Computer Networks. Fall 2012 (M 6:15-9:00 in Jbarry 201B) Mirela Damian.

Transcription

1 Computer Networks Fall 2012 (M 6:15-9:00 in Jbarry 201B) Mirela Damian Slides by Princeton & Slides accompanying the Internet Lab Manual, slightly altered by M.D. 1 The Internet is an Exciting Place 2

2 Over Two Billion Internet Users ~5 Billion Devices (PCs, laptops, smart phones, etc.) 3 Internet Applications 1.9B people used 294B s sent /day Web 255M Web sites (2011) 550M Web sites (2012) YouTube 2B videos watched /day 35 hrs of video uploaded/min Blogs 152M blogs Twitter 100M new Twitter accounts 25B tweets Facebook 20M Facebook apps installed per day 36B photos uploaded/yr almost 1B users 4

3 How does the design of the Internet support growth and foster innovation? 5 The Internet is an Tense Place 6

4 Internet Traffic to/from Egypt

5 Stop Online Piracy Act (SOPA) 9 Network Neutrality FCC Rules Against Comcast P2P Throttling The U.S. Federal Communications Commission has ordered Comcast to stop interfering with peer-to- peer traffic on its broadband network 10

6 IP Address Space Exhaustion Currently, the Internet is built using IPv4, but on February 3, 2011, the global supply of unassigned IPv4 Internet addresses was exhausted. On that date, the Internet Assigned Numbers Authority has distributed the final five blocks of approximately 16 million IPv4 addresses among the five Regional Internet Registries. 6 June Cyber Attacks 12

7 How does the design of the Internet create or exacerbate these tensions? 13 What is the Internet?

8 Wikipedia: The Internet is the worldwide, publicly accessible network of finterconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions of smaller domestic, academic, business, and government networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked Web pages and other documents of the World Wide Web Best-Effort Packet Delivery Service packets THE INTERNET 16

9 A Stack of Protocol Layers Modularity Each layer relies on services from layer below Each layer exports services to layer above Interfaces Hides implementation details Layers can change without disturbing other layers Application Application-to-application to application channels Host-to-host connectivity Link hardware 17 The Internet (TCP/IP) Protocol Suite FTP HTTP NV TFTP Applications HTTP FTP SMTP TCP IP UDP Waist TCP UDP IP NET 1 NET 2 NET n Data link layer protocols Physical layer protocols The waist facilitates interoperability The Hourglass Model 18

10 Example: HyperText Transfer Protocol GET /index.html HTTP/1.1 Host: User-Agent: Mozilla/4.03 CRLF Request Response HTTP/ OK Date: Mon, 27 Aug :09:05 GMT Server: Netscape-Enterprise/3.5.1 Last-Modified: d Mon, 27 Aug :12: GMT Content-Length: 21 CRLF Site under construction 19 End Hosts vs. Routers host HTTP HTTP message host HTTP TCP TCP segment TCP router router IP IP packet (datagram) IP IP packet IP IP packet IP Ethernet interface frame Ethernet interface SONET interface SONET interface Ethernet interface Ethernet interface 20

11 Layers in the Example 00:20:af:03:98:28 21 Layers in the Example Send HTTP Request to neon 00:20:af:03:98:28

12 Layers in the Example Establish a connection to at port 80 00:20:af:03:98:28 Layers in the Example Open TCP connection to port 80 00:20:af:03:98:28

13 Layers in the Example Send a datagram (which contains a connection request) to :20:af:03:98:28 Layers in the Example Send IP datagram to :20:af:03:98:28

14 Layers in the Example Send datagram to :20:af:03:98:28 Layers in the Example Send Ethernet frame to 00:e0:f9:23:a8:20 00:20:af:03:98:28

15 Layers in the Example Frame is an IP datagram a 00:20:af:03:98:28 Layers in the Example Send IP datagram to :20:af:03:98:28

16 Layers in the Example Send datagram to :20:af:03:98:28 Layers in the Example Send Ethernet frame to 00:20:af:03:98:28 00:20:af:03:98:28 32

17 Layers in the Example Frame is an IP datagram 00:20:af:03:98:28 33 Layers in the Example IP datagram is a TCP segment for port 80

18 Different Views of Networking Different Layers of the protocol stack have a different view of the network. This is HTTP s and TCP s view of the network. Argon Neon HTTP client HTTP server HTTP server TCP client TCP server TCP server IP Network 35 Network View of IP Protocol Router /24 Network /24 Network 36

19 Network View of Ethernet Ethernet s view of the network Argon ( ) 00:e0:f9:23:a8: Router137 ( ) Ethernet Network 37 Layers and Services Service provided by TCP to HTTP: reliable transmission of data over a logical connection Service provided by IP to TCP: unreliable transmission of IP datagrams across an IP network Service provided by Ethernet to IP: transmission of a frame across an Ethernet segment Other services: DNS: translation between domain names and IP addresses ARP: Translation between IP addresses and MAC addresses 38

20 Sending a packet from Argon to Neon DNS: What is the IP address of neon.tcpip-lab.edu? 39 Sending a packet from Argon to Neon DNS: The IP address of neon.tcpip-lab.edu is

21 Sending a packet from Argon to Neon is not on my local network. Therefore, I need to send the packet to my default gateway with address Sending a packet from Argon to Neon ARP: What is the MAC address of ?

