Grundlagen der Rechnernetze. Introduction

Transcription

1 Grundlagen der Rechnernetze Introduction

2 Overview Building blocks and terms Basics of communication Addressing Protocols and Layers Performance Historical development Grundlagen der Rechnernetze - Introduction 2

3 Building blocks and terms Grundlagen der Rechnernetze - Introduction 3

4 Hosts and links H1 H2 Link Host Grundlagen der Rechnernetze - Introduction 4

5 Hosts and links H1 H2 Link Host Host is a computer or more general a device that communicates with the other host on a network Link is (in the context of computer networks) connection between two hosts Point to point connection designates communication connection between two hosts (nodes) or endpoints Grundlagen der Rechnernetze - Introduction 5

6 Types of communication Simplex Half-duplex Duplex (full duplex) Source: Grundlagen der Rechnernetze - Introduction 6

7 Medium Wired communication Wireless communication Light(?) Sound (ultrasound) Grundlagen der Rechnernetze - Introduction 7

8 Communication channel between the nodes Communication channel refers to a physical transmission medium (wired or wireless) but it also covers logical connection over multiplexed medium Grundlagen der Rechnernetze - Introduction 8

9 Message, stream, packet [1] M H1 H2 H3 S H4 P 1 P 2 P n Header Payload Trailer Bytes First Bit Last Bit Grundlagen der Rechnernetze - Introduction 9

10 Message, stream, packet Message Communication primitive, usually consists of multiple packets; usually used in the higher layers of communication Stream A sequence of signals that we use to transmit data Packet Formatted unit of data consisting of user data and control data (header and trailer). Essentially a part of a message; several packets together form a message Grundlagen der Rechnernetze - Introduction 10

11 Multiple access H 1 H 2 H 3 H n Collision domain A network connected by a shared medium; in this network packets may collide with one another when they are sent. A term coming from early versions of Ethernet and wireless networks Single hop communication Basically communication within one collision domain; packet reaches destination within one hop Grundlagen der Rechnernetze - Introduction 11

12 Multiplexing [1] H 1 H 4 H 2 H 5 H 3 H 6 H 1 H 2 H 4 H 5 H 3 H 6 Grundlagen der Rechnernetze - Introduction 12

13 Multiplexing [2] Static multiplexing (predefined) Statistical multiplexing (can adapt over time) Queueing Packet scheduling the way of controlling packet transmission Grundlagen der Rechnernetze - Introduction 13

14 Scalability of computer networks Scalability how networks adapt to the grow of load? how networks adapt to the increase of hosts? how networks adapt to the increase of links? Grundlagen der Rechnernetze - Introduction 14

15 Scalability of multiple access networks H 1 H 2 H 3 H n Assuming that all node pairs communicate the same number of times. What is the share s of the medium per node pair? Grundlagen der Rechnernetze - Introduction 15

16 Scalability of multiple access networks H 1 H 2 H 3 H n Assuming that all node pairs communicate the same number of times. What is the share s of the medium per node pair? ss = [nn (nn 1)/2] 1 = OO( 1 nn 2) Grundlagen der Rechnernetze - Introduction 16

17 Scalability of fully connected network H11 H1 H2 What is the number of links k per node and total number of links l? H10 H3 H9 H4 H8 H7 H6 H5 Grundlagen der Rechnernetze - Introduction 17

18 Scalability of fully connected network H10 H11 H1 H2 H3 What is the number of links k per node and total number of links l? kk = nn 1 ll = nn (nn 1)/2 H9 H4 H8 H7 H6 H5 Grundlagen der Rechnernetze - Introduction 18

19 Switched network H8 H1 H2 H3 S1 Switch a network device that provides dedicated communication between the hosts Switched network computer network that uses network switches S2 S3 S4 H4 H7 S5 H6 H5 Grundlagen der Rechnernetze - Introduction 19

20 Switched network H1 H2 H3 Packet switched network a type of network that uses packets for communication; packet switching is a form of grouping of the data sent over the network; in here network links can be shared H8 H7 S2 S1 S3 S4 H4 Circuit switched network a dedicated communication channel (circuit) is established between two hosts; in here network links are dedicated to one specific communication between the hosts S5 H6 H5 Grundlagen der Rechnernetze - Introduction 20

21 Switched network H8 H1 H2 H3 S1 Store and forward a packet is sent to an intermediate station where it can be either kept or forwarded Cut through switching a bigger chunk of the data (frame) is forwarded in smaller pieces even before the whole chunk is received H7 S2 S3 S4 H4 Multi-hop communication using multiple stations to transmit data between two hosts S5 H6 H5 Grundlagen der Rechnernetze - Introduction 21

22 Cloud representation Grundlagen der Rechnernetze - Introduction 22

23 Internet [1] H1 H2 H3 N1 H9 R1 R2 H4 N3 N2 H8 R3 H5 H7 H6 Grundlagen der Rechnernetze - Introduction 23

24 Internet [2] What is internet? Router Network interface The Internet and a internet Physical network Intranet Grundlagen der Rechnernetze - Introduction 24

