RSS
Twitter
Facebook
• Business applications
• Resource sharing: end systems
(hosts):
• run application programs
• e.g. Web, email
• at “edge of network”
• client/server model
• client host requests, receives
service from always-on server
• e.g. Web browser/server; email
client/server
• Client/server model is
applicable in an intranet.
E-mail: Now all the companies
uses email as the means of communication
E-commerce: Now teleshopping and
marketing is very popular and finding the
application in business
Mobile users are connected using
network such as laptops palmtops etc
Like wise even home users have increased now and
becoming popular.
Notes
• A Protocol can be defined as a
set of rules governing the exchange of data
between two entities.
• Used for communications between
entities in a system
• Two entities have to speak the
same language to successfully communicate
• Networks are complex and
consist of many “pieces”:
• hosts
• routers
• switches
• links of various media
• applications
• protocols
• reliability
• connection type
How to simplify the complex
structures. A layered structured can be used to reduce the complexity. Most of
the network are organized as a stack of layers or levels each one built over
the other. The number of layers and the name of the layers and the function of each
layer differ from network to network. The purpose of each layer is to offer
service to layer above it. Layer n on one machine carries conversation with
layer n on another machine. The rules and conventions used collectively known
as the layer n protocol. For example consider a five layered network.
The entities comprising the
corresponding layers on different machines are called peers. The peers may be
processes or hardware devices or human beings. Peers communicate using
protocol. No data is sent from layer n to layer n instead they send to the
layer below until the last layer is reached. Between the layers it is the
virtual communication. Between each pair of layers is the interface. It defines
the primitive operation and services what the lower layer makes available to
the upper one. Network designers decide about the function and the number of
layers. It is very important to define a clear interfaces. A set of protocol
and layers is called the network architecture. A list of protocol used by a
certain system one protocol per layer is called a protocol stack.
Consider the above figure
This shows how communication
happens between two systems. A message M is
produced by the layer 5. It is
given to layer 4 and it puts the header in front of the
message and passes to layer 3.
The header includes the control information such as
sequence numbers to allow the
layer 4 on the destination machine to deliver messages in the right order. The
layer 3 breaks up the message into smaller units called packets adding layer 3
header to each packet. In this example M is split into 2 packets M1 and M2.
Layer 3 decides which of the outgoing line to use and sends on that line to
layer 2. Layer 2 adds a header and also a trailer and give the resulting unit
to layer 1 for physical transmission. At the receiving machine the message move
upwards from layer to layer, with header being stripped off as it progresses.
0 comments