Multi Client/Server Discovery in C#

Question

I'm developing a multiple client / multiple server program in C#, and before I got down to the nitty gritty, I was wondering if anyone has ever worked on a similar project and might be able to share their tips / ideas for implementation.

• The servers will sit on many PCs, and listen for incoming connections from clients (Or should the Servers broadcast, and the clients listen?).
• When a client starts, it should populate a list of potential server IP addresses automatically.
• When a server closes, the client should remove that server from it's list.
• When a new server starts, the clients should be notified and have it added to their list.
• A server may also act as a client, and should be able to see itself, as well as all other servers.
• A message sent from a client to the server, that affects the server, should broadcast the change to all connected clients.
• Should my server be a Windows Service? What advantages/disadvantages does that present?

Any ideas on how I might go about getting started on this? I've been looking into UDP Multicast, and LAN Scans. I'm using C# and .NET 4.0

EDIT: Found this: http://code.google.com/p/lidgren-network-gen3/ Does anyone have any experience with it and can recommend/not recommend it?

Answer 1

I would suggest NetPeerTcpBinding WCF communications to create a Peer Mesh. Clients and Servers would all join a mesh using a Peer resolver. You can use PNRP or create a custom peer resolver (.Net actually provides you with an implementation called CustomPeerResolverService). See Peer To Peer Networking documentation.

Also you can implement a Discovery service using DiscoveryProxy. With a discovery service, services can announce their endpoints. The discovery service can then service find requests (see FindCriteria) to return endpoints that match the requests. This is referred to as Managed Discovery. Another mode is Ad Hoc Discovery. Each service will announce their endpoints via UDP and discovery clients will probe the network for these endpoints.

I have actually implemented a Managed Discovery service in combination with Peer 2 Peer WCF networking to provide a redundant mesh of discovery services that all share published service endpoints via P2P. Using Managed Discovery I have found performs far better as Ad Hoc Discovery using UDP probing is slower and has some limitations crossing some network boundaries while Managed Discovery leverages a centralized repository of announced service endpoints.

Either/both technologies I think can lead to your solution.

Answer 2

So is this effectively a peer to peer style network (almost like bittorrent), where all servers are clients, but not all clients are servers.

and the requirements are every client should hold a list of all other servers (which are, in turn, clients).

The problem lies in getting the server IPs to the clients in the first place. You can use a master server that has a fixed DNS to act as a kind of tracker, which all of the servers check in to, and the clients check periodically.

Another option (or an additional method) is to use a peer exchange style system, where each of the clients and servers use UDP broadcast packets over a local network to discover each other and then transfer the servers they know of, kind of like a routing protocol. However if the PCs are spread out over a non local network such as the internet, there's little chance that they will ever discover each other on their own, making this method only useful when used in conjunction with other methods of finding servers. Also, you will probably have to deal with router UPnP to allow clients to connect to each other through each others router NAT, so this method is probably too complex for the gains you get. (However, if you're just on a LAN, this is all you need!)

A third option (and again, this sounds a lot like torrent technology), is to use Distributed Hash Tables to store information about the IPs of your servers in the cloud, without having to rely on a central master server.

I have had a shot at a project like this before (a pure P2P, server-less messaging system), but could never get it to work. Without a huge amount of peers, or a master server to track all of the other servers, it is very difficult to reliably retrieve the IPs of all the servers.