1 i206: Lecture 21: Networking, WWW, and Internet Protocols Marti Hearst Spring 2012

2 Network Bits & Bytes Binary Numbers Number Systems Gates Boolean Logic Circuits CPU Machine Instructions Assembly Instructions Program Algorithms Application Memory Data compression Compiler/ Interpreter Operating System Data Structures Analysis I/O Memory hierarchy Design Methodologies/ Tools Process Truth table Venn Diagram DeMorgan ’ s Law Numbers, text, audio, video, image, … Decimal, Hexadecimal, Binary AND, OR, NOT, XOR, NAND, NOR, etc. Register, Cache Main Memory, Secondary Storage Context switch Process vs. Thread Locks and deadlocks Op-code, operands Instruction set arch Lossless v. lossy Info entropy & Huffman code Adders, decoders, Memory latches, ALUs, etc. Data Representation Data storage Principles ALUs, Registers, Program Counter, Instruction Register Network Distributed Systems Security Cryptography Standards & Protocols Inter-process Communication Searching, sorting, Encryption, etc. Stacks, queues, maps, trees, graphs, … Big-O TCP/IP, RSA, … Confidentiality Integrity Authentication … Formal models Finite automata regex

3 Topics Network abstractions Network architecture How the WWW works, end to end –Illustrated with the example of a web search engine

4 Network as Communication Channel Source: Coulouris, Dollimore and Kindberg

5 Network Cloud client server Network

6 Network: Routers & Links Hosts Links or local networks A DE B C Routers Source: Coulouris, Dollimore and Kindberg

7 7 Local Exchange Carrier (LEC) Router ISP Backbone Provider 1 Router Client Tandem Switch Inter-exchange Carrier (IXC) Long- Distance Network Corporate LAN Firewall Analog Modem Content Provider Server Router Remote ISP Point of Presence xDSL Modem Cable Modem Packet Network Headend Cable ISP Local Loop DNS Local Ingress Switch Exchange Point Router Internet Service ProvidersCustomer Premises Internet backbonesTelephone Network Local Egress Switch Backbone Provider 2 router Mobile Client Wireless ISP Network: More Details

8 Network Utilities Run from Terminal in unix/mac –Ping: round trip time on an IP network from the originating host to the destination computer –Traceroute: displaying the route (path) and measuring transit delays of packets across an IP network ends a sequence of Internet Control Message Protocol(ICMP) echo request packets addressed to a destination host. $ ping PING ( ): 56 data bytes 64 bytes from : icmp_seq=0 ttl=61 time=0.846 ms 64 bytes from : icmp_seq=1 ttl=61 time=0.915 ms

9 TraceRoute $ traceroute traceroute to ( ), 64 hops max, 52 byte packets 1 g2-11.inr-270-doecev.berkeley.edu ( ) ms ms ms 2 g3-3.inr-202-reccev.berkeley.edu ( ) ms ms ms 3 t5-5.inr-211-srb.berkeley.edu ( ) ms ms ms 4 www ( ) ms ms ms $ traceroute traceroute: Warning: has multiple addresses; using traceroute to ( ), 64 hops max, 52 byte packets 1 g2-11.inr-270-doecev.berkeley.edu ( ) ms ms ms 2 g3-3.inr-201-sut.berkeley.edu ( ) ms ms ms 3 xe inr-001-sut.berkeley.edu ( ) ms ms ms 4 dc-svl-agg1--ucb-10ge.cenic.net ( ) ms ms ms 5 dc-svl-core1--svl-agg1-10ge.cenic.net ( ) ms ms ms 6 dc-svl-px1--svl-core1-10ge-2.cenic.net ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms 11 nuq04s07-in-f19.1e100.net ( ) ms ms ms

10 Network Types RangeBandwidth (Mbps)Latency (ms) LAN1-2 kms WANworldwide MAN2-50 kms Wireless LAN km Wireless WANworldwide Internetworldwide  An internet: a set of interconnected networks  The Internet: the global internetwork based upon the Internet Protocol (IP) Source: Coulouris, Dollimore and Kindberg circa 2000

