Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
E-Commerce is taking over the traditional commerce practices. It is of special concern for the IT students. Following are the key points of these Lecture Slides : The Application Layer, Network Services, Application Layer, Transparent, Bottom Layers, Middle Layers, Uppermost Layers, Error Conditions, Physical Connectivity, Signal Transmission
Typology: Slides
1 / 10
This page cannot be seen from the preview
Don't miss anything!
21
22
24
Data Transmission in the OSI Model^ The sending process has some data it wants to send tothe receiving process.^ It gives the data to the application layers, which thenattaches the application header
AH^ to the front of it and
gives the resulting item to the presentation layer. The presentation layer may transform this item invarious ways, and possibly add a header to the front,giving the result to the session layer. It is important tonote that the presentation layer is not aware whichportion of the item is
AH^ and which is user data.
This process is repeated until the data reach thephysical layer, where they are actually transmitted to thereceiving machine. On that machine the various headersare stripped off one by one as the message propagatesup the layers until it finally arrives at the receivingprocess (application).
25
Data Transmission in the OSI Model^ The
key idea
throughout is that
although actual data
transmission is vertical
in Fig. 2.,
each layer is
programmed as though it were horizontal
. (each layer
thinks it is communicating directly (horizontally) with itspeer on the other machine) For example, when the sending transport layer gets amessage from the session layer, it attaches a transportheader (with information to be used by the receivingtransport layer) and sends it to the receiving transportlayer. From its point of view, the fact that it must actuallyhand the message to the network layer on its ownmachine is an unimportant technicality.
27
The TCP/IP Reference Model This architecture later became known as the
Reference model
, after its two primary protocols. It was
first defined in 1974, and updated in 1985 and 1988. Given the DoD’s worry that some of its precious hosts,routers, and internetworking gateways might get blownto pieces at a moment’s notice, another major goal wasthat the network be able to survive loss of subnethardware, with existing conversations not being brokenoff. In other words, DoD wanted connections to remainintact as long as the source and destination machineswere functioning even if some of the machines ortransmission lines in between were suddenly put out ofoperation. Furthermore, a flexible architecture wasneeded, since applications with divergent requirementswere envisioned, ranging from transferring files to real-time speech transmission.
28
TCP/IP – The Internet Layer All these requirements lead to the choice of a packet-switching network based on a connectionlessinternetwork layer. This layer, called the
internet layer
, is
the glue that holds the whole architecture together. Its job is to
permit hosts to inject packets into any network
and have them
travel independently to the
destination
(potentially on a different network). They may even arrive in a different order
than they were sent,
in which case it is the job of higher layers to rearrangethem, if in-order delivery is desired. Note that “internet” is used here in a generic sense,even though this layer is present in the Internet.
30
TCP/IP – The Internet Layer
