Communication Systems Chair of Communication Systems Department of Applied Sciences University of Freiburg 2006 1 | 43.

Communication Systems

Chair of Communication SystemsDepartment of Applied Sciences

University of Freiburg2006

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Communication SystemsCourse Information – General

● Summer course: 04/25/2006 – 07/28/2006● Instructors: Prof. Dr. G. Schneider, Rui Zhou & Dirk von Suchodoletz● Hiwis: Christoph Hanke, Ahmad Abdul Majeed● 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 SystemsCourse Information - Lecturers

● Office hours: Prof. Schneider - after the lecture, Dirk von Suchodoletz – Tuesday 6:30 – 8:00 pm

– subject to change – see homepage

– after the Tuesday lecture ...

Rui Zhou – Tuesday 6:30 – 8:00pm (Office: RZ 104)

● E-mail: [email protected],[email protected], [email protected]

● Homepage of this course: http://www.ks.uni-freiburg.de/php_veranstaltungsdetail.php?id=11

● Lecture plan given on the homepage– dates for practical courses

– additional information and papers

– date(s) for the written exam

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Communication SystemsCourse Information – Course Layout

● Lecture earns 6 credit points● Area of specialization: “communication and data bases (6)”● Typical 3 + 1 course

– Three quarters are lectures (here in this room)

– One quarter is a practical course, variable dates – see lecture plan!!

– 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)

– 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 SystemsCourse Information - Examinations

● Written exam at the end of lecture– two hour written exam

– possible dates:

● Thursday, 27th of July, 6 – 8 pm● Friday, 28th of July, 10 – 12 am● Friday, 28th of July, 1 – 3 pm

● We pass around a participants list– please put name, email and matrikel to it

– 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– simple decision of the vote of majority

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Communication SystemsPractical Course and Exercises

● 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– 50% mandatory - otherwise no "Übungsschein"

– 60% +0.1, 70% +0.2, 80% +0.3 (=one third off the grade)

– 90% +0.5, 100% +0.6 (=two thirds off the grade)

● Bonus will improve the grade of written exam

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Communication SystemsSyllabus and Scope of course

● Communication systems lecture is on the broad topic of communication– data and voice communication in circuit switched and packet

orientated networks

– 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)

– broad overview on different kind of networks

– partly in depth discussion of some concepts

● Different kind of networks for different purposes

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Communication SystemsSyllabus and Scope of course

● Communication models among networked devices● Focuses on network layer and application layer

– for underlying hardware, LAN, W-LAN, WAN technologies and

– 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 :-))– not all topics are handled in the lecture!

– practical exercises will introduce new topics too and deepen the insight into topics presented in lecture

– 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 SystemsSyllabus and Scope of course

● This lecture is an updated version of the former Internet Working course held the last three summer semesters

– shift of focus towards voice communication

– so about 33% of the lectures content is exchanged (mostly for digital telephony systems)

● Sources of information– lecture slides and exercise sheets of past lectures

– literature hints (given on the lectures homepage) and via email (we will setup a mailing list for this course)

– 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 SystemsCourse Outline

● May be modified throughout the course, number of lectures in brackets

● Networks and IP - base protocol of the Internet [1]● Dynamic routing [2]● DNS/ENUM the phone book of the Internet [1]● The future of IP - IPv6 [1]● Quality of service (QoS) in packet oriented networks [1]

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Communication SystemsCourse Outline

● Protocols and technologies of telephone networks [1]● ISDN (integrated services digital network) [1]● GSM (global standard for mobile communication) [1]● GPRS and UMTS [2]● Other wireless technologies [1]● WLAN, Wimax, Bluetooth and AAA (802.1x) [1]● Telephony services on IP, SIP, H323 [3]

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Communication SystemsLiterature on IP part

● Books– Kurose & Ross, Computer Networking (best at the moment)

– Douglas E. Comer, Computer Networks and Internets

– Andrew S. Tanenbaum, Computer Networks

– Patterson & Davie, Computer Networks, A Systems Approach

– R. Stevens, TCP/IP Illustrated Vol. 1

● Other useful texts– ... are given during the lectures or on the web page

– Presentation slides will be available from the home page

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Communication SystemsLiterature on Voice over IP and telephony networks

● Books– E. Pehl, Digitale und analoge Datenübertragung

– Flaig, Hoffmann, Langauf: Internet-Telefonie VoIP mit Asterisk und SER

– Sinnreich, Johnston: Internet Communications using SIP

– Hersent, Gurle, Petit: Beyond VOIP Protocols

– Kaaranen, Ahtiainen, Laitinen: UMTS Networks Architecture Mobility and Services

● Other useful texts– ... are given during the lectures or on the web page

– Presentation slides will be available from the home page

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IntroductionWhat are communication networks?

● Telephony (mostly voice) networks exists for more than 100 years– 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

– digital mobile telephony networks of the second generation (2G) extremely changed the style of human communication in the last decade

– 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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IntroductionWhat are communication networks?

● 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

– IP connections use traditional telephone lines (modem connections over POTS, ISDN data connections, ...)

– Mobile Telephone systems of third generation (3G, UMTS) provide broader bandwidth for data centric applications

– Voice over IP replaces parts of traditional telephony networks (beginning at the core system and from the end user devices)

– UMTS moves towards IP in network subsystem (NSS)

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IntroductionWhat is the Internet?

