OSI
(Open System Interconnect)
A network is two or more nodes connected so that they can share information. The most common type of network is the local area network(LAN), in which all the nodes reside in the same geographic location. A typical LAN is a small office that has two or more computers that are connected and share a common printer.
LANs originated with the emergence of the personal computer. They filled the need for PC users in close geographical proximity to share resources and information. Shared access to file servers, application servers, printers, and the ability to exchange information directly, are all economic benefits of the LAN.
LANs originated with the emergence of the personal computer. They filled the need for PC users in close geographical proximity to share resources and information. Shared access to file servers, application servers, printers, and the ability to exchange information directly, are all economic benefits of the LAN.
OSI was developed by the International Organization for Standardization (ISO) and introduced in 1984.
The
OSI, or Open System Interconnection, model defines a networking framework to
implement protocols in seven layers. This article explains the 7 Layers of the
OSI Model.
One of the best ways to understand networking is to study the process by which computers and other networking devices transfer data. Developed by the Organization for Standardization (ISO) in 1984, the OSI model conceptually describes the foundation of how data is transferred from an application on one computer to an application on another. The OSI model comprises seven different parts called layers. Each layer handles a specific function in transferring data through a network. The layers are generally separated into two groups -- layers one through four are considered the "Lower" layers, while layers five through seven are the "Upper" layers. The lower layers transport data and the upper layers manage application specific tasks. The seven layers are as follows:
It is a layered architecture (consists of seven layers).
Each layer defines a set of functions which takes part in data
OSI was developed by the International Organization for Standardization (ISO) and introduced in 1984.
The
OSI, or Open System Interconnection, model defines a networking framework to
implement protocols in seven layers. This article explains the 7 Layers of the
OSI Model.
The OSI, or Open System Interconnection, model defines a networking framework to implement protocols in
seven layers. Control is passed from one layer to the next, starting at the
application layer in one station, and proceeding to the bottom layer, over the
channel to the next station and back up the hierarchy.
One of the best ways to understand networking is to study the process by which computers and other networking devices transfer data. Developed by the Organization for Standardization (ISO) in 1984, the OSI model conceptually describes the foundation of how data is transferred from an application on one computer to an application on another. The OSI model comprises seven different parts called layers. Each layer handles a specific function in transferring data through a network. The layers are generally separated into two groups -- layers one through four are considered the "Lower" layers, while layers five through seven are the "Upper" layers. The lower layers transport data and the upper layers manage application specific tasks. The seven layers are as follows:
One of the best ways to understand networking is to study the process by which computers and other networking devices transfer data. Developed by the Organization for Standardization (ISO) in 1984, the OSI model conceptually describes the foundation of how data is transferred from an application on one computer to an application on another. The OSI model comprises seven different parts called layers. Each layer handles a specific function in transferring data through a network. The layers are generally separated into two groups -- layers one through four are considered the "Lower" layers, while layers five through seven are the "Upper" layers. The lower layers transport data and the upper layers manage application specific tasks. The seven layers are as follows:
It is a layered architecture (consists of seven layers).
Each layer defines a set of functions which takes part in data
Application Layer
Application Layer is responsible for providing an interface for the users to interact with application services or Networking Services .
This layer supports application and end-user processes. Communication
partners are identified, quality of service is identified, user authentication
and privacy are considered, and any constraints on data syntax are identified. Everything at this
layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely
in the application level. Tiered application architectures are part of this
layer.
Ex:Web browser, Telnet etc.Service Port No.
HTTP 80
FTP 21
SMTP 25
TELNET 23
TFTP 69
The Presentation Layer
Presentation Layer It is responsible for
defining a standard format to the data.
It deals with data presentation.
The major functions described at this layer
are..
Encoding – Decoding
Eg: ASCII, EBCDIC (Text)
JPEG,GIF,TIFF (Graphics)
MIDI,WAV (Voice)
MPEG,DAT,AVI (Video)
Encryption – Decryption
Compression – Decompression
This layer provides independence from
differences in data representation (e.g., encryption) by translating from
application to network format, and vice versa. The presentation layer works to
transform data into the form that the application layer can accept. This layer
formats and encrypts data to be sent across a network, providing freedom from
compatibility problems. It is sometimes called the syntax layer.
Session Layer
It is responsible for establishing,maintaining and terminating the sessions. Session ID is used to identify a session or interaction.
