Lecture 1 internet architecture
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Lecture 1: Internet Architecture Architecture of the Internet Network Internetwork Router Protocol Accessing the Internet Residential access Dedicated access Institutional access Communicating over the Internet Protocol layering (covers only BASIC idea) Internet Addressing

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Lecture 1 internet architecture l.jpg
Lecture 1: Internet Architecture

  • Architecture of the Internet

    • Network

    • Internetwork

    • Router

    • Protocol

  • Accessing the Internet

    • Residential access

    • Dedicated access

    • Institutional access

  • Communicating over the Internet

    • Protocol layering (covers only BASIC idea)

    • Internet Addressing

1: Introduction

1 what s the internet l.jpg
1. What’s the Internet

  • The Internet is a collection of networks connected by interconnectingdevices.

  • The connecting devices

    • are specialized computing devices, e.g. routers

    • forward data from one network to another.

1: Introduction

1 1 computer network l.jpg

Client-Server Model




(Local Processing)





1.1 Computer network

  • An interconnected collection of computers

1: Introduction

1 1 classifications of networks l.jpg
1.1 Classifications of Networks

  • Based on size:

    • System/Storage area networks (SAN)

      • within the same room

    • Local area networks (LAN)

      • in a close proximity

    • Metropolitan area networks (MAN)

      • span a city

    • Wide area networks (WAN)

      • connecting computers situated anywhere

      • Connects many networks together

1: Introduction

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1.2 internetwork

  • A collection of networks

1: Introduction

1 2 internetwork another example l.jpg
1.2 Internetwork: Another example

Figure 15.3(text book) An example of internet with six networks

and three computers attached.

1: Introduction

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1.2 The Internet Topology

See http://www.cybergeography.org/atlas/topology.html for more Internet topologies.

1: Introduction

1 2 the illusion of a giant network l.jpg
1.2 The Illusion Of A Giant Network

  • Any computer can send data to any other computer providing they have IP software installed.

  • The Internet operates like a virtual network.

Fig. 15.1 (text book)

1: Introduction

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1.2 The Reality Of Internal Structure

  • The Internet contains a complex physical structure users never see

    • Interconnecting networks with routers

Fig. 15.2 (text book)

1: Introduction

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communication infrastructure: enables distributed applications:

WWW, email, games, e-commerce, database.,


1.2 Internet: a service view

1: Introduction

1 2 internet nuts bolts view l.jpg

millions of connected computing devices: hosts, end-systems

pc’s workstations, servers


communication links

fiber, copper, radio, satellite

routers: forward packets (chunks of data) across networks





local ISP

regional ISP



1.2 Internet: “nuts & bolts” view

1: Introduction

1 2 internet nuts bolts view12 l.jpg

protocols: control sending, receiving of msgs

e.g., TCP, IP, HTTP, FTP

Internet: “network of networks”

public Internet versus private intranet

collection(s) of SAN, LAN, MAN, WAN

1.2 Internet: “nuts & bolts” view





local ISP

regional ISP



1: Introduction

1 2 connecting a computer to a remote network l.jpg

Cables connecting a computer to a LAN are usually short, but may be extended.

Modems used to send data across wire, telephone system & optical fibres

Fiber optic cable can provide connections across long distances.

Requiring optical modems

Using light instead of electricity to carry data

1.2 Connecting a Computer to a Remote Network

Fig 13.1 (text book)

1: Introduction

1 3 incompatible network technologies l.jpg
1.3 Incompatible Network Technologies may be extended.

  • Not all networks are compatible.

  • Networks:

    • Vary in speed

    • Vary in electrical voltages

    • Differ in addressing scheme

  • Each technology designed to meet speed, dist, cost constraints.

  • It is impractical to make computers in an enterprise use the same network technology.

  • Allow groups to select a network technology based on need

1: Introduction

1 3 routers l.jpg

Special-purpose computers are used to interconnect networks may be extended.

Using standard hardware (CPU, memory, and network interfaces)

Running special-purpose software

Forwarding packets from one network to another

Determining where to send packets

Transforms packets as necessary to meet standards for each network

Fig. 13.2 (text book)

1.3 Routers

1: Introduction

1 3 routers16 l.jpg
1.3 Routers may be extended.

  • Interconnecting LAN to LAN

  • Interconnecting LAN to WAN

Fig 13.3 (text book)

1: Introduction

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1.4 Network Protocol may be extended.

  • A common language computers use to exchange messages.

    • Specifying exact format and meaning of each message

    • specify actions taken during sending and receiving of data

1: Introduction

1 4 network protocol18 l.jpg

a human protocol and a computer network protocol: may be extended.

