How to write a bad paper.

There was a presentation on writing papers and giving talks. See Tom
about the notes he handed out. There is additional information at
http://www.cs.utexas.edu/users/dahlin/advice.html

Quality of Services

Reservations Protocols. Two main questions: 1) How to get reservations to
occur? And 2) How to do scheduling?

How to get reservations to occur.

- have request for some guarantee

- decide to make it (reply)

- apply it to all elements in path

Zeroth way

- Given a path of routers, each maintains a record of all
reservations. Make a request to all routers on the path. If it is not OK,
the router says NO; otherwise, the router allocates the capacity

- If there doesn't exist the capacity half way through the
path, what about the ones that already committed?

- We have to have some mechanism to release
 o Maybe a three way handshake, eventually a commit message, if lost -> timeout
- If commit lost, retry, use timeout (if not refreshed, commitment disappears)

- If send to host fails? Retry.

-  RSVP -- packet network generates

- Periodic re-reservations: path change -> eventually re-reserve; old path times out.

- Asymmetric routing, receiver driven reservations.

- Stoica -- bound reserved capacity

- Reservation: at every node: rate, time refreshed, queue
packets.

Scheduling QoS

- what does the router have to do with each packet to provide
some end to end guarantee?

- FIFO -- Not very good, best effort

- Priority queues -- depends upon what the priority is. If
you assign highest priority < minimum single link capacity, then
it's OK.

o # of pkst with priorities < capacity

- RIO (RED with In Out) pkt markings; Single FIFO queue and
preferentially dropped packets

o Good for out but not in

- WFQ (Weighted Fair Queuing) -- each flow gets its own
queue, round robin (proportional to packet size), corrects for different
packet sizes and preference to reservations. Parekh & Gallaher.

- It does guarantee but only by reserving buffer space.

- Stoica

o Jitter virtual clock (non-working conserving)

o Emulate it without per flow state

- Overlay QoS

o Talk about next week