Transcript electures.informatik.uni

Communication
Systems
Chair of Communication Systems
Department of Applied Sciences
University of Freiburg
2006
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Communication Systems
Course Information – General
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Summer course: 04/25/2006 – 07/28/2006
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Instructors: Prof. Dr. G. Schneider, Rui Zhou & Dirk von Suchodoletz
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Hiwis: Christoph Hanke, Ahmad Abdul Majeed
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Office: Rechenzentrum, Hermann-Herder-Str. 10, 1st floor & building 079
/ 00017
Time & Place of lecture: Tuesday, Thursday 4:00 – 6:00 pm
in lecture room 00-034 in building 051
Place for practical exercises: basement of comp. Dept.
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Communication Systems
Course Information - Lecturers
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Office hours: Prof. Schneider - after the lecture,
Dirk von Suchodoletz – Tuesday 6:30 – 8:00 pm
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subject to change – see homepage
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after the Tuesday lecture ...
Rui Zhou – Tuesday 6:30 – 8:00pm (Office: RZ 104)
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E-mail: [email protected],
[email protected], [email protected]
Homepage of this course: http://www.ks.unifreiburg.de/php_veranstaltungsdetail.php?id=11
Lecture plan given on the homepage
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dates for practical courses
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additional information and papers
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date(s) for the written exam
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Communication Systems
Course Information – Course Layout
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Lecture earns 6 credit points
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Area of specialization: “communication and data bases (6)”
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Typical 3 + 1 course
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Three quarters are lectures (here in this room)
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One quarter is a practical course, variable dates – see lecture plan!!
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Practical course takes place in seminar room at the computing
department (basement, SR -101 or -113, you will need an valid
account (RZ ID) for the computing department facilities)
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Theoretical exercises sheets are handed out every Thursday (if
public holiday, the lecture, practical before or after)
For an introduction into the PC pool of the computing department and
introduction into the use of Linux and Vmware please ask the Hiwis
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Communication Systems
Course Information - Examinations
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Written exam at the end of lecture
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two hour written exam
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possible dates:
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Thursday, 27th of July, 6 – 8 pm
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Friday, 28th of July, 10 – 12 am
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Friday, 28th of July, 1 – 3 pm
We pass around a participants list
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please put name, email and matrikel to it
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try to write at least the email address in readable writing
Thursday the 27th April we ask for the preferred date based on that list
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simple decision of the vote of majority
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Communication Systems
Practical Course and Exercises
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Practical course is part of the lecture, theoretical exercise sheets are
supplementary (may earn bonus points)
Conducted by the assistant and the hiwis
Excercise sheets will be handed out at the end of every Tuesday lecture
on a weekly base. Exception: we have two practical courses in one week
(depends on the schedule of Prof. Schneider)
The LSfKS bonus system
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50% mandatory - otherwise no "Übungsschein"
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60% +0.1, 70% +0.2, 80% +0.3 (=one third off the grade)
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90% +0.5, 100% +0.6 (=two thirds off the grade)
Bonus will improve the grade of written exam
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Communication Systems
Syllabus and Scope of course
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Communication systems lecture is on the broad topic of communication
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data and voice communication in circuit switched and packet
orientated networks
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that means telephony networks and the Internet
Introduction to terminology, concepts and approaches of different
communication systems
Presentation of a wide variety of protocols and concepts (with detailed
introduction to some of them)
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broad overview on different kind of networks
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partly in depth discussion of some concepts
Different kind of networks for different purposes
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Communication Systems
Syllabus and Scope of course
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Communication models among networked devices
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Focuses on network layer and application layer
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for underlying hardware, LAN, W-LAN, WAN technologies and
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Internet programming (sockets, services, ...) you will find other
lectures and seminars
Detailed information at the homepage (lecture plan)!!
Please note (for your personal advance in this topic or for the written
exam – put it as you like :-))
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not all topics are handled in the lecture!
