paper - Research Laboratory of Electronics

Network Coding as a WiMAX Link Reliability
Mechanism: An Experimental Demonstration
Surat Teerapittayanon1, Kerim Fouli1 , Muriel M´edard1,
Marie-Jos´e Montpetit1 , Xiaomeng Shi1 , Ivan Seskar2 , and Abhimanyu Gosain3
1
Research Laboratory of Electronics (RLE), Massachusetts Institute of Technology
(MIT), Cambridge, MA 02139, USA
{steerapi,fouli,medard,mariejo,xshi}@mit.com
2
WINLAB, Rutgers University, Piscataway, NJ 08854, USA
[email protected]
3
Raytheon BBN Technologies, Cambridge, MA 02138, USA
[email protected]
Abstract. Our demonstration showcases a network-coding (NC)–
enabled reliability architecture for next generation wireless networks. Our
NC architecture uses a ﬂexible thread-based design, applying systematic
intra-session random linear network coding as a packet erasure code at
the IP layer. Using GENI WiMAX platforms, a series of point-to-point
transmission experiments are conducted to compare NC with Automatic
Repeated reQuest (ARQ) and Hybrid ARQ (HARQ). At the application
layer, Iperf and UFTP are used to measure throughput, packet loss and
ﬁle transfer delay. In our selected scenarios, NC oﬀers up to 5.9 times gain
in throughput and 5.5 times reduction in ﬁle transfer delay, compared
to HARQ and joint HARQ/ARQ. Our demonstration hence illustrates
that lower-layer redundancy mechanisms such as HARQ and ARQ incur
high cost since they operate at the packet-level. Conversely, running NC
at higher layers (e.g., IP) amortizes the cost of redundancy over several
packets, thus leading to higher eﬃciency.
Keywords: ARQ, GENI, HARQ, Network Coding, WiMAX.
1
Introduction
NC enables nodes to combine or separate transient bits, packets, or ﬂows through
coding and decoding operations, in addition to storing and forwarding [1]. Despite the demonstrated eﬀectiveness of NC in WLANs [1], NC for Wireless
Metropolitan Area Networks (WMANs) has gained attention only recently, as
the telecommunication industry moves toward next generation wireless networks
such as 4G Worldwide Interoperability for Microwave Access (WiMAX) [2].
To ensure the fast and reliable transfer of information between wireless nodes,
we propose an NC architecture using a ﬂexible thread-based design, with each
encoder-decoder instance applying systematic intra-session random linear network coding as a packet erasure code at the IP layer. In our selected scenarios,
B. Bellalta et al. (Eds.): MACOM 2012, LNCS 7642, pp. 75–78, 2012.
c Springer-Verlag Berlin Heidelberg 2012
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the proposed architecture substantially decreases packet loss from around 1132% to nearly 0%. Compared to the HARQ and joint HARQ/ARQ mechanisms,
the NC architecture oﬀers up to 5.9 times gain in throughput and 5.5 times
reduction in end-to-end ﬁle transfer delay [3,4].
In this demonstration, we implement our NC-enabled reliability architecture
in a WiMAX platform provided by the Global Environment for Network Innovations (GENI) collaborative research framework [5] and located at Rutgers
University’s WINLAB, New Jersey, USA. Our friendly web-interface enables the
demonstrator to select a reliability conﬁguration, run the corresponding experiment remotely, and compare the results of diﬀerent reliability conﬁgurations.
The targeted audience for the demonstration includes the GENI and MACOM
communities and other academic researchers involved in NC. We also believe the
demonstration to be useful for network operators and equipment providers who
want to experiment with NC before development or deployment decisions.
2
NC-Enhanced Architecture
Our proposed NC-enabled reliability architecture is implemented in the form of
an NC module at the IP layer of the network protocol stack, as shown in Fig. 1.
In the NC-enhanced architecture, ARQ and HARQ, run from the upper and
lower MAC sublayer respectively, are switched oﬀ.
Fig. 1. IP-based NC architecture: 1) A Linux packet ﬁltering framework (netfilter )
[6] intercepts and forwards IP packets to the NC module. 2) Implemented in user-space,
the latter acts as an encoder at the base station (BS) or as a decoder at the subscriber
station (SS). 3) The NC module then injects processed packets back into the IP layer.
The NC module uses a ﬂexible thread-based design, where Np parallel encodingdecoding instances are generated to process packets concurrently and systematic
intra-session random linear network coding is applied [3,4]. The encoding process comprises the following steps: (1) Incoming IP packets are buﬀered at the
Demo: Network Coding as a WiMAX Link Reliability Mechanism
77
master thread, forming a coding buﬀer list. (2) At each worker thread, the list
is concatenated into a coding block. (3) The number of segments and segment
length are determined, then byte padding is added. (4) The block is segmented.
