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What is the maximum download speed in a 2Mbps broadband. Is there any relationship between the bandwidth and downloading speed?

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This sound suspiciously like a homework question –  Mark Henderson Jul 16 '09 at 21:14

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up vote 6 down vote accepted

Rule of thumb: Divide your mega-bit speed by 8 to achieve the theoretical maximum download speed in bytes. E.g. 8Mbps connection = 1MBps, 4Mbps = 512KBps so on and so forth.

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use large 'B' to denote Byte. It's the standard. 'b' is bit. So 8Mbps=1Mb/s is just as wrong as saying 8 pies = 1 pie –  Thomas Jul 16 '09 at 6:58
    
References for that: wikipedia on Bit references IEEE 1541 Standard (2002) and on Byte it points to the same standard. –  Thomas Jul 16 '09 at 7:04
    
both the p and the slash mean "per". –  Thomas Jul 16 '09 at 7:04
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It's no "rule of thumb" - there are 8 bits in a byte, fact. 8 megabits is therefore 1 megabyte. In terms of actual achieved transfer rate given a (for example) 8 Mbps net connection, you will lose a little to overheads in the various OSI layers. –  tomfanning Jul 28 '09 at 8:56
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I acutally use 10:1 to acount for various overheads. So, 2Mbit (simply said) 200kbyte / second. –  TomTom May 10 '10 at 10:32

Download speed also depends on server which is serving your requests. Having 2mbps (which is 2 mega bits per second, equivalent to 256 kilo bytes per second) speed does not mean you can download files from Internet at 2mbps always. Also usually when provider says 2mbps, the actual speed one gets is less than that.

As far as relation ship between bandwidth and download speed is concerned

Download speed <= Bandwidth

That is, you cant download at speeds greater than your bandwidth.

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Also, most providers measurements in bit rate includes the entire frame, where most applications will report on application throughput. This is part of the reason you appear to get less than advertised speed. –  Kevin Nisbet Jul 16 '09 at 5:21
    
Not to mention distance to local hub, quality of cable, type of cable (copper/fiber, telephone/cable) type of shielding and amount of EMI, and about 1000 other conditions that can have a non-negligible effect. –  Unkwntech Jul 16 '09 at 5:26
    
In addition, most broadband services are contended, i.e. the available bandwidth is shared between customers both at the Telco switch and network and within the ISP network. This may have little effect at some times and locations but can be noticeable at peak usage times. –  mas Jul 16 '09 at 6:25

2Mbpm is 2,000,000 bits per second or 250,000 bytes per second (divide by 8), or just under 245 Kbytes per second (divide by 1024).

This does not include overheads of the protocols used at the various levels of the network stack. If I remember rightly, when I had a connection rated at 2Mbit the best sustained rate I saw from applications that I trusted to give accurate readings was a little over 230Kbytes/sec.

Also note though that the rate you get for any given transfer will depend on many other things like the capacities of the service(s) you are talking to, the bandwidth on each hop between you and them, and any traffic shaping your ISP applies. Also if your upstream flow is close to saturation this can severely throttle your downstream rate (a common problem reported by new P2P users).

And if your 2Mbit rate is actually "up to 2Mbit" (i.e. it is a rate adaptive DSL service rather than a fixed speed service) then the quality and length of the line that the link is provided over will have a large effect (my "up to 24Mbit" line is usually around 11mbit) and even "fixed speed" DSL services can be noticeably affected by local interference anywhere along the line on particular frequencies.

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1024-based units.... So you haven't gone "ISO" yet? (kibibytes and all that) :-) –  Thomas Jul 16 '09 at 7:06
    
Old habits die hard! That and kibibytes and mebibytes sound daft when spoken... I usually just make an effort to be clear which I mean when there is room for ambiguity. –  David Spillett Jul 16 '09 at 12:04
    
Actually, for transfer rates, we don't use 1024-based units, it's 1000 based. 1024 based was more use for things that are actually arranged in powers of 2 like memory, and disk sectors rather than in things like networks, that have no physical reasons for using weird bases. –  Kibbee Sep 14 '09 at 1:29

A better rule of thumb is to divide connection speed by 10, because this tends to compensate for bits lots for frames and packet headers. You should also bear in mind that some sites will only send you data at a certain speed, to prevent them using up too much of their bandwidth on one person. Using a download manager that uses multiple threads might help, or something like Bittorrent with a good seed/leech ratio.

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