Transcript Deployment of Sensing Devices on Critical Infrastructure

Advanced Programming
Rabie A. Ramadan
Lecture 3
Network Programming
An Overview
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Computer Network

A computer network is an interconnected collection of
autonomous computers.
Network topology

A topology is a way of “laying out” the network.
Topologies can be either physical or logical.

Physical topologies describe how the cables are run.

Logical topologies describe how the network messages
travel
Network topology (cont.)

Bus (can be both logical and physical)
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Star (physical only)
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Ring (can be both logical and physical)
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Mesh (can be both logical and physical)
Network topology (cont.)
Bus


A bus is the simplest physical topology. It consists of a single
cable that runs to every workstation
This topology uses the least amount of cabling, but also covers
the shortest amount of distance.
Network topology (cont.)

It is difficult to add a workstation

Have to completely reroute the cable and possibly run
two additional lengths of it.

If any one of the cables breaks, the entire network is
disrupted. Therefore, it is very expensive to
maintain.
Network topology (cont.)
Star Topology


A physical star topology branches each network device off a
central device called a hub, making it very easy to add a new
workstation.
Also, if any workstation goes down it does not affect the entire
network.
Network topology (cont.)

Star topologies are more expensive to install than
bus networks,
• There are several more cables that need to be installed,
plus the cost of the hubs that are needed.
Network topology (cont.)
Ring

Each computer connects to two other computers,
joining them in a circle creating a unidirectional path
where messages move workstation to workstation.
Network topology (cont.)

The ring makes it difficult to add new computers.

Unlike a star topology network, the ring topology
network will go down if one entity is removed from the
ring.

Physical ring topology systems don’t exist much
anymore, mainly because the hardware involved was
fairly expensive and the fault tolerance was very low.
Network topology (cont.)
Mesh


The mesh topology is the simplest logical topology in
terms of data flow, but it is the most complex in terms of
physical design.
In this physical topology, each device is connected to
every other device
Network topology (cont.)

The physical mesh topology is very expensive to
install and maintain.

Cables must be run from each device to every
other device. The advantage you gain from it is its
high fault tolerance.

There will always be a way of getting the data
from source to destination.
Network topology (cont.)

Advantages and Disadvantages of Network Topologies
Topology
Advantages
Disadvantages
Bus
Cheap. Easy to install.
Difficult to reconfigure.
Break in bus disables
entire network.
Star
Cheap. Easy to install.
Easy to reconfigure.
Fault tolerant.
More expensive than bus.
Ring
Efficient. Easy to install.
Reconfiguration difficult.
Very expensive.
Mesh
Simplest. Most fault tolerant.
Reconfiguration extremely difficult.
Extremely expensive.
Very complex.
Computer Network

A network includes:
• Special purpose hardware devices that:
• Interconnect transmission media
• Control transmission of data
• Run protocol software
• Protocol software that:
• Encodes and formats data
• Detects and corrects problems encountered during
transmission
Network Hardware
Repeaters
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Repeaters are very simple devices.
Allow a cabling system to extend beyond its maximum allowed
length by amplifying the network voltages so they travel
farther.
Repeaters are nothing more than amplifiers and, as such, are
very inexpensive.
Network Hardware
Hubs

Hubs are devices used to link several computers together.

They repeat any signal that comes on one port and copy it to the
other ports (a process that is also called broadcasting).

There are two types of hubs: active and passive.

•
•
Passive hubs simply connect all ports together electrically and are usually not
powered.
Active hubs use electronics to amplify and clean up the signal before it is
broadcast to the other ports.
In the category of active hubs, there is also a class called
“intelligent” hubs, which are hubs that can be remotely
managed on the network.
Network Hardware
Hubs
Network Hardware
Bridges
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They join similar topologies and are used to divide network segments.
For example, with 200 people on one Ethernet segment, the performance
will be bad, because of the design of Ethernet and the number of
workstations that are fighting to transmit. If you divide the segment into
two segments of 100 workstations each, the traffic will be much lower
on either side and performance will increase.

They are more intelligent than repeaters but are unable to move data
across multiple networks simultaneously.

Unlike repeaters, bridges can filter out noise.

