Distributed multi-source streaming models in peer-to-peer overlay networks

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Abstract

A multimedia contents are distributed to peer computers (peers) and a contents peer which holds contents can provide other peers with the contents in peer-to-peer (P2P) overlay networks. Here, contents peers are mainly realized in less-reliable and low-performance personal computers. Multimedia streaming is more significant than downloading ways in multimedia applications from security and economical reasons. We discuss distributed multi-source streaming models to support peers with reliable and scalable multimedia streaming service. Here, a collection of multiple contents peers in parallel transmit packets of a multimedia content to a leaf peer to realize the reliability and scalability. Each of the contents peers send different packets from the other contents peers at slower rate. Even if not only some number of peers stop by fault and are degraded in performance but also some number of packets are lost and delayed in networks, a leaf peer has to receive every data of a content at the required rate. We discuss how to replicate data of a multimedia content by creating a parity packet for some number of packets and to allocate packets to each contents peer so that a leaf peer can deliver a packet without waiting for preceding packets from other contents peers in presence of the faults. Next, multiple contents peers are required to be synchronized to send packets to a leaf-peer so that the leaf-peer can receive every data of a content at the required rate. We discuss a pair of gossip-based flooding-based protocols, directed acyclic graph (DAG)-based coordination protocol (DCoP) and tree-based (TCoP) coordination protocol to synchronize multiple contents peers to send in parallel send to a leaf peer. First, some number of contents peers are selected and start transmitting packets to a leaf peer. Then, each of the selected peers selects some number of peers. Here, a peer can be selected by multiple peers in DCoP but by at most one peer in TCoP. Finally, every contents peer transmits packets to the leaf peer at the allocated rate. We evaluate the coordination protocols DCoP and TCoP in terms of how long it takes and how many messages are transmitted to synchronize multiple contents peers.

Introduction

Multimedia streaming applications [9], [12], [13] like music streaming and movie on demand are getting more significant than downloading service in the Internet applications from the security and financial reasons [1]. Here, multimedia contents have to be reliably delivered to users from providers of the contents while real-time constraints are satisfied. In peer-to-peer (P2P) overlay networks [2], [11], [16], multimedia contents are in nature distributed to peer computers (peers) in various ways like downloading and caching. Peers which have parts of multimedia contents can support other peers with the contents if it is legal. Here, a peer can play any role of contents and leaf. Contents peers support multimedia contents. Leaf peers receive multimedia contents from contents peers.

New approaches to realizing scalable and reliable multimedia streaming service in P2P overlay networks are discussed in multi-source streaming (MSS) models [5], [8] where multiple contents peers send packets of a multimedia content to a leaf peer. A large number of leaf peers are required to be supported by even low-performance, less reliable personal computers. Itaya et al. discuss a centralized protocol [5] similar to the two-phase commitment (2PC) protocol [14] to coordinate multiple contents peers. It takes at least three rounds to synchronize multiple contents peers. Liu and Voung [8] also discuss a centralized protocol where a requesting leaf peer sends a transmission schedule of a content to multiple contents peers. Each contents peer synchronously send packets according to the schedule. Although it is simple to implement the centralized approach, it takes time for multiple contents peers to start transmitting packets [3].

In the distributed multi-source streaming models [3], [4], [5], all the contents peers do not start transmitting packets of a multimedia content but contents peers gradually start transmitting packets. In this paper, we newly propose protocols based on gossip-based flooding protocols [6], [7] to reduce the communication overhead. First, a leaf peer sends a request packet to some number H of the contents peers. On receipt of the content request, a contents peer starts transmitting packets to the leaf peer. Here, each contents peer sends one Hth of the packets at one Hth of the transmission rate of the content rate, e.g. 30 Mbps of movie content. Then, the contents peer selects some number H of the contents peers. Here, there are two algorithms; a contents peer may be selected by multiple peers and by at most one peer. The former is a directed acyclic graph (DAG)-based coordination protocol (DCoP) and the latter is a tree-based coordination protocol (TCoP). A request packet carries information on which packets the contents peer has sent to a leaf peer at what rate. Each of the selected peers makes a decision on which packets to be sent at what rate by using the information. In addition, parity packets for some number of packets [15] are transmitted so that a leaf peer can receive every data of a content even if some number of packets are lost and contents peers are faulty. Furthermore, we discuss how to allocate packets of a multimedia content to each contents peer. Due to the heterogeneity of the P2P overlay networks, each contents peer sends packets at transmission rate and loss ratio different from others. We discuss a packet allocation algorithm where a leaf peer can deliver a packet on receipt of the packet without waiting for preceding packets from other contents peers even if some number of contents peers are faulty and packets are lost with a channel in a bursty manner.

In Section 2, we present the multi-source streaming (MSS) model. In Section 3, we discuss how to allocate packets of a content to contents peers in heterogeneous environment. In Section 4, we discuss a pair of the coordination protocols DCoP and TCoP. In Section 5, we evaluate the coordination protocols DCoP and TCoP in terms of how long it takes to synchronize all the contents peers and how many redundant packets are transmitted.

Section snippets

A multi-source streaming (MSS) model

Multimedia contents are distributed to peer computers (peers) in various ways like downloading and caching ones in a peer-to-peer (P2P) overlay network. For example, a peer obtains a free movie from an acquaintance peer by downloading and then supports some part of the movie to other peers [12]. A contents peer which holds whole or a part of a content can send the content to other peers. A peer receiving a content from a contents peer and using it is referred to as leaf peer. Each peer can play

Packet allocation to contents peer

Let pkt be a packet sequence 〈t1, …, tl 〉 (l  1) of multimedia content c. Each contents peer CPi (i = 1, …, n) sends a part of a sequence pkt to a leaf peer LPs. Here, ∣pkt = l. Suppose three contents peers CP1, CP2, and CP3 transmit packets in a sequence pkt = t1, …, t7, …〉 of a multimedia content C to the leaf peer LPs where the bandwidth ratio bw1:bw2:bw3 is 4:2:1. Each contents peer CPi transmits a subsequence pkti of the packet sequence pkt to the leaf peer LPs. ∣pkti  pktj∣ if bwi  bwj. For example,

Types of distributed coordinations

Multiple contents peers CP1, …, CPn are required to cooperate to reliably deliver packets of a multimedia content C to a leaf peer LPs. Here, we assume each contents peer CPi supports the same transmission rate to the leaf peer LPs for simplicity. Let pkt be a sequence of packets t1, …, tl of a multimedia content C. While transmitting packets of the content CLPs, each contents peer CPi informs the other contents peers of which packets CPi has sent at what rate and the view showing which contents

Evaluation

We evaluate a pair of the DAG-based coordination protocol (DCoP) and tree-based coordination protocol (TCoP) for synchronizing multiple contents peers in terms of the coordination time, the number of redundant parity packets, and receipt and transmission rates. Suppose there are n contents peers CP1, …, CPn which transmit packets of a content to a leaf peer LPs. Let H be the number of child contents peers to be selected by each parent (H  n). (H  h) shows packet interval. Suppose each communication

Concluding remarks

In this paper, we discussed the multi-source streaming model for transmitting continuous multimedia contents from multiple contents peers to a leaf peer. In peer-to-peer (P2P) overlay networks, peers on various types of computers can support other peers with multimedia contents. We discussed two types of the distributed coordination protocols, DAG-based coordination protocol (DCoP) and tree-based coordination protocol (TCoP) for multiple contents peers to transmit packets to a leaf peer. In

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