BELLSOUTH E911 SERVICE INTERFACES

1. Introduction…………………………………………………………………………1

2. Overview Of Enhanced 911 Service……………………………………………….. 1

Figure 1 – E911 System Overview………………………………………… 2

3. E911 Interfaces………………………………………………………………………3

Figure 2 – Format Of Text Portion Of Response From E911 Data Base ….. 10

(a) Calling Number Identification

The telephone number of the station calling into the PSAP is delivered to the PSAP equipment using standard Automatic Number Identification (ANI) techniques over the E911 tandem trunks. Operation of ANI number delivery is described in TR-TSY-000350, E9-1-1 Public Safety Answering Point Interface Between a 1/1A ESS Switch and Customer Premise Equipment [4]. Typically the number delivered to the PSAP is displayed at the answering position by the customer premises equipment. The PSAP is also required to formulate a request for associated data from the E911 database on this number. See section 3.2 for a description of this activity.

Once the PSAP detects that the E911 tandem has seized an idle trunk by the presence of an off-hook condition, the PSAP is expected to send a start pulsing signal (250 ± 50 ms wink) within 4 seconds. If the wink signal is not received within 4 seconds, the E911 tandem will retry once on a different E911 trunk after placing the original trunk on a maintenance list.

The E911 tandem will begin outpulsing the calling number as multifrequency (MF) tones within 4 seconds of receipt of the wink signal. If no calling number is received or if distorted tones are received, the PSAP should assume ANI failure has occurred and proceed to return audible ringing to the calling party and signal an attendant to answer. Although no calling information would be available to present to the attendant in this case, the customer provided equipment shall send the appropriate ANI failure digits to the E911 database system.

Once the ANI digits are received, the customer provided equipment shall return audible ringing to the 911 calling party at the same time as attendant positions are alerted of the incoming call by the customer provided system. Once an attendant answers, the customer provided equipment should remove audible ringing and cut the incoming call through to the position. At the same time, the customer provided equipment database request message is sent to the BellSouth E911 database system. This system will return information, relating to the calling telephone number, suitable for display on a terminal at the attendant position answering the call. The customer provided equipment is responsible for decoding the ANI MF data and formatting the ASCII encoded request to the BellSouth E911 database system. This database interface is described in section 3.2 of this document.

The format of the information sent by the E911 tandem will be one of the following:

 

(b) Call Transfer Interface

Transfer of an incoming call to an alternate PSAP is available as a standardservice. The primary
PSAP may implement transfer to a secondary PSAP using the standard Call Transferand Speed
Calling features of the E911 tandem office. These features are implemented byswitch hook
flashes and abbreviated dialed digits issued by the customer provided equipmentto the E911
tandem office trunks. The answering position may be provided a single buttoninterface to these
features by the customer premises control equipment if so arranged or they maybe manually
exercised by a standard station set at the answering position.

Normal call transfer sequences are used to initiate call transfer. The PSAPequipment should send
an on-hook flash signal of 500 ± 50 ms to the E911 tandem office. Normally theE911 tandem
will seize a three port conference circuit and a DTMF (Dual ToneMulti-Frequency) receiver will
be attached to the trunk to receive the transfer digits and dial tone will bereturned to the PSAP
initiating the transfer. If these facilities are not available in the E911tandem due to load
conditions, the flash signal will be ignored. After detecting dial tone, thedesired transfer
destination should then be sent by the PSAP as DTMF pulses conveying either theSpeed Calling
digits or regular directory number of the destination.

Three types of Call Transfer may be provided: selective, fixed and manual.

Selective Call Transfer – activated by receipt of a *1X speed calling sequencefrom the
PSAP equipment, where X is 1 to 6. The E911 tandem will selectively route thecall to
the desired type (specified by the “X” code) of secondary PSAPdesignated for the calling
party’s jurisdiction. The association of various PSAPs with selective SpeedCalling codes
should be done as part of the installation process for the E911 system.

Fixed Call Transfer – activated by receipt of *NX speed calling sequences,where N is 2
to 4 and X is 0 to 9. Only single direct translation to a prespecified directorynumber will
be performed by the E911 tandem in this case.

Manual Call Transfer – the PSAP attendant manually performs the on-hook flash
sequence and then directly dials either the Speed Calling Code as specified inthe Fixed
Call Transfer or the directory number of the destination.

