[Question] 1. in FR, when we specify clock rate for 64k, we use clock rate 64000, why not 64 x 1024 = 65536 ? and for 1.544 mbps, we use 148000, why not 1.544 x 1024 x 1024 ?
Partial answer: Transmission speeds are in bits per second (temporal), storage is in bytes (spatial), although you'll find reference to octets (usually not expressed as bytes) in the speeds when they're discussing frame formats. When you see 1.544 mbps, it's 1.544 x 10^6 = 1.544 x 1000 x 1000. As long as you're measuring speed, you don't make a conversion from a decimal number to a power-of-2 number. The 1.544 mbps came from the original T carrier system, when we had T1, T2 (4 x T1) and T3 (28 x T1) encapsulations (or whatever it was called) and DS0 (64 kbps), DS1 (24 x DS0), DS2 (4 x DS1) and DS3 (28 x DS1) speeds. If I remember correctly, the T carrier system was deployed way back in the 1960's in the US, and in Europe as the E system. The research was probably finished at Bell Labs and the universities in the 1950's; they also had specifications for optical that we are still trying to figure out how to deploy. Those old guys were pretty smart, especially when you consider the state of the art at that time. The DS0 speed came from 8 x 8000 = 8 x 8 kHz. That works out to a speed of 1,536,000 bps when you combine 24 DS0 channels. Adding 8000 bps (8 kbps) for framing gives 1,544,000 bps or 1.544 mbps. To say that DS1 is 24 DS0 channels is slightly misleading unless you realize that the extra 8 kbps framing is implied. You'll have to do some mulitplication to check the DS2 and DS3, and look up some of the old books (this is considered ancient history now). I have no idea what to say about 148x 10^x. Where did you get that? -- TT Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=38917&t=38908 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
