TSB121
TIA/EIA
TELECOMMUNICATIONS
SYSTEMS BULLETIN
Cellular Subscriber Unit Interface
for TDD
TSB121
June 2001
TELECOMMUNICATIONS INDUSTRY ASSOCIATION
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represents the communications sector of
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TIA/EIA/TSB121
1
1. INTRODUCTION
4
This Telecommunications Systems Bulletin (TSB) describes a possible
implementation of the interface between a mobile station and a TTY.
Recognizing that:
5
•
FCC Rule and Order CC Docket No. 94-102 "E9-1-1/TTY Compatibility"
requires wireless service providers to support TTY compatibility for
contacting assistance in an emergency.
•
The CTIA/PCIA TTY Forum requested that TIA TR-45 specify a 2.5mm
connection with appropriate electrical parameters which would allow
reliable audio interconnection between TTYs and mobile wireless handsets.
•
The majority of legacy TTY terminals only support audio connection to the
telephone network via: (See Section 6.: Interconnect Options)
2
3
6
7
8
9
10
11
12
13
−
Acoustic coupling utilizing the wire-line handset placed into flexible cups
designed for Type G or Type K handsets. .
−
FCC Type RJ-11 modular connection.
14
15
16
•
Due to the wide variety of shapes and sizes of modern wireless handsets,
neither of these modes of connection are applicable to mobile wireless
handsets.
•
TIA/EIA/IS-789-A describes electrical specifications to adapt wireless
handsets to a vehicular environment.
17
18
19
20
22
This TSB specifies an interface that will support direct audio connections
between TTYs and mobile wireless handsets based upon TIA/EIA/IS-789-A.
23
2. REFERENCES
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24
25
26
27
28
29
30
31
32
33
34
The following standards pertaining to mobile stations may be useful in
implementing this TSB. At the time of publication, the editions indicated were
valid. All standards are subject to revision, and parties to agreements based
on this TSB are encouraged to investigate the possibility of applying the most
rece nt editions of the standards indicated below:.
2.1. TIA/EIA/IS-789-A: Electrical Specification for the Portable Phone to
Vehicle Interface
2.2. TIA/EIA-690: Recommended Minimum Standard for 800 MHz Cellular
Subscriber Units
2.3. ANSI/TIA/EIA-98-C: Recommended Minimum Performance Standards for
Dual-Mode Spread Spectrum Cellular Mobile Stations
i
TIA/EIA/TSB121
1
2
3
4
5
6
7
8
2.4. TIA/EIA-136-270-B (March 31, 2000) TDMA Third Generation Wireless Mobile Stations Minimum Performance
3. GENERAL INFORMATION AND OVERVIEW
This TSB describes a convenient audio connection between a TTY and a mobile
unit through the use of a 2.5mm jack and a plug for the physical connection
and this TSB refers to electrical characteristics specified in TIA/EIA/IS-789-A.
This interface is defined at a point between the modulator/demodulator of the
TTY and the audio input/output of the mobile wireless handset (See Figure 1).
9
Audio Link Interface
Mobile
Station
TTY
Figure 1
10
11
4. PHYSICAL INTERFACE
12
The physical connection is a 2.5mm stereo jack and plug.
13
2
TIA/EIA/TSB121
1
2
3
5. ELECTRICAL CONTACTS AND CHARACTERISTICS
TIP: Mobile Station Microphone (input to Mobile Station)
TIA/EIA/IS-789-A Signal Reference: MICPOS/MICNEG
4
5
CENTER: Mobile Station Speaker (out of Mobile Station)
TIA/EIA/IS-789-A Signal Reference: LSPPOS/LSPNEG
6
7
SLEEVE: Ground
MIC
8
SPKR
GND
9
10
11
12
13
14
15
16
Reference Electrical Parameters from TIA/EIA/IS-789-A
( Note: SPEAKER (LSPPOS/LSPNEG) and MIC (MICPOS/MICNEG) are
differential signals in TIA/EIA/IS-789-A )
Table 1
17
Name
(referenced to mobile)
Speaker
(LSPPOS, LSPNEG)
MIC
(MICPOS, MICNEG)
18
19
20
21
Vnom
Characteristic
Impedance (Z)
50
mVrms
150Ω
Output
50
mVrms1
100Ω
Input
NOTE:
If lower signal voltages and/or higher impedances are used, the
interconnection between the TTY and wireless handset may be more
susceptible to Radio Frequency Interference (RFI).
22
1 -26dBV (50mV RMS) Nominal corresponds to typical telephone system level of –18dBmo.
3
TIA/EIA/TSB121
1
INTERCONNECT OPTIONS
2
"CONVENTIONAL" CONNECTIONS
(NOT TSB-121 )
3
4
WIRELINE TYPE
HANDSET
5
6
PSTN
"RJ-11"
7
8
9
10
Headset Connection
(See NOTE 1)
11
12
13
14
15
16
T
T
Y
17
TTY TERMINAL
18
19
TTY GA SK
TSB-121
"Direct Connect"
TTY Adapter
(Vendor-Specific)
×
20
21
TSB-121 Signal
22
Reference Point
23
24
25
26
27
28
29
30
NOTES:
1) "HEADSET CONNECTION" may be adapted to "Wireline Handset"
OR to a TSB-121 Direct Connection.
2) If the TTY adapter contains a battery, a battery charge status indicator
should be included.
3) Label TTY Adapter "FOR TTY". To avoid a possible interaction with the land
network, it is suggested that the RJ-11 connection to the PSTN should not
be used while connected to the wireless terminal.
31
4
TIA/EIA/TSB121
1
6. HEARING CARRY-OVER (HCO) AND VOICE CARRY-OVER (VCO) EXAMPLE
2
3
4
5
6
Vendor-Specific
TTY Adapter and
Headset
7
8
50mV
9
Headset
10
To
Mobile
Station
To TTY
Switc
TTY
Adapte
HCO
TTY
VCO
11
12
×
13
×
TSB-121 Signal Reference
Point
14
15
16
17
18
Common TTY, VCO/HCO Interface provided by phone manufacturer
19
NOTE:
20
21
If the HCO/VCO switch contains a battery, a battery charge status indicator
should be included.
22
23
24
25
5
TIA/EIA/TSB121
1
2
ANNEX A.
End-to End Path
3
4
5
The following illustration is an example of typical signal levels expected along an end-to-end
path connection between the two TTY devices.
TTY
TSB-121
Interface
Cable
Wireless
Telephone
Phone
Specific
Interface
ì
RF
BSC/
Signal "Cell"
y
ì
MSC
PSTN
TTY
Wireless User to Land User
TTY TX
Standard
Audio
Level
Interface
and
Adapter
Level
Air Interface
⇒
TX Audio
0.51Vrms
⇒
Levels
received
from PSTN
at typical
level from
TTY
⇒
1-100mVrms
Typical=100mV
Signals
received at
Optimal
Level
⇒
Signal
= -10dBm
typical
Typ. Signal
= -25dBm to
–45dBm. (Loop
Loss attenuates)
Levels are sent
from PSTN at
typical level from
TTY
Signals
Transmitted at
Optimal Level
Land User to Wireless User
TTY RX
Audio Level
from Cable
Interface
Interface
and Adapter
Level
⇐
RX Audio
= 78mV RMS
Typical
8-450mV
Air Interface
⇐
⇐
50-200mV RMS
with –20dBm
PSTN signal
⇐
Signal
= -12 to –25dBm
typical
(Use Wireless
phone volume
control
to optim ize.)
TSB-121
Interface
6
TX Signal
= -10dBm
(max.)
TIA/EIA/TSB121
1
7