Abstract /08/$ IEEE 601

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1 PeerCDN: A Novel P2P Network Assisted Streaming Content Delivery Network Scheme Jie Wu Zhihui lu Bisheng Liu Shiyong Zhang Department of Computing & Information Technology Fudan University, Shanghai, China, {jwu, lzh, bsliu,szhang}@fudan.edu.cn Abstract Providing scalable streaming media service over the internet is a demanding task nowadays, CDN(Content Delivery Network) and P2P are the main approaches while both have pros and cons. We propose a novel hybrid architecture -- PeerCDN to combine the two approaches seamlessly with their inherited excellent features. PeerCDN is a two-layer streaming architecture. Upper layer is a server layer which is composed of original CDN servers including origin servers and replica servers. Lower layer consists of groups of clients who request the streaming services, each client is considered as a client peer in the group. Each group of client peers is led by the nearby replica server. Client peers contribute their resource through the coordination of the leader peer. The scheme uses a revised Kademlia-like protocol for peer-to-peer topology management and DHT for data retrieval. It constructs a topology-aware overlay network and results reduced jitter. PeerCDN makes best use of original investment and infrastructure. The service capacity is larger than traditional CDN system with the participation of the client peers. Also, the topology-aware overlay network restricts the unnecessary backbone bandwidth consuming during client peer sharing. The experiment result shows that PeerCDN has better features than the CDN and pure p2p approaches.. 1.Introduction The ongoing growth of broadband technology in the worldwide market has been driven by the hunger of customers for improved performance, quality and new rich media services. In particular, the use of multimedia formats (audio and video) has become common for content distribution and delivery (CDD) of rich media information to the public - both residential and business[1]. While consumption of rich media content is steadily increasing, the usage of rich media has not fully caught on because of the bandwidth limitations, low quality of service (QoS), and the resulting poor user experience. To overcome this challenge of massive rich media consuming, only deploying more high-speed main pipes will not be enough; service providers need a more intelligent infrastructure layout to grow with this explosive market. Therefore, today s service providers are improving quality, bandwidth availability and profitability by using edge technologies, such as CDN (Content Delivery Networks), caching, streaming, Web serving, and IP traffic management, to provide services[1]. CDN is a mainstream trend of these edge technologies. The purpose of CDN is to quickly give users the most current rich media content in a highly available fashion. In a word, the goal is to push content as close to the user as possible to minimize content delivery latency (the time it takes for the requesting device to receive a response) and jitter (unpredictable, large fluctuations in latency) and to maximize available bandwidth speed. Although CDN is an effective means of information access and delivery, there are two barriers to making CDN a more common service: cost and replication integrity. Deploying a CDN for publicly available content is expensive[1]. Supporting one user s streaming services is likely to take at least $1,000. It requires administrative control over nodes with large storage capacity at geographically dispersed locations with adequate connectivity. The difficulty in maintaining replication integrity over a CDN is not because of inadequate corruption detection of single files, but the delay caused by the replication of very large files. In order to more effectively address the requirements to access rich media services from everywhere at anytime, recent research has focused on the development of new scalable, efficient, and flexible "next generation" middleware platforms. These middleware platforms are intended to support the deployment of wide-area applications including Content delivery networks and Video-on demand. One such next-generation middleware platform is the P2P /08/$ IEEE 601 CIT 2008

