TempData["sipModel"] = 1;
return RedirectToAction("Index", "Home", new { area = "SIP" });

TempData["sipModel"] = 2;
return this.TransferToAction("Index", "Home", new { area = "SIP"});

public static TransferToRouteResult TransferToAction(this System.Web.Mvc.Controller controller, string actionName, string controllerName, object routeValues)
        {
            controller.TempData.Keep();
            controller.TempData.Save(controller.ControllerContext, controller.TempDataProvider);
            return new TransferToRouteResult(controller.Request.RequestContext, actionName, controllerName, routeValues);
        }