CSE524: Lecture 3

Network programming

Physical layer

Administrative

● CSE524 e-mail list created– E-mail TA if you have not received the introductory

message

● Homework assignments– http://www.cse.ogi.edu/class/cse524/

– Homework #1 due Monday, Oct. 13th

– Programming homework coming soon

● Access to machine resources– Get yourself an account

– Use class laboratory

Where we're at....

● Internet architecture and history● Internet in a nutshell

– Packet trace example of protocols in action

– Programming Internet applications (this class)

● Physical, Data-link, Network, Transport, Application layers (rest of the class)

Network programming

● How do I program all of this?– Layering allows programmers to write programs without

understanding underlying functions of TCP/IP

– You will be evaluating this for yourselves...

– API to transport layer● BSD socket API● java.net API

Network programming

● How can applications programmatically access TCP/UDP/IP?– Many possible interfaces– Too many to teach adequately in detail– Socket APIs

● BSD socket API● Java socket API

– Other APIs● Client-side Java URLconnections● Server-side Java servlets● RPC, CORBA, Java RMI (not covered)

Socket programming

Socket API● introduced in BSD4.1 UNIX, 1981● client/server paradigm ● socket API supports three main usages

– unreliable datagram (UDP)– reliable, byte stream (TCP)– raw IP datagrams (IP)

a host-local, application-created/owned,

OS-controlled interface (a “door”) into which

application process can both send and

receive messages to/from another (remote or

local) application process

socket

Socket-programming using TCP

Socket: a door between application process and end-end-transport protocol (UCP or TCP)

TCP service: reliable transfer of bytes from one process to another

process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperating

system

host orserver

process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperatingsystem

host orserver

internet

Socket programming with TCP

Client must contact server● server process must first be

running● server must have created a

“listening” socket that welcomes client’s initial contact

Client contacts server by:● creating client-local TCP

socket● specifying server IP address

and port number of server process

● When client creates socket: client TCP establishes connection to server TCP

● When contacted by client, server TCP creates new socket for server process to communicate with client

– allows server to talk with multiple clients (using multiple sockets)

TCP provides reliable, in-order transfer of bytes (“pipe”) between client and server

application viewpoint

Sockets in action

*,SIP:80

CIP:1099,SIP:80

*,SIP:80

CIP:1099,SIP:80

CIP:1099,SIP:80

CIP:1100,SIP:80

*,SIP:80

CIP:1099,SIP:80

CIP:1099,SIP:80

CIP:1100,SIP:80

CIP:1100,SIP:80

BSD sockets in C/Unix

● Socket API (socket.h)● socket(): create unnamed socket (data structure)

– UDP (SOCK_DGRAM), TCP (SOCK_STREAM)– IP (SOCK_RAW)

● bind(): name socket (bind local address to socket)● listen(): enable socket to accept connections● accept(): get connect() request from listen queue, allocate file descriptor for

new socket● connect(): initiate connection on a socket (TCP handshake)● send(), sendto(), sendmsg(), writev(), write(): send data● recv(), recvfrom(), recvmsg(), readv(), read(): receive data● setsockopt(), getsockopt(): set socket options (such as buffer sizes, flag

fields)● close(), shutdown(): teardown connection

BSD sockets in action

serverclient

bind()

socket() socket()

recvfrom()

sendto()

bind()

recvfrom()

UDP example TCP example

sendto()

connect()

socket()

socket()

bind()

serverclient

listen()

accept()

write()

read()

write()

read()

BSD example

● For reference only...– http://www.cse.ogi.edu/class/cse524/socket_example

Java network programming

Java network applications

java.net package

System-dependent implementations

Java installation on church/state

● J2SE– javac

● java compiler– java

● java interpreter

• http://www.ibiblio.org/javafaq/javatutorial.html

java.net classes● Low-level networking classes (Sockets and Packets)● High-level URL networking classes

• http://java.sun.com/j2se/1.3/docs/api/index.html● java.lang.Object

– java.net.Socket– java.net.ServerSocket– java.net.DatagramSocket

● java.net.MulticastSocket– java.net.DatagramPacket– java.net.URL– java.net.URLConnection

