Re: [codec] #22: Memory Usage?

["codec issue tracker" <[e-mail]>]

#22: Memory Usage?
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 Reporter:  hoene@…                 |       Owner:     
     Type:  defect                  |      Status:  new
 Priority:  major                   |   Milestone:     
Component:  requirements            |     Version:     
 Severity:  -                       |    Keywords:     
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Comment(by hoene@…):

 [Raymond]: (IPend-to-transcoding_gateway-to-PSTNend), the transcoding
 gateway, or VoIP gateway, often has to encode and decode thousands of
 voice channels in a single box, so not only the computational complexity,
 but also the per-instance RAM size requirement of the codec become very
 important for achieving high channel density in the gateway.

 [JM]: Agreed here, although I would say that per-instance RAM -- as long
 as it's reasonable -- is probably a bit less important than complexity.

 [Raymond]: per-instance RAM is definitely not unimportant.  I have worked
 in a team that designed high-density VoIP gateways, and I know people did
 all kinds of tricks to reduce the RAM usage as much as possible because of
 the high cost of the external high-speed SRAM used by high-speed DSPs in
 such gateways.
 Currently, high-density VoIP gateways can have several tens of thousands
 of voice channels per box or per equipment rack.  If codec A uses X kbytes
 more per-instance RAM than codec B, than implementing codec A rather than
 codec B in all channels will require X * (number of channels) more kbytes
 of high-speed SRAM, which can be a substantial additional cost.
 Similarly, if codec A requires a substantially higher DSP MHz than codec
 B, then implementing codec A in all channels will mean that more high-
 speed DSP chips need to be used to maintain the same number of channels.
 That's additional cost.  Actually, the more likely scenario is that the
 number of DSP chips has already maxed out due to board space or heat
 dissipation constraint, then the gateway can only support a substantially
 smaller number of voice channels when compared with using codec B.
 Consequently, the channel density per box or per rack goes down
 substantially, and the per-channel deployment cost goes up substantially.
 Thus, even if implementing codec A or codec B makes no practical
 difference in a PC, it can make a very real and substantial cost
 difference in VoIP gateways.

-- 
Ticket URL: <http://trac.tools.ietf.org/wg/codec/trac/ticket/22#comment:1>
codec <http://tools.ietf.org/codec/>