NETWORK PROGRAMMING INTRO TO DISTRIBUTED SYSTEMS FALL 2015 L3-socket Dongsu Han Some material taken...

NETWORK PROGRAMMINGINTRO TO DISTRIBUTED SYSTEMSFALL 2015

L3-socketDongsu Han

Some material taken from publicly available lec-ture slides including Srini Seshan’s and David Anderson’s

Today’s Lecture

Lecture Transport protocols: UDP and TCP Version control using SVN

TA-led programming session Editor, socket programming Debugging with gdb

Announcement Programming Assignment 1 is out. (Due in two weeks-- 추석 )

Review of Previous Lectures

What is a distributed system? (L1) Definition Example

What are some of the important decisions made in the In-ternet architecture? (L2) Narrow waist: Network provides minimal functionality (best-ef-

fort) Why?: to connect existing networks that are heterogeneous

Stateless architecture: no per-flow state inside network Why? For survivability

Principles

P1: IP over all network (narrow waist) P2: Layering Principle 3: Fate Sharing Principle 4: Soft-state Principle 5: End-to-End Argument Next lecture Principle 6: network layer provides one simple

service: best effort datagram (packet) delivery

Principle 4: Soft-state5

Soft-state (as oppose to hard-state) Announce state Refresh state Timeout state

Penalty for timeout – poor performance Robust way to identify communication flows (firewall)

Possible mechanism to provide non-best effort service Helps survivability

Goal 2: Types of Service6

Principle 6: network layer provides one simple service: best effort datagram (packet) delivery All packets are treated the same

Network layer (IP) provides “best effort” service. Relatively simple core network elements

Other functions are implemented at the end-host at the transport layer (TCP/UDP) Building block from which other services (such as reliable data stream)

can be built Contributes to scalability of network

Issues: No QoS support assumed from below Hard to implement without network support QoS is an ongoing debate…

Summary

Successes: IP on every-thing!

Drawbacks…

but perhaps they’re to-tally worth it in the con-text of the original Inter-net. Might not have worked without them!

“This set of goals might seem to be nothing more than a checklist of all the desirable network features. It is impor-tant to understand that these goals are in order of impor-tance, and an entirely dif-ferent network architecture would result if the order were changed.”

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8

Transport Protocols

Lowest level end-to-end proto-col. Header generated by sender is in-

terpreted only by the destination Routers view transport header as

part of the payload; they are not supposed to see the transport header.

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6

5

7

6

5

Transport

IP

Datalink

Physical

Transport

IP

Datalink

Physical

IP

router

2 2

1 1

What does the transport layer do?

No per-flow (connection) state in the network Transport layer maintains the connection state. Transport

layer identifies an end-to-end connection.

How does the transport layer identify an end-point (ap-plication)?

De-multiplexing: Port numbers

Network layer gets you to the host. A port identifies the sending or receiving socket (appli-

cation). A socket is one endpoint of a two-way communication

between two programs running on the network. A socket is bound to a port number so that the transport layer can identify the application that data is destined to be sent.

Identifying two end-points: An endpoint = <IP address, Port #> Source endpoint = <SrcIPAddr, SrcPort> destination endponit = <DestIPAddr, DestPort>

11

Protocol and Port Demultiplexing

Multiple choices at each layer Applications open a socket (identified by the port

number)

Port 80 Port 22 Port 22Port 80

TCP UDP

IP

NET1 NET2 NETn…

TCP/UDPIP

Port Number= 80

Network

Protocol Field= TCP

Type Field=IP

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Server and Client

TCP/UDP

IP

Ethernet Adapter

Server

TCP/UDP

IP

Ethernet Adapter

Clients

Server and Client exchange messages over the net-work through a common Socket API

Socket API

hardware

kernel space

user spaceports

Transport protocols

UDP Provides only integrity and de-multiplexing

TCP adds…

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UDP: User Datagram Protocol [RFC 768]

“bare bones” Internet transport protocol, “Best effort” service

UDP segments may be: Lost, duplicated (bug, spurious re-

transmission at L2) Delivered out of order to app

Connectionless: No handshaking between UDP

sender, receiver Each UDP segment handled inde-

pendently

Why is there a UDP?• No connection establishment

(which can add delay)• Simple: sender, receiver

state is minimal• Small header• No congestion control: UDP

can blast away as fast as desired

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UDP, cont.