25 Recursive use of cloud representation H1 H2 H3 N1 R1 R2 H4 H9 N3 N N2 H8 R3 H5 H7 H6 Grundlagen der Rechnernetze - Introduction 25

26 Network sizes LAN local-area network WAN wide-area network MAN metropolitan area network; larger than local area network (LAN) but smaller than the area covered by a wide area network (WAN). SAN storage area network is a high-speed network of storage devices that also connects those storage devices with servers. CAN Controller Area Network (also known as CAN bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. PAN personal area network; network of localized and personalized devices. GAN global area network; connecting everything. Grundlagen der Rechnernetze - Introduction 26

27 Network sizes Source: Grundlagen der Rechnernetze - Introduction 27

28 Networks and graphs [1] H1 H2 H3 H1 H2 H3 R1 N1 R2 H4 R1 N1 R2 H4 H9 H8 N3 R3 N2 H5 H9 N3 R3 N2 H5 H7 H6 H8 H7 H6 Grundlagen der Rechnernetze - Introduction 28

29 Networks and graphs [2] Nodes Links Topology Formal definition of a network graph: GG = VV, EE wwwwwww EE VV VV Grundlagen der Rechnernetze - Introduction 29

30 Topology examples Bus Tree Star Ring Mesh Grundlagen der Rechnernetze - Introduction 30

31 Basics of communication Grundlagen der Rechnernetze - Introduction 31

32 Types of communication H9 H8 H1 H7 R1 N3 H2 N1 R3 H3 R2 N2 H6 H5 H4 Unicast communication where a piece of information is sent from one point to another point. In this case there is just one sender, and one receiver. Multicast describe communication where a piece of information is sent from one or more points to a set of other points. In this case there is may be one or more senders, and the information is distributed to a set of receivers (theer may be no receivers, or any other number of receivers). Broadcast communication where a piece of information is sent from one point to all other points. In this case there is just one sender, but the information is sent to all connected receivers. Grundlagen der Rechnernetze - Introduction 32

33 Types of communication H9 H1 R1 N3 H2 N1 R2 H3 N2 H4 Forwarding Packet (frame ) forwarding is the relaying of packets from one network segment to another by nodes in a computer network. Usually refers to the effective transfer of a packet (frame...) Routing process of selecting a path for traffic in a network, or between or across multiple networks. Path actual path used for transmission between two hosts H8 R3 H5 H7 H6 Grundlagen der Rechnernetze - Introduction 33

34 Forwarding table Destination Next hop R Grundlagen der Rechnernetze - Introduction 34

35 Timeouts and acknowledgements H9 H1 R1 N3 H2 N1 R2 H3 N2 H4 Timer Timeout Acknowledgement ACK H8 R3 H5 H7 H6 Grundlagen der Rechnernetze - Introduction 35

36 Connection oriented and connectionless communication H1 H2 H3 N1 Connection oriented Telephone, File transfer R1 R2 H4 Connectionless VoIP, Post H9 N3 N2 H8 R3 H5 H7 H6 Grundlagen der Rechnernetze - Introduction 36

37 Client-Server principle H N S Client Server Grundlagen der Rechnernetze - Introduction 37

38 Client-Server principle H N S Client Request Server Grundlagen der Rechnernetze - Introduction 38

39 Client-Server principle H N Response S Client Server Grundlagen der Rechnernetze - Introduction 39

40 Client-Server principle H N S Client Server stateful server remembers client data (state) from one request to the next. stateless server does not keep state information. Using a stateless file server, the client must specify complete file names in each request, specify location for reading or writing. Grundlagen der Rechnernetze - Introduction 40

41 Adressing Grundlagen der Rechnernetze - Introduction 41

42 Motivation H1 H2 H3 N1 How do we transfer message from H8 to H4? H9 R1 R2 H4 Which path do we use? Can we always reach the destination? N3 N2 H8 R3 H5 H7 H6 Grundlagen der Rechnernetze - Introduction 42

43 Physical address Ethernet example : 00 : 2B : E4 : B1 : 02 Broadcast FF:FF:FF:FF:FF:FF Multicast 1XXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX {8X,,FX}:XX:XX:XX:XX:XX Grundlagen der Rechnernetze - Introduction 43

44 Address space H1 H2 H3 H7 H8 H H R R R H H6 Grundlagen der Rechnernetze - Introduction 44

45 Forwarding table and address space H1 H2 H3 H7 H8 H H H R H6 R R3 4.4 Dest H1 H2 H3 H4 H5 H6 H7 H8 Next-Hop After R1 After R1 After R1 Direct Direct Direct After R3 After R3 Dest Next-Hop 1.X After R1 2.X Direct 4.X After R3 H9 After R3 Grundlagen der Rechnernetze - Introduction 45

46 IP addresses 32 bits approximately 4 billion addresses Binary representation 4 groups of 8 bits Dot notation 4 decimal numbers representing 4 groups of bits Example: Grundlagen der Rechnernetze - Introduction 46

47 Classful IP addresses What does it mean classful? Which are different classes? Network address Host address Broadcast address Source: William Stallings Data and Computer Communications, Eight Edition Grundlagen der Rechnernetze - Introduction 47

