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• Lecture 01, 02 • Introduction and Basic Concepts

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Lecture 01 - Objectives

• Introduction• Course Objectives, Outline and Grading Policies• What is the Internet?

– Nuts and Bolts View– Service Oriented View

• Network Edge• Network Core

– Circuit Switched Networks– Packet Switched Networks

• Datagram • Virtual Circuits

• Network Access and Physical Media

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Course Objectives

 To understand the design philosophy of the Internet and its basic architectural components.

 To provide in-depth knowledge of major Internet technologies.

 To understand the components of Internet service provider and its role in Internet architecture.

 To strengthen the concepts of TCP/IP Protocol Suite.

 To provide comprehensive knowledge and implementation of routing protocols.

 To realize the need of Quality of Service based communication and to understand various QoS techniques.

 To introduce the basic concepts of real time communications.

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What is the Internet?• A Nuts and Bolts Description

– End systems– Communication Links, Bandwidth– Routers, Packet– ISPs– Protocols, TCP/IP– Internet Standards, RFCs

• A service Description– Distributed Applications– Connection Oriented Reliable Service– Connectionless Unreliable Service

• What is a protocol?

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Describing the Internet• Two ways to describe the Internet

– Nuts and Bolts View• The basic hardware and software

components– Service Oriented View

• The networking infrastructure that provides services to distributed applications

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Nuts and Bolts View of the Internet

• Hosts or End Systems– Computing Devices such as PCs, PDAs

(Personal Digital Assistants), TVs, servers, mobile computers, automobiles, etc. connected to the Internet are called hosts or end systems.

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Nuts and Bolts View of the Internet

• Communication links– End systems are connected together by communication

links.– Communication links are made up of different types of

media, including twisted pair, coaxial cable, fiber optics, and radio spectrum.

• Bandwidth – Different links can transmit data at different rates. – The link transmission rate is often called the bandwidth

(i.e, the width of the band) of the link which is measured in bits per second (bps).

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Nuts and Bolts View of the Internet• Routers

– End systems are not directly connected to each other via a single communication link.

– They are indirectly connected to each through intermediate switching devices known as routers.

– A router receives chunk of information from one of its incoming communication link and forwards it to one of its outgoing communication link.

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Nuts and Bolts View of the Internet

• Packets– The chunk of information is called packet.

• Route or Path– The path that the packet takes from the sending end

system, through a series of communication links and routers, to the receiving end system is known as a route or path.

• Packet switching– The Internet uses a technique known as packet

switching that allows multiple communicating end systems to share a path, or parts of path at the same time.

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Nuts and Bolts View of the Internet

• Internet Service Providers (ISPs)– End systems access the Internet through the

Internet Service Providers (ISPs). – The different ISPs provide a variety of different

types of network access to the end systems, including 56Kbps dial up modem access, cable modem or DSL, high speed LAN access, and wireless access.

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Nuts and Bolts View of the Internet

• Protocols – End systems, routers, and other pieces of the

Internet, run protocols that control the sending and receiving of information within the Internet.

– TCP (Transmission Control Protocol) and IP (Internet protocol) are two of the most important protocols in the Internet.

– The Internet’s principal protocols are collectively known as TCP/IP Protocol Suite.

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Nuts and Bolts View of the Internet

• Intranets– There are many private networks, such as

many corporate and government networks, whose hosts cannot exchange messages with hosts outside of the private network (unless the messages pass through so-called firewalls, which restrict the flow of messages to and from the network).

– These private networks are often referred to as intranets, as they use the same types of hosts, routers, links, and protocols as the public Internet.

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Nuts and Bolts View of the Internet

• Internet Standards– At the technical and development level, the Internet is

made possible through creation, testing, and implementation of Internet Standards.

– These standards are developed by Internet Engineering Task Force (IETF).

• RFCs– The IETF standards documents are called RFCs (Request

for comments). – RFCs started out as general request for comments

(hence the name) to resolve architecture problems of the Internet.

– They define protocols such as TCP, IP, HTTP, SMTP.

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Some Pieces of the Internet

companynetwork

local ISP

regional ISP

router workstationserver

mobile

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Service Oriented View of the Internet

• Distributed Applications– The Internet allows distributed applications

running on its end systems to exchange data with each other.

– These applications include remote login, electronic mail, web surfing, instant messaging, audio and video streaming, Internet telephony, distributed games, peer-to-peer (P2P) file sharing, and much more.

• Communication Services– Connection oriented reliable service– Connectionless unreliable service

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Service Oriented View of the Internet

• Internet Provides two services to its distributed applications:– Connection Oriented Reliable Service

• It guarantees that data transmitted from a sender to a receiver will eventually be delivered to the receiver in order and in its entirety.

– Connectionless Unreliable Service

• It does not make any guarantees about eventual delivery.

– Note: Distributed applications makes use of one or the other (but not both) of these two services.

• Thus, Internet is an infrastructure in which new applications are being constantly invented and deployed.

