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Does STORE mode ZIP (uncompressed) still offer CRC checks?
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huejahfink
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7th May 2013
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Does STORE mode ZIP (uncompressed) still offer CRC checks?

Does anyone know if the uncompressed 'STORE' option in ZIP archiving still offer CRC checks to ensure data integrity like their compressed counterparts?

I like the fact that my masters are delivered in a container that will not extract properly if there is data error during transfer, but the amount of space saved by using compression is generally so minimal I'm starting to think it might be better to use a non compressed zip - faster to pack and unpack at both ends, and avoids any extra mathematics (even if it is lossless.)

Thanks
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ok - just opened a zip as a text file, deleted a few lines of data from the middle and then saved again as a zip file. It didn't open properly, so I guess my answer is probably YES.

Would still be interested to hear any knowledgeable info on the subject though.
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I dunno 100% about zip, but .rar has crc checksum implemented for sure
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I prefer to put them in a Zip with no compression which speeds up the process quite a bit on both ends.
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As long as they are still safer wrapped in a zip than they are as single files, I think this is the way forward for me. Thanks.

I really like RAR but the problem I found is that some people are not familiar with it and it therefore causes more problems than it solves.
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Zip uses CRC-32 7Zip uses CRC-32 | CRC64.

Even the IP4 header uses a basic checksum for every datagram it transmits which is not as robust as CRC but these things work in layers on top of each other.

So transmitting packets in an archive with CRC is a gain in error checking though using no compression will not really save you that much time.

On this particular machine an average size wave file ~20MB takes 2.1 seconds (operation time reported by 7zip) to compress at ultra vs none, the difference is 20.1 MB file, no compression vs a 16MB file with compression.

The difference doesn't seem that big but consider how much longer it takes to transmit 4 extra megabytes or download 4 extra megabytes. Again on this particular machine my max download speed from a server with good push I can get 3.5MB/sec. I can send at 1.5MB/Sec. So on one song the extra size of the non-compressed version is almost negligible though with headers and such I would gain much more than the seconds invested in packing the file. On 10 songs the difference becomes much more significant, ect....

The question should be where would you rather waste your time packing or unpacking which is much faster and less error prone than wasting your time sending or downloading. The ratio of the pros vs cons gets even more skewed towards local processing the slower the internet connection becomes. Just cause you or I have 50Mbps/50Mbps connections I would not think it is safe to assume the same applies on the other side of the socket.

On lossless compressed formats there is no point in compression though, the headers and error correction are still worth it but the fie size will inflate.
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Thanks for your input
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8th May 2013
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Quote:
Originally Posted by RRCHON View Post
Zip uses CRC-32 7Zip uses CRC-32 | CRC64.

Even the IP4 header uses a basic checksum for every datagram it transmits which is not as robust as CRC but these things work in layers on top of each other.
Actually, this is not quite correct.
The IP (IP V4/6)-header uses a basic checksum for only the IP header. This has to be recalculated on every hop (router), because the TTL is changed.
Datagrams are one layer above (OSI layer 4), the protocols there (TCP/UDP) are the ones with checksums for the whole datagram.
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Quote:
Originally Posted by kosmokrator View Post
Actually, this is not quite correct.
The IP (IP V4/6)-header uses a basic checksum for only the IP header. This has to be recalculated on every hop (router), because the TTL is changed.
Datagrams are one layer above (OSI layer 4), the protocols there (TCP/UDP) are the ones with checksums for the whole datagram.
Thank you for the correction, though the details are always going to be a bit beyond me. I always considered IP4 TCP to be spread across from network to session layers, a layman's understand of the protocol.

I appreciate you taking the time to correct that and I will remember it, even if it still it a bit confusing to me.

So there are actually two sets of checksums one from router to router that checks for bad packets between routers and secondary one at the transport layer that checks datagrams? NVM I can just go buy a more up to date book on this stuff, and try to understand it better, kind of all gets jumbled up in my brain after years of not thinking about it.

Thanks again for setting me straight, I appreciate taking the time to educate me and prevent the dissemination of incorrect information, even if it still a bit fuzzy for me.
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Doesn't FLAC also contain CRC checking, and compress much more than zip or rar?
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Quote:
Originally Posted by RRCHON View Post
Thank you for the correction, though the details are always going to be a bit beyond me. I always considered IP4 TCP to be spread across from network to session layers, a layman's understand of the protocol.

I appreciate you taking the time to correct that and I will remember it, even if it still it a bit confusing to me.

So there are actually two sets of checksums one from router to router that checks for bad packets between routers and secondary one at the transport layer that checks datagrams? NVM I can just go buy a more up to date book on this stuff, and try to understand it better, kind of all gets jumbled up in my brain after years of not thinking about it.

Thanks again for setting me straight, I appreciate taking the time to educate me and prevent the dissemination of incorrect information, even if it still a bit fuzzy for me.
No prob.
Actually it's not that hard. IP is on layer 3, TCP and UDP on layer 4.
IP and TCP are completely different protocols, and on different layers of the OSI model.
A lot of other upper-layer-protocols can be transported via IP.
The TCP datagrams are 'encapsulated' in the IP packet, which then gets encapsulated in an ethernet frame or similar (layer 2).

Think of it like an onion.

Actually there are checksums on almost all layers, which are examined by the devices working on the respective layer. So a normal switch would only check the ethernet header, a router normally the IP header, a multilayer switch even the upper layers (up to layer 7). Of course, the higher the layer, the more sophisticated the stuff that can be done (QoS etc.).
But a normal switch will never see the checksums or anything else in the layers 3 to 7.

We're way offtopic though. This is maybe interesting if you're learning for your CCNA exam, but for normal mastering engineers a bit beyond what's necessary to know about IP networking.
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Quote:
Originally Posted by Babaluma View Post
Doesn't FLAC also contain CRC checking, and compress much more than zip or rar?
FLAC on highest settings is currently about as good a file compression as you can get for lossless audio afaik.

But FLAC is not the format my clients want their masters delivered in. Their distributors request WAV.

Unzipping an archive is one thing, expecting my clients to convert masters to a different format before they can be used is something else entirely and something I would not deem appropriate for them. of course YMMV etc
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OK, agreed, that's also why I switched from .rar back to .zip (too many "Huh?")
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Yes exactly. The good thing about zip is that it can be opened in both Windows and Mac OS without any external programs required.
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