48 Need for additional hierarchical layer H1 H2 H3 H7 H8 H H R R R H H6 Entrance to the University network Grundlagen der Rechnernetze - Introduction 48

49 Subnetworks For example class B Address Network Host Subnet mask ( ) Solution Network number Subnet Host Grundlagen der Rechnernetze - Introduction 49

50 Subnetting example Example: Using one class B network: X.X = = XXXXXXXX XXXXXXXX Subnet number : = Subnet mask : = H = R = = = = = H2 Grundlagen der Rechnernetze - Introduction 50

51 Changes in forwarding tables Subnet number : Subnet mask : H Interface 1 R Interface 2 Subnet number Subnet mask Next hop direct (if 1) direct (if 2) after R2 (if 2) R3 Network number Next Hop H R Grundlagen der Rechnernetze - Introduction 51

52 Address resolution IP address Physical address IP address Physical address :FF:AA:36:AB: :48:A4:28:AA: ??? :48:A4:28:AA: :35:FE:36:42:55 H :FF:AA:36:AB:11 85:48:A4:28:AA:18 R1 H2 Grundlagen der Rechnernetze - Introduction 52

53 Supernetting motivation Lets assume, for example, the IT department of a university campus, which "autonomously" uses a lot of IP addresses. With subnetting, we can efficiently use given set of IP addresses. The problem is that the IT department still has to request / manage IP addressing in the granularities Class-A-, -B-, or -C-network. Grundlagen der Rechnernetze - Introduction 53

54 Supernetting motivation What happens when for example we need 257 hosts? 1. We can apply for Class B network address. The problem is efficiency Grundlagen der Rechnernetze - Introduction 54

55 Supernetting motivation What happens when for example we need 257 hosts? 1. We can apply for Class B network address. The problem is efficiency ,39% Grundlagen der Rechnernetze - Introduction 55

56 Supernetting motivation What happens when for example we need 257 hosts? 1. We can apply for Class B network address. The problem is efficiency ,39% 2. We can also consider 2 class C networks. Grundlagen der Rechnernetze - Introduction 56

57 Supernetting motivation What happens when for example we need 257 hosts? 1. We can apply for Class B network address. The problem is efficiency ,39% 2. We can also consider 2 class C networks. This means that we have 2 routing entries in each internet router Grundlagen der Rechnernetze - Introduction 57

58 Solution: Classless Inter-Domain Routing (CIDR) We can aggregate network addresses. Example: Lets assume that we have 16 * hosts. We use 16 addresses of Class-C networks. Not arbitrary addresses, but consecutive, e.g.: Grundlagen der Rechnernetze - Introduction 58

59 Solution: Classless Inter-Domain Routing (CIDR) We can aggregate network addresses. Example: Lets assume that we have 16 * hosts. We use 16 addresses of Class-C networks. But not arbitrary addresses, but consecutive, e.g.: Now we can observe following: all addresses begin with the same 20 bits: Grundlagen der Rechnernetze - Introduction 59

60 Solution: Classless Inter-Domain Routing (CIDR) Observation: all addresses begin with the same 20 bits: That means that we need a 20-bit network address This is between Class-C (24-bit) and Class-B (16-bit) Required output of 2 ^ 4 = 16 Class C addresses General question: How many class-c networks requires i-bit network address? Grundlagen der Rechnernetze - Introduction 60

61 Solution: Classless Inter-Domain Routing (CIDR) Observation: all addresses begin with the same 20 bits: That means that we need a 20-bit network address This is between Class-C (24-bit) and Class-B (16-bit) Required output of 2 ^ 4 = 16 Class C addresses General question: How many class-c networks requires i-bit network address? 2 24 ii Grundlagen der Rechnernetze - Introduction 61

62 Solution: Classless Inter-Domain Routing (CIDR) We need a notation for the scheme. In our example: Notation can be summarized as: / 20 So this additional number / 20 means network address consists of first 20 bits and summarizes the 2 ^ 4 = 16 successive class-c networks beginning with Grundlagen der Rechnernetze - Introduction 62

63 Quiz How to represent the class-c networks from to using / X notation? Grundlagen der Rechnernetze - Introduction 63

64 Quiz How to represent the class-c networks from to using / X notation? / 19 Grundlagen der Rechnernetze - Introduction 64

65 Quiz How to represent the class-c networks from to using / X notation? / 19 How to represent the single class-c network in / X notation? Grundlagen der Rechnernetze - Introduction 65

66 Quiz How to represent the class-c networks from to using / X notation? / 19 How to represent the single class-c network in / X notation? / 24 Grundlagen der Rechnernetze - Introduction 66

67 Solution: Classless Inter-Domain Routing (CIDR) How are aggregated addresses handled in the router: Addresses in the routing tables are pair <length, value> This is comparable to the pair <mask, value> in subnetting if the mask consists of successive 1-bit values Grundlagen der Rechnernetze - Introduction 67

68 Solution: Classless Inter-Domain Routing (CIDR) CIDR allows further route aggregation. For example: Client networks Advertise / /24 Internet provider /24 We don t even need to use 8 consecutive addresses Grundlagen der Rechnernetze - Introduction 68