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practical exercises will introduce new topics too and deepen the
insight into topics presented in lecture
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the theoretical exercises could not be answered completely out of
the lecture, but you have to consult other sources too
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Communication Systems
Syllabus and Scope of course
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This lecture is an updated version of the former Internet Working course
held the last three summer semesters
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shift of focus towards voice communication
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so about 33% of the lectures content is exchanged (mostly for digital
telephony systems)
Sources of information
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lecture slides and exercise sheets of past lectures
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literature hints (given on the lectures homepage) and via email (we
will setup a mailing list for this course)
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sources of similar lectures found at other universities
Lecture will recorded an available then from the computer science dept.
e-lectures server
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Communication Systems
Course Outline
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May be modified throughout the course, number of lectures in brackets
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Networks and IP - base protocol of the Internet [1]
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Dynamic routing [2]
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DNS/ENUM the phone book of the Internet [1]
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The future of IP - IPv6 [1]
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Quality of service (QoS) in packet oriented networks [1]
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Communication Systems
Course Outline
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Protocols and technologies of telephone networks [1]
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ISDN (integrated services digital network) [1]
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GSM (global standard for mobile communication) [1]
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GPRS and UMTS [2]
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Other wireless technologies [1]
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WLAN, Wimax, Bluetooth and AAA (802.1x) [1]
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Telephony services on IP, SIP, H323 [3]
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Communication Systems
Literature on IP part
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Books
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Kurose & Ross, Computer Networking (best at the moment)
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Douglas E. Comer, Computer Networks and Internets
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Andrew S. Tanenbaum, Computer Networks
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Patterson & Davie, Computer Networks, A Systems Approach
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R. Stevens, TCP/IP Illustrated Vol. 1
Other useful texts
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... are given during the lectures or on the web page
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Presentation slides will be available from the home page
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Communication Systems
Literature on Voice over IP and telephony networks
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Books
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E. Pehl, Digitale und analoge Datenübertragung
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Flaig, Hoffmann, Langauf: Internet-Telefonie VoIP mit Asterisk und
SER
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Sinnreich, Johnston: Internet Communications using SIP
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Hersent, Gurle, Petit: Beyond VOIP Protocols
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Kaaranen, Ahtiainen, Laitinen: UMTS Networks Architecture Mobility
and Services
Other useful texts
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... are given during the lectures or on the web page
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Presentation slides will be available from the home page
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Introduction
What are communication networks?
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Telephony (mostly voice) networks exists for more than 100 years
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the technology of end users systems (TE for terminal equipment in
Telco lingo) has not changed much – try your grandmothers old dial
phone to your “analogous” telephone line or ISDN a/b connector
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digital mobile telephony networks of the second generation (2G)
extremely changed the style of human communication in the last
decade
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but rapid changes are under the way – reason for the outline of this
lecture
Different kinds of mobile networks allow “ubiquious communication”
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Introduction
What are communication networks?
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Internet is complex, both in terms of hardware and software
components, so difficult to provide “one-sentence-description”
The public computer network most of you using throughout the day
Other way – networking infrastructure that provides services to
distributed applications
We experience a merging of networks
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IP connections use traditional telephone lines (modem connections
over POTS, ISDN data connections, ...)
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Mobile Telephone systems of third generation (3G, UMTS) provide
broader bandwidth for data centric applications
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Voice over IP replaces parts of traditional telephony networks
(beginning at the core system and from the end user devices)
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UMTS moves towards IP in network subsystem (NSS)
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Introduction
What is the Internet?
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Start with introduction to TCP/IP and Internet
Distinction: TCP/IP is merely the set of protocols usable for network
communication
Internet is
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using TCP/IP
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Public network interconnecting millions of computing devices spread
over the whole world
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Most of them traditional desktop PCs and workstations of any kind,
servers for web pages and mail, ...
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Nontraditional internet endsystems: PDAs, mobile computers, TV set
top boxes, cell phones, fridges, ...
In network terminology they are end systems or hosts
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Introduction
What is the Internet?
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End systems connected together by communication links
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Many types of links
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copper wire of different type, like twisted pair, telephone line, coaxial
cable (e.g. broadband TV)
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Fiber optics (most of wide area connections up to connections of
continents)
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Radio spectrum for air transmission
Link transmission rate is bandwidth
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Introduction
What is the Internet?
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Hosts seldom connected by direct links but over intermediate switching
devices called routers
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Routes get chunks of information and forward it to one of its other links
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The term for chunks of information is packet
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Way of packet through the net – path or route
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Seldom dedicated paths, so we speak of packet switching networks
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Introduction
What is the Internet?
