Olum-fonoon Babol Computer networks course Chapter 1 Introduction

Olum-fonoon Babol Computer networks course Chapter 1 Introduction Fall 2005 By: H. Veisi

Basic information q Text book ¥ Necessary Ø Andrew Tanenbaum, “Computer Networks, 3 rd Edition”, 1996. [4 th edition is available] ¥ Recommended Ø James F. Kurose and Keith W. Ross, “Computer Networking , A Top-Down Approach Featuring the Internet”, 2001. Ø Stallings, William, “Data and Computer Communications, 6 th Edition”, 2000. q Feel free to contact me ¥ veisi@ce. sharif. edu Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 2

Evaluation q Weekly quiz 15% ¥ two ones in term q Mid term exam q Final exam 30% 45% ¥ chapters in mid-term will ignore q Project and homework 20% ¥ Project has extra grade Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 3

What You Will Learn q q q q Lots of terminology Basics of communications Internetworking Network hardware Protocols and Layering Network Addressing Routing, Flow, Error and Congestion Control Basics Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 4

What You Will NOT Learn! q Network operating systems q How to configure/operate equipment in a vendorspecific way q How to design and implement network software You will not learn working with networks! You will learn how to learn working with them Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 5

What is a Computer Network? q A collection of transmission hardware and facilities, terminal equipment, and protocols q Provides communication that is ¥Reliable ¥Fair ¥Efficient ¥From one application to another q Automatically detects and corrects ¥Data corruption ¥Data loss ¥Duplication ¥Out-of-order delivery q Automatically finds optimal path from source to destination Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 6

Network examples q Telephone q Satellite q TV programs q Internet ¥ftp ¥mail ¥Chat ¥… Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 7

Uses of Computer Networks q Business Applications ¥ online buying q Home Applications ¥ mail, chat q Mobile Users ¥ wireless: laptops, PDA, mobile, in plane q Social Issues Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 8

Business Applications of Networks q A network with two clients and one server. ¥ Check bank account ¥ Pay bills ¥ Reserve ticket q The client-server model involves requests and replies. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 9

Home Network Applications q. Access to remote information ¥ Leaning online, downloading q. Person-to-person communication ¥ chat, phone q. Interactive entertainment ¥ games, movies, … q. Electronic commerce Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 10

Home Network Applications (2( q Peer-to-peer (P 2 P) ¥Kazaa, Emule, q E-commerce Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 11

Mobile Network Users q Combinations of wireless networks and mobile computing. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 12

Social Issues q Discussions about ¥ politics, ¥ religion, ¥ … q Hack and robbery Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 13

What A Network Includes q Transmission hardware q Special-purpose hardware devices ¥ interconnect transmission media ¥ control transmission ¥ run protocol software q Protocol software ¥ encodes and formats data ¥ detects and corrects problems Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 14

Network Hardware q Transmission technology (2 types) ¥ Broadcast links ¥ Point-to-point links q Scale q Media ¥ Local Area Networks (LAN) ¥ Metropolitan Area Networks (MAN) ¥ Wide Area Networks (WAN) ¥ Wireless Networks ¥ Home Networks ¥ Internetworks Computer networking, Olum-Fonoon Babol ¥ Wire line ¥ Wireless H. Veisi Fall 2005 Page 15

Broadcast Networks q There are A single communication link for all systems in network = Broadcasting ¥ TV programs: IRIB (Islamic Republic of Iran Broadcast), … q Messages (Packets) contain destination address q Multicasting: A subset of systems can get the message q Usually used in small networks like LANs Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 16

Point-to-point q Individual connections between pairs of machines. q There are many paths from one machine to another ¥ Need efficient routing algorithms q Usually used in large scale networks like WAN Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 17

So… q Packets ¥ Messages - the "chunk" of data transmitted from one machine to the next. q Addressing ¥ One to one: Packet contains specific target address. ¥ Broadcasting: All machines on the network receive and process the packet. ¥ Multicasting: A subset of machines receive and process the packet Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 18

Classification by scale Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 19

Local Area Networks (1( q Privately owned. Can be up to several kilometers long; Ex. in a building q Separated by their: Size: Restricted so worst case transmission time can be contained. Transmission technology: Single channel with multiple machines connected to it. Run at speeds of 10, 100, or more Mbps. Topology: two popular broadcast networks: Ø Bus Ø Ring Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 20