69 Solution: Classless Inter-Domain Routing (CIDR) What happens with CIDR and routing table entries? Prefixes may overlap. Lets consider following routing table: Where do we route the message for ? Where do we route the message ? Network address Next hop /16 if /24 if Grundlagen der Rechnernetze - Introduction 69

70 Solution: Classless Inter-Domain Routing (CIDR) What happens with CIDR and routing table entries? Prefixes may overlap. Lets consider following routing table: Where do we route the message for ? if2 Where do we route the message ? Network address Next hop /16 if /24 if if1 Grundlagen der Rechnernetze - Introduction 70

71 Solution: Classless Inter-Domain Routing (CIDR) What happens with CIDR and routing table entries? Prefixes may overlap. Lets consider following routing table: Where do we route the message for ? if2 Where do we route the message ? if1 Network address Next hop /16 if /24 if In general: Longest-Prefix-Match (requires efficient algorithms / data structures to find the longest matching prefix.) Grundlagen der Rechnernetze - Introduction 71

72 Subnetting vs CIDR Subnetting allows splitting a network address into subnets Distribution almost anywhere; everything that can be expressed with the subnet mask CIDR is used to aggregate network addresses in a single address Aggregation not arbitrary; network addresses must be consecutive; only 2^i sized networks can be aggregated Certain flexibility using "dummy networks" Grundlagen der Rechnernetze - Introduction 72

73 Subnetting and addresses revisited Smaller networks using one network address Hierarchy Better organization Better use of resources Addresses (network, host, broadcast) Grundlagen der Rechnernetze - Introduction 73

74 Subnetting example [1] We have been given one class C network address: that we want to divide it into two subnets. The questions are: How many hosts can we have in each subnet? What are the subnet addresses for these two subnets? What are corresponding subnet masks? What set of IP addresses cover these subnets? What are CIDR notations for subnets? Grundlagen der Rechnernetze - Introduction 74

75 Subnetting example [1] We have been given one class C network address: that we want to divide it into two subnets. The questions are: How many hosts can we have in each subnet? 2 subnets = address space of 2^7 addresses Number of hosts = 2^7 host address broadcast address = 126 Grundlagen der Rechnernetze - Introduction 75

76 Subnetting example [1] We have been given one class C network address: that we want to divide it into two subnets. The questions are: What are the subnet addresses for these two subnets? Grundlagen der Rechnernetze - Introduction 76

77 Subnetting example [1] We have been given one class C network address: that we want to divide it into two subnets. The questions are: What are corresponding subnet masks? Grundlagen der Rechnernetze - Introduction 77

78 Subnetting example [1] We have been given one class C network address: that we want to divide it into two subnets. The questions are: What set of IP addresses cover these subnets? Grundlagen der Rechnernetze - Introduction 78

79 Subnetting example [1] We have been given one class C network address: that we want to divide it into two subnets. The questions are: What are CIDR notations for subnets? 25 for both networks / / 25 Grundlagen der Rechnernetze - Introduction 79

80 Subnetting example [2] We have been given one class C network address: that we want to divide it into three subnets, the first having 101 hosts, second 44 and the third 60. The questions are: What are the subnet addresses for these three subnets? What are corresponding subnet masks? What set of IP addresses cover these subnets? What are CIDR notations for subnets? Grundlagen der Rechnernetze - Introduction 80

81 Subnetting example [2] We have been given one class C network address: that we want to divide it into three subnets, the first having 101 hosts, second 44 and the third 60. The questions are: Actual first question is what are the sizes of those three subnets 64 < 101 < 128 => = < 44 < 64 => = < 60 < 64 => = 62 Grundlagen der Rechnernetze - Introduction 81

82 Subnetting example [2] We have been given one class C network address: that we want to divide it into three subnets, the first having 101 hosts, second 44 and the third 60. The questions are: What are the subnet addresses for these three subnets? Grundlagen der Rechnernetze - Introduction 82

83 Subnetting example [2] We have been given one class C network address: that we want to divide it into three subnets, the first having 101 hosts, second 44 and the third 60. The questions are: What are corresponding subnet masks? Grundlagen der Rechnernetze - Introduction 83

84 Subnetting example [2] We have been given one class C network address: that we want to divide it into three subnets, the first having 101 hosts, second 44 and the third 60. The questions are: What set of IP addresses cover these subnets? Grundlagen der Rechnernetze - Introduction 84

85 Subnetting example [2] We have been given one class C network address: that we want to divide it into three subnets, the first having 101 hosts, second 44 and the third 60. The questions are: What are CIDR notations for subnets? / / / 26 Grundlagen der Rechnernetze - Introduction 85

86 Addresses example Given are following IP addresses in CIDR notation. Determine whether these addresses are subnet, host or broadcast addresses / / / / 16 Grundlagen der Rechnernetze - Introduction 86

87 Addresses example Given are following IP addresses in CIDR notation. Determine whether these addresses are subnet, host or broadcast addresses / 24 => Host address, host bits are different from 0 Grundlagen der Rechnernetze - Introduction 87

88 Addresses example Given are following IP addresses in CIDR notation. Determine whether these addresses are subnet, host or broadcast addresses / 26 => Broadcast address, host bits are all equal to 1 Grundlagen der Rechnernetze - Introduction 88

