[asterisk-ss7] didicated channel for signaling

Mostafa Ibrahim mostafa.ibrahim at valuesys.net
Fri Oct 26 05:58:44 CDT 2007

On Fri, 2007-10-26 at 08:21 +0200, Kristian Nielsen wrote:

> Mostafa Ibrahim <mostafa.ibrahim at valuesys.net> writes:
> > I found that chan_ss7 has some clustering support starting from version 0.8.
> > This is the feature as mentioned in the read me file "Supports multiple hosts
> > (cluster) configuration with load sharing and failover". Which is exactly what
> > I need. Has anyone tested this configuration.
> >
> > What I understood from the configuration templates included with the source
> > code that the interconnect will not only be used for keep alive "heart beats"
> > it will also carry the signaling between the nodes which means that the
> > signaling might terminate on one host and be used on an other node passing
> > through the interconnect which is the perfect solution to my problem.
> Yes, this is basically correct.
> >From the start, chan_ss7 was designed for full support of MTP3 failover and
> fault tolerance. Thus the purpose of implementing clustering was primarily to
> enable the setup of a system with no single point of failure. So cable
> failure, host crash, or even a dead network switch will not lead to any
> downtime (except loosing a few existing calls currently running on affected
> curcuits).
> Thus, while the basic facilities are there for routing the signalling across
> the interconnect, it was never intended for a setup with only one signalling
> link, so currently that may not work very well.
> I would also think that with ~900 phone lines, you _would_ want some kind of
> redundancy? Otherwise just the need to switch cabling or reboot the host
> carrying the link will take down _all_ 900 lines! With two links, one on each
> host, you can just set the lines on one host to maintenance mode, wait for
> existing calls to end, then reboot/recable/whatever with no noticable effect
> on users. This also holds true for the other end, who might assume this
> functionality (as it is a mandatory part of the SS7 specs).

I might ask the provider to provide me with another redundant signaling
channel on another E1 line which should be on the other server.

> Also, I think the clustering still only supports two hosts. So you could put 4
> quad-span cards into each server (4 PCI slots should be possible I guess), but
> I don't know if/how Asterisk will handle that many simultaneous lines.
> Maybe if the SS7 boxes do nothing but route over IAX to a larger number of
> Asterisks that do the real work (transcoding, SIP, DB auth, whatever) it would
> increase the chance of Asterisk being able to cope with 450 lines? But that is
> just speculation on my part.

This is typically what I planning to do. The first tier asterisk servers
will carry out routing only and their will be a second tier servers
containing the business logic of the IVR applications and other database
servers if needed by certain application. The dimensioning of the first
tier servers might enforce me to buy an 8 processors dual core with 64
GB RAM for example which is not a big deal in such huge deployments. 

I want to use the current implementation as a base to start developing
a mechanism to distribute "SS7 signaling over IP". Thus I can receive
the SS7 signaling on any channel on any E1 link on any host and then
implement a client server message bus that can be used to distribute
these signaling among multiple hosts. Thus other hosts will set all
their channels to voice channels and get the ss7 signaling through the
message bus.

There might be an opensource implementations for such tcp/ip
communications that can be directly included (multicast implementation
will be suitable). The main issue it to implement the hooks inside the
chan_ss7 code to deal with this message bus. I think the starting point
is to extend the current implementation of cluster_send_packets and
cluster_receive_packets functions to deal with this bus. 

>  - Kristian.
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Mostafa Ibrahim 
Security Department Manager
website: http://www.valuesys.net 
Tel:         +202 22682552 +202 2682887
Fax:         +202 22674346
Mobile:    +2 0181008194
Email: mostafa.ibrahim at valuesys.net
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