EITF25 Internet Techniques and Applications L5: Wide Area Networks (WAN) Stefan Höst

Transcription

1 EITF25 Internet Techniques and Applications L5: Wide Area Networks (WAN) Stefan Höst

2 Data communication in reality In reality, the source and destination hosts are very seldom on the same network, for example web surf. Internet 2

3 Internetworking Therefore, we need protocols and mechanisms for sending data across networks of different types. LAN LAN LAN LAN 3

4 Link protocols are not enough 4

5 Addressing and routing We need an address system that is universal for all networks. This is called the network address. We need rules for how data is forwarded from network to network to the destination. This is called routing. We need network entities that are connected to several networks and can forward data between networks. These entities are called routers. 5

6 Network protocol Therefore, we need a universal network protocol that handles the connection across networks. source destination Application Application Network Network protocol router Network Network protocol Network Link Link Link PHY PHY PHY 6

7 Host-to-host delivery 7

8 Datagram networks In this course, we basically only consider packet switched datagram networks, where each packet is treated independently of all others

9 Transmission delay Each router has buffers so that packets can be stored when waiting for service. The end-to-end transmission delay includes both waiting time and transmission time on links. 9

10 One network protocol: IP Internet protocol (IP) is the only network protocol used in the Internet. Addressing with IP addresses Example: (IPv4) Data is sent as IP packets (or datagrams) Datagram delivery Checksum used but no Error control or Flow control. 10

11 IP addresses (IPv4) Every host and router that are connected to the Internet have a unique network address (IP address) that is 32 bits long. The address is usually written in a dotted-decimal format. 11

12 Routing table Each router has a table with information about the next hop. The routing decision is based on the destination address. The source and destination address are included in the packet header. 12

13 Routing algorithm Routing tables are updated using a routing algorithm. The general idea is to find the route with the least cost between source and destination. Note: The networks between the routers are only represented as costs. 13

14 Transport protocol Each client computer may have several applications running. Therefore, you need a protocol that handles the end-to-end control for each application. This protocol is called the Transport Protocol. The main objective of the Transport protocol is to ensure that the data is transmitted from source to destination applications. 14

15 Transport protocol application transport network link PHY Application protocol Transport protocol application transport network link PHY 15

16 Process-to-process delivery 16

17 Logical end-to-end connection The transport protocol creates a logical (virtual) connection between source and destination. 17

18 Function of transport protocol The transport protocol encapsulates the data from the application and ensures that it is sent to the correct receiving application where the data is decapsulated. 18

19 Port numbers The transport protocol uses port numbers (addresses) for separating applications.

20 Socket address The IP address + port number becomes the socket address. 20

21 IP addresses versus port numbers 21

22 Multiplexing of applications Also, the transport protocol multiplexes and demultiplexes data from/to different applications. 22

23 A Transport protocol: TCP Transmission Control Protocol (TCP) is one of the transport protocols used in the Internet. Provides a connection-oriented service with error and flow control. TCP uses a Go-back-N ARQ algorithm for error control. 23

24 Connection-oriented service Packet 2 24

25 A Transport protocol: UDP User Datagram Protocol (UDP) is another transport protocol used in the Internet. UDP provides a connectionless service without error or flow control. 25

26 Connectionless service 26

27 Layered protocol models By using layers of protocols, the development process becomes easier since each protocol has specific tasks. The development of new applications also becomes much easier since they don t have to know that much of the underlying network infrastructures or protocols. 27

28 The OSI model In the middle of the 70s, the standardisation organisation ISO started work on a standard that should cover all aspects of network communication. In 1983, the Open System Interconnection (OSI) model was presented. The OSI model has since then been used as a framework for the design of network systems. 28

29 The OSI-model 29

30 Protocol interaction in several layers 30

31 Physical layer The physical layer is responsible for movements of individual bits from one hop (node) to the next. 31

32 Data link layer The data link layer is responsible for moving frames from one hop (node) to the next. 32

33 Network layer The network layer is responsible for the delivery of individual packets from the source host to the destination host. 33

34 Transport layer The transport layer is responsible for the delivery of a message from one process to another. 34

35 Session layer The session layer is responsible for dialog control and synchronization. 35

36 Presentation layer The presentation layer is responsible for translation, compression, and encryption. 36

37 Application layer The application layer is responsible for providing services to the user. 37

38 Connecting devices (1) Sender Application Data Protocol Receiver Application Presentation Presentation Session Session Transport Transport Network Link Physical Switch Link PHY PHY Network Link Physical 38

39 Switches are used within a network 39

40 Connecting devices(2) Sender Application Data Protocol Receiver Application Presentation Presentation Session Session Transport Network Router Network Transport Network Link Link Link Link Physical PHY PHY Physical 40

41 Routers are used between networks using the same network protocol IP network IP network 41

42 Connecting devices (3) Sender Application Data Gateway Application Receiver Application Presentation P. P. Presentation Session S. S. Session Transport T. T. Transport Network Net Net Network Link Link Link Link Physical PHY PHY Physical 42

43 Gateways are used between networks of different types (However, the definition is not really clear) IP-network Mobile network 43

44 So what happens with the data? Assume that the sender application wants to send a message to a receiver. What happens with this message in the different protocol layers on the way to the destination? Network 1 router Network 2 44

45 The sender side application transport network NH S AH S TH S AH S AHS TH S link LH S NH S TH S AH S PHY

46 Switches A switch changes the link header so that it fits the next link. To outgoing link LH X NH S TH S AH S New link header LH S NH S TH S AH S Old link header PHY 46

47 Routers A Router handles both the link and network protocol. To next network NH Z TH S AH S LH U NH S TH S AH S LH X New headers Old headers PHY 47

48 The receiver side application AH S transport TH S AH S network NH Z TH S AH S link NH Z LH U TH S AH S PHY

49 Layered data communication 49

50 Fragmentation If data from an upper layer cannot fit in one data packet, the data is fragmented (according to some prespecified rules) Layer 1 H1 data Layer 2 H2 H1+data H2 data 50

51 Reassembly At the receiver side the data is reassembled. Layer 1 H1 data Layer 2 H2 H1+data H2 data 51

52 Maximum transfer unit (MTU) A protocol may define a Maximum Transfer Unit (MTU) that specifies the maximum length of the payload that can be encapsulated. Example: 52