Examples :
RPC Remote Procedural Call
SQL Structured Query Language
ASP Apple Talk Session protocol
This layer establishes, manages and
terminates connections between applications. The session layer sets up,
coordinates, and terminates conversations, exchanges, and dialogues between the
applications at each end. It deals with session and connection coordination.
Transport Layer
It provides data delivery mechanism between the applications in the network.The major functions described at the
Transport Layer are..
•Identifying Service
•Multiplexing & De-multiplexing
•Segmentation
•Sequencing & Reassembling
•Error Correction
•Flow Control
This layer provides transparent
transfer of data between end systems, or hosts, and is responsible for end-to-end
error recovery and flow control. It ensures complete data
transfer.
Network Layer
It provides Logical addressing & Path determination (Routing).The protocols that work in this layer are:
Routed Protocols:
IP, IPX, Apple Talk.. Etc
Routed protocols used to carry user data between hosts.
Routing Protocols: RIP, OSPF.. Etc
Routing protocols performs Path determination (Routing)
This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling,congestion control and packet sequencing
This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling,congestion control and packet sequencing
Data link Layer
Data link Layer It has 2 sub layers
• MAC (Media Access Control) It provides reliable transit of data across a physical link.It also provides ERROR DETECTION using CRC (Cyclic Redundancy Check) and ordered delivery of Frames.
Ex: Ethernet, Token ring…etc
• LLC (Logical Link Control)
At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls framesynchronization, flow control and error checking
The Physical Layer
It defines the electrical, Mechanical & functional specifications for communication between the Network devices. The functions described at this layer are.Encoding/decoding It is the process of converting the binary data into signals based on the type of the media.
Copper media : Electrical signals of different voltages Fiber media: Light pulses of different wavelengths
Wireless media: Radio frequency waves
Modes of transmission of signals:
Signal Communication happens in three different modes
1.Simplex
2.Half-duplex
3.Full-duplex
Protocols works at physical layer: 10BaseT, 100BaseT, V.35,RS-232..etc
This layer conveys the bit stream -
electrical impulse, light or radio signal -- through the network at the electrical and mechanical level.
It provides the hardware means of sending and receiving data
on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.
DATA Transfer between two computers
TH----->Transport header(Source and destinations port address)
NH----->Network Header(source and destinations IP address)
DH----->Data link Header (source and destinations mac address)
DT----->Data link tail
What is an Internetwork?
Internetworks are multiple networks that are connected in such a way that they act as one large network, connecting multiple office or department networks. Internetworks are connected by networking hardware such as routers, switches, and bridges. An example of an internetwork is two office branches connected together by a T1 line.
Internetworking is a solution born of three networking problems: isolated LANs, duplication of resources, and the lack of a centralized network management system. With connected LANs, companies no longer had to duplicate programs or resources on each network. This in turn gave way to managing the network from one central location instead of trying to manage each separate LAN.
Collision domain: Refers to a "shared" Ethernet segment. Hubs enable you to add more users to a single collision domain. Switches enable you to segment collision domains.
Ethernet: Popular LAN technology based on the IEEE 802.3 standard. Ethernet can run in 10Base, 100Base and 1000Base speeds. It uses CSMA/CD (Carrier Sense Multiple Access Collision Detection) for its media detection method. Unlike token ring, it is possible for two users to transmit at the same time -- resulting in a collision.
Token Ring: A token-passing LAN technology based on IEEE 802.5. Token Ring operates at 4 or 16Mbps. Connectivity is provided by an MSAU (Multi-Station Access Unit).
FDDI: Fiber Distributed Data Interface. FDDI is a token-passing LAN media that runs at a speed of 100Mbps for distances up to 2 kilometers.
CDDI: Copper Distributed Data Interface. CDDI is a variation of FDDI that is run over copper cable. CDDI runs at a speed of 100Mbps for distances up to 100 meters.
ATM: Asynchronous Transfer Mode. ATM is standard for cell relay in which multiple service types (such as voice, video, or data) are carried in fixed-length cells. Fixed length cells allow cell processing to occur in hardware, thereby reducing transit delays -- ATM cells are 53 bytes long. ATM is designed to run on high speed interfaces such as DS-3, OC-3, etc.