11 Network Building Blocks Transmission media –Copper (coax, twisted pair), optical fiber, free space (wireless) Signals –Electrical currents, light, RF (radio-frequency), microwave Hardware devices –End hosts, network interfaces –Routers, switches, hubs, bridges, repeaters Software components –Communication protocol stack

12 Network Architecture

13 Network Architecture Networking can be quite complex and requires a high degree of cooperation between the involved parties. Cooperation is achieved by forcing parties to adhere to a set of rules and conventions (protocol). The complexity of the communication task is reduced by using multiple protocol layers: Each layer is implemented independently. Each layer is responsible for a specific subtask. Layers are grouped in a hierarchy. A structured set of protocols is called a network architecture, protocol architecture, or protocol suite.

14 TCP/IP Model Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2 end-to-end point-to-point end-to-end

15 TCP/IP Model Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2 end-to-end point-to-point end-to-end client server (ping)

16 Message Flow Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2

17 Encapsulation Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2 Data

18 Encapsulation Example: Sending HTTP message using TCP/IP over Ethernet HTTP message TCP header IP header Ethernet header Ethernet frame port TCP IP IP datagram/packet TCP segment HTTP message Adapted from Coulouris, Dollimore and Kindberg

19 ISO layer model Application (layer 7): specific to application need Presentation (layer 6): conversion of data representation Session (layer 5): access mgt, synchronization Transport (layer 4): end-to-end delivery, congestion and flow control Network (layer 3): addressing, routing Data Link (layer 2): framing, error detection Physical (layer 1): bits (0/1), voltages, frequencies, wires, pins, … Application layer Presentation layer Session layer Transport layer Network layer Data link layer Physical layer Layer 1 Layer 2 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 ISO/OSI Reference Model

20 Layered Protocol Architecture Application layer Transport layer Network layer Link layer TCP/IP Model Physical layer Layer 1 Layer 2 Layer 7 Layer 4 Layer 3 Software Operating System Hardware Application layer Presentation layer Session layer Transport layer Network layer Data link layer Physical layer Layer 1 Layer 2 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 ISO/OSI Reference Model Socket API

21 The “ IP Hourglass ” IP TCP, UDP HTTP, FTP, SSH, SMTP, Your python program,... coax, twisted pair, fiber, wireless, pigeons,... Ethernet, WiFi, SONET Physical Layer Data Link Layer Network Layer Transport Layer Application Layer A single protocol

22 Ensuring Reliability Layering: –Hourglass: many different applications and underlying network technologies, but Internet Protocol establishes universal addressing scheme –Envelope/Encapsulation: layer-specific functionalities; isolation between layers Reliable communication over unreliable network –IP provides “ best-effort ” packet delivery service –TCP supports retransmission of lost packets

23 Internet and Web are not synonymous Internet is a global communication network connecting millions of computers. World Wide Web (WWW) is one component of the Internet, along with , chat, etc. Now we’ll talk about both. Internet vs. WWW

24 How Does the WWW Work? Let’s say Oski received with the address for the i206 web page, or saw it on a flyer. He goes to a networked computer, and launches a web browser. He then types the address, known as a URL, into the address bar of the browser. What happens next? (URL stands for Uniform Resource Locator)

25 How Does the WWW Work? Say Marti has written some web pages for her class on her PC. This computer is connected to the Internet and runs a program called Apache. This allows herald to act as a web server. She copied the pages to a directory on a computer on her local network at the ischool. The computer’s name is herald. Web server

26 How Does the WWW Work? How does the computer at Oski’s desk figure out where the i206 web pages are? In order for him to use the WWW, Oski’s computer must be connected to another machine acting as a web server (via his ISP). This machine is in turn connected to other computers, some of which are routers. Routers figure out how to move information from one part of the network to another. There are many different possible routes. iSchool Network

27 How Does the WWW Work? How do Oski’s server and the routers know how to find the right server? First, the url has to be translated into a number known as an IP address. Oski’s server connects to a Domain Names Server (DNS) that knows how to do the translation. DNS server

28 Slide adapted from CIW foundations Domain Name Syntax Domain names are read right to left, from general to more specific locations For example, can be interpreted as follows: com — commercial site top-level domain xyz — registered company domain name www — host name (it is a convention to name web server hosts “www” which stands for “world wide web”)

29 Slide adapted from CIW foundations Typical Domain Name Server (host) name Registered company domain name Domain category (top-level domain) Domain names are part of URLs, used in web pages.

