What's on IPTV's neighbourhood?

Monday, 24 August 2009


Session 3: Network Architecture (Chair: Renata Teixeira, LIP6)

De-anonymizing the Internet Using Unreliable IDs

Yinglian Xie (Microsoft Research Silicon Valley), Fang Yu (Microsoft Research Silicon Valley), Martín Abadi (Microsoft Research Silicon Valley and UCSC)

· The Internet is open and anonymous. Therefore, attackers that generate malicious traffic cannot typically be held accountable.

· HostTracker is presented. It tracks dynamic bindings between hosts and IP addresses by leveraging application-level data with unreliable IDs.

· They use a month-long user login trace from a large email provider

· HostTracker can attribute most of the activities reliably to the responsible hosts, despite the existence of dynamic IP addresses, proxies, and NATs.

SmartRE: An Architecture for Coordinated Network-wide Redundancy Elimination

Ashok Anand (University of Wisconsin-Madison), Vyas Sekar (Carnegie Mellon University), Aditya Akella (University of Wisconsin-Madison)

· Application-independent Redundancy Elimination (RE) (identifying and removing repeated content from network transfers), is used to improve network performance.

· A network-wide RE service would be beneficial for ISPs (to reduce link loads, increase effective network capacity)

· The authors present SmartRE, a architecture for network-wide RE.

· SmartRE enables more effective utilization of the available resources at network devices.

· They used real and synthetic traces to evaluate.

Design and Implementation of High Performance Dual-radio Mesh Networks

Aditya Dhananjay (New York University), Jinyang Li (New York University), Lakshminarayanan Subramanian (New York University), Hui Zhang (Tsinghua University)

· How to realise the full potential of a multi-radio mesh network? 1) how to assign channels to radios at each node to minimize interference; 2) how to choose high throughput routing paths in the face of lossy links, variable channel conditions and external load?

· ROMA is a distributed channel assignment and routing protocol that achieves good multi-hop path performance.

· They assign non-overlapping channels to links along each gateway path to eliminate intra-path interference.

· They reduce inter-path interference by assigning different channels to paths destined for different gateways whenever possible.

· They evaluated on a 24-node dual-radio testbed.

Session 4: Novel Aspects to Networking (Chair: Jon Crowcroft, Cambridge University)

Pathlet Routing

P. Brighten Godfrey (University of Illinois at Urbana-Champaign), Igor Ganichev (UC Berkeley), Scott Shenker (ICSI and UC Berkeley), Ion Stoica (UC Berkeley)

· Pathlet is a new routing protocol.

· Networks advertise fragments of paths (pathlets) that sources concatenate into end-to-end source routes.

· Pathlet routing can emulate the policies of BGP, source routing, and several recent multipath proposals.

· When a router's routing policy has only local constraints, it can be represented using a small number of pathlets, leading to very small forwarding tables

· Pathlet does not impose a global requirement on what style of policy is used, but rather allows multiple styles to coexist.

Cutting the Electric Bill for Internet-Scale Systems

Asfandyar Qureshi (MIT), Hari Balakrishnan (MIT), John Guttag (MIT), Bruce Maggs (Akamai/CMU), Rick Weber (Akamai)

· Energy expenses are becoming an increasingly important fraction of data center operating costs.

· Energy expense per unit of computation can vary significantly between two different locations.

· The paper characterizes the variation due to fluctuating electricity prices.

· Existing distributed systems should be able to exploit this variation for significant economic gains.

· Electricity prices exhibit both temporal and geographic variation.

· They use simulation to quantify the possible economic gains for a realistic workload.

· Existing systems may be able to save millions of dollars a year in electricity costs.

Persona: An Online Social Network with User-Defined Privacy

Randolph Baden University of Maryland Adam Bender (University of Maryland), Daniel Starin (University of Maryland), Neil Spring (University of Maryland), Bobby Bhattacharjee (University of Maryland)

· In OSNs users share private content, and trust the OSN service.

· Persona is an OSN where users dictate who may access their information.

· They hide user data with attribute-based encryption (ABE), allowing users to apply fine-grained policies over who may view their data

· They describe an implementation of Persona that replicates Facebook applications and show that Persona provides acceptable performance.