Often used for streaming multimedia apps (e.g., Skype) Loss tolerant Rate sensitive

Other UDP uses (why?): DNS

Reliable transfer over UDP Must be at application layer Application-specific error re-

covery

Source port # Dest port #

32 bits

Applicationdata

(message)

UDP segment format

Length ChecksumLength, in

bytes of UDPsegment,includingheader

Transport protocols

UDP Provides only integrity and de-multiplexing

TCP adds… Connection-oriented Reliable (error control) Ordered byte stream (in-order delivery) Bi-directional byte-stream Flow and congestion controlled

TCP

Protocol implemented entirely at the ends Fate sharing

Abstraction provided Connection oriented protocol (hand-shake or connection establish-

ment) In-order byte-stream

Implemented functionality (next lecture) Flow control Reliability (error control) Reassembly (in-order delivery) Congestion control

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/* get the server host entry */hp = gethostbyname(argv[1]);if (hp == NULL) {perror("gethostbyname");return -1;}

/* create stream socket */sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);if (sockfd < 0) {perror("socket");return -1;}

/* set the destination address */daddr.sin_family = AF_INET;memcpy(&daddr.sin_addr.s_addr, hp->h_addr, hp->h_length);daddr.sin_port = htons(PORT);

TCP Client Example

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/* connect to the destination */

if (connect(sockfd, (struct sockaddr *)&daddr, sizeof(struct sockaddr_in))) {

close(sockfd);

perror("connect");

return -1;

}

inet_ntop(AF_INET, &daddr.sin_addr, s, sizeof(s));

printf("client: connecting to %s\n", s);

/* receive message sent from the server */

if ((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1) {

perror("recv"); exit(1);

}

/* print the received message */

buf[numbytes] = '\0';

printf("client: received '%s'\n", buf);

close(sockfd);

TCP Client Example

Difference in abstraction

UDP Recv(len) call gives you a packet (the payload part)

TCP Connection establishment (hand-shake) Will see in the TA

led session. Recv(len) call give you a sequence of bytes

UDP segment (packet)

Byte stream

UDP segment (packet)

len len

Incoming stream

ApplicationRecv()

len len

Byte stream

Applicationsend()

TCP– What goes on underneath

Byte stream Packet (1~7) Packet (8~10)

Receive buffer

Packet (9~11)

Packet (8~10)

I need seq# 8.

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User Datagram Protocol(UDP): An Analogy

Example UDP applicationsMultimedia, voice over IP

UDP Single socket to receive mes-

sages No guarantee of delivery Not necessarily in-order delivery Datagram – independent packets Must address each packet

Postal Mail Single mailbox to receive letters Unreliable Not necessarily in-order delivery Letters sent independently Must address each reply

Transmission Control Pro-tocol (TCP): An Analogy

TCP Reliable – guarantee delivery Byte stream – in-order delivery Connection-oriented – single

socket per connection Setup connection followed by

data transfer

Telephone Call Guaranteed delivery In-order delivery Connection-oriented Setup connection followed by

conversation

Example TCP applicationsWeb, Email, Telnet

REVISION CONTROL & MAKE

Overview

Revision control systems Motivation Features Subversion primer

Make Simple gcc Make basics and variables Testing

Useful Unix commands

Dealing with large codebases

Complications Code synchronization Backups Concurrent modifications

Solution: Revision Control System (RCS) Store all of your code in a repository on a server Metadata to track changes, revisions, etc… Also useful for writing books, papers, etc…

Basic RCS features (1/2)

Infinite undo go back to previous revisions

Automatic backups all your code ever, forever saved

Changes tracking see differences between revisions

Basic RCS features (2/2)

Concurrency Multiple people working at the same time

Snapshots Save stable versions on the side (i.e. handin)

