using System;

using System.Collections.Generic;

using Newtonsoft.Json;

using Newtonsoft.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var data = new SiteData()

        {

            SiteName = "Foo",

            ConnectionTypes = new Dictionary<string, object>() 

            {

                { "1", WrapInDictionary( new dialup() { Speeds = new Dictionary<string, uint>() { {"1", 9600}, {"2", 115200} }, PhoneNumber = "0118 999 881 999 119 725 ... 3" } ) },

                { "2", WrapInDictionary( new Ethernet() { Speed = "1000" } ) },

                { "3", WrapInDictionary( new ipv4() { SomeCapability=true } ) }

            }

        };

        var json = JsonConvert.SerializeObject(data, prettyJson);

        Console.WriteLine(json);

    }

​

    private static Dictionary<string, object> WrapInDictionary(object value) 

    {

        return new Dictionary<string, object>()

        {

            { value.GetType().Name, value }

        };

    }

​

    private static readonly JsonSerializerSettings prettyJson = new JsonSerializerSettings()

    {

        ContractResolver = new CamelCasePropertyNamesContractResolver(),

        Formatting = Formatting.Indented

    };

}

​

public class dialup

{

    public Dictionary<string, uint> Speeds;

    public string PhoneNumber;

}

​

public class Ethernet

{

    public string Speed;

}

​

public class ipv4

{

    public bool SomeCapability;

}

​

public class SiteData

{

    public string SiteName;

    [JsonExtensionData]

    public Dictionary<string, object> ConnectionTypes;

}

​