Chapter 1: Conceptual Basis Section 1

Transcription

1 1 Chapter 1: Conceptual Basis Section 1 V 2.2 Based on textbook Conceptual Computer s by: 2019 José María Foces Morán, José María Foces Vivancos. All rights reserved

2 Leading questions 2 What are the principles guiding the communication between two parties? When can a communication be considered fast and efficient? What are the landmarks about the development of Internet? Why is networking essential for progress? What is a network architecture? 2018 José María Foces Morán, José María Foces Vivancos

3 Flow of topics 3 Motivation architecture Core Concepts Patterns Core metrics Media Hosts and s Layers and service interfaces Signals Essential Data Communications Performance of networks Information and Coding 2018 José María Foces Morán, José María Foces Vivancos

4 Cooperating host applications 4 s are computer programs Communicate over the Internet At work, at home and mobile s Vastly differing requirements smtp, pop3, imap File Sharing, file transfer: ftp, rcp, scp Printer sharing Virtual terminal: telnet, ssh (Secure Shell) e-commerce Geolocation World Wide Web (www) Social s Instant Messaging (Whatsup, ) Elastic Delay intolerant Real time storage Streaming Audio/Video Video conferencing IP Telephony Tolerant Non-delay adaptive Delay-adaptive Speed-adaptvie Delay-adaptive 2018 José María Foces Morán, José María Foces Vivancos Summary graph by Larry Peterson and Bruce Davie (From Clark, Schenker and Zangh)

5 Essential Internet service: www 5 n Web pages are downloaded by the client from the server n Client and server speak the http protocol n http = Hyper Text Transfer Protocol Server n n www = World Wide Web: n A distributed, Client/Server application n n Server program (e.g., Apache) Client program (e.g., Firefox) URL n Uniform Resource Locator n Client C Internet n HTTP, in turn uses the TCP protocol for reliability n TCP = Transmission Control Protocol n TCP provides reliability n In case of packet loss, duplication, errors, etc 2018 José María Foces Morán, José María Foces Vivancos

6 Units and multipliers 6 Bandwidth Directly related to the acceptable speed of bit transmission over some medium Number of bits transmitted in one second: Bps (Bits Per Second = Bits/Sec) Since bandwidth is a rate, the multipliers take on the following values: K (Kilo = 10 3 ) M (Mega = 10 6 ) G (Giga = 10 9 ) T (Tera = ) Delay Seconds How much time it takes to transport one bit from a source to a destination directly connected Propagation delay Jitter The variance of the delay 2018 José María Foces Morán, José María Foces Vivancos

7 7 Architecture Manage the complexity of networks 2018 José María Foces Morán, José María Foces Vivancos

8 Logical channels 8 s communicate over the Internet The channel between two communicating applications is logical Client S-1 Client S-2 Client U-1 Server S Server T Server U Each channel: Connects two applications Android Client T-2 Client T-1 Internet Hosts must be identified: Linux n IP address s must be identified: n Port numbers How to hide network complexity from application programmers? 2018 José María Foces Morán, José María Foces Vivancos

9 Layering in hosts and network End host A TCP UDP IP Subnetwork NETWORK IP Subnetwork End host B TCP UDP IP Subnetwork Server Internet Client C 2018 José María Foces Morán, José María Foces Vivancos

10 Internet Architecture 10 complexity is organized into 4 layers Each layer Offers a set of services to the upper layers The mechanism that attains each service is a protocol An upper layer avails one service from a lower layer by calling its interface 4 3 Internet 1. Subnetwork: Ethernet, Wi-Fi, Bluetooth 2. : Only IP!!! 3. : TCP and UDP 4. : Whatsup and innumerably others 2 1 Subnetwork 2018 José María Foces Morán, José María Foces Vivancos

11 Internet Architecture 11 4 Internet Subnetwork 1 Subnetwork 2018 José María Foces Morán, José María Foces Vivancos

12 Typical Internet Protocol Stack 4 ssh http Ntp DHCP 3 TCP UDP ICMP 2 ARP IP Subnetwork 1 Wi-Fi Ethernet Bluetooth 2018 José María Foces Morán, José María Foces Vivancos

13 Implementation of protocols Process 1 Process 2 Process n Linux kernel Internet Architecture FIFOs Subnetwork TCP module (software) IP module IP input buffer (FIFO) Frame (bits) Interface Card (NIC) 2018 José María Foces Morán, José María Foces Vivancos Frame (signals) Transmission media (Copper wires)

