Networks and Protocols

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Networks and Protocols
- What is really going on when we send emails and
surf the web?
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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,-
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Excercises and Instructors
Rooms 3.15 and 3.16, Glentevej 67. Monday
Afternoon (1300 1530) Anders Ejlev,
(anders_at_ejlev.dk) Monday Evening (1900
2130) Sune Kloppenborg Jeppesen,
(jaervosz_at_it-c.dk)
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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.
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Outline feb 4. 2002

• What is the internet?
• What is a Protocol?
• Connection-Oriented service.
• Connectionless service.
• Multiplexing.
• Message switching (demo).
• Packet switching (demo).
• Routing.
• Access Networks.
• Delay and Packet loss i a network.
• Protocol Layering.
• 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
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A service description

• The Internet
• Allows distributed applications running on its
  end systems to exchange data with each other.
• Provides a connection-oriented and a
  connectionless service.
• Makes no promises about time of delivery.

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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

• Initial handshake.
• Reliable data transfer, using acknowledgements.
• Flow Control.
• 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

• No Initial handshake.
• Unreliable data transfer.
• No Flow Control.
• No Congestion Control.

Note The User Datagram Protocol (UDP) implements
a connectionless service.
Used by audio on demand, intertenet telephony,
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The Network Core
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How to share a communication link?

• In Curcuit switching (e.g. ordinary telephone) a
  curcuit is reserved for the duration of the
  session.
• 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)
Frame
Time-division Multiplexing Each connection get
one slot in each Frame.
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Multiplexing for Packetswitching.
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Message Switching
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Packet switching
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Example Message Switching
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Example Packet Switching
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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
VC number translation table for PS1
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Routing Datagram Networks
Using Hierarchical adresse, e.g
Tom Jones (name) Walnut Street 421
(street) Philadelphia (city) Pennsylvania
(state) USA (country)
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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 intensity
Packet size L bits Transmission Rate R
bits/second Average packet arrival a packets /
second Traffic intensity La/R Hopefully
Traffic intensity lt 1 If Traffic Intensity gt 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