End system are also referred to as host because they host (i.e. run) application program such
as a web browser program, a web server program, an email reader program.
Host are further divided into two categories:
Informally, clients tend to be desktop and mobile pc’s and so on, whereas servers tend to be
more powerful machine that stores and distribute web pages, stream video so on.
Clients and Servers
A client is a program running on one end system that requests and receive a service from a
server running on other end system.
Not all internet applications are client-server model, they are also peer-to-peer model like Bit
Torrent and eMute.
It means the approach to moving data through a network of links and switches.
There are two types:
In circuit switched network, the resources needed along a path (buffer, link transmission
rate) to provide for communication between the end systems are reserved for the duration of
the communication session between the end systems.
It reserves a constant transmission rate in the network’s links for the duration of the
communication. Since bandwidth has been reserved for this sender-to-receiver. Connection,
the sender can transfer the data to the receiver at the guaranteed constant rate.
In packed switched network, the resources are not reserved; a session’s message use the
resources on demand, and as a consequence, may have to wait (i.e. queue) for access to a
The packet is sent into the network without reserving bandwidth and if one of the links is
busy because other packets need to be transmitted over the link at the same time, our packet
will have to wait in a buffer at the sending side of the transmission link, and suffer a delay.
There are two approaches in packet switched network
1. Datagram Network
Any network that forwards the packets according to the destination address is called a
The routers in the internet forwards packets according to the destination address. Hence,
internet is datagram network.
2. Virtual Circuit Network
Any network that forwards the packets according to virtual circuit identifier (fixed route)
is called a virtual circuit network.
Preplanned route established before packets sent.
Examples are X.25, Frame relay, ATM technologies.
Er. Loknath Regmi