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Connection Oriented Service

– Reliable Data Transfer• Using acknowledgements & retransmissions

– Flow Control• sender won’t overwhelm receiver

– Congestion Control• senders “slow down sending rate” when

network congested– TCP

• Applications using TCP are:– HTTP (Web), FTP (file transfer), Telnet (remote

login), SMTP (email)

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Connectionless Service

– Unreliable Data Transfer• no flow control• no congestion control

– Fast• connectionless

– UDP• Applications using UDP are:

– multimedia, videoconferencing, DNS, Internet telephony

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TCP vs. UDP

• Reliable Protocol• Connection Oriented• Performs three ways

handshake• Provision for error

detection and retransmission

• Most applications use TCP for reliable and guaranteed transmission

• Unreliable Protocol• Connectionless • Much faster than TCP• No acknowledgement

waits• No proper sequencing

of data units• Suitable for

applications where speed matters more than reliability

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What is a Protocol?• A Human Analogy

– “Assalam u Alaikum”– “What’s the time?”

• In human protocols specific messages are sent, and specific actions are taken in response to messages received, or other events.

• Network protocols– All activity in the Internet that involves two or

more communicating remote entities is governed by a protocol.

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What is a protocol?

A human protocol and a computer network protocol

Hi

Hi

Got thetime?

2:00

TCP connection req

TCP connectionresponse

<file>

time

Get http://www.awl.com/kurose-ross

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What is a Protocol?…• A Protocol is a set of rules and regulations that

governs the exchange of information between two or more entities.

• It takes two (or more) communicating entities running the same protocol in order to accomplish a task.

• All communication activity in Internet governed by protocols.

• A protocol defines the format, order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.

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Net Surfing• Some Good Hyperlinks:

– http://www.ietf.org– http://www.iab.org– http://www.w3.org– http://www.ieee.org– http://www.acm.org– http://www.acm.org/sigcomm– http://www.computer.org– http://www.comsoc.org

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The Network Core• Mesh of interconnected

Routers• The fundamental question:

how is data transferred through network?

– circuit switching• dedicated circuit per

call: telephone net– packet-switching

• data sent through net in discrete “chunks”

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Network Core• Long distance transmission is typically

done over a network of switched nodes• Nodes not concerned with content of data• End devices are stations

– Computer, terminal, phone, etc.

• A collection of nodes and connections is a communications network

• Data routed by being switched from node to node

• Node to node links usually multiplexed

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Simple Switched Network

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Network Core: Circuit Switching

End-to-end resources reserved for “call”

• link bandwidth, switch capacity

• dedicated resources: no sharing

• circuit-like (guaranteed) performance

• call setup required

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Network Core – Circuit Switching

• Switched circuits allow data connections that can be initiated when needed and terminated when communication is complete

• Circuit switched network - a network in which a dedicated circuit is established between sender and receiver and all data passes over this circuit.

• The telephone system is a common example.

• The connection is dedicated until one party or another terminates the connection.

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Circuit Switching

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Network Core – Circuit Switching

• Dedicated communication path between two stations

• Three phases (Establish, Transfer, Disconnect)

• Inefficient (for data traffic)– Channel capacity dedicated for duration of

connection– Much of the time a data connection is idle– If no data, capacity wasted

• Set up (connection) takes time– Once connected, transfer is transparent– Circuit switching designed for voice– Constant Data rate (Both ends must operate at the same

rate)

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Network Core - Circuit Switching

• Multiplexing in Circuit Switched Networks– Multiplexing is a technique, in which a single

transmission medium is being shared among multiple users.

• Types of Multiplexing– Frequency Division Multiplexing FDM– Time Division Multiplexing TDM

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Circuit Switching: FDM and TDM

FDM

Frequency

timeTDM

Frequency

time

4 usersExample:

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Synchronous TDM

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Synchronous TDM with empty time slots

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Statistical TDM or Asynchronous TDM

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Network Core: Packet Switching

• Packet switched network– A network in which data is transmitted in the

form of packets – Multiple users share network resources – No dedicated bandwidth is allocated– No resources are reserved, resources used as

needed – Each packet uses full link bandwidth – Good for bursty traffic, simpler, no call setup– Packets queued and transmitted as fast as

possible– Packets are accepted even when network is

busy, which causes the delivery to slow down

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Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern statistical multiplexing.

A

B

C10 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for output

link

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Network Core: Packet Switching

• The goal of packet switching is to move packets through routers from source to destination

• Packets sent one at a time to the network

• Two approaches are used:– Datagram Approach– Virtual Circuits Approach

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Packets Forwarding• Two broad classes of packet switched networks are:

– Datagram Networks• Any network that forwards the packet

according to the destination address is called a datagram network

• The routers in the Internet forwards packets according to host destination addresses; hence the Internet is a datagram network.

