Adaptive Packet Marking for Maintaining EndtoEnd Throughput in a DifferentiatedServices Internet

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Adaptive Packet Marking for Maintaining
End-to-End Throughput in a Differentiated-Services
Internet

• Feng, Kandlur, Saha, and Shin
• Transactions on Networking
• Oct. 1999

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Abstract

• Adaptive Priority Marking provides soft bandwidth
  guarantee in a differentiated-service Internet.
• It does not required resource reservation.
• It can be supported with minimum changes to the
  network in the form of priority handling for
  marked packets at the edges of the network.

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I. Introduction

• Best-Effort Service
• used in the current Internet
• Integrated Service (INTSERV) /RSVP (Resource
  Reservation Protocol)
• ? QoS guaranteed? Significant changes to the
  Internet infrastructure? Complexity
• Differentiated Service (DIFFSERV)
• Keep the network core as simple as possibleand
  leave the complexity (intelligence) to the
  network edges
• At the edges
• Packet classification and Type-of-Service (TOS)
  marking
• At the core
• Priority handling of packets according to TOS
• ? Simplicity? QoS not guaranteed

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• This paper
• Offers
• a modest enhancement to the best-effort service
• Assumes
• an one-bit priority scheme with lower loss rates
  for higher priority traffic
• Assumes
• TCP as the transport layer protocol that makes
  use of the feedback mechanism for measuring the
  throughput
• Can be adapted for any transport protocol that is
  responsive to network congestion
• Assumes
• some incentives that encourage users from
  continually requesting the highest priority, such
  as usage-based pricing
• ? Simple mechanisms for calculating near-optimal
  pricing based on congestion costs ?

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• Adaptive packet marking
• The user or network administrator
• specifies a desired minimum service rate for a
  connection or connection group
• and communicates this to a control engine
  (Packet-Marking Engine, PME)
• By default, all packets are generated as
  low-priority packets
• The PME monitors and sustains the requested level
  of service by setting the ToS bits in the packet
  headers appropriately
• If the observed service rate at the low-priority
  level either meets or exceeds the requested
  service rate, the PME simply monitors.
• If the observed throughput falls below the
  minimum target rate, the PME starts prioritizing
  packets until the desired target rate is reached.
• Once the target is reached, it strives to reduce
  the number of priority packets without falling
  below the minimum requested rate.

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II. TOS Architecture

• Assumes
• Two traffic types
• Priority
• Best-effort
• The traffic types are carried by the ToS bit in
  the IP header

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• Handling of multi-priority trafficat the core
  routers / gateways
• Separate queues
• for different classes
• with different scheduling priority
• A common queue ?
• for all traffic
• with different packet drop preferences? simplify
  scheduling? maintain packet ordering ? help
  TCP? Used by this paper

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• This paper takes
• the common queue approach
• and an enhanced RED (Random Early Detection)
  algorithm
• Classical RED
• Packets are dropped randomly with a given
  probability when the queue length exceeds a
  certain threshold.
• The drop probability depends on the queue length
  and the time elapsed since the last packet was
  dropped.
• Enhanced RED ?
• The drop probabilities of marked packets are
  lower than that of unmarked packets

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• The goal of this paper is
• to develop packet marking schemes deployed at
  the host network interface that will allow an
  individual connection or a connection group to
  achieve a target throughput specified by the
  user or the network administrator.
• The objective of the packet marking scheme is
• to monitor the throughput and to adjust the
  packet marking so that the sustained rate is
  maintained satisfying all the policy constraints.
• Packet remarking is allowed at the provider
  boundary, but this paper considers where packets
  are marked only once.

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• Two marking flavors
• Source-Transparent Marking
• The PME is transparent and external to the host
• It can be integrated into the infrastructure
  without affecting the hosts and routers
• Source-Integrated Marking ?
• The PME is integrated with the host
• It can adapt better with the flow and congestion
  control used at the transport layer

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III. Source-Transparent Marking

• The PME measures the local throughput instead of
  end-to-end goodput
• Simplicity
• It does not have to know the semantics of the
  transport layer in order to know whether or not
  the application data was actually delivered.
• Even if it is aware of the transport layer
  semantics, it may not have access the stream of
  ACKs from the receiver to computer goodput,
  especially when the forward and return paths are
  different.
• Protection from malicious or non-adaptive sources
• The throughput is counted against itself
• Measurement
• Average bandwidth amount of data packets /
  time window
• Small window biased to recent observation ?
• Large window biased to long-term observation

