MB: Mega Bytes or Mega Bits?

Some reviewers have asked about the use of “MB/s” as a measure of transfer speed.  In the Guccifer 2.0 NGP/VAN Metadata Analysis report.  “MB/s” refers to Mega Bytes per second where “Mega” is one million (1,000,000).  Some reviewers have confused this notation with “Mb/s”, or mega bits per second often quoted by ISP’s.   Those two measures of transfer can be confused with each other, and there are articles on the Internet that discuss this topic, for example here and here.

This handy calculator will let us do all sorts of what if comparisons and that particular “calculator” link will convert 22.6 MB/s (the estimated transfer rate cited in the report) into the following chart.

compare_22_6_MB_s_to_Network_Speeds

As you can see it is at about the 80% level of a 1 Gb/s local area network (LAN), which is typical of many wired enterprise/SOHO wired networks, but as far as “carriers” go, you’re up there in the stratosphere.  OC stands for “Optical Carrier”, as in “optical link”, fast but expensive.  For the gory details, see this Wikipedia article on Optical Carrier transmission rates.

Let’s talk transmission overhead.  Going from MB/s to Mb/s when we’re referring to network transfer rates should also account for communication overhead.  Basically, when you send stuff around on network, you need to break it up into packets and each packet has a header, maybe a trailer, and all that is overhead.  From the Wikipedia link, you’ll see this statement for OC-3: “OC-3 is a network line with transmission data rate of up to 155.52 Mbit/s (payload: 148.608 Mbit/s; overhead: 6.912 Mbit/s, including path overhead) using fiber optics.”.  In that statement “payload” is what we care about and “overhead” is the extra information the protocol adds.  If we measure the part we care about (payload), we need to account for the 5% overhead to come up with an accurate estimate (in this case).  The calculator doesn’t do that, but it is something to keep in mind.

Let’s fire up the calculator again and ask it to compare our 22.6 MB/s transfer rate to that seen for peripherals.

compare_22_6_MB_s_to_Peripheral_Speeds

Cutting to the chase, USB 2.0 maybe — USB 3.0 likely.

One more, disk drives.compare_22_6_MB_s_to_Disk_Drives

Okay, a disk drive can do the job.

Caveat: we don’t know how accurate or current the data is that was used for that calculator.  There are lots of variables to consider like overhead, and especially with public networks such as the Internet other factors need to be considered: contention, rate-limiting, and so on.

We are just trying to place the 22.6 MB/s rate in perspective, and add support for the conclusion that the initial copy operation was likely done locally, either with direct access to the system where the data is stored, or over a high speed LAN.

That is not the whole story, however.  The file copy operations observed in this analysis were performed file-by-file.  There is a lot more overhead, both in file transmission and file and directory creation for file-by-file transmission than would be seen in a best case, single big file scenario.

More on that later, but it will take a day/two to pull the data together.

 

 

 

 

3 thoughts on “MB: Mega Bytes or Mega Bits?

  1. Excellent presentation for the basics. The band-width for HDisks is actually for the bus; performance of the disk itself, well, depends, but rarely comes even close to the theoretical throughput. In terms of the network throughput, there is packet overhead on the data level(s), on the network level (routing and reassembly of packets), and at the transmission level (acknowledge, re-order, status, encryption, whatever). Real world performance will generally be lower than your examples.

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  2. If the metadata gives us the exact time and date that the files were downloaded locally.. why doesn’t someone find a timetable for who entered and exited the DNC around that time. Who was in the building? Was Seth Rich?

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