The main disadvantage to bridges is that they can’t connect dissimilar
network types or perform intelligent path selection. For that function,
you would need a router.
Network Hardware
Bridges
Network Hardware
Routers
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Routers are highly intelligent devices that connect multiple
network types and determine the best path for sending data.
The advantage of using a router over a bridge is that routers
can determine the best path that data can take to get to its
destination.
Like bridges, they can segment large networks and can filter
out noise.
However, they are slower than bridges because they are more
intelligent devices;
Network Hardware
Switch
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Just like a hub
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A network switch conserves network bandwidth and offers generally better
performance than a hub.

A vital difference between a hub and a switch is that all the nodes connected
to a hub share the bandwidth among themselves, while a device connected to a
switch port has the full bandwidth all to itself.

For example, if 10 nodes are communicating using a hub on a 10-Mbps
network, then each node may only get a portion of the 10 Mbps if other nodes
on the hub want to communicate as well. .

But with a switch, each node could possibly communicate at the full 10 Mbps.
Network Hardware
Switch
Addressing and Routing

Address: byte-string that identifies a node

Routing: process of forwarding messages to the
destination node based on its address

Types of addresses
• usually unique
• unicast: node-specific
• broadcast: all nodes on the network
• multicast: some subset of nodes on the network
IP Addresses and Classes
IPv6 addresses have a size of 128 bits
IP Addresses and Classes
IP Addresses and Classes
IP Addresses and Classes
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Subnet Mask
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Network Architecture

A network architecture is a set of layers and protocols used
to reduce network design complexity.

The TCP/IP Protocol Suite (also called the Internet
Architecture) is an important example of a network
architecture.

The OSI (Open Systems Interconnection) 7-Layer
Reference Model [ISO,1984] is a guide that specifies what
each layer should do, but not how each layer is implemented.
ISO/OSI Reference Model
ISO 7-Layer Reference Model
End host
End host
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Network
Network
Data link
Data link
Data link
Data link
Physical
Physical
Physical
Physical
One or more nodes
within the network
TCP/IP Model
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Internet Model
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Protocols

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A protocol is a set of rules of communication.
Protocols are the building blocks of a network architecture.
Term “protocol” is overloaded
• specification of peer-to-peer interface
• module that implements this interface
Network Programming

A network allows arbitrary applications to
communicate.

However, a network programmer doesn’t need to
know the details of all lower-level network
technologies.

Network facilities are accessed through an
Application Programming Interface (API);
e.g., a Service Interface.
Basic Paradigm for
Communication
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Most network applications can be divided into two
pieces: a client and a server.

A Web browser (a client) communicate with a Web
server.
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A Telnet client that we use to log in to a remote host.

A user who needs access to data located at remote
server.
Basic Paradigm for
Communication
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Establish contact (connection).
Exchange information (bi-directional).
Terminate contact.
Client-Server Paradigm
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Server waits for client to request a connection.
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Client contacts server to establish a connection.
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Client sends request.
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Server sends reply.
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Client and/or server terminate connection.
Two types of Communication

Connection-oriented
• Setup the link before communication.
• Similar to the phone call. We need the phone number
and receiver.

Connectionless
• No link needed to be set up before communication.
• Similar to send a letter. We need the address and
receiver.
TCP and UDP
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TCP (Transmission Control Protocol) is a connection-oriented
protocol.
UDP (User Datagram Protocol) is connectionless (UDP)
protocol.
Ports
Identifying the ultimate destination


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IP addresses identify hosts
Host has many applications
Ports (16-bit identifier)
Application
Port
WWW
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E-mail
Telnet
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192.18.22.13
Sockets
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A socket is defined as an endpoint for communication.
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Concatenation of IP address and port
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A socket pair (local IP address, local port, foreign IP address,
foreign port) uniquely identifies a communication.
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The socket 161.25.19.8:1625 refers to port 1625 on host
161.25.19.8
Sockets
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Sockets and Ports
socket
any port
agreed port
socket
message
client
server
other ports
Internet address = 138.37.94.248
Internet address = 138.37.88.249
TCP Socket
Bind() binds the socket to the specified
address. The address parameter specifies
the local component of the address, e.g. IP
address and UDP/TCP port
UDP Socket
Types of Sockets

