Lecture 7 : Common Protocols

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Lecture 7 Common Protocols

• Pourya Dehnadi

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• HTTP
• Hyper Text Transfer Protocol
• Intended for loading web pages over the net
• Primary request formats
• ltform action methodPOSTgtlt/formgt
• GET
• Simplest form carries a single URL into the
  server
• Can be found in the location field of the
  browser
• name-value pairs begin after ? and are
  separated by
• Special characters are encoded with hex number
  following
• space 20
• Limited amount of information can be sent this
  way
• POST
• Transmits more information than GET
• Sends data from client to server in multiple
  lines following the original request
• HEAD
• Used to obtain limited information about a web
  page, not the whole web page itself

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• HTTP (continued)
• Default port number is 80, but any free port
  number can be used
• By convention 80xx
• HTTP is stateless
• Not an issue for static content
• Major issue for applications
• Shopping Cart example
• Ways to maintain state across multiple requests
• Cookies
• Name-value pair stored in a file on the browser
• Client queries the value of a given cookie to
  associate a new request with earlier requests
• Poor implementation of cookies has lead to
  security breaches
• URL Rewriting
• Server modifies every link in a web page so that
  the URLs are unique to the particular client.
• Issues when typing in a URL or bookmarking
• HTTP REFERRER can read the URL and can
  potentially break into the user session.

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• HTTP (continued)
• Ways to maintain state across multiple requests
  (continued)
• SSL
• SSL connections have state and that state can be
  used by the application layer
• More secure than cookies and URL rewriting, but
  slower because it has to encrypt/decrypt
• Applets or other clients
• Applet can open a dedicated connection to a
  server and maintain state inherently
• The connection is held open
• Pro faster communication, since the overhead of
  making and breaking connections is eliminated
• Con maintaining an open connection has resource
  demands on the server that results in scaling
  issues

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• HTTPS
• Not a single protocol, but a double layer
  protocol
• Combines HTTP and SSL transport
• Benefits
• Encryption of data
• Encryption protocol can vary (e.g. 40 bit vs. 128
  bit)
• Identification of parties
• When setting up a connection a certificate can be
  sent to establish identity
• State of session

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• IIOP
• Internet Inter-ORB Protocol
• Used by CORBA systems to call methods and pass
  arguments and returned data over the network.
• CORBA APIs and IIOP are available for many
  platforms and languages
• The use of Java RMI directly with JNI is always
  an alternative to installing IIOP code
• Good for connecting to legacy systems
• CORBA provides robust services, IIOP can access
  those services, for example
• Naming
• Security
• Transaction management
• IIOP can get through firewalls by tunneling
  messages across HTTP through port 80

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• JRMP
• Java Remote Method Protocol
• Native transport protocol of RMI
• Like IIOP, it can handle methods and passing
  their parameters and return values
• Unlike IIOP, does not restrict values to data
  type but can handle objects
• Can transfer the class file of an object into the
  recipient of an argument or returned value, or
  even an exception
• Can handle mobile agents since it can support
  passing of objects

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