● java.net.HttpURLConnection– java.net.URLencoder– java.net.InetAddress

java.net.Socket● Constructors

– Socket(InetAddress, int) – Socket(String, int)– Socket(InetAddress, int, InetAddress, int)

● Some methods– getInputStream()– getOutputStream– getInetAddress()– getPort()– getLocalAddress()– getLocalPort()– get/set individual socket options

java.net.ServerSocket● Constructors

– ServerSocket(int) – ServerSocket(int, int) // backlog specified– ServerSocket(int, int, InetAddress) // local address and backlog specified

● Some methods– accept()– getInetAddress()– getLocalPort()

Socket programming with TCP

Example client-server app:● client reads line from standard input

(inFromUser stream) , sends to server via socket (outToServer stream)

● server reads line from socket● server converts line to uppercase,

sends back to client● client reads, prints modified line from

socket (inFromServer stream)

Input stream: sequence of bytes into process

Output stream: sequence of bytes out of process

client socket

inFromUser outToServer

iinFromServer

Java client/server socket interaction: TCP

wait for incomingconnection requestconnectionSocket =welcomeSocket.accept()

create socket,port=x, forincoming request:welcomeSocket =

ServerSocket()

create socket,connect to hostid, port=xclientSocket =

Socket()

closeconnectionSocket

read reply fromclientSocket

closeclientSocket

Server (running on hostid) Client

send request usingclientSocketread request from

connectionSocket

write reply toconnectionSocket

TCP connection setup

Example: Java client (TCP)

import java.io.*; import java.net.*; class TCPClient {

public static void main(String argv[]) throws Exception { String sentence; String modifiedSentence;

BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));

Socket clientSocket = new Socket("hostname", 6789);

DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());

Createinput stream

Create client socket,

connect to server

Createoutput stream

attached to socket

Example: Java client (TCP), cont.

BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

sentence = inFromUser.readLine();

outToServer.writeBytes(sentence + '\n');

modifiedSentence = inFromServer.readLine();

System.out.println("FROM SERVER: " + modifiedSentence);

clientSocket.close(); } }

Createinput stream

attached to socket

Send lineto server

Read linefrom server

Example: Java server (TCP)

import java.io.*; import java.net.*;

class TCPServer {

public static void main(String argv[]) throws Exception { String clientSentence; String capitalizedSentence;

ServerSocket welcomeSocket = new ServerSocket(6789); while(true) { Socket connectionSocket = welcomeSocket.accept();

BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));

Createwelcoming socket

at port 6789

Wait, on welcomingsocket for contact

by client

Create inputstream, attached

to socket

Example: Java server (TCP), cont

DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());

clientSentence = inFromClient.readLine();

capitalizedSentence = clientSentence.toUpperCase() + '\n';

outToClient.writeBytes(capitalizedSentence); } } }

Read in linefrom socket

Create outputstream, attached

to socket

Write out lineto socket

End of while loop,loop back and wait foranother client connection

Socket programming with UDP

UDP: no “connection” between client and server

● no handshaking● sender explicitly attaches IP

address and port of destination● server must extract IP address,

port of sender from received datagram

UDP: transmitted data may be received out of order, or lost

application viewpoint

UDP provides unreliable transfer of groups of bytes (“datagrams”)

between client and server

java.net.DatagramSocket● Constructors

– DatagramSocket() – DatagramSocket(int) // bind to specific port– DatagramSocket(int, InetAddress) // specify local address

● Some methods– getLocalAddress()– getLocalPort()– receive(DatagramPacket)– send(DatagramPacket)– get/set individual socket options

java.net.DatagramPacket● Constructors

– DatagramPacket(byte[], int) // receiving packets – DatagramPacket(byte[], int, InetAddress, int) // sending packets

● Some methods– getAddress() // remote address– getPort() // remote port– getLength() // get packet length– getData() // return data received or to be sent– setAddress(InetAddress) // set remote address– setData(byte[]) // set packet data– setLength(int) // set packet length– setPort(int) // set remote port

