What is Multiplexing ? discuss Statistical Multiplexing.

Multiplexing

• Physical links/switches must be shared among users

1. (synchronous) Time-Division Multiplexing (TDM)
2. Frequency-Division Multiplexing (FDM)

Statistical Multiplexing

• On-demand time-division, possibly synchronous (ATM)
• Schedule link on a per-packet basis
• Buffer packets in switches that are contending for the link
• Packets from different sources interleaved on link
• An application needs to break-up its message in packets and re-assemble at the receiver
• Fair allocation of link capacity: FIFO, round-robin or QoS
• If congestion occurs at a switch - buffer may overflow, packets may be lost

What are Switched Networks in Computer Networking and Switching Strategies?

 Switched Networks in Computer Networking:

A network can be defined recursively as...

• two or more nodes connected by a link
• circular nodes (switches) implement the network
• squared nodes (hosts) use the network

A network can be defined recursively as...

• two or more networks connected by one or more nodes: internetworks
• circular nodes (router or gateway) interconnects the networks
• a cloud denotes “any type of independent network”

Switching Strategies:

Circuit switching:   

carry bitstreams

• establishes a dedicated circuit
• links reserved for use by a communication channel
• send/receive bitstream at a constant rate
• example: original telephone network

Packet switching: 

store-and-forward messages

• operates on discrete blocks of data
• utilizes resources dynamically according to traffic demand
• send/receive messages at a variable rate
• example: Internet

Dicuss Computer Network in Details.

Computer Network :

• Set of serial lines to attach terminals to mainframe?
• Telephone network carrying voice traffic?
• Cable network to disseminate video signals?

What Distinguishes a Computer Network?

• Generality
• Built from general-purpose programmable hardware
• Supports a wide range of applications

Applications – Consumers of Networks:

• On a simple click, several messages may be exchanged over the Internet
• In a web browser, 17 messages may be exchanged

1. up to six messages to translate the server name
2. three messages to set up a TCP connection
3. four messages to send HTTP “get” request + response
4. four messages to tear down the TCP connection

• Moreover, millions of messages are exchanged each day by Internet nodes to make their presence and services known 

Applications – the Driving Force:

1. Streaming audio and video is an emerging application

• The source generates and sends the video stream in messages across the Internet

      2. Video-on-demand: reads a preexisting movie

• One-way data transfer

     3.Videoconferencing: interactive session

• Very tight timing constraints

    4.Diversity of applications that can be built on top of the Internet hint at the complexity of the

      Internet design

Some Protocol Acronyms in computer networking

• (T)FTP – (Trivial) File Transfer Protocol
• HTTP – HyperText Transport Protocol
• NV – Network Video
• SMTP – Simple Mail Transfer Protocol
• NTP – Network Time Protocol
• TCP – Transmission Control Protocol
• UDP – User Datagram Protocol
• IP – Internet Protocol
• FDDI – Fiber Distributed Data Interface
• ATM – Asynchronous Transfer Mode

What are models of network computing or Network models?

Discuss TCP/IP Architecture ?

TCP/IP Architecture:

• Developed with ARPANET and NSFNET
• Internet Engineering Task Force (IETF)

1. Culture: implement, then standardize
2. OSI culture: standardize, then implement

• Became popular with the release of Berkeley Software Distribution (BSD) Unix; i.e. free software
• Standard suggestions traditionally debated publically through “Request For Comments” (RFC’s)
• Implementation and design have done together
• Hourglass Design (the bottleneck is IP)
• Application vs Application Protocol (FTP, HTTP)

What is OSI Architecture?

OSI Architecture

Open System Interconnect (OSI) Architecture

• International Standards Organization (ISO)
• International Telecommunications Union (ITU), formerly CCITT
• “X dot” series: X.25, X.400, X.500
• Primarily a reference model