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This is the support site for Andrews & Arnold Ltd, a UK Internet provider. Information on these pages is generally for our customers but may be useful to others, enjoy!
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There are a number of protocol layers involved in data transfer over a broadband line, each of which adds some overhead.
==Line rate==
The actual line carries data using a protocol called ADSL. This includes layers of data framing and control information which we do not have to consider. What matters is the line rate that is quoted. This is what your ADSL router will quote on its management interface as the sync rate and is what BT quote to us in line tests, etc. This is the headline line rate and it is this rate which can get up to
This rate is actually the ATM data rate - the rate at which the bits that make up the 53 byte ATM cells can carry. So
==ATM cells==
ATM cells are 53 bytes long. So at
==AAL5==
==BRAS rate==
On 20CN lines, BT also have a system whereby they rate limit traffic to one of a number of pre-set limits. This could mean as much as
==Doing the sums==
So considering the throughput of TCP on a line syncing at
24,000,
21,735,
21,254,
21,226,
20,943,
2,617,924B/s TCP payload rate
2.496MiB/s data transfer rate
8128K 7.15M
There is also a low level 135K BRAS profile which is normally an indication of a serious problem with a line. For ADSL2+ there are BRAS rates of
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