Home > IEEE Papers > Toward a Synergy Between P2P and Grids

Toward a Synergy Between P2P and Grids

Authors:  Domenico Talia and Paolo Trunfio

P2P has emerged as a new trend in the internet and have got enormous media attention for two reasons:
• file sharing, in which peers share files with each other.
• highly parallel computing, in which an (inherently) parallel application runs on available nodes.

P2P model has emerged as a distributed paradigm because of its potential to harness the computing, storage and communication power of hosts in the network to make underutilized resources available to other peers.

Grid, which was designed to provide access to remote computing resources for high-performance applications, data-intensive applications, or both. Grid computing can be seen as an answer to drawbacks such as overloading, failure, and low QoS, in client–server systems. Such problems can occur in the context of high-performance computing, for example, when a large set of remote users accesses a supercomputer. Grid nodes typically make their own
resources available at the same time they are accessing resources on other nodes. Some recently developed P2P systems also require nodes to act as servers, at least when joining the network.

P2P comprises several kinds of applications with different design goals, such as anonymity (typically in file-sharing applications), scalability (typically in highly parallel computing applications), or availability (in both application classes). Moreover, P2P systems are based on several different designs:
• systems such as Napster use centralized resource indexes,
• systems such as Gnutella use flooding-based search,
• some experimental systems such as Gridella use structures with distributed resource indexes,
• hybrid networks, such as the superpeer model (described later), combine the P2P and client–server models.

Here we compare the similarity and dissimilarity between P2P and Grids in various fields

Security

Security is most desirable thing in Girds, several efforts are devoted to integrating relevant mechanisms for authentication, authorization, integrity, and confidentiality in grid platforms. By their nature, such security mechanisms allow anonymity of neither users nor resources.
In contrast, P2P systems originate in “open communities,” in which users share more generic goals (such as retrieving music from the Internet), rather than specific objectives (such as participating in high-energy physics simulations). For this reason, security mechanisms in the most widespread P2P systems generally don’t address authentication and content validation, but rather offer protocols that assure anonymity and censorship resistance.
Connectivity

Grids are usually cluster of powerful machines that are statically conneted thriugh high-performance networks. The number of accessible nodes must be scalable because of rigorous accounting mechanism.

Conversely, P2P systems are composed mainly of common desktop computers that are connected intermittently to the network, remaining available for a limited time with reduced reliability. The number of nodes connected in a P2P network at a given time is much greater than in a grid.

Thus, the grid connectivity approach is still too stiff for new nodes and user access and accounting; it could benefit from the more flexible connectivity models used in P2P networks today.

Access Services

Access to remote resources was the main motivation for building grids, and it remains the primary goal today. Grid toolkits provide secure services for  submitting batch jobs or executing interactive applications on remote machines; they also include mechanisms for efficiently sharing and moving data across nodes.
Current P2P systems do not support mechanisms for explicitly allocating remote cycles and storage, but they do provide protocols for sharing and exchanging data among nodes. P2P job-submission models and P2P job scheduling might thus be very attractive topics for research into applying the P2P approach to grid scheduling and job management.

Resource Discovery and Presence Management
Resource discovery in grid environments is based mainly on centralized or hierarchical models. In the Globus Toolkit (www.globus.org/toolkit), for instance, a user or an application can directly gain information about a given node’s resources by querying a server application running on it or running on a node that retrieves and publishes information about a given organization’s node set. Because such information systems are built to address the requirements of organizational-based grids, they do not deal with more dynamic, large-scale distributed environments, in which useful information servers are not known a priori. The number of queries in such environments quickly makes a client–server approach ineffective. Resource discovery includes, in part, the issue of presence management discovery of the nodes that are currently available in a grid — because global mechanisms are not yet defined for it.

On the other hand, the presence-management protocol is a key element in P2P systems: each node periodically notifies the network of its presence, discovering its neighbors at the same time.

Future grid systems should implement a P2P-style decentralized resource discovery model that can support grids as open resource communities.

Fault Tolerance
The dynamic nature of grids necessitates some level of fault tolerance especially for highly distributed code, such as parameter-sweep applications, which can fork numerous similar, independent jobs on many nodes. Beyond simple checkpointing and restarting, reliability and fault tolerance are largely unexplored in grid models and tools. The Globus information system allows fault detection, for instance, but developers must implement fault tolerance at the application level. For greater reliability, designers of fault-tolerance mechanisms and policies for grids should consider using decentralized P2P algorithms, which avoid centralized services that can represent critical failure points.

Where We Should Go
Despite the interest in P2P and grid networks, few noteworthy research efforts are currently devoted to finding commonalities and synergies between them.
In a significant exception, Fox and colleagues have sketched a P2P architecture for grid-connected resources (www.communitygrids.iu.edu), but much more remains to be done by members of both communities. We believe a P2P approach is needed both to
• implement grid tools and services,
• design and develop grid applications that must access and coordinate remote resources and services.
Developers and users could exploit the many contact points between P2P and grid networks by recognizing P2P’s relevance to corporations and public organizations rather than viewing it as just a home computing technology.

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