Local Area Networks (2( q Topology … ¥ Bus Ø Ethernet (IEEE 802. 3): § Bus based broadcast network with decentralized control at 10 or 100 Mbps. ¥ Ring Ø Token Ring (IEEE 802. 5): § Ring based broadcast network with token arbitration at 4 or 16 Mbps. Low delay. High reliability. Requires collision arbitration Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 21

Metropolitan Area Networks q Larger version of LAN ("city" wide). ¥Public or private / data or voice. ¥Broadcast - no switches. ¥ Can be distinguished from LANs based on wiring mechanism. Ø DQDB (Distributed Queue Dual Bus), IEEE 802. 6 q Ex. A metropolitan area network based on cable TV Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 22

Wide Area Networks (1( q Networks spanning large distances. q Ex. Relation between hosts on LANs and the subnet. q Hosts or End Systems: ¥ Machines running user applications. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 23

Wide Area Networks (2( q (Communication) Subnet: ¥ Connections between hosts - transmission lines + switches. ¥ A "locality" understanding each other's addresses. q Circuits (Channels, Trunks): ¥ Transmission lines move the bits. q Packet switching nodes (Router, Intermediate systems): ¥ Specialized computers moving data between several inputs to several outputs. q Point-to-point/Store-and-forward/Packet-switched ¥ Moving through a series of routers, packets are received at a router, stored there, then forwarded to the next router. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 24

Wide Area Networks (3( q Ex. A stream of packets from sender to receiver. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 25

Wireless Networks (1( q Used where computer is mobile or far away from wires. ¥ ¥ ¥ Only 1 - 2 Mbps, higher error rates, interference q Use ¥ ¥ ¥ Sound Light and mirrors Infrared RF Microwave Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 26

Wireless Networks (2( q Bluetooth configuration q Wireless LAN q Ex. A flying LAN Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 27

Network Software (1( q Primary networks more depend on hardware q It talks about the philosophy of connecting together two entities. q “Layering” is the key word ¥Protocol Hierarchies ¥Design Issues for the Layers ¥The Relationship of Services to Protocols Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 28

Network Software (2( q Layers : ¥The concept that network software is organized functionally into levels. A level on one host talks to the same level on another host (its peer). q Protocol : ¥The protocol is the convention or standard that a layer uses to talk to the other layer. An agreement or standard on the conversation Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 29

Network Software (3( q Protocol Hierarchies ¥Layers, Important that each layer perform specific actions. ¥protocols, ¥Interfaces Defines the services That one layer offers another (either up or down. ) Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 30

Network Software (4( q Ex. Protocol of philosopher-translator-secretary architecture. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 31

Network Software (5( q Ex. Protocol Hierarchies ¥ information flow supporting virtual communication in layer 5 Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 32

Network Software (6( q Physical Medium: ¥ Underneath the layers is the wire or fiber or whatever. q Network architecture: ¥ A set of layers and protocols. It contains details on what happens in the layer and what the layers says to its peer. ¥ Functional interfaces and implementation details are not part of the spec, since that's not visible outside the machine. q Protocol stack: ¥ A list of protocols used by a system, one protocol per layer. q Information flow: ¥ "Send_to_peer" rather than "call_next_layer_down". Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 33

Design Issues for the Layers Connection Both Directions Simultaneous Simplex No Half duplex Yes No Full duplex q q q q No Yes Addressing Error control. (garbled or missing. ) Preservation of message ordering. Flow control. Breaking up messages into a smaller chunks (and reassembly. ) Multiplexing messages on same connection. Routing - how to get from one host to another. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 34

Connection-Oriented and Connectionless Services (1) q Connection oriented service: ¥ Like the phone system. The system establishes a connection, uses it, and closes it. Acts like a tube. Data comes out the other end in the same order as it goes in. » Connection Setup » Data Transfer » Connection Termination q Connectionless service: ¥ Like the post office. Each message has the entire address on it. Each message may follow a different route to its destination. Ordering not maintained. » Data Transfer Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 35

Connection-Oriented and Connectionless Services (2) q Quality of service (Qo. S): ¥ Will the message arrive? Ø A reliable connection-oriented service guarantees success. § Message sequence - message boundaries and order are maintained. § Byte streams - messages are broken up or combined; flow is bytes. Can pair mechanism with upper-layer requirements. q Datagram Service: ¥ Like junk mail. It's not worth the cost to determine if it actually arrived. Needs a high probability of arrival, but 100% not required. Connectionless, no acknowledgment. q Acknowledged datagram service: ¥ As above, but improved reliability via acknowledgment. q Request-reply service: ¥ Acknowledgment is in the form of a reply. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 36

