lect-18 - Multimedia & QoS ECE/CS 438 Fall 2011 Slides...

Info iconThis preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
ECE/CS 438 1 Multimedia & QoS ECE/CS 438 Fall 2011 Slides mostly from Peterson & Davies
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Problem n From the network s perspective, application programs send messages to each other. n Each of these messages is just an uninterpreted string of bytes. n From the application s perspective, however, these messages contain various kinds of data— arrays of integers, video frames, lines of text, digital images, and so on. In other words, these bytes have meaning.
Background image of page 2
Problem n We now consider the problem of how best to encode the different kinds of data that application programs want to exchange into byte strings.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Presentation Formatting n One of the most common transformations of network data is from the representation used by the application program into a form that is suitable for transmission over a network and vice versa. n This transformation is typically called presentation formatting.
Background image of page 4
Presentation Formatting n The sending program translates the data it wants to transmit from the representation it uses internally into a message that can be transmitted over the network; that is, the data is encoded in a message. n On the receiving side , the application translates this arriving message into a representation that it can then process; that is, the message is decoded. Encoding is sometimes called argument marshalling, and decoding is sometimes called unmarshalling. This terminology comes from the RPC world.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Presentation Formatting Presentation formatting involves encoding and decoding application data
Background image of page 6
Presentation Formatting Big-endian and little-endian byte order for the integer 34,677,374.
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Presentation Formatting n Taxonomy ¡ Data Types n The first question is what data types the system is going to support. In general, we can classify the types supported by an argument marshalling mechanism at three levels. ¡ At the lowest level, a marshalling system operates on some set of base types. Typically, the base types include integers, floating-point numbers, and characters. The system might also support ordinal types and booleans. ¡ At the next level are flat types—structures and arrays. ¡ At the highest level, the marshalling system might have to deal with complex types— those types that are built using pointers ¡ In summary, depending on how complicated the type system is, the task of argument marshalling usually involves converting the base types, packing the structures, and linearizing the complex data structures, all to form a contiguous message that can be transmitted over the network
Background image of page 8
Presentation Formatting Argument marshalling: converting, packing, and linearizing
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Presentation Formatting n Conversion Strategy ¡ Once the type system is established, the next issue is what conversion strategy the argument marshaller will use. There are two general options: n canonical intermediate form and receiver-makes-right
Background image of page 10
Presentation Formatting n Conversion Strategy n The idea of canonical intermediate form is to settle on an external representation for each type; the sending host
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 49

lect-18 - Multimedia & QoS ECE/CS 438 Fall 2011 Slides...

This preview shows document pages 1 - 12. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online