Kuliah 2
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Komunikasi Data Pengantar – kuliah ke 2 •
OSI model arsitektur ¾ Lapisan dan struktur model ¾ Fungsi setiap lapisan
1
ISO Reference Model •
•
•
ISO has taken a model to overcome difficulties to test and modify softwares; since the software for a communication subsystem, were often based on a single, complex, unstructured program, (written in assembly language) with many interacting components The communication subsystem here consists of a complex piece of hardware and software ISO Reference Model has taken a layered approach, where the complete communication subsystem is broken down into a number of layers, each of which performs a well-defined function Conceptually, each layers can be considered as performing generic functions: ¾ Network-dependent functions ¾ Application-oriented functions 2
ISO Reference Model •
Three different operational environments: ¾ Network environment: concern with the protocols and standards relating to the different types of underlying data communication networks ¾ OSI environment; include the network environment and adds additional application-oriented protocols and standards to allow end systems (computers) to communicate with one another in an open way ¾ Real systems environment; build on the OSI environment and concerned with a manufacturer’s proprietary software and services; have been developed to perform a particular distributed information processing task
3
ISO Reference Model Diagram environment: Computer A
Computer B
AP
AP
Application-oriented functions
Application-oriented functions
Network-dependent functions
Network-dependent functions
Data network Network environment OSI environment Real systems environment
4
ISO Reference Model •
Network-dependent and application-oriented (network-independent) components of the OSI model are implemented as a number of layers
•
Each layer performs a well-defined function in the context of the overall communication subsystems; and has a well-defined interface with the layers immediately above and below
•
The function of each layer is specified formally as a protocol that defines the set of rules and conventions used by the layer to communicate (exchanging messages, both user data and additional control information), with a corresponding (similar) peer layer in another (remote) system
•
The implementation of a particular protocol layer is independent of all other layers
5
ISO Reference Model The logical structure of ISO Reference Model: Computer A
Computer B
AP
AP
Application layer
AL (7)
Presentation layer
PL (6)
Session layer
SL (5)
Transport layer
TL (4)
Network layer
NL (3)
Link layer
LL (2)
Physical layer
PL (1)
Data network Network environment OSI environment Real systems environment
6
ISO Reference Model •
The network-dependent layers (three lowest layers) are concerned with the protocols associated with the data communication network being used to link the two communicating computers
•
The application-oriented layers (three upper layers) are concerned with the protocols that allow two end-user application processes to interact with each other, normally through a range of services offered by the local operating system
•
The intermediate transport layer (4) masks the upper application-oriented layers from the detailed operation of the lower network-dependent layers; it develops the services provided by providing the application-oriented layers with a network-independent message interchange service
7
Function of each layer of the OSI model: End-user application process Distributed information services File transfer, access and management, document and message interchange, job transfer and manipulation
Application layer
Syntax-independent message interchange services Transfer syntax negotiation, data representation transformations Dialog and synchronization control for application entities
Presentation layer Session layer
Network-independent message interchange services End-to-end message transfer (connection management, error control, fragmentation, flow control) Network routing, addressing, call set-up, and clearing
Data link control (framing, data transparency, error control)
Mechanical and electrical network interface definitions
Transport layer
Network layer Link layer Physical layer
Physical connection to network termination equipment Data communication network
8
ISO Reference Model •
Each layer provides a defined set of services to the layer immediately above; also uses the services provided by the layer immediately below it to transport the message units associated with the protocol to the remote peer layer example: transport layer provides a network-independent message transport service to the session layer above it and uses the service provided by network layer below it to transfer a set of message units associated with the transport protocol to a peer transport layer in another system
9
ISO Reference Model •
Network-dependent layers ¾ Physical layer ¾ Link layer ¾ Network layer
•
Application-oriented layers ¾ Transport layer ¾ Session layer ¾ Presentation layer ¾ Application layer
10
ISO Reference Model Physical layer •
Concern with the physical and electrical interfaces between the user equipment and the network terminating equipment
•
Provide the link layer with a means of transmitting a serial bit stream between two equipments
•
Examples: wires, connectors, voltages, data rates
11
ISO Reference Model Link layer •
Develop a physical connection provided by the particular network to provide network layer with a reliable information transfer facility
•
Responsible for functions such as error detection and retransmission messages (if there is a transmission error)
•
Examples: physical addressing, network topology, error notification, flow control
•
Two types of services: ¾ Connectionless, treats each information frame as a self-contained entity that is transferred using a best-try approach. If errors are detected in a frame, then the frame is simply discarded ¾ Connection oriented, try to provide an error-free information transfer facility 12
ISO Reference Model Network layer •
