Modem Speed Information

MODEM TRANSMISSION SPEED INFORMATION

Connection	Capability	Bytes per sec	KB per min	MB per hour	Min/Sec/MB
Modem	9,600	1200	70	4	14m 33s
Modem	14,400	1800	106	6	9m 42s
Modem v.34	28,800	3600	211	12	4m 51s
Modem	33,600	4200	246	14	4m 09s
Modem v.90	42,000	5250	308	18	3m 19s
Modem v.90	50,000	6250	366	22	2m 48s

KB or Kilobyte = 1024 Bytes, or roughly a thousand

MB or Megabyte = 1024 x1024, or 1048576 Bytes, or roughly a million

These calculations are for uncompressed data in order to provide you with a reference on raw data throughput or transmission. When data is compressed, throughput can increase by as much as a factor of 2 or 3. Because graphic images on web pages are already compressed, the realistic multiplier for web browsing generally becomes 1.5 to 2x that shown above. You should divide the times by 1.5 or 2 to approximate real world download times presuming a 2 to 1 compression. Obviously, faster is better, therefore it is easy to justify the added cost of a 56K modem based upon the value your time alone.

Connect speeds for V.90 modems will vary because your connect speed is solely dependent upon the quality of your phone line and the distance to your telephone company’s local central office or facilities. A data grade (or near data grade line) should be able to connect at about 48 to 50K. A generalized rule of thumb is that people who live within 3 1/2 miles of their telephone company’s central office will get significantly better connect speeds using a V.90 modem over using a V.34 modem.

DTE vs. DCE speed:

Modem users who are currently using 22.8 and 33.6 modems often ask why they should buy a 56K modem, when their computer says that the modem is  “connected at 57600” or “connected at 115200”. This is a common misunderstanding of what the reported connect speed means. These speeds are the DTE (Data Terminal Equipment) speed, which is the speed of the connection between your PC and your modem. The DCE (Data Communications Equipment) speed is the bottleneck. The DCE speed is the speed between your modem and the other modem you connect to over the telephone line. Prior to 56K modems, the best speed you could obtain between two modems was 33600 bits per second. Now, with 56K technology, rates approach 50000 bits per second.

Asymmetric Data:

The V.90 standard calls for ‘asymmetric’ data rates, just as both K56flex and X2 did before standards were developed. This means that the send and receive data speeds are different when you connect in V.90 mode. Fortunately, high speed (up to 54Kbps) can be realized in the downstream direction, which is fine since this is where the bulk of the data is when you are downloading graphics and large files from the internet through your modem. The upstream direction is limited to 33.6Kbps, which is barely acceptable, but since most of the data users send are their mouse click commands, which do not require much data to be transmitted.

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