Internet Protocols I

1
Internet Protocols I
Incheon Paik
2
Some Protocols

• HTTP Communication
• Connectionless Communication
• Stateless Communication

(1) TCP Connection Request
(2) HTTP Request
Server
Client
(3) HTTP Response
(4) TCP Connection Close
3
Some Protocols

• HTTP Message
• Start Line Client Request Information /
  Response Status Information
• Message Header Additional Information for HTTP
  Message such as Date, Program Name, Version,
  Cookie, User Authentication, Cache
• Message Body Contents for Request or Response.
  In case of POST, Input data consists of data
  stream encoded in request message.

4
Some Protocols

• Client Request Message in HTTP
• Request HTTP Command, URI, and HTTP Version,
  Header NameHeader Value, Request Message Body
• HTTP Command GET, HEAD, POST/ OPTIONS, PUT,
  DELETE, LINK, UNLINK, TRACE
• Server Response Message in HTTP
• Response Message HTTP Version, Status Code,
  Code Description, Response Header, Response
  Message Body
• Response Status Code (Reference 100-199),
  (Success 200-299), (Redirection 300-399),
  (Incomplete 400-499), (Server Error 500-599)

5
Some Protocols

• HTTP Message Header
• HTTP Header Used for transmitting any kinds of
  information between client and server, Header
  Name Blank Header-value
• General Header Client Request, Server Response,
  Cache setup, Connection, Date, etc
• Client Request Header Client information and
  preferred data type, Accept Character set,
  encoding type, and authorization
• Response Header Server Information, Message
  processing methods for response message. Web
  server information, Cookie setup, authenticate
  information.
• Entity Header HTTP message body information,
  encoding method of message, contents length, MD5
  information, encoding method of contents
  transmission, MIME type

6
Some Protocols

• MIME Type
• As HTTP transmission deal with multimedia
  documents, pre-defined method to deal with that
  data by client should be described.
• MIME(Multipurpose Internet Mail Extension) Type
• Client Using Accept Header, Clients can define
  their preferred media type
• Server Describe MIME Type in Content-Type
  Header
• MIME Type form Type/Subtype (ex
  application/x-javascript)
• Standard MIME Type
• Text, Multipart, Message, Application, Image,
  Audio, Video

7
CGI Communication

• CGI(Common Gateway Interface)
• Transmit Messages by GET/POST Method
• Characteristics
• Extend Web Server, Dynamic Response, Only Install
  in Server Side
• Overhead, Security, Interactive pages, Cannot
  keep the connection Problems

Process 1
Process 1
Process 1
Web Server
CGI Program
Processes
8
Extended CGI

• ASP (Active Server Page) of Microsoft
• Combine HTML, Server side Script, and Server side
  Component
• Written in Jscript, VBScript, and run on IIS
  Server
• Can use COM Component
• Java Servlet and JSP
• Platform Independent, Safe and Effective Thread
  Service, Object Oriented Paradigm
• Easy to interoperate with Legacy Application
• JSP is similar to ASP, and provide HTML script
  language and JavaBeans Component
• Object Web
• CORBA (Common Object Request Broker Architecture)
• EJB (Enterprise JavaBeans)
• DCOM (Distributed Common Object Model)

9
Motivations of Servlet and JSP
Slide 9-18, Used the Material by Philippe Rochat

• Faster than CGI (no process creation overhead)
• Java is Internet oriented
• Servlet API
• Security
• Session support
• Code reuse and portability
• JDBC support
• Next step Enterprise Java Beans (EJB)

10
Object Web
RMI/IIOP
JSP
DBMS
EJB
HTML/XML
HTTP
Web Server
IIOP
CORBA
HTTP
Servlet
Applet
Legacy Application
11
Servlet and Servlet Container
Servlet Application 1
Servlet Application 2
Servlet Application N
Java Servlet API
Servlet Container 1
Servlet Container 2
Servlet Container N

• Servlet Container
• - To run servlet, there need to be JVM to run
  Java servlet class and
• servlet container to provide servlet
  applications with system service.
• Deliver HTTP request of a client to servlet
  application,
• and HTTP response of the servlet applcation to
  the client

12
How-to Write Servlet

• Very Similar to applet
• Must inherits
• HttpServlet
• Must implements one of
• doGet
• doPost
• doPut
• Receives
• HttpServletRequest
• HttpServletResponse