2 computing system. Many research works have been taken in P2P live streaming and P2P VoD streaming[6,7,8,9]. The emergence and maturity of Peer to Peer technique, which is widely known as P2P, has incredibly developed the usage of the network. Now we can remarkably improve the performance of many network applications, since server end is less likely to be a bottleneck by making the full use of the client end resource, such as bandwidth, CPU, etc. In this paper, we propose a novel hybrid architecture -- PeerCDN to combine the two approaches seamlessly with their excellent features. This kind of research has begun to become hot, in [5], authors propose and analyze a hybrid architecture that integrates both CDN- and P2P-based streaming media distribution. The remainder of this paper is organized as follows: In section 2 we begin with PeerCDN architecture design. A PeerCDN deploy scheme in MAN Metropolitan Area Network is discussed in section 3. We present our CDN-Kad-fixed P2P streaming scheme implementation and experiment results analysis in section 4. In section 5, we conclude the paper. 2. PeerCDN Architecture Design: A Novel P2P Network assisted Streaming Content Delivery Network Scheme Figure1. PeerCDN Architecture 2.1 CDN-P2P Two-layer Streaming Architecture PeerCDN is a two-layer streaming architecture. Upper layer is a CDN framework layer which is composed of original CDN servers, including origin servers and replica servers. Lower layer is called Peer node layer, which consists of multiple groups of clients who request the streaming services, each client is considered as a peer node in the group. Each client plays or downloads the media file, it, when running agent, can become a potential "microserver" to provide content for other future neighbored or peered requestors of the content. 2.2 Strong Node Acting as the connecting point between CDN framework layer and Peer node layer The connecting point between CDN framework layer and Peer node layer is located in the nearest replica server, we call it Strong Node. it s the Strong Node s duty to coordinate the resource for each request. Through these strong nodes, we realize the management of regional autonomy when constructing overlay network. We described it in the following part. Unlike most P2P schemes that construct overlay networks logically, in PeerCDN, the overlay network is constructed geographically to become topology-aware overlay network. The topology-aware thought is inherited from CDN that the content will be pushed to edge of the network, thus the clients get content service from the nearest replica server to ensure the best QoS and reduce the consuming the valuable backbone bandwidth. 2.3 The Model of controllable regional autonomy in P2P overlay network In our PeerCDN architecture, each group of client peers is led by the nearest replica server-strong Node. In order to prevent the fail-over of that server, other nearby replica servers can also be candidate leaders, if the nearest replica server fails, one of the candidate leaders will be selected to be the leader of that group. Client peer nodes assigned in the same group are usually region -neighboring, they may in the same subnetwork or in the same gateway, so the network condition between client peer node is usually good, it makes it possible for client peer node to collaborate each other with fairly-well QoS. Through these strong nodes as leader of multiple peer nodes in each region, we realize a model of controllable regional autonomy in P2P overlay network. Client peer node cache portion of the streaming media content during they get service, they may contribute their limited storage and up-link bandwidth to others in the same group through the coordination of Strong Node. The sum service capacity of client peer nodes may be considerable especially for the popular streaming media. 602

3 3. A PeerCDN Deploy Scheme in MAN Metropolitan Area Network In paper[2], we have designed the relationships architecture of content delivery grid service model, just like Figure2. As Figure2 showing, in a Metropolitan Area Network, CDN architecture of a three-tier hierarchy is composed of: initial media sources (original content providers), metropolitan media centers and regional media centers acting as caches for popular media content. in this architecture, regional media centers are installed in consumers neighborhoods (at the inner end of the so-called last mile ). Here, based on this architecture, we utilize the regional media centers and client node to build a novel PeerCDN architecture. Our PeerCDN is deployed in the regional media centers layer, and the regional media centers act as Strong Node. Each Strong Node manages a number of peer nodes in its region, such as a telecom ADSL broadband district. In a same region, there are one or several groups to be managed by Strong Node. The function of metropolitan media centers is to aggregate a number of neighbored regional media centers, for instance of a metropolitan area. Regional media centers are interconnected among each other according to their geographic neighborhoods. Consumer clients are connected to one associated regional media center from which they obtain media content[2]. Figure2. A PeerCDN Deploy Scheme in MAN At the same time, such relationship architecture is not static. The Operating System and content service platform of the peered media centers may be heterogeneous, but they can be dynamically constructed to Virtual Neighbor Organization (VNO). On request of a consumer, if the media content is available in the media center, the media content is directly provided from the regional media center to the consumer s