Avder - DSL Interleaving over PPPoA (NZ doesn't have PPPoE DSL) is a method of reducing the number of "Noise Disconnects":
Q: What is interleaving? Is it better on or off?
A: Interleaving is an extra level of error correction.
It makes sure that all ATM packets that come from the DSLAM to you and from you to the DSLAM are not corrupted, and if any are, it forces a re-send.
Having Interleaving off may introduce packet loss depending upon how clean your line is. If it is a rather clean line, packet loss may be as low as 3%, but if it is a dirty line, packet loss may be as high as 50%.
Having Interleaving off does have its advantages though. It lowers your ping times for instance, and also makes playing in multiplayer games more enjoyable since multiplayer games don't require that all packets reach the destination.
The stupid thing about NZ Telecom's decision to use Interleaving (and the maximum 48ms) is that the phone line system in NZ is "World Class and one of the world's most up to date systems" (According to the CIA report on NZ's telecommunications capabilities!) and therefore Interleaving is NOT required AT ALL.
Telecoms can use Interleaving to increase the distance from the exchange they will allow customers to have DSL. However, NZ Telecom has a flat policy: more then 5Km from the exchange = NO DSL. (How facked is that? I am 3.9 km from the exchange and handshake at 6.752 Mb/s and 697Kb/s upstream!)
So - it's not needed because of the quality of our lines, and it isn't used because they won't signup peeps beyond 5km! IDIOTS. *sigh*
I know of several telecom employees who've had their interleaving reduced to zero (i.e. 0ms first hop to the DSLAM!) and they NEVER get disconnected and don;t have lossy connects!
The absolutely crazy thing is that Interleaving is a software setting which can be changed easily (5 seconds or so!) but Telecom REFUSE POINT BLANK to even DISCUSS Interleaving with ANYONE.
There was a petition that got over 5000 signatures last year. Telecom just ignored it.