Best link for studying Computer Network

Introduction to Networking

* introduction: what is a network
* elements of network architecture
* layered network architecture
* examples
* history
* internetworking
* Reading: sections 1.1-1.5, 1.7-1.9



What is a Computer Network?

* a set of computer and/or switches connected by communication links
* many ``topologies'' possible:

* local area networks (LAN) versus wide-area networks (WAN)
* many different media: fiber optic, coaxial cable, twisted pair, radio, satellite
* for us: topology and media unimportant

What is a Computer Network?

a software/hardware infrastructure:

* original justification: allows shared access to computing resources (e.g., computers, files, data)
* a medium through which geographically dispersed users communicate (e.g., email, teleconferencing)
* a medium through distributed services/applications are implemented
* an electronic village
* an information highway, national information infrastructure
* cyberspace - "a consensual [environment] experienced daily by billions of operators, in every nation, ...." Hotlink: Wiliam Gibson on Cyberspace

Packet-Switching

* data entering network divided into chunks called "packets''
* packets traversing network share network resources (e.g., link bandwidth, buffers) with other packets
o on demand resource use: statistical resource sharing

* resources demands may exceed resources available:
o e.g., A and B packets arrive at R1, destined for C
o resource contention: queueing (waiting), delay

Circuit Switched Networks

* all resources (e.g. communication links) needed by call dedicated to that call for duration
* example: telephone network

* resource demands may exceed resources available
* A and B want to call C
* resource contention: blocking (busy signal)
* drawbacks: ??
* advantages: ?? Hotlink: Keith Ross on Circuit-switching versus packet-switching

Why statistically share resources?

* save/make money!
* example: 1 Mbit/sec link; each user requires 100 Kbits/sec when transmitting; each user has data to send only 10% of time.
o circuit-switching: give each caller 100 Kbits/sec capacity. Can support 10 callers.
o packet-switching: with 35 ongoing calls, probability that 10 or more callers simultaneously active < 0.0004!
+ Can support many more callers, with small probability of` "contention.''
* if users are ``bursty'' (on/off), then packet-switching is advantageous (Baran, 1965)

Elements of a Network

* communication links:
o point-to-point (e.g., A-to-B)
o broadcast (e.g.,: Ethernet LAN)

* host: computer running applications which use network (e.g.: H1)
* router: computer (often w/o applications-level programs) routing packets from input line to output line. (e.g., C)
* gateway: a router directly connected to two+ networks (e.g. A)
* network: set of nodes (hosts/routers/gateways) within single administrative domain
* internet: collection of interconnected networks

Protocols

* protocol: rules by which active network elements (applications, hosts, routers) communicate with each other
* protocols define :
o format/order of messages exchanged
o actions taken on receipt of message
* rules by which two or more people communicate to provide a service, or to get something done
* protocols in every day life:


Layered Architecture

* complex system architecture simplified by layering.
* layer N relies on services of layer N-1 to provide a service to layer N+1

* service from lower layer independent of how that service implemented
o information/complexity hiding
o layer N change doesn't affect other layers
* interfaces define how services requested

Layered network architecture

* the network consists of geographically distributed hardware/software components
* a distributed layered view:


Layering and protocols

* peer entities (e.g., processes) in layer N provide service by communicating (sending "packets") with each other, using communication service provided by layer N-1.
* logical versus physical communication:



The Internet and ISO/OSI reference models

Hot Link: an IETF view of standards
Layers of a protocol architecture

* application layer


* process-to-process communication
* examples: WWW, email, teleconferencing, info. retrieval

* socket layer (Internet only)
o buffering and delivery of data at end systems
* presentation layer (OSI only)
o conversion of data to a common format (e.g., little endian versus big-endian byte orders, integer and floating point numbers).
o Internet stack: data conversion a user-level concern

Layers of a protocol architecture (cont)

* session layer (OSI only)
o session set up (e.g., authentication), recovery from failure (broken session)
o a "thin" layer
* transport layer
o transport service: end-to-end delivery of data
o may multiplex several streams from higher layers
o sender/receiver speed matching
o Internet: TCP and UDP


Layers of a protocol architecture (cont)

* network layer
o at end hosts: start packets on their way
o at routers: control packet routing
o bottleneck avoidance, congestion control
o Internet: IP packets, BGP, RIP



Layers of a protocol architecture (cont)

* data link layer
o point-to-point error free communication over a single link
o multiaccess LAN protocols
o speed matching between sender/receiver
o Ethernet, HDLC, PPP

* physical layer: stuff of EE's
o transmitting raw bits (0/1) over wire

Eid : Id-Ul-Fitr or Eid-Ul-Fitr

Id-Ul-Fitr or Eid-Ul-Fitr, commonly known as Eid is the most
important festival of Islamic calendar. Id Ul Fitr means 'festival
of breaking the fast' and is celebrated on the first day after sighting
the moon of 'Shawaal' (tenth month of Islamic calendar) that marks
the end of the month of Ramzan(the month of fasting). During the
auspicious month of Ramzan, Muslims observes day long fast and offer
special prayers to almighty. Eid festival marks the end of Ramzan
and people all over celebrates this pious festival with
utmost devotion.

Mahatma Gandhiji

Mohandas Karamchand Gandhi affectionately called Bapu (2 October 1869 – 30
January 1948) was a major political and spiritual leader of India and the
Indian independence movement. He was the pioneer of Satyagraha, firmly
founded upon ahimsa or total non-violence, which led India to
independence.He is officially honoured in India as the "Father of the
Nation"; and his birthday, 2nd October, is commemorated as Gandhi Jayanti,
a national holiday, and world-wide as the International Peace Day.

One of the significant figure of the India independence movement and the
third Prime Minister of independent India, Shri Lal Bahadur Shastri was
born on 2 Oct 1904 at Mughalsarai, Uttar Pradesh. All his lifetime,
Shastri was known for honesty and humility. He was the first person to be
posthumously awarded the Bharat Ratna. He was immoralised by famous quotes
such as "Jai Jawan, Jai Kisan" ("Hail the soldier, Hail the farmer") and
"If one person
gives up one meal in a day, some other person gets his only meal of the day".