22 Sending a packet from Argon to Neon ARP: The MAC address of is 00:e0:f9:23:a8:20 43 Sending a packet from Argon to Neon is on my local network. Therefore, I can send the packet directly. frame 44

23 Sending a packet from Argon to Neon ARP: What is the MAC address of ? ? frame 45 Sending a packet from Argon to Neon ARP: The MAC address of is 00:20:af:03:98:28 frame 46

24 Sending a packet from Argon to Neon frame 47 Encapsulation and Demultiplexing As data is moving down the protocol stack, each protocol is adding layer-specific control information HTTP User data HTTP Header User data TCP TCP Header HTTP Header User data IP TCP segment IP Header TCP Header HTTP Header User data Ethernet IP datagram Ethernet t Hdr. IP Header TCP Header HTTP Header User data Ethernet t Trailer Ethernet frame 48

25 Layer Encapsulation in HTTP User A User B Application App-to-app channels Host-to-host connectivity Link hardware Get index.html Connection ID Source/Destination Link Address 49 What if the Data Doesn t Fit? Problem: Packet size On Ethernet, max IP packet is 1500 bytes Typical Web page is 10 kbytes Solution: Split the data across multiple packets ml x.ht inde GET GET index.html 50

26 What if the Data gets Dropped? Problem: Lost Data GET index.html Internet Solution: Timeout and Retransmit GET index.html GET index.html Internet GET index.html 51 What if the Data is Out of Order? Problem: Out of Order ml inde x.ht GET GET x.htindeml Solution: Add Sequence Numbers ml 4 inde 2 x.ht 3 GET 1 GET index.html 52

27 Resource Allocation: Queues Sharing access to limited resources E.g., a link with fixed service rate Simplest case: first-in-first out queue Serve packets in the order they arrive When busy, store arriving packets in a buffer Drop packets when the queue is full 53 Resource Allocation: Congestion Control What if too many folks are sending data? Senders agree to slow down their sending rates in response to their packets getting dropped The essence of TCP congestion control Key to preventing congestion collapse of the Internet 54

28 Key Networking Concepts Protocols Speaking the same language Syntax and semantics Layering Standing on the shoulders of giants A key to managing complexity Resource allocation Dividing scare resources among competing parties Memory, link bandwidth, wireless spectrum, paths, Naming What to call computers, services, protocols, 55 Course Organization 56

29 What You Learn in This Course Skill: network programming Socket programming Designing and implementing protocols Knowledge: how the Internet works IP protocol suite Internet architecture Applications (Web, , P2P, VoIP, ) Insight: key concepts in networking Protocols Layering Resource Allocation Naming, etc. 57 Structure of the Course (1 st Half) Start at the bottom Link technologies (Ethernet, wireless, ) Then study the narrow waist of IP IP best-effort packet-delivery service IP addressing and packet forwarding And how to build on top of the narrow waist Transport protocols (TCP, UDP) Domain Name System (DNS) Glue (ARP, DHCP, ICMP) How applications view the Internet Sockets 58

30 Structure of the Course (2 nd Half) Then how to get the traffic from here to there Internet routing architecture (the inter in Internet) Intradomain and interdomain routing protocols Building applications Web and content-distribution networks Peer-to-peer file sharing Multimedia streaming and voice-over-ip Other approaches to building networks Circuit switching (e.g., ATM, MPLS, ) More on wireless networks, multicast, P2P Network Security 59 Learning the Material Lecture (Mirela Damian) When: M 6:15-9:00pm in Jbarry 201B Office hours: M 4:00 5:00pm, W 1:30 3:30pm Slides available online at course Web site Textbooks Computer Networks: A Systems Approach (5th edition), by Peterson and Davie [Ok to use the 4 rd edition] Online resources E.g. on socket programming 60

31 Assignments OpNet Labs Network simulation experiments Hands-on Labs (networks lab) Get real experience and using real equipment Programming Sockets assignment IP or TCP protocol assignment Research Project Survey of a topic or implementing a protocol Project of your choice Topic due before October 8 th 61 Grading and Schedule Two exams (40%) Assignments (45%) Research Project (15%) 62

32 Policies: Write Your Own Code Programming in an individual creative process much like composition. You must reach your own understanding of the problem and discover a path to its solution. During this time, discussions with friends are encouraged. However, when the time comes to write code that solves the problem, such discussions are no longer appropriate - the program must be your own work. 63 Policies: Write Your Own Code If you have a question about how to use some feature of C, UNIX, etc., you can certainly ask your friends or the TA, but do not, under any circumstances, copy another person's program. Letting g someone copy your program or using someone else's code in any form is a violation of academic regulations. "Using someone else's code" includes using solutions or partial solutions to assignments provided by commercial web sites, instructors, preceptors, teaching assistants, friends, or students from any previous offering of this course or any other course. 64

33 This Lecture Key concepts in networking Protocols Layers Naming Resource allocation 65