A stream socket uses TCP for
connection-oriented communication.
It is also called a TCP socket.
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A datagram socket uses UDP for
connectionless communication. It is
also called a UDP socket.
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A raw socket uses IP directly. It is
used in such applications as in ICMP
protocol
ICMP: Internet Control Message
Protocol

ICMP: Internet Control
Message Protocol
• ICMP handles error and
control information between
gateways and hosts.
• The messages are transmitted
using IP datagrams.
• They are normally generated
and processed by the
TCP/IP software itself, not
user processes.
UNIX TCP Communication


Normally, a server would first listen and accept a connection
and then fork a new process to communicate with the client.
It uses the listen operation to listen for connections on a socket.
 int listen (int sockfd, int backlog) :
- Sockfd a socket descriptor created by the socket call.
- The backlog parameter defines the maximum length the
queue of pending connections may grow to.
UNIX TCP Communication

The server uses the accept system call to
accept connection requested by a client.

After a connection has been established,
both processes may then use the write
(send) and read (recv) operations to send
and receive messages.
Establishing a TCP Connection
Passive Open



Server process does a ‘passive’ open on a port
It waits for a client to connect
At this stage there is no Internet network traffic
Establishing a TCP Connection
Active Open

Client process
usually on a
different
machine

Performs an
‘active’ open on
the port
Windows Sockets
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Similar to UNIX, only the interface is different
We call it Windows Socket or WinSock
Fits above the transport layer
It is not a Protocol -- Located in a dynamic linked library (DLL).
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Steps in creating Clients in Java
What is the difference between
String and BufferedReader?
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Steps in creating Clients in Java
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References
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http://www.sockets.com/winsock.htm
http://tangentsoft.net/wskfaq/
Core Web Programming book
Chapter 17. Network Programming
Dynamic Programming
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Dynamic Programming
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JavaScript ….
Server-Side Java: Servlets
XML
Remote Method Invocation (RMI)
Java Server Pages (JSP)
Others…
Reference
Marty Hall, Larry Brown, Core Web Programming,
Second Edition.
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What are Servelts?
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Servlets are programs that run on a web
server,

Act as a middle layer between a request
coming from a web browser or other http
client and databases or applications on
the http server.
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What is their Job?
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Read any data sent by the user.
•
•
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Look up any other information about the request
that is embedded in the HTTP request.
•
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A form on a Web page
An applet or
A custom HTTP client program.
This information includes details about browser capabilities, cookies,
the host name of the requesting client, and so forth.
Generate the results.
•
This process may require talking to a database, invoking a legacy
application, or computing the response directly.
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What is their Job?
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Format the results inside a document.
•
In most cases, this involves embedding the information inside an
HTML document.
Set the appropriate HTTP response parameters.
•
This means telling the browser what type of document is being
returned (e.g., HTML), setting cookies and caching parameters, and
other such tasks.
Send the document back to the client.
•
This document can be sent in text format (HTML), binary format (GIF
images), or even in a compressed format like gzip that is layered on
top of some other underlying format.
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Common Gateway Interface (CGI)
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Is Simply a program interprets the Client request to the server
and forms the response back to the client .
A new process is created for each request.
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Servlet vs. CGI
Request
Request CGI1
CGI1
Request
RequestCGI2
CGI2
Request
Request CGI1
CGI1
Request
Request Servlet1
Servlet1
Request
Request Servlet2
Servlet2
Request Servlet1
Child
Childfor
forCGI1
CGI1
CGI
CGI
Based
Based
Webserver
Webserver
Child
Childfor
forCGI2
CGI2
Child
Childfor
forCGI1
CGI1
Servlet
Servlet Based
BasedWebserver
Webserver
JVM
JVM
Servlet1
Servlet1
Servlet2
Servlet2
Advantages of Servlets Over
"Traditional" CGI

Efficient
• Uses threads instead of O.S. processes for each request

Convenient
• Ready made components to automatically parse and decode HTML
form data, read and set HTTP headers, handle cookies, track
sessions, and many other such high-level utilities

