Composable Services Working Group
Notes from DARPA meeting
March 9-10, 1998
Tucson, AZ

-------------------Monday afternoon session ------------------------

Issues on original (Mon afternoon) agenda [many not covered]

- presentations on ideas for composition (PLAN, LIANE, Netscript)
- types of composition 
  o intra-EE
  o inter-EE
- location of composition
  o inter-node
  o intra-node
- goals/characteristics of composition methods
  o for evaluating "success" of composition method
  o for advertising characteristics of comp. method
- relationship to security
- priorities: near and long-term useful composition functionality
- defining composition

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Scott Nettles (U. Penn) gave an overview of PLAN.

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Key points: PLAN

- linear composition of protocol stacks
- "wrapper model" of protocol creation (tree-structure)
- entities to compose are (fairly) static
- emphasis on lightweight composition (w/associated sacrifice
  in flexibility)
- computation carried with communication

Other issues:

- dynamic composition
- inserting value added stuff in the middle
  [-> must have access to understandable representation of pkt content]
- how does transparent functionality (e.g., Boosters) relate 
  to composition?

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Samrat Bhattacharjee (GT) gave an overview of LIANE.

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Inter-EE issues

- composition/communication
- what seems reasonable to allow?
- what benefits are possible? why to do it?
- what methods are there?
- how can methods be evaluated?


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Note that during the discussion with the entire AN group,
the decision was made to focus on intra-EE composition.
The Tuesday working group discussion reflects that decision.


-----------------Tuesday afternoon session ---------------------------


Terminology:
   - components - entities put together by composition method
   - composite - entity that results from composition of components
   - composition method - mechanism for putting together components
			  into a composite


Properties of a composition method:
   
- recursive? i.e., can a composite be a component?

- structure of composition supported
  o layering (i.e., on-the-wire nesting of protocols)
  o linear composition
  o parallel composition
  
Q: is a graph a sufficient description of the structure?
A: no

- structure of composite: static or dynamic?
  i.e., when does binding occur to a structure?

- components: static or dynamic?
  i.e., when does binding of components to a structure occur?

- division of functionality
  o packet content
  o node-resident content

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More properties of a composition method:

- how do components interact (share info)?
  o shared variables
  o message passing
  o procedure call/return

Note that interaction may fit unicast, multicast, broadcast models

- naming
  o what is named?
  o how are names known? used?
  o required: ability to name composite

- inter-node composition
  o all previous properties/questions apply
  o note that wire format may become important here since
    the wire is the only mechanism for communicating between
    components on different nodes

- non-packet-driven invocation of components
  o needs timers


Meta properties:
- amenable to network management
- performance
- security
- impact on network and node
  


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Errors that can result from/during composition:

   - component not present at node
   - composite not present at node
   - generally: node resident "facility" not present at node
   - resource exhaustion (not specific to composition)
   - packet resident content not present
   - security-related "errors" - e.g., not allowed to compose this way
   - logic errors [are these different? how? meaning?]

Error handling:
   - local and global (e.g., error returned somewhere)
   - propagation of errors within composite

authorized composition (security issue)

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Challenge problems:

- Solve the name resolution and resource discovery problem.
- Develop a composition method with useful functionality
  that can make guarantees.
- Demonstrate composition to create a multicast protocol that has
  CBT routing, reliability, and at-most-once semantics.
- Demonstrate a known, reasonable complex, protocol using composition.
  

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Draft document content:

- terminology
- goals of composition
- reference examples of composite behavior
- list of properties and meta-properties of composition method
- examples of composition methods (with tie to properties)
- other issues
  o errors and error handling
  o naming and resource discovery
  o node-resident content deployment
  o interface between security and composition
- comment on inter-EE composition
- challenge problems