Frame Relay: Popular WAN technology that handles multiple circuits through one physical connection. Allows one WAN connection on a router to connect with multiple remote sites. Frame relay is a packet switched network that determines the path through the frame relay cloud (internetwork) based on PVC information.
Leased Line: A dedicated WAN connection. This is a private connection with guaranteed throughput between sites.
ISDN: Integrated Services Digital Network. A WAN connection that can carry voice, data and video. ISDN is offered as a BRI or a PRI. BRI (Basic Rate Interface) has two 64k B channels and a 16k D channel. PRI (Primary Rate Interface) has twenty-three 64k B channels and one 24k B channel. B channels are used to carry voice, data, video traffic; D channels are used to establish and tear down connections.
DSL: Digital Subscriber Line. High speed public network media that provides high bandwidth over standard phone lines. DSL is limited by distance. It requires a DSL "modem" at the central office and at the customer premises. DSL does not use the entire bandwidth of a wire, leaving room for a voice connection.
T1/E1: T1 lines transmit at 1.544Mbps through the public telephone network, and are typically used in North America. E1s transmit at 2.48 Mbps through the public telephone network, and are typically used in Europe and South America.
T3/E3: T3s transmit at 44.736 Mbps, and are typically used in North America. E3s transmit at 34.368 Mbps, and are used in Europe and South America.
Internetworks are multiple networks that are connected in such a way that they act as one large network, connecting multiple office or department networks. Internetworks are connected by networking hardware such as routers, switches, and bridges. An example of an internetwork is two office branches connected together by a T1 line.
Internetworking is a solution born of three networking problems: isolated LANs, duplication of resources, and the lack of a centralized network management system. With connected LANs, companies no longer had to duplicate programs or resources on each network. This in turn gave way to managing the network from one central location instead of trying to manage each separate LAN.
Collision domain: Refers to a "shared" Ethernet segment. Hubs enable you to add more users to a single collision domain. Switches enable you to segment collision domains.
Ethernet: Popular LAN technology based on the IEEE 802.3 standard. Ethernet can run in 10Base, 100Base and 1000Base speeds. It uses CSMA/CD (Carrier Sense Multiple Access Collision Detection) for its media detection method. Unlike token ring, it is possible for two users to transmit at the same time -- resulting in a collision.
Token Ring: A token-passing LAN technology based on IEEE 802.5. Token Ring operates at 4 or 16Mbps. Connectivity is provided by an MSAU (Multi-Station Access Unit).
FDDI: Fiber Distributed Data Interface. FDDI is a token-passing LAN media that runs at a speed of 100Mbps for distances up to 2 kilometers.
CDDI: Copper Distributed Data Interface. CDDI is a variation of FDDI that is run over copper cable. CDDI runs at a speed of 100Mbps for distances up to 100 meters.
ATM: Asynchronous Transfer Mode. ATM is standard for cell relay in which multiple service types (such as voice, video, or data) are carried in fixed-length cells. Fixed length cells allow cell processing to occur in hardware, thereby reducing transit delays -- ATM cells are 53 bytes long. ATM is designed to run on high speed interfaces such as DS-3, OC-3, etc.
Frame Relay: Popular WAN technology that handles multiple circuits through one physical connection. Allows one WAN connection on a router to connect with multiple remote sites. Frame relay is a packet switched network that determines the path through the frame relay cloud (internetwork) based on PVC information.
Leased Line: A dedicated WAN connection. This is a private connection with guaranteed throughput between sites.
ISDN: Integrated Services Digital Network. A WAN connection that can carry voice, data and video. ISDN is offered as a BRI or a PRI. BRI (Basic Rate Interface) has two 64k B channels and a 16k D channel. PRI (Primary Rate Interface) has twenty-three 64k B channels and one 24k B channel. B channels are used to carry voice, data, video traffic; D channels are used to establish and tear down connections.
DSL: Digital Subscriber Line. High speed public network media that provides high bandwidth over standard phone lines. DSL is limited by distance. It requires a DSL "modem" at the central office and at the customer premises. DSL does not use the entire bandwidth of a wire, leaving room for a voice connection.
T1/E1: T1 lines transmit at 1.544Mbps through the public telephone network, and are typically used in North America. E1s transmit at 2.48 Mbps through the public telephone network, and are typically used in Europe and South America.
T3/E3: T3s transmit at 44.736 Mbps, and are typically used in North America. E3s transmit at 34.368 Mbps, and are used in Europe and South America.
