What is Packet

Packet Radio

What is Packet?

Packet is a modification of Radio Teletype, also called RTTY. RTTY transmits characters with or without spacing, with no attempt at verification or correction. Bytes can be sent slowly, or with close spacing. Data is sent incrementally as soon as any part of the data is available at the transmitter. Generally the decision of when to start and stop transmission is under operator control.

Packet is a scheme for bundling addressing info, control info, data, and error checking into a single transmission which is sent all at once.

Because packet radio messages include addressing info, many stations could be on the same channel or frequency and a packet message could be directed by one station to one specific other station. This permits multiple conversations to take place on the same channel where pairs of stations could each have what looks like a private conversation. See Why do we packet later on this page.

In packet radio, a computer takes control of the Push To Talk on your radio. That computer then decides when it is time to transmit. When it is time, the computer keys the transmitter (causes it to transmit), sends a packet (of address, control, information, and error checking) and then unkeys, automatically. The computer is responsible for generating the the transmit audio to the transmitter, and it listens to the receiver as well.

The computer at the receive station takes the combined block of bits heard in the transmission and can make some decisions on what to do with that block. The computer can know whether the entire contents was received intact, who it was sent by and who it was sent to. Based on what has come before, the the computer can also ignore the incoming data, or it can use the data and pass it on to the operator or some operating program. It can also send an acknowledgement for the data or even forward it on to another station down the line, as if the receiving station was one step along a path for movement of the message.

Packetized transmission is used in most digital communications, wired or otherwise, although that has only been true since the 1970s. The Internet, telephones, alarm systems, and many other common electronic systems use packets for data delivery. Most systems where there are multiple computers (even very small computers) communicating in a network, are probably using packets for communications.

In ham radio, packet is used for sending text and data. Text is used on HF and VHF, both for chatting and for email operations. Data is used for location plotting of hams and objects, and also for band condition monitoring, weather monitoring, and other interesting applications.

Sometimes a small computer is used to do most of the radio operating, tone generating, and receive tone decoding for a packet station. That small computer could be a Terminal Node Controller, or TNC. In other stations the generating and decoding operation is performed in a desktop PC using the audio inputs and outputs provided by the desktop computer's sound card peripheral.

Amateur Radio packet is used on our entire spectrum, from very low frequencies to microwave.

Packet messaging can be used with acknowledgements or without. In some applications Packet is mostly used for sending text messages between stations. On HF, packet looks a little like RTTY except that the messages are not sent until you hit ‹ENTER› on your keyboard.

When a packet is used in a mode called CONNECTED, your message is sent and verified for unique error-free-content by the recipient before the message is displayed, then the recipient acknowledges your message. If they don't acknowledge, your end will automatically resend the message. Redundant copies of the message are ignored. You are guaranteed either a perfect copy, or you give up on the QSO. Packet can be used to send blocks of text with high reliability and this capability is very handy in traffic handling or emergency communications.

In another mode, called UNPROTO, your packets can be displayed without verification for uniqueness and without an acknowledge. In many application of UNPROTO mode the sending station repetitively (once a minute or less) sends a message containing the current status of something (like weather or location). Then if the receive station misses, or declares corrupted (with errors), a message, only that point of data on a graph is lost. The remainder of the points of data are enough to serve whatever the purpose is. Thus no retries or acknowledgement are used or required.

Packet can be used from ham to computer, or from ham to ham, or from computer to computer. You can also use the computers to relay messages to the next computer along a path, allowing us to connect from ham to computer to computer to computer to ham. This kind of packet is called networking.

Why do we packet?

Of all of the modes of communications used in ham radio, packet is the only mode which inherently allows several conversations to occur in the same piece of spectrum over the same path. This means that on a network link between two sites, there can be several conversations at once without hindering each other. We can take advantage of a linked network of packet stations without worrying about keeping other stations from doing the same. We can connect our station or computer to other stations to run operations that might last for hours or even years! This could be useful to tie together stations that would be used for a long coordinated operation, or to receive telemetry from a remote station.

Packet messages can be routed. A packet network allows that you could have multiple routes for packet to travel. So you could go
from Ham1 to ComputerA to ComputerB to ComputerC to Ham2
while another message could go
from Ham1 to ComputerA to ComputerP to computerQ to Ham3.

Packet can be operated on HF and VHF with or without a network, and it can be used to send text messages or for transmitting data encoded from some application.

On VHF and UHF the primary use of packet radio is the Automatic Packet Reporting System, or APRS, which is used to send GPS coordinates, weather data, and other telemetry from an automated station, through (relatively) dumb relays, and eventually through an Internet Gateway to a server which processes the received signals. APRS is infrequently used between mobile stations with a local non-internet display.

What is Packet like today?

There are several kinds of packet radio activities today. These are the most popular:

• APRS Automatic Position Reporting System -- transmit GPS coordinates of portable stations to Internet servers
• Winlink -- Enables a disaster site to be connected back to the Internet via packet radio -- also can be used to connect two sites together entirely via packet radio.
• BBS & CHAT -- G8BPQ node stations connected to both packet radio and Internet allows packet-radio style emails to be sent via Internet to other cities. Also has a world-wide chat feature.
• Broad Band HamNet (BBHN) -- microwave and high UHF links using commercial-off-the-shelf WiFi equipment to create wide area high-speed networks. Many regional networks exist covering multiple cities using exclusively Amateur owned equipment. There are also many BBHN systems which are mixed commercial (Internet) and Amateur owned hardware.Broadband-hamnet.org and Amateur Radio Emergency Digital Network
• ROSE, TheNET, G8BPQ -- there are several Amateur Radio only systems which use VHF/UHF radio hardware to do wide area networks. The Central North Carolina TARPN is one such. The SEDAN network in Florida is another. FLA-SEDAN

What is TARPN and why re-invent the wheel?

TARPN is not re-inventing the wheel as much as using old technology in a new way. There are several non-features of each of the ways packet radio have been used and are being used that TARPN addresses. We're not trying to stamp out the other ways. I believe that our system is unique in that it results in network hardware in ham's shacks, and that it is an expanding group of network nodes.

We're trying to come up with something that appeals to enough of the population that we can build a large network and have fun doing it.

TARPN suggests a networking technology which is easy for all hams to participate in, and which promotes Amateur Radio.

TARPN is a design philosophy and operational philosophy. I think if we abide by this set of rules and use this design, the network can be built and promoted. My (KA2DEW's) particular part of this is to document the methods we're using so other people may duplicate them. I'm also working on developing methods to supplement the system.