14 Internet Architecture 14 Defined by IETF (Internet Engineering Task Force) Three main features Does not imply strict layering. The application is free to bypass the defined transport layers and to directly use IP or other underlying networks An hour-glass shape wide at the top, narrow in the middle and wide at the bottom. IP serves as the focal point for the architecture In order for a new protocol to be officially included in the architecture, there needs to be both a protocol specification and at least one (and preferably two) representative implementations of the specification

15 15 Protocols and their Services Protocols offer services 2018 José María Foces Morán, José María Foces Vivancos

16 7-layer OSI Architecture 16 A Reference Model Not used today Layering is strict OSI host 1 OSI host 2 NETWORK 2018 José María Foces Morán, José María Foces Vivancos

17 Description of Layers 17 Layer Handles the transmission of raw bits over a communication link Data Link Layer Collects a stream of bits into a larger aggregate called a frame adaptor along with device driver in OS implement the protocol in this layer Frames are actually delivered to hosts Layer Handles routing among nodes within a packet-switched network Unit of data exchanged between nodes in this layer is called a packet OSI Architecture The lower three layers are implemented on all network nodes 2018 José María Foces Morán, José María Foces Vivancos

18 Description of Layers 18 Layer Implements a process-to-process channel Unit of data exchanges in this layer is called a message Layer Provides a name space that is used to tie together the potentially different transport streams that are part of a single application Layer Concerned about the format of data exchanged between peers Layer Standardize common type of exchanges OSI Architecture The transport layer and the higher layers typically run only on end-hosts and not on the intermediate switches and routers 2018 José María Foces Morán, José María Foces Vivancos

19 Strict layering in OSI OSI 19 A layer just uses the services provided by the layer below The internal mechanisms of each layer remain hidden Layer N+1 knows nothing about the internal mechanisms of layer N Example: layer can only use the layer X 2018 José María Foces Morán, José María Foces Vivancos

20 Layering in Internet 20 A layer may use the services provided by any layer below The internal mechanisms of each layer remain hidden Layer N+1 knows nothing about the internal mechanisms of layer N Example: An protocol may use whichever lower layer Subnetwork 2018 José María Foces Morán, José María Foces Vivancos

21 Protocol: The foreman of a service 21 Layer N Layer N+1 uses a service from Layer N Layer N + 1 Layer N 2 Layer N at host A sets protocol N in motion to fulfil the service requested by N + 1 Layer N A B 2018 José María Foces Morán, José María Foces Vivancos

22 Layer N+1 uses a service at Layer N 22 Layer N Several services: SVC1, SVC2 Each service is accessed through its Service Interface: SIF1, SIF2 The protocol N (Host A) fulfils the functionality offered by SVC by exchanging messages with protocol N at Host B These messages comprise the Peer-to-Peer Interface Layer N+1 Protocol N + 1 Protocol N + 1 SIF 1 SIF 2 SIF 3 SIF 1 SIF 2 SIF 3 Layer N SVC1 SVC2 SVC3 SVC1 SVC2 SVC3 Protocol N Protocol N Peer-to-peer Interface Host A Host B 2018 José María Foces Morán, José María Foces Vivancos

23 Layer N+1 uses a service at Layer N 23 Example: Host A runs Windows, host B runs Linux Services at each host are exactly the same However, Service Interfaces might be vastly different in each system The Peer-to-peer interface must be honored by each instance of Protocol N Layer N+1 Protocol N + 1 Protocol N + 1 SIF 1 SIF 2 SIF 3 SIF 1 SIF 2 SIF 3 Layer N SVC1 SVC2 SVC3 SVC1 SVC2 SVC3 Protocol N Protocol N Peer-to-peer Interface 2018 José María Foces Morán, José María Foces Vivancos Host A Host B

24 Peer-to-peer interface 24 The syntax and the semantics of the messages exchanged by the two peers must follow a formal specification Normally, we refer to the peer-to-peer interface with the same word: protocol Protocols of Internet are specified by the IETF RFC: Request For Comments Example: The ICMP protocol is specified in RFC José María Foces Morán, José María Foces Vivancos

25 Encapsulation and Multiplexing 25 What information is sent from N+1 to N through the SIF (Service Interface)? Protocol N+1 sends a N+1 Data Unit to Protocol N Protocol N encapsulates the N+1 Data Unit into a fresh N Data Unit: n Payload(N+1) + (N) n This scheme is reproduced at each service use Layer N+1 N+1 Data Unit Layer N N Data Unit N+1 Data Unit Payload 2018 José María Foces Morán, José María Foces Vivancos