Branching Create diverging code paths for experimentation

Typical RCS workflow

1. Create repository on RCS server2. Checkout the repository to your local machine3. Work locally: create, delete and modify files4. Update the repository to check for changes other

people might have made5. Resolve any existing conflicts6. Commit your changes to the repository

RCS implementations

Concurrent Versions System (CVS) Concurrency, versioning of single files

Subversion (SVN) File and directory moving and renaming, atomic commits

Git Modern, de-facto standard

Concurrent edits (1/2)

John DavidFile v1

Both check out file

Edits (lines 1-20)

File v2

Edits (lines 30-40)

commit

Update

Merged automatically!

Concurrent edits (2/2)

John DavidFile v1

Both check out file

Edits (lines 1-20)

File v2

Edits (lines 10-20)

commit

Update

Conflict needing manual in-tervention!

Resolving conflicts

When changes can’t be merged automatically SVN gives you 3 files:

file.mine : your file file.rx : the remote file file : original file with marked conflicts

You can Discard your changes Discard others’ changes Go over each conflict and arbitrate as appropriate

Interacting with SVN

Command line Readily available on your lab machines

Graphical tools Easier to use Subclipse for Eclipse gives IDE/SVN integration tortoiseSVN

실습 server

IP: 143.248.141.40, 143.248.141.42~143.248.141.44 ID: ee<your student id> (e.g., ee20110111) Password: ee324EE#@$

Svn password

20100456 6390020100667 2683420100967 4801320110198 81020110227 3961720110319 1641120110468 5770020110548 6430220110968 3086020120184 1942420120277 1297620120508 1727820120677 4002920120973 61034

20121092 42821

20130098 4280720130185 3079120130234 1344820130363 1442120130394 2079620130451 1300820130477 5370520130478 4512220130505 480520130842 74220140055 2038920140244 4533620140544 2379320153347 5044

Command line SVN example (1/2)

$ svn co –-username=<<student id>> https://ina.kaist.ac.kr/svn/test

$ cd test

$ vim <<student id>>.txt$ vim <<student id>>.$ svn add <<student id>>.txt

$ svn commit -m 'adding a text file with my student id‘$ svn update

$ cd ../$ svn cp trunk tags/<<student id>>_submission$ svn commit -m 'making a tag of the trunk for submission!‘

$ svn up$ echo -e ”<<student id>>" >> student.txt$ svn commit –m “added my student id”

Command line SVN example (2/2)

Revision control lets you note (and then see) what you changed:

> svn log student.txtr986 | ntolia | 2006-08-01 17:13:38 -0400 (Tue, 01 Aug 2006) | 6 lines

This allows the sp to get rid of chunks early before a transfer is complete.Useful when a file is requested in-order and the file size > mem cache size

> svn diff -r 1:2 student.txtIndex: file===================================================================--- file (revision 1)+++ file (revision 2)@@-1,2+1,3@@ This isatestfile -It startedwithtwolines +It nolongerhastwolines +it hasthree

General SVN tips

Update, make, test, only then commit Merge often (svn up) Comment commits Avoid commit races Modular design avoids conflicts

Know more

subversion.tigris.org for SVN software & info svnbook.red-bean.com for SVN book

Makefile

You are on your own.

Make

Utility for executable building automation Saves you time and frustration Helps you test more and better

Simple gcc

If we have files:• prog.c: The main program file• lib.c: Library .c file• lib.h: Library header file

% gcc -c prog.c -o prog.o

% gcc -c lib.c -o lib.o

% gcc lib.o prog.o -o binary

gcc flags

• Useful flags1. -g: debugging hook

2. -Wall: show all warnings

3. -Werror: treat warning as errors

4. -O0, -O1, -O2, -O3: optimization level

5. -DDEBUG: macro for DEBUG (#define DEBUG)

• Avoid using dangerous optimizations that could af-fect correctness

More gcc

% gcc -g -Wall -Werror -c prog.c -o prog.o

% gcc -g -Wall -Werror -c lib.c -o lib.o

% gcc -g -Wall -Werror lib.o prog.o -o binary

This gets boring, fast!