89 Addresses example Given are following IP addresses in CIDR notation. Determine whether these addresses are subnet, host or broadcast addresses / 14 => Host address, host bits are different from 0 Grundlagen der Rechnernetze - Introduction 89

90 Addresses example Given are following IP addresses in CIDR notation. Determine whether these addresses are subnet, host or broadcast addresses / 16 => Network address, host bits are equal to 0 Grundlagen der Rechnernetze - Introduction 90

91 Protocols and layers Grundlagen der Rechnernetze - Introduction 91

92 Protocol and interface Host 1 Host 2 High-Level Object High-Level Object Service Interface Service Interface Protocol Peer-to-peer Interface Protocol Grundlagen der Rechnernetze - Introduction 92

93 Protocol and interface Host 1 Host 2 High-Level Object Service Interface High-Level Object Service Interface Interoperability Protocol vs algorithm Protocol Peer-to-peer Interface Protocol Grundlagen der Rechnernetze - Introduction 93

94 Message sequence chart (MSC) H1 H2 Grundlagen der Rechnernetze - Introduction 94

95 Message sequence chart (MSC) H1 H2 RTS RTS request to send CTS CTS clear to send Data Data useful data Grundlagen der Rechnernetze - Introduction 95

96 Protocol state machine connection request/ connection response file request/ file response Wait for connection request Wait for file request close request Grundlagen der Rechnernetze - Introduction 96

97 Example H N S Service primitives: File f GET_FILE(), void ABORT_FILE_RETRIVAL(),... States: CLIENT_IDLE, CLIENT_WAITS_FOR_FILE,... Timeline: if client waits 1000ms then change to state CLIENT_ERROR Message format: FILE_REQUEST_MESSAGE: CLIENT_ADR SERVER_ADR FILE_NAME Grundlagen der Rechnernetze - Introduction 97

98 Protocol graph Host 1 Host 2 Protocol 1 Protocol 2 Protocol 1 Protocol 2 Protocol 3 Protocol 3 Protocol 4 Protocol 4 98

99 Message encapsulation Host 1 Application 1 Data Protocol 1 Host 2 Application 1 Data Protocol 1 H1 Data H1 Data Protocol 2 Protokoll 2 H2 H1 Data H2 H1 Data Protocol 3 Protocol 3 H3 H2 H1 Data 99

100 Multiplexing and demultiplexing Host 1 Host 2 Protocol 1 Protocol 2 Protocol 1 Protocol 2 Protocol 3 Protocol 3 Protocol 4 Protocol 4 100

101 Protocol stack practical example Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 101

102 OSI model OSI Open System Interconnection Communication subnet boundary Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 102

103 OSI model concepts Service set of operations that layer provides to the layer above it Protocol set of rules that determine the format and meaning of the packets (messages) that are exchanged Analogy with OO programming languages: services abstract data types; protocols implementation of services Source: Andrew S. Tanenbaum, Computer Networks, Fifth Edition, 2011 Grundlagen der Rechnernetze - Introduction 103

104 OSI model OSI Principles: 1. A layer should be created where a different abstraction is needed. 2. Each layer should perform a well-defined function. 3. The function of each layer should be chosen with an eye toward defining internationally standardized protocols. 4. The layer boundaries should be chosen to minimize the information flow across the interfaces. 5. The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity and small enough that the architecture does not become unwieldy. Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 104

105 OSI model Physical layer transmitting raw bits (or signal in general) over the communication channel Data link layer organizes raw data into the data frames (order of of bytes) and transmits frames sequentially. Sending back ACK in reliable services. Traffic regulation when we have fast transmitter and slow receiver. Control of access to the shared medium separate sublayer media access control Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 105

106 OSI model Network layer controls operation of subnet, determines how packets are routed from source to destination. Possible different types of routes static tables, routes that can be updated (at the start of each conversation) and highly dynamic routes. Handling congestion (too many packets received). Transport layer accepts data above it and splits it in smaller units, passing them to the lower layers. End-to-end layer carries communication from source to the destination. Delivering in the order in which bytes were sent or delivering isolated messages or broadcast to multiple destinations Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 106

107 OSI model Session layer allows different machines (users) to establish sessions: dialog control (whose turn is to transmit), token management (preventing two parties to attempt same critical operation) and synchronization. Presentation layer syntax and semantics of the information. Manages abstract data structures Application layer protocols needed by users Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 107

108 Internet model (TCP/IP reference model) Source: Andrew S. Tanenbaum, Computer Networks, Fifth Edition, 2011 Grundlagen der Rechnernetze - Introduction 109

109 Internet model (TCP/IP reference model) Link layer interface between hosts and transmission (not a layer in standard sense) Internet layer corresponds to network layer. Internet between the networks. Modeled over snail mail, series of packets delivered using one or more gateways. Internet Protocol (IP) and Internet Control Message Protocol (ICMP) Source: Andrew S. Tanenbaum, Computer Networks, Fifth Edition, 2011 Grundlagen der Rechnernetze - Introduction 110

