[Bloat] RED against bufferbloat

[MUSCARIELLO Luca IMT/OLN]

On 02/25/2015 05:09 PM, Mikael Abrahamsson wrote:
> On Wed, 25 Feb 2015, MUSCARIELLO Luca IMT/OLN wrote:
>
>> Doing FQ in silicon is easy. It must be very easy as I did myself in 
>> a MIPS Ikanos Vx185 chipset and I am not an hardware expert. This was 
>> for a CPE with a 5X1Gbps ports.
>
> I guess we have different definitions on what "silicon" is. Mine is 
> "ASIC". If it has a MIPS CPU (and the CPU does forwarding), then it's 
> not "silicon", then it's done in CPU.

MIPS based board with a central unit and several programmable asics as 
accelerators.
Fast path is not managed by the central unit.

>
> I keep hearing from vendors that queues are expensive. The smallest FQ 
> implementation that seems to be reasonable has 32 queues. Let's say we 
> have 5k customers per port on a BNG, that equates to 160k queues.
>
> Compare that to an efficient active ethernet p-t-p ETTH deployment 
> without BNG at all, where the access L2 switch is the one doing 
> policing. What would be the cost to equip this device with FQ per port?
>
>> If you go a little deeper in the network and you pick an OLT you won't
>
> I don't do PON.
>
>> find much intelligence. A little deeper and in a local aggregation 
>> router (all vendors) you'll find what you would need to implement FQ. A
>
> If it's a BNG yes. These linecards with hundreds of thousands of 
> queues are a lot more expensive than a linecard without these queues. 
> Usually today there are 3-4 queues per customer, now we want to expand 
> this to 32 or more. What is the cost increase for this?

Yes I have BNG in mind. Downstream equipment has not enough resources on 
a per user basis.
However I do not think that static per-flow queues is the right 
implementation for FQ.
That requires a lot of resources just for instantiation and if the 
hardware polls the
queues the cost can be very high for the user fanout and the rates we 
are considering here.

A single FQ instantiation has to consume no more memory than a single 
FIFO instantiation.
Per-flow queues should be managed as virtual queues. On a per customer 
basis.

>
> If you put a BNG in there with lots of intelligence then the cost of 
> adding the FQ machinery might not be too bad. If you don't have the 
> BNG at all, what is the cost then? I still believe it will be cheaper 
> to try to do this in the CPE.

I think this should also be done in the CPE but not in ingress for the 
downlink. If that's what you meant.
Only in egress for the uplink.

>
>> Some "positive" view: access with Gbps (up to 1Gbps) with a range of 
>> RTT (1ms to 100ms) will need smarter mechanisms in the equipment as 
>> inefficiencies will be crystal clear and business consequences will 
>> be substantially different.
>
> Please elaborate. I'd say FIFO is less harmful at these speeds because 
> of TCP inefficiencies meaning most end systems won't come up in high 
> enough transfer rates to saturate that part of the network. Now the 
> bottle neck will move elsewhere.

I assume you want TCP to be able to do 1Gbps if this is what you sell to 
the customers.

Also if you sell 1Gbps, you might want to do shaping instead of policing 
in the BNG
because the BDP of a 1Gbps flow can be pretty high depending on the RTT,
and downstream equipment (OLT, switch, DSLAM...) can have much smaller
queues than what you have in a BNG.

That is where inefficiencies come from. If in addition you have a mix of 
applications
in this customer queue than you'll need FQ because the traffic mix can 
be very heterogeneous
and flow isolation bec necessary.
omes