Modems request bandwidth by minislots, when they want bandwidth they ask for minislots, not bytes or bits. The size of these is in ticks of 6.25 microseconds. There's a parameter for how many ticks are in each minislot, that's the minislot size.
If the minislot size is too small the modem can't deliver full speed as each time it wants bandwidth it has to ask for it, and it can't ask enough times per second to get enough minislots for the bandwidth. With a minislot size of 1 it has to ask for 4 times as many minislots to send the same amount of data.
Modems have to run through a request - grant - send process when they want to transmit, they wait for a timed window then they send a request for upstream bandwidth, they are then given a time to send their data. This isn't instantaneous, it takes a little while, and there's a restriction on how much data a modem can request permission to send at once, 255 minislots, so the modem may not be able to go through this process enough times to get enough minislots to send the full, say, 5Mbit/s it needs to transmit on a 50Mb customer's upstream.
---------- Post added at 20:58 ---------- Previous post was at 20:57 ----------
Quote:
Originally Posted by jb66
It's like a regular slot but much smaller  |