Client/server socket interaction: UDP

Server (running on hostid)

create socket,clientSocket = DatagramSocket()

Client

Create, address (hostid, port=x,send datagram request using clientSocket

closeclientSocket

read reply fromclientSocket

create socket,port=x, forincoming request:serverSocket = DatagramSocket()

read request fromserverSocket

write reply toserverSocketspecifying clienthost address,port umber

Example: Java client (UDP)

import java.io.*; import java.net.*; class UDPClient { public static void main(String args[]) throws Exception { BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); DatagramSocket clientSocket = new DatagramSocket(); InetAddress IPAddress = InetAddress.getByName("hostname"); byte[] sendData = new byte[1024]; byte[] receiveData = new byte[1024]; String sentence = inFromUser.readLine();

sendData = sentence.getBytes();

Createinput stream

Create client socket

Translate hostname to IP

address using DNS

Example: Java client (UDP), cont.

DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876); clientSocket.send(sendPacket); DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); clientSocket.receive(receivePacket); String modifiedSentence = new String(receivePacket.getData()); System.out.println("FROM SERVER:" + modifiedSentence); clientSocket.close(); }

}

Create datagram with data-to-send,

length, IP addr, port

Send datagramto server

Read datagramfrom server

Example: Java server (UDP)

import java.io.*; import java.net.*; class UDPServer { public static void main(String args[]) throws Exception { DatagramSocket serverSocket = new DatagramSocket(9876); byte[] receiveData = new byte[1024]; byte[] sendData = new byte[1024]; while(true) { DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);

serverSocket.receive(receivePacket);

Createdatagram socket

at port 9876

Create space forreceived datagram

Receivedatagram

Example: Java server (UDP), cont

String sentence = new String(receivePacket.getData()); InetAddress IPAddress = receivePacket.getAddress(); int port = receivePacket.getPort(); String capitalizedSentence = sentence.toUpperCase();

sendData = capitalizedSentence.getBytes(); DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port); serverSocket.send(sendPacket); } }

}

Get IP addrport #, of

sender

Write out datagramto socket

End of while loop,loop back and wait foranother datagram

Create datagramto send to client

High-level Java networking classes

● Socket/Packet– Low level building blocks– Must implement all application-level logic

● Many protocols based on URLs and/or tunneled in HTTP– Program at a higher-level to hide underlying protocol

details– Do not re-implement HTTP, URL parsing, MIME

handling for each application

High-level client-side Java networking classes

● java.net.URL– Represent a URL object

● java.net.URLConnection– Represent a connection to a URL which can be read and

written from● java.net.HttpURLConnection

– Subclass of URLConnection for http:// URLs● Example

– http://www.cse.ogi.edu/class/cse524/java_example

High-level server-side Java networking classes

● Servlets– Dynamically generate content– Implement common protocol header logic

● Example http servlets– Cookies– Content-type– Content-length

● Servlet classes– javax.servlet.Servlet javax.servlet.HttpServlet

● init()● service()● destroy()

– javax.servlet.ServletRequest javax.servlet.ServletResponse– javax.servlet.HttpServletRequest javax.servlet.HttpServletResponse

The rest of the course

● From birds-eye view, we will now focus on specific components

● Review these lectures for perspective when looking at the components

● Mostly classical material with some references to newer technologies

Physical Layer

● Plethora of physical media– Fiber, copper, air– Specifies the characteristics of transmission media– Too many to cover in detail, not the focus of the course– Many data-link layer protocols (i.e. Ethernet, Token-Ring,

FDDI. ATM run across multiple physical layers)– Physical characteristics dictate suitability of data-link layer

protocol and bandwidth limits

PL: Good URLs

● Get ‘em while they last….– ftp://rtfm.mit.edu/pub/usenet-by-hierarchy/comp/answers/LANs/cabling-

faq– http://fcit.coedu.usf.edu/network/

PL: Common Cabling

● Copper– Twisted Pair

● Unshielded (UTP)– CAT-1, CAT-2, CAT-3, CAT-4, CAT-5, CAT-5e

● Shielded (STP)

