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The Application Services Layer (ASL)

The Application Services Layer (ASL). George, Jim, Joe, Tal, Yitao CS 294-3 – Spring 2002. The Application Services Layer (ASL). Provides coherent, available, and customized services which the application can use. Stock. Application. Map. Translation. ASL.

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The Application Services Layer (ASL)

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  1. The Application Services Layer (ASL) George, Jim, Joe, Tal, Yitao CS 294-3 – Spring 2002

  2. The Application Services Layer (ASL) • Provides coherent, available, and customized services which the application can use Stock Application Map Translation ASL Distributed Processing, underlying network

  3. Functionality at ASL • Service Composition (pipelining underlying services, such as text to translation) • Lookup of the appropriate Dist. Computing layer • Aggregation of information from lower layers into coherent format • Masking heterogeneity (XML to HTTP, Video to sequence-of-images, French to Greek) • Synchronication/Serialization of possibly asynchronous lower elements • Measurement coordination/control

  4. Interface to ASL Application Callback (notification) Msg_handler { … } XML{ n = “map service”, r = “99.9% uptime”, c <= “$X/month”, loc = (x,y,z), lang = Fr,Gk

  5. Need to parameterize services offered (uptime in percentage, bandwidth in Kb/s, storage in gigabytes, service-specific information for translation, mapping, etc) Need to express what we want from below Conceptually like SQL Select * from Translate where inp_lang=En and out_lang=Fr and reserve=100_flows Requirements from below

  6. Role of message handler • Message handler used to give lower level a way of “understanding” requirements from upper level • The ASL might not understand what a requirement means, and this mechanism allows the app to program the ASL with this knowledge • A general purpose way to add detection and enforcement for new services

  7. Role of callback mechanism • An application might ask for a connection with no more than 60ms latency • The underlying network might not be able to support that anymore • Need a way to notify the application that the underlying conditions have changed (no longer to guarantee this anymore, or perhaps can provide better service now that some flows have left the system)

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