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1、 J-STD-042-2002 (A Joint Standard Developed by EIA and SCTE) Approved: December 3, 2002 AMERICAN NATIONAL STANDARD Emergency Alert Message for Cable December 2002 J-STD-042 NOTICE EIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandin
2、gs between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards and Publications shall not in any respect preclude a
3、ny member or nonmember of EIA from manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of such Standards and Publications preclude their voluntary use by those other than EIA members, whether the standard is to be used either domestically or i
4、nternationally. Standards and Publications are adopted by EIA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, EIA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard or Publi
5、cation. This EIA Standard is considered to have International Standardization implication, but the International Electrotechnical Commission activity has not progressed to the point where a valid comparison between the EIA Standard and the IEC document can be made. This Standard does not purport to
6、address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. (From Project No. 502
7、3, formulated under the cognizance of the CEA/NCTA Digital Standards Subcommittee) Published by ELECTRONIC INDUSTRIES ALLIANCE 2002 Phone 202-828-3130; Fax 202-828-3131; Internet http:/www.atsc.org/stan Phone 800-854-7179; Fax 303-397-2740; Internet http:/; Email IEC Central Office, 3, rue de Varem
8、be, PO Box 131, CH-1211 Geneva 20, Switzerland; Phone +41 22 919 02 11; Fax +41 22 919 03 00; Internet http:/www.iec.ch; Email pubinforiec.ch ITU Standards: International Telecommunications Union, Place des Nationas, CH-1211 Geneva 20, Switzerland; Phone +41 22 730 5111; Fax +41 22 733 7256; Interne
9、t http:/www.itu.ch/publications/bookstore.html; Email itumailitu.int 47 CFR 11 U.S. Code of Federal Regulations (CFR), U.S. Government Printing Office, Washington, D.C. 2040; http:/www.fcc.gov/wtb/rules.html FIPS Standards: U.S. Government Printing Office, Washington, D.C. 2040; http:/www.fcc.gov/wt
10、b/rules.html ; FIPS http:/www.itl.nist.gov/fipspubs/fip604.htm SCTE Standards: Society of Cable Television Engineers (SCTE), 140 Philips Road, Exton PA 19341; Phone 800-542- 5040; Fax 610-363-5898; Internet http:/www.scte.org; Email infoscte.org 4 Emergency Alert Message (Normative) The cable_emerge
11、ncy_alert() message shall be delivered to the terminal device in packets identified with the SI_base PID value. For transport streams carrying one or more programs in the clear, packets identified by PID 0x1FFB shall be used. For out-of-band use on the Extended Channel, SI_base PID value 0x1FFC shal
12、l be used. The syntax of the cable_emergency_alert() message that shall be used is defined in Table 1. The MPEG-2 table_ID for this message is 0xD8. Refer to ISO/IEC 13818-1, MPEG-2 systems for a description of the fields common to the MPEG-2 private section syntax. The cable_emergency_alert() messa
13、ge is limited to 4096 bytes maximum length, which means that the section_length field may have a maximum value of 4093 decimal. table_ID This is an 8-bit field which shall be set to 0xD8, identifying this table as the cable_emergency_alert() message. 2 ANSI J-STD-042 section_syntax_indicator This 1-
14、bit field shall be set to 1. It denotes that the table section follows the generic MPEG-2 section syntax beyond the section_length field 3 ANSI J-STD-042 SyntaxBitsDescription cable emergency alert() table_ID 8uimsbf value 0xD8 section_syntax_indicator 11 zero 10 reserved 211 section_length 12uimsbf
15、 table_id_extension 16uimsbf 0x0000 reserved 211 sequence_number 5uimsbf current_next_indicator 1bslbf section_number 8 uimsbf last_section_number 8uimsbf protocol_version 8uimsbf EAS_Event_ID16uimsbf EAS_originator_code 24uimsbf three ASCII characters EAS_event_code_length 8uimsbf (N) EAS_event_cod
16、e 8*Nuimsbf N ASCII characters nature_of_activation_text_length8uimsbf nature_of_activation_text() varuimsbf alert_message_time_remaining8uimsbf seconds range 0120 event_start_time 32uimsbf event_duration 16uimsbf minutes range 156000 reserved 12bslbf alert_priority 4uimsbf details_OOB_source_ID 16u
17、imsbf reserved 6111111 details_major_channel_number10uimsbf reserved 6111111 details_minor_channel_number10uimsbf audio_OOB_source_ID 16uimsbf alert_text_length 16uimsbf alert_text() varPer ATSC A/65-A, Sec. 6.8 location_code_count 8uimsbf range 131 for (i=0; ilocation_code_count; i+) state_code 8ui
18、msbf range 099 county_subdivision 4uimsbf range 09 reserved 211 county_code 10uimsbf range 0999 exception_count 8uimsbf for (i=0; iexception_count; i+) in_band_reference 1bslbf reserved 71111111 if (in_band_reference) reserved 6111111 exception_major_channel_number10uimsbf reserved 6111111 exception
19、_minor_channel_number10uimsbf else reserved 16bslsbf exception_OOB_source_ID16uimsbf reserved 6111111 descriptors_length 10uimsbf for (i=0; IN; i+) descriptor() varOptional CRC_32 32rpchof Table 1 Emergency Alert Message Format 4 ANSI J-STD-042 zero This 1-bit field shall be set to 0. reserved Field