13
Execution of JSP
Handler Request
JSP Request
JSP Handler Servlet
Servlet Container
Web Browser
Web Server
Servlet Invocation
JSP File Check
Java file Compile
Class Loading
JSP file Compile
JSP Servlet
Class File (.class)
JSP File (.jsp)
Java File (.java)

• A user requests .jsp file through URL.
• Web server requests JSP handler to process .jsp
  file
• JSP/Servlet container pass the corresponding
  .jsp file to JSP handler servlet
• JSP Handler Servlet
• Check JSP file, execute the existing .class
  servlet when no change
• When there was change, generate .java source
  code from .jsp
• Compile the java source
• when .class file was generated normally, execute
  the servlet.

14
Servlet and JSP Examples

• Refer to Apache Tomcat
• When you install Apache Tomcat,
• http//localhost8080/examples/servlets/
• http//localhost8080/examples/jsp/

15
Introduction toJava Remote Method Invocation
(RMI)
16
Distributed Objects

• Objects that can communicate with objects on
  heterogeneous run-time environments
• Distribute Objects Standard Protocol ex JRMP
• Robust
• Reliable
• Transparent
• Distributed Objects Technology
• Multi-Platform
• Transparent access to distributed objects
• Language Neutral RMI, CORBA, DCOM

17
Java Remote Method Invocation (RMI)

• Can use objects on remote different run-time
  environments as like objects on a local run-time
  environment
• Abstraction of low-level network code on
  distributed network to provide developers an
  environment where they focus on their application
  development.

18
Introduction to RMI

• Distributed Processing on Network
• Define of Remote Interface
• Object Serialization
• java.rmi and java.rmi.server
• Create Stub and Skeleton

19
Communication of Remote Object and Client
JVM
JVM
Remote Object
Client
Stub
Skeleton
RMI Client Application
RMI Server Application
Network
20
Writing Java RMI Application

• Writing RMI Application
• Definition of Remote Interface
• Definition of Remote Implementation Class
• Write RMI Server Application
• Write Client Application

• Compile and Run the Application
• Compilation of the Implementation Class
• Creation of Stub and Skeleton using rmic
  command
• Compilation of the Server Application
• Run the RMI Registry and Start the Server
  Program
• Compilation of the Client Program
• Run the Client

21
Hello Example RMI
Interface
import java.rmi.Remote import
java.rmi.RemoteException public interface
Hello extends Remote String sayHello()
throws RemoteException
22
Hello Example RMI
HelloImpl object
Implementation (Server)
import java.rmi.Naming import
java.rmi.RemoteException import
java.rmi.RMISecurityManager import
java.rmi.server.UnicastRemoteObject public
class HelloImpl extends UnicastRemoteObject
implements Hello public HelloImpl() throws
RemoteException super()
public String sayHello() return "Hello
World!" public static void
main(String args) // Create and
install a security manager if
(System.getSecurityManager() null)
System.setSecurityManager(new RMISecurityManager()
)
try HelloImpl obj new HelloImpl()
// Bind this object instance to the name
"HelloServer" Naming.rebind("HelloServer",
obj) System.out.println("HelloServer bound
in registry") catch (Exception e)
System.out.println("HelloImpl err "
e.getMessage()) e.printStackTrace()

Compile Skeleton Creation javac
Hello.java javac HelloImpl.java rmic HelloImpl
23
Hello Example RMI
A Client Application
import java.rmi.Naming import
java.rmi.RemoteException public class
HelloClient public static void main(String
args) String message "Hello This is my
test message" // "obj" is the identifier
that we'll use to refer // to the remote
object that implements the "Hello" //
interface Hello obj null try
obj (Hello)Naming.lookup("//"
"/HelloServer") message obj.sayHello()
catch (Exception e)
System.out.println("HelloClient exception "
e.getMessage()) e.printStackTrace()
System.out.println("Message " message)
// end of main // end of HelloClient
24
Hello Example RMI
File policy
grant // Allow everything for now permission
java.security.AllPermission
Start Registry Server Run Server and Client
rmiregistry java Djava.security.policypoli
cy HelloImpl javac examples/hello/HelloClient.j
ava java Djava.security.policypolicy
HelloClient
Run the RMI Server
Compile the Client
Please ensure there is the policy file in the
current directory
Run the Client
25
RMI Structure

