Discussion:
[Asterisk-Users] Backup Proxy & Automatic Failover
Adthrawn
2003-12-30 18:49:51 UTC
Permalink
Hi,

I read in the Asterisk Whitepaper, that you can run two cloned servers,
one as a primary, one as a backup, and have them automatically failover
to the other unit when it crashes, or when you need to restart it. The
primary application of course, would be ensuring calls can be made when
frequent updates are being handled, or when an update must be restarted
on a busy network.

The term TDM is banded around too, but from my knowledge, TDM is
trunking (probably some clever acronym relating to trunking), and in
Asterisk's case, using the IAX protocol. This leads me to the big
question;

Is there anyway of shifting the load of one Asterisk server to another
without breaking or loosing a call?

I know that with Survivable Routing (Cisco's big on this), the ISDN
interface is actually a router; so the Proxy is just used to decide the
destination and LCR functions, and then hands off to a router. This of
course, if a Proxy went down, would just prevent new calls from being
made, whilst existing calls can continue merrily - until someone
switches the Router off, or corrupts the IOS settings :-)

At least with Routers, you can configure them to load manager
effectively, but how do you backup and load manage Asterisk??

I using SIP, and will be using a bit of SCCP too, so any suggestions
would be most grateful!!

Regards,
Ad.
Steve Dolloff
2003-12-30 19:08:52 UTC
Permalink
I simply have 2 asterisk servers and have the clients point to a DNS SVR
record for their proxy. The DNS record lists the primary and secondary
with preference for the primary. This won't stop calls from being
dropped if the primary goes down if you are routing them through the
server, but it does ensure that calls placed while the primary is down
will still go through.

You could do some load management by putting multiple servers in the DNS
record and use a DNS server that supports round robin responses.

Stephen
-----Original Message-----
Sent: Tuesday, December 30, 2003 12:50 PM
Subject: [Asterisk-Users] Backup Proxy & Automatic Failover
Hi,
I read in the Asterisk Whitepaper, that you can run two cloned
servers,
one as a primary, one as a backup, and have them automatically
failover
to the other unit when it crashes, or when you need to restart it. The
primary application of course, would be ensuring calls can be made
when
frequent updates are being handled, or when an update must be
restarted
on a busy network.
The term TDM is banded around too, but from my knowledge, TDM is
trunking (probably some clever acronym relating to trunking), and in
Asterisk's case, using the IAX protocol. This leads me to the big
question;
Is there anyway of shifting the load of one Asterisk server to another
without breaking or loosing a call?
I know that with Survivable Routing (Cisco's big on this), the ISDN
interface is actually a router; so the Proxy is just used to decide
the
destination and LCR functions, and then hands off to a router. This of
course, if a Proxy went down, would just prevent new calls from being
made, whilst existing calls can continue merrily - until someone
switches the Router off, or corrupts the IOS settings :-)
At least with Routers, you can configure them to load manager
effectively, but how do you backup and load manage Asterisk??
I using SIP, and will be using a bit of SCCP too, so any suggestions
would be most grateful!!
Regards,
Ad.
_______________________________________________
Asterisk-Users mailing list
http://lists.digium.com/mailman/listinfo/asterisk-users
Olle E. Johansson
2003-12-30 22:54:39 UTC
Permalink
Post by Steve Dolloff
I simply have 2 asterisk servers and have the clients point to a DNS SVR
record for their proxy. The DNS record lists the primary and secondary
with preference for the primary. This won't stop calls from being
dropped if the primary goes down if you are routing them through the
server, but it does ensure that calls placed while the primary is down
will still go through.
You could do some load management by putting multiple servers in the DNS
record and use a DNS server that supports round robin responses.
Please note that Asterisk itself only reads the FIRST DNS SRV record.
So Asterisk can't load balance this way, when using DNS SRV for outbound calls.

I would love to fix this, if I knew how.

/O

Nicolas Bougues
2003-12-30 19:17:55 UTC
Permalink
Post by Adthrawn
Hi,
The term TDM is banded around too, but from my knowledge, TDM is
trunking (probably some clever acronym relating to trunking), and in
Asterisk's case, using the IAX protocol. This leads me to the big
question;
TDM is time division multiplex. It's how phone calls are sliced on
digital lines.

FDM is frequency domain multiplex : to have two (or more) phone calls
on the same wire, you shift the frequencies used for each call. That's
similar to the way ADSL can work at the same time as telephone.

TDM is far more efficient : you digitalize the phone data (sound), it
gets you 8000 bytes per second (64kbps/s). Then, you take a T1 link
for instance, you put on it a carrier that allows you to transfer 1536
kbits/s. And you realize that every 8000th of a second, your T1 can
transport 24 bytes. This way, every 8000th of a second, you send 24
bytes from 24 simultaneous phone calls. That's TDM.

Asterisk (zaptel) does TDM over Ethernet as well : instead of using a
sync link such as a T1 or E1, you send multiplexed frames across the
Ethernet.
Post by Adthrawn
Is there anyway of shifting the load of one Asterisk server to another
without breaking or loosing a call?
No. If you're talking about ISDN, that would mean asking the telco to
transfer the call from one span to another, transparently. If you're
talking about VoIP, that would mean doing tricky re-routing, which
could be nasty if NAT is involved.

In any case, that would mean transfering a whole call context as well,
like a running AGI script for instance, which is simply not possible.
Post by Adthrawn
I know that with Survivable Routing (Cisco's big on this), the ISDN
interface is actually a router; so the Proxy is just used to decide the
destination and LCR functions, and then hands off to a router. This of
course, if a Proxy went down, would just prevent new calls from being
made, whilst existing calls can continue merrily - until someone
switches the Router off, or corrupts the IOS settings :-)
What if the "ISDN router" goes down ?? Asterisk is much more of an
ISDN router kind than a proxy kind. Maybe you could try to use SER as
a front end ?
--
Nicolas Bougues
Axialys Interactive
John Breeden
2003-12-30 21:32:05 UTC
Permalink
-----Original Message-----
Bougues
Sent: Tuesday, December 30, 2003 9:18 AM
Subject: Re: [Asterisk-Users] Backup Proxy & Automatic Failover
Post by Adthrawn
Hi,
The term TDM is banded around too, but from my knowledge, TDM is
trunking (probably some clever acronym relating to trunking), and in
Asterisk's case, using the IAX protocol. This leads me to the big
question;
TDM is time division multiplex. It's how phone calls are sliced on
digital lines.
Adthrawn
2003-12-30 22:46:30 UTC
Permalink
Hi,

Would it be possible to use an ISDN router instead of an ISDN card?

In addition to the failover issue, I'm also considering running a copy
off a Mac OS X machine, and as such I do not have access to ISDN4Linux
or CAPI toolsets. The only work-round I can imagine is to use a SIP
aware ISDN router (probably a Cisco).

Any thoughts?

I know Vocal is built in this way (Vocal is owned and funded by
Cisco)...

Regards,
Ad.
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