Packet loss characteristics of IPTV-like traffic on residential links

Packet loss is one of the principal threats to quality of experience for IPTV systems. However, the packet loss characteristics of the residential access networks which carry IPTV are not widely understood. We present packet level measurements of streaming IPTV-like traffic over four residential access links, and describe the extent and nature of packet loss we encountered. We discuss the likely impact of these losses for IPTV traffic, and outline steps which can ameliorate this

Meeting Real-Time Constraint of Spectrum Management in TV Black-Space Access

The TV set feedback feature standardized in the next generation TV system, ATSC 3.0, would enable opportunistic access of active TV channels in future Cognitive Radio Networks. This new dynamic spectrum access approach is named as black-space access, as it is complementary of current TV white space, which stands for inactive TV channels. TV black-space access can significantly increase the available spectrum of Cognitive Radio Networks in populated urban markets, where spectrum shortage is most severe while TV whitespace is very limited. However, to enable TV black-space access, secondary user has to evacuate a TV channel in a timely manner when TV user comes in. Such strict real-time constraint is an unique challenge of spectrum management infrastructure of Cognitive Radio Networks. In this paper, the real-time performance of spectrum management with regard to the degree of centralization of infrastructure is modeled and tested. Based on collected empirical network latency and database response time, we analyze the average evacuation time under four structures of spectrum management infrastructure: fully distribution, city-wide centralization, national-wide centralization, and semi-national centralization. The results show that national wide centralization may not meet the real-time requirement, while semi-national centralization that use multiple co-located independent spectrum manager can achieve real-time performance while keep most of the operational advantage of fully centralized structure.Comment: 9 pages, 7 figures, Technical Repor

Streaming media over the Internet: Flow based analysis in live access networks

Multimedia service delivery over the Internet is a success. The number of services available and the number of people accessing them is huge. In this paper, we investigate multimedia streaming services over the Internet. Our analysis is based on traffic measurement in live access fiber-to-the-home networks. We study parameters like traffic volume and flow characteristics for selected services. Especially the Swedish P2P video service Voddler and the Swedish P2P music service Spotify are studied. We show that indeed these services are widely used (20% of local hosts using Voddler, 65 % of local hosts using Spotify). We also show that they are different concerning the flow characteristics, with many short flows for Voddler and longer flows for Spotify. One thing that they have in common in our measurements is that the outbound, or uplink, traffic volume is larger than the inbound

Meeting Real-Time Constraint of Spectrum Management in TV Black-Space Access

The TV set feedback feature standardized in the next generation TV system, ATSC 3.0, would enable opportunistic access of active TV channels in future Cognitive Radio Networks. This new dynamic spectrum access approach is named as black-space access, as it is complementary of current TV white space, which stands for inactive TV channels. TV black-space access can significantly increase the available spectrum of Cognitive Radio Networks in populated urban markets, where spectrum shortage is most severe while TV whitespace is very limited. However, to enable TV black-space access, secondary user has to evacuate a TV channel in a timely manner when TV user comes in. Such strict real-time constraint is an unique challenge of spectrum management infrastructure of Cognitive Radio Networks. In this paper, the real-time performance of spectrum management with regard to the degree of centralization of infrastructure is modeled and tested. Based on collected empirical network latency and database response time, we analyze the average evacuation time under four structures of spectrum management infrastructure: fully distribution, city-wide centralization, national-wide centralization, and semi-national centralization. The results show that national wide centralization may not meet the real-time requirement, while semi-national centralization that use multiple co-located independent spectrum manager can achieve real-time performance while keep most of the operational advantage of fully centralized structure

Distributed Management of Application Layer Multicast Trees for IPTV Services

Este trabajo es una ponencia recogida en el IX Jornadas de Ingeniería Telemática (JITEL 2010), celebradas en la Universidad de Valladolid, los días 29 de septiembre y 1 de octubre de 2010 en Valladolid (España). La web del evento es http://jitel2010.tel.uva.es/IP multicast is an eff cient mechanism to distribute IPTV content towards multiple users, but nowadays Internet Providers f lter out this kind of traff c, mainly due to security and accounting issues. In order to overcome this f ltering, the same idea of IP multicast can be implemented at the end user terminals, but implementing multicast trees at the application layer, also known as Application Layer Multicast (ALM). ALM has some drawbacks, mainly due to dynamic behavior of users, joining and leaving the trees. In order to minimize the impact of this behavior, this paper proposes a distributed management for ALM in IPTV, instead of a centralized one, where some nodes connected to a tree will be on charge of the management of that tree. Furthermore, all nodes are dynamically conf gured with the substitute of its parent node in order to accelerate the reconnection process. Results presented in this article show that this proposal provides fast reconstructions and low management load per node, while keeping a balanced tree topology.Este artículo está financiado parcialmente por el proyecto MEDIANET (S-2009/TIC-1468) de la Comunidad de Madrid y por la Cátedra Telefónica en Internet del Futuro para la Productividad de la Universidad Carlos III de Madrid.Publicad

Heat Pipe Dryout and Temperature Hysteresis in Response to Transient Heat Pulses Exceeding the Capillary Limit

The balance between the capillary pressure provided by the wick in a heat pipe or vapor chamber and the flow resistance to liquid resupply at the evaporator determines the maximum heat load that can be sustained at steady state. This maximum heat load is termed as the capillary limit; operation at steady heat loads above the capillary limit will result in dryout at the evaporator wick. However, different user needs and device workloads can lead to highly transient heat loads in applications ranging from con- sumer electronic devices to server processors. In these instances, the operation of heat pipes must be assessed in response to brief transient heat loads which could be higher than the notional capillary limit that governs dryout at steady state. In the current study, experiments are performed to characterize the transient thermal response of a heat pipe subjected to heat input pulses of varying duration that ex- ceed the capillary limit. Transient dryout events due to a wick pressure drop exceeding the maximum available capillary pressure can be detected from an analysis of the measured temperature signatures. It is demonstrated that under such transient heating conditions, a heat pipe can sustain heat loads higher than the steady-state capillary limit for brief periods of time without experiencing dryout. If the heating pulse is sufficiently long as to induce transient dryout, the heat pipe may experience an elevated steady- state temperature even after the heat load is reduced back to a level lower than the capillary limit. The steady-state heat load must then be reduced to a level much below the capillary limit to fully recover the original thermal resistance of the heat pipe. This characteristic temperature hysteresis following tran- sient dryout has significant implications for the use of heat pipes for pulsed power dissipation. Further experiments are performed to bound the range of heat loads over which the temperature hysteresis is present following a transient dryout event

Examining the power-law distribution among eWOM communities: a characterisation approach of the Long Tail

Nowadays electronic word-of-mouth (eWOM) communities symbolise a significant source of information that helps customers to make informed purchasing decisions. Through eWOM communities, a great audience of users is able to acquire knowledge from reviews concerning products and services that are less popular to the majority. The Long Tail effect is a manifestation of such redistribution of demand from popular products to niche products. In this paper, a new methodology that mathematically fits the relationship between the power-law distribution and the Long Tail from an eWOM community is developed. In addition, this paper defines a tool for finding niche products inaccessible through conventional channels. The results are consistent in showing that not all the categories fitting a power-law distribution are characterised by the Long Tail phenomenon, and conversely some of those having a Long Tail do not fit a power-law distribution