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C O N F I G U R I N G C O M S I F T E R
User Guide | ComSifter CS-8D Pro
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Quality of Service (QOS)
Overview
An Internet connection consists of an upstream and a downstream connection. Typically, these connection
speeds are asymmetrical, a high speed for downloading, and a lower speed for uploading. To provide fast
uploading and downloading, the Internet Service Provider (ISP) will configure large buffers that optimize file
transfer performance. These large buffers help file transfer performance but degrade the interactive
performance of the network.
One example is when one user is uploading a large file from the local network to another location on the
Internet (this could be a file transfer, large email, or even an FTP upload). As this file is being uploaded,
another user starts downloading a file. It would be assumed that the downloading would not be affected by the
upload, but this is not true. As downloaded packets arrive, they are acknowledged back to the sender by way
of an ACK packet. This packet must traverse the same path as the file being uploaded. Since the uploaded file
is filling the buffers at the ISP, the ACK packet must wait its turn to be processed at the ISP. This delay causes
the downloaded file to begin to slow, as the ACK packets have not made their way back to the sender.
To resolve this dilemma ComSifter incorporates a QOS feature that removes the upstream buffer from the ISP
and moves it to the ComSifter. Since ComSifter has control over the buffer, we can now configure the buffer.
Note: ComSifter can only control the upstream buffer, i.e. data that has not been sent.
ComSifter cannot control the downstream data as this data has already been
sent.