1. TELEMEDICINE

2. Why Use Protocol Architecture?
Data communications requires complex procedures
Sender identifies data path/receiver
Systems negotiate preparedness
Applications negotiate preparedness
Translation of file formats
For all tasks to occur, high level of cooperation is required

3. Modular Approach Breaks complex tasks into subtasks
Each module handles specific subset of tasks
Communication occurs
between different modules on the same system
between similar modules on different systems

4. Advantages of Modularity
Easier application development
Network can change without all programs being modified

5. Three-Layer Model
Distributed data communications involves three primary components:
Networks
Computers
Applications
Three corresponding layers
Network access layer
Transport layer
Application layer

6. Network Access Layer
Concerned with exchange of data between computer and network
Includes addressing, routing, prioritizing, etc
Different networks require different software at this layer
Example: X.25 standard for network access procedures on packet-switching networks

7. Transport Layer
Concerned with reliable transfer of information between applications
Independent of the nature of the application
Includes aspects like flow control and error checking

8. Application Layer Logic needed to support various applications
Each type of application (file transfer, remote access) requires different software on this layer

9. Addressing
Each computer on a network requires a unique address on that network
Each application requires a unique address within the computer to allow support for multiple applications (service access points, or SAP)

10. Data Transmission Application layer creates data block
Transport layer appends header to create PDU (protocol data unit)
Destination SAP, Sequence #, Error- Detection Code
Network layer appends another header
Destination computer, facilities (e.g. “priority”)

11. Simplified Architecture

12. Standardized Protocol Architectures
Vendors like standards because they make their products more marketable
Customers like standards because they enable products from different vendors to interoperate
Two protocol standards are well- known:
TCP/IP: widely implemented
OSI: less used, but widely known and still useful for modeling/conceptualizing

13. Tasks involved in sending a letter

14. Introduction OSI
The Open System Interconnection Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer network protocol design.
It divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data Link, and Physical Layers. It is therefore often referred to as the OSI Seven Layer Model.

15. OSI History
In 1978, the International Standars Organization (ISO) began to develop its OSI framework architecture.
OSI has two major components: an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols.

16. OSI History
The concept of a 7 layer model was provided by the work of Charles Bachman, then of Honeywell.
 Various aspects of OSI design evolved from experiences with the Advanced Research Projects Agency Network (ARPANET) and the fledgling Internet.

17. OSI Layers
OSI Model
Data unit
Layer
Function
Host layers
Data
7. Application
Network process to application
6. Presentation
Data representation, encryption and decryption
5. Session
Interhost communication
Segments
4. Transport
End-to-end connections and reliability, Flow control
Media layers
Packet
3. Network
Path determination and logical addressing
Frame
2. Data Link
Physical addressing
Bit
1. Physical
Media, signal and binary transmission
Going from layer 1 to 7: Please Do Not Throw Sausage Pizza Away
Going from layer 7 to 1: All People Seem To Need Data Processing

18. The interaction between layers in the OSI model

19. An exchange using the OSI model

20. Physical layer

21. Layer1: Physical Layer
The Physical Layer defines the electrical and physical specifications for devices. In particular, it defines the relationship between a device and a physical medium.
This includes the layout of pin, voltages, cable specification, hubs, repeaters,  network adapters, host bus adapters, and more.
network adapters, host bus adapters, and more.

22. Layer1: Physical Layer
The major functions and services performed by the Physical Layer are:
Establishment and termination of a connection to a communication medium.
Participation in the process whereby the communication resources are effectively shared among multiple users. For example, flow control.
Modulation, or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. These are signals operating over the physical cabling (such as copper and optical fiber) or over a radio link.

23. Layer1: Physical Layer con.
The same applies to local-area networks, such as Ethernet.
ITU-T( International Telecommunication Union Telecommunication Standardization Sector) and IEEE802.1I.
Personal area networks such as Bluetooth and IEEE

24. Data link layer

25. Layer 2: Data Link Layer
The Data Link Layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer.
Originally, this layer was intended for point-to-point and point-to-multipoint media, characteristic of wide area media in the telephone system.
The data link layer is divided into two sub-layers by IEEE.

26. Layer 2: Data Link Layer
One is Media Access Control (MAC) and another is Logical Link Control (LLC).
Mac is lower sub-layer, and it defines the way about the media access transfer, such as CSMA/CD/CA(Carrier Sense Multiple Access/Collision Detection/Collision Avoidance)
LLC provides data transmission method in different network. It will re-package date and add a new header.

27. Hop-to-hop delivery

28. Network layer

29. Layer 3: Network Layer
The Network Layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks, while maintaining the quality of service requested by the Transport Layer.

30. Layer 3: Network Layer The Network Layer performs
network routing functions,
perform fragmentation and reassembly,
report delivery errors.
Routers operate at this layer—sending data throughout the extended network and making the Internet possible.

31. the source host to the destination host.
Note
The network layer is responsible for the delivery of individual packets from
the source host to the destination host.

32. Source-to-destination delivery

33. Transport layer

34. Layer 4: Transport Layer
The Transport Layer provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers.
The Transport Layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control.

