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An Improved Hop-by-hop Interest Shaper for Congestion Control in Named Data Networking. Yaogong Wang, NCSU Natalya Rozhnova , UPMC Ashok Narayanan , Cisco Dave Oran, Cisco Injong Rhee, NCSU. NDN Congestion control. Two important factors to consider: - PowerPoint PPT Presentation
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1© 2013 Cisco and/or its affiliates. All rights reserved.
An Improved Hop-by-hop Interest Shaper for Congestion Control in Named Data Networking
Yaogong Wang, NCSU
Natalya Rozhnova, UPMC
Ashok Narayanan, Cisco
Dave Oran, Cisco
Injong Rhee, NCSU
3© 2013 Cisco and/or its affiliates. All rights reserved.
NDN Congestion control• Two important factors to consider:
1. Receiver-driven: one interest generates one data packet
2. Symmetric: Content retrieved in response to an interest traverses the same path in reverse
• Content load forwarded on a link is directly related to interests previously received on that link
• Given these properties, shaping interests can serve to control content load and therefore proactively avoid congestion.
• There are multiple schemes that rely on slowing down interests to achieve congestion avoidance or resolution
• But, detecting the congestion in question is not simpleBecause it appears on the other side of the link where interests can be slowed
4© 2013 Cisco and/or its affiliates. All rights reserved.
Interest shaping• Different schemes have been proposed
• HoBHISFirst successful scheme, demonstrated the feasibility of this methodSlows down interests on the hop after congestionRelies on backpressure to alleviate congestion
• ICP/HR-ICPRuns per-flow AIMD scheme to manage outstanding interestsTracks estimated RTT as a mechanism to rapidly detect congestion & lossEndpoints control flow requests by shaping interest issue rateMain congestion control operates end-to-end, some hop-by-hop shaping for special cases
5© 2013 Cisco and/or its affiliates. All rights reserved.
Basic interest shaping• Assume constant ratio r of content-size/interest-size
• Simple unidirectional flow with link rate c
• Ingress interest rate of c/r causes egress content rate of c
• If we shape egress interest rate to c/r, remote content queue will not be overloaded
• Issues with varying content size, size ratio, link rate, etc.
• But the biggest issue is…
6© 2013 Cisco and/or its affiliates. All rights reserved.
What about interests?• Interests consume bandwidth
(specifically, c/r in the reverse direction)
• Bidirectional data flow also implies bidirectional interest flow
• Therefore, the reverse path is not available to carry c bandwidth of data, it also needs to carry some interests
• And similarly, the rate of interests carried in the reverse direction cannot budget the forward path entirely for data, it needs to leave space for forward interests as well
• Ordinarily there is no way to predict and therefore account for interests coming in the other direction, but…
• There is a recursive dependence between the interest shaping rate in the forward and reverse directions.
7© 2013 Cisco and/or its affiliates. All rights reserved.
Problem overview
8© 2013 Cisco and/or its affiliates. All rights reserved.
Problem formulation• We can formulate a mutual bidirectional optimization as follows
• u(.) is link utility function This must be proportionally fair in both direction, to avoid starvation We propose log(s) as utility function
• i1 = received forward interest load• i2 = received reverse interest load• c1 = forward link bandwidth• c2 = reverse link bandwidth• r1 = ratio of received content size to
sent interests size• r2 = ratio of sent contents size to
received interests size
9© 2013 Cisco and/or its affiliates. All rights reserved.
Optimal solution• Feasible region is convex
• First solve for infinite load in both directions
• Optimal solutions at the Lagrange points marked with X
• If Lagrangian points do not lie within feasible region (most common case), convert to equality constraints and solve
10© 2013 Cisco and/or its affiliates. All rights reserved.
