code: public Observable<Page<ExpressRouteLinkInner>> listAsync(final String resourceGroupName, final String expressRoutePortName) {
          return listWithServiceResponseAsync(resourceGroupName, expressRoutePortName)
              .map(new Func1<ServiceResponse<Page<ExpressRouteLinkInner>>, Page<ExpressRouteLinkInner>>() {
                  @Override
                  public Page<ExpressRouteLinkInner> call(ServiceResponse<Page<ExpressRouteLinkInner>> response) {
                      return response.body();
                  }
              });
      }
docs: Retrieve the ExpressRouteLink sub-resources of the specified ExpressRoutePort resource.
  
  @param resourceGroupName The name of the resource group.
  @param expressRoutePortName The name of the ExpressRoutePort resource.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the PagedList&lt;ExpressRouteLinkInner&gt; object