Administrative

 - Note schedule change.  Classes cancelled next week.
 - Papers due next tuesday at 5pm. Send email, and hand in 2 hard copies.
 - Presentations Thursday (and Friday).  In systems lab.  Can use a 
   laptop (but suggest trying it out first to make sure it works).
 - Presentation schedule on web page.  Hard stop after 30 minutes.
   Suggest 20 minutes presentation, 10 minutes Q and A. If you have a
   demo, fit it into 30 minutes, or send email to Tom to schedule demo
   during one of the breaks.  Max demo: 5-10 minutes.
 - No peer reviews of presentations, but we are required to attend two -
   our own (hopefully!!!) plus one other.
 - Final will be handed out in sealed envelopes on day of presentations.
    - Take home
    - Open book
    - Individual
    - Must finish 48 hours from when you open envelope
    - Suggest spending a couple days thinking about questions, writeup
      of answers should only require a couple hours.
    - Final deadline is December 19, 5pm.  Email to Janet and Tom (or
      hard copies to both).

Today: Architectural visions for the Internet

Active Networks/ANTS paper

 - Users running code in middle of network
 - Good idea or bad idea?
 - Goal: code in middle of network
 - Mechanism: Capsules.  Packets annotated with code.
 - Why need code in network?
    - Deployment and flexibility (for changing protocols)
    - Heterogeneity of networks.  Discontinuities are where action in
      net occurs.  Ability to manage is limited with end-to-end 
      protocols.
 - Is this the right mechanism?
    - API restricted
    - Tradeoff between too restricted and performance
    - Difficulties
       - Network measurements
       - Computation on payload
       - Reliable communication models not available
 - ANTS:  code applies to individual data packet.  Alternatives: code
   applies to whole data stream, code applies to all data streams.
 - Since code only applies to individual packet, administrator can't
   insert code that modifies all packets.
 - Security issues: DoS attacks?
 - Predictions: Pro - Faster deployment of services by ISP's. 
   Con: Security, Performance at high speed, No service guarantees,
        No killer apps - anything which we can do with active nets
        (eg, IPv6, IP multicast) could instead be rolled out directly
 - Can we just use overlays instead?

Internet Indirection (i3)

 - Communicate via asynchornous transfer
 - Allocate mailboxes in mid-network, used for synchronization
 - Host A sends packets to host B's mailbox.  Host B requests packets
   from mailbox when it wants them.
 - Good for mobile hosts (changing attachment points).
 - Can also be used to construct a multicast tree - children request
   packets from parent when ready.
   
Overlays
 - Dificult to change IP infrastructure.
 - Use Internet paths as virtual links.
 - Route packets through overlay hosts using Internet as transmission
   medium.
 - Can sometimes find a better path through overlay network than the
   Internet would normally give you.