Responsible for establishing and clearing a network wide connection between two transport layer protocol entities
•
It includes functionality as network routing (addressing) and, flow control across the computer-to-network interface
•
In internetworking, it provides various harmonizing functions between the inter-connected networks
13
ISO Reference Model Transport layer •
Interface between the higher application-oriented layers and the underlying network-dependent protocol layers
•
Provide the session layer (one layer above) with a message transfer facility that is independent of the underlying network type; therefore transport layer hides the detailed operation of the underlying network from the session layer
•
It offers a number of classes of service to compensate for the varying quality of service (QOS) provided by the network layers associated with the different types of network
•
Five classes of services ranging from class 0 (provides only basic functions needed for connection establishment and data transfer) to class 4 (provides full error control and flow control procedures 14
ISO Reference Model Session layer •
Interhost communication: establishes, manages and terminates sessions between applications
•
Allows two application layer protocol entities to organize and synchronize their dialog and manage their data exchange
•
Responsible for setting up (& clearing) a communication (dialog) channel between two communicating application layer protocol entities (presentation layer protocol entities in practice) for the duration of the complete network transaction
•
A number of optional services provided: ¾ Interaction management; data exchange associated with a dialog may be duplex or half-duplex (where each protocol here provides facilities for controlling the exchange of data/dialog units in a synchronized way) 15
ISO Reference Model Session layer •
A number of optional services provided: ¾ Synchronization; for lengthy network transactions, the user (through the services provided by the session layer) may choose periodically to establish synchronization points associated with the transfer. If a fault develops during a transaction, the dialog may be restarted at an earlier synchronization point ¾ Exception reporting; non-recoverable exceptions arising during a transaction can be signaled to the application layer by the session layer
16
ISO Reference Model Presentation layer •
Concerned with the representation (syntax) of data during transfer between two communicating application processes
•
Data security; encrypted/enciphered (using a key) data sent is (hopefully) known only by the intended recipient presentation layer, and later the key is used to decrypts (deciphers) the received data before passing it onto the intended recipient
17
ISO Reference Model Application layer •
Provides the user interface (an application program/process) a range of network wide distributed information services examples: file transfer access and management, general document and message interchange services (e-mail)
•
The layer provides other services as: ¾ Identification of the intended communication partner by name or by address ¾ Determination of the current availability of an intended communication partner ¾ Establishment of authority to communicate ¾ Agreement on privacy (encryption) mechanism 18
ISO Reference Model Application layer •
The layer provides other services as: ¾ Authentication of an intended communication partner ¾ Selection of the dialog discipline, including the initiation and release procedures ¾ Agreement on responsibility for error recovery ¾ Identification of constraints on data syntax (character sets, data structures, etc.)
19
Data Encapsulation
20
Data Encapsulation
21
ISO vs TCP/IP Reference Model
22
TCP/IP Reference Model The importance of TCP/IP Although the OSI model is universally recognized, the historical and technical open standard of the Internet is TCP/IP (Transmission Control Protocol/Internet Protocol) The TCP/IP model and the TCP/IP protocol stack make data communication possible between any computers, anywhere in the world Four layers in TCP/IP model: Application; Transport; Internet; Network
23
TCP/IP Reference Model Application layer • The designer felt that the higher level protocols should include the session and presentation layer details • They created this layer that handles high-level protocols, issues of representation, encoding and dialog control • The TCP/IP combines all application-related issues into one layer, and assumes this data is properly packaged for the next layer
24
TCP/IP Reference Model Transport layer • It deals with the quality of service issues of reliability, flow control and error correction • One of its protocols, the transmission control protocol (TCP), is a connection-oriented protocol that provides excellent and flexible ways to create reliable, well-flowing, low-error network communications • It dialogues between source and destination while packaging application layer information into units called segments
25
TCP/IP Reference Model Internet layer • It governs by the Internet protocol (IP) • Send source packets from any network on the internetwork and have them arrive at the destination independent of the path and networks they took to get there • Best path determination and packet switching • Example: when we mail a letter, we do not know how it gets there (various possible routes), but we do care that it arrives
26
TCP/IP Reference Model Physical layer • It also called the host-to-network layer • Concerned with all issues that an IP packet requires to actually make a physical link • This includes a LAN and WAN technology details, and all the details in the OSI physical and data link layers
27
TCP/IP Reference Model
28
Comparing TCP/IP with OSI • TCP/IP combines the presentation and session layer issues into its application layer • TCP/IP combines the OSI data link and physical layers into one layer • TCP/IP appears simpler because it has fewer layers • TCP/IP protocols are the standards around which the internet developed, so the TCP/IP model gains credibility just because of its protocols.
