Broadcast like UDP with the reliability of TCP


I'm working on a .net solution that is run completely inside a single network. When users make a change to the system, I want to launch an announcement and have everyone else hear it and act accordingly. Is there a way that we can broadcast out messages like this (like UDP will let you do) while keeping guaranteed delivery (like TCP)?

This is on a small network (30ish clients), if that would make a difference.

8/28/2008 2:55:23 AM

Accepted Answer

Almost all games have a need for the fast-reacting properties (and to a lesser extent, the connectionless properties) of UDP and the reliability of TCP. What they do is they build their own reliable protocol on top of UDP. This gives them the ability to just burst packets to whereever and optionally make them reliable, as well.

The reliable packet system is usually a simple retry-until-acknowledged system simpler than TCP but there are protocols which go way beyond what TCP can offer.

Your situation sounds very simple. You'll probably be able to make the cleanest solution yourself - just make every client send back an "I heard you" response and have the server keep trying until it gets it (or gives up).

If you want something more, most custom protocol libraries are in C++, so I am not sure how much use they'll be to you. However, my knowledge here is a few years old - perhaps some protocols have been ported over by now. Hmm... RakNet and enet are two C/C++ libraries that come to mind.

9/1/2008 4:24:25 AM

You could use Spread to do group communication.


@epatel - I second the SCTP suggestion (I voted up, but can't comment yet so additional stuff here).

SCTP has many great features and flexibility. You can sub-divide your connection into multiple streams, and choose the reliablity of each and whether it is ordered or not. Alternatively, with the Partially Reliability extension, you can control reliability on a per message basis.


Broadcast is not what you want. Since there could and probably will be devices attached to this network which don't care about your message, you should use Multicast. Unlike broadcast messages, which must be sent to and processed by every client on the network, Multicast messages are delivered only to interested clients (ie those which have some intention to receive this particular type of message and act on it).

If you later scale this system up so that it needs to be routed over a large network, multicast can scale to that, whereas broadcast won't, so you gain a scalability benefit which you might appreciate later. Meanwhile you eliminate unnecessary overhead in switches and other devices that don't need to see these "something changed" messages.


You might want to look into RFC 3208 "PGM Reliable Transport Protocol Specification".

Here is the abstract:

Pragmatic General Multicast (PGM) is a reliable multicast transport
protocol for applications that require ordered or unordered,
duplicate-free, multicast data delivery from multiple sources to
multiple receivers. PGM guarantees that a receiver in the group either receives all data packets from transmissions and repairs, or is able to detect unrecoverable data packet loss. PGM is specifically intended as a workable solution for multicast applications with basic reliability requirements. Its central design goal is simplicity of operation with due regard for scalability and network efficiency.


You could use a Message Broker, such as ActiveMQ.
Publish your messages to a topic and have the clients register durable subscriptions to the topic, so that they won't miss any messages even if they are not online.

Apache ActiveMQ is a message broker written in Java together with a full JMS client. However Apache ActiveMQ is designed to communicate over a number of protocols such as Stomp and OpenWire together with supporting a number of different language specific clients.

Client platform support includes c# and .net


Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Email: [email protected]