TCP connection


Get http://gaia.cs.umass.edu/index.htm

Got the





1.4 Network Protocol


TCP connection



1: Introduction

1 4 network protocol19 l.jpg

human protocols: may be extended.

“what’s the time?”

“I have a question”


… specific messages sent

… specific actions taken when messages received, or other events

network protocols:

machines rather than humans

all communication activity in Internet governed by network protocols

1.4 Network Protocol

protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt

1: Introduction

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1.4 Internet Protocol (IP) may be extended.

  • IP defines computer communication details.

    • Specifying how packets are formed

    • Specifying how routers forward each packet

  • Computers connecting to the Internet must follow the IP rules.

1: Introduction

1 4 ip software on every machine l.jpg
1.4 IP Software On Every Machine may be extended.

  • Computer hardware does not understand IP.

    • Connecting a computer to the Internet does not mean it can use the Internet

  • Computers need IP software before using the Internet.

1: Introduction

2 accessing the internet l.jpg

access network may be extended.

The Internet

access network

2. Accessing the Internet

  • User’s computers or hosts connect to the Internet through an access network.

    • Residential access:

      • dial-up access vs. dedicated access.

      • dial-up access advantages: least expensive.

      • dedicated access advantages: higher speed of delivery and remains connected at all times.

        • instantaneous access

        • continuous availability

    • Institutional access

      • dedicated access.

1: Introduction

2 1 access network residential access l.jpg
2.1. may be extended.Access Network: Residential access

  • Residential access is normally through an ISP (Internet Service Provider)

  • Most ISPs offer dial-up access through a telephone-based system.

    • Requires a modem and software that uses the modem.

    • Speed: up to 56Kbps.

Fig. 14.1

(text book)

1: Introduction

2 2 access network dedicated access l.jpg
2.2. may be extended.Access Network: dedicated access

  • Three newer technologies used by ISPs to offer inexpensive dedicated access:

    • Cable modems

      • use cable television wiring (most homes already have cable TV wiring).

      • Cable modems send data over coax cable but transmission does not interfere with TV signals

        • cable system is designed to carry many more signals than are currently available, cable modem use the unused bandwidth

      • advantages:

        • deliver data faster than a dial-up connection.

        • provide continuous connectivity.

        • use existing wiring system.

      • chief disadvantage:

        • customers share the wiring (share bandwidth) - data transmission may slow down if many customer send data at the same time; but even at the slowest speed it still operate faster than dial-up modem

1: Introduction

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2.2. may be extended.Access Network : dedicated access

  • DSL (Digital Subscriber Line) technology

    • use conventional telephone wiring

    • unlike dial-up modem (which encode data with sound), DSL does not use the telephone system. Instead DSL transfer data by using the underlying telephone wires to send electrical signals

    • does not affect normal telephone service

    • e.g. ADSL: asymmetric digital subscriber line.

      • 6.144 Mbps downstream (data flowing to user), 576Kbps upstream (data flowing from user).

    • advantages

      • use existing wiring

      • provide continuous connectivity.

      • does not share bandwidth with other subscribers (unlike cable modem)

1: Introduction

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2.2. may be extended.Access Network : dedicated access

  • Wireless access similar to cellular phones

    • use radio transmissions

    • a transmitter runs all the time to to provide continuous access

    • chief advantage is the ability to reach remote areas.

1: Introduction

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2.3. may be extended.Access Network: Institutional access

  • Institutional access is mainly through company/university local area network (LAN).

    • E.g. using Ethernet:

      • shared cable connects user computers

      • speeds: 10 Mbs, 100Mbps, Gigabit Ethernet


1: Introduction

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3. may be extended.Communicating over the Internet

  • To communicate over the Internet, the computers must:

    • use a common language or a protocol to govern the exchange of messages.

    • have a way to address one another.

  • Protocol:

    • specifies exact format, order of messages sent and received among network entities, and actions taken on message transmission and receipt.

  • Addressing:

    • defines where to deliver the messages.

1: Introduction

3 1 protocol layering l.jpg
3.1 may be extended.Protocol Layering

  • Internet has a large collections of protocols organized in a layering model.

    • Application: enables the user, whether human or software, to access the network.

    • Transport: responsible for reliable source-to-destination (end-to-end) delivery of the entire message.

    • Network: responsible for routing a packet (also called datagram) from source-to-dest (possibly) across multiple (different) networks.

    • Data link (also called network interface): specify how to organize data into frames and how to deliver a frame over a network.