The E911 tandem maintains supervision of the off-hook status in bothdirections. To drop an
incoming call, the PSAP equipment must present an on-hook condition greater than1.2 seconds.
The E911 tandem will disconnect the call in both directions, sending on-hook tothe PSAP, and
idling the incoming trunk. This prevents an incoming call that remains off-hookfrom tying up the
PSAP trunk.

If a three party call has been established by the call transfer feature, thefollowing disconnect
supervision applies:

Primary PSAP

(1) Receipt of a flash signal (500 ± 50 ms on-hook) from the initial PSAP in a3 party call
setup will release the added party and maintain a 2 party connection between thecalling
party and the primary PSAP.

(2) Receipt of an on-hook signal longer than the minimum disconnect timinginterval (1.2
seconds) from the initial PSAP will disconnect that PSAP from the call andmaintain the
connection between the calling party and the added party.

Added Party

If an added party sends an on-hook signal for longer than 16 seconds, it will be disconnected but the original PSAP will remain connected to the calling party.

If the added party returns off-hook before a 16 second interval has expired, it will be returned to the 3 party connection.

If the primary PSAP sends a flash signal during the 16 second interval after the added party has sent an on-hook signal, the added party is disconnected immediately. The primary PSAP remains connected to the calling party.

If one of the original parties disconnects before the added party’s disconnect timing interval expires, that party is immediately released. However, the E911 tandem office continues the timing interval and will reconnect the added party to the party remaining off-hook if the added party returns off-hook within the interval.

Calling Party

Upon detection of the calling party disconnect, the calling party is released. The primary PSAP and the added party remain connected until either disconnects or the primary PSAP releases the added party.

(d) Night Service / Alternate PSAP

All calls destined for a PSAP may be automatically directed to an alternate PSAPor other
answering location. This feature is available for each PSAP. A single directorynumber is
assigned in the E911 tandem office for alternate routing and is used in any ofthe conditions where
an alternate is needed. These conditions could be traffic busy, night service,power loss, or other
failure at the PSAP.

Whenever calls are routed to an alternate PSAP, the ANI information of thecalling party is also
made available to the alternate PSAP. The E911 tandem presents the calling partynumber to the
secondary PSAP using the same mechanism described in section (a) as used for aprimary PSAP.

Alternate or night service is activated from the PSAP by key activation of acontrol lead to the
E911 tandem office. The network interface required for this separate controllead is given in
Telcordia Technical Reference TR-TSY-000349 [5].

(e) Tones Used

Standard tones (dial, busy, reorder, and audible ringing) are provided by theE911 tandem office
for attendant transfer calls. Interrupted high tone (120 ipm) is also providedwhen speed dialing
transfer is attempted, but not subscribed to by the PSAP.

(f) Trunk Maintenance Test Calls

From time to time the telephone company will place a test call to verify theintegrity of the trunk
circuit to the customer’s premises. This call will be identified by the specialANI code given in
Table 1 (KP-8-ST). The PSAP shall connect the trunk so identified to a permanentbusy tone
(continuous 60 ipm tone). This must be done within 20 seconds after receipt ofthe wink start
pulse, otherwise, the E911 tandem office would consider the trunk test afailure. The E911
tandem will disconnect approximately 5 seconds after receiving the 60 ipm tone.The PSAP
should then immediately release the trunk.

3.2 Database Interface

BellSouth provides a centralized database including information for eachdirectory number used
by wireline subscribers to the network. This information usually contains callerlocation and other
information useful for a public safety response to emergency situations where acall is placed from
a phone near the site of the emergency. A unique protocol is used over redundantdata links
between a PSAP and the BellSouth ALI Computers to retrieve this information. ThePSAP
equipment is responsible for formatting a request for ALI per this protocol andplacing it on the
data links. The returned information is available to the PSAP equipment todisplay on a terminal
at an attendant position or in some other manner per the design of the equipmentprovider.

