Custom Jayrock JsonRpcDispatcher demonstrating how to get the JSON-RPC request Id in the called method; https://groups.google.com/forum/#!topic/jayrock/J8MgyMgwrPI

CustomJsonRpcDispatcher.cs

using System.Collections;
using System.Web;
using Jayrock.Json;
using Jayrock.JsonRpc;
using Jayrock.Services;

public sealed class CustomJsonRpcDispatcher : JsonRpcDispatcher
{
    const string RequestIdKey = "JsonRpcRequestId";

    public CustomJsonRpcDispatcher(IService service) : 
        base(service) {}

    public static object GetRequestIdFromCurrentHttpContext()
    {
        return GetRequestId(null);
    }

    public static object GetRequestId(HttpContext context)
    {
        return (context ?? HttpContext.Current).Items["JsonRpcRequestId"];
    }
        
    protected override IDictionary ParseRequest(JsonReader input)
    {
        var request = base.ParseRequest(input);
        HttpContext.Current.Items[RequestIdKey] = request["id"];
        return request;
    }
}

Global.asax

<%@ Application Language="C#" %>
<%@ Import Namespace="Jayrock.JsonRpc" %>
<script runat="server">

    void Application_Start(object sender, EventArgs e)
    {
        JsonRpcDispatcherFactory.Current = service => new CustomJsonRpcDispatcher(service);
    }

</script>

HelloWorld.ashx

<%@ WebHandler Class="HelloWorld" Language="C#" %>

using System.Web;
using Jayrock.JsonRpc;
using Jayrock.JsonRpc.Web;

public class HelloWorld : JsonRpcHandler
{
    [JsonRpcMethod("echoTest")]
    public string EchoTest(string test)
    {
        var requestId = CustomJsonRpcDispatcher.GetRequestId(HttpContext.Current);
        return "Response " + requestId + " : " + test;
    }
}