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* TCP/IP Networks - Protocol Layers *
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by shaun2k2
--[ 1.0 INTRODUCTION ]--
The intent of this very short and brief paper is to explain the protocol layer
concept/OSI Protocol Model necessary to comprise any TCP/IP network.
--] 1.1 Physical Layer
The physical layer is the 'protocol' in which data transmitted across a TCP/IP
network actually travels across, physically. Perhaps the most common Physical
layer is copper wires, used very commonly among home networks, small businesses
and school networks etc. A more reliable and modern, not to mention a
considerably faster, physical layer are fiber optics.
Although the Network Security trend aims more towards securing the software
sideof the Network, considerable effort should still be taken in the interests
of
security to protect the physical layer of any Network. An example of why this
should be done is the possibility of a potential attacker installing a hardware
sniffer onto the physical protocol layer of the network. In doing this, the
attacker has almost circumvented all efforts of the network admistrator, as most
seem to see the software side of the network as worth protecting.
To put it in short, the Physical layer is the network hardware.
--] 1.2 The Data Link Layer
The data link layer is the protocol which actually, as the name says, links the
network clients together. Common, and very popular Link layer protocols include
Ethernet and Token Ring.
The data link layer controls timing on the network, among various other things,
such as adding frame types, error checking control, and addresses, whilst still
on
the network.
--] 1.3 Network Layer
The network layer is responsible for choosing the best route for packets on the
network, and efficiently routing the packets. The network layer handles the
lower level things, such as determining if a host is alive, routing the packets,
and error checking at a low level.
Well-known examples of Network layer protocols are;
IP, ICMP, IPX and AppleTalk to name to a few.
--] 1.4 Transmission layer
The transmission layer is the layer responsible for transmitting the packets
across the network, whilst at the same time ensuring that the data is in order,
and is in the correct sequence. Some transmission protocols are
connection-oriented, whilst others aren't. Some well-known transmission layer
protocols are:
TCP and UDP.
TCP is a connection oriented protocol, meaning that a connection must first be
established before two hosts can communicate via the TCP protocol. UDP,
however, is entirely non-connection oriented, meaning that datagrams sent are
very much less complex, and no connection is made before two hosts can
communicate using the protocol.
--] 1.5 Session Layer
The session layer is responsible for tracking, and keeping track of connections.
The session layer can determine when the connection ("session") was started and
host.
The session layer's primary responsibility is to manage and organise connections
between hosts.
--] 1.6 Presentation Layer
The job of the presentation layer is to "translate" or "convert" data formats to
an understandable format the local host can understand. One example of when
this layer might be used is during an FTP session, when a user is downloading a
particular file of interest from the FTP server.
The presentation layer converts data formats, so that machines can "present"
data on other systems, in an understandable format.
--] 1.7 Application Layer
The application layer is responsible for allowing users to interact with the
network. The application layer is the application in use by the user, such as
Telnet, SSH or a web browser. The Application Layer interfaces with the
Presentation Layer to in cooperation supply the visual output a user (human
being) sees on the output display (monitor).
--] 1.8 FURTHER READING
After my brief explanation of the OSI protocol model theory, you may want to
continue your research. Here's a few links for further reading:
http://www.lex-con.com/osimodel.htm
http://warlock.cs.waikato.ac.nz/~312/ 2003/lectures/link-4pp.pdf
http://www.inetdaemon.com/tutorials/theory/osi/
http://www.cisco.com/univercd/cc/td/doc/ci...oc/osi_prot.htm
http://www.archimedia.gr/hpcn/english/isdn/layer1.htm
--[ 1.9 CONCLUSION ]--
I hope this paper has been beneficial to you in someway, if not for any other
reason than the laughs you got reading this short paper.
Comments and Feedback to <shaunige@yahoo.co.uk>
-Shaun2k2
.