Powerful
• Can talk directly to HTTP server ,
• Multiple servlets can also share data, making it easy to implement
database connection pooling and similar resource-sharing
optimizations
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Advantages of Servlets Over
"Traditional" CGI

Portable
• By the end of the day it is java

Secure
• Filter out characters such as backquotes and semicolons that are
treated specially by the shell
• No Buffer overflow

Inexpensive
• Free of charge
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Basic Servlet Structure
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Basic Servlet Structure Analysis
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To be a servlet, a class should extend HttpServlet and override
doGet or doPost, depending on whether the data is being sent by
GET or by POST.
HttpServletRequest has methods by which you can find out about
incoming information such as form (query) data, HTTP request
headers, and the client's hostname.
The HttpServletResponse lets you specify outgoing information
such as HTTP status codes (200, 404, etc.) and response headers
(Content-Type, Set-Cookie, etc.).
It lets you obtain a PrintWriter with which you send the
document content back to the client.
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Handler Functions

Each HTTP Request type has a separate handler
function.
•
•
•
•
•
GET -> doGet(HttpServletRequest, HttpServletResponse)
POST -> doPost(HttpServletRequest, HttpServletResponse)
DELETE -> doDelete (HttpServletRequest, HttpServletResponse)
TRACE -> doTrace (HttpServletRequest, HttpServletResponse)
OPTIONS -> doOptions (HttpServletRequest, HttpServletResponse)
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Generating HTML
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Generating Simple HTML Page
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Analysis
response.setContentType("text/html");
You can use it to generate other document types :
GIF images (content type image/gif)
Excel spreadsheets (content type application/vnd.ms-excel).
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Servlet Life Cycle
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A Servlet Template
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class ServletTemplate extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// Use "request" to read incoming HTTP headers
// (e.g. cookies) and HTML form data (e.g. data the user
// entered and submitted).
// Use "response" to specify the HTTP response status
// code and headers (e.g. the content type, cookies).
PrintWriter out = response.getWriter();
// Use "out" to send content to browser
}
}
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Hello World Servlet
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWWW extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<HTML>\n" +
"<HEAD><TITLE>Hello WWW</TITLE></HEAD>\n" +
"<BODY>\n" +
"<H1>Hello WWW</H1>\n" +
"</BODY></HTML>");
}
}
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Your Assignment
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Read chapter 19 from the “Core Web
Programming” book and implement the
last example of the chapter (19.12
Session tracking)
E-mail: [email protected]
Subject “3S-Assignment 2”
http://rabieramadan.org/classes/Advprog/
Hello.rar
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Web Programming (continue)
HTML Basics
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Basic HTML Document Format
<HTML>
<HEAD>
<TITLE>WENT'99</TITLE>
</HEAD>
<BODY>
Went'99
</BODY>
</HTML>
See what it
looks like:
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HTML 5 Parsing

