code: func (r Hardware_Server) GetPrivateBandwidthGraphImage(startTime *string, endTime *string) (resp []byte, err error) {
  	params := []interface{}{
  		startTime,
  		endTime,
  	}
  	err = r.Session.DoRequest("SoftLayer_Hardware_Server", "getPrivateBandwidthGraphImage", params, &r.Options, &resp)
  	return
  }
docs: // Retrieve a graph of a server's private network bandwidth usage over the specified time frame. If no time frame is specified then getPublicBandwidthGraphImage retrieves the last 24 hours of public bandwidth usage. getPublicBandwidthGraphImage returns a PNG image