7 - Rate Limiting and Traffic Shaping Flashcards
(33 cards)
Leaky Bucket with a Token bucket
Composite Shaper
Motivation for Traffic classification and shaping
resource control on network
ensure no traffic flow exceeds particular pre-specified rate
Data traffic
bursty, periodic, regular
Audio traffic
continuous, periodic
Video traffic
continuous, bursty (compression), periodic
Two kinds of traffic (sources)
1) Constant bit rate source(CBR) (i.e audio) -> shape it according to a “peek” rate
2) Variable bit rate (VBR) (i.e. video, data) -> shape it according to both an average rate and a peek rate
A way of shaping traffic. Each flow has its own bucket (Buffer)
Leaky Bucket
Traffic is divided into t-bit frames and a flow can inject <= r-bits in any t-bit frame
(r,t) traffic shaping
A flow that obeys the (r,t) traffic shaping rule
(r,t) smooth
Priorities can be assigned at the
Sender: Application may mark its own packets since it knows best which packets may be less important
or
Network: The routers may mark packets with lower priority - which is sometimes called “policing”
Use this for shaping bursty traffic patterns:
Token bucket
1) Permits burstiness, but bounds it by the rate rho
- > in any interval T, rate < beta (bucket size) + t * rho
2) No discard or priority policies
3) difficulty with policing (but composite shaper helps - which is combining Token bucket with leaky bucket)
Token Bucket
1) Forces the bursty traffic to be smooth
2) Priority policies
Leaky Bucket
Token Bucket Shaper: Size of bucket (beta) = 100kb Rho = 10 packets per second packet size = 1kb or ~8000 bits Interval T = 1 second
Remember that in any given interval…
a flow can never send more than beta plus T * rho bits of data (B+T*P)
100kb + 10kb = 110kb
880kb/sec
Traffic shaping mechanism first deployed by Comcast.
allows a subscriber to send at a higher rate for a brief period of time (June 2006)
Power Boost
2 types of power boosts
Capped - limits the peek sending rates
uncapped - configuration is simple
Calculating powerboost rates
Beta = d*(r - Rsus) d = Beta/(r - Rsus)
Rsus = 10mbps
r = 15mbps
Beta = 1 MB or 8 Megabits
How long can the sender send in the higher rate (decimal form in seconds)
d = Beta/r-Rsus) d = 8megabits/15 - 10) d = 8/5 d = 1.6 seconds
Also has effect on latency
Powerboosts
Delay = Data in Buffer/Rsus
BufferBloat
Solutions to buffer bloat problem:
1) use smaller buffers (hard to do in most devices)
2) Shaping traffic
Network Measurement (How to see what traffic is being sent on the network)
Passive Measurement - Collect packets, flow statistics, etc… of traffic already being sent on the network
Active Measurement - Inject additional traffic to measure various characteristics (ping, traceroute)
Often used to measure the delay to a particular server
Ping
often used to measure the network level or the IP level path between two hosts on a network
Traceroute
Why measure?
- Billing - 95th percentile (CIR = Committed information rate)
- Security - What type of traffic to detect rogue behavior (Botnets, DDOS, etc…)
