On Wed, 12 Aug 2015, Juliusz Chroboczek wrote:
I think Alia was speaking about parallel WiFi links. That's pretty
common -- double-band routers are slowly becoming the norm.
I don't think she was speaking for wifi links, I think she was speaking of
any kind of link.
If you load-share between the two links, the resulting latency of the
stream will be the largest of the two latencies (assuming in-order
delivery). The packet loss will be the average, which is larger than
the packet loss of the link with the lower packet loss of the two.
Plus there's the interference issues.
When you say ECMP to a routing person, it's generally something that is
set up by an IGP or using BGP. It's something that has the same metric,
and the FIB then starts load sharing over these (equal IGP cost) links. In
core or access networks networks this is typically done by hashing 5 tuple
information so each flow gets in-order delivery, but if you have multiple
flows (which you usually have on these kinds of links, many tens of
thousands of them), you can use most of the available capacity.
I believe this is what Alia was refering to.
I'm not saying it cannot be done, I'm just saying that we mustn't do it
until we fully understand the tradeoffs.
if I hook up two wired GIGE between two homenet routers, why not use it?
Agreed. But even if you have a NAS that can handle more than a Gbit/s
sustained, this use case is rather marginal.
Well, if you have a NAS that supports two NICs, you can for instance use
LACP to bond them together and then when you have multiple clients, the
router can hash each L4 session to (hopefully) a separate link in the
homenet if they're several routers away.
So as I said before: it's desireable for me that the homenet routing
protocol supports ECMP and can take use parallel links between devices in
simultaneous use.
2 or 4 GE links is going to be cheaper than a single 10GE link for quite
some time. While some might believe this is pure SciFi that a home would
need this kind of capacity, I'd say in 5-10 years (which is when I think
homenet really should have taken off), this is going to be a lot more
common. So ruling out ECMP right now seems short sighted.
--
Mikael Abrahamsson email: [email protected]
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