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CHAPTER 12 ■ DEVELOPING PEER-TO-PEER APPLICATIONS WITH WCF 375ramrameshreddy.blog.comEnd-to-end connectivity: Because of the loose and disparate nature of a mesh, from adevelopment and debugging perspective, ensuring that the various peers can seamlesslyconnect to each other is a challenge. Furthermore, complicating this is the fact that thepeers connecting to the mesh might be using one or more communication technologies.Because of the nature of P2P applications, this also needs to support communication overvarious networks.Common foundation: This is the “administrative” functionality that every P2P applicationneeds in order to manage the various peers on the mesh. This includes identity management,contact management, node discovery, node naming, secure session management,multipeer communication, and so on.Secure and scalable deployment: This is the ability to build on protocols specifically engineeredfor large-scale deployment, and it provides built-in security.How Are Nodes Identified?On a mesh, each node needs to be identified by a unique ID usually called a peer ID or meshID. To resolve these peer IDs to their corresponding Internet address, the Peer Name ResolutionProtocol (PNRP) is used instead of DNS. Each peer node irrespective of type (such ascomputer, user, group, device, service, and so on) can have its own peer ID. This list of IDs isdistributed among the peers using a multilevel cache and referral system that allows nameresolution to scale to billions of IDs while requiring minimal resources on each node.An endpoint is defined as a combination of a peer ID, port number, and communicationprotocol. Using an endpoint, data can be sent between nodes in two ways. One of these is for apeer to directly send the data to another peer. And the other is for a peer to send the data to allthe other peers on the same mesh; this is also known as flooding. A flooded message couldarrive at the same peer multiple times via different routes on the mesh.Installing the Windows P2P Networking StackWindows P2P networking stack is not installed on Windows XP by default. If you are runningWindows XP with Service Pack 2, then perform the following steps to install the P2P networkingstack:1. Click Start ➤ Control Panel ➤ Add/Remove Programs.2. Click Add/Remove Components.3. In Components, click Networking Services, and then select Details.4. Select the Peer-to-Peer check box, and then select OK.ramrameshreddyramrameshreddy5. Click Next, and follow the instructions on the screen.If you are running Windows XP with SP1, then you will need install the Windows AdvancedNetworking Pack for Windows XP, which is a free download available at http://tinyurl.com/6ze98.If you are running Windows Vista, then this is already installed; however, you might haveto enable the firewall exceptions. To do so, follow these steps: