Load Balancing

I know this one has been done to death in the past, but...

I'm curious to know what exactly Zen are "load balancing". Is it customer connections/sessions across the centrals, or what?

It is customer connections/sessions across the centrals.

OK, we're talking centrals, right - as in BT centrals? Not "gateways"?

*BUMP*

I'm not trying to be difficult or anything, I'd really like to know whether the use of the term "centrals" by Zen staff when they talk about load balancing means the BT Centrals or their (Zen's) gateways.

See this thread as well which suggests that ISPs cannot load balance centrals, only BT can do it.

I just want to be clear about whether the terms are being used correctly (or at least as I would understand them).

"I'm not trying to be difficult or anything, I'd really like to know whether the use of the term "centrals" by Zen staff when they talk about load balancing means the BT Centrals or their (Zen's) gateways."

They're the same thing. Load balancing is typically done by disconnecting a users PPP session on the home gateway which forces them to reconnect. When they reconnect they can do so to any of the ISPs gateways (providing they all accept the same realm). Simply disconnecting a bunch of users from a heavily utilised gateway spreads the load.

"See this thread as well which suggests that ISPs cannot load balance centrals, only BT can do it."

Smaller ISPs tend to have BT managed home gateways, typically Cisco 7200VXRs. Zen have their own gateways manufactured by Redback.

TT

Cheers.

I guess then in the thread I linked to previously, the others who have been discussing this would be talking about ISPs using BT managed home gateways.

Sorry Babylon 5, think i must have missed your follow up question.

TT is correct, load balancing is done by dropping users connections, they naturally reconnect across different centrals which spreads the load more evenly.

Just to be accurate, it is centrals that we kick from. Each gateway can (and does) have more than one central.

Sorry to keep on at this, but in this post it's claimed that Zen are NOT performing load balancing at all but are simply (and I quote) "...relying on the numbers game...".

So who is correct?

Its all just semantics really though, in the end it balances the load across the platform and I think it would be fair to say that a lot of ISPs refer to it this way. Calling it "Disconnecting users to evenly distribute load among the centrals" is a bit long winded and IMHO isn't as easily understandable as calling it load balancing.

Unfortunately BT do not use load balancers and users are put onto a central in round robin fashion (although I think that technically this is a very primitive form of load balancing), if you get a higher proportion of high usage end users on a single central that one could become congested while the others are at 10% load (this is an extreme example just to illustrate the point).

Also while it may not be the networking definitiion of load balancing it is definitely fair to say we are balancing the load across the platform, trying to get the utilisation of each pipe so that it is approximately equally low; as I began with it is just semantics really.

Edited by deleted (Tue 12-Jun-07 19:39:27)

Zen are forcing the load to become balanced. I just posted to the other thread, but essentially by disconnecting users (who then reconnect) Zen force the BT system to redistribute the load. BT *must* have some way of distributing the load as an ISP can have multiple pipes and gateways.

Therefore as you know that the BT system will spread the load, you disconnect users, knowing that the users you disconnect will then be 'evenly spread' over the available pipes when they reconnect.

So, say you have 2 pipes and 1 is at 75% capacity and one at 25%. To balance (assuming simple round robin balancing) you kick 50% of the users on pipe 1. That reduces both pipes to 25%, but with a whole bunch of users about to reconnect. Those users will be evenly spread across both pipes (in this example bringing both pipes to 50%).

Of course, it gets more complicated with more pipes and gateways, but it *is* load balancing.

Ruz