4 ms·

If you hashed every 1000 symbols with a 512 bit hash to check message integrity and retransmit, a hash collision would be practically impossible, so "no transmi

If you hashed every 1000 symbols with a 512 bit hash to check message integrity and retransmit, a hash collision would be practically impossible, so "no transmission errors are possible" is perfectly fair to say under some circumstances.

malik9 5y ago
If you're concerned about one or two bits being toggled, a 512-bit hash will merely increase the chance of bit errors; on a noisy medium, using such a big "checksum" will BOTH detect and cause a high number of packet faults.
lazide 5y ago
Also possible they are using a 1 byte CRC heh
- kabdib 5y ago
  A piece of communications gadgetry even mentioning checksums is like a car salesman proudly claiming "... and this baby comes with working brakes!" The very pronouncement leads to worry, and additional questions (like this very thread, QED :-) ). My inexpert digging came up with: They use APRS packets, which use AX.25, whose framing includes a 16-bit Frame Check Sequence, which looks like it came from HDLC, and is a 16-bit CRC-CCITT. Phew.
Isamu 5y ago
Is this what they are doing? Seems unlikely that you would transmit so much overhead when the data rate is so low, unless you needed to overcome a lot of noise. It’s about the numbers, there’s trade-offs for each specific application. I would encourage people to do the math and see if their design makes sense for their goals.
- AlotOfReading 5y ago
  There's virtually no benefit to dedicating so much of your message to checksums with any remotely efficient algorithm. More practically, any CRC >= 32 bits is probably overkill and any CRC > 64 bits is definitely overkill until you get up into gargantuan message sizes.
  - Isamu 5y ago
    Agreed, for this application (texting) a simple approach is probably best. You have to look at the particulars of your domain, it’s not one size fits all.
xyzzy21 5y ago
Sounds like you don't understand secure communications and basic concepts like bit-error-rate, QoS and reliability. Hash collisions have NOTHING to do with effectiveness or reliability of communication. A feature is a benefit!
- WithinReason 5y ago
  Sounds like you simply didn't understand my point.

malik9 5y ago

If you're concerned about one or two bits being toggled, a 512-bit hash will merely increase the chance of bit errors; on a noisy medium, using such a big "checksum" will BOTH detect and cause a high number of packet faults.

lazide 5y ago

Also possible they are using a 1 byte CRC heh

kabdib 5y ago
A piece of communications gadgetry even mentioning checksums is like a car salesman proudly claiming "... and this baby comes with working brakes!" The very pronouncement leads to worry, and additional questions (like this very thread, QED :-) ). My inexpert digging came up with: They use APRS packets, which use AX.25, whose framing includes a 16-bit Frame Check Sequence, which looks like it came from HDLC, and is a 16-bit CRC-CCITT. Phew.

Isamu 5y ago

Is this what they are doing? Seems unlikely that you would transmit so much overhead when the data rate is so low, unless you needed to overcome a lot of noise. It’s about the numbers, there’s trade-offs for each specific application. I would encourage people to do the math and see if their design makes sense for their goals.

AlotOfReading 5y ago
There's virtually no benefit to dedicating so much of your message to checksums with any remotely efficient algorithm. More practically, any CRC >= 32 bits is probably overkill and any CRC > 64 bits is definitely overkill until you get up into gargantuan message sizes.
- Isamu 5y ago
  Agreed, for this application (texting) a simple approach is probably best. You have to look at the particulars of your domain, it’s not one size fits all.

xyzzy21 5y ago

Sounds like you don't understand secure communications and basic concepts like bit-error-rate, QoS and reliability. Hash collisions have NOTHING to do with effectiveness or reliability of communication. A feature is a benefit!

WithinReason 5y ago
Sounds like you simply didn't understand my point.