Providing Guaranteed Services without Per Flow Management

1
Providing Guaranteed Services without Per Flow
Management

• Todays Internet offers best-effort delivery
  service and IP routers are stateless (except
  coarse-grained routing state) gt scalable and
  robust
• Solutions for better services
• - stateless, e.g. RED for congestion
  control, Diffserv for QoS
• - stateful (per flow management), e.g. FQ,
  Intserv
• Stateful solutions provide more powerful and
  flexible services, but require per flow state,
  classification, buffers and scheduling
• Goal want to emulate stateful services (per flow
  bandwidth and delay guarantees) at the cost of
  stateless solutions (only edge routers perform
  per flow management)

2
Dynamic Packet State (DPS)

• Ingress router computes and inserts per flow
  state in packets header
• Core router processes packet based on its state
  and nodes state
• Core router updates both packet and nodes state
• Egress router removes state from packets header

3
Reference Stateful Network

• Want to emulate a network where
• - each router implements Jitter-VC discipline
  on data path
• - each router performs per flow admission
  control on control path
• On data path, use DPS to approximate Jitter-VC
  with Core-Jitter-VC, where core routers do not
  maintain per flow state

4
Jitter Virtual Clock

• Delay-jitter rate-controller VC scheduler
• Assign each packet eligible time and deadline
• Keep packet in rate-controller until it becomes
  eligible
• Schedule packets in increasing order of their
  deadlines
• A network of Jitter-VC servers can provide the
  same guaranteed service as a network of WFQ
  servers
• Intuition eligible time and deadline of a packet
  in a flow with reservation r ltgt start and
  finish time of transmitting the packet in an
  ideal network in which flow has dedicated links
  of capacity r
• Eligible time max of
• arrival time ahead time (departure time
  at previous router prop delay) (deadline at
  previous router - departure time) deadline at
  previous router prop delay
• deadline of previous packet (this is the
  per flow state!)
• Deadline eligible time (packet length / flow
  reserved rate)

5
Core-Jitter VC

• Goal eliminate per flow state at core routers
• - eliminate dependence on previous packet
  deadline
• Solution introduce a slack variable s, such that
  at each core router
• packet deadline at previous router prop
  delay s gt
• deadline of previous packet
  for every packet
• Then eligible time
• packet deadline at previous router
  prop delay s
• s is inserted in packets header by ingress
  router, depends on
• - lengths of previous and current packets
• - slack of previous packet
• - number of hops (known at admission control
  time)
• Each packet carries its slack, flow reserved
  rate, and ahead time at previous router
• No per flow classification and no per flow
  scheduling state

6
No per Flow Admission Control

• Goal light-weight signaling protocol that does
  not require core routers to maintain per flow
  state (the reserved rate of the flow)
• A router admits a reservation r, if r lt C - R
• Solution maintain aggregate reservation R
• Problem requires per flow state to handle
  partial reservation failures and message loss (to
  maintain consistency)
• Solution Estimate aggregate reservation Re
• Account for approximations and compute upper
  bound Rb, Rbgt R
• Admit a reservation if r lt C - Rb

7
Estimate Aggregate Reservation

• If all flows were sending at their reserved
  rates, computing Re is trivial just measure
  traffic throughput
• Problem what if flows do not send at their
  reserved rates?
• Solution Associate with each packet a virtual
  length
• - virtual length r (time now - transmit
  time of previous packet)
• Use virtual lengths instead of actual lengths to
  compute Re
• Ingress router inserts virtual length in packets
  header
• Core router uses virtual lengths to compute Re on
  each output link
• Re can underestimate R, because it ignores jitter
  and packet inter-departure times, and
  reservations accepted or terminated in the middle
  of an estimation interval

8
Computing Upper Bound

• Rb (sum of virtual lengths / estimation
  interval)/(1-f) Rn
• where
• f (max inter-departure time max jitter) /
  estimation interval
• Rn new reservations made during estimation
  interval
• The estimation algorithm is robust in presence of
  control message loss and duplication
• - their effect is forgotten after one time
  interval
• If no packet of a flow departs during a
  predefined interval (i.e., maximum
  inter-departure time), ingress router generates a
  dummy packet

9
Implementation

• Where to insert the state?
• Possible solutions
• - between link layer and network layer
  headers
• - as an IP option
• - find room in IP header (e.g. TOS byte and
  fragment offset)