110 Internet model (TCP/IP reference model) Transport layer above internet layer, allows conversation between the source and destination. Transport Control Protocol (TCP) reliable transmission and User Datagram Protocol (UDP) connectionless protocol Application layer high level protocols. Early examples: Telnet (virtual terminal), FTP (file transfer), SMTP (electronic mail) Source: Andrew S. Tanenbaum, Computer Networks, Fifth Edition, 2011 Grundlagen der Rechnernetze - Introduction 111

111 Internet protocols Source: Andrew S. Tanenbaum, Computer Networks, Fifth Edition, 2011 Grundlagen der Rechnernetze - Introduction 112

112 Comparisons (critique) of OSI and TCP/IP model OSI model Model made before protocols were made (good and bad) Bad technology and implementations (empty layers, big and slow) TCP/IP Protocols then models Not general - it cannot describe anything else but TCP/IP Does not distinguish services, services and protocols Link layer not a real layer; no distinction between physical and data layer In general a lot of ad-hoc solutions Grundlagen der Rechnernetze - Introduction 113

113 How do we use TCP (or UDP) Creating a socket int socket(int domain, int type, int protocol) domain : PF_INET, PF_UNIX, PF_PACKET,... type : SOCK_STREAM, SOCK_DGRAM,... protocol : UNSPEC,... Passive open on the server side int bind(int socket, struct sockaddr *address, int len) int listen(int socket, int backlog) int accept(int socket, struct sockaddr *address, int *len) address : enthält IP-Adresse und Port backlog : Anzahl erlaubter Pending-Connections Active open on the client side int connect(int socket, struct sockaddr *address, int len) Sending and receiving data int send(int socket, char *message, int len, int flags) int recv(int socket, char *buffer, int len, int flags) Grundlagen der Rechnernetze - Introduction 114

114 How do we use TCP (or UDP) Server side: Client side: Grundlagen der Rechnernetze - Introduction 115

115 Addresses in internet model Host 1 Host 2 Application Application Application Application Port TCP UDP UDP TCP Demux-Key IP IP IP address LINK physical Physical address LINK physical Grundlagen der Rechnernetze - Introduction 116

116 Performance Grundlagen der Rechnernetze - Introduction 117

117 Bandwidth µs 1 second Bandwidth b in this example: Grundlagen der Rechnernetze - Introduction 118

118 Bandwidth µs 1 second Bandwidth b in this example: bb = 10 6 bbbbbb = 1 MMMMMMMM Grundlagen der Rechnernetze - Introduction 119

119 Bps and bps Bytes per second vs bits per second Parameter Order of value Value KBps 2 10 Byte/s MBps 2 20 Byte/s GBps 2 30 Byte/s TBps 2 40 Byte/s Kbps 10 3 Bits/s Mbps 10 6 Bits/s Gbps 10 9 Bits/s Tbps Bits/s Grundlagen der Rechnernetze - Introduction 120

120 Bps and bps Parameter Order of value Value KBps 2 10 Byte/s MBps 2 20 Byte/s GBps 2 30 Byte/s TBps 2 40 Byte/s Kbps 10 3 Bits/s Mbps 10 6 Bits/s Gbps 10 9 Bits/s Tbps Bits/s Simplification of surpluses: Simplification: BBBBBBBB 20 nn MMMMMMMM = nn 2 ss nn 10 6 BBBBBBBB ss = 8nn 10 6 BBBBBB = 8nn MMMMMMMM ss Grundlagen der Rechnernetze - Introduction 121

121 Propagation delay d H1 H2 x Time x needed for transmission of one bit at distance d and with signal propagation speed l Grundlagen der Rechnernetze - Introduction 122

122 Propagation delay d H1 H2 x Time x needed for transmission of one bit at distance d and with signal propagation speed l xx = dd ll [ mm mm ss = ss] Grundlagen der Rechnernetze - Introduction 123

123 Delay of one 1-hop transmission d H1 H2 x Time x needed for transmission of n bits at distance d and with signal propagation speed l and bandwidth b: Grundlagen der Rechnernetze - Introduction 124

124 Delay of one 1-hop transmission d H1 H2 x Time x needed for transmission of n bits at distance d and with signal propagation speed l and bandwidth b: xx = dd ll + nn bb [ bbbbbbbb bbbbbbbb ss = ss] Grundlagen der Rechnernetze - Introduction 125

125 Delay of one 1-hop transmission H1 Propagation delay: d H2 x PPPP = dd ll Transmission delay: TTTT = nn bb [ bbbbbbbb = ss] bbbbbbbb ss Time x needed for transmission of n bits at distance d and with signal propagation speed l and bandwidth b: xx = PPPP + TTTT Grundlagen der Rechnernetze - Introduction 126

126 Delay of one multi-hop transmission H1 d H2 x Time x needed for transmission of n bits at distance d and with signal propagation speed l and bandwidth b and queuing time q: Grundlagen der Rechnernetze - Introduction 127

127 Delay of one multi-hop transmission H1 d H2 x Time x needed for transmission of n bits at distance d and with signal propagation speed l and bandwidth b and queuing time q: xx = dd ll + nn bb + qq [ss] Grundlagen der Rechnernetze - Introduction 128