home. If content is not present, the regional media center asks its neighbor or peer regional media centers at the same VNO for the content. On the other hand they can cooperate to provide content service. If the content cannot be obtained from there, the regional media center asks its associated metropolitan media center. This procedure of asking peers before the higher-ordered element or cooperative service intends to avoid load at metropolitan media centers. Metropolitan media centers behave similarly as regional centers. If content that is asked for by assigned regional media centers is not available, metropolitan media centers contact their VNO peers and obtain content from there. If content cannot be obtained from peer metropolitan media centers, content is obtained from the original content provider at the top of the distribution hierarchy. In paper[4], we have designed a novel Kademlia P2P network -based VoD Streaming Scheme. In this paper, we utilized Kademlia technology to construct overlay network in a global network, and we didn t use it together with CDN. Here, we merge CDN architecture with Kademlia P2P network. We do not use Kademlia P2P network in CDN global range, but we use it in every region. In every region, we take the advantage of Kademlia technology to construct the P2P overlay network. In every region, there are several groups, every peer node can attend one or more groups. Through managing these groups in every region, we will avoid the problem of excessive freedom of P2P network itself, and realize one kind of controllable regional autonomic P2P delivery mechanism, making CDN to extend scale in network edge-side (so-called last mile ). The paper[3] describes Kademlia, a peer-to peer distributed hash table(dht) has already successfully used in large scale P2P network, such as BT and emule network. The P2P technique is mainly used on file sharing and live broadcasting. However there are not so many researches about the VoD systems using P2P technique. Kademlia[3], is a peer-to-peer (key,value) storage and lookup system. Kademlia has a number of desirable features not simultaneously offered by any previous peer-to-peer system. It minimizes the number of configuration messages nodes must send to learn about each other. Configuration information spreads automatically as a side-effect of key lookups. Nodes have enough knowledge and flexibility to route queries through low-latency paths. Kademlia uses parallel, asynchronous queries to avoid timeout delays from 603

4 failed nodes. The algorithm with which nodes record each other s existence resists certain basic denial of service attacks. Finally, several important properties of Kademlia can be formally proven using only weak assumptions on uptime distributions (assumptions we validate with measurements of existing peer-to peer systems). Kademlia takes the basic approach of many peer topeer systems. Keys are opaque, 160-bit quantities (e.g., the SHA-1 hash of some larger data). Participating computers each have a node ID in the 160-bit key space. (key,value) pairs are stored on nodes with IDs close to the key for some notion of closeness. Finally, a node-id-based routing algorithm lets anyone locate servers near a destination key. 3.1 Controllable Regional Autonomic Group Formation In Kademlia, each node has a unique 160-bit id, as the identity of the node. The number is randomly selected during the initiation of a node, as described in the section 3. But the generation of the id doesn t take the network address of the node into consideration. Actually we can make some modification of the generation algorithm to make the full use of the node identity. Our basic idea is to include the node IP in the initiation procedure. We describe our design as follows: bits 128 bits The identity of a node consists of two parts: the first 32 bits is the binary expression of the IP address of the node; while, the second 128 bits are still randomly selected. By this way, we can remain the original idea of Kademlia. Besides, the distance between two nodes, d(x,y) = x y, has other useful logical meaning. As we can see, the IP address is in the more significant parts of the number, which means the smaller the distance, the closer two nodes are in the network space. This feature is conducive to the formation of controllable regional autonomic group. In every region, the Strong Node, as leader, will organize several group based the node distance. If the nodes distance is smaller, they are more possible to be arranged the same group 3.2 PeerCDN Overlay Network Formation Firstly, some last-layer severs in CDN are selected as Strong Nodes, which are registered into the directory center. Every Strong Node are in charge of a region. When a common node enters into network, the first step is to join the P2P overlay network. Firstly, the new node can get the information of one or several Strong Nodes via the directory center; and then based on its node ID, it will be arranged