[j-nsp] M10i FPC PIC Throughput Questions
Christopher E. Brown
chris.brown at acsalaska.net
Tue Feb 26 16:05:05 EST 2013
If you oversubscribe the bus you oversubscribe the bus. Traffic load
v.s. average packet size v.s. level of oversubscrip v.s. burstiness will
determine loss potential.
On 2/26/13 11:59 AM, Matt Bentley wrote:
> Thanks very much. So confirm, there is nothing that says one PIC will
> get a certain amount at minimum right?
>
> What determines what is dropped when there is contention on the bus?
> Are there any commands I could use to see whether a bus is/was
> congested and how much of what was dropped?
>
> On Sat, Feb 23, 2013 at 9:37 PM, Christopher E. Brown
> <chris.brown at acsalaska.net <mailto:chris.brown at acsalaska.net>> wrote:
>
>
> Bus is _shared_, with CFEB you have guaranteed 3.2Gbit shared by up to 4
> PICs, with E-CFEB is non issue single PIC limit is 1G and E-CFEB will do
> full 1G per no matter what.
>
> If you try to handle more than 3.2Gbit on a CFEB bus (X-0/X/X or
> X-1/X/X) you may see bus contention depending on packet size.
>
> Load 4xGE and maybe. Load 3xGE + 4xDS3 is pushing limit but OK.
>
> With E-CFEB, non issue.
>
> With CFEB summ the bandwith make make sure is 3200Mbit or less, and 3200
> is shared by all 4 PICs.
>
>
> On 2/23/13 6:51 PM, Matt Bentley wrote:
> > Thanks! So it would be correct to say you should NEVER see
> > oversubscription on a channelized DS3 card right? Obviously, you can
> > overdrive a single T1, but you'd never see drops due to the PIC
> itself?
> > I guess what I'm asking is whether or not the bandwidth
> availalble on a
> > FPC is allocated equally per PIC, or if everyone sort of shares it.
> >
> > On Sat, Feb 23, 2013 at 8:13 PM, Christopher E. Brown
> > <chris.brown at acsalaska.net <mailto:chris.brown at acsalaska.net>
> <mailto:chris.brown at acsalaska.net
> <mailto:chris.brown at acsalaska.net>>> wrote:
> >
> >
> > With the std cfeb after internal overhead per bus capacity is
> 3.2Gbit of
> > traffic, this is worst case minimum small packets, etc.
> >
> > Raw bus capacity is IIRC ~ 4Gbit, difference is overhead.
> >
> > Unless you are doing all small packet, actual limit is higher
> than 3.2.
> >
> > Enhanced CFEB bumps the raw bus capacity to something around
> 5Gbit, and
> > the after all overheads forwarding capacity to 4Gbit (based on
> the 1G
> > per PIC limit).
> >
> > Summ...
> >
> > CFEB
> > Up to 1Gbit per PIC, 3.2Gbit per bus _worst case small
> packet_
> >
> > E-CFEB
> > Up to 1Gbit per PIC
> >
> >
> > These figures are
> > On 2/23/13 6:01 PM, Matt Bentley wrote:
> > > OK - so there has been a lot of discussion around this that I've
> > seen, but
> > > I've searched for hours and still can't find concrete answers.
> > Can someone
> > > help?
> > >
> > > 1. Does the 3.2 Gbps throughput limitation include
> overhead? In
> > other
> > > words, Is the "raw" throughput 4 Gbps with effective
> throughput of 3.2
> > > Gbps? Or is it 3.2 Gbps of raw throughput with effective
> > throughput of 2.5
> > > Gbps?
> > > 2. Is this throughput per PIC on the FPC? So let's say I have
> > three 4x
> > > GigE IQ2 PICs and one channelized DS3 IQ PIC. Does each PIC get
> > bandwidth
> > > allocated equally between them? So is it 800 Mbps per PIC, and
> > the PICs
> > > can't "steal" bandwidth from another one?
> > > 3. Where, and based on what, is traffic dropped with Juniper
> > head of line
> > > blocking (ie where multiple high speed input interfaces try
> to go
> > out the
> > > same lower speed exit interface)?
> > >
> > > Thanks very much!
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> > --
> >
> ------------------------------------------------------------------------
> > Christopher E. Brown <chris.brown at acsalaska.net
> <mailto:chris.brown at acsalaska.net>
> > <mailto:chris.brown at acsalaska.net
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> <tel:%28907%29%20550-8393>
> > <tel:%28907%29%20550-8393>
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> > IP Engineer - ACS
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> --
> ------------------------------------------------------------------------
> Christopher E. Brown <chris.brown at acsalaska.net
> <mailto:chris.brown at acsalaska.net>> desk (907) 550-8393
> <tel:%28907%29%20550-8393>
> cell (907)
> 632-8492 <tel:%28907%29%20632-8492>
> IP Engineer - ACS
> ------------------------------------------------------------------------
>
>
--
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Christopher E. Brown <chris.brown at acsalaska.net> desk (907) 550-8393
cell (907) 632-8492
IP Engineer - ACS
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