• Choose a category
• All
• Classic-Fiction

By Root 2581 0

or form of game play. The user is no longer alone with her computer. She shares an activity with others in which the group experience is greater than the sum of its parts.

The application in question can be a remote control for another device, the main application, or the companion application to a larger project. It can also be part of a cluster of devices communicating with one other.

In this chapter, I chose to demonstrate Adobe’s Cirrus service in detail because, at the time of this writing, it is free and demonstrates some multiuser possibilities without any server setup. It is well suited for mobile development.

RTMFP UDP

Peer-to-peer (P2P) communication is the real-time transfer of data and media between clients.

Real Time Media Flow Protocol (RTMFP) is an Adobe proprietary protocol. It enables peer-to-peer communication between applications running in Flash Player or the AIR runtime. It is meant to provide a low-latency, secure, peering network experience.

Real Time Messaging Protocol (RTMP) uses Transmission Control Protocol (TCP). RTMFP uses User Datagram Protocol (UDP), which provides better latency, higher security (128-bit AES encryption), and scalability. RTMP is faster than RTMFP, but does not guarantee perfect message ordering and delivery.

RTMP was designed to connect via an RTMFP-capable server, such as the Cirrus service (RTMP uses the Flash Media Server), but it can also be used over a local network using WiFi without the need for a server. Note that Flash Media Server 4.0 speaks RTMFP as well.

P2P Over a Local Network

If your local network supports broadcasting, you can create peer-to-peer direct routing. All the clients need to be on the same subnet, but you do not need to manage them. Verify that your devices have WiFi enabled and are using the same network.

The code to create a peer-to-peer application with RTMFP is quite simple but introduces new concepts. Let’s go over all the steps one at a time.

The connection is established using the flash.net.NetConnection class. Set a listener to receive a NetStatusEvent event. Create the connection by calling the connect function and passing rtmfp as an argument:

import flash.net.NetConnection;

import flash.events.NetStatusEvent;

var connection:NetConnection = new NetConnection();

connection.addEventListener(NetStatusEvent.NET_STATUS, onStatus);

connection.connect("rtmfp:");

Wait for the connection to be established. Then several objects need to be created:

function onStatus(event:NetStatusEvent):void {

switch(event.info.code) {

case "NetConnection.Connect.Success" :

trace("I am connected");

// object creation can now happen

break;

}

}

NetGroup is the group of peers. Its capabilities are defined in the GroupSpecifier. The IPMulticastAddress property stores the IPv4 multicast address. It needs to be in the range 224.0.0.0 through 239.255.255.25. The UDP port should be higher than 1024. A group name is passed in its constructor. Try to make it unique. The IPMulticastMemberUpdatesEnabled property must be set to true for clients to receive updates from other clients on a LAN. The postingEnabled property allows clients to send messages to the group:

import flash.net.GroupSpecifier;

var groupName:String = "com.veronique.simple/";

var IPMulticastAddress:String = "230.0.0.1:3000";

var groupSpec:GroupSpecifier = new GroupSpecifier(groupName);

groupSpec.addIPMulticastAddress(IPMulticastAddress);

groupSpec.ipMulticastMemberUpdatesEnabled = true;

groupSpec.postingEnabled = true;

Now create the NetGroup. Pass the connection and the GroupSpecifier in its construction. The latter is passed with an authorization property to define the communication allowed: groupspecWithAuthorizations to post and multicast, or groupspecWithoutAuthorizations to only receive messages. Note that this setting is only relevant if a posting password is set (as defined by your application):

import flash.net.NetGroup;

var netGroup = new NetGroup

(connection, groupSpec.groupspecWithAuthorizations());

netGroup.addEventListener(NetStatusEvent.NET_STATUS,