Application Level QoS in Multimedia Peer-to-Peer (P2P) Networks Alireza Goudarzi Nematiy and Makoto Takizawa¤ Tokyo Denki University 報告者 : 饒展榕 1

Outline Introduction Mobility in a P2P Overlay Network System Model Peer-to-Peer Communication Protocols Concluding Remarks 2

Introduction In peer-to-peer (P2P) overlay networks, each peer process (peer) can play a role of not only client but also server. multimedia contents are in nature distributed in peers by downloading and caching. A peer may have a full replica and another peer may have only a part. In this paper, we would like to discuss how source peers efficiently deliver multimedia contents to receiver peers in a streaming model. 3

It is critical to support a receiver peer with enough QoS to satisfy the receiver’s requirements, e.g. play a fully colored video movie in the streaming service in change of QoS of networks and peers. In this paper, we discuss a multi-source streaming protocol where a receiver peer can receive packets of a multimedia content from a source peer which can support enough QoS out of multiple source peers. 4

Mobility in a P2P Overlay Network A peer-to-peer (P2P) overlay network includes various types of computers and devices like personal computers and mobile devices. Peers in mobile computers can move in networks by changing their locations in a same way as people are walking and driving cars. even if computers do not move, a peer can move from one computer to another computer in a mobile agent technologies. 5

Suppose a pair of peers pi and pj are communicating with one another and the peer pi moves in a network. There are the following cases: 1.p i is in a wired peer-to-peer (P2P) network: The peer p i is first disconnected from the network. After changing the position, the peer makes a new connection with the peer p j in the overlay network. 2.The peer pi is in the wireless ad-hoc P2P network: The peer pi can communicate with the peer pj while the peer pi is moving. 6

We discuss a P2P overlay network where peers can move so that the peer continues communicating with other peers without disconnection while moving. Peers have to support other peers with enough QoS through cooperation with other peers at the application level even if QoS at a physical layer like bandwidth e.g. is changed. Users at application level should be able to take usage of distributed objects without being conscious of viewing any change. 7

In this paper, we aim at realizing a P2P model where the peer can take enough service even during movement of the peer. Differently from wired P2P networks, multimedia contents are deployed independently out of the overlay topology in a mobile P2P network. According to the movement of a peer, QoS of the logical communication channel among a receiver peer po and a source peer p1 might be changing. 8

If QoS of the channel is too degraded to satisfy QoS requirement,the source peer p1 or receiver peer po have to find another source peer p2 which can support enough QoS. Here, the new source peer p2 has to start sending packets of the multimedia content m to the receiver peer po where the source peer p1 is still sending packets. The new source peer p2 is required to be synchronize with the current source peer p1 so then the receiver peer po can receive every packets without any message gap and with less redundant packets. Then, p2 takes over the source peer p1. 9

System Model-Network architecture In this paper, we consider a fully distributed, unstructured P2P overlay network where mobile peers are exchanging multimedia contents in a streaming model with each other while not only receiver peers but also source peers of the multimedia contents are moving. In unstructured P2P overlay networks, each peer has to find another acquaintance peer by using the detection algorithms and communicating with its acquaintance peers. The peers can communicate and share information, i.e. multimedia contents with the acquaintance peers. 10

Peers may hold multiple replicas m1 and m2 of a multimedia movie content m. Multiple replicas of a multimedia content exist in multiple computers but QoS of each replica might be different from others. 11

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We consider a P2P overlay network for supporting multimedia streaming service where every peer which holds not only a whole multimedia content but also a part of a multimedia content with different levels of QoS can send the multimedia content to another peer. In addition, peers are movable and do not have a static location. Each multimedia content is characterized in terms of QoS parameters, like frame rate and number of colors. 13

System Model-Application level QoS QoS obtained by a receiver peer depends on not only QoS of a multimedia content itself in a source peer but also QoS of a network between the source and receiver peers. QoS of application level depends on the following types of QoS; peer QoS, network QoS, and content QoS. QoS of application level which a receiver peer can perceive depends on the minimum QoS among them. 14

In this paper, we assume QoS values are totally ordered. QoS QPi of a source peer pi influences QoS value. There are parameters as processing speed and memory size which the source peer can use. The total QoS QSi of a multimedia content c which a source peer pi can support is given min (QPi;QCc). 15

The network QoS QPi from a source peer pi to a receiver peer po is characterized in the following parameters of network; bandwidth, packet loss rate, jitter, and delay. QoS QCc of a multimedia content c is referred to as quality of content (QoC). There are QoC parameters; resolution, frame rate, file size, and file duration. It is critical to discuss how much QoS of a multimedia content m a receiver peer po can obtain from a source peer pi in a network. 16

Peer-to-Peer Communication Protocols A receiver peer po finds a source peer pi which can support po with multimedia content steaming source of enough QoS. If QoS supported is getting degraded, the receiver peer po finds another source peer pj which can support po with enough QoS i.e. Q · Qi. 17

Suppose a receiver peer po would like to obtain the streaming service of a multimedia content c. First, the receiver peer po finds source peers p1,..., pn which support the multimedia content c in a P2P overlay network. The receiver peer po selects one source peer, say pi whose QoS satisfies the application requirement, Q · Qi. 18

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seq = REQ + minTRk *ðk, 20

On receipt of a packet pk from pk { if REQ > pk:seq, discard pk; else REQ = pk:seq, { receive pk; REQ = REQ + 1 ; * change the source peer to pk and stop pi; current = pk; } 21

On receipt of a packet pk from pj, { if current = pj, { if REQ = pk:seq, { receive pk; REQ = REQ + 1; } else /* current = pk */ { send disconnect to pj ; } 22

If the receiver peer po decides on changing the current source peer, the receiver peer po sends a disconnect request to the source peer pi. On receipt of the disconnect request from the receiver peer po, the source peer pi stops transmitting packets to the receiver peer po. 23

[Receiver peer po] po finds another source peer pi; po sends a content request with QoC QCc and Q to pi { On receipt of an ACK message from pi, f send a start message to pi; } 24

On receipt of a NACK message from pi, { find another source peer; go to the beginning of this procedure; } On receipt of a packet pk from pi, { if REQ = pk.seq, { receives pk; REQ = REQ + 1; } 25

[Source peer pi ] On receipt of a content request with QoC QCc and Q from peer po, { if Qi > Q, send an ACK message to po else send a NACK message to po; } On receipt of a start request from po, { send content packets to po; } On receipt of a disconnect request from po, { stop sending packets to po; } 26

Concluding Remarks In this paper, we discuss how to support a receiver peer with enough QoS of the multimedia steaming service by multiple source peers. QoS supported by source peer is changing according to the movement of the receiver peer and source peer. In this paper, a receiver peer changes a source peer with another peer if the source peer might not support enough QoS. We are now implementing the protocol and evaluating the protocol. 27