Lesson 7: Rate Limiting and Traffic Shaping Flashcards Preview

CS6250 Test 2 > Lesson 7: Rate Limiting and Traffic Shaping > Flashcards

Flashcards in Lesson 7: Rate Limiting and Traffic Shaping Deck (37):

What are 3 traffic shaping approaches

leaky bucket, (r, T) traffic shaper, token bucket


How can data be classified

busty, periodic, regular


How can audio be classified

continuous, periodic


How can video be classified

continus, bursty (compression), periodic


Classify sources to 2 classes:

CBR (constant bit rate) and VBR (variable bit rate)


CBR (constant bit rate)

Traffic arrives are regular intervals and packets are the same size as the arrive
i.e. audio
Shaped by peak rate


VBR (variable bit rate)

I.e. video, data transfers
Shaped by average and peak rate


Examples of vbr (variable bit rate traffic)

video and data transfers. NOT audio


Leaky bucket

each flow has its own bucket. Dad arrives in a bucket of size beta, drains at rate rho (controls the average rate). Data can arrive faster or slower in the bucket but cannot drain faster than rho (rho is smooth rate).


Leaky bucket: What controls max burst size the sender can send to the bucket

bucket size


The leaky buckets allows flow to

periodically burst


The regulator at the bottom of the leaky bucket ensures that

the average rate does not exceed the drain rate of the bucket


Leaky bucket: Larger bucket size can account for

larger burst size


(r, T) traffic shaping

Traffic divided into T-bit frames
Flow can inject less than or equal to r bits in any T-bit frame
If sender wants to send more than one packet of r bits, it has to wait for the next t-bit frame
This means it as (r,T) smooth


(r, T) traffic shaping range is limited to

fix rate flows typically


Why is (r,T) traffic shaping not good for variable flows

Variable flows need to request for peak rate which is a big waste


Which is more relaxed: leaky bucket or (r, T) traffic shaper

(r, T) traffic shaper


Token bucket

Tokens arrive in a bucket at a rate Rho
Beta= capacity of the bucket.
traffic may arrive an average rate Lambda average, and a peak rate Lambda peak.
Traffic can be sent by the regulator as long as there are tokens in the bucket.
token bucket vs leaky bucket, s


Token bucket is full, what happens to packet

packet is sent, and b tokens are removed.


Token bucket is empty, what happens to packet

packet must wait until b tokens drip into the bucket.


Token bucket is partially full, what happens to packet

then it depends. If the number of tokens In the bucket exceed little b then the packet is sent immediately, otherwise we have to wait until there are little b tokens in the bucket before we can send the packet


What is power boost

Allows subscriber to send at higher rate for a brief period of time
Eventually shaped back to rate at which you were subscribed at


What are two types of power boost

Capped - if rate won’t exceed certain rate
Uncapped - otherwise


Power boost: Formula for calculating how long can a sender send at a rate that exceeds the sustained rate?

d = Beta/(r - R-sustained)


Power boost is introduces

power boost allows users to send at a higher traffic rate but they might experience high latency and loss at that higher rate because TCP sends at a higher rate without seeing packet loss (as the packets are stuck in the buffer)


To solve power boost traffic latency and packet loss

Sender might shape it’s rate to never exceed the sustained rate, R
If it did this it could avoid seeing the latency effect
OR put a traffic shaper in front of power boost


Buffer Bloat

If there is a buffer in the network that can support the higher rate, the buffer will start filling up with packets, but can still only drained at R-sustained. Even though sender can send fast, they are still queued up in the buffer and are seeing higher delays than usual


2 types of network measurements

passive and active


Passive network measurements

collect packets, flow stats, that are already on the network
i.e. Packet traces, application level logs


Active network measurements

inject additional traffic to measure various characteristics
i.e. Measure speed of downloads, ping, trace route


Ping network measurement

measure delay to particular server


Trace-route network measurement

measure IP level path between 2 hosts on the network


Why measure network?

Billing and security


3 ways to measure network passively

SNMP, packet monitoring, flow monitoring


SNMP (simple network management protocol)

Management information base (MIB)
can be pulled or queried for particular information
Interface byte and packet counts
Pro: SNP is ubiquitous
Con: coarse- - can’t see what host did what


Packet monitoring

Full packet contents (or packet headers) that traverse a particular link
Example to explore: TCP dump, ethereal, or wireshark
Sometimes done with expensive hardware that can be mounted in routers
Optical link is somethings split to send along network and also send to monitoring
Advantages of packet monitoring: lots of details (timing, header info)
Disadvantage of packet monitoring - overhead, often requires separate monitoring advice


Flow Monitoring

A monitor records statistics per flow
Flow- consists of packets that share a common source and dest IP, source and dest port, protocol type, TOS byte, and interface (could also group together by time)
Flow records may contain additional info like next hop IP, src/dest AS and prefixes
Flow monitoring is much less overhead
Flow monitoring is more course, no packets/payloads