Finite load scenarios• Optimal shaping rate assumes unbounded load in both directions
We can’t model instantaneously varying load in a closed-form solution
• If one direction is underloaded, fewer interests need to travel in the reverse direction to generate the lower load
• As a result, the local shaping algorithm need not leave as much space for interests in the reverse direction
Extreme case: unidirectional traffic flow
• Actual shaping rate needs to vary between two extremes depending on actual load in the reverse path
• BUT, we don’t want to rely on signaling reverse path load
11© 2013 Cisco and/or its affiliates. All rights reserved.
Practical interest shaping algorithm• We observe that each side can independently compute both
expected shaping rates
• Our algorithm observes the incoming interest rate, compares it to the expected incoming interest shaping rate, and adjusts our outgoing interest rate between these two extremes
• On the router, interests and contents are separated in output queues. Interests are shaped as per the equation above, and contents flow directly to the output queue.
12© 2013 Cisco and/or its affiliates. All rights reserved.
Explicit congestion notification• When an interest cannot be enqueued into the interest shaper queue,
it is rejected
• Instead of dropping it, we return it to the downstream hop in the form of a “Congestion-NACK”
• This NACK is forwarded back towards the client in the place of the requested content
Consumes the PIT entries on the way
• Note that the bandwidth consumed by this NACK has already been accounted for by the interest that caused it to be generated
Therefore, in our scheme Congestion-NACKs cannot exacerbate congestion
• Clients or other nodes can react to these signals
• In our current simulations, clients implement simple AIMD window control, with the NACK used to cause decrease
13© 2013 Cisco and/or its affiliates. All rights reserved.
Simulation results – basic topology
ScenarioData Throughput
(Mbps)Data loss
(%)Interest rejection rate
(%)Client 1 Client 2 R1 R2 Client 1 Client 2
Baseline25B Interest, 1KB Data
9.558±0.001
9.559±0.002
0 0 0.015±0.0006
0.015±0.0011
Varying Pkt SizeData from 600-1400B
9.432±0.005
9.434±0.008
0 0 0.018±0.0014
0.017±0.0015
Asymmetric data size1000B/500B
9.373±0.014
9.326±0.001
0 0 0.007±0.0006
0.016±0.0006
Asymmetric bandwidth10 Mbps/1 Mbps
9.774±0.001
0.719±0.001
0 0 0.012±0.0005
0.058±0.0000
14© 2013 Cisco and/or its affiliates. All rights reserved.
Simulation results – dumbbell topology
ScenarioData Throughput
(Mbps)Data loss
(%)Interest rejection rate
(%)
Client 1Server 3
Client 2Server 4
R1 R2 Client 1Server 3
Client 2Server 4
Homogeneous RTT 5.142±0.5
4.692±0.5
0 0 0.515±0.011
0.063±0.013
Heterogeneous RTTR2—S4 link now 20ms
5.209±0.38
4.624±0.38
0 0 0.513±0.009
0.042±0.007
Flipped data flowsClient1Server3, Client4Server2
9.566±0.001
9.419±0.007
0 0 0.148±0.0004
0.012±0.0005
15© 2013 Cisco and/or its affiliates. All rights reserved.
Client window and queue evolution• Queue depth on bottleneck queues is small
1 packet for homogeneous RTT caseVaries slightly more in heterogeneous RTT case, but is quite low (<17 packets)
• Client window evolution is quite fair
16© 2013 Cisco and/or its affiliates. All rights reserved.
Benefits of our scheme• Optimally handles interest shaping for bidirectional traffic
• No signaling or message exchange required between routersCorollary: no trust required between peers
• No requirement of flow identification by intermediaries
• Fair and effective bandwidth allocation on highly asymmetric links
• Congestion NACKs offer a timely and reliable congestion signal
• Congestion is detected downstream of the bottleneck link
17© 2013 Cisco and/or its affiliates. All rights reserved.
Future work• Use congestion detection and/or NACKs to offer dynamic reroute
and multi-path load balancing
• Use NACKs as backpressure mechanism in the network to handle unco-operative clients
• Investigate shaper under different router AQM schemes (e.g. RED, CoDEL, PIE) and client implementations (e.g. CUBIC).
18© 2013 Cisco and/or its affiliates. All rights reserved.
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