A Peer-Assisted Server-Based Error Recovery Approach for IPTV. Networks. Aytac Azgin and Yucel Altunbasak. School of Electrical and Computer Engineering.
The 8th Annual IEEE Consumer Communications and Networking Conference - Work in Progress (Short Papers)
A Peer-Assisted Server-Based Error Recovery Approach for IPTV Networks Aytac Azgin and Yucel Altunbasak School of Electrical and Computer Engineering Georgia Institute of Technology
Abstract—To achieve the desired service quality in IPTV networks, we need effective and resource-efficient error recovery techniques to overcome the problems encountered during the delivery of the IPTV content to the end-users. To enable quick recovery from packet losses, one idea is to utilize an error recovery server (ERServ) that is placed in-between the end-users and the content delivery server. Within this framework, error recovery process is initiated once an enduser sends a repair packet request to the ERServ, and the process is finalized when the repair packet transmitted by the ERServ in response is successfully delivered to the end-user. Even though the use of an ERServ presents an effective solution to improve the perceived quality at the end-users, as the number of users connected to the ERServ increases, we may observe scalability related problems (e.g., dropped requests or increased response times). Consequently, during such overloaded periods, we cannot guarantee the timely delivery of the repair packets, which may lead to significant performance degradations at the end-users. To prevent this from happening, we propose to utilize peer-based error recovery in addition to serverbased recovery, for which the main objective is to prevent the ERServ from entering a non-responsive state. We achieve this objective by redirecting the error recovery load towards the end-users during times when the ERServ reaches a critical server-load level.
I. I NTRODUCTION Successful deployment of the IPTV service relies on the promise of creating a reliable content delivery network that can provide the subscribers with the desired quality of experience (QoE). However, the problems encountered during the delivery of the IPTV service make this a challenging task because of stringent service quality requirements (e.g., packet loss and latency). Furthermore, since the subscribers are distributed over networks with varying loss and delay characteristics, simultaneously accommodating the needs of each of these subscribers may cause inefficient utilization of the network resources, which may introduce stability problems. To minimize these problems, various approaches have been proposed to reduce the error recovery load in the network. These approaches typically focused on utilizing dedicated error recovery servers, which are placed in between the content delivery server and the end-users, to help the users quickly recover from their packet losses. By using error recovery servers and retransmitting the lost packets to end-users using a unicast-based approach, we can also improve the effectiveness of multicast proactive repair streams. However, because of the possibility of simultaneously serving thousands of subscribers, error recovery servers are not capable of supporting these many users on a consistent basis. To minimize the occurrence rate of server overload cases, peer-based recovery techniques are proposed to distribute the error recovery load towards the user side (i.e., subscribers of the IPTV network). These approaches typically utilize the error recovery server on a
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need-basis, i.e., error recovery server acted as a backup to peerbased recovery. The main disadvantage for approaches that rely on peer-based error recovery is the additional latency incurred during the recovery process. Since the repair packets are delivered from the end-users, the limitations observed along the last mile (e.g., high propagation delay and low uplink bandwidth availability) will have a direct impact on the latency performance. To overcome this limitation while still taking advantage of the peer-based recovery process, our objective in this paper is to develop a serverbased error recovery framework that only utilizes the peer-support mechanism on a need-basis. Utilizing the error recovery server as the initial source for the repair packets, we plan to increase the efficiency of the error recovery process. Furthermore, by utilizing support-peers, and thereby countering the main weakness of a pure server-based recovery approach, i.e., limited number of users that can be supported by the same error recovery server, we also plan to improve the reliability performance of the IPTV networks. In our joint error recovery framework, we essentially utilize peerbased recovery during overload periods to minimize the number of recovery requests, to which the server cannot respond in time. In the next section, we give an overview of the proposed approach and the method of analysis. II. P ROPOSED A PPROACH The main objective of the proposed research is to develop a scalable server-based error recovery framework, for which the session peers are used to assist with the IPTV recovery so that the service quality constraints at the end-users are satisfied. Within the proposed framework, error recovery server (ERServ) acts as the sole coordinator to initiate the peer-based error recovery process. Because of the bandwidth limitation on the peers’ uplink channel, the peer selection process during the error recovery process needs to avoid overutilizing the session peers. The optimization problem is stated as follows: min s.t.
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