29
OSI model arsitektur ¾ Lapisan dan struktur model ¾ Fungsi setiap lapisan
1
ISO Reference Model •
•
•
ISO has taken a model to overcome difficulties to test and modify softwares; since the software for a communication subsystem, were often based on a single, complex, unstructured program, (written in assembly language) with many interacting components The communication subsystem here consists of a complex piece of hardware and software ISO Reference Model has taken a layered approach, where the complete communication subsystem is broken down into a number of layers, each of which performs a well-defined function Conceptually, each layers can be considered as performing generic functions: ¾ Network-dependent functions ¾ Application-oriented functions 2
ISO Reference Model •
Three different operational environments: ¾ Network environment: concern with the protocols and standards relating to the different types of underlying data communication networks ¾ OSI environment; include the network environment and adds additional application-oriented protocols and standards to allow end systems (computers) to communicate with one another in an open way ¾ Real systems environment; build on the OSI environment and concerned with a manufacturer’s proprietary software and services; have been developed to perform a particular distributed information processing task
3
ISO Reference Model Diagram environment: Computer A
Computer B
AP
AP
Application-oriented functions
Application-oriented functions
Network-dependent functions
Network-dependent functions
Data network Network environment OSI environment Real systems environment
4
ISO Reference Model •
Network-dependent and application-oriented (network-independent) components of the OSI model are implemented as a number of layers
•
Each layer performs a well-defined function in the context of the overall communication subsystems; and has a well-defined interface with the layers immediately above and below
•
The function of each layer is specified formally as a protocol that defines the set of rules and conventions used by the layer to communicate (exchanging messages, both user data and additional control information), with a corresponding (similar) peer layer in another (remote) system
•
The implementation of a particular protocol layer is independent of all other layers
5
ISO Reference Model The logical structure of ISO Reference Model: Computer A
Computer B
AP
AP
Application layer
AL (7)
Presentation layer
PL (6)
Session layer
SL (5)
Transport layer
TL (4)
Network layer
NL (3)
Link layer
LL (2)
Physical layer
PL (1)
Data network Network environment OSI environment Real systems environment
6
ISO Reference Model •
The network-dependent layers (three lowest layers) are concerned with the protocols associated with the data communication network being used to link the two communicating computers
•
The application-oriented layers (three upper layers) are concerned with the protocols that allow two end-user application processes to interact with each other, normally through a range of services offered by the local operating system
•
The intermediate transport layer (4) masks the upper application-oriented layers from the detailed operation of the lower network-dependent layers; it develops the services provided by providing the application-oriented layers with a network-independent message interchange service
7
Function of each layer of the OSI model: End-user application process Distributed information services File transfer, access and management, document and message interchange, job transfer and manipulation
Application layer
Syntax-independent message interchange services Transfer syntax negotiation, data representation transformations Dialog and synchronization control for application entities
Presentation layer Session layer
Network-independent message interchange services End-to-end message transfer (connection management, error control, fragmentation, flow control) Network routing, addressing, call set-up, and clearing
Data link control (framing, data transparency, error control)
Mechanical and electrical network interface definitions
Transport layer
Network layer Link layer Physical layer
Physical connection to network termination equipment Data communication network
8
ISO Reference Model •
Each layer provides a defined set of services to the layer immediately above; also uses the services provided by the layer immediately below it to transport the message units associated with the protocol to the remote peer layer example: transport layer provides a network-independent message transport service to the session layer above it and uses the service provided by network layer below it to transfer a set of message units associated with the transport protocol to a peer transport layer in another system
9
ISO Reference Model •
Network-dependent layers ¾ Physical layer ¾ Link layer ¾ Network layer
•
Application-oriented layers ¾ Transport layer ¾ Session layer ¾ Presentation layer ¾ Application layer
10
ISO Reference Model Physical layer •
Concern with the physical and electrical interfaces between the user equipment and the network terminating equipment
•
Provide the link layer with a means of transmitting a serial bit stream between two equipments
•
Examples: wires, connectors, voltages, data rates
11
ISO Reference Model Link layer •
Develop a physical connection provided by the particular network to provide network layer with a reliable information transfer facility
•
Responsible for functions such as error detection and retransmission messages (if there is a transmission error)
•
Examples: physical addressing, network topology, error notification, flow control
•
Two types of services: ¾ Connectionless, treats each information frame as a self-contained entity that is transferred using a best-try approach. If errors are detected in a frame, then the frame is simply discarded ¾ Connection oriented, try to provide an error-free information transfer facility 12
ISO Reference Model Network layer •
Responsible for establishing and clearing a network wide connection between two transport layer protocol entities
