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Bitswapping

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kezzaman:
Hi guys,

Wondered, if there's alot of bitswapping on a line does it indicate that there might be an issue?
and does all that swapping affect latency, like are packets having to wait while bits are being swapped, or am i just not getting what bitswapping is about?  :D

burakkucat:

--- Quote --- . . . or am i just not getting what bitswapping is about?  :D

--- End quote ---

Possibly.  ;)

Kitz has a very nice write-up on the subject.

snadge:
just too add. no it wont affect latency... 

as you talk of latency I suspect your a gamer? Gaming latency relies on many small packets (per second) being sent & received, this uses a fraction of your available bandwidth.

# think of your broadband connection like a multi-lane highway (many hundreds of lanes), with broadband speed (throughput) its how many cars you can get down that highway in X amount of time, dodging traffic and roadworks on the way, you can send many hundreds of cars all behind each other until all your available lanes are full, and however many get down that highway in X amount of time is how fast it is... now with Latency its how quick one single car get down the highway and back on its own - so when your gaming its like a small convoy of cars all running in a line one after the other down just a couple lanes on this wide open highway, if traffic becomes too much on this highway then it can affect each cars finish time (response time) , where as how fast you can download is like sending every car you have until all lanes are full - i think thats a good metaphor... :) - full download speed is congesting your highway to get as many cars through as poss and latency is just a small trickle of cars going through.

Anyway, like I say Bit-Swapping is normal and will not affect your latency, well, unless you had a very long line with a really slow & noisey connection and the bits constantly being swapped consisted of a large percentage of all available bits/tones, and the router cpu was slow at swapping them?? ..perhaps anyway, maybe someone can clarify that? :) - but as far as Im aware it will not

kitz:
Good analogy there snadge with the car lanes :)

Latency is how long it takes a single packet of data to reach from point A to point B.  Latency should remain the same regardless of your adsl speed.  eg someone on a 512kbps connection could very well have exactly the same latency as someone on a 24Mbps connection.

adsl works by opening up lots of different channels (lanes) and allowing more data packets to traverse at the same time which is what increases the bandwidth speed.  Think of a hosepipe.. it takes the same time for a drop of water (data packet) to reach the tap to the end of the hose, but if you have a wider pipe then more water (datapackets) can pass through the hose at the same time.

>> all that swapping affect latency,

No, bit swapping makes sure that the maximum databits can pass through on each channel (lane) and if one channel cant handle x no of bits it swaps them to another channel if that has any spare.  kinda like lane hopping..  except that your router is constantly monitoring the bit allocation and is in advance thinking which traffic (bits) to send down which lanes (channels).   It would be more like a policeman directing traffic to the best route.

Interleaving and error correction can affect latency though.   This is because of 1) the slight extra time whilst data is interleaved by the router and reassembled at the other end  2) Error correction carries redundant data - therefore less useful data per transmit (speed)..  and of course the time taken by the routers at both ends to code/decode the data.

>> unless you had a very long line with a really slow & noisey connection and the bits constantly being swapped consisted of a large percentage of all available bits/tones, and the router cpu was slow at swapping them?? .... maybe someone can clarify that

Correct, bit swapping only works to a certain extent.. if the line becomes too noisy, then theres not enough 'spare' for bits to be swapped to... and data may have to be retransmitted...  and yes lots of bitswapping can cause a router cpu to work hard.

kezzaman:
Thx guys  :)

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