Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 1

Networks and Protocols

- What is really going on when we send emails and surf the web?

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 2

The Book:

Computer Networking

A Top-Down Approach Featuring the Internet,

by James F. Kurose og Keith W. Ross, Addison-Wesley Longman, Inc., se http://www.awl.com/kurose-ross/

Kan købes på IT-Højskolen d. 6. – 7. Feb 2002 i lokale 1.05 fra 11.00 til 15.00. Pris: Kr. 645,-

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 3

Excercises and Instructors

Rooms: 3.15 and 3.16, Glentevej 67.

Monday Afternoon (13:00 – 15:30):

Anders Ejlev, (anders@ejlev.dk)

Monday Evening (19:00 – 21:30):

Sune Kloppenborg Jeppesen, (jaervosz@it-c.dk)

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 4

Examination – June 2002

20 min individual oral examn without preparation, judged using the, Dansih 13-scale, external censor. It is allowed to bring a disposition (one sheet of A4 paper for each question) The book will be available at the exam.

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 5

Outline feb 4. 20021. What is the internet?2. What is a Protocol?3. Connection-Oriented service.4. Connectionless service.5. Multiplexing.6. Message switching (demo).7. Packet switching (demo).8. Routing.9. Access Networks.10. Delay and Packet loss i a network.11. Protocol Layering.12. Course overview.

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Some Internet Applications

•Email

•Streaming multimedia

•www

•File transfer

•Internet telephony

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Some pieces of the Internet

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 8

A service description

The Internet:

• Allows distributed applications running on it’s end systems to exchange data with each other.

• Provides a connection-oriented and a connectionless service.

• Makes no promises about time of delivery.

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 9

What is a protocol?

A human protocol and a computer network protocol.

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Definition (protocol):

A protocol defines the format and the 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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End systems, Clients and Servers

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Connection-Oriented Service

1. Initial handshake.

2. Reliable data transfer, using acknowledgements.

3. Flow Control.

4. Congestion Control.

Note: The Transmission Control Protocol (TCP) implements a connection-oriented service.

Used by: Email, www, FTP, Telnet.

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Connectionless Service

1. No Initial handshake.

2. Unreliable data transfer.

3. No Flow Control.

4. No Congestion Control.

Used by: audio on demand, intertenet telephony, …

Note: The User Datagram Protocol (UDP) implements a connectionless service.

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The Network Core

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How to share a communication link?

1. In Curcuit switching (e.g. ordinary telephone) a curcuit is reserved for the duration of the session.

2. In Packet switching (e.g. internet) the ressource is used on demand.

Note: Sharing is called Multiplexing.

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Multiplexing (FDM)

Frequency-division multiplexing (FDM):

Each Connection gets 4 KHz of the total frequency spectrum.

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Multiplexing (TDM)

Time-division Multiplexing: Each connection get one slot in each Frame.

Frame

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Multiplexing for Packetswitching.

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Message Switching

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 20

Packet switching

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 21

Example: Message Switching

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 22

Example: Packet Switching

Feb. 4., 2002. Kåre J. Kristoffersen Networks and Protocols - Introduction 23

Demo: Packet Switching

Run the JAVA Applet on:

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

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Break

• Table Tennis

• Table soccer

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Routing: Virtual Curcuit Networks

Incoming Interface Incoming VC# Outgoing Interface Outgoing VC#

1 12 3 22

2 63 1 18

3 7 2 17

1 97 3 87

… … … …

VC number translation table for PS1:

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Routing: Datagram Networks

Tom Jones (name)

Walnut Street 421 (street)

Philadelphia (city)

Pennsylvania (state)

USA (country)

Using: Hierarchical adresse, e.g:

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Access Networks and Physical Media

•Residental access networks

•Institutional access networks

•Mobile access networks

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Residental Access Networks

• Modem (telephone line, e.g. 56 kbps)

• ISDN, 128 kbps

• ADSL, up to 8Mbps using frequency Multiplexing

- A high speed downstream channel 50 kHz – 1 MHz

- A medium-speed upstream channel 4 kHz – 50 kHz

- Ordinary telephone 0 – 4 kHz.

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HFC: Hybrid Fiber coaxial cable

Note: Cable modem needed!

Note: HFC is a shared broadcast medium.

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Company Access Networks

A Local Area Network (LAN) is used to connect end systems to an edge router.

Ethernet: A shared medium using twisted-pair copper wire or coaxial cable.

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Mobile Access

AP = Access Point.

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Delay and packet-loss

Delay through router A:

- nodal processing delay+

- Queuing delay +

- Transmission delay+

- Propagation delay

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Traffic intensityPacket size: L bits

Transmission Rate: R bits/second

Average packet arrival: a packets / second

Traffic intensity: La/R

Hopefully: Traffic intensity < 1

If Traffic Intensity > 1 then queue will overflow and packets are lost.

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Average Queuing Delay

(Traffic Intensity)

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Protocol Layering

PDU = Protocol Data Unit.

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Internet Protocol stack

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Moving data in a network

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Course overview• Introduction (today)

•Application Layer

• Transport Layer

• Network Layer

• Link Layer + Physical Layer

• Multimedia Networking

• Security – Encryption

•Network Management