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• TCP-Independent Algorithm

(Updated Periodically)

• mprob marking probability
• obw observed bandwidth
• tbw target bandwidth
• increment
• scale difference between obw and tbw

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• Simulation by the ns simulator

• Six nodes n0 n5
• Bandwidth as shown
• Delay 10ms
• ERED minth 10 packets, maxth 80
  packets initial drop probability 0.05
  (unmarked)
• Three connections
• C1 Infinite TCP best-effort
• C2 Infinite TCP tbw 4Mbps
• C3 50s off/on TCP tbw 4Mbps
• Update period 100ms
• Measured at n1 (edge router) ?

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• (a) Step 0.01
• Step (scale increment)
• Marking rate of C2 lags behind the changes in the
  network load (C1C2C3)

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• (b) Step 1
• mprob 1 (all marked) or 0 (none marked)
• Marking rate adapts quickly
• Significant burstiness in both marked and
  unmarked streams
• Achieving target bandwidth even at increased load

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• (a) Packet trace of packet marking
• The target rate is reached
• Marked packets are cut down
• Unmarked packets are increased
• The target rate is not maintained
• Marked packets are increased
• Marked packets are cut down

• Problem Burstiness of both marked and unmarked
  streams

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• TCP-Like marking probability update algorithm

• Estimated number of packets in flight obw rtt
• Estimated number of marked packets in flight
  (i.e. priority window) pwnd mprob obw rtt
• For each ACK update pwnd as shown in Fig.5
• Mprob pwnd / (obw rtt)

?TCP-like 1/cwndincrease no more than one per
RTT (round trip time)
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• (b) Packet trace of TCP-Like packet marking
• Increase and decrease slowly

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• TCP-like (a)Transient
• Very reactive to network load
• C2 remains at or above its tbw most of the time
• Changes in mprob is more network friendly (i.e.
  stable)

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• TCP-like (b) Aggregate
• BW 10Mbps
• One group of three TCP connections with total tbw
  6Mbps
• One group of four best-effort TCP connections
• (1)No BE traffic,?Group 1 gets all 10Mbps
• (2) One BEs, ? 10/437.5Mbps
• (3) Four Bes, ?10/734.3 lt 6 ?marking begins
• (4) Group 1 stops, ? Group 2 gets all 10Mbps

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IV. Source-Integrated Approach

• Source-Transparent Approach has little control on
  the flow and congestion control at the source, it
  often marks more packets than required.
• TCP source fails to compete fairly with
  best-effort connections for its share of
  best-effort bandwidth.
• Thus this paper experiments with a PME that is
  integrated with TCP sender in order to minimize
  the amount of marked packets.

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• Another Source Transparent Marking Exp.
  (Bandwidth)
• C1TCP tbw 3M
• C2C6 BEs
• C1 10/6 1.67M?marking begins?C1 stays at 3M
• C2 (10-3)/5 1.4M
• C1 must mark a larger portion of its packets than
  it should(Why? See the next graph.)

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• Another Source Transparent Marking Exp.
  (Window)
• C1 cannot compete with a large amount of
  BEs,?its window gets to zero??need marking
  more packets?
• Thus a Source-Integrated Marking is needed!

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Customized TCP congestion control

• Two windows
• pwnd (Priority window)
• the number of marked packets that are in the
  network
• bwnd (best-effort window)
• the number of unmarked packets that are
  outstanding
• When a loss
• If marked, reduce both pwnd and bwnd (?severe
  congestion)
• If unmarked, reduce bwnd only (?minor congestion)
• Two additional threshold values
• pssthresh (priority slow start threshold)
• bssthresh (best-effort slow start threshold)
• Like two fairly independent connections
• Slow start when (pwnd lt pssthresh) (bwnd lt
  bssthresh)
• Congestion Avoidance when gt ...

