[Asterisk-Dev] 答复: Asterisk-Dev digest, Vol 1 #740 - 2 msgs

Thu Jul 8 00:08:33 MST 2004

Dear all,

I      can't    understand lock_get() function in the memory management.
who can tell me some information?=20

Thanks,
Sky Wang=20
Tel:86-0510-8080888, ext:15310

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=D6=F7=CC=E2: Asterisk-Dev digest, Vol 1 #740 - 2 msgs

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Today's Topics:

   1. RE: Re[2]: [Asterisk-Dev] channel driver sample (Ben Miller)
   2. Re: proposal for channel driver (Michael Sandee)

--__--__--

Message: 1
Subject: RE: Re[2]: [Asterisk-Dev] channel driver sample
Date: Fri, 2 Jul 2004 11:25:20 -0500
From: "Ben Miller" <bgmiller at nframe.com>
To: <asterisk-dev at lists.digium.com>
Reply-To: asterisk-dev at lists.digium.com

Are you talking about creating stand alone DSP resource board that =
Asterisk can use?  Or are you talking about other network termination =
board?

-----Original Message-----
From: asterisk-dev-admin at lists.digium.com
[mailto:asterisk-dev-admin at lists.digium.com] On Behalf Of Miroslav =
Nachev
Sent: Thursday, July 01, 2004 11:20 AM
To: Tilghman Lesher
Subject: Re[2]: [Asterisk-Dev] channel driver sample

Hi,

I think that the best and cheap solution is one PCI Card with one or =
more DSP chips. For example I plan to design and develop one board using =
TI DSP TNETV2021, TNETV2510 and TNETV2840. Using this DSP we can have =
from 8 up to 64 channels per low profile board. This will be very =
powerful for Conference Systems and other applications.
If somebody would like to help me with the Linux drivers and the Codecs =
firmware will be very helpful for me.

--=3D20
Best regards,
 Miroslav                            mailto:miro at space-comm.com

=3D20
Thursday, July 1, 2004, 6:15:48 PM, you wrote:

TL> On Wednesday 30 June 2004 17:37, mark spowage wrote:
>> shoving a dsp on a pci bus can easily take care of a zillon fax
calls.
>> a trivial way to do this is via the voicepump chips and a pci chip.

TL> And it's also opposite of the code philosophy of Asterisk -- build
inexpensive
TL> hardware devices and do the programming in software.

>> why  channel driver development is not an active issue  ? arent there =

>> any h/w hackers in the crowd ?

TL> Because most people are satisfied with the existing channel drivers?
And
TL> those that aren't are already working on improving them.

>> well we all have some hidden agenda's i guess

TL> Like why you want to build channel drivers in (ugh!) Java?

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--__--__--

Message: 2
Date: Fri, 02 Jul 2004 15:44:15 +0200
From: Michael Sandee <ms at zeelandnet.nl>
To: asterisk-dev at lists.digium.com
Subject: Re: [Asterisk-Dev] proposal for channel driver
Reply-To: asterisk-dev at lists.digium.com

>
>
>> e. add on aes for security ?
>
>
> This could be added to IAX2. However, it will add significant latency=20
> if you wish to be able to cope with dropped packets vaguely elegantly.
> AES is a stream cipher. If you miss a chunk, it will invalidate the=20
> rest of the decrypt. Of course, you can encrypt each packet=20
> individually (not the audio stream itself) but that would seriously=20
> weaken the encryption. This is relative - it'd probably good enough=20
> anyway. :)

This is wrong, AES is not a stream cipher. AES can work on single byte
streams... but it can also work as a block cipher (more secure
actually). You will have to encrypt each IAX packet as a whole... and
you miss some point in network layering regarding the added latency.

ECB will have no problem in recovering from packet drops, but is less
secure. CBC and CTR for example, with the last one used in SRTP iirc,
have problems with recovering and will take 1 block (128bits in AES) to
recover. The latency is only a problem for the reliably transmitted
packets, and noone cares about a few extra ms there... With CBC/CTR
drops will be twice more audible since two voice frames are dropped
instead of one...

I will pick up this occasion again to note that using a fixed crypto
cipher such as AES in CTR mode is extremely retarded... if someone
manages to crack AES in general (or just CTR) in a while, you will have
to redistribute the entire protocol stack in all devices... while it
could be just a matter of "disallow=3Daes-ctr" with a decent
implementation. (Lets not discuss the likelyhood of this, just the
possibility... and learn from the... "You HAVE to support DES" nonsense
in IPSec)

Regards,

Michael Sandee

--__--__--

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