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Seven Layers of ISO OSI Model

The ISO OSI model are explained below. TheUDP (Universal Data gram Protocol): UDP
seven  layers  of  the  OSI  model  are:simply transmits packets over the internet.
It does not wait for an acknowledgement. It
is the responsibility of upper layer
protocols to ensure that the information had
Applicationreached the intended partner(s). Hence, UDP
is  often  called  connectionless  protocol.
Presentation
Session
Application programs that do not need
Transportconnection-oriented protocol generally use
UDP.
Network
5. Network layer: Network layer is
Antiqua">Data  Linkresponsible for the routing of packets
through the entire network. The layer uses
Physicallogical addressing for this purpose. Note
that the physical address (like MAC address)
1 Application layer: This layer provides akeeps changing from hop to hop when a packet
means for the user to access information ontravels from source to destination. As a
the network through an application. Many userresult, an address that doesn't change is
applications that need to communicate overrequired to ensure continuity between hops.
the network interact with the ApplicationThis is nothing but logical address. For IP
layer protocol directly. The usernetworks, IP address is the logical address;
applications are not part of OSI Applicationand for Novell network, IPX address is the
layer, use the networking services offered bylogical address, and so on. This layer also
the networking protocol suite. Applicationprovides for congestion control, and
layer functions typically include identifyingaccounting information for the network. IP
communication partners, and determining(Internet Protocol) is an example of a
availability of required resources. Somenetwork layer protocol. 6. Data link layer:
examples of application layer implementationsData link layer provides delivery of
include Telnet, File Transfer Protocol (FTP),information frames between communicating
and Simple Mail Transfer Protocol (SMTP). 2partners. This layer is responsible for flow
Presentation layer: Presentation layerregulation, error detection and correction,
converts local host computer dataand framing of bits for transmission. The
representations into a standard networknetwork data frame is made up of checksum,
format for transmission on the network. Onsource address, destination address, and the
the receiving side, it changes the networkdata itself. The largest frame size that can
format into the appropriate host computer'sbe sent is known as the maximum transmission
format so that data can be utilizedUnit (MTU).Important features of Data link
independent of the host computer. ASCII andlayer:
EBCDIC conversions, cryptography, and the
like  are  handled  here.Assembles bits into frames, making them
ready  for  transmission  over  the  network.
Examples of Presentation layer coding and
conversion schemes include common dataProvides error detection, and correction to
representation formats, conversion oftransmitted frames. If the checksum is not
character representation formats, common datacorrect, it asks for retransmission. (Send a
compression schemes, and common datacontrol  message).
encryption schemes. Presentation layer
implementations are not typically associatedConsists  of  two  sub  layers:
with a particular protocol stack. Some
well-known standards for video includeLogical Link Control (LLC): Defines how data
QuickTime and Motion Picture Experts Groupis transferred over the cable and provides
(MPEG). QuickTime is an Apple Computerdata  link  service  to  the  higher  layers.
specification for video and audio, and MPEG
is a standard for video compression andMedium Access Control (MAC): Controls media
coding.3. Session layer: The session layeraccess by regulating the communicating nodes
establishes, manages, and terminatesusing pre-defined set of rules. (i.e. Token
communication sessions. Communicationpassing, Ethernet [CSMA/CD] all have MAC
sessions consist of service requests andsub-layer  protocol).
service responses that occur between
applications located in different network
devices. These requests and responses are
coordinated by protocols implemented at the
session layer. Some examples of session-layer
implementations include AppleTalk's Zone
Information Protocol (ZIP), and Decent Phase
Session Control Protocol (SCP).4.Transport
layer: Transport layer is responsible for
providing reliable service between the hosts.Different Data link layer protocols define
Upper layer datagrams are broken down intodifferent network and protocol
manageable datagrams and then appropriatecharacteristics, including physical
header information (such as sequence number,addressing, network topology, error
port number, etc.) is added to the datagramnotification, sequencing of frames, and flow
before passing it on to the Network layer.control. Physical addressing (as opposed to
Two frequently used transport protocols arelogical addressing) defines how devices are
the TCP (Transmission Control Protocol) andaddressed at the data link layer. The
the UDP (User Datagram Protocol). Importantprotocols used in Data link layer are SLIP,
features  of  Transport  layer:PPP, and CSLP.7. Physical layer: This is the
bottom-most layer of the OSI model. The
Transport  layer  ensures reliable service.Physical layer handles the bit-level
communications across the physical medium.
The physical medium could be made up of wired
electrical signals, or light, or radio
Breaks the message (from sessions layer)(wireless) signals. Physical layer
into smaller datagrams, and appendsspecifications define characteristics such as
appropriate  unit  header  information.media, data rates, maximum transmission
distances,  and  physical  connectors.
Some of the important standards that deal
Responsible for communicating with thewith  physical  layer  specifications  are:
Session  layer
RS-232(for serial communication lines),
Important  features  of  TCP/UDP:X.21,  EIA  232,  and  G730.
TCP/IP widely used protocol for TransportPhysical layer and Data link layer
Network  layersimplementations can be categorized as either
LAN or WAN specifications. Vijayanand has
TCP: (Transport Control Protocol) TCPdone his post graduation (M.E.) in
ensures that a packet has reached itsCommunication Systems. He has several years
intended destination by using anof experience in electronic assembly and
acknowledgement. If not, it retransmits thedesign, rf testing, and networking. He is a
lost messages. Hence, TCP is called aCisco Certified Networking Professional, and
connection  oriented  protocol.an MCSE (Microsoft Certified Systems
Engineer). He is a director of Anand Software
and Training Pvt. Ltd. Complete tutorial on
Networking is available at SimulationExams.



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