30 Slide adapted from CIW foundations Top-Level Domains com, biz, cc — commercial or company sites edu — educational institutions, typically universities org — organizations; originally meant for clubs, associations and nonprofit groups mil — U.S. military gov — U.S. civilian government net — network sites, including ISPs int — international organizations (rarely used) Many other top level domains are available

31 Slide adapted from CIW foundations Converting Domain Names Domain names are for humans to read. The Internet actually uses numbers called IP addresses to describe network addresses. The Domain Name System (DNS) – resolves IP addresses into easily recognizable names For example: – = A domain name and its IP address refer to the same Web server.

32 Internet Addresses The internet is a network on which each computer must have a unique address. The Internet uses IP addresses; for example, herald’s IP address is Internet Protocol version 4 (IPv4) – supports 32-bit dotted quad IP address format –Four sets of numbers, each set ranging from 0 to 255 –UC Berkeley’s LAN addresses range from to –Other addresses in the iSchool LAN include Using this setup, there are approximately 4 billion possible unique IP addresses Router software knows how to use the IP addresses to find the target computer.

33 Slide adapted from CIW foundations How the Internet Works Network Protocols: –Protocol – an agreed-upon format for transmitting data between two devices Like a secret handshake –The Internet protocol is TCP/IP –The WWW protocol is HTTP Network Packets: Typically a message is broken up into smaller pieces and re-assembled at the receiving end. These pieces of information, surrounded by address information are called packets

34 IP Packet Format (v4) Total Length in bytes (16) Time to Live (8) Options (if any) Bit 0Bit 31 Version (4) Hdr Len (4) TOS (8) Identification (16 bits) Flags (3) Fragment Offset (13) Source IP Address (32) Destination IP Address (32) Header Checksum (16)Protocol (8) Data (variable length) Header Data Field length in bits

35 How Does the WWW Work? What happens now that the request for information from Oski’s browser has been received by the web server herald at The web server processes the url to figure out which page on the server is requested. It then sends all the information from that page back to the requesting address. iSchool Network

36 Reading a URL ischool.berkeley.edu/i206/s12/index.html = HyperText Transfer Protocol courses = service name (often is www).ischool = host name.berkeley = primary domain name.edu/ = top level domain i206/= directory name s12/= directory name index.html = file name of web page

37 Web Pages and HTML So what do we see at ?

38 Web Pages and HTML What does HTML look like?

39 HTML HyperText Markup Language –Uses which mark up the text and tell the browser how to display the content. –A backslash tag means the end of the command but is sometimes optional Examples –This is boldface text. – indicates a paragraph break – This is a large heading – This is a smaller heading

40 HTML Hyperlinks Hyperlink is the most important: 100 Genetics & Plant Biology Bldg –The green part is called anchor text It’s the text you see on the link –The pink part is the url that the link will take you to if you click on it. The at the front indicates the http (Web) protocol. –The … is the command that indicates the enclosed information is a hyperlink, and the that text between the tags is the anchor text. A hyperlink can be clicked on by a person OR followed by a computer program.

41 HTTP HTTP is the protocol used by the WWW When a user clicks on a hyperlink in their web browser, this sends an HTTP command to the Web server named in the URL This command usually is to “GET” the contents of the web page and return them to the user’s browser. It is a very simple protocol –It relies on the TCP/IP functionality

42 HTTP Request: Example Request line GET i141/s07/index.html HTTP/1.1 Host: courses.ischool.berkeley.edu Blank line Request header This information is received by the web server at : Because HTTP is built on TCP/IP, the web server knows which IP address to send the contents of the web page back to.

43 How Does the WWW Work? When Oski typed in the url for the i206 home page, this was turned into an HTTP request and routed to the web server in Berkeley. The web server then decomposed the url and figured out which web page in its directories was being asked for. The server then sends the HTML contents of the page back to Oski’s IP address. iSchool Network Oski’s browser receives these HTML contents and renders the page in graphical form. If he clicks on a hyperlink in that page, a similar sequence of events occurs.