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
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