(a) Physical Interface

Access to the BellSouth centralized E911 database is provided by asynchronousprivate line
modem links to duplicated ALI Computers. These computers are located indifferent BellSouth
Centers for redundancy and diversity. Two links are required for reliability;they are functionally
identical. The ALI Computers receive the ALI request message from the PSAP,query the
database and return the stored information to the PSAP over the data link. Theactual network
interface is that of a private line digital data service. Digital facilitiesshall be ordered with
secondary channel. This feature is necessary in order to deploy an end-to-enddiagnostic and
configuration capability from the master end (BellSouth Center) withoutdisruptive consequences.
The characteristics of the equipment used to modulate these data links are:

2400 baud digital Channel Service Unit/Data Service Unit (CSU/DSU)
10 bit data character
1 start bit
8 data bits (8^th bit ignored)
1 stop bit
Full Duplex
Continuous Carrier

For reliability, an individual ALI request message is expected to be receivedfrom the PSAP over
both links simultaneously by the duplicated ALI Computers. Responses from thedatabase system
are presented over one of the data links only. Both links must be monitored bythe PSAP for
responses since they are randomly chosen by the ALI Computers. If one data linkis out of
service, only the good link will be chosen by the ALI Computers for responses.

(b) Link Protocol

The protocol used over the data links consists of a request message sent fromthe PSAP to the ALI
Computers and the response message from the database to the PSAP. In addition, astatus
message or “heartbeat” is expected from the PSAP during idle periods.The ALI Computers will
respond with an “ACK” to the PSAP when a heartbeat is received.

(1) Request Message Format

Requests from the PSAP for additional data contained in the ALI databasemaintained by
BellSouth shall consist of 13 or 15 ASCII encoded digits terminated by acarriage return.
The message format for a request is given in Table 2.

TABLE 2
DATABASE REQUEST MESSAGE

Example: “0555121201020<CR>” would be transmitted for 555-1212 on position 01
trunk 02 for 14 character request messages. Note the check digit is 0 since the sum equals 24 which is evenly divisible by 8. Digit position 1 is transmitted on the data link first in sequence.

“404555121201020<CR>” would be transmitted for 404-555-1212 on position 01 trunk 02 for 16 character request messages. Note the check digit is 0 since the sum equals 32 which is evenly divisible by 8.

NOTE: A request of all zeroes, “0000000000000<CR>” would be interpreted as indication that repair is needed on the PSAP ANI equipment. Upon occurrence of a large number of such messages, the BellSouth E911 Maintenance Center would notify responsible PSAP maintenance personnel.

ALI Response Message Format

The ALI Computers provide an immediate response to a request message with either an ASCII ACK (hex 06) or NAK (hex 15) character. If the negative acknowledgement, NAK, is received, the request message should be retransmitted only once by the PSAP.

The ALI response message must use the format described in Table 3. The ALI response message is delimited by the ASCII STX (hex 02) and ETX (hex 03) characters. Response messages are presented over one of the two data links randomly chosen.

TABLE 3

ALI RESPONSE MESSAGE

<CR> 1 hex 0D

punctuation 1 ( hex 28

NPA 3 205

punctuation 1 ) hex 29

space 1 hex 32

NXX 3 456

punctuation 1 – hex 2D

Line Number 4 7890

space 3 hex 32

Time 5 14:25

space 4 hex 32

Date 5 08/12

<CR> 1 hex 0D

House Number 8 8600

House Number Suffix 4 -1/2

space 1 hex 32

Prefix Directional 2 NW

space 1 hex 32

Street Name 48 WALNUT ST

Community 18 BIRMINGHAM

State 2 AL

space 1 hex 32

ESN 3 056

space 1 hex 32

Class of Service 4 BUSN

<CR> 1 hex 0D

Customer Name 32 JOHN DOE INC

Location Information 20 BLG 3, FLR 10

space 1 hex 32

punctuation 2 P#

space 1 hex 32

Main NXX 3 454

punctuation 1 – hex 2D

Main Number 4 7891

<CR> 1 hex 0D

Additional Information 20 ALT# 205-454-7800 (see Note 1)

space 1 hex 32

punctuation 4 LEC:

Telco Company ID 5 BELSO

<CR> 1 hex 0D

<LF> 1 hex 0A

ESN Text (variable) 71 JEFFERSON COUNTY SO

FIRE STATION 2

JEFFERSON EMS

Optional <CR> 1 hex 0D (see Note 2)

Optional Longitude/X Coordinate 11 +000.000000 or spaces (see Note 2)

Optional Space 1 hex 32 (see Note 2)

Optional Latitude/Y Coordinate 10 +00.000000 or spaces (see Note 2)