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Monday, August 5, 2013

PPT On Network Basics


Network Basics Presentation Transcript:
1.Network Basis

Types of communication services   
Implementation of communication services
Network performance measures

3.Types of service
establish a connection
use the connection (for data transfer)
release the connection
modeled on the telephone system
essential feature: sender pushes objects (e.g. bits, packets) in one end of the connection, and receiver takes them out in the same order at the other end

each message is sent independently from the sender to the receiver
modeled on the postal service
essential features: each message must include the receiver’s address, and messages can be received in a different order to the order in which they were transmitted

5.Each type of service is characterized by its reliability.
whether or not the service guarantees to correctly deliver the data
Reliable service: receiver confirm to the sender that it correctly received each message (which introduces extra overhead and delays)
Reliable connection-oriented service has 2 variations:
message stream: preserves message boundaries
    (e.g. 2 1-kBmessages are received as 2 1-kBmessages, not1 2-kBmessage, 4 512-byte messages, or anything else)
byte stream: doesn’t preserve message boundaries
            (e.g. 2 1-kBmessages are received as a 2048-byte stream)
Unreliable connection-oriented service
e.g. real-time audio or video: tolerates some errors or losses in transmission (quality decreases as errors/losses increase)

6.Connectionless service can be unreliable(no 100% delivery guarantee), acknowledged(receipt confirmed), or request-reply(a single short message contains a request, another the reply)

7.a single network could offer more than one type of service
e.g. the Internet supports all of them, more or less
may have different implementations of the same service
e.g. connection-oriented delivery of a voice bit stream can be implemented by packet voice or a dedicated circuit

8. Implementation of Communication Services
It is economically infeasible to directly connect every pair of sender-receiver pairs (e.g. mesh or star) in a large network
Network resources must be shared between the users, while still allowing senders to transmit data to their receivers

9.Basic Techniques of Connectivity
Two basic techniques that permit connectivity while sharing resources are switching and multiplexing
switching: sharing network resources among multiple transmissions
multiplexing: sharing a single link among multiple transmissions

10.Types of switching
Circuit Switching
Packet Switching
Datagram packet switching
Virtual circuit packet switching

11.Circuit Switching
a path is set up in the network between the sender and the receiver (by making the appropriate connections in the switches)
the necessary network resources are reserved for the connection prior to any data transfer; if this is not possible, the connection request is blocked
these reserved resources are then held for the duration of the connection links are not shared at the same time
the links in a path are monopolized for the duration of the connection, then released so that they are available for other connections
circuit switching is ideal for “smooth” network traffic
e.g. telephone network

13.if the traffic from sender to receiver is “bursty” (varies widely around its average value)
computer-to-computer traffic can be very bursty
could set up a new circuit for each burst
could hold original circuit for duration of data transfer
both of these solutions are wasteful of network resources

14.packet = string of bits (up to a few thousand, typically)
uses store-and-forward operation

15.Types of Packet Switching
Two types of packet switching
Datagram packet switching
Virtual circuit packet switching

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