Connection-Oriented and Connectionless Services (3) q Summary of six different types of service. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 37

Connection-Oriented and Connectionless Services (4) q Service Primitives for connection-oriented service ¥ Example Connect. request Connect. indication Connect. confirm Data. request Data. indication Data. request Disconnect. confirm Disconnect. indication Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 38

Connection-Oriented and Connectionless Services (5) q Example: Connection-Oriented Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 39

Services to Protocols Relationship q Services are primitives that a layer provides for the layer above it. q Protocols are rules governing the meaning of frames/packets/messages exchanged with the peer entity. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 40

Layering Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 41

Reference Models q Headers, Data, and Trailers q Encapsulation Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 42

Reference Models (1( q There are two competing models for how the software is layered. These are the OSI and the TCP models. q OSI (Open Systems Interconnection) ¥ Developed by ISO (International Standards Organization) ¥ 7 layers q TCP (Transfer Control Protocol) ¥ Used in the Arpanet and in the Internet. Common mechanism that is surpassing the OSI Model. ¥ 5 layers Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 43

Reference Models (2( Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 44

OSI Reference Model (1( q Principles used to develop OSI Layering: 1. 2. 3. 4. Need a layer for each different level of abstraction. Each layer performs a well defined function. Each layer should be standardizable. Layer boundaries should minimize data flow across those boundaries. 5. The right number of layers - don't put too many functions together, but not too many layers either. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 45

OSI Reference Model (2( Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 46

OSI Reference Model (3( Physical Layer: ¥ Purpose: Transmits raw bits across a medium. ¥ Electrical: Concerns are voltage, timing, duplexing, connectors, etc. Data Link Layer: ¥ Framing: Breaks apart messages into frames. Reassembles frames into messages. ¥ Error handling: solves damaged, lost, and duplicate frames. ¥ Flow control: keeps a fast transmitter from flooding a slow receiver. ¥ Gaining Access: if many hosts have usage of the medium, how is access arbitrated. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 47

OSI Reference Model (4( Network Layer: ¥ Routing: What path is followed by packets from source to destination. Can be based on a static table, when the connection is created, or when each packet is sent. ¥ Congestion: Controls the number packets in the subnet. ¥ Accounting: Counts packets/bytes for billing purposes. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 48

OSI Reference Model (5( Transport Layer: ¥ Reliability: Ensures that packets arrive at their destination. Reassembles out of order messages. ¥ Hides network: Allows details of the network to be hidden from higher level layers. ¥ Service Decisions: What type of service to provide; error-free point to point, datagram, etc. ¥ Mapping: Determines which messages belong to which connections. ¥ Naming: "Send to node ZZZ" must be translated into an internal address and route. ¥ Flow control: keeps a fast transmitter from flooding a slow receiver. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 49

OSI Reference Model (6( Session Layer: ¥ Sessions: Provides services that span a particular message. For instance, a login session could be logged. ¥ Synchronization: Provide way to subdivide a long mechanism for reliability. Presentation Layer: ¥ Prettiness: Syntax and semantics of information transmitted. Understands the nature of the data being transmitted. Converts ASCII/EBCDIC, big endian/little endian Application Layer: ¥ Interfacing: Terminal type translation. ¥ File transfer: Programs able to understand directory structures and naming conventions and map them onto various systems. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 50

OSI Reference Model (7( q Data Transmission in the OSI Model Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 51

TCP/IP Reference Model (1( Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 52

TCP/IP Reference Model (2( Internet Layer ¥ Connector: Provides packet switched connectionless service. ¥ Routing : The IP (Internet Protocol) does delivery and congestion control. Transport Layer ¥ TCP (Transmission Control Protocol): provides a reliable connection oriented protocol that delivers a byte stream from one node to another. Guarantees delivery and provides flow control. ¥ UDP (User Datagram Protocol) provides an unreliable connection-less protocol for applications that provide their own. Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 53

TCP/IP Reference Model (3( Application Layer ¥Terminal ¥File transfer ¥The Web ¥Mail Telnet FTP HTTP SMTP Computer networking, Olum-Fonoon Babol H. Veisi Fall 2005 Page 54