Access for 9-1-1 and Telephone Emergency Services

Switching Between Voice and TTY Modes

All call takers must have the capability to switch back and forth easily from TTY mode to voice mode during the same call. This capability is necessary especially for silent calls, since call takers are required to first query the line by voice and then quickly switch to query the line by TTY. This capability is also necessary for VCO and HCO, which are described below. VCO and HCO shorten the lengths of calls that would otherwise be conducted exclusively by typing. Call takers who use stand-alone TTYs can switch from TTY mode back to voice mode simply by removing the telephone handset from the TTY couplers. TTY-compatible consoles for call takers should have built-in switching capability.

Q: What is VCO? Who uses it?

A: VCO is voice carryover. It is a communication hybrid of TTY and voice. VCO allows a person with hearing loss to speak directly to the call taker and read the response that is typed back. Many persons who became deaf or hard of hearing later in life prefer to speak instead of type. They use what is called voice carryover (VCO). With VCO, the caller speaks directly into the phone, and the call taker types back via TTY to the caller. VCO can be accomplished with standard stand-alone TTY equipment simply by having the call taker alternate between listening on the handset when the caller is speaking and placing the handset in the TTY couplers to type a response.

Q: What is HCO? Who uses it?

A: HCO is hearing carryover. People with speech impairments who are not deaf or hard of hearing often prefer HCO. HCO allows them to type their words on a TTY to call takers and hear call takers' spoken responses through their handset. HCO can be accomplished by a call taker using standard stand-alone TTY equipment by alternating speaking into the handset and placing the handset in the TTY when the caller types a response.