    • Physical: coordinates the functions required to transmit a bit stream over a physical medium.

1: Introduction

3 1 protocol layering30 l.jpg
3.1 may be extended.Protocol Layering

1: Introduction

3 1 protocol layering31 l.jpg
3.1 may be extended.Protocol Layering

1: Introduction

3 1 protocol layering32 l.jpg
3.1 may be extended.Protocol Layering

  • TCP/IP Protocol Suite.

1: Introduction

3 1 protocol layering33 l.jpg
3.1 may be extended.Protocol Layering

  • Two key protocols are:

    • IP (Internet Protocol)

      • Oversee end-to-end delivery of individual packets

      • Does not recognize relationships among packets

      • Treats each packet independently, as if they belong to different message

    • TCP (Transport Control Protocol)

      • Ensure whole message arrive intact and in order

      • (eg, check if packets are missing or arrive out of order)

1: Introduction

3 1 router overrun with datagrams l.jpg
3.1 Router Overrun with Datagrams may be extended.

  • Router becomes overrun with datagrams

    • Eg, routers 1 & 2 each receives 5000 datagrams

    • both routers send all datagrams they received (5000+5000) across network d to router 3

    • but router 3 can only handle 5000 datagrams

  • Analogy: traffic jam

    • Eg, cars from roads a and b attempt to merge into road d, causing traffic congestion

1: Introduction

3 1 transmission control protocol l.jpg
3.1 Transmission Control Protocol may be extended.

  • When a router is overrun with datagrams, some of them will be discarded.

    • As a result some datagrams will be lost

    • TCP checks for lost datagrams

  • When hardware in a router or network system fails, other routers start sending datagrams through new (alternative) paths.

    • As a result, some datagrams arrive in a different orderthan they were sent

    • TCP checks for out-of-order datagrams

  • Network hardware failure sometimes result in duplication of datagrams

    • TCP checks for duplication of datagrams

1: Introduction

3 1 recovering lost datagrams tcp retransmission l.jpg
3.1 Recovering Lost Datagrams: TCP Retransmission may be extended.

  • TCP includes an identification of each datagram.

  • Ignores duplicate copies

  • Receiver uses identification (sequence numbers) to put out-of-order datagram back in order

  • Recovers lost datagrams

    • Uses timers

    • Sends an acknowledgementback to the source - this guarantees that all data arrives

    • If timer expires before an acknowledgement arrives, TCP assumes the datagram is lost and retransmit the datagram

1: Introduction

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3.2 Internet Addresses may be extended.

  • Every Computer Is Assigned A Unique Address

    • Each computer attached to the Internet must be assigned a unique address.

  • IP Addresses Are Not Random

    • Computers on the same network have the same prefix (Netid).

1: Introduction

3 2 internet addressing l.jpg
3.2. may be extended.Internet Addressing

  • IP or Internet address is a 32-bit (4 byte) address that uniquely defines every computing devices on the Internet.

  • Decimal notation to make it easier to read.

1: Introduction

3 2 classes of ip addresses l.jpg

Designers chose a compromise - multiple address formats that allow both large and small prefixes

Each format is called an address class

Class of an address is identified by first four bits

3.2 Classes of IP addresses

1: Introduction

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3.2 Dotted decimal notation allow both large and small prefixes

  • Class A, B and C all break between prefix and suffix on byte boundary

  • Dotted decimal notation is a convention for representing 32-bit internet addresses in decimal

  • Convert each byte of address into decimal; display separated by periods (``dots'')

1: Introduction

3 2 ip address classes at a glance l.jpg
3.2 IP Address classes at a glance allow both large and small prefixes

  • Class A, B and C are primary classes

  • Used for ordinary host addressing

  • Class D is used for multicast, a limited form of broadcast

  • Class E is reserved

1: Introduction

3 2 internet addressing an example l.jpg
3.2. allow both large and small prefixes Internet Addressing: An Example

1: Introduction

Further reading l.jpg
Further Reading allow both large and small prefixes

  • Chapters 13, 14, 15, & 16 of the textbook.

  • Note: This lecture is designed with the objective of providing an introduction tothe architecture of the Internet and communicating over the internet.

  • Details of these topics are beyond the scope of this course and will NOT be taught or discussed. Students who wish to invest more time on studying more details for these topics are referred to:

    • Forouzan Chapter 2.

    • Doug Comer, Computer Networks & Internetswith Internet Applications, chapter 17, 18, 20 & 24

    • Details of protocol layering will be covered in IEG3310

1: Introduction