20、s in this standard marked reserved shall not be assigned by the creator of the message, but shall be available for future use. Decoders are expected to disregard reserved fields for which no definition exists that is known to that unit. Each bit in the fields marked reserved shall be set to one unti
21、l such time as they are defined and supported. section_length 12-bit field specifying the number of remaining bytes in this section immediately following the section_length field up to the end of the section. The value of the section_length shall be no larger than 4093. table_id_extension This 16-bi
22、t field shall be set to zero (0x0000). sequence_number This 5-bit field is the sequence number of this cable_emergency_alert() message. The sequence_number shall be incremented by 1 modulo 32 when any change in the information carried in the cable_emergency_alert() message changes. Terminal devices
23、shall process the sequence_number in order to detect and discard duplicate transmissions. Duplicates of any alert may be sent to overcome possible message loss due to channel noise. A cable_emergency_alert() message shall be discarded if the sequence_number matches the last received cable_emergency_
24、alert() message. When the last-used sequence_number is known, generating equipment shall increment sequence_number by one (modulo 32) when any data in the alert message changes. In case the last-used sequence_number is unknown (which can occur if a new piece of equipment is brought on line), generat
25、ing equipment shall send an Emergency Alert with alert_priority zero to establish a new sequence_number in all terminal devices before sending any actual alerts. Terminal devices shall use sequence_number to discard duplicate transmissions of the same alert. current_next_indicator This 1-bit indicat
26、or is always set to 1 indicating that the table sent is always currently applicable. section_number The value of this 8-bit field shall always be 0x00 (this table shall be at most one section long). last_section_number The value of this 8-bit field shall always be 0x00. protocol_version An 8-bit uns
27、igned integer field whose function is to allow, in the future, this table type to carry parameters that may be structured differently than those defined in the current protocol. At present, the only valid value for protocol_version is zero. Non-zero values of protocol_version may only be processed b
28、y decoders designed to accommodate the later versions as they become standardized. EAS_Event_ID A 16-bit value that identifies the particular EA event. Each time a new EAS message is distributed throughout the cable system, a new EAS_Event_ID shall be assigned. A new EAS_Event_ID shall be assigned i
29、f any parameter defining the event changes; that is, any field following the EAS_Event_ID itself. Terminal devices may use the EAS_Event_ID to disregard cable_emergency_alert() messages that describe the same event. EAS_Event_ID values held in terminal devices for duplicate detection shall be discar
30、ded at the expiration of the event, as given by event_start_time plus event_duration. NOTE An EA event with EAS_Event_ID value A may be followed later by another event with EAS_Event_ID value B. Since B represents a change to the contents of the cable_emergency_alert() message, the sequence_number f
31、or B must be incremented. The notification of event A could then be repeated, with the sequence_number incremented yet again. As long as no aspect of event A was changed, the originally assigned EAS_Event_ID value for that event could be used for the repeat notification. Terminal devices that had se
32、en and processed the original event A, could then recognize this as a repetition and discard it. 5 ANSI J-STD-042 EAS_originator_code The EAS originator code defined by 47 CFR FCC Part 11, indicating the entity that originally initiated the activation of the EAS. Processing of the EAS_originator_cod
33、e in terminal devices is optional, but may be used with EAS_event_code to trigger various alarms or attention-getting behavior in the equipment beyond the action required for handling the cable_emergency_alert() message. EAS_originator_code is coded as three ASCII characters. The originator codes de
34、fined in 47 CFR Part 11.31(d) are reprinted in Table 2. EAS_originator_code Meaning EAN Emergency Action Notification Network PEP Primary Entry Point System WXR National Weather Service CIV Civil Authorities EAS Broadcast station or cable system Table 2 EAS Originator Code EAS_event_code_length An 8
35、-bit unsigned integer that indicates the length in bytes of the EAS_event_code field to follow. EAS_event_code The EAS event code defined by FCC Part 11, indicating the nature of the EAS activation. Processing of the EAS_event_code in terminal devices is optional, but may be used to trigger various
36、alarms or attention-getting behavior in the equipment beyond handling the mandatory actions required by the cable_emergency_alert() message. EAS_event_code is coded as N ASCII characters, where N is given by EAS_event_code_length. The event codes defined in 47 CFR 11.31(e) are reprinted in Table 3.
