Part I: INTRODUCTION 吳俊興 國立高雄大學資訊工程學系. Fall 2006

Transcription

1 CSC521 Communication Protocols 網路通訊協定 Part I: INTRODUCTION Ch.1 Introduction And Overview Ch.2 Review Of Underlying Network Technologies 吳俊興 國立高雄大學資訊工程學系 Fall 2006

2 Internetworking With TCP/IP Douglas Comer Computer Science Department Purdue University 250 N. University Street West Lafayette, IN Copyright All rights reserved.

3 Chapter 1 Introduction and Overview 1. The Motivation for Internetworking 2. The TCP/IP Internet 3. Internet Services 4. History and Scope of the Internet 5. The Internet Architecture Board 6. The IAB Reorganization 7. Internet Request for Comments 8. Future Growth and Technology 9. Organization of the Text 10.Summary 3

4 1.1 The Motivation for Internetworking Internetworking Provide a way to internet the networks Define a set of communication conventions that the networks use to interoperate The internet technology: open system interconnection open: the specifications are publicly available Anyone can build the software needed to communicate across an internet vendor-independent The entire technology has been designed to foster communication among machines with diverse hardware architectures accommodate a wide variety of applications accommodate arbitrary computer operating systems For computer engineers, the internet technology hides the details of network hardware permits computers to communicate independent of their physical network connections 4

5 1.2 The TCP/IP Internet The TCP/IP Internet Protocol Suite Resulted from research funded by the Defense Advanced Research Projects Agency (DARPA) Two main protocols: TCP and IP aka Internet, IP networks The Internet is everywhere Most applications are distributed Other sources of network protocols Specific vendors such as IBM or Digital Equipment Standards bodies such as the ITU (formerly known as CCITT) TCP/IP 5

6 1.3 Internet Services Application Level Internet Services World Wide Web (HTTP) Electronic Mail (SMTP, POP3, IMAP) File Transfer (FTP) Remote Login and Remote Desktop (TELNET, SSH, VNC) Network-Level Internet Services Connectionless packet delivery service Reliable stream transport service Features of TCP/IP Network technology (vendor) independence Universal interconnection End-to-end acknowledgements Application protocol standards: open for reference 6

7 Who Built TCP/IP? 7

8 1.5 The Internet Architecture Board The Internet Architecture Board (IAB) Set the technical direction and decided when protocols became standard Originally known as Internet Activities Board formed in 1983 by DARPA when reorganizing the Internet Control and Configuration Board Evolved from Internet Research Group Forum for exchange among researchers About a dozen members 8

9 1.6 The IAB Reorganization Political and commercial challenges: Hundreds of vendors and researchers over the world introduce new ideas or develop new applications Reorganization of IAB in 1989 A new IAB board Limited to a few individuals Internet Research Task Force (IRTF) IAB subsidiary group for researchers Focused on long term problems in Internet i.e. Peer-to-peer, Mobility, Management, Multicast Internet Engineering Task Force (IETF) Responsibility for protocol standards and other technical aspects A large open international community Composed of working groups (volunteers) Much of the work is handled via mailing lists The IETF holds meetings three times per year Divided into N areas (N is 10 plus or minus a few) Each area managed by Area Directors Headed by Internet Engineering Steering Group (IESG) 9

10 Questions? 10

11 Chapter 2 Review of Underlying Network Technologies 1. Introduction 2. Two Approaches to Network Communication 3. Wide Area and Local Area Networks 4. Ethernet Technology 5. Switched Ethernet 6. Asynchronous Transfer Mode 7. Summary 11

12 2.1 Introduction The TCP/IP Concept Use existing network hardware Network hardware plays only a minor role in the overall design Interconnect networks Wide varieties of physical networks Accommodate all possible network hardware Question: what kinds of hardware exist? Add abstractions to hide heterogeneity We will Review basic network concepts Examine example physical network technologies Introduce physical (hardware) addressing 12

13 2.2 Two Approaches to Network Communication 1. Circuit-switched (connection-oriented) Operate by forming a dedicated connection or circuit between two points Traditional telephone systems 2. Packet-switched (connectionless) Data to be transferred across a network is divided into small pieces called packets that are multiplexed onto high capacity inter-machine connections 13

14 2.3 Wide Area and Local Area Networks Two categories of packet-switched data networks Wide Area Networks (WANs) Engineered for long distances Indirect interconnection via special-purpose hardware Usually higher cost and lower capacity i.e. TANet, HiNet, ARPANET, NSFNET Local Area Networks (LANs) Engineered for low cost and high capacity Direct connection among computers Limited distance i.e. Ethernet, Wi-Fi Categories are informal and qualitative 14

15 Invented at Xerox PARC in early 1970s Xerox, Intel and DEC standardized Ethernet in 1978 Compatible version of IEEE standards CSMA/CD (Ethernet) based LANs Extremely popular, can run over copper (twisted pair -T) and optical fiber (-X) Three generations 10Base-T operates at 10 Mbps 100Base-T (fast Ethernet) operates at 100 Mbps 1000Base-T (gigabit Ethernet) operates at 1 Gbps Power Over Ethernet (PoE) Send a small amount of electrical power over the same copper cable used for Ethernet insufficient for a computer, but important for small devices (i.e. IP phone) 2.4 Ethernet Technology 15

16 Ethernet Frame Format Preamble Destination Source Frame Frame Data CRC Address Address Type 8 octets 6 octets 6 octets 2 octets octets 4 octets Header format fixed (Destination, Source, Type fields) Frame data size can vary from packet to packet Maximum 1500 octets Minimum 46 octets Preamble and CRC removed by framer hardware (Network Interface Card, NIC) before frame stored in computer s memory 16

17 Example Ethernet Frame In Memory ba b 0d 44 a f f a a b d4 6d b 8c d a 0b 0c 0d 0e 0 f a 1b 1c 1d 1e 1 f a 2b 2c 2d 2e 2 f Octets shown in hexadecimal Destination is ba Source is b.0d.44.a7 Frame type is (IP) 17

18 Hardware Address Unique number assigned to each machine on a network Used to identify destination for a packet Also known as media access address (MAC address), hardware address, physical address, layer 2 address Use Of hardware address Sender supplies Destination s address Source address (in most technologies) Network hardware Uses destination address to forward packet Delivers packet to proper machine Each technology defines its own addressing scheme 18

19 Example: Ethernet Hardware Address Static MAC addressing: 48-bit Ethernet address Unicast address assigned when device manufactured All 1s address reserved for broadcast One-half address space reserved for multicast (restricted form of broadcast) 19

20 Bridge Hardware device that connects multiple LANs and makes them appear to be a single LAN Repeats all packets from one LAN to the other and vice versa Introduces delay of 1 packet-time Does not forward collisions or noise Called Layer 2 Interconnect or Layer 2 forwarder Makes multiple LANs appear to be a single, large LAN Often embedded in other equipment (e.g., DSL modem) Watches packets to learn which computers are on which side of the bridge Uses hardware addresses to filter Discussion: Hub, cyclic bridging 20

21 2.5 Switched Ethernet Ethernet switch: a device extends the concept of bridging frame forwarding like a bridge viewed as a multi-port bridge: provides multiple connections, called ports 21

22 Questions? 22