• Protocol
• Java Remote Method Protocol (JRMP)
• For distribute object environment by pure Java
  environment
• RMI/IIOP Can communicate with CORBA

• JRMP
• Communication Mechanism between Stub and
  Skeleton
• Object Serialization Types of parameters and
  return type of a remote method should follow Java
  serialization mechanism

26
Stub and Skeleton
JVM
JVM
Remote Method Invocation
Remote Method Invocation
Remote Object
Client
Stub
Skeleton
Data Transformation
Remote Method Return
RMI Client Application
RMI Server Application
Unmarshalling
Unmarshalling
Marshalling
Marshalling
Object Serialization
Network
27
Stub and Skeleton

• Stubs and Skeleton
• When RMI client invokes a remote method of a
  remote object, it uses stub reference of the
  remote object instead of remote object reference.
• For marshalling and unmarshalling of stub and
  skeleton, object serialization and
  deserialization are used.
• Condition of Object for Object Serialization
• Object should implementjava.io.Serialization
  interface
• Built-in types can be serialized basically
• Member variables should implement the
  Serializable interface or be declared as
  transient
• Static member variables can not be serialized.

28
JRMP Class
Marshall/Unmarshall (Object Serialization)
Virtual connection
Network connection
Creation of reference to remote object
Managing connection to remote object
29
Introduction toCommon Object Request Broker
Architecture(CORBA)
30
Contents

• Overview of distributed programming challenges
• Overview of CORBA architecture
• CORBA programming with Java ORB
• WWW, Java and CORBA
• GIOP and IIOP
• Trends in Internet

31
CORBA Contributions

• CORBA addresses two challenges of developing
  distributed system
• Making distributed application development no
  more difficult than developing centralized
  programs.
• Easier said than done due to
• Partial failures
• Impact of latency
• Load balancing
• Event Ordering
• Providing an infrastructure to integrate
  application components into a distributed system
• i.e., CORBA is an "enabling technology"

32
CORBA Architecture
33
Related Works

• Related technologies for application integration
  include
• Traditional RPC
• Provides "procedural" integration of application
  serveices
• Doesn't provide object abstractions
• Does not address inheritance of interfaces
• Widows DCOM

34
CORBA Components

• The CORBA specification is comprised of several
  parts
• 1. An Object Request Broker (ORB)
• 2. Basic Object Adapter (BOA), Portable Object
  Adapter(POA)
• 3. An Interface Definition Language (IDL)
• 4. A Static Invocation Interface (SII)
• 5. A Dynamic Invocation Interface (DII)
• 6. A Dynamic Skeleton Interface(DSI)
• 7. Interface and implementation repositories
• 8. Programming language mappings
• 9. An Interoperability Spec(GIOP and IIOP)
• Other documents form OMG descirbe common object
  services built upon CORBAservices
• e.g. , Event services, Name services, Lifecycle
  service

35
Object Request Broker

• The Object Request Broker(ORB) is the central
  component in CORBA
• An ORB provides mechanisms for invoking methods
  on local/remote objects
• ORB mechanisms automate
• Object location, creation, activation and object
  management
• Message exchange between objects
• CORBA ORB provides security also.

36
Interface Definition Language (IDL)

• Developing flexible distributed applications
  on heterogeneous platforms requires a strict
  separation of interface from implementation(s)
• Benefits of using an IDL
• Ensure platform independence
• e.g., Windows NT to UNIX
• Enforce modularity
• e.g., must separate concerns
• Increase robustness
• e.g., reduce opportunities for network
  programming errors
• Enable language independence
• e.g., C, Smalltalk, COBOL to C, Java

37
CORBA IDL

• OMG IDL is an object-oriented interface
  definition language
• Used to specify interfaces containing operations
  and attributes
• OMG IDL support interface inheritance (both
  single and multiple inheritance)
• OMG IDL is designed to map onto multiple
  programming languages
• e.g., C, C, Smalltalk, COBOL, Modula 3, DCE,
  Java, etc.
• OMG IDL is similar to Java interfaces, class and
  C class