into one or more groups in one region leaded by Strong Node, which manages the Kad network in a region. According to the definition of Kademlia, the node needs to know at least one neighbor to bootstrap. once a node has successfully joins the group, it can get more neighbor information. Once the node gets the neighbor information, it pushes the neighbor into its k-buckets. As we know, the most important procedure a Kademlia participant must perform is to locate the k closest nodes to some given node ID, which is called this procedure a node lookup[3]. We simply find some closest neighbors and ask them about my closest neighbors from their knowledge. By this recursive procedure, a new joined node can quickly get the information of his neighbors in the same region. Since closest here means geographically-topological close in network region, the peer nodes are restricted in a scale of region, which is helpful for the peer nodes to more quickly find media content. 3.3 Full-Media Publishing and Part-Media Republishing Full-Media Publishing means how CDN publishes full media file to all layers. Firstly, the source of media file is from the original center provider. And then the part of media files are propagated into all layers of CDN, including the last layer-strong Node. In our scheme, each media has a unique 160-bit identity, which is obtained by some hash algorithm. When one peer node has joined the PeerCDN network, it firstly can get some parts of a full media file for downloading or VoD playing. According to the idea of P2P network, once the requesting node gets some part of the requested media, it should publish itself as a source node. Therefore, it should tell some neighbors it holds some parts of the full media file, in order for other peer nodes to be served by it. Therefore, Part-Media Republishing means that when one peer node get some parts of one media file, it will re-publish the message of its holding Part-Media to its leader-strong Node and our peer node in the same group. Our recommended message format is as follow Media ID Peer ID GroupID and RegionI D Timestamp Optional 604

5 As mentioned, to maintain the freshness of the stored message, the target node should periodically checks the freshness of the local message and the source node should also periodically republishes the media info. According to our experience, the time interval can be selected as half length of the average of total media length. 3.4 Media Searching Media searching is the premise of media services. How to efficiently find the media services source (including Strong Nodes and Peer Nodes) is our goal. Besides, we need to consider the distance between the media source and media user is close in topology. As we know, the PeerCDN network is typically divided into multiple regions according to their geographical position. The process of media searching is top-down style. Firstly, when one new node search a media, the new node can firstly get the media information from the directory center; The directory service maintains relatively static information. Currently that information relates to users, computing, content and storage resources and content profiles. And then based on its node ID and IP, it will be guided into of one or several Strong Nodes who hold the required media and located in the geographically close region. For example, we assume Strong Node A-1 and Strong Node B-1 are two source nodes to provide same media K. Strong Node A-1 is in region A and Strong Node B-1 is in region B. When peer node P1 in region A joins the PeerCDN network and search the media K, Strong Node A-1should be chosen, not Strong Node B- 1. But we should know that it is not enough to provide media service just through one or several Strong Nodes. The user should continuously get several peer nodes to provide parallel media services. The second-time media searching is finished in Kad regional network. According to the standard searching procedure in Kademlia [3], the client ask its group neighbors closest to the media ID about their knowledge of the source node streaming the media in a recursive way. Which is different here, we ask the requested neighbor to return the source nodes according to two rules: the node closest to the file and the node closest to the requested node. By the group management, it is convenient to find the closest node. In this way, we can restrict the P2P content service activity in each local region. At the same time, other region s node can still be chosen as source, in case there are no sources in the local region. Once the client gets the requested source nodes, it can select several nodes as final source. The procedure of the final selection can be done by a higher layer protocol, such as by monitoring the node bandwidth, local history or other metrics, which is out of the scope of this paper, however, we will cover some aspects in the implementation section. 