Data Communications w01b - Introduction_compressed.pdf

Data Communications LECTURE: INTRODUCTION AND CONCEPTS Macquarie University Data communications WHAT ARE WE LOOKING AT? What do we mean by data communications? How can we use these / plan these? Some quick definitions to help us… Macquarie University - Data Communications 2 Data communications “PROC...

Data Communications LECTURE: INTRODUCTION AND CONCEPTS Macquarie University Data communications WHAT ARE WE LOOKING AT? What do we mean by data communications? How can we use these / plan these? Some quick definitions to help us… Macquarie University - Data Communications 2 Data communications “PROCESS” Applications are made up from one or more processes Processes are independent: They run separately Progress at different rates (they are asynchronous) Macquarie University - Data Communications 3 Data communications “MESSAGES” Messages provide synchronisation between processes, as well as exchange of information. Macquarie University - Data Communications 4 Data communications “COMMUNICATION” Processes communicating by sending and receiving messages Macquarie University - Data Communications 5 The end! Questions? Data Communication HOW? What we’ll look at in this unit are some ways of managing the “how” we can communicate. Including: Sending messages over different networks What could go wrong when sending a message Core principles of computer networks Kinds and topologies of networks The “Things” we send are called “Packets” Protocols, encapsulation, and a few other concepts. Macquarie University - Data Communications 7 Concept SENDING MESSAGES We Need three things: The contents of the message The identity of the recipient How to get the message from the sender to the recipient Macquarie University - Data Communications 8 Example SENDING MESSAGES I WANT TO SEND A MESSAGE TO A COLLEAGUE: “Let’s grab a coffee later today” Macquarie University - Data Communications 9 Example SENDING MESSAGES “Let’s grab a coffee later today” Macquarie University - Data Communications 10 EASTERN ROAD SIR CHRISTOPHER ONDA ATJE AVENUE East 5 2 SCIENCE 3 ROAD 11 TECHNOLOGY PL ACE 3 75 Hospital East 4 14 6 11 WALLY’S 9WALK 11 9 7 4 5 East 2 2 Ainsworth Building 1 4 Macq R ROAD 3 EASTERN ROAD AVENUE 6 East 3 4 IN RR South 2 G RO A 12 11 HE CENTRAL SECOND WAY SECOND WAY AY WESTERN ROAD W Australian Hearing Hub 16 OR Macquarie University - Data Communications 17 OT MACQUARIE WALK M Library 8 2 S 2 M 4 WALK AD FIRST 6 RO 14 12 4 10 RA Michael Kirby Building VE Macquarie Theatre 17 13 Mason Theatre 12 PARK DRIVE 16 LA 21 Lincoln Building 15 13a 6 14 18 Mercure Hotel Parking 18 1 Central Courtyard TA 17 Service Connect Tech Bar 17 East 6 1CC Student Accommodation Price Theatre The Chancellery 19 15 23 CH SENDING MESSAGES Lighthouse GY Theatre MN AS IU M port & RO AD tic Centre AR 11 SE Amphitheatre RE NORTH Example A,B,C 3 MANAGEMENT DRIVE 5 6 7 RESEARCH PARK DRIVE Learning Circle North 4 S What we have so far AS FAR AS USER OR THE PROCESSES ARE CONCERNED Message The recipient THE NETWORK IS CONCERNED WITH MESSAGE The route – how the message gets there Macquarie University - Data Communications 12 What could go wrong? SENDING MESSAGES FOUR THINGS CAN GO WRONG — MESSAGES CAN GET Lost Delayed — causing out-of-order delivery Corrupted Duplicated Macquarie University - Data Communications 13 Concept WHAT IS A NETWORK? Macquarie University - Data Communications 14 Example NETWORKS Macquarie University - Data Communications 15 Example NETWORKS Macquarie University - Data Communications 16 Thinking about computer-based networks MANY OF THE PRINCIPLES AND CONCEPTS ARE THE SAME Entities Connections — between entities Transporting Messages — high level Bits — low level Macquarie University - Data Communications 17 Network Components ABSTRACTLY NETWORKS ARE COMPRISED OF THREE THINGS: Node: each computer system in a network Some nodes are end-points, the termination points of communication, Others are intermediary systems, forwarding traffic between links Link: connects one node to an adjacent node, with no intervening nodes. Path (route): A group of links that allows a message to move from its point of origin to its destination. Macquarie University - Data Communications 18 Example HELP ME SEND A MESSAGE TO “BOB” Macquarie University - Data Communications 19 Classifying Networks WE CAN CLASSIFY NETWORKS IN MANY DIFFERENT WAYS: 1. How they operate 2. The geographic area they cover 3. The “shape” of the network — its topology Macquarie University - Data Communications 20 1. Operational classifications “KINDS OF NETWORKS” CIRCUIT SWITCHED Point-to-point Creation and termination