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End users, organizations or enterprises connected to the Internet
through Internet Service Providers (ISPs) of different levels
End user providers mostly telecommunication firms like German
Telekom, ARCOR, ...
Companies often use regional ISPs
Universities have their own ISPs, like BelWue in south-west of germany,
the DFN (broadband and gigabit infrastructure) and GEANT on the
european level (next slides)
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BelWue
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DFN (B-Win)
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DFN (G-Win,
successor)
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GEANT
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Introduction
Service Description
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Internet allows distributed applications running on different end systems
to exchange data
Services include: remote login, mail, web services, databases, instant
messaging, audio and video streams, ...
Internet provides two types of services
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Connection orientated, reliable service, guaranteeing the user
delivering of data in order and entirety (hopefully)
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Connectionless, unreliable service, which does not make any
guarantees about eventual delivery
But no services which makes promises on how long delivery takes
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Introduction
What is a protocol?
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Hosts, routers and other networking pieces run protocols controlling the
sending and receiving of packets
IP (Internet Protocol) and TCP (Transmission Control Protocol) most
important protocols used in Internet communication
Protocols and Internet standards are often discussed in RFCs (Request
for Comment)
In telephony networks protocols defined to, like
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ISDN D channel or Q.931 call setup and info signaling
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Signaling System 7 (SS7, core network (CN) signaling)
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DTAP for signaling between mobile stations (MS – end user device
in GSM) and base stations (BS)
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Introduction
What is a protocol?
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Telephony networks aim at interoperability through definition of
interfaces
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centralized standardization bodies, nationally and internationally, like
ITU (International Telecommunications Union)
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interoperability is a much stronger issue in the Internet community
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Telcos hope to cut off competitors using incompatible protocols –
e.g. the ISDN used for telecommunication within the university is not
compatible to the ISDN used in public networks
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One reason, that pace of technology is much faster in the Internet
domain than in telephony networks, example is the data rate in G2
mobile telephony networks (much to slow for most modern
networked applications)
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Introduction
What is a protocol?
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Human analogy: Ask for the time
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If polite: You do not ask directly someone you do not know
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So “protocol” of exchanging information between A and B on time of
the day may be as follow:
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A: Hi
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B: Hi
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A: May I ask the time?
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B: Yes, it is 5 p.m.
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B could answer “I do not know”, “I dont understand you”, ..., so
protocol should have ability to handle unsuccessful cases
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Introduction
What is a protocol?
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In this analogy
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If not using a know protocol, you do not get an answer
Protocols in networking operate the same way: Host H asks the
webserver W for a specific page:
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H: TCP connection request to W
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W: TCP connection reply
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H: GET http://www.ks.uni-freiburg.de
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W: deliver <file>
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Introduction
Network protocols
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Occur when two or more internet entities communicate
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Often more than one protocol must be run, i.e.
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Protocols running on hardware to encode data to physical states on
wire
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Controlling the flow of bits between two network adaptors
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Routing protocols to determine path of packets from source to
destination
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Congestion control protocols
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Protocol for retrieving webpages from a webserver
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Introduction
Protocol - Definition
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A protocol defines the format and the order of messages exchanged
between two or more communicating entities, als well as the actions
taken on the transmission and/or receipt of a message or other event.
(Kurose&Ross)
The layering of different protocols is one of the most important parts in
understanding the internet
This layering will be defined later in so called protocol stack
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Introduction
Edges of networks
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After rough overview more detailed description of parts defining internets
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Hosts called end system, because sitting at the edge of internet
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End users directly interface to them
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Every end user device able to run TCP/IP could be connected to the net
and is an end system in internet terminology
Hosts run end user applications, often divided into two categories:
clients and servers
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Introduction
Client-Server-Model
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A client program requests a service from a server program
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client/server model is most prevalent structure of internet applications
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Most applications, like mail, ssh, web, ... work that way
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Intermediate infrastructure serves as black box
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Of course not all applications and servers work that way
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Peer-to-peer networks, like bittorrent, edonkey, gnutella, ...
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Servers may receive services from other servers as clients, e.g. DNS
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Communication
Different services ...