128 Round-trip time (RTT) H1 d H2 RTT Round-trip time time needed for the signal to be sent plus time it takes to get the acknowledgment for that signal RRRRRR = 22 PPPP Grundlagen der Rechnernetze - Introduction 129

129 Bandwidth delay product Bandbreite Delay Definition: Number of the bits n that are contained in one channel with latency of l and bandwidth of b nn = ll bb Grundlagen der Rechnernetze - Introduction 130

130 Bandwidth delay product Bandbreite Delay Example: Number of the bits n that are contained in one channel with latency of 100ms and bandwidth of 50Mbps nn = bbbbbbbb ss 0,1ss = bbbbbbbb Grundlagen der Rechnernetze - Introduction 131

131 Transfer time and effective throughput H1 l H2 x Grundlagen der Rechnernetze - Introduction 132

132 Transfer time and effective throughput H1 l H2 x Example: Calculation of transfer time z and effective throughput d and when retrieving a 1MB file over a channel with bandwidth of 1Gbps and RTT of 92ms. zz = 1MMMM 8MMMM + 0,092 1GGGGGGGG 1GGGGGGGG + 0,092 = bb bb dd = 1MMMM ss 8MMMM ss ss + 0,092 = 0, ,008 = 0,1ss = 80MMMMMMMM 1GGGGGGGG!!! Grundlagen der Rechnernetze - Introduction 133

133 Bit error rate and packet error rate Bit error rate (BER) Packet 1 Packet 2 Packet 3 Packet 4 Packet error rate (PER) Grundlagen der Rechnernetze - Introduction 134

134 Bit error rate and packet error rate Bit error Packet 1 Packet 2 Packet 3 Packet 4 Packet error Connection between BER and PER for n bit message without correction: PPPPPP = 1 (1 BBBBBB) nn Grundlagen der Rechnernetze - Introduction 135

135 Additive and bottleneck costs H1 10ms 5ms R2 10ms 20ms e e 2 e 1 3 e4 1Mbps R1 1Gbps 1Gbps R3 1Mbps H2 Grundlagen der Rechnernetze - Introduction 136

136 Additive and bottleneck costs H1 10ms 5ms R2 10ms 20ms e e 2 e 1 3 e4 1Mbps R1 1Gbps 1Gbps R3 1Mbps H2 Example: What is delay d und bandwidth b between hosts H1 and H2 nn dd = DDDDDDDDDD(ee ii ) = 45mmmm ii=1 bb = min 1 ii nn BBBBBBBBBBBBBBBBB(ee ii) = 1MMMMMMMM Grundlagen der Rechnernetze - Introduction 137

137 Multiplicative costs H1 p p 1 =2/3 2 =1/3 R2 p 3 =1/2 p 4 =1/2 e e 2 e 1 3 e4 R1 R3 H2 Grundlagen der Rechnernetze - Introduction 138

138 Multiplicative costs H1 p p 1 =2/3 2 =1/3 R2 p 3 =1/2 p 4 =1/2 e e 2 e 1 3 e4 R1 R3 H2 Example: What is the total packet success rate with given packet error rates per link. nn rr = 1 (1 pp ii ) ii=1 Grundlagen der Rechnernetze - Introduction 139

139 Performance example of effective throughput with packet switching Grundlagen der Rechnernetze - Introduction 140

140 Delay savings Circuit switching Message switching Packet switching H1 R1 R2 H2 H1 R1 R2 H2 H1 R1 R2 H2 Grundlagen der Rechnernetze - Introduction 141

141 Delay savings Circuit switching Message switching Packet switching H1 R1 R2 H2 H1 R1 R2 H2 H1 R1 R2 H2 Grundlagen der Rechnernetze - Introduction 142

142 Delay savings Circuit switching Message switching Packet switching H1 R1 R2 H2 H1 R1 R2 H2 H1 R1 R2 H2 Grundlagen der Rechnernetze - Introduction 143

143 Delay savings Circuit switching Message switching Packet switching H1 R1 R2 H2 H1 R1 R2 H2 H1 R1 R2 H2 Grundlagen der Rechnernetze - Introduction 144

144 Influence of the packet size H1 R1 R2 H2 Message size Packet payload Packet header Bandwidth Delay per hop Number of hops n bits k bits c bits b bps d seconds h Effective throughput x xx = nn tt ; tt = PPPP + TTTT Grundlagen der Rechnernetze - Introduction 145

145 Influence of the packet size H1 R1 R2 H2 Message size Packet payload Packet header Bandwidth Delay per hop Number of hops n bits k bits c bits b bps d seconds h Effective throughput x xx = nn tt ; tt = PPPP + TTTT = hh dd + (nn kk + hh 11) kk + cc bb Grundlagen der Rechnernetze - Introduction 146

146 Example plot Effective Throughput in Gbps Message size 1 GB Bandwidth 1 Gbps Header size 64 Byte Number of hops 10 Delay per hop 10 ms Packet size in KB Grundlagen der Rechnernetze - Introduction 147

147 History and present Grundlagen der Rechnernetze - Introduction 148

148 Packet switching the first generation The end of 1950s Cold war at its peak; DoD (USA department of defense) looks for command and control center that could survive nuclear attack During 1960s Contract with RAND corporation (still looking for a solution). Paul Baran develops a distributed and fault tolerant system as a basis for packet switching. AT&T thinks it is not feasible. Structure of telephone systems Baran s distributed switching system Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 149