Exclusive Telephone network PACKET SWITCHED Multiple paths No setup Shared Data networks https://upload.wikimedia.org/wikipedia/commons/ 5/50/Telephone_operators%2C_1952.jpg Macquarie University - Data Communications 21 2. Geographic classifications “KINDS OF NETWORKS” LOCAL AREA NETWORKS Nodes are near to each other Generally a single building, or More commonly a single floor of a building BACKBONE NETWORKS Connects LANs or other networks together Normally constrained to a single organisation Macquarie University - Data Communications METROPOLITAN AREA NETWORKS Connects networks together across a single metropolitan area Normally operated by a communications provider WIDE AREA NETWORKS Connects networks together at a larger scale Scales from between cities to between continents 22 3. Topological classifications “KINDS OF NETWORKS” Point-to-point Bus (multi-drop) Tree Ring Star (Full) Mesh Macquarie University - Data Communications Partial mesh 23 Network Layouts LOGICAL VS PHYSICAL REPRESENTATIONS Physical Layout EXAMPLE USING A TRAIN NETWORK Macquarie University - Data Communications 25 Logical / Abstract Layout EXAMPLE USING A TRAIN NETWORK Macquarie University - Data Communications 26 Representations “KINDS OF NETWORKS” LOGICAL TOPOLOGY How it operates Algorithmic The “logic” of operation PHYSICAL TOPOLOGY How it looks How does it “plug together” WE WILL TAKE A CLOSER LOOK AT THIS IN THESE TWO TOPICS: Local Area Networks The data-link layer Macquarie University - Data Communications 27 As Previously Mentioned NETWORKS CAN BE EITHER BE CIRCUIT SWITCHED Like a telephone conversation An exclusive pathway is established between the two end-points. Simultaneous conversations can occur but only between strictly separate pairs of end-points Macquarie University - Data Communications PACKET SWITCHED Like the postal service Items of varying sizes are passed between multiple pairs of end-points over a shared network For this to occur we must break our communication into discrete chunks called packets 28 “Packetisation” WE CAN’T SEND EVERYTHING AT ONCE - SO BREAK IT UP PACKETS CONSIST OF 2 THINGS A Header which contains Metadata A Payload or Body which contains Data Macquarie University - Data Communications 29 Metadata “DATA ABOUT DATA” What would a courier need to know about the packet to work out what to do with it? Macquarie University - Data Communications 30 Metadata “DATA ABOUT DATA” What are some other metadata examples for packets What is the destination What time was is sent Who sent it? Can you think of other examples of Metadata more generally? Macquarie University - Data Communications 31 Protocols and Standards IN DATA COMMUNICATIONS Communicating (protocol) “OPERATIONAL CLASSIFICATION” HUMAN PROTOCOL NETWORK PROTOCOL Hi TCP connection req. Hi TCP connection reply. Got the time? Get http://gaia.cs.umass.edu/index.htm 2:00 ti Macquarie University - Data Communications 33 Protocols vs Standards WHAT IS THE DIFFERENCE KEY DIFFERENCES: Level of detail step-by-step vs broad guidelines Development individual companies/groups vs recognised organisations Implementation Directly implemented on devices vs definition on how to implement protocols Macquarie University - Data Communications 34 Protocols HOW DO THEY WORK? At the sending computer, the protocol: Breaks the data into smaller sections, called packets, that the protocol can handle. Adds addressing information to the packets so that the destination computer on the network will know the data belongs to it. Prepares the data for actual transmission through the network adapter card and out onto the network cable. Macquarie University - Data Communications 35 Protocols HOW MANY PROTOCOLS ARE THERE? Communicating computers need to send a lot of information to each other, for example: are you still there? this message is to be sent to X the last message was in error the number of bits in this message is N we could use a single protocol to carry all the necessary information not a good idea - the implementation would be large and difficult to maintain Macquarie University - Data Communications 36 Protocol Layers BREAK THE “ROLES AND RESPONSIBILITIES INTO LAYERS” PROTOCOLS WORK TOGETHER Sending data from one node to the next along a single link is a different problem than sending data from one building to another, which is a different problem to sending data to the other side of the world Good engineering practice, take a large complicated problem and break it into smaller problems which can be more easily solved. Different protocols solve different problems Macquarie University - Data Communications 37 These layers form a “Protocol