kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England)) (07/26/88)
In article <Jul.22.20.57.24.1988.24248@athos.rutgers.edu> hedrick@athos.rutgers.edu (Charles Hedrick) writes: >To use a whole T1 circuit with a bridge or router, you >have to use a box that takes a generic 1.5 Mbps signal and puts it >into the funny T1 format. I call such a box a T1-izer. [...] >In general the bridges and routers don't know and >don't care exactly how fast a line is. They just lock onto the clock >that comes from the T1-izer of multiplexer. That raises some interesting questions. Depending how "smart" the T1-izer is in doing the required bit stuffing, it might present a higher or lower clock rate to the bridge. What differences are there among T1-izers and do vendors advertise what the true clock rate to the interface is? Are any T1-izers capable of data compression and if so what is the expected gain? Could we get effective throughputs of 2Mbps over a T1 circuit? Or is this capability best left outboard of a T1-izer? Kent England, Boston University
hedrick@athos.rutgers.edu (Charles Hedrick) (07/27/88)
Many T1-izers have options to select how much encoding is needed. Generally the specs tell you exactly what clock rate they present for each combination of options. E.g. there are options to say whether your telco well let you get away with bipolar violations (one specific kind of bipolar violation can be used to provides ones density more efficiently), and whether your signal has any known properties that will allow more bit-efficent processing (e.g. ours will do a better job if the signal is known to be HDLC). I think in some you can specify whether it has to worry about ones density, whether the signal already has T1 framing, etc. Typically you can get from something like 1.528Mbps to 1.544Mbps depending upon the kind of coding the box can do and what options you set. I haven't seen any that do compression. We're talking about slightly jazzed-up CSU's here (the official product name is normally "clear-channel CSU"). I think compression (particularly at this data rate) takes a bit more processing power than they have.