CS360 Special Topics: Computer Networking

1. CS360 Special Topics:Computer Networking Chadd Williams Office Hours: chadd@pacificu.edu Mon 11:00 - Noon 202 Strain Tues  3:00 – 4:00 PM Fri  10:00 – Noon and by appointment http://zeus.cs.pacificu.edu/chadd/cs360s07/

2. Syllabushttp://zeus.cs.pacificu.edu/chadd/cs360s07/syllabus.htmlSyllabushttp://zeus.cs.pacificu.edu/chadd/cs360s07/syllabus.html • Computer Networks, Andrew S. Tanenbaum (4th edition) • I may assign problems out of this book • I will expect you to read the book Grades: • Homework/Quizzes: 10% • 2 Midterms: 20% each • 1 Final 20% (Comprehensive) • Programming Projects 30% Dates: • Midterm 1, Tues Mar 8 • Midterm 2, Tues Apr 17 • Final, Mon May 14 (3:00 – 5:30 PM) Policies: • Assignments are due at the beginning of class. Late assignments will not be accepted. • The cheating policy is defined in the Catalog but read the syllabus! • Silence all electronic devices • Class starts promptly at 1pm!

3. Programming Projects • 30% of the final grade • Fairly intense programming problems • Network programming is always tricky – things happen asynchronously! • Start the day the project is assigned • You’ll be using lots of new libraries and tools • I’ll expect you to look at the man pages to learn the details of the socket library • Projects (through Project 4) build on code written for earlier projects • Project 5: Routing project with donated CISCO hardware! • All assignments are individual projects

4. Programming Projects • You must program on Linux • I will not accept Visual Studio projects • Eclipse • Integrated Development Environment • 3.2.1 • subclient plugin • CDT plugin • may use gcc from the command line • Subversion • source code control • you are required to use this • Machines to use • zeus: Linux: Intel ♦ • ada: Linux: Intel • lab machines: Linux: Intel • circe: OpenBSD: SPARC ♦ • g3ubuntu: Linux: PowerPC

5. Coding on Linux/Unix • Wednesday, 8 – 10 pm in Strain 222 • Linux programming basics with Doug and Chadd • if you cannot make this, let me know ASAP • one class later in the semester will be cancelled • submit script • allows you to submit your project electronically • I still need a hardcopy! • You can do this exactly once for each assignment! • must be run from zeus zeus$ ~chadd/submit cs360s07filename.tar.gz

6. Overview • How do we send data from here to there on the Internet? • we will talk about non-Internet networks (Bluetooth) • Internetworking • implement the protocol • join the network • Computer Networks are complex things • we will use a model of the network to guide us through • Open Systems Interconnection Basic Reference Model • TCP/IP reference model • breaks down the functionality of the network into layers • from Mozilla Firefox to radio waves in the air • How to write networking code • network socket libraries

7. It’s a joke, laugh. • Will I learn to set up my wireless router in my house? • Will I learn how my wireless router assigns my laptop an IP address? NO I don’t know, read the owner’s manual YES this is a well defined standard that all routers use But, it’s funny because it’s true.

8. Terms • Read Chapter 1 (1.1 – 1.5) • 1.4 is especially important • describes models of the network • 1.6 is interesting and we may return to it later • Network Application: a piece of software that interacts with the network • Network Protocol: “an agreement between the communicating parties on how communication is to proceed” – Tanenbaum, pg 27 • very strict, to the bit, description of how to do things Hello?