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• Source-Integrated Marking (Window Opening)

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• Source-Integrated Marking (Window Closing)

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• Source Integrated Marking Exp. vs. Fig. 7
  (Bandwidth)
• C1 totalsame as Fig. 7
• C2same as Fig. 7
• C1 markedlt that of Fig. 7C1 unmarkedgt that
  of Fig. 7? C2

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• Source Integrated Marking Exp. vs. Fig. 7
  (Window)
• bwnd ? pwnd
• i.e. Fair Bandwidth Sharing

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• Assume
• B bandwidth of the bottleneck link
• n number of connections
• Ri target rate of connection i
• ri optimal marking rate with of Ri
• b best-effort bandwidth / excess for priority
• If Ri lt b, then no need to mark, i.e. using BE
• The system constrains
• ri b Ri (marked unmarked target)
• Sri nb B (total marked total unmarked
  bottleneck BW)

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• Integrated Marking Exp. (Bandwidth)
• B 10Mbps
• C1 tbw 3MC2 tbw 2M6 BEs
• t0 C1, C2t100 2 BEst200 2 BEst300 2
  Bes
• 0-100 C1C210/25
• 100-20010/42.5?C1 marks to 3?Other
  (10-3)/32.33 ?C1 marks3-2.330.67

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• Integrated Marking Exp. (Bandwidth)
• 200-30010/61.67?C1 marks to 3?C2 marks to
  2?other (10-3-2)/41.25?C1 marks 3-1.25
  1.75?C2 marks 2-1.25 0.75
• 300-40010/81.25?C1 marks to 3?C2 marks to
  2?other (10-3-2)/60.83?C1 marks 3-0.83
  2.17?C2 marks 2-0.83 1.17

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• Integrated Marking Exp. (Marking Rate)
• Ideal marking rates for C1 and C2

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• Transparent Marking Exp. (Bandwidth)
• Compared with Fig. 11(a)
• More marked packets generated by the PME
• More fluctuation

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• Transparent Marking Exp. (Marking Rates)
• Compared with Fig. 11(b)
• More marked packets generated by the PME
• More fluctuation

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V. Handling Over-Subscription

• Adaptive Packet Marking relieves from the use of
  reservation signaling protocol, e.g. RSVP, and
  admission control.
• When aggregate demand exceeds capacity, all
  connections with nonzero target rates carry only
  marked packets. ERED degrades to RED since there
  are only marked packets in the queue.
• For transparent marking, TCP still behaves well.
• For integrated marking, Modified TCP simply works
  the same as normal TCP.
• Weighted-bandwidth sharingadditional priority
  bits, different ERED queue (weighted fair queuing
  or class-based queuing)

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• Integrated Marking Exp. For Over-Subscription
• C1,C1 tbw 5C3,C4 tbw10

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• Integrated Marking Exp. For Over-Subscription
• Fair share10/42.5

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• Integrated Marking Exp. For Over-Subscription
• C1,C1 tbw 5C3,C4 tbw10

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• Integrated Marking Exp. For Over-Subscription
• C1,C1 tbw 5C3,C4 tbw10

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VI. Dealing with Non-Responsive

• Non-responsive applications
• Applications which do not adapt to network
  dynamics
• Can lead to severe network performance
  degradation and even congestion collapse

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• Non-responsive Flow (1)
• B 10Mbps
• Four TCP T1 T4aggregate target rate 7Mbps
• A non-responsive flow M1target rate 3Mbps
• When M1 gt 3, M1 stays at 3??target rate
  3?same marking? drop rate ?

• Note M3 marked 0 M3 unmarked 3Solution
  adopting FRED queue (Fair)

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• Non-responsive Flow (2) - FRED
• M1 marked 0
• M1 unmarked 10/5 2(fair share)
• T1T4 unmarked 10-28 gt 7?T1T4 marked 0

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VII. Deployment Issues

• The Internet is heterogeneous and slow-evolving,
  thus most routers do not support service
  differentiation.
• What if the network does not support end-to-end
  service differentiation?
• For transparent marking, TCP still behaves well,
• For integrated marking, it may be twice as
  aggressive?Solution This paper turns off the
  marking and window modifying.

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VIII. Conclusion

• Adaptive Priority Marking provides soft bandwidth
  guarantee in a differentiated-service Internet.
• Both the Transparent and Integrated Marking
  algorithms have advantages and disadvantages from
  the stand point of performance and deployment
  issues.
• Future works
• Marking packets at multiple places in the network
• Interaction and interoperability of other QoS
  supporting schemes
• Two-priority to multiple-priority ToS schemes