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Old 30-08-2010, 11:02   #1
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Caution to Mid Atlantic AIS Users



Between July 27 and August, 2010, while conducting development testing of its Nationwide Automatic
Identification System (NAIS), the Coast Guard inadvertently tele-commanded most AIS users transiting the Eastern United States between lower Connecticut and North Carolina to switch to AIS frequencies other than the AIS default frequencies (161.975 MHz - Channel 87B - 2087 and 162.025 MHz - Channel 88B - 2088). As a result, those users within uniquely defined channel management regions (as shown in the picture) will neither see nor be seen by vessels operating on the default AIS channels when within these regions. Similarly, vessels operating on default frequencies will not see or be seen by those vessels that were inadvertently switched to other frequencies. No other AIS users or areas are impacted.

One of the lesser known and potent features of
AIS is its ability to operate on multiple channels within the VHF-FM marine band. This frequency agility ensures AIS can be used even when the default channels are otherwise unavailable orcompromised. In such conditions, competent authorities, such as the Coast Guard, can use an AIS base station to tele-command shipborne AIS devices to switch to other more appropriate channels when within defined regions of 200 to 2000 square nautical miles. This can be done automatically (and without user intervention) through receipt of the AIS channel management message (AIS message 22) or manually entered via the AIS Minimal Keyboard Display (MKD) or similar input device. Once commanded or manuallynentered, the channel management information will stay in memory for 5 weeks or until an affected vessel moves more than 500 nautical miles from the defined region. AIS channel management commands can only be manually overridden or erased by the user via the unit's channel (regional frequencies) management function1 or automatically overridden via another channel management message for the same defined region. Reinitializing or resetting your AIS or transmission channels will not necessarily reprogram your unit back to the default channels.

Commencing September 1st and continuing for the subsequent 5 weeks, the Coast Guard will broadcast
new channel management messages that will tele-command all AIS users back to default channels. This broadcast will occur each hour between hh.05:30 and hh.05:59, but may change as needed. To ensure that these messages are received, they will be broadcast on Channel 70--Digital Selective Calling (DSC), which is also monitored by all type-certified shipboard AIS. While this will ensure all AIS users will get the message regardless of what AIS channel the unit is operating on, it could however cause a minor inconvenience to owners of older DSC radios who may receive an alert (tone) upon receipt of this message. It will have no other effect on DSC radios.

AIS users are encouraged to inform others whom they believe may be affected and are therefore not
being seen by others. All AIS users are reminded to maintain their AIS in effective operating condition and to validate their AIS data prior to each voyage and as needed.

This safety alert is provided for informational purposes only and does not relieve any domestic or international
safety, operational or material requirement. The Coast Guard has developed policy and procedures to ensure such inadvertent broadcast do not happen again and we apologize for any inconvenience this may have caused. For further information on AIS Channel Management or reprogramming your AIS read FAQ#19 at or contact Developed by the Office of Waterways Management, U.S. Coast Guard Headquarters,
Washington, DC.

1 The following settings, if found in your AIS Channel Management / Regional Frequency pane, should be overridden (as denoted) prior to navigating therein; if you do not find these settings / regions in this pane you are not affected and need do nothing.

Setting / Region X (MD, DE, PA, J, NY Area)
NE Corner: 41º 07.60 N, 073º 49.10' W (41.1266667 -73.8183333)
SW Corner: 38º 21.90' N, 078º 10.40 W (38.3650000 -78.1733333)
Channel 1/ A / AIS1: 1022 / Ch.22B [should be change to 2087 / 87B]
Channel 2 / B / AIS2: 2022 / Ch.22 [should be change to 2088 / 88B]

Setting / Region Y (VA Area)
NE Corner: 37º 42.00' N, 76º 43.80' W (37.7000000 -76.7300000)
SW Corner: 36º 32.00' N, 79º 8.00' W (36.5333333 -79.1333333)
Channel 1 / A / AIS1: 1027 / Ch.27B [should be change to 2087 / 87B]
Channel 2 / B / AIS2: 2006 / Ch.6 [should be change to 2088 / 88B]

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Old 30-08-2010, 11:44   #2
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non cant you see why the rest of the world tried to remove the requirement for remote telecommandind

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Old 10-09-2010, 09:32   #3
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The remote command has some definate downsides. 1. AIS is big brotherish already, now they can not only see you, they can control who see's you. 2. What's to stop a terrorist from intentionally causing a collision by manipulating the signals?. 3. What will stop a lightening strike or other electrical fault from accidentally switching channels? 4. Or inexperienced user?
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Old 10-09-2010, 10:07   #4
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This is not so alarming Bill, because the technology is far more advanced than you suggest. For example, when you make a cellphone call while driving around, your phone and a number of relay towers make a lot of frequency changes that you will never notice, for a number of technical reasons. In this particular case, an AIS frequency change occurs only on those transceivers within VHF range, and it happens to all of them at the same time. There is no way to single out a particular vessel. Life, and the pursuit of nautical purposes goes on virtually without interruption. If there is a way to corrupt the AIS system, it goes away and we revert to the pre-AIS chaos and everyone reverts to Rules of the Road. To the accompaniment of many, many warnings from competent authority.

I think we need to find out which early AIS transceivers and receivers are likely to be adversely effected, but I suspect that since this feature is part of the original spec, it would be tested at certification. As in, "It's already Fixed."
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Old 21-09-2010, 12:20   #5
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Back to the downside a group of vessels in an area get the signal change freq, and go to another area, or a group of vessels out of range enter after freq change signal has been sent. Cell phones use a handshaking protocol that includes several frequencies and a digital code, and monitors all available freqs to send request for unused channel when switching towers. Even with this level of tech it drops calls sometimes.
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