Technologies for sharing and collaborating on the Net

This paper is an overview of the technologies that are needed for Peer-to-Peer (P2P) computing. It represent a high level overview of material covered in much greater detail in Barkai, (2001). P2P means different things to different people, and we start by defining P2P and categorizing applications that use P2P. Server-mediated P2P is included as a legitimate P2P architecture. The applications space is divided into three types: distributing computing, content sharing, and collaboration. After a discussion of what is required from an infrastructure for P2P we describe some solutions that address a class of applications each, but also include a start towards a general-purpose architecture. The same basic services are needed by each platform and application, and all will benefit from common middleware. This is one way, though not the only one, to achieve interoperability - that will be useful to users and application developers; in particular, when we reach the integrated applications stage. Regardless of how the infrastructure is constructed, the technical topics which need to be addressed are the same: communication through gateways and firewalls; naming and discovery of peers and resources when DNS is not enough; availability and persistence of resources in spite of intermittent connectivity and dynamic presence; security in a distrustful environment and locally managed systems; and, management of distributed resources in a heterogeneous setting. There are a number of interesting ways in which people have applied P2P technologies. We give an example in each of the three application categories. The final segment of the talk summarizes the challenges that need to be overcome if P2P is to be widely adopted. The major technical challenges are direct communication, security, naming and interoperability. There are also social and cultural barriers. These are the result of decentralization, and loss of direct control over resources. They also have to do with trust, reputation, and online communities. Nonetheless, there are some promising activities around the industry-working groups and initiatives, and a great opportunity.