9. Terms • Protocol Stack: all the protocols an application uses, in order of abstraction • ~1 per layer of the model • Packet: (small) chunk of data sent across the network

10. Network Models (quick preview) Computer Networks, 4th edition, Tanenbaum, page 43.

11. Applications and Protocols • Network Applications (protocol) • Lower level protocols: • IEEE 802.11[a|b|g] is a wireless networking standard • differences in letters are speed and security • what does a 1 and 0 look like? • TCP (Reliable transport) • IP (Internet protocol) • Bluetooth (wireless keyboard/mice) High level protocols

12. Protocols • Open/standardized protocols allow anyone to write code that uses the protocol • all web- servers/browsers understand HTTP • anyone can write a web browser! • two independently developed network applications can communicate • Protocols specify a by the bit communication scheme • packet layout • error checking

13. Proprietary protocols • Proprietary protocols are not released to the public • OSCAR (AOL IM) is not actually an open protocol • however it has been reverse engineered • therefore, other chat clients can implement it • AOL used to change the protocol very often to frustrate the efforts of those trying to build an AIM chat client • Microsoft never fully disclosed the protocol for MSN Messenger • Why would a company do this?

14. Example HTTP • The client (web browser) can send a set of predefined, specifically formatted requests to the server (web server) • The server (web server) responds with a status code and possibly some data

15. Example: HTTP • The HTTP protocol defines a way to request data across the network • client (web browser) http://zeus.cs.pacificu.edu/index.html • server (web server) GET /index.html HTTP/1.1 Host: zeus.cs.pacificu.edu HTTP/1.1 200 OKDate: Tue, 16 Jan 2007 19:58:22 GMTServer: Apache-AdvancedExtranetServer/2.0.53 (Mandriva·Linux/PREF Last-Modified: Mon, 05 Sep 2005 23:13:58 GMTETag: "4f8-9a2-4000e774e3980"Accept-Ranges: bytesContent-Length: 2466Connection: closeContent-Type: text/html <html> …. Website that allows you to view the HTTP traffic for your request: http://web-sniffer.net/

16. Network Models (1.4) Computer Networks, 4th edition, Tanenbaum, page 43.

17. Why layers? • Each layer performs a different function • called service primitives • upper layers rely on the lower layers working • Layering allows information hiding • remember this from OO programming? • upper layers don’t care how the lower layers operate • Lower layers can change and the upper layers won’t notice (waves hands quickly) • wired Ethernet, 802.11 wireless, carrier pigeon (RFC 1149)

18. Application • User level code • Standardize data exchanges • High level protocols • HTTP • FTP • DHCP • Where the actual real, end-user important data gets transferred • everything else is really just supporting code

19. Presentation • Syntax and semantics of data • Translate data representations between machines • big or little endian • which character encoding? • which image encoding? • Often not used (not in the TCP/IP model) • this is usually left to the Application level

20. Session • Share/combine data from two independent connections between machines • Dialog control • whose turn is it to transmit • Token management • who has the mutex? • Synchronization • check point long transmissions so the can restart • Often not used (not in the TCP/IP model) • Canonical example: Multimedia • make sure the audio and video streams match up

21. Transport • Key interface: where the application accesses the net • end to end principle: put all the smarts above the network layer • Transmission Control Protocol (the TCP in TCP/IP) • reliable transport • track acknowledgement of data and retransmit as necessary • breaks data into packets • reassemble packets at destination in order • flow control: don’t swamp the receiver • connection based • User Datagram Protocol (UDP) • unreliable, connectionless • fire and forget: maybe it gets there, maybe not

22. Network • Routing data around the network • congestion control • allow heterogeneous networks to interact (internetworking) • negotiate packet size • negotiate addressing • Internet Protocol (the IP in TCP/IP) • uses packets, stateless/connectionless (dumb), unreliable • best effort delivery • though the IP header is error free • Internet layer in the TCP/IP reference model • QoS: area of recent research! • delay/transit time/jitter • Other examples: IPX, ICMP

23. Data link • Take data from physical layer and pass it up to the network layer • uses data frames • chunks of data of a 100-1000s of bytes • may provide reliable service • acknowledge data frames and request retransmissions of missing data frames • provides some error checking • don’t pass data up that is full of static from the line • Flow control (rate control) • prevent the sender from overwhelming the receiver • how big is your buffer? • Regulate access to a shared medium (not always necessary) • Ethernet is one shared bus (or tube!) • collisions cause each sender to back off exponentially • medium access control sub-layer

