Why Mbps?

Why do speeds still get quoted in bits per second? Its like saying my car does 193,121,280 mm per hour..... or 193 Mmmph

Because those are the units for data transmission speeds. Car speeds are expressed in mph.

Its like saying my car does 193,121,280 mm per hour..... or 193 Mmmph

What's wrong with kilometres per hour or as more commonly used in the UK miles per hour?

Mbps is OK for me as my long line rarely gets above 3meg shunted down it from the exchange, so why not Mbps?

Harry

Until we get above Gbps as standard, Mbps will have to suffice.

It's always been done that way, mainly because there's no ambiguity- a bit is a bit.

These days it wouldn't be unreasonable to use megabytes/second on the basis that there are 8 bits in a byte, but it was not always thus.

Back in the day a byte could be anything from 4 to 8 bits depending on the system. Wiki has some history of the term.

It's just they way things have always been done. The speeds of serial data transmission systems are traditionally quoted in bits per second. SATA and USB are the most common examples.

I notice loop lengths are in kft.

Or even nine bits which is still in current use.

If the powers that be delivered a USC of 8Mbps throughput, we could all switch to 1 Meg (abytes) speak.

I prefer Mb to MB anyway. It helps to differentiate between data transfer and data storage.

In reply to a post by mrpaperclip:

Why do speeds still get quoted in bits per second?

Cuz the transmission is in bits. Not all the bits that are transmitted are actual data that you would see on your PC; some are protocol overheads (say about 17%), like the addresses of the sender and destination.

So when you download a file to your PC and you see it measured in Bytes, more bits than 8 x its Byte size were transferred to you over ADSL and the Net, and those bits have to fit within your Bandwidth (i.e. Sync Speed).

Megabytes per second was (as you will remember) on parallel comms interfaces where there would be one (8 bit) byte of data sent across 8,9 or 10 parallel data lines with two providing some form of parity capability or with 16bit byte systems across 18 or more data lines. Plenty of ambiguity there.


And definitely "bits" is the only non-ambiguous way. Even kb & Mb are ambiguous!

In reply to a post by mrpaperclip:

Why do speeds still get quoted in bits per second? Its like saying my car does 193,121,280 mm per hour..... or 193 Mmmph

No, Mm - Mega-milli is not an acceptable prefix. 10⁶ x 10^-3 = 10³ or k - kilo. So your car does 193 kmph or kmh^-1

Shouldn't it be K|M baud anyway? Or was that only used for analogue systems?

Edited by deleted (Sat 04-Aug-12 16:13:36)

No that's the symbol rate and a symbol can represent several bits.

A nice long discussion here.

Baud is symbol rate. For most UK broadband, it would be a fixed 4 kBaud service - all ADSL standards deployed in the UK, plus the VDSL2 used by BT FTTC is 4kBaud, but with many bits per symbol to get the data rate up - 80M service is over 20 kilobits per symbol.

Cable is a slightly different beast - because it's not an OFDM (aka DMT) system, it uses many more symbols, but typically only 8 bits per symbol. At the data rates used here (around 56MBit/s/channel), you'd get 7 MBaud.