|
GLENSHANE PERSONAL COMPUTER USERS GROUP |
|
|
GLENCOM NEWSLETTER |
|
|
Volume 7 Issue 8 |
August 2000 |
| NEXT MEETING | |||||||||
| The next meeting is on Monday 21st August 2000 @ 8pm. | |||||||||
| THE FLOATING LOCAL AREA NETWORK | |||||||||
| This
is a look at the new Automatic Identification System (AIS) to be fitted
to merchant ships from 2002. The Foylebank is on the final leg of her voyage as she approaches the English channel. Her newly-installed AIS system broadcasts her position every two minutes to all ships within a radius of 20 nautical miles. The VHF radio channel she uses for the transmission is shared by all other ships in the world, so a clever protocol has been devised to prevent interference. SOTDMA Each minute in time is divided into timeslots just long enough to hold the packet of data a ship transmits. Although it takes only miiliseconds to send, each packet contains a lot of information about the ship; her name and radio callsign, her position, course, speed and so on. Then comes the clever bit. Included in the packet is details of how many more minutes she intends to occupy that particular radio timeslot and the next timeslot she has chosen randomly to occupy. Approaching her from the north is the Pride of Bilbao, bound for Spain. She too has been fitted with an AIS and receives the Foylebank's data packet. Forewarned that Foylebank intends to skip to another timeslot she announces her presence to all other AIS equipped ships within range. The software in her AIS is careful to choose a random timeslot which no other ship has announced that it intends to occupy. The name for this fancy protocol is Self Organising Time Domain Multiple Access (SOTDMA). As ships pass they form floating local area networks, taking care not to interfere with each other. As they steam out of range of a network, they continue to broadcast their positions, all the time listening for other networks to join. ECDIS Generations of 2nd mates spent much of their careers on the 12 to 4 watch updating the ships folio of nautical charts.Very soon this drudgery and even the actual paper charts will be replaced by the Electronic Chart Display (ECDIS). Apart from displaying the ships position ECDIS can be overlaid with other data from the ships radar and from the new Automatic Identification System. G
|
Email
Address for Life Members - please help Glencom find you, sign up with Bigfootand we'll aim all your ONEList traffic at it. That way you won't miss the traffic, or the Glencom Newsletter no matter how often you change your ISP. Visit Rootsweb WorldConnect
to see if your name is up there
|
||||||||
| COMPUTER TABLES | |||||||||
| On Monday night members will have the opportunity to choose their free computer tables.They are used, but perfectly servicible and very well constructed. First come first served. G | |||||||||
| GLENCOM SMS REMINDERS | |||||||||
| This month we have been running a pilot scheme to alert
members of the imminent Glencom meeting using SMS. The Short Message
Service (SMS) is a facility available on all digital mobile phones.
Members with mobile phones who would like a monthly reminder of the
Glencom meeting should submit their phone numbers to Alex or John. It goes without saying that the number will be kept confidential, and you won't be pestered with trivial SMS. G |
|||||||||