•
It includes functionality as network routing (addressing) and, flow control across the computer-to-network interface
•
In internetworking, it provides various harmonizing functions between the inter-connected networks
13
ISO Reference Model Transport layer •
Interface between the higher application-oriented layers and the underlying network-dependent protocol layers
•
Provide the session layer (one layer above) with a message transfer facility that is independent of the underlying network type; therefore transport layer hides the detailed operation of the underlying network from the session layer
•
It offers a number of classes of service to compensate for the varying quality of service (QOS) provided by the network layers associated with the different types of network
•
Five classes of services ranging from class 0 (provides only basic functions needed for connection establishment and data transfer) to class 4 (provides full error control and flow control procedures 14
ISO Reference Model Session layer •
Interhost communication: establishes, manages and terminates sessions between applications
•
Allows two application layer protocol entities to organize and synchronize their dialog and manage their data exchange
•
Responsible for setting up (& clearing) a communication (dialog) channel between two communicating application layer protocol entities (presentation layer protocol entities in practice) for the duration of the complete network transaction
•
A number of optional services provided: ¾ Interaction management; data exchange associated with a dialog may be duplex or half-duplex (where each protocol here provides facilities for controlling the exchange of data/dialog units in a synchronized way) 15
ISO Reference Model Session layer •
A number of optional services provided: ¾ Synchronization; for lengthy network transactions, the user (through the services provided by the session layer) may choose periodically to establish synchronization points associated with the transfer. If a fault develops during a transaction, the dialog may be restarted at an earlier synchronization point ¾ Exception reporting; non-recoverable exceptions arising during a transaction can be signaled to the application layer by the session layer
16
ISO Reference Model Presentation layer •
Concerned with the representation (syntax) of data during transfer between two communicating application processes
•
Data security; encrypted/enciphered (using a key) data sent is (hopefully) known only by the intended recipient presentation layer, and later the key is used to decrypts (deciphers) the received data before passing it onto the intended recipient
17
ISO Reference Model Application layer •
Provides the user interface (an application program/process) a range of network wide distributed information services examples: file transfer access and management, general document and message interchange services (e-mail)
•
The layer provides other services as: ¾ Identification of the intended communication partner by name or by address ¾ Determination of the current availability of an intended communication partner ¾ Establishment of authority to communicate ¾ Agreement on privacy (encryption) mechanism 18
ISO Reference Model Application layer •
The layer provides other services as: ¾ Authentication of an intended communication partner ¾ Selection of the dialog discipline, including the initiation and release procedures ¾ Agreement on responsibility for error recovery ¾ Identification of constraints on data syntax (character sets, data structures, etc.)
19
Data Encapsulation
20
Data Encapsulation
21
ISO vs TCP/IP Reference Model
22
TCP/IP Reference Model The importance of TCP/IP Although the OSI model is universally recognized, the historical and technical open standard of the Internet is TCP/IP (Transmission Control Protocol/Internet Protocol) The TCP/IP model and the TCP/IP protocol stack make data communication possible between any computers, anywhere in the world Four layers in TCP/IP model: Application; Transport; Internet; Network
23
TCP/IP Reference Model Application layer • The designer felt that the higher level protocols should include the session and presentation layer details • They created this layer that handles high-level protocols, issues of representation, encoding and dialog control • The TCP/IP combines all application-related issues into one layer, and assumes this data is properly packaged for the next layer
24
TCP/IP Reference Model Transport layer • It deals with the quality of service issues of reliability, flow control and error correction • One of its protocols, the transmission control protocol (TCP), is a connection-oriented protocol that provides excellent and flexible ways to create reliable, well-flowing, low-error network communications • It dialogues between source and destination while packaging application layer information into units called segments
25
TCP/IP Reference Model Internet layer • It governs by the Internet protocol (IP) • Send source packets from any network on the internetwork and have them arrive at the destination independent of the path and networks they took to get there • Best path determination and packet switching • Example: when we mail a letter, we do not know how it gets there (various possible routes), but we do care that it arrives
26
TCP/IP Reference Model Physical layer • It also called the host-to-network layer • Concerned with all issues that an IP packet requires to actually make a physical link • This includes a LAN and WAN technology details, and all the details in the OSI physical and data link layers
27
TCP/IP Reference Model
28
Comparing TCP/IP with OSI • TCP/IP combines the presentation and session layer issues into its application layer • TCP/IP combines the OSI data link and physical layers into one layer • TCP/IP appears simpler because it has fewer layers • TCP/IP protocols are the standards around which the internet developed, so the TCP/IP model gains credibility just because of its protocols.
29
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