4. PeerCDN Mode based VoD Scheme Implementation and Experiment Analysis In this section, the prototype of our scheme is presented. Our prototype is divided into three layers: network layer, kad layer and application layer. While the network layer is in charge of the transportation of messages, the KAD Overlay Network layer is the main part of the implementation of our scheme, which provides three services for the higher layer: media publishing service, media searching service and neighbor routing service in a region, every region is leaded by Strong Node. The application layer consists of Peer Node module and Strong Node module. Peer Node module consist of Media Play, Media Transfer, Part-media republish and other sub-modules. Figure3. PeerCDN 3 Layer Architecture Strong Node module consist of Media Publish, Media Transfer, Buffer Management, and other submodules. These strong nodes are more reliable than the peer nodes. Considering the practical deployed CDN network, former deployed proxies can be easily transformed into strong nodes, who are located in the last-layer of CDN. In this section, we evaluate the performance of our proposed PeerCDN scheme with traditional CDN solution and Only-P2P solution. Our experiment is carried out in Campus Network environment.in the first simulation, four sub networks 605

6 A, B,C and D are included, connecting with each other via a router. Four servers are respectively deployed in network A,B,C and D as Strong Nodes, while 100 peer nodes are deployed on every sub network. One server as Web portal server and directory server. 400 client nodes start to click on 10 different video files through the Web portal, with three model test cases, including traditional only CDN model, the only P2P mode and mixed PeerCDN mode. In traditional only CDN model, all VoD service is provided through 4 Strong Nodes. Every Strong Node s maximum load is 70 parallel VoD streaming service, so the total service capability is 280 VoD service. In the only P2P mode, we do not use Strong Node, just only use Kad mode. In the mixed mode, we use our proposed PeerCDN scheme. From the Figure4, we can see the experiment results comparison of 3 Mode. In the early period, because of the absence of strong node involvement, the only P2P mode will take longer response time, while KAD network are constructing process, the routing information will be collected in about 10 seconds. Both only CDN and PeerCDN have smaller response time, thanks to the Strong Node s contribution. When the request number arrives above 280, the only CDN mode CDN mode has already saturated, while PeerCDN mode arrive a more stable response time. The PeerCDN s service capability can arrive at 400 parallel VoD service in our experiment condition. Only P2P mode also can be close to this level this level, but the PeerCDN mode have more quick startup speed than only P2P mode, which is one important user experience in VoD service. Figure4. Experiment Results Comparison of 3 Mode 5.Conclusion PeerCDN is an inherited architecture from CDN and P2P with their excellent features. It makes best use of original investment and infrastructure. Obviously the service capacity is larger than traditional CDN system with the participation of the client peers. Also, the topology-aware overlay network restricts the unnecessary backbone bandwidth consuming during client peer sharing. Simulations are done to compare our strategy to others, the results show that ours is more reasonable than the other two systems. The PeerCDN is a ISP-friendly, distributed, scalable and cost-effective one. 6. References [1] Zhihui Lv, Yiping Zhong, Shiyong Zhang, Jie Wu. Study of Main Technology in Rich Media Grid Delivery. In the Proc. of ICCNMC 03, IEEE Computer Society Press, 2003, p [2] ZhiHui L., ShiYong Z., YiPing Z.: Research on Service Model of Content Delivery Grid. In the Proc. of APWeb'04, Lecture Notes in Computer Science, Vol Springer-Verlag, Hangzhou (2004), [3] Petar Maymounkov and David Mazieres, "Kademlia: A Peer-to-peer Information System Based on the XOR Metric", New York University, [4] Jie Wu, BiSheng Liu, ShiYong Zhang, ZhiHui Lu, and YiPing Zhong,KadStreaming: A Novel Kademlia P2P Network -based VoD Streaming Scheme, Proceeding of the 7th International Conference on Computer and Information Technology (CIT2007), IEEE Computer Society, [5] Dongyan Xu, Sunil Suresh Kulkarni, Catherine Rosenberg, Heung-Keung Chai; Analysis of a CDN P2P hybrid architecture for cost-effective streaming media distribution Multimedia Systems (2006) 11(4): [6] D. Tran, K. Hua, T. Do, A Peer-to-Peer Architecture for Media Streaming, in IEEE JSAC [7] H. Deshpande, M. Bawa, H. Garcia-Molina, Streaming live media over a peer-to-peer network, in Work at CS-Stanford [8] Y. Guo, K. Suh, J. Kurose, D. Towsley, P2Cast: P2P Patching Scheme for VoD Service, in WWW [9] Tai T.Do, Kien A. Hua, Mounir A. Tantaoui, "P2VoD: Providing Fault Tolerant Video-on- Demand Streaming in Peer-to-Peer Environment," in IEEE International Conference on Communications, Paris, June