Introduction to Information Science and Technology 2017 Networking I. Sören Schwertfeger 师泽仁

Transcription

1 I Sören Schwertfeger 师泽仁

2 Outline Internet History of the Internet Internet Structure Internet Protocols Network layer details 1. Physical Layer 2. Data Link Layer 3. Network Layer

3 Internet: Huge network of networks Billions of hosts (computers)

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5 Internet History Internet is a network of interconnected computers that is now global Internet born in called ARPANET 1969 ARPANET was connection of computers at UCLA, Stanford, UCSB, Univ. of Utah All large mainframe computers in late 60s Mid 1970s initial personal computers Altair: Box with blinking lights Late 1970s Apple 2, first usable PC

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7 WWW Tim Berners-Lee releases World Wide Web! TBL is computer programmer at CERN, a physics lab in Europe Mosaic (becomes Netscape) designed by graduate students at University of Illinois first point-and-click browser later developed into Netscape Navigator These are the two most significant events in the formation of the WWW

8 Growth exponential

9 Elements of the Internet Millions of connected computing devices (hosts): PC, Server, Laptops, Smartphones, Things (IoT) (cars, watches, refrigerator) Communication links: Optical fiber, copper, radio, satellite Packet Switches Routers & switches

10 Internet Structure Network Edge: End systems with hosts & access networks Access Network: Connect end systems to edge routers Network Core: Interconnected routers Network of networks

11 Enterprise Access Network (Ethernet) Typically used in companies, universities, etc.

12 Wireless Access Network Wireless LAN Within building (20 meters) a, b, g, n ( Mbps) Wide-area wireless access Provided by telecom companies 10 s of km Between 1 and 10 Mbps 3G, 4G (LTE)

13 Home Access Network

14 Network Core Mesh of interconnected routers Packet Switching: Hosts break messages into packets Forward packets from one router to the next Across links on a path from source to destination

15 Protocols: Laws of Networks

16 Protocols: Laws of Networks Protocols define format, order of messages sent and received among network entities, and actions taken on message transmission & receipt All communication activity in Internet governed by protocols Examples: TCP, UDP, IP, BGP, HTTP, 802.1

17 The Big Question Networks are complex, with many pieces : hosts routers links of various media applications protocols hardware software Question: How to organize the structure of the network?

18 The Problem Do we re-implement every application for every technology? Obviously not, but how does the Internet architecture avoid this?

19 Architecture Architecture is not the implementation itself Architecture is how to organize implementations what interfaces are supported where functionality is implemented Architecture is the modular design of the network

20 Layering Layering is a particular form of modularization The system is broken into a vertical hierarchy of logically distinct entities (layers) The service provided by one layer is based solely on the service provided by layer below Rigid structure: easy reuse, performance may suffers

21 Computer Models OSI 7-layer model Simplified 4/5-layer model Application Presentation Session Transport Network Data Physical Application Transport Network Data Physical Application: supporting network applications FTP, SMTP, HTTP Transport: process-process data transfer TCP, UDP Network: routing of datagrams from source to destination IP, routing protocols Data: data transfer between neighboring network elements Ethernet, (WiFi) Physical: bits on the wire OSI (Open Systems Interconnection) mnemonic: All People Seem To Need Data Processing. 21

22 Encapsulation

23 Layering Solves Problem Application layer doesn t know about anything below the presentation (or transport) layer, etc. Information about network is hidden from higher layers This ensures that we only need to implement an application once!

24 Physical Layer (Layer 1) Medium: Cat 5 (or Cat 5e or Cat6) twisted pair copper wire microwave (wireless) Fiber Other: coaxial copper, Cable Modem, plain phone (DSL), microwaves (wireless Ethernet), etc. Physical transportation of bits: Modulation and Demodulation of physical signal (=> MoDem) Last lecture: a, b, g, n TDM/ FDM 24

25 Data Layer (Layer 2) Sending and receiving of data packets (frames) between hosts using the same physical connection Detect (and maybe correct) errors Often divided into Media Access Control (MAC) and Logical Link Control (LLC) Examples: Ethernet, IEEE , PPP, I2C, 25

26 Data Layer: Ethernet CSMA/CD: Carrier Sense, Multiple Access, Collision Detect. Since Ethernet was designed for shared media (2 or more users) listen to see if anyone else is talking before starting to talk (Carrier Sense) Collision Detect: Detect if anybody else is speaking at the same time => both stop and repeat after random time Ethernet: 10Mbit (10 million bits per second) Fast Ethernet:, is 100Mbit Gigabit Ethernet 1000Mbit Upcoming for high-end consumers: 10Gbit 26

27 Ethernet: Addressing Users need unique address => Media Access Control (or MAC) address (Ethernet address, physical address, adaptor address, hardware address) 12-digit (48 bit) hexadecimal address unique to that Ethernet adaptor, e.g. 00:30:65:83:fc:0a or fc0a or :83fc0a or fc-0a First 6 digits are the Vendor code, ( belongs to Apple), the last 6 are the individual inteface s own. See to look up some vendor codes For most network cards the MAC address can be set to anything you wish! 27

28 Ethernet addresses: now what? To send someone a message, start with a broadcast (FFFF.FFFF.FFFF) asking where s Bob? Everyone s supposed to look at broadcasts. Bob replies, in his reply, he includes his ethernet address. Since every ethernet packet has the destination and sender address listed, Bob knows your address (from your broadcast packet) so doesn t have to start with a broadcast. For the rest of the conversation, you ll put each other s address as the destination (and yours as the sender), so the conversation can pass along the ethernet media between you. Who s Bob and how did he get that name? That s a layer 3 (Network) problem, layer 2 (Data) doesn t care. 28

29 Network Layer (Layer 3) Main point: packet forwarding: routing! Packages can be passed from one local network to another. Through a router which is connected to more than one network. Packages are encapsulated inside layer 2 frames. Network Layer Protocol: IP (Internet Protocol) 29

30 Network Layer: IP IPv4: 32bit addresses (4 byte) Broadcast: Loopback: Private networks: Link-local: About 4 billion addresses IPv6: 128bit addresses (16 byte) addresses! Other improved features (security, multicasting, ) 30

31 IP routing

32 IP: Domain Name Resolution (DNS) Translate between IP address and name DNS name: domains separated by. Distributed directory service DNS record not only for IP addresses. Also: mail server, DNS server, 32

33 Outlook Next lecture: Transport & Application Layer!