computers in medical field

OSI MODEL
Virtually all networks in use today are based in some fashion on the Open Systems Interconnection (OSI) standard. OSI was developed in 1984 by the International Organization for Standardization (ISO), a global federation of national standards organizations representing approximately 130 Countries. The ISO created the OSI to make the IOS more efficient.
Where,
ISO stands for International Organization for Standardization.
OSI stands for Open System Interconnection.
IOS stands for Internet work Operating System.

OSI LAYERS
The OSI model is divided into 7 layers distributed in 2 sets:
APPLICATION SET Layer 7: Application Layer 6: Presentation Layer 5: Session
TRANSPORT SET Layer 4: Transport Layer 3: Network Layer 2: Data
Layer 1: Physical

1. APPLICATION LAYER:
This is the layer that actually interacts with the operating system or application whenever the user chooses to transfer files, read messages or perform other network related activities. This layer deals with networking applications.

RESPONSIBLE FOR APPLICATION LAYER
1. Provides Interface between the user & the computer (applications & Gateways).
2. Provides services that directly support user applications, such as the USER INTERFACE, E-MAIL, FILE TRANSFER, TERMINAL EMULATION, DATABASE ACCESS, etc.
3. Allows applications to use the network.
4. Handles Network access, flow control & error recovery.

CORRESPONDING PROTOCOLS 1. SNMP
2. FTP
3. TELNE
4. WWW
5. HTTP

CORRESPONDING DEVICES
GATEWAYS
2. PRESENTATION LAYER:
The Presentation layer performs code conversion and data reformatting (syntax translation). It is the translator of the network, making sure the data is in the correct form for the receiving application. This layer is responsible for presenting the data in the required format which may include:
· Encryption
· Compression

RESPONSIBLE FOR PRESENTATIOAN LAYER
1. In this layer Translation of data into understandable format for transmission occurs.
2. It handles character encoding, bit order and byte order issues. Encodes and decodes data.
3. Data compression and encryption takes place at this layer.
4. It generally determines the structure of data.
5. The redirector works at this layer.
6. It is responsible for protocol conversion.
7. Messages are sent between layers
8. Communicates through GATEWAYS and APPLICATION INTERFACES.
CORRESPONDING PROTOCOLS
JPEG· MIDI· MPEG·
All kinds of music pictures & movie formats are used at this layer.

CORRESPONDING DEVICES
GATEWAY
3. SESSION LAYER:
This Layer establishes, maintains and ends communication with the receiving device. The Session layer decides when to turn communication on and off between two computers. It provides the mechanisms that control the data-exchange process and coordinates the interaction between them. It sets up and clears communication channels between two communicating components. This layer establishes, manages, and terminates sessions between two communicating hosts.
Example:
· Client Software (Used for logging in)

RESPONSIBLE FOR SESSION LAYER
1. It is Responsible for opening, using and closing session. It allows applications on connecting systems to establish a session.
2. Provides synchronization between communicating computers (nodes), messages are sent between layers (i.e. Manages upper layer errors).
3. Also places checkpoints in the data flow, so that if transmission fails, only the data after the last checkpoint needs to be retransmitted.
4. Handles remote procedure calls.
5. Communicates through Gateways & application interfaces.

CORRESPONDING PROTOCOLS
Network File System (NFS

CORRESPONDING DEVICES
GATEWAYS
4. TRANSPORT LAYER:

The Transport layer ensures data is successfully sent and received between the two computers. If data is sent incorrectly, this layer has the responsibility to ask for retransmission of the data. This layer acts as an interface between the bottom and top three layers. By providing the session layer with a reliable message-transfer service, it hides the detailed operation of the underlying network from the session layer. This layer maintains flow control of data and provides for error checking and recovery of data between the devices. This layer breaks up the data from the sending host and then reassembles it in the receiver.
It also is used to insure reliable data transport across the network.

RESPONSIBLE FOR TRANSPORT LAYER
1. This layer is responsible for PACKET HANDLING. Ensures error free delivery. Repackages messages, divides messages into smaller packets (Fragments and reassembles data), and handles error handling
2. It ensures proper sequencing and without loss and duplication.
3. Takes action to correct faulty transmissions.
4. Controls flow of data.
5. Acknowledges successful receipt of data.
6. TCP/SPX - connection oriented communication for applications to ensure error free delivery.
7. Communicates through Gateway Services, routers & B-routers.

