def describe_bandwidth_rate_limit(GatewayARN=None):
    """
    Returns the bandwidth rate limits of a gateway. By default, these limits are not set, which means no bandwidth rate limiting is in effect.
    This operation only returns a value for a bandwidth rate limit only if the limit is set. If no limits are set for the gateway, then this operation returns only the gateway ARN in the response body. To specify which gateway to describe, use the Amazon Resource Name (ARN) of the gateway in your request.
    See also: AWS API Documentation
    
    Examples
    Returns a value for a bandwidth rate limit if set. If not set, then only the gateway ARN is returned.
    Expected Output:
    
    :example: response = client.describe_bandwidth_rate_limit(
        GatewayARN='string'
    )
    
    
    :type GatewayARN: string
    :param GatewayARN: [REQUIRED]
            The Amazon Resource Name (ARN) of the gateway. Use the ListGateways operation to return a list of gateways for your account and region.
            

    :rtype: dict
    :return: {
        'GatewayARN': 'string',
        'AverageUploadRateLimitInBitsPerSec': 123,
        'AverageDownloadRateLimitInBitsPerSec': 123
    }
    
    
    """
    pass