38
Initial OMG IDL Bank Specification

• // Bank.idl
• module Bank
• interface Account
• float balance()
• interface AccountManager
• Account open(in string name)

39
OMG IDL Compiler

• A OMG IDL compiler generates client stubs and
  server skeletons
• Stubs and skeletons automate the following
  activities (in conjunction with the ORB)
• Client proxy factories
• Prameter marshalling/demarshalling
• Implementation class interface generation
• Object registration and activation
• Object location and binding

40
Producing IDL file, Client, and Object
Implementation
41
Application Interfaces

• Interfaces described using OMG IDL may be
  application-specific, e.g.,
• Databases
• Spreadsheets
• Spell checker
• Network manager
• Air traffic control
• Documents
• Medical imaging systems
• Objects may be defined at any level of
  granularity
• e.g., from fine-grained GUI objects to multi-mega
  byte multimedia "Blobs"

42
OMG IDL Features

• OMG IDL is a superset of C, Java, etc.
• Note, it is not a complete programming language,
  it only defines interfaces
• OMG IDL supports the following features
• Modules
• Interfaces
• Operations
• Attributes
• Inheritance
• Basic types(e.g., double, long, char, etc).
• Arrays
• Sequence
• Struct, enum, union, typedef
• Consts
• Exceptions

43
Object References

• An "Object reference" is an opaque handle to an
  object
• Object references amy be passed among processes
  on separate hosts
• The underlying CORBA ORB will correctly convert
  object references into a form that can be
  transmitted over the network
• Presumably by converting it to a "stringfied"
  reference
• The ORB passes the receiver's implementation a
  pointer to a proxy in its own address space
• This proxy refers to the object's implementation
• Object references are a powerful feature of CORBA
• e.g., supports "peer-to-peer" interactions

44
Object Adaptor

• CORBA "object adaptors" provide services for
  binding object references to their associated
  object implementations
• Several types of object adaptors are available
• Basic Object Adaptor(BOA)
• Objects and object references are known to the
  ORB
• Thus, an object implementation has to explicitly
  register objects to be activated
• Object-Oriented Database Adaptor(OODA)
• This adapter uses a connection to an o-o db to
  access the objects stored in it.
• Since the OODB provides the emthods and
  persistent storage, object may be registerd
  implicitly.

45
Object Adaptor

• Creation and Analysis of Object Reference
• Method Invocation
• Interaction
• Activation and Deactivation of Object and
  Implementation
• Matching to Object Implementation According to
  Object Reference
• Registration of Object
• Problem of BOA
• Inconsistency of Specification
• Difference of BOA Implementation
• Problem in Server Portability

46
Portable Object Adaptor

• Allow the Persistent Object
• Allow more Object Implementation
•  
• Characteristics
• Map an Object Reference to the Servant that
  Implements that object
• Allow Transparent Activation of Objects
• Associate Policy Information With Objects
• Make a CORBA object persistent over several
  server process lifetimes
• Object ID Namespace
• Policy of Multi-Threading, Security, Object
  Management
• Multi POA with different policy and name space
  exist in a server

47
EXAMPLE

• Hello Example
• Look at the demonstration
• You can exercise the CORBA programming using JDK
  simply.

48
Internet Inter-ORB Protocol (IIOP)

• The mapping of the GIOP message transfer to
  TCP/IP connections is called IIOP
• GIOP can map to Novell IPX and OSI also
• TCP/IP Connection Usage
• Servers must listen for connection requests.
• A client needing a objects services must
  initiate a connection with the address specified
  in the IOR, with a connection request
• The listening server may accept or reject the
  connection.
• Once a connection is accepted, the client may
  send Request, LocateRequest, or CancelRequest
  messages by writing to the TCP/IP socket it owns
  for the connection.

49
CORBA Common Services

• Basic Services to build distributed object system
• Naming, Event, Persistence, Life Cycle,
  Concurrency, Externalization, Relation,
  Transaction, Timing, License, Security,Property,
  Query, Trader, Collection, Startup, Interface
  type Version Management Services

50
CORBA Common Facilities

• Software Components to provide some application
  function
• Horizontal facilities, Vertical facilities
• Horizontal facilities Compound Presentation,
  Compound Interchange, Internalization, Time
  Operations, Mobile Agent, System Management
• Vertical facilities Healthcare, Financial
  Facilities.