CORRESPONDING PROTOCOLS
TCP, UDP, SPX, NetBEUI

CORRESPONDING DEVICES
GATEWAYS, ROUTERS AND B-ROUTERS
5. NETWORK LAYER:
The Network layer establishes, maintains, and terminates logical and/or physical connections. The network layer is responsible for translating logical addresses, or names, into physical addresses. It provides network routing and flow-control functions across the computer-network interface. This layer provides transparent transfer of data between end systems. It is sometimes referred to as the “Cisco Layer”. It makes “Best Path Determination” decisions based on logical addresses (usually IP addresses).
RESPONSIBLE FOR NETWORK LAYER
1. Logical addressing - software addresses to hardware addresses are resolved (ARP/RARP).
2. It is responsible for Routing of message (Packets) between hosts & networks (IP/IPX).
3. It determines the best route (Makes routing decisions & forwards packets for devices that could be farther away than a single link).
4. Moves information to the correct address.
5. Sends messages and reports errors regarding packet delivery (ICMP)
6. Communicates through GATEWAY SERVICES, ROUTERS & BROUTERS.
CORRESPONDING PROTOCOLS
1. IP 4. ARP 7. ICMP
2. IPX 5. RARP 8. DLC
3. RIP 6. OSPF 9. NetBEUI
CORRESPONDING DEVICES
ROUTERS & B-ROUTERS
6. DATA LINK LAYER:
The Data-Link layer handles the physical transfer, framing, flow control and error-control functions (and retransmission in the event of an error) over a single transmission link. It is responsible for getting the data packaged and onto the network cable. The data link layer provides the network layer reliable information-transfer capabilities. This layer provides reliable transit of data across a physical link. Makes decisions based on physical addresses (usually MAC addresses). The data-link layer is often subdivided into two parts.
Logical Link Control (LLC)
Medium Access Control (MAC)

LLC (Logical Link Control) – It is the upper sub-layer, which establishes and maintains links between communicating devices. It is also responsible for frame error correction and hardware addresses. MAC (Media Access Control) – It is the lower sub-layer, which Controls how devices share a media channel, either through CONTENTION or TOKEN PASSING.

RESPONSIBLE FOR DATALINK LAYER
1. The Data Link Layer provides flow of data over a single link from one device to another.
2. It controls access to communication channel.
3. Controls flow of data.
4. Packets placed into frames at this layer.
5. It also identifies the specific computer on the network.
6. CRC is added at this Layer (Error detection).
7. If CRC fails at the receiving computer, this layer will request re-transmission.
8. MAC addresses are resolved at this Layer (switches, B-routers and bridges function on this layer using the MAC sub layer)
9. Sends data from network layer to physical layer.
10. Manages physical layer communications between connecting systems.
11. Data frames are sent between layers.
12. Communicates through: SWITCHES, BRIDGES & INTELLIGENT HUBS.

CORRESPONDING PROTOCOLS HDLC - (High-level Data Link Control)
It Supports Asynchronous & synchronous Transmissions. It uses LLC flow control.

CORRESPONDING DEVICES
BROUTERS, BRIDGES and SWITCHES
7. PHYSICAL LAYER:
The Physical layer provides the electrical and mechanical interface to the network medium (the cable). This layer gives the data-link layer its ability to transport a stream of serial data bits between two communicating Systems. It conveys the bits that move along the cable. It is responsible for making sure that the raw bits get from one place to another, no matter what shape they are in. This is the physical media through which the data, represented as electronic signals, is sent from the source host to the destination host.
Examples:
· CAT5
· Coaxial
· Fiber optic

RESPONSIBLE FOR PHYSICAL LAYER
1. In this layer data (BITS) is sent across physical media like wires and hubs.
2. It is Responsible for encoding scheme.
3. Defines cables, cards and physical aspects.
4. Provides electrical and mechanical interfaces for a network.
5. Specifies how signals are transmitted on network
6. Communicates through: REPEATERS, HUBS, SWITCHES, CABLES, CONNECTORS, RECEIVERS, & MULTIPLEXERS

CORRESPONDING PROTOCOLS
None

CORRESPONDING DEVICES
1. B-routers 4. Amplifiers 7. Receivers 10. Cables
2. Hubs 5. Transceivers 8. Transmitters 11. Switches
3. Repeaters 6. Multiplexers 9. Connectors