Stack” A protocol stack is a combination of protocols arranged in a layered format. Each layer specifies a different protocol for handling a function or subsystem of the communication process. Each layer has its own set of rules. Standard Protocol stack – examples OSI model Internet (TCP/IP) protocol stack. Macquarie University - Data Communications 38 Protocols and Standards A SYMBIOTIC RELATIONSHIP A protocol is embodied in a standard A standard specifies a protocol A standard can describe one protocol in one layer, a standard can describe an entire stack… Macquarie University - Data Communications 39 Standards WHO SETS THESE STANDARDS? The lowest layers in a protocol stack are generally defined by the IEEE The middle layers of the TCP/IP stack are defined by the IETF The upper layers may or may not be standardised Example, the protocols that operate the web are defined by the W3C Macquarie University - Data Communications 40 Network Models OSI AND TCP/IP OSI reference model LAYER 1 CLOSER TO PHYSICS, UPPER LAYERS CLOSER TO YOUR APPLICATION Macquarie University - Data Communications 42 The OSI reference model HOW TO REMEMBER THE LAYERS? Please Do Not Throw Sausage Pizza Away Macquarie University - Data Communications 43 Internet Model AKA TCP/IP MODEL Macquarie University - Data Communications 44 Side by side OSI AND THE TCP/IP MODELS Network Models from the textbook, “Business Data Communications and Networking”, FitzGerald et al, 13 ed, pg 8 Macquarie University - Data Communications 45 “Protocol headers” EACH LAYER ADDS ITS OWN HEADER Data in each header layer is only for corresponding layer at the receiver. Other layers may not (in general touch this information) – encapsulation In practicals we will analyse these headers (one week for each layer) This will help us understand what each layer does. Macquarie University - Data Communications 46 Encapsulation ENVELOPE INSIDE AN ENVELOPE INSIDE AN … NESTING PACKET HEADERS The application layer contains the actual message generated by the application (or user) Each lower layer wraps the message with its own header (metadata) Macquarie University - Data Communications 47 Encapsulation ENVELOPE INSIDE AN ENVELOPE INSIDE AN … Macquarie University - Data Communications 48 “Headers” THE METADATA FOR A PACKET … IPv4 Header: 192 bits IPv6 Header: 320 bits Macquarie University - Data Communications 49 Addressing WHERE TO SEND THE MESSAGE TO? Addressing WHERE TO SEND MESSAGES TO In general to send anything to a destination we need an address We have several different kinds of addresses at different layers Carl’s address is one location, but what if the office number gets renamed? Is it still the same location? Macquarie University - Data Communications 51 Addressing in different layers Layer Address Kind Applicati on Application Dependent HTTP - URLs Port - destination Transport Network Data Link Physical application IP Address IPv4 IPv6 MAC address (Ethernet) Computer Representati on String Human Representati on String Example 16 bit field Number 0-65,535 24 32 bit field 128 bit field 48 bit field (6 octets) 4 decimals 0-255 6x2 hex digits 134.57.33.2 4534:4EF3:4AFD:A43F:4567:E34F:236B: AE:56:23:F4:65:D3 N/A Bits are broadcast on link, i.e.., flood. Bits put in one end N/A come out the other! … Types of addresses in different layers, Textbook, page 120 Macquarie University - Data Communications 52 Addressing on the Internet WHO’S WHO ON THE INTERNET? Every computer needs a unique address In the Internet this is a called an IP address IP stands for Internet Protocol IP is the network layer protocol for the internet, responsible for addressing and delivery of messages Macquarie University - Data Communications 53 IPv4 Addresses WHO’S WHO ON THE INTERNET? 32 bit (4 byte) addresses In the computer stored in binary, but for human convenience written in decimal A byte can hold values in the range 0-255 Each byte in an IP address written separately using so-called “dotted decimal” notation, so an example IP address is: 127.97.201.4 Questions: What is the maximum number of addresses IPV4 can support? How many computing devices do we have on the internet? Macquarie University - Data Communications 54 Big Ideas from today WHAT HAVE WE BEEN FOCUSING ON? Concepts: applications, processes, messages, packetising. Views of a network (Logical, physical) Network classifications: Circuit-switched, packet-switched. Local, backbone, metropolitan, and wide area networks. Topologies Layouts Packets, Metadata, and packet headers OSI and Internet models for layers Addressing at different layers After the lecture >>> Complete the Minute paper for Week 1 (see iLearn)