Stateful Header Compression

1
Stateful Header Compression

• Kris Pister
• UC Berkeley
• Dust Networks

2
The Motivation

• In many sensor networks, gt90 of packets
• Flow along paths with lots of shared state
• Final destination, sometimes source
• Link and end-to-end crypto
• Source destination ports
• Route
• Have very short fundamental payloads
• 2B, 4B not uncommon. Data, or (data, timestamp)
• Todays minimum multi-hop overhead
• Application 0-20B
• TransportNetwork 12B (HC1, HC2_UDP)
• Link 11B 9B (security)
• PHY 6B
• gt10x overhead
• Why fix our part?

3
Example

• Once per second, mote A wakes up and sends a
  packet with exactly the same
• 5B Mesh header
• 3B Dispatch, HC1, HC2
• 1B UDP compressed ports
• For a period of hours or days (thousands to
  millions of packets) this information doesnt
  change

4
Flow-based compression

• Perhaps instead a flow label could be sent
• New dispatch byte
• Header compression associated with flows
• Flow label index into a table with all HCx
  values
• Soft state nodes along path can reconstruct
  full packet if necessary
• Checksums, MICs performed on full packet w/
  virtual headers
• Crazy talk
• Both Dispatch Flow label could come from L2
• Implicit in link type
• Dozer, SCP, TSMP all have mechanisms for uniquely
  determining flows

5
The Dream

• Provide a continuum of header compression from 0
  to 100 depending on shared state
• Application
• Transport
• Network
• Link
• Requires cooperation between IEEE and IETF

6
TSMP as an example

• Time Synchronized Mesh Protocol
• Basis of Wireless HART, SP100 (? 15.4E)
• Sub-ms time synch across network
• ltlt 0.1 radio duty cycle maintains synch
• Additional duty cycle allocated as needed by
  traffic
• Uses a flow label to associate L2 resources and
  L3 routes with L4 QoS
• L2 activity uniquely associated with particular
  flows
• If its 84206.351 AM, you must be node X with a
  message from node Y to node Z and the next hop is
  Q.