24. Physical • Transmitting raw bits over the wire • real computer engineering stuff • mechanical, electrical and timing issues • what does the wire look like? • how many strands of copper? • how many volts at how long for a 1? 0? • We will not deal too much with this layer

25. Circuit vs Packet switched • What’s a packet? • a chunk of data sent across the network • Circuit switched • like the (old) telephone network • build, and maintain, a complete circuit to transmit data on • dedicate resources throughout the network to a connection • “All lines are busy, please call again later” • easy to guarantee QoS • Packet switched • each packet is routed independently from end to end • no overhead • no wasted resources • hard to guarantee QoS • one packet may run into a bottle neck • Canonical example: Snail mail!

26. Internet Addresses • IPv4 addresses: 64.59.233.197 • each number is 0-255 (why?) • more specific left to right • Connection between machines • IP address and socket number • socket: numbered interfaces to a single machine • allows a machine to be connected to multiple machines • 0 – 65535 (why?) • 0 - 1023 are reserved for well known services • Servers listen on a specific port then create a new socket to continue communication • 80: webserver • 25: smtp • 22: ssh • 127.0.0.1 is always the localhost 64.59.233.197:8012 64.59.233.197:80 64.59.233.200:2030

27. Socket Libraries (Unix/Linux) #include <sys/types.h> // data types #include <sys/socket.h> // socket interface #include <netinet/in.h> // Internet interface • The socket is the common Unix interface to the network • a socket represents an end point for network communication • Berkeley Software Distribution socket API • 4.2 BSD Unix • most OSes now provide a BSD socket interface for networking • Microsoft Windows almost provides it • defacto standard • a socket is represented by an int

28. API Usage: Call Sequences • UDP over IP (connectionless): • TCP over IP (connection-based): socket() sendto() close() client socket() bind() recvfrom() close() server socket() connect() send()/recv() close() client socket() bind() listen() accept() recv()/send() close() server

29. Socket library functions • UDP over IP • domain (protocol family): PF_INET • type: SOCK_DGRAM • protocol: 0 (IP) • see /etc/protocols for a list • address family: AF_INET int socket(int domain, int type, int protocol) int bind(int sockfd, const struct sockaddr *my_addr, socklen_t addrlen) • actually use struct sockaddr_in for IP networking

30. Socket library functions ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen) • again, use struct sockaddr_in for IP connections • this struct is filled with address information specifying the source of the data • this can be used to send a message back to the source. • flags tells the function how to behave • OR together zero or more options: • MSG_WAITALL – wait until the full request is satisfied • MSG_PEEK – retrieve data but don’t remove it from the receive queue • subsequent calls to recvfrom return the same data sendto() is the complement of recvfrom • man sendto close(int sockfd) • just like closing a file

31. Network Byte Order • Intel machines use little-endian encoding • 32-bit int: 0x01000000 is what? • PowerPCs (Macs), SPARC (Sun), use big-endian encoding • 32-bit int: 0x00000001 is what? • On the network, everything is transferred as big-endian • says the protocol • API to help us: • htonl – transform 32 bits from host- to network- byte order • on Intel this goes from little to big endian • on SPARC this has no effect • htons • ntohl/ntohs – transform 16 bits • Bit fields int version:4; int priority:8;

32. Programming Assignment • DUE Feb 13, 2007, 1 pm • electronic copy • submit script • paper copy • use the color printer for source code only • UDP over IP • client and server • calculation server: perform simple math tasks • The packet format is specified • size of data is specified in bits • this size may be different than the native data type • Test on big- and little-endian machines • I have a reference implementation server running on • 64.59.233.204:9999 (circe.cs.pacificu.edu, big endian) • 64.59.233.197:9999 (zeus.cs.pacificu.edu, little endian)

33. Programming Assignment • Server: ./server 9891 • Client ./client 127.0.0.1 9891 a 4 5 Result: 9 • Extra Credit • accept either a DNS name or IP address at the command line • ./client zeus.cs.pacificu.edu 9891 a 4 5 • hint: man inet_addr • Be prepared to demo your code in class!