37、6 ANSI J-STD-042 EAS_event_code Nature of Activation National Codes: EAN Emergency Action Notification (National only) EAT Emergency Action Termination (National only) NIC National Information Center RMT Required Monthly Test RWT Required Weekly Test NPT National Periodic Test Local Codes: ADR Admin
38、istrative Message BZW Blizzard Warning CEM Civil Emergency Message EVI Evacuation Immediate FFS Flash Flood Statement FFW Flash Flood Warning FFA Flash Flood Watch FLS Flood Statement FLW Flood Warning FLA Flood Watch HWW High Wind Warning HWA High Wind Watch HLS Hurricane Statement HUW Hurricane Wa
39、rning HUA Hurricane Watch DMO Practice/Demo Warning SVR Severe Thunderstorm Warning SVA Severe Thunderstorm Watch SVS Severe Weather Statement SPS Special Weather Statement TOR Tornado Warning TOA Tornado Watch TSW Tsunami Warning TSA Tsunami Watch WSW Winter Storm Warning WSA Winter Storm Watch Tab
40、le 3 Example EAS Event Codes nature_of_activation_text_length An 8-bit unsigned integer that indicates the total length in bytes of the nature_of_activation_text() field to follow. A value of zero indicates the nature_of_activation_text() field is not included in this alert message. nature_of_activa
41、tion_text() A data structure containing a multiple_string_structure() which represents a short textual representation of the event code for on-screen display. The multiple_string_structure() is defined in ATSC A/65-A Section 6.8. Table 3 shows examples of text representing different types of events.
42、 alert_message_time_remaining An 8-bit unsigned integer field in the range 0 to 120 that indicates the time remaining in the alert message, given in seconds. The start time of the message is defined as the time the last bit of the CRC has been received. A value of zero shall indicate an alert messag
43、e period of indefinite duration. For the purposes of this specification, the “end point” of any given cable_emergency_alert() message is defined as the point in time N seconds following the start time, where N is given by alert_message_time_remaining. When alert_message_time_remaining is zero, the e
44、nd point 7 ANSI J-STD-042 may be considered to be in the indefinite future. alert_message_time_remaining shall be used as shown in the flowchart given in Figure 1. It shall indicate the duration, in seconds, that processing of this EA message shall continue before return to the interrupted service i
45、s made. event_start_time A 32-bit unsigned integer quantity representing the start time of this alert event as the number of seconds since 00 hours UTC2, January 6th, 1980, with the count of intervening leap seconds included. The event_start_time may be converted to UTC without use of the GPS_UTC_of
46、fset value provided by the System Time table. An EAS event with a zero event_start_time should be processed immediately, and not stored in memory by the terminal device for later use. A value of zero indicates that the event start time is immediate. event_duration A 16-bit unsigned integer that, whe
47、n nonzero, represents the number of minutes (in the range 15 to 6000) the alert is expected to last. A value of zero indicates that the event duration is unknown (indefinite). For example, the event_duration for a hurricane watch may be four hours. The duration given in event_duration is relative to
48、 the start time of the event as given in event_start_time. A terminal device implementation may use event_duration and event_start_time to discard obsolete EA events if these events are kept in memory for possible review by the user. A terminal device implementation may choose not to store events sp
49、ecified with a valid event_start_time but with an indefinite duration, or may choose to store them. alert_priority A 4-bit unsigned integer value that indicates the priority of the alert. alert_priority shall be coded according to Table 4. NOTEA terminal device may process any alert in a way consistent with a higher value of alert_priority, at its discretion. For example, a user option could cause text display for alert_priority 1 e