asterisk users - May 2004 - "Glare" condition - How well does asterisk handle?

Hi-

I have an upcoming application that requires use of PRI channels that are
primarily used for high-volume incoming traffic, but that are to be used for
outbound calling as well.  Of course, one option is to have dedicated
outbound channels reserved, but this is an inefficient use of channel
resources.

Normally PBX's are designed to have the CPE yield to an incoming call if a
particular channel is seized by both ends at the same time (a condition
known as "glare"), but I'm wondering if anyone has real-world
experience
with asterisk to say how well this is handled.

Thanks
Scott Stingel
 
Scott M. Stingel
President,
Emerging Voice Technology, Inc.
Palo Alto California & London England
www.evtmedia.com

On Tue, 2004-05-25 at 13:53, Scott Stingel wrote:
> Hi-
> 
> I have an upcoming application that requires use of PRI channels that are
> primarily used for high-volume incoming traffic, but that are to be used
for
> outbound calling as well.  Of course, one option is to have dedicated
> outbound channels reserved, but this is an inefficient use of channel
> resources.
> 
> Normally PBX's are designed to have the CPE yield to an incoming call
if a
> particular channel is seized by both ends at the same time (a condition
> known as "glare"), but I'm wondering if anyone has real-world
experience
> with asterisk to say how well this is handled.
While I may be wrong, I don't think "glare" happens on PRI. The
difference being that the call isn't sent over a channel until there had
been communications on the D channel. This means a send and a receive.
"Glare" would happen on a channelized T1 where it is possible for each
end to try and seize the channel at the same time, since there isn't any
out of band communications.
-- 
Steven Critchfield  <critch@basesys.com>

Hi Scott,

SS> Normally PBX's are designed to have the CPE yield to an incoming
SS> call if a particular channel is seized by both ends at the same
SS> time (a condition known as "glare"), but I'm wondering if
anyone
SS> has real-world experience with asterisk to say how well this is
SS> handled.

Earlier this year I had experience of this scenario in a UK carrier and in
the end I opted for split working with the top 10 channels of the PRI
dedicated for outbound traffic. Admittedly the platform may have been a
little under specified for the job (E100P installed in an HP 1U PIII 750MHz
Rack Server) but I was surprised that it could not cope with the contention
on a single E1. The symptoms were loss of channels and excessive alarms from
the public switch during peak traffic resulting in the need to reset the PRI
from the public switch console and a quick 'init 6' for the * machine.

The problem was captured on an MPA, I'm hoping to find a copy of the trace
to share with the list. From memory it appeared that * stopped responding to
some messages from the switch which left channels in an unknown state. The
CPU was occasionally busy so perhaps the poor signalling was related to CPU
load and timing constraints.

I'll post the trace when it surfaces...

HTH

Darren
--
Comgate
Telco>Internet<Broadcast
Tel: +44(0)700 COMGATE

-----Original Message-----
From: asterisk-users-admin@lists.digium.com
[mailto:asterisk-users-admin@lists.digium.com]On Behalf Of Scott Stingel
Sent: 25 May 2004 19:54
To: asterisk-users@lists.digium.com
Subject: [Asterisk-Users] "Glare" condition - How well does asterisk
handle?


Hi-

I have an upcoming application that requires use of PRI channels that are
primarily used for high-volume incoming traffic, but that are to be used for
outbound calling as well.  Of course, one option is to have dedicated
outbound channels reserved, but this is an inefficient use of channel
resources.

Normally PBX's are designed to have the CPE yield to an incoming call if a
particular channel is seized by both ends at the same time (a condition
known as "glare"), but I'm wondering if anyone has real-world
experience
with asterisk to say how well this is handled.

Thanks
Scott Stingel

Scott M. Stingel
President,
Emerging Voice Technology, Inc.
Palo Alto California & London England
www.evtmedia.com


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Scott Stingel wrote:
> Hi-
> 
> I have an upcoming application that requires use of PRI channels that are
> primarily used for high-volume incoming traffic, but that are to be used
for
> outbound calling as well.  Of course, one option is to have dedicated
> outbound channels reserved, but this is an inefficient use of channel
> resources.
> 
> Normally PBX's are designed to have the CPE yield to an incoming call
if a
> particular channel is seized by both ends at the same time (a condition
> known as "glare"), but I'm wondering if anyone has real-world
experience
> with asterisk to say how well this is handled.
PRIs do not experience glare.

A little more research on this:

I found a Dialogic flow diagram that seems to indicate what happens when
glare occurs on an IDSN line.  So it looks like perhaps it can occur?
Re-phrasing my original question:  "Does the asterisk PRI driver properly
re-try an outgoing call that is dropped due to a glare condition?" 

Note the chart entitled "Glare (call collision)":
http://resource.intel.com/telecom/support/releases/winnt/sr60cpci/onldoc/htm
lfiles/gcisdn/app_isdn.htm

Regards...