35. Layer 4: Transport Layer
Feature Name
TP0
TP1
TP2
TP3
TP4
Connection oriented network
Yes
Connectionless network No
Concatenation and separation
Segmentation and reassembly
Error Recovery
Reinitiate connection (if an excessive number of PDUs are unacknowledged)
multiplexing and demultiplexing over a single virtual circuit
Explicit flow control
Retransmission on timeout
Reliable Transport Service

36. Session layer

37. Note
The session layer is responsible for dialog control and synchronization.

38. Layer 5: Session Layer
The Session Layer controls the dialogues (connections) between computers.
It establishes, manages and terminates the connections between the local and remote application.
It provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures. 

39. Layer 5: Session Layer
The OSI model made this layer responsible for graceful close of sessions, which is a property of the Transmission Control Protocol, and also for session check pointing and recovery, which is not usually used in the Internet Protocol Suite. The Session Layer is commonly implemented explicitly in application environments that use remote procedure calls.

40. Presentation layer

41. Note
The presentation layer is responsible for translation, compression, and encryption.

42. Layer 6: Presentation Layer
The Presentation Layer establishes a context between Application Layer entities, in which the higher-layer entities can use different syntax and semantics, as long as the presentation service understands both and the mapping between them.
This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa.
This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems.
It is sometimes called the syntax layer.

43. Application layer

44. Layer 7: Application Layer
 The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application.
Application layer functions typically include:
identifying communication partners,
determining resource availability,
synchronizing communication. 

45. Layer 7: Application Layer
Identifying communication partners
Determines the identity and availability of communication partners for an application with data to transmit.
Determining resource availability
Decide whether sufficient network or the requested communication exist.
Synchronizing communication
All communication between applications requires cooperation that is managed by the application layer.

46. Summary of layers

47. OSI Feature Open system standards over the world
Rigorously defined structured, hierarchical network model
Complete description of the function
Provide standard test procedures

48. TCP/IP - OSI Comparison

49. TCP/IP - OSI Comparison
Application
Presentation
Session (Layers 7-5)
Transport
Transport (Layer 4)
Internet
Network (Layer 3)
Network Interface
Data Link
Physical (Layers 1-2)

50. TCP/IP Transmission Control Protocol/Internet Protocol
Developed by DARPA
No official protocol standard
Identifies 5 Layers
Application
Host-to-Host (transport)
Internet
Network Access
Physical

51. TCP/IP Physical Layer
Physical interface between a DTE (Data Terminal Equipment) (e.g. computer or terminal) and a transmission medium
Specifies:
Characteristics of medium
Nature of signals
Data rate

52. TCP/IP Network Access
Exchange of data between systems on a shared network
Utilizes address of host and destination
Can also prioritize transmission
Software at this layer depends on network
Segregation means that no other software needs to be concerned about net specifics

53. TCP/IP Internet Layer
An Internet is an interconnection of two or more networks
Internet layer handles tasks similar to network access layer, but between networks rather than between nodes on a network
Uses IP for addressing and routing across networks
Implemented in workstations and routers

54. TCP/IP Transport Layer
Also called host-to-host layer
Reliable exchange of data between applications
Uses TCP protocols for transmission

55. TCP/IP Application Layer
Logic needed to support variety of applications
Separate module supports each type of application (e.g. file transfer)

56. TCP & UDP Most TCP/IP applications use TCP for transport layer
TCP provides a connection (logical association) between two entities to regulate flow check errors
UDP (User Datagram Protocol) does not maintain a connection, and therefore does not guarantee delivery, preserve sequences, or protect against duplication

57. IP and IPv6 IP provides for 32-bit source and destination addresses
IPv6 (1996 standard) provides for 128-bit addresses
Migraqtion to IPv6 will be a very slow process

58. TCP/IP Applications SMTP (Simple Mail Transfer Protocol)
Basic facility, transferring messages among hosts
FTP (File Transfer Protocol)
Sends files from one system to another on user command
Telnet
Remote login capability, allowing a user to emulate a terminal on the remote system

59. Internetworking Interconnected networks, usually implies TCP/IP
Can appear to users as a single large network
The global Internet is the largest example, but intranets and extranets are also examples

60. Routers Equipment used to interconnect independent networks
Several essential functions
Provide a link between networks
Provide routing and delivery of data between processes on systems from different networks
Provide the above functions without requiring modification of the attached networks

61. Router Issues Addressing schemes Maximum packet size Interfaces
Reliability

62. TCP Segment (TCP PDU) Source port (16 bits) Destination port (16 bits)
Sequence number (32 bits)
Acknowledgment number (32 bits)
Data Offset (4 bits)
Reserved (6 bits)
Flags (6 bits) : Ex. ACK
Window (16 bits)
Checksum (16 bits)
Urgent Pointer (16 bits)
Options (variable)

63. IPv4 Header Version (4 bits) Internet header length (4 bits)
Type of Service (8 bits)
Total Length (16 bits)
Identification (16 bits)
Flags (3 bits)
Fragment Offset (13 bits)
Time to Live (8 bits)
Protocol (8 bits)
Header Checksum (16 bits)
Source Address ( 32 bits)
Destination Address (32 bits)
Options (variable)
Padding (variable)

64. TCP/IP Stack

65. TCP/IP Encapsulation

66. Why Layering Considered Harmful?
As a result of inter-layer dependencies, increased layering can quickly lead to violation of the Simplicity Principle.
Industry experience has taught us that increased layering frequently increases complexity.