Correct syntax for retrieving features from GML format in OpenLayers

Question

Yesterday I made with qgis the shapefiles of my town and now I wanted to add them in a web application I'm making with OpenLayers. The problem is that, while it loads them perfectly with the wms service, the vector layers fail to get the feature from the xml/gml file and I don't know why. I don't even get any error. Here is a some part of my code:

OpenLayers.ProxyHost = 'proxy.php?url=';

    var map = new OpenLayers.Map("map", {
        //projection: new OpenLayers.Projection('EPSG:900913'),
        projection: new OpenLayers.Projection('EPSG:3857'),
        units: 'm',
        maxResolution: 4.777314266967774,//156543.0339,
        maxExtent: new OpenLayers.Bounds(-1718.3524101391, -3513.9879361762, 3058.9618568286, 785.5949040948),
        numZoomLevels: 4
    });

var mroads = new OpenLayers.Layer.WMS( 'Major Roads', 'http://andri.ns0.it:8080/geoserver/Grottole/wms', { layers: 'Grottole:MajorRoads' }, { isBaseLayer: false, opacity: .9 });

var mRoadsVector = new OpenLayers.Layer.Vector(
            'Major Roads Vector',
        {
            projection: new OpenLayers.Projection('EPSG:3857'),
            protocol: new OpenLayers.Protocol({
                url: 'mroads.xml',
                format: new OpenLayers.Format.GML()
            }),
            strategies: [new OpenLayers.Strategy.Fixed()]
        }
        );

I believe I made everything good so far, so I really hope you can help me.

Answer 1

Ok, I found where was the problem. Of course, you have to specify which kind of protocol to use, so the correct syntax was:

protocol: new OpenLayers.Protocol.HTTP({...})