149 ARPANET 1967 Feasibility of packet switched networks Donald Davies (at NPL) independently developed packet switching system as a campus network. They referenced work from Paul Baran 1969 (D)ARPA contracted consulting company BBN to develop that kind of network and necessary software. Graduate students from the University of Utah developed host software. Result: ARPANET Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Structure of packet switched subnet according to Clark Dec 1969 Jul 1970 Mar 1971 Apr 1972 Sep 1972 Development of ARPANET Grundlagen der Rechnernetze - Introduction 150

150 ARPANET and NSFNET 1974 First ARPANET protocol (Vinton Cerf and Robert Kahn) ARPA pushed usage of TCP/IP; University of California Berkeley integrated these protocols in Berkeley Unix Late 1970s end of 1980s TCP/IP emerged in its nearly final form Associated standards were published in 1981 Form the 1. January 1983 TCP/IP became the only approved part of ARPANET NSF backbone 1988 Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 151

151 Commercialization of Internet During 1980s IP addresses becoming more expensive (scarce); development of hierarchical name structure DNS domain name system Further growth of network (universities, research labs, libraries, ); problems with overload; NSF contract MERIT (consortium from Chicago) to continue operating the network; upgrade of backbone (56kbps -> 448kbps ->1.5Mbps) Merger of ARPANET and NSFNET followed by many other regional networks (Canada, Europe, Pacific) 1990 First step of commercialization of internet NSFNET donated to nonprofit corporation ANS (Advanced Networks and Services MERIT, MCI, IBM); further upgrade of the backbone 1.5 Mbps -> 45Mbps NSF ensures fair competition (through the agreements with PacBell, Ameritech, MSF and Sprint) 1995 ANSNET sold to American Online. Real commercialization of IP services Grundlagen der Rechnernetze - Introduction 152

152 WWW During 1990s Development in other countries EuropaNET and EBONE (started at 2Mbps then upgraded to 34Mbps) Until early 1990s Internet was mainly used in academia. Everything changed with development of world wide web (WWW) Tim Berners-Lee (CERN physicist) and Mosaic Browser Marc Andersen (National Center for Supercomputer Applications in Urbana Illinois) Rise of Internet Service Providers increased number of home computers on the internet (dial-up service) Grundlagen der Rechnernetze - Introduction 153

153 Simplified overview of Internet today Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 154

154 Wide area data networks evolution 1970s X.25 system connection-oriented wide area data networks of the first generation. System was used for a decade. 1980s Frame relay system mostly used for connections of LANs (even until today) 1990s Development of ATM (asynchronous transfer mode); the main aim was transfer of speech, data, cable TV, telegraph using one type of data network. ATM did not achieved awaited success but it is used for data transport of Internet traffic Grundlagen der Rechnernetze - Introduction 155

155 Local area networks Early 1970s Norman Abrahamson and colleagues from the university of Hawaii developed wireless (short range radio) ALOHANET. They were using computers from neighboring islands to communicate with main computer in Honolulu 1976 Using previous work from Abrahamson, Bob Metcalfe and David Boggs (Xerox PARC) developed the first LAN, called Ethernet, data rate of 2,94Mbps 1978 Xerox Ethernet is standardized by DEC, Intel and Xerox (10 Mbps Ethernet) Grundlagen der Rechnernetze - Introduction 156

156 Local area networks 1978 onwards Bob Metcalfe founded company 3Com which sold over 100 Millions of Ethernet adapters Development of Ethernet (100 Mbps and 1000 Mbps, switching, cabling) Token bus and token ring were added Middle of 1990s Standardization of Ethernet compatible wireless communication network WiFi Grundlagen der Rechnernetze - Introduction 157

157 Standardization communities Telecommunication ITU International Telecommunication Union International Standards ISO IEEE International Standards Organization Institute of Electrical and Electronics Engineering Internet standards ISOC IAB IRTF IETF Internet Society Internet Architecture Board Internet Research Task Force Internet Engineering Task Force IEEE 802 Working-Groups Source: Andrew S. Tanenbaum, Computer Networks, Fourth Edition, 2003 Grundlagen der Rechnernetze - Introduction 158

158 Overview and conclusion Definition of a network Scalability (hierarchical aggregation) Addressing, routing, forwarding Multiplexing Layering and protocols (separation of concerns) OSI model and Internet (TCP/IP) model Latency and bandwidth Standardization Grundlagen der Rechnernetze - Introduction 159

159 Literature [PetersonDavie2007] Larry L. Peterson and Bruce S. Davie, Computer Networks: A Systems Approach, Edition 4, Requirements 1.3 Network Architecture Application Programming Interface (Sockets) 1.5 Performance What is an Internetwork? Global Addresses Datagramm Forwarding in IP Subnetting Classless Routing (CIDR) [Tanenbaum2003] Andrew S. Tanenbaum, Computer Networks, Fourth Edition, Example Networks 1.6 Network Standardization Grundlagen der Rechnernetze - Introduction 160