ASP.NET Chatting using WCF Services and JSon

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ServiceModel;
namespace ChatServiceLibrary
{
    [ServiceContract]
    public interface IChatService
    {
        [OperationContract]
        string SendMessage(ChatMsg chMsg);

        [OperationContract]
        List<ChatMsg> GetMessages(string strChatId, string strUserId, ChatMsgStatus chStatus);

        [OperationContract]
        List<ChatMsg> GetMessagesByUserId(string strUserId);

        [OperationContract]
        void ClearMessages(string strChatId);

        [OperationContract]
        void ClearOldMessages();

        [OperationContract]
        void MessageStatusToRead(string strMsgId);
    }
}