Reverse engineering current browsers

Compatible with existing browsers and web
pages

Thoroughly defines error handling
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New Structures
<div<header>
id="header">
<div class="article">
<article>
<div
<nav>
id="nav">
<div <section>
id="content">
<div<footer>
id="footer">
<div
<aside>
id="right">
New Semantics
<canvas>
<datagrid>
<meter>
<progress>
And many
more…
<m>
<command>
<details>
<dialog>
<figure>
<time>
<menu>
<embed>
Rating:
New Controls
<input type="datetime">
<input type="text" list="list">
<datalist id="list">
<option value="Mr">
...<input
<input
type="number">
type="range">
<input
type="url">
<input
type="email">
</datalist>
And many more…
Repetition Model
<tr id="member"
repeat-template="member"
repeat="template"
repeat="0">
repeat-start="2">
Team
Members
<td><input type="text" name="member[member].rank"></td>
name="member0.rank"></td>
<td><input
name="member0.name"></td>
Ranktype="text" name="member[member].name"></td>
Name
<td><button type="remove">Remove</button></td>
Colonel
Jack O'Neill
</tr>
<tr repeat-template="member" repeat="1">
<td><input
type="text" name="member1.rank"></td>
Major
Sam Carter
<td><input type="text" name="member1.name"></td>
<td><button type="remove">Remove</button></td>
Civilian
Daniel Jackson
</tr>
<tr id="member" repeat="template" repeat-start="2">
<td><input
type="text"
Alien
Add Team
Membername="member[member].rank"></td>
Teal’c
<td><input type="text" name="member[member].name"></td>
<td><button type="remove">Remove</button></td>
</tr>
Remove
Remove
Remove
Continue
Remove
<button type="add" template="member">Add Team Member</button>
Client-Side Form Validation
Regular
Expressions
Minimum
and
Maximum
Values
MaxLength
for
textarea
Required Fields
And many more…
<input type="text" pattern="[A-Za-z0-9_\-]+">
<input
type="email"
required="required">
<input
type="range"
min="20" max="80">
<textarea
maxlength="2000"></textarea>
XML Technologies and
Applications
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Sample XML Data
<orders>
<order>
<onum>1020</onum>
<takenBy>1000</takenBy>
<customer>1111</customer>
<recDate>10-DEC 94</recDate>
<items>
<item>
<pnum>10506</pnum>
<quantity>1</quantity>
</item>
<item>
<pnum>10507</pnum>
<quantity>1</quantity>
</item>
<item>
<pnum>10508</pnum>
<quantity>2</quantity>
</item>
<item>
<pnum>10509</pnum>
<quantity>3</quantity>
</item>
</items>
</order>
...
</orders>
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Sample Data
startDocument
<orders>
<order>
<onum>1020</onum>
<takenBy>1000</takenBy>
<customer>1111</customer>
<recDate>10-DEC 94</recDate>
<items>
<item>
<pnum>10506</pnum>
<quantity>1</quantity>
</item>
Parsing Event
<item>
<pnum>10507</pnum>
<quantity>1</quantity>
</item>
<item>
<pnum>10508</pnum>
<quantity>2</quantity>
</item>
<item>
<pnum>10509</pnum>
<quantity>3</quantity>
</item>
</items>
</order>
...
endDocument
</orders>
Sample Data
<orders>
<order>
<onum>1020</onum>
<takenBy>1000</takenBy>
<customer>1111</customer>
<recDate>10-DEC-94</recDate>
<items>
<item>
<pnum>10506</pnum>
<quantity>1</quantity>
</item>
startElement
<item>
<pnum>10507</pnum>
<quantity>1</quantity>
</item>
<item>
<pnum>10508</pnum>
<quantity>2</quantity>
</item>
endElement
<item>
<pnum>10509</pnum>
<quantity>3</quantity>
</item>
</items>
</order>
...
</orders>
Sample Data
<orders>
<order>
<onum>1020</onum>
<takenBy>1000</takenBy>
<customer>1111</customer>
<recDate>10-DEC-94</recDate>
<items>
characters
<item>
<pnum>10506</pnum>
<quantity>1</quantity>
</item>
<item>
<pnum>10507</pnum>
<quantity>1</quantity>
</item>
<item>
<pnum>10508</pnum>
<quantity>2</quantity>
</item>
<item>
<pnum>10509</pnum>
<quantity>3</quantity>
</item>
</items>
</order>
...
</orders>
XML-Parsing Standards
Two parsing methods that implement W3C standards for accessing XML

SAX (Simple API for XML)
• event-driven parsing
• “serial access” protocol
• Read only API

DOM (Document Object Model)
• convert XML into a tree of objects
• “random access” protocol
• Can update XML document (insert/delete nodes)
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SAX Parsers
<?xml version="1.0"?>
.
.
.
SAX Parser
When you see
the start of the
document do …
When you see
the start of an
element do …
When you see
the end of an
element do …
The DOM Tree
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Using a DOM Tree
XML File
DOM Parser
DOM Tree
A
P
I
Application
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Node Navigation
getPreviousSibling()
getFirstChild()
getChildNodes()
getParentNode()
getLastChild()
getNextSibling()
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SAX vs DOM Parsing: Efficiency

The DOM object built by DOM parsers is usually complicated and requires
more memory storage than the XML file itself
A lot of time is spent on construction before use
For some very large documents, this may be impractical

SAX parsers store only local information that is encountered during the
serial traversal

Hence, programming with SAX parsers is, in general, more efficient
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