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The Packets of Data

By Charles Miller

All of the traffic moving back and forth across the Internet is contained in small “packets” of data. Because these packets are too small to contain emails, image files, videos, and other media, the larger file formats must be chopped up into smaller packets for transmission, then reassembled at their destination. Fortunately for all of us, our computer have no problem breaking a large image file into hundreds of smaller pieces to send, and the computer receiving all the pieces of this jigsaw puzzle can easily put it back together.

Let us say you want to email a digital photograph to a friend.  Your computer breaks up your file into small packets. The smaller these packets, the more inefficient the transmission, so it should be self-evident that if your image file is broken into 100 packets it will take longer to reassemble than if you had broken it into only 50 packets. The problem with doing that is that there is a Maximum Transmission Unit (MTU) that each server on the Internet can handle, and if the size of the packets your computer used exceeds the size any server along the line can handle, then the transmission will not go through to its destination.

The way oversized packets are handled goes something like this imaginary conversation: Your computer says to its Internet connection, “Hello, please send all these packets to the next server down the line.” The next server, perhaps in Guadalajara or Mexico City, then sends it on to Los Angeles, then to Dallas, from where it is sent perhaps to Chicago with its ultimate destination being Boston. A problem can arise if the server in Dallas says back to your computer, “Whoa! I can’t handle packets that big. Break up the transmission into smaller packets and send everything again.” That message has to be sent back from Dallas to LA to DF to Guadalajara all the way back to your computer, which then has to start all over again, this time creating slightly smaller packets. This whole process might be repeated several times before your computer finally steps down to a packet size small enough to go all the way through. That can waste a lot of milliseconds. When enough of those milliseconds add up, users complain about their computer being “so slow!”

So, if you are following this so far, you should now understand that it is desirable to have your computer send the largest possible packets for the best speed and efficiency; but sending packets that are too big is no good either. Too large packets will be rejected and force your computer to waste time sending transmissions over and over and over and over until it gets down to a packet size that does not exceed the MTU of every single server along the entire route of your connection. It is unfortunate that users who fail to understand this sometimes complain that Telmex or Megacable is so slow, or that their computer needs more memory, when all they really need to do is change one setting in their router.

As an informed consumer, now you should know to ask the technician responsible for setting up your home network if you are using the optimum MTU for your needs.

Charles Miller is a freelance computer consultant, a frequent visitor to San Miguel since 1981 and now practically a full-time resident. He may be contacted at 415 101-8528 or email FAQ8 (at)


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