26 Illustration of encapsulation in OSI Internetwork header (Preamble) header header header 2018 José María Foces Morán, José María Foces Vivancos

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30 Payload

31 Payload

32 Payload

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36 Encapsulation at layer 4 is encapsulated into a Protocol Data Unit (TPDU) = + Payload()

37 Encapsulation at layer 4 is encapsulated into a Protocol Data Unit (TPDU) = + Payload()

38 Encapsulation at layer 4 is encapsulated into a Protocol Data Unit (TPDU) = + Payload()

39

40 Payload

41 Payload

42 Payload

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45 Encapsulation at layer 3

46 Encapsulation at layer 3

47 Payload

48 Payload

49 Payload

50 Payload

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55 Encapsulation at layer 2

56 Encapsulation at layer 2

57 Encapsulation at layer 2 Payload

58 Payload

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60 Preamble (Phys layer synchronization) Phys hdr Bit stream to be transmitted over the wire

61 Preamble (Phys layer synchronization) Phys hdr Bit stream to be transmitted over the wire

62 Preamble (Phys layer synchronization) Phys hdr Bit stream to be transmitted over the wire

63 Preamble (Phys layer synchronization) Phys hdr Bit stream to be transmitted over the wire

64 Preamble (Phys layer synchronization) Phys hdr Bit stream to be transmitted over the wire

65 (Preamble)

66 ? (Preamble)

67 ? (Preamble)

68 De-encapsulation at layer 1 (Supress the preamble) Preamble (Phys layer synchronization) XPhys hdr Bit stream received over the wire T

69 De-encapsulation at layer 1 (Supress the preamble) Preamble (Phys layer synchronization) XPhys hdr Bit stream received over the wire T

70 Bit stream received over the wire T

71 Bit stream received over the wire T

72 Bit stream received over the wire T

73 De-encapsulation at layer 2 X Bit stream received over the wire T

74 Bit stream received over the wire T

75 Bit stream received over the wire T

76 Bit stream received over the wire T

77 De-encapsulation at layer 3 X Bit stream received over the wire T

78 Bit stream received over the wire T

79 Bit stream received over the wire T

80 Bit stream received over the wire T

81 De-encapsulation at layer 4 X Bit stream received over the wire T

82 Bit stream received over the wire T

83 Bit stream received over the wire T

84 Bit stream received over the wire T

85 Bit stream received over the wire T

86 Bit stream received over the wire T

87 Bit stream received over the wire T

88 Bit stream received over the wire T

89 Preamble (Phys layer synchronization) Phys hdr Bit stream received over the wire T

90 Multiplexing 90 Transmitter multiplexes several flows by having each layer add its header which contains addressing information Multiplex Demultiplex Phys hdr Phys hdr Bit stream transmitted over the wire Bit stream received over the wire T

91 Demultiplexing 91 Receiver demultiplexes several flows by having each layer analyze its header which contains addressing information about the upper-layer protocol that is to receive the payload Multiplex Demultiplex Phys hdr Phys hdr Bit stream transmitted over the wire Bit stream received over the wire T 2018 José María Foces Morán, José María Foces Vivancos

92 92 Connectivity Computer s connect computers; the many more, the better

93 Theoretical connectivity Connectivity is the capacity of connection of a network If a network has N hosts, its connectivity is: N (N-1) N 2 Metcalf s law: The connectivity of a network grows fast as we add more nodes (N 2 ) Connectivity = 1 Connectivity = 2 Connectivity = 3 x 2 = 6 + Connectivity = = 12 6 nodes Connectivity = 6 x 5 = 30 6 nodes

94 Theroretical connectivity is bounded by network technology Metcalf s law: Represents the potential connectivity of a network Nodes communicate by sending/receiving messages through the links which bandwidth is limited Each node must have some knowledge about the topology of the network These factors limit the use of the potential connectivity Connectivity = 1 Connectivity = 2 Connectivity = 3 x 2 = 6 + Connectivity = = 12 6 nodes Connectivity = 6 x 5 = 30 6 nodes

95 Scalable connectivity Not all network technologies use the available connectivity with the same efficiency Ethernet can function efficiently up to certain network size: we say that Ethernet scales well up to that limit. Then, how come the Internet has 2000M hosts? How can the Intenet scale to such a huge size so well? IP protocol

96 Scalable connectivity

97 97 Based on textbook Conceptual Computer s by: 2018 José María Foces Morán, José María Foces Vivancos. All rights reserved End of Ch 1 Section 1