C# 4 and .NET 4

1346 ❘ ChaPTer 45 peer-tO-peer netwOrkinG
alternative key scheme, but the keys must be 256-bit integer values (just like PNRP IDs). This means that you
can use any scheme you want, but you are then responsible for the generation and security of the keys. By
using this component you can create new cloud topologies beyond the scope of PNRP, and indeed, beyond the
scope of this chapter as this is an advanced technique.
Windows 7 also introduces a new way of connecting to other users for the Remote Assistance application:
Easy Connect. This connection option uses PNRP to locate users to connect to. Once a session is created,
through Easy Connect or by other means (for example an e-mail invitation), users can share their desktops
and assist each other through the Remote Assistance interface.
People near me
PNRP, as you saw in the previous section, is used to
locate peers. This is obviously important as an enabling
technology when you consider the discovery/connection/
communication process of a P2P application, but in itself
is not a complete implementation of any of these stages.
The People Near Me service is an implementation of the
discovery stage, and enables you to locate peers that are
signed in to the Windows People Near Me service in your
local area (that is, in a link local cloud that you are
connected to).
You may have come across this service because it is built into
Vista and Windows 7, and is used in the Windows Meeting
Space application, which you can use for sharing applications
among peers. You can configure this service through the
Change People Near Me settings control panel item (you can
navigate to this quickly by typing “people” in the Start menu
search box). This control panel item displays the dialog box
shown in Figure 45-6.
After you have signed in, the service is available to any application
that is built to use the PNM service.
At the time of writing, PNM is available only on the Windows Vista family of operating systems (and it has
been removed from Windows 7). However, it is possible that future service packs or additional downloads
may make it available on Windows XP.
building P2P aPPliCaTions
Now that you have learned what P2P networking is and what technologies are available to .NET developers
to implement P2P applications, it’s time to look at how you can build them. From the preceding discussion
you know that you will be using PNRP to publish, distribute, and resolve peer names, so the first thing you
look at here is how to achieve that using .NET. Next you look at how to use PNM as a framework for a P2P
application. This can be advantageous because if you use PNM you do not have to implement your own discovery
mechanisms.
To examine these subjects you need to learn about the classes in the following namespaces:
➤
➤
System.Net.PeerToPeer
System.Net.PeerToPeer.Collaboration
figure 45-6
To use these classes you must have a reference to the System.Net.dll assembly.
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