For each systematic block to be transmitted, Nm coded redundancy segments
are generated. (5) Coded segments are encapsulated into coded IP packets and
queued for transmission. More detail on the designed encoding, decoding, and
feedback mechanisms can be found in [3,4].
3
Demonstration Setup
We implement our architecture over a GENI WiMAX IEEE-802.16 downlink.
More details on the testbed hardware can be found at [7].For our demonstration,
one ﬁxed downlink Modulation and Coding Scheme (MCS) and transmission
power level (64 QAM CTC 5/6 at 20 dBm) is available at the BS. When using
HARQ or ARQ, the default settings of the GENI BS are employed [3,4].
The available reliability conﬁgurations include a number of ARQ, HARQ and
NC arrangements, where the diﬀerent NC conﬁgurations use a varying number
of redundancy segments transmitted with each ﬁxed block of 120 systematic
segments (Nm ). Furthermore, a ﬁxed packet size of 1400 bytes and a single
thread (Np = 1) are used. More detail on the implemented PHY, MAC and
reliability conﬁgurations is given in [3,4].
For each of the reliability conﬁgurations, two transmission trials may be conducted through Iperf [8] and UDP-based File Transfer Protocol (UFTP [9]) so as
to measure throughput/loss and ﬁle transfer delay, respectively. An applicationlayer load of 6 Mbps is oﬀered for both. Each individual Iperf trial is terminated
after a ﬁxed duration of 30 seconds, whereas the UFTP transmissions are run
until a 10 MByte ﬁle is successfully transferred.
4
Demonstration Interface and Requirements
The demonstration interface is a web application that allows the demonstrator
to schedule experiments on the WiMAX GENI platform at WINLAB (Rutgers
University, NJ, USA) and view live results. This demo hence requires a reliable
high-speed Internet connection to WINLAB.
Fig 2 represents the conﬁguration screen and a sample result from our demonstration interface. The demonstrator chooses between two types of experiments:
Throughput and Loss (Iperf trial) and File Transfer (UFTP trial). Furthermore,
three diﬀerent base station conﬁgurations are available: HARQ/ARQ, HARQ
only and NC where the BS is conﬁgured to use both HARQ and ARQ, only
HARQ and only NC with neither HARQ or ARQ, respectively. If NC is selected,
the demonstrator is able to specify the redundancy percentage (i.e., Nm /120):
The web interface suggests a redundancy percentage from the available 10%–
100% range, based on the most recent loss measurement.
The result of each experiment is be fed back live to the web application for
audience to view. Once the demonstrator schedules an experiment, the status
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S. Teerapittayanon et al.
Fig. 2. Demonstration Interface: (a) conﬁguration and (b) result screen, showing
throughput (left) and application-layer packet loss (right) in four scenarios
and result of the experiment can be found under the Scheduled Experiments tab,
where viewers can also compare results of the diﬀerent reliability conﬁgurations.
5
Conclusion and Future Work
With the NC demonstration, we provide easy access to our results and illustrate
the advantages of NC in future 4G networks. In particular, we show that the use
of NC makes lower-layer error management mechanisms unnecessary and leads
to major bandwidth performance improvements. Our demonstration provides a
tool for researchers and developers alike to evaluate the impact of NC. In the
future, we intend to expand the use cases supported by the demo to include, for
example, live and on-demand video streaming, peer-to-peer (P2P) and machineto-machine (M2M) communications, as these represent future traﬃc patterns.
References
1. M´edard, M., Sprintson, A. (eds.): Network Coding: Fundamentals and Applications.
Academic Press (2011)
2. Andrews, J., Ghosh, A., Muhamed, R.: Fundamentals of WiMAX: understanding
broadband wireless networking. Prentice Hall (2007)
3. Teerapittayanon, S., Fouli, K., M´edard, M., Montpetit, M.J., Shi, X., Seskar, I.,
Gosain, A.: Network coding as a WiMAX link reliability mechanism. Arxiv (2012)
4. Teerapittayanon, S.: Performance enhancements in next generation wireless networks using network coding: A case study in WiMAX. Master’s thesis, MIT (2012)
5. Global Environment for Network Innovations (GENI), http://www.geni.net
6. The netﬁlter.org project, http://www.netfilter.org
7. ORBIT testbed, http://www.orbit-lab.org/wiki/Hardware/gDomains/dSB4
8. Iperf, http://sourceforge.net/projects/iperf/
9. Bush, D.: UFTP, http://www.tcnj.edu/~ bush/uftp.html

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