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RE: Voice over IP - performance

  • From: Mathew Lodge
  • Date: Wed Feb 12 18:52:01 2003

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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