ID decoders, or the channels were recorded for later analysis where unit IDs were decoded from the recordings, the encoders should be turned off for tactical channels to reduce air time used. It also sounded like some vehicle radios may have had status buttons using the data bursts. If true, the operator presses a button on the vehicle radio which sends a short data burst to dispatch. Dispatch gets the unit identity and the new status from a data decoder. These can cause interruptions in voice traffic but cut down on total air time required to conduct business because they occupy the channel for less time than it takes to say, "Engine fifty on scene." Tactical 1 This channel was the primary method of communication in the North tower. It was a simplex channel. Users complained it would only reach from the lobby to floors in the thirties. Tactical 1 was a default channel for use at some fire scenes. Some users who realized Repeater 7 was functional switched to that channel and were afforded better coverage than simplex users on Tactical 1. Audio recordings on the documentary film and NIST analysis show Tactical 1 was overloaded with heavy radio traffic. In contrast, the audio CD of Repeater 7 shows the channel was mostly idle. The 9-11 commission report said a new portable repeater system had been developed to address shortcomings of Tactical 1 at a large incident. The system, called, "the post", is carried to an area near the incident and set up for the duration to augment weak signals. Command channel The command channel used by officers at the incident was either called Channel 5 or Command 5 in documentation. Documents suggest the channel had a repeater but it was not clear if the repeater was citywide, installed in the Field Comm van, or housed in a battalion chief's vehicle. Recordings of this channel were lost when the Field Comm van was destroyed. The documentary film and oral history records show the channel being used effectively. Interoperability The federal 9/11 Commission Report included recommendations on communications systems used by police, fire, and emergency medical services (EMS) at the WTC incident. In the report and in appearances on television news programs, commissioners said the capabilities of communications systems lacked the ability to communicate across department lines. That is to say, police units could not communicate with fire units directly