Speed matching (e.g., indicates flow control)
Sequencing (e.g., avoid packet duplication)

4. Protocol Architecture
Implementation of File Transfer
File transfer example can have 4 problems
Implementation of “File Transfer” could use three modules
File transfer application (Top most layer)
Communication service module (Middle Layer)
Network access module (Lower Layer)

5. Implementation of File Transfer Architecture
Module-1 Determine weather file transfer app at sys Y is ready to receive file?
Layer1  Determine weather file translation is required or not?
Module-2 Determine weather Computer Y is ready to receive the Data?
Module-3 Determine weather a direct link or an indirect link exists between X & Y

6. Open Systems Interconnection (OSI)

7. OSI  Definition Open Systems Interconnection
Developed by the International Organization for Standardization (ISO)
It has seven layers
TCP/IP is the refinement of OSI
Questions
Why TCP/IP doesn’t have presentation & session layers?
How many layers a reference model should have ?

8. OSI – Advantage of 7 Layers Model
Each layer performs a subset of the required communication functions
Sub tasks are assigned to one of the layers depending on the nature
Each layer relies on the next lower layer to perform more primitive functions
such as application layer relies on transport layer to send the data and commands..
Each layer provides services to the next higher layer
Such as Network layer offer services to Transport layer that can be used at N/W-Layer SAP
Changes in one layer should not require changes in other layers
Layers are entirely independent and transparent to other layers

9. The OSI 7-Layers functioning

10. OSI as Framework for Standardization
Services are well defined: (Service Definition)
Protocols are well defined:
(Protocol Specification)

11. Service Primitives and Parameters
Services need to be well defined by means of service definition
Services between adjacent layers expressed in terms of primitives and parameters
Primitives specify function to be performed
Just like Op-code in Assembly
Parameters pass data and control info
Just like Op-rand in Assembly

12. TCP/IP Protocol Architecture
TCP/IP was originally developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)
5 Layers of TCP/IP.
Application Layer
Transport Layer or Host to host
Internet Layer or Network Layer
Network Access Layer or Data Link Layer
Physical Layer

13. 1- Physical Layer
Responsible to deal with interface between source & destination
Physical interface between data transmission device (e.g. computers) and transmission medium or network
Characteristics of transmission medium
Signal levels
Data rates
etc.

14. 2- Network Access Layer or Data Link Layer
Exchange of data between end system and the network
Responsible to deliver frames reliably from hop to hop (hop could be DLL device such as bridges or switches)
If within the LAN, upper layers can leave reliability issues (error/flow control) on the DLL
Guarantee Error Free Delivery of Data from one hop to the other (not N/W to N/W OR not end-to-end)
DLL is divided into 2 sub layers
Host A
Router
Host B
Host C
Host D
LAN-1
LAN-2
DLL
Network

15. Functions of Data link Layer
Framing
Divides the stream of bits into manageable data units called ‘frames’
Physical Addressing
adds a header to the frame of sender and the receiver(on the same network)
For different network ….receiver address is the address of the device that connects the network to the next node.
Flow control
data rate control…..(both sender and receiver should have the same data rate for efficient data transmission)

16. Function of Data link Layer
Error control
Adds reliability to physical layer by adding mechanism to detect and retransmit damaged or lost frames.
Detection of duplicate frames..
Its done by adding a trailer to the end of the frame.
Access control
controls the access over the same transmission link (Multi point layout of nodes)

17. 3- Internet Layer (IP) or Network Layer
Systems may be attached to different networks (such as Host-A at LAN-1 & Host-D at LAN-2)
Lowest layer that deals with end-to-end transmission
Implemented in end systems and router
Guarantee Error Free Delivery of Packets from one N/W to the other N/W (not end-to-end)
Host A
Router-1
Host B
Host C
Router-2
Host D
LAN-1
LAN-2
DLL
Network R R R R
N/W Layer
N/W Layer

18. Functions of Network layer
Logical Addresssing
its necessary to transmit packets out side one network to another…
adds a header to the packet coming from upper layer(transport layer) ..includes a logical address of the sender and the receiver to the packet.

19. Function of network Layer
Routing
switchin or routing the packets to the final destination
its usually done through router or switches..
Routing of packets is needed when data communication is taken place in internetworks or larger networks.

20. Functions of Transport layer
it does process to process delivery of messages
Service point addressing
Delivery of packets not from source computers to destination computers but from particular process to intended process.
port addressing (correct process on the destination computer)

21. Functions of Transport Layer
Segmentation and Re-assembly
Messege is divided into transmittable segments.
adds a number to the segment
segment number helps the destinations device to reassemble segments correctly upon arriving as well as to identify and replace segments that were lost in the transmission

22. Transport layer functions cont….
Connection Control
connectionless or connection oriented
connectionless
all segments are independent. A segment is transmitted as a single unit regardless of its process..
Connection Oriented
connection is established first….then transmission of data occurs.. After data is being transmitted connection is terminated

23. Functions of tranpor layer conti..
Flow control
End to End flow control…..rather than a single link…
Error Control
process to process …rather than a single link.
Error control for damage,loss or duplication of messeges….usually achieved through retransmission of messeges

24. Functions of Session Layer
It acts as dialogue controller(Establishes,mantains and synchronize the interaction among communicating devices)
Dialogue control
allows the communicating devices to enter into a dialogue
communicating modes(half duplex….or full duplex)

25. Functions of Session Layer..
Synchronization
adds a check point to a stream of data.
it adds flexibility to the data transmission

26. Functions of presentation Layer
Its concerned with the syntax and semantics of the information exchanged between the two communicating systems…
Translation
Information is usually exchanged in the form of string,number or others….these must be transformed into bit stream before being transmitted…
Different computer systems use different encoding techniques…
sender-dependent code common formatreceiver dependent format

27. Functions of Presentation Layer
Encryption
provide privacy to the information sent by converting the original information into another form..(sender side)
Decryption ….a process to reverse the encrypted informtion(receiver side)
Compression
Reduced the size of the data….particularly in the transmission of tex, audio, and video

28. Functions of Application Layer
Network Virtual Terminal
a software version of physical terminal…allows users to log on to remote host.
Software Emulation….logically connected not physically..
File transfer,Access and Management
Ftp….transfer of files between local and remote computers and to manage or control files in romote computers locally

29. Functions of Application Layer
Mail Services…
….SMTP,POP etc.
Directory Services
provides distributed data base sources and access for global information about various objects and services

30. OSI v TCP/IP

31. TCP and UDP TCP (connection oriented Protocol)
Establish a reliable logical connection between the source & the destination hosts
Need to know the source & destination port addresses
Logical connection is monitored by TCP
TCP segments (TCP PDU) can be transmitted through the secure connection
TCP is reliable but allow relatively slower communication
UDP (Connection Less Protocol)
Is a connection less protocol
Does not guarantee the reliable transmission of UDP segments
UDP header has limited control information
Faster but not reliable at all
Which protocol should I use then (TCP or UDP ???)

32. TCP/IP Concepts

33. PDUs in TCP/IP

34. Some Protocols in TCP/IP Suite