Session 5: Wireless Networking 2 (Chair: Suman Banerjee, University of Wisconsin at Madison)

In Defense of Wireless Carrier Sense

Micah Z. Brodsky (MIT), Robert T. Morris (MIT)

· The wireless medium is semi shared

· Carrier Sense: “Can I talk now?”. Interference protection and space reuse. Very simple.

· Is it too simple? If networks are far apart, concurrency is the best option. If they are close, time mux. What about in the middle?

· Main question: How well does CS work?

· When does CS works well? When interferer is very far away, or when it is very close to the sender. Intermediate distance is the hard case. What about shadows and obstacles?

· They start with a simple model, only 2 contending tx, with same power, omni antennas

· The effect of varying sender-sender distance is investigated.

· They use a standard model for radio propagation that include path loss and environmental shadowing. They ignore multipath fading because wideband channels average this away.

· They use Shannon capacity as a model for throughput (Adaptive bit rate)

· Answer for intermediate problem: Adaptive Bit Rate.

· Obstacles aren’t fatal. Usually you have alternate propagation paths.

· By analysing average throughput, they realise Carrier Sense works.

· Intuitions summary: Distant interferers affect receivers uniformly; nearby interferes don’t but they’re loud so everybody prefers mux anyway; rate adaptation helps in intermediate situation; and shadowing is not such a big problem.

· Implications for future research: adaptive bit rate is essential.; hidden terminals can be a problem in terms of reliability, but they don’t matter much for average performance; exposed terminals don’t cost very much, if ABR is working.

· Carrier sense does work. There is room for improvement, but not much in overall performance.

Interference Alignment and Cancellation

Shyamnath Gollakota (MIT), Samuel D. Perli (MIT), Dina Katabi (MIT)

· MIMO LANs increase throughput by sending more concurrent packets.

· In this paper the authors present a technique that doubles concurrent packets in MIMO LAN

· Concurrent MIMO decodes as many concurrent packets as there are antennas per AP. Can we do better?

· With 2 antennas, current MIMO LANs can decode only 2 packets. All current MIMO LANs are limited by number of antennas per AP.

· What if the APS coordinate over the Ethernet? 2 APs with 2 antennas each could communicate via Ethernet, and then decode more than 2 packets. But there is an impractical overhead in this solution. Can we leverage the Ethernet with minimal overhead?

· Their solution: Interference Alignment and Cancelation (IAC)

· IAC overcomes the antennas per AP throughput limit. A packet is decoded then broadcasted once on the Ethernet, with minimal overhead.

· Contributions of the work: first MIMO LAN to overcome the antennas per AP limit; IAM synthesises interference alignment and cancelation; IAM doubles MIMO throughput; implementation of the scheme in software radios to prove this.

· For a large number of antennas, IAC doubles MIMO throughput

· They tested with a 20 node testbed. Uplink gain: IACs median gain is 2.1x better than current MIMOs. Gain is partially due to diversity but even more to concurrency. Downlink: IAC median gain is 1.5x. IAC is beneficial across the operational range of SNRs.

DIRC: Increasing Indoor Wireless Capacity Using Directional Antennas

Xi Liu (Carnegie Mellon University), Anmol Sheth (Intel Research Seattle), Michael Kaminsky (Intel Research Pittsburgh), Konstantina Papagiannaki (Intel Research Pittsburgh), Srinivasan Seshan (Carnegie Mellon University), Peter Steenkiste (Carnegie Mellon University)

· Driving demand for wireless capacity. Interference can be a big issue.

· Goal: use directional antennas to improve wireless capacity by increasing spatial reuse.

· They use phased array antennas – they electronically steer the signal to a specific direction, hence having small reconfiguration time. They assume that only APs use these antennas – they are too bulky for clients.~

· Limitations in indoor environment: LOS may be blocked, indoor space is rich scattered. The conventional wisdom is that directional antennas are not effective in indoors environment.

· Key idea: leverage multiple paths and obstacles to improve spatial reuse

· How to find antenna orientations? 1) Naive solution, max cap, is too slow. The objective is to find optimal antenna orientations quickly.

· How to coordinate between antennas? They use a centralised controller, and TDMA scheduling MAC. They also separate directional and omni-directional antennas.

· They made measurements in 2 indoor environments: 3 directional APs and 6 omni clients in each testbed.

· 2x improvement over OMNI CSMA and 1.6x over MAX SNR.

· Conclusion: coordination is required to use directional antennas effectively in indoors environments

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