Scott M. Stingel
President,
Emerging Voice Technology, Inc.
Palo Alto California & London England
www.evtmedia.com 

-----Original Message-----
From: asterisk-users-admin@lists.digium.com
[mailto:asterisk-users-admin@lists.digium.com] On Behalf Of Scott Stingel
Sent: Tuesday, May 25, 2004 11:54 AM
To: asterisk-users@lists.digium.com
Subject: [Asterisk-Users] "Glare" condition - How well does asterisk
handle?

Hi-

I have an upcoming application that requires use of PRI channels that are
primarily used for high-volume incoming traffic, but that are to be used for
outbound calling as well.  Of course, one option is to have dedicated
outbound channels reserved, but this is an inefficient use of channel
resources.

Normally PBX's are designed to have the CPE yield to an incoming call if a
particular channel is seized by both ends at the same time (a condition
known as "glare"), but I'm wondering if anyone has real-world
experience
with asterisk to say how well this is handled.

Thanks
Scott Stingel
 
Scott M. Stingel
President,
Emerging Voice Technology, Inc.
Palo Alto California & London England
www.evtmedia.com 


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Well that certainly seems to say there can be glare, but a read of the
q.931 protocal stack seems to suport that it's not possible.  If I were
a leser man, I could say a snide remark about that if you click the home
icon, it is apparent the document is referring to a driver and s/w for
the Microsoft operating system to implement the PRI protocol ;)

W. Kevin Hunt
CCIE #11841
www.huntbrothers.com
 
-----Original Message-----
From: asterisk-users-admin@lists.digium.com
[mailto:asterisk-users-admin@lists.digium.com] On Behalf Of Scott
Stingel
Sent: Tuesday, May 25, 2004 9:44 PM
To: asterisk-users@lists.digium.com
Subject: RE: [Asterisk-Users] "Glare" condition - How well does
asterisk
handle?

A little more research on this:

I found a Dialogic flow diagram that seems to indicate what happens when
glare occurs on an IDSN line.  So it looks like perhaps it can occur?
Re-phrasing my original question:  "Does the asterisk PRI driver
properly re-try an outgoing call that is dropped due to a glare
condition?" 

Note the chart entitled "Glare (call collision)":
http://resource.intel.com/telecom/support/releases/winnt/sr60cpci/onldoc
/htm
lfiles/gcisdn/app_isdn.htm

Regards...


Scott M. Stingel
President,
Emerging Voice Technology, Inc.
Palo Alto California & London England
www.evtmedia.com 

-----Original Message-----
From: asterisk-users-admin@lists.digium.com
[mailto:asterisk-users-admin@lists.digium.com] On Behalf Of Scott
Stingel
Sent: Tuesday, May 25, 2004 11:54 AM
To: asterisk-users@lists.digium.com
Subject: [Asterisk-Users] "Glare" condition - How well does asterisk
handle?

Hi-

I have an upcoming application that requires use of PRI channels that
are primarily used for high-volume incoming traffic, but that are to be
used for outbound calling as well.  Of course, one option is to have
dedicated outbound channels reserved, but this is an inefficient use of
channel resources.

Normally PBX's are designed to have the CPE yield to an incoming call if
a particular channel is seized by both ends at the same time (a
condition known as "glare"), but I'm wondering if anyone has
real-world
experience with asterisk to say how well this is handled.

Thanks
Scott Stingel
 
Scott M. Stingel
President,
Emerging Voice Technology, Inc.
Palo Alto California & London England
www.evtmedia.com 


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http://lists.digium.com/mailman/listinfo/asterisk-users
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> PRIs do not experience glare.
Never say Never... pigs can fly too!

bkw
PS: Pack a pig in a box and next day fedex it across the country... they
fly! :P

"W. Kevin Hunt" <Kevin@hbcorporate.com> wrote:
__________
>Well that certainly seems to say there can be glare, but a read of the
>q.931 protocal stack seems to suport that it's not possible.  If I were
>a leser man, I could say a snide remark about that if you click the home
>icon, it is apparent the document is referring to a driver and s/w for
>the Microsoft operating system to implement the PRI protocol ;)
Which would be unfair, because 
Dialogic implement the pri protocols
on the card, with a 486 and a heap of
dsps on the one I have. Microsoft don't get a look in.
This is a blessing and a curse.
The good points are that they can get the card authorised for various telcos
without reference to the os or cpu. Also it means that as a developer you are
isolated from the
os (somewhat). Also you can use it in
an underpowered box, my E1 card is in a 180Mhz pentium pro!
The downside is that the card is big and runs _hot_. Also Asterisk doesnt 
like it because it wants to get closer to the metal.

On which subject, has anyone else 
got time to work with me on a chan_dialogicGC ? It looks do-able but I am
ignorant of how asterisk does threading.
>
>W. Kevin Hunt
>CCIE #11841
>www.huntbrothers.com

On Wed, 2004-05-26 at 14:23, tpanton@attglobal.net
wrote:
> On which subject, has anyone else 
> got time to work with me on a chan_dialogicGC ? It looks do-able but I am
ignorant of how asterisk does threading.
Do you have GPL drivers for the dialogic card? Follow previous comments
about licensing. There is a dialogic driver from Digium for a cost.

-- 
Steven Critchfield <critch@basesys.com>