● Start with introduction to TCP/IP and Internet● Distinction: TCP/IP is merely the set of protocols usable for network

communication● Internet is

– using TCP/IP

– Public network interconnecting millions of computing devices spread over the whole world

– Most of them traditional desktop PCs and workstations of any kind, servers for web pages and mail, ...

– 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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IntroductionWhat is the Internet?

● End systems connected together by communication links● Many types of links

– copper wire of different type, like twisted pair, telephone line, coaxial cable (e.g. broadband TV)

– Fiber optics (most of wide area connections up to connections of continents)

– Radio spectrum for air transmission

● Link transmission rate is bandwidth

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IntroductionWhat is the Internet?

● Hosts seldom connected by direct links but over intermediate switching devices called routers

● Routes get chunks of information and forward it to one of its other links● The term for chunks of information is packet● Way of packet through the net – path or route● Seldom dedicated paths, so we speak of packet switching networks

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IntroductionWhat is the Internet?

● 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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IntroductionService Description

● 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– Connection orientated, reliable service, guaranteeing the user

delivering of data in order and entirety (hopefully)

– 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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IntroductionWhat is a protocol?

● 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– ISDN D channel or Q.931 call setup and info signaling

– Signaling System 7 (SS7, core network (CN) signaling)

– DTAP for signaling between mobile stations (MS – end user device in GSM) and base stations (BS)

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IntroductionWhat is a protocol?

● Telephony networks aim at interoperability through definition of interfaces

– centralized standardization bodies, nationally and internationally, like ITU (International Telecommunications Union)

– interoperability is a much stronger issue in the Internet community

– 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

– 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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IntroductionWhat is a protocol?

● Human analogy: Ask for the time– If polite: You do not ask directly someone you do not know

– So “protocol” of exchanging information between A and B on time of the day may be as follow:

– A: Hi

– B: Hi

– A: May I ask the time?

– B: Yes, it is 5 p.m.

– B could answer “I do not know”, “I dont understand you”, ..., so protocol should have ability to handle unsuccessful cases

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IntroductionWhat is a protocol?

● In this analogy– 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:

– H: TCP connection request to W

– W: TCP connection reply

– H: GET http://www.ks.uni-freiburg.de

– W: deliver <file>

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IntroductionNetwork protocols

● Occur when two or more internet entities communicate● Often more than one protocol must be run, i.e.

– Protocols running on hardware to encode data to physical states on wire

– Controlling the flow of bits between two network adaptors

– Routing protocols to determine path of packets from source to destination

– Congestion control protocols

– Protocol for retrieving webpages from a webserver

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IntroductionProtocol - Definition

● 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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IntroductionEdges of networks

● After rough overview more detailed description of parts defining internets

● Hosts called end system, because sitting at the edge of internet● End users directly interface to them● 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

● A client program requests a service from a server program● client/server model is most prevalent structure of internet applications● Most applications, like mail, ssh, web, ... work that way● Intermediate infrastructure serves as black box● Of course not all applications and servers work that way

– Peer-to-peer networks, like bittorrent, edonkey, gnutella, ...

– Servers may receive services from other servers as clients, e.g. DNS

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CommunicationDifferent services ...

● May be used by networking applications● When applications use connection-orientated-service they exchange

control packets before sending data● Procedure is called handshaking● This service provides reliable data transfer, flow and congestion control● Reliability ensures proper order of packets and no errors (achieved

through acknowledgment and retransmission of packets)

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CommunicationDifferent services ...

● Flow control avoids overwhelming of each side with data packets● Congestion control helps preventing of grid-locking the internet● 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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CommunicationNetwork Core (taxonomy of networks)

● Network core inside of the network not visible to the end user (application)

● Sample pictures of (IP based) network cores given some slides before● Main distinction of network types● Important concepts of network taxonomy● Two fundamental approaches in network cores:

– Circuit switching

– Packet switching

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Network CoreCircuit Switching (CS)

● 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 CoreCircuit Switching (CS)

● 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

– 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-over-IP services (in contrast to traditional Telco services)

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Network CorePacket Switching (PS)

● 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

– Packet must be received completely before it could sent out an outgoing line

– It is queued into outbound packet queue to handle busy links

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Network CorePacket Switching

● Packets therefore suffer from– Transmission delays – if packet consists of L bits and the outgoing

link handles R bps delay is L/R seconds

– Switching delays (routing decisions are to be made)

– 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 CorePacket Switching

● 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– Cheaper, easier to implement (less complex)

– More efficient, no waste of bandwidth

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CommunicationComparison

● Efficiency of the use of a 10 Mbps link shared by some users– Suppose users generate data at 1 Mbps in 10 percent of there

online time (idle reading webpages, analyzing data, ...)

– Circuit switching would reserve 1 Mbit per user, so at max 10 Users may share the link

– 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

– Thus probability that less than 10 users share the link is 0.9996 (no delay or packet discarding occurs)

– Packet switching allows much more users sharing one link!

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CommunicationEnd / literature

● Next lectures is on Thursday– please check in the meantime

● 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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CommunicationEnd / literature

● Literature– network introduction from the view of telephony people: Kaaranen

and others, “UMTS Networks”, Wiley 2005, first chapters

– homepages of belwue, DFN, GEANT

– Dark fiber in Germany: Holger Bleich, “Bosse der Fasern”, ct 7/05

– packet and circuit switching: Kurose ...

– Peterson, Davie "Computer Networks - A Systems Approach" 2nd edit. pages 2-58

– Tanenbaum, "Computer Networks" 3rd edit. pages 3-71

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