– Virtual Circuit Networks• Any network that forwards the packet

according to the virtual circuit identifier is called a virtual circuit network

• Examples are X.25, Frame Relay, ATM technologies

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Packet Switching - Datagram

• Datagram Approach: – Each packet is treated independently– No reference to packets that have gone before– Each node chooses next node on path using

destination address– Packets with same destination address may not

follow same route– Packets may arrive out of sequence, may be lost– It is up to receiver to re-order packets and

recover from lost packets– No Call setup – For an exchange of a few packets, datagram

quicker – Analogy: driving, asking directions

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Packet Switching - Datagram

• The Internet is a Datagram network• Datagram network is not either

connection-oriented or connectionless.• Internet provides both connection-

oriented (TCP) and connectionless services (UDP) to applications.

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Datagram Networks• A datagram network is not either a

connectionless or a connection oriented network.

• It can provide connectionless service to some of its applications and connection-oriented service to other applications.

• Example– The Internet, which is a datagram network,

provides both connectionless (UDP) and connection oriented (TCP) services to its applications

• Networks with Virtual Circuits are, however, always connection-oriented.

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Packet Switching - Datagram

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Packet Switching – Virtual Circuits

• Virtual Circuit Approach:– Virtual circuit packet switched network create

a logical path through the subnet– Call request and call accept packets establish

a virtual connection– Virtual route remains fixed through the call.– All packets from one connection follow this

path.– Each packet contains a virtual circuit identifier

instead of destination address to determines the next hop

– Not a dedicated path– No routing decisions required for each packet

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Switching Technique – Virtual Circuit

• Preplanned route established before packets sent• All packets follow same route • Similar to circuit in circuit-switching network

– Hence virtual circuit

• Each packet has virtual circuit identifier– Nodes on route know where to direct packets– No routing decisions

• Not dedicated path, as in circuit switching– Packet still buffered at node and queued for output – Routing decision made on before that virtual circuit

• Network may provide services related to virtual circuit– Sequencing and error control

• Packets should transit more rapidly• If node fails, all virtual circuits through node lost

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Virtual Circuits vs. Datagram

• Network can provide sequencing and error control

• Packets are forwarded more quickly– No routing decisions to

make

• Less reliable– Loss of a node looses all

circuits through that node

• Less Processing Delay at a node

• No call setup phase– Better if few packets

• More flexible– Routing can be used to

avoid congested parts of the network

• More reliable– If a node fails, packets

may find an alternate route that bypass that node

• More Processing Delay at a node

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Circuit Switching vs. Virtual Circuits

• Path– A dedicated path is

established between two devices for the duration of session.

• Reserved Resources– The link (multiplexed /

not multiplexed) that makes the path are dedicated, and cannot be used by other connections

• constant data rates.

• Route– No dedicated path is

established. Only a route is defined. Each switch creates an entry in its routing table for the duration of virtual circuit

• Shared Links– The link that makes a

route can be shard by other connections

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Features of Circuit and Packet Switching

Feature Circuit Switching

Packet Switching

Data sent as packets? No Yes

Packets follow same route? N/A Yes (VC), No (Datagram)

Resources reserved in network? Yes No

Data send can have variable latency (response time)

No Yes

Connection made? Yes VC: Yes, Datagram: No

State info stored at network nodes? N/A VC: Yes, Datagram: No

Addressing info needed? only when call is set up

VC: virtual circuit number  Datagram: destination Address

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Network Taxonomy

Telecommunicationnetworks

Circuit-switchednetworks

FDM TDM

Packet-switchednetworks

Networkswith VCs

DatagramNetworks

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Network Access• Network Access:

– The physical link that connects an end system to its Edge Router, which is the first router on a path from the end system to any other distant end system.

• Classification of Network Access:– Residential Access

• Connecting a home end system to an edge router• Dial-up modems, DSL, HFC system

– Company Access• Switched Ethernet LANs

– Mobile Access• Wireless LAN (802.11b)• Wide Area Wireless Access Networks (GPRS, 3G,

WAP)• Note: these categories are not hard and fast

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Physical Media• Twisted Pair Cable

– UTP Cat 5

• Coaxial Cable– Baseband and Broadband Cable

• Fiber Optics– Multimode and single mode

• Terrestrial Radio Channels– Local Area Radio Channels (Wireless LANs)– Wide Area Radio Channels (WAP, I-mode, 3G)

• Satellite Radio Channels– Geostationary Satellites (36000 km)– Low Altitude Satellites

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Food for thought!• Internet vs. internet• Difference between:

– internet, intranet and extranet

• Data sensitive traffic vs. Delay sensitive traffic

• LAN vs. WAN– Beyond theoretical definitions

• Why Circuit Switching is not appropriate for data traffic?

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References• Computer Networking; A Top Down Approach

Featuring the Internet– 3rd Edition: Chapter 1, Jim Kurose and Keith Ross

• Data and Computer Communications– 7th Edition, William Stallings

• Data Communications and Networking– 3rd Edition, Behrouz A. Forouzan

• Data Communications and Computer Networks– Curt M. White

• Computer Networks– 4th Edition, by Andrew S. Tanenbaum

• Note: Slides are adapted from the companion web sites of referenced books.