Data Communications and Networks

Transcription

1 Data Communications and Networks Deirdre O Donovan Deirdre.odonovan@gmit.ie Ext : 2142 Data Comms & Networks 1

2 Module Content ISO Model 5% Function of various layers Comparison with TCP/IP layers Data Transmission Overview 10% Physical Layer Data Link Layer Error handling: Parity, Checksum, CRC, etc Ethernet History Frame Formats Topology Fast Ethernet, Gigabit Ethernet, Switched Ethernet Data Comms & Networks 2

3 Module Content contd Internet Core Protocols 30% IP IP Addressing Subnetting ARP IP Routing TCP UDP Network Programming 25% Client / Server Applications Sockets Interface / Sockets API Development of network-based applications Port Usage Data Comms & Networks 3

4 Module Content contd Internet Support Protocols 20% DNS DHCP NAT IPSec Other Services Local Area Network Technologies 10% Fast Ethernet Token Ring / Token Bus FDDI ATM Switched / Virtual LANs Network Management Data Comms & Networks 4

5 Suggested Reading Data and Computer Communications, 7 th Ed, W. Stallings (2007) Computer Networks with Internet Protocols and Technology, 1 st Ed, W. Stallings (2004) Computer Networks, 4 th Ed, A.Tanenbaum (2003) Internetworking with TCP/IP, 5 th Ed, (Vol 1 Principles, Protocols & Architecture) D. Comer ( 2006) Internetworking with TCP/IP, 4 th Ed, (Vol 2 Design, Implementation and Internals) D. Comer ( 2001) Other text and reference journals Data Comms & Networks 5

6 OSI Open Systems Interconnection Developed by the International Organisation for Standardization (ISO) in 1984 A theoretical system delivered too late! Key points Modular Hierarchical Boundaries between layers -> Interfaces Seven layers TCP/IP is the de facto standard Data Comms & Networks 6

7 OSI - The Model A layer model Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers Modular, ties in very well with modern day OO paradigm Data Comms & Networks 7

8 OSI - The Model Divides the communication problem into subpieces called layers It is a not a protocol, a prototcol suite or a piece of software. It is simply a model or guideline for protocol designers. The model divides the communication problem into subpieces or layers. The ISO model identifies seven subpieces to solving the problem. Data Comms & Networks 8

9 OSI Layers Application Layer 7 Presentation Layer 6 Session Layer 5 Transport Layer 4 Network Layer 3 Data Link Layer 2 Physical Layer 1 Data Comms & Networks 9

10 The OSI Environment Data Comms & Networks 10

11 Layers And Packet Headers Each layer : Prepends header to outgoing packet. Removes header from incoming packet. Software implementing layer N at the destination receives exactly the message sent by software implementing layer N at the source. Data Comms & Networks 11

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13 OSI Layers Physical Physical interface between devices Responsible for transmission of raw bits Always implemented through hardware Encompasses mechanical - connectors, electrical - voltage, and functional interfaces e.g. RS-232 Data Link (Media Access) Responsible for error-free, reliable transmission of data Flow control, error correction e.g. Ethernet Data Comms & Networks 13

14 OSI Layers contd Network Handles routing between networks Packet Forwarding Higher layers do not need to know about underlying technology Concerned with type of switching used (circuit v. packet) Concerned with congestion control, quality of service, etc Transport Accept data from above, split it and pass it down Ensure that piece all arrive correctly at other end Efficiently - Error free, No losses, No duplicates, In sequence True End to End layer ( Sockets in labs) Data Comms & Networks 14

15 OSI Layers contd Session Establishes logical connections between systems, i.e. session Manages log-ins, password exchange, log-offs Terminates connection at end of session Presentation Provides format and code conversion services E.g. ASN.1, Big Endian, Little Endian, ASCII to EBCDIC Data compression Encryption Application Logic needed to support various applications Data Comms & Networks 15

16 TCP/IP Protocol Architecture Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) Used by the global Internet No official model but a working one. Application layer Host to host or transport layer Internet layer Network access layer Physical layer Data Comms & Networks 16

17 The TCP/IP reference model Data Comms & Networks 17

18 Application Layer Support for higher level protocols e.g. http, SMPT, FTP, TELNET, DNS Data Comms & Networks 18

19 Transport Layer Two end-to-end protocols Transmission Control Protocol (TCP) Reliable connection-oriented protocol that allows stream of bytes be delivered without errors on another machine Reliable delivery of data Ordering of delivery User Datagram Protocol (UDP) Unreliable connectionless protocol Used for once off requests / responses ( http requests / responses) Speed Data Comms & Networks 19

20 Internet Layer (IP) Purpose of internet layer is to deliver IP packets where they are supposed to go, i.e. routing functions across multiple networks Analogy with snail mail Hosts may be attached to different networks Implemented in end systems and routers Data Comms & Networks 20

21 Host to Network Layer Great big void in reference model! Data Comms & Networks 21

22 Standards Organisations Standards in the Telecommunications World Standards in the International World Standards in the Internet World International Telecommunications Union - Telecommunication Standardization Sector (ITU-TSS). Formerly called CCITT International Organization for Standards (ISO). Member of the ITU, makes technical recommendations about data communications. American National Standards Institute (ANSI) Institute of Electrical and Electronics Engineers (IEEE) Internet Engineering Task Force (IETF) Electronic Industries Association (EIA) National Institute of Standards and Technology (NIST) Data Comms & Networks 22

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24 Internet Engineering Task Force A protocol proposed by a vendor IETF working group study the proposal IETF issues a request for comment (RFC) IETF reviews the comments IETF proposes an improved RFC The RFC becomes a proposed standard The proposed standard becomes a draft standard if two or more vendors adopt it Data Comms & Networks 24