Ethernet Traffic

1
Ethernet Traffic
2
Self Similarity

• No natural length of a burst, at every time
  scale, similar-looking traffic bursts are
  evident.
• Aggregating streams of such traffic intensifies
  the self-similarity instead of smoothing it
• Aggregation causes more burstiness and requires
  larger buffers

3
Over 4 year period

• Ethernet traffic is self-similar irrespective of
  when and were the data were collected
• External and Internal TCP traffic are both
  self-similar
• Hurst parameter gives index of self similarity

4
Significance of Self-Similarity

• No characteristic length of a busy period or
  packet train
• Same statistics found with VBR traffic
• Congestion control doesnt behave the same with
  self-similar traffic
• When congestion occurs, losses are severely
  concentrated and are far greater than the
  background loss rate.

5
Parsimonious Models

• FGN uses mean, variance and H (Hurst self
  similarity parameter, a function of utilization)
• These models are simpler and may provide better
  results than conventional overparameterized
  models.
• In curve fitting, if you have points that do not
  fit the model (self similarity), the model
  becomes less effective

6
Conclusions

• Ethernet traffic is self similar
• Aggregation does not produce Poisson-like streams
• Congestion produced by ethernet traffic will not
  match the models during burst periods
• Use Hurst parameter models for flows with high
  degrees of self similarity

7
WAN technologies

• Why not run ethernet over WAN?
• Minimum packet size required for collision
  detection CSMA/CD.
• Window size for TCP determined by DelayBandwidth
• Delay includes SOL delays and queuing delays

8
Collisions
Jam Signal
9
Min Packet Size

• Packet must fill whole pipe in order to block
  other hosts from starting transmission
• The packet must continue until a collision is
  detected from a transmission starting just before
  the original frame arrived
• The minimum packet size is twice the number of
  bits needed to fill the pipe

10
Example

• 100Km 1Gbps At Speed of Light 2108m/s

Average LAN packet is 100 bytes Wasted bandwidth
11
Delay Issues

• Packetization Delay (for K switches, Kdelay)
• For 64kbps and ATM cell 6ms each switch
• SOL Delay
• Head of Line queuing
• Bandwidthdelay product required to maintain
  bandwidth
• window size must be 1Mbit