Makefile basics

• Build targetstarget: dependency1 dependency2 ...

unix command (start line with TAB)unix command

binary: lib.o prog.ogcc -g -Wall lib.o prog.o -o binary

lib.o: lib.cgcc -g -Wall -c lib.c -o lib.o

prog.o: prog.cgcc -g -Wall -c prog.c -o prog.o

clean:rm *.o binary

Makefile example

Makefile variables (1/7)

• Variables

CC = gcc

CFLAGS = -g -Wall -Werror

OUTPUT = binary

binary: lib.o prog.ogcc -g -Wall lib.o prog.o -o binary

lib.o: lib.cgcc -g -Wall -c lib.c -o lib.o

prog.o: prog.cgcc -g -Wall -c prog.c -o prog.o

clean:rm *.o binary


CC = gccCFLAGS = -g -WallOUTPUT = binary

$(OUTPUT): lib.o prog.o$(CC) $(CFLAGS) lib.o prog.o -o binary

lib.o: lib.c$(CC) $(CFLAGS) -c lib.c -o lib.o

prog.o: prog.c$(CC) $(CFLAGS) -c prog.c -o prog.o

clean:rm *.o $(OUTPUT)


CC = gccCFLAGS = -g -WallOUTPUT = binary

$(OUTPUT): lib.o prog.o$(CC) $(CFLAGS) lib.o prog.o -o binary





CC = gccCFLAGS = -g -WallOUTPUT = binaryOBJFILES = lib.o prog.o

$(OUTPUT): $(OBJFILES)$(CC) $(CFLAGS) $(OBJFILES) -o binary







%.o: %.c# $<: dependency (%.c)# $@: target (%.o)$(CC) $(CFLAGS) -c $< -o $@



Simple Test Script (1/2)

% ./server 6667 &

% cat testfile.01 | ./testscript.py

% cat testfile.02 | ./testscript.py

% killall -9 server

Simple Test Script (2/2)#/bin/sh

echo “Starting server on port 6667.”./server 6667 &SERVERPID = $!

echo “Running test files.”cat testfile.01 | ./testscript.pycat testfile.02 | ./testscript.py

echo “Killing server process.”kill $(SERVERPID)


all: $(OUTPUT)


%.o: %.c# $<: dependencies (%.c)# $@: target (%.o)$(CC) $(CFLAGS) -c $< -o $@


Augmenting the Makefile for testing (1/2)


all: $(OUTPUT) test


%.o: %.c# $<: dependencies (%.c)# $@: target (%.o)$(CC) $(CFLAGS) -c $< -o $@

test: $(OUTPUT)sh ./testscript.sh


Augmenting the Makefile for testing (2/2)

Using the Makefile

% make

% make test

% make clean

• Know more

Google– “makefile example”– “makefile template”– “make tutorial”– Chapter 3 of Dave Andersen’s notes

Extra: useful Unix commands (1/2)

• find “func_name” in files% grep -r func_name .

• replace “bad_func_name” to “good_func_name”% sed -e “s/bad_func_name/good_func_name/g”\

prog.c > prog.c.new

Extra: useful Unix commands (2/2)

• find a file named “prog.c”% find -name prog.c

• download files from the Internet% wget http://address/to/file.tar.gz

• untar and unzip a file% tar xzvf file.tar.gz

Assignment

You have access to svn repository at https://ina.kaist.ac.kr/svn/<student id>

However, we will change your password (to some un-known integer).

Luckily, we made a server that gives you a hint. When your client asks whether the username and the

password match, the server can tell you whether the password provided is less than, equal to, or greater than your real password.

https://ina.kaist.ac.kr/svn/%3Cstudent

Assignment I

Protocol is defined in the document. (See course web page).

Query

Response

Server (provided by the in-structor)Client

Part I: Assume the network is reliable. (due 9/14) Part II: The server may drop a packet. (due 9/24)

NETWORK PROGRAMMING INTRO TO DISTRIBUTED SYSTEMS FALL 2015 L3-socket Dongsu Han Some material taken...

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