RE: Voice over IP - performance

["Bender, Andrew" <abender () taqua com>]

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 () CPlane com]
> Sent: Wednesday, February 12, 2003 6:46 PM
> To: Charles Youse; Bill Woodcock
> Cc: nanog () 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 () pch net]
> > Sent: Wednesday, February 12, 2003 2:43 PM
> > To: Charles Youse
> > Cc: nanog () 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