Voice over IP - performance
Bender, Andrew
abender at taqua.com
Thu Feb 13 16:54:34 UTC 2003
Don't forget that the signaling agents that drive the DSPs also contribute to load on the host / control CPU.
We have found that this can be a very willing consumer of utilization on the platforms under discussion... folks with super low hold calls would be the ones likely to be challenged by this; particuarly with those boxes that still have the 4500-class processor in them.
Regards,
Andrew
taqua.com
> -----Original Message-----
> From: Mathew Lodge [mailto:Mathew at CPlane.com]
> Sent: Wednesday, February 12, 2003 6:46 PM
> To: Charles Youse; Bill Woodcock
> Cc: nanog at nanog.org
> Subject: RE: Voice over IP - performance
>
>
>
> At 03:23 PM 2/12/2003 -0500, Charles Youse wrote:
> >I'm assuming in the case of, e.g., a 2650 + dual T-1 PRI
> interface can
> >actually encode/decode 48 simultaneous g729a voice streams without
> >issues? Any idea what the CPU utilisation is - or is this
> handled in
> >separate DSPs in the voice network module itself?
>
> On these particular Cisco boxes, the DSP does the all audio
> filtering,
> CODEC functions, echo cancellation, jitter buffering &
> adjustment, silence
> suppression (AKA voice activity detection, if you turned it
> on), and also
> prepends the RTP and IP headers. The router CPU just has to
> forward the
> packet that's generated by the DSP.
>
> Router CPU utilization is therefore a function of the number
> of packets per
> second that the voice card generates and the size of each
> packet, plus
> signaling overhead. The packet size and rate depend on the
> CODEC itself
> (higher compression CODECs generate smaller packets), the
> sample size (20ms
> is the Cisco default, reducing or increasing it makes the
> packets smaller
> or larger and the packet rate higher or lower, respectively),
> and whether
> voice activity detection is on (roughly halves the packet rate).
>
> If you leave the default settings in place (no VAD, 20ms
> sample size),
> you'll be OK with any of the CODECs.
>
> Mathew.
>
>
> >C.
> >
> >-----Original Message-----
> >From: Bill Woodcock [mailto:woody at pch.net]
> >Sent: Wednesday, February 12, 2003 2:43 PM
> >To: Charles Youse
> >Cc: nanog at nanog.org
> >Subject: Re: Voice over IP - performance
> >
> >
> > > Does anyone have any real-world figures for VoIP
> performance on
> > > various platforms? In other words, how many calls
> can an otherwise
> > > unused e.g., Cisco 2600 be expected to handle if it's
> the conversion
> > > point from trunked voice calls to IP. Some rough numbers for
> > > different codecs on different hardware would be very
> useful. Most
> > > specifically I'm interested in Cisco router platforms
> but other
> > > vendor stats would be appreciated as well.
> >
> >Actually I just ran the dollars-per-simultaneous-call numbers for
> >different models for some friends. I'll append it.
> Basically, if you run
> >g711, you're limited by the number of PRI channels on the
> box. If you run
> >g729a, you're limited by the number of DSPs you can fit in
> the box. The
> >numbers I ran were assuming g729a.
> >
> > -Bill
> >
> >
> >
> > Cost
> > per
> >Package which can handle 23 simultaneous calls: call
> >CISCO1760 10/100 Modular Router $1,595
> >VWIC-1MFT-T1 1-Port RJ-48 Multiflex T1 $1,300
> >PVDM-256K-12 3-DSP Module (9 calls) $1,200
> >PVDM-256K-20HD 5-DSP Module (15 calls) $4,000
> >Total $8,095 $352
> >
> >Different package which can handle 23 simultaneous calls:
> >CISCO2650 10/100 Modular Router $3,295
> >NM-HDV-1T1-24E Single-Port T1 Voice NM $9,100
> >Total $12,395 $539
> >
> >Package which can handle 45 simultaneous calls:
> >CISCO2650 10/100 Modular Router $3,295
> >NM-HDV-2T1-48 Dual-Port T1 Voice NM $9,800
> >Total $13,095 $291
> >
> >Package which can handle 46 simultaneous calls:
> >CISCO2650 10/100 Modular Router $3,295
> >NM-HDV-2T1-48 Dual-Port T1 Voice NM $9,800
> >PVDM-256K-20HD 5-DSP Module (15 calls) $4,000
> >Total $17,095 $372
> >
> >Upgradeable package which can handle 46 simultaneous calls:
> >AS535-2T1-48-AC-V AS5350-V/2T1 $18,900 $411
> >
> >Package which can handle 92 simultaneous calls:
> >AS535-4T1-96-AC-V AS5350-V/4T1 $33,600 $366
> >
> >Package which can handle 184 simultaneous calls:
> >AS535-8T1-192-AC-V AS5350-V/8T1 $58,700 $319
> >
> >Upgradeable package which can handle 184 simultaneous calls:
> >AS54HPX-8T1-192AC AS5400HPX/8T1 $65,500 $356
> >
> >Package which can handle 644 simultaneous calls:
> >AS54HPX-CT3-648AC AS5400HPX/CT3 $170,300 $265
>
>
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