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May be used by networking applications
When applications use connection-orientated-service they exchange
control packets before sending data
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Procedure is called handshaking
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This service provides reliable data transfer, flow and congestion control
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Reliability ensures proper order of packets and no errors (achieved
through acknowledgment and retransmission of packets)
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Communication
Different services ...
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Flow control avoids overwhelming of each side with data packets
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Congestion control helps preventing of grid-locking the internet
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Congested routers discard packets which require informing the sender
and requires retransmission
TCP will be inherently used and introduced during this course
UDP is very simple, connectionless, with none of the services named
above
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Communication
Network Core (taxonomy of networks)
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Network core inside of the network not visible to the end user
(application)
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Sample pictures of (IP based) network cores given some slides before
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Main distinction of network types
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Important concepts of network taxonomy
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Two fundamental approaches in network cores:
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Circuit switching
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Packet switching
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Network Core
Circuit Switching (CS)
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Resources needed along a path, like bandwidth, buffers reserved for the
duration of communication
Telephone systems operate that way – a connection is called a circuit
Reservation procedure may require a lot of complexity (and therefore
delays) and may produce costs
Connection quality in terms of bandwidth, delay, error rate, ... will remain
the same during communication
Quality of Service (QoS) is a big issue in telephony networks: Voice
connections are heavily influenced through delays, packet loss and
changing bandwidth)
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Network Core
Circuit Switching (CS)
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Concept known from the traditional world of analogous telephony
systems
Guaranteed reserved constant bandwidth may use a given connection
much below real capacity
Hardware protocols designed mostly for telephony, like ISDN and ATM
use circuit switching
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ATM still forms the backbone (core network) of UMTS mobile phone
network
Costs usually calculated in terms of time usage and possible maximum
bandwidth of a link not in term of transferred volumes
Problems can be seen with designing and establishment of Voice-overIP services (in contrast to traditional Telco services)
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Network Core
Packet Switching (PS)
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Completely different concept
Source breaks long messages (e.g. FTP file) into smaller data chunks
called packets
Each packet travels through communication links and most inevitably
crosses packet switches called routers
Packet switches use store-and-forward mechanism
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Packet must be received completely before it could sent out an
outgoing line
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It is queued into outbound packet queue to handle busy links
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Network Core
Packet Switching
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Packets therefore suffer from
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Transmission delays – if packet consists of L bits and the outgoing
link handles R bps delay is L/R seconds
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Switching delays (routing decisions are to be made)
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Queuing delays (wait in outgoing buffer)
If queue is full – packets are discarded and packet loss occurs
Share of bandwidth in packet switching networks via statistical
multiplexing
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Network Core
Packet Switching
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Circuit switching uses frequency division multiplexing (FDM) or time
division m. (TDM) instead
Statistical multiplexing is much more flexible than FDM or TDM (with
fixed frequencies and time slots) and can utilize a given bandwidth much
better
Packet switching networks
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Cheaper, easier to implement (less complex)
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More efficient, no waste of bandwidth
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Communication
Comparison
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Efficiency of the use of a 10 Mbps link shared by some users
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Suppose users generate data at 1 Mbps in 10 percent of there online
time (idle reading webpages, analyzing data, ...)
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Circuit switching would reserve 1 Mbit per user, so at max 10 Users
may share the link
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For packet switching the probability of user activity is 10%, if there
are 35 users probability of 11 active users (less bandwidth for every
user than required) is 0.0004
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Thus probability that less than 10 users share the link is 0.9996 (no
delay or packet discarding occurs)
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Packet switching allows much more users sharing one link!
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Communication
End / literature
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Next lectures is on Thursday
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please check in the meantime
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that you own a computing dept. UserID (every participant should
have one)
you should be able to handle Linux&VMware (for the practical
exercises)
that you were put to the mailing list
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Communication
End / literature
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Literature
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network introduction from the view of telephony people: Kaaranen
and others, “UMTS Networks”, Wiley 2005, first chapters
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homepages of belwue, DFN, GEANT
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Dark fiber in Germany: Holger Bleich, “Bosse der Fasern”, ct 7/05
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packet and circuit switching: Kurose ...
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Peterson, Davie "Computer Networks - A Systems Approach" 2nd
edit. pages 2-58
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Tanenbaum, "Computer Networks" 3rd edit. pages 3-71
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