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RE: Voice over IP - performance
From: "Bender, Andrew" <abender () taqua com>
Date: Thu, 13 Feb 2003 11:54:34 -0500


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




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