– Coaxial Cable● Fiber

– Single-mode– Multi-mode

PL: Twisted Pair

● Most common LAN interconnection● Multiple pairs of twisted wires● Twisting to eliminate interference

– More twisting = Higher data rates, higher cost

● Standards specify twisting, resistance, and maximum cable length for use with particular data-link layer

PL: Twisted pair

● 5 categories– Category 1

● Voice only (telephone wire)

– Category 2● Data to 4Mbs (LocalTalk)

– Category 3● Data to 10Mbs (Ethernet)

– Category 4● Data to 20Mbs (16Mbs Token Ring)

– Category 5 (100 MHz)● Data to 100Mbs (Fast Ethernet)

– Category 5e (350 MHz)● Data to 1000Mbs (Gigabit Ethernet)

PL: Twisted Pair

● Common connectors for Twisted Pair– RJ11 (6 pairs)– RJ45 (8 pairs)

● Allows both data and phone connections● (1,2) and (3,6) for data, (4,5) for voice● Crossover cables for NIC-NIC, Hub-Hub connection

(Data pairs swapped)

PL: UTP

● Unshielded Twisted Pair– Limited amount of protection from interference– Commonly used for voice and ethernet

● Voice: multipair 100-ohm UTP

PL: STP

● Shielded Twisted Pair– Not as common at UTP– UTP susceptible to radio and electrical interference– Extra shielding material added– Cables heavier, bulkier, and more costly– Often used in token ring topologies

● 150 ohm STP two pair (IEEE 802.5 Token Ring)

PL: Coaxial cable

● Single copper conductor at center● Plastic insulation layer● Highly resistant to interference

– Braided metal shield – Support longer connectivity distances over UTP

PL: Coaxial cable

● Thick (10Base5) – Large diameter 50-ohm cable– N connectors

● Thin (10Base2) cables– Small diameter 50-ohm cable– BNC, RJ-58 connector

● Video cable– 75-ohm cable– BNC, RJ-59 connector– Not compatible with RJ-58

PL: Fiber

● Center core made of glass or plastic fiber● Transmit light versus electronic signals

– Protects from electronic interference, moisture● Plastic coating to cushion core● Kevlar fiber for strength● Teflon or PVC outer insulating jacket

PL: Fiber● Single-mode fiber

– Smaller diameter (12.5 microns)– One mode only– Preserves signal better over longer distances– Typically used for SONET or SDH– Lasers used to signal– More expensive

● Multi-mode fiber– Larger diameter (62.5 microns)– Multiple modes– LEDs used to signal– WDM and DWDM

● Photodiodes at receivers

PL: Fiber connectors

● ESCON

● Duplex SC

● ST

● MT-RJ (multimode)

● Duplex LC

PL: Wireless

● Entire spectrum of transmission frequency ranges– Radio– Infrared– Lasers– Cellular telephone – Microwave – Satellite– Acoustic (see ESE sensors)– Ultra-wide band

● http://www.ntia.doc.gov/osmhome/allochrt.html

PL: What runs on them?

Protocol Summary

Protocol Cable Speed Topology

Ethernet Twisted Pair, Coaxial, Fiber 10 Mbps Linear Bus, Star, Tree

Fast Ethernet Twisted Pair, Fiber 100 Mbps Star

LocalTalk Twisted Pair .23 Mbps Linear Bus or Star

Token Ring Twisted Pair 4 Mbps - 16 Mbps Star-Wired Ring

FDDI Fiber 100 Mbps Dual ring

ATM Twisted Pair, Fiber 155-2488 Mbps Linear Bus, Star, Tree

PL: Physical-link lingo

● Specifies capacities over physical media● Electronic

– T1/DS1=1.54 Mbps – T3/DS3=45Mbps

● Optical (OC=optical carrier)– OC1=52 Mbps– OC3/STM1=156 Mbps– OC12=622 Mbps– OC48=2488 Mbps– OC192=10 Gbps – OC768=40 Gbps