1. Telecommunications Industry AssociationTR-30.1/02-09-117 (TIA) McLean, VA September 10 - 12, 2002 COMMITTEE CONTRIBUTION Technical Committee TR-30 Meetings SOURCE:TR-30 Chair CONTACT:Fred Lucas FAL Associates TITLE:TTY Presentation at Signaling for VoIP Summit PROJECT:PN-4628 DISTRIBUTION:Members of TR-30.1 ABSTRACT This contribution provides a copy of a presentation made to the August 2002 Signaling for VoIP Summit by Jim Turner, ATIS. It describes a problem with the transport of TTY Signals over VoIP. The presentation is provided to TR-30.1 for information.

2. August 13-14, 2002 Washington, DC Jim Turner Technical Coordinator TTY, TTSI, & IITC (202)662-8662 Wk (630)972-1454 Wk @ Hm jturner@atis.org

3. August 13-14, 2002 Washington, DC TTY & VoIP GAP Analysis All Public Safety Answering Points must support TTY (The American for Disabilities Act) All wireless digital phones must support TTY (FCC 94-102) Under 1% Total Character Error Rate (TCER) is the accepted performance standard

4. August 13-14, 2002 Washington, DC TTY & VoIP GAP Analysis VoIP May not be able to support under 1% TCER for TTY calls. Reasons: –TTYs are silent when not transmitting –TTY Operation is “half Duplex” –Each TTY character is made from seven individual tones and is several VoIP packets in length

5. August 13-14, 2002 Washington, DC TTY & VoIP GAP Analysis Baudot - 5 bit character code Start bit 1400 Hz = 1 1800 Hz = 0 Start bit Stop Bit 22 MS +/- 0.4MS Pulse Width 0 0 0 1 1 A

6. August 13-14, 2002 Washington, DC TTY & VoIP GAP Analysis Baudot Continued AFiguresDash -Mark Hold With 5 bits there are 32 possible characters. Figures and letters extend this to 64 characters. Line Feed, Space, Carriage Return, Figures, and letters have the meaning in Figures and Letters. St 0 0 0 1 1 stp St 1 1 0 1 1 Stp St 0 0 0 1 1 stp

7. August 13-14, 2002 Washington, DC TTY & VoIP GAP Analysis All techniques used for digitizing voice are able to digitize TTY tones (1400 & 1800 HZ are in the audible range) The issue is not caused by the sampling standards (G.711, IS 825, etc.) The issue is caused by VoIP latency There are QoS standards addressing latency (Diffserv & RSVP)

8. August 13-14, 2002 Washington, DC Mobile to Land Circuit Switched V Send Letter A Receive Letter A Cell MSC PSAP Central Office

9. August 13-14, 2002 Washington, DC TTY & VoIP GAP Analysis Typical VoIP packet is 20ms of the digitized audio sample. A TTY Character is at least 154 ms long. Packet loss of 0.2% is considered very good while packet loss of 2.0% is typical. Statistically a 4% TCER is expected with a packet loss of 0.5% assuming a typical 20 ms packet size. IP phones have ways of making up for these loses so they are not detected by the human ear.

10. August 13-14, 2002 Washington, DC Mobile to land VoIP Send Letter A Cell MSC Receive PSAP Central Office Delayed Packet

11. August 13-14, 2002 Washington, DC TTY over VoIP Sample Send: your checking account balance is $146.45 as of 6pm Missed part of the figures packet for a packet loss of 2% Receive: YOUR CHECKING ACCOUNT BALANCE IS DBRYNBT AS OF 6 PM 7 characters missed out of 50 for a TCER of 14%

12. August 13-14, 2002 Washington, DC What is being done about it? Issue is being submitted to NRIC VI Focus Group 3 from the Voice & Data Interoperability working group Contact Jim Turner with Proposed Solutions & will add to the submission

13. August 13-14, 2002 Washington, DC Possible Solutions Move from Baudot to some other form of lifeline communication. Come up with a Standards Solution. –V.18 Sup[port Baudot for a defined period of time & then transition to ASCCII As areas convert to VoIP users in the area would transition. Visitors would suffer errors. –Some other out of the box solution Replace all Baudot devices with computers

14. August 13-14, 2002 Washington, DC SUMMARY TTY is the Hearing & Speech Impaired community’s current means of communication for Lifeline Services. VoIP may not support error rates of under 1% TCER for TTY users. Need to insure this issue is resolved before VoIP can be deployed. NRIC VI FG 3 is working issue.