load share and redundancy for 800 users

yesmat

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#1
Hi All,

We have a "Potential" opportunity for 800 user single site setup.

Some of the requirements are:

1- High availability (meaning 2 servers backup to each other if the primary fails the secondary picks up) I believe DRBD and Linux Heartbeat is the way to go with this rquirement.

2- Due to the large number of users, we may need to have load balancing between the 2 servers. Not sure how to do that otherthan DNS SRV. Any ideas about drawbacks or alternatives are appreciated.

3- All users need to have presence clients. Openfire 3.6.4 should do the job??

Questions are:

what kind of hardware we need?
is this setup possible at all with Elastix?
are 2 servers enough, or we need more?
having all 800 users with spark Openfire client does that pose any load on servers?
if we use the single CODEC every where (G729) and get rid of any transcoding, would that ease any CPU load?

Any other ideas and feedback are welcome.

Thanks
 

dicko

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#2
HA works fine (I suggest you use drbd83) and with 800 users you would be negligent by not using it.

Load balancing is probably not going to work successfully with Elastix/Asterisk (you need an intermediary proxy server, I suggest freeswitch, which with a lot of work might be all you need)

Openfire works, within it's limitations. (if the memory leak has been fixed)

The Telcos have been working on resources v. users for 150 years. basically there is no real answer (The industry uses between 10 and 15 percent usage), you need to examine the usage you envision, 50-100 concurrent calls should be fine on quad core 2G hardware with 16G memory, if it's a call center, well, I would think twice here . . .

Yes, 800 users on one Presence server will of course create a load, I suggest that that might be moved to a separate cluster.

If there is any traditional (g711) telephony involved (Including Faxes) then g729 will in fact CAUSE trans-coding loads, use g711 if you have the bandwidth and save load on your servers and improve quality in your calls.

(A cautinary word, If you provision 800 users without TDM backup you will sooner or later get one really pissed of client, unless you actually have a five nines network)



dicko
 

yesmat

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#3
Agreed drbd83 is a must have in this scenario.

I thought load sharing should be ok with DNS SRV record where the DNS server will respond with alternate IP addresses for the alternate servers and load sharing will be achieved this way. The drawback with this setup though is that DNS doesn't detect a server failure and will strill serve the IP address of a dead server untill admin removes that DNS entry untill the server is fixed.

In regards to the use of Freeswitch, don't you think it is easier or better to use OpenSER for that ourpose?

Using G711 will not conserve expensive WAN bandwidth, that's why i suggested to remove all other CODECS from Elastix including 711, this way we will not need transcoding at all.

E1 ISDN lines will be definitely used for inbound calls at least and as backup measure for outbound calls. Will probably use Patton's PRI gateways.

did you say 16G of RAM? isn't that too much. I was thinking around 4G only.

cheers
 

dicko

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#4
16G was a typo I did indeed mean 4G (voice is CPU not memory intensive)

The whole problem with Asterisk as we know it, is it is a back-to-back user agent, hence it can not get itself out of the way.If you have an HA solution, no matter what, the current calls will be dropped.

If you want to scale outside a BTBUA, then analytically , I suggested you need a proxy , choose what you want. Personally I see a trend to Freeswitch (as does FreePBX).

Any way you choose, If properly implemented with BGP, then you will be be busy but less nervous.


Your logic is I believe flawed

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if we use the single CODEC every where (G729) and get rid of any transcoding,
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and


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E1 ISDN lines will be definitely used for inbound calls at least and as backup measure for outbound calls. Will probably use Patton's PRI gateways.
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how are you going to that without trans-coding?, your call, I find bandwidth to be way cheaper than TDM and CPU power, YMMV of course.

dicko
 

yesmat

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#5
sorry which part of my logic is falwed?

The only point that we disagree on is transcoding. We all know that Asterisk servers can be configured in G729 passthrough mode and that will enable end points to talk, through the B2BUA, with each other using that CODEC only (even VM prompts work). Now when it comes to PSTN, my Patton gateway, I believe, supports G729 and it will be doing the SIP-TDM conversion not Asterisk.

The other point is using DNS for load sharing. There are large ITSPs use that technique to load share between multiple Asterisk servers. Check "sip.faktortel.com.au". You can use the simple nslookup command to see what I am talking about.
I am not saying that this is the best option or best-practice, but it is an option. A OpenSER or Freeswitch server would be the better option, but if configuring a Freeswitch is a daunting task then ......
 

dicko

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#6
. . falwed . . Your spelling ? :) :)

As to your logic, I must admit I am not familiar with Patton stuff, If they do indeed do the 729 thing, then I think you might have hit on a nice solution. I thusly retract my statement.

regards

dicko
 

yesmat

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#7
always good to have a chat with you dicko :)
 

dicko

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#8
Unless you can successfully assign inbound and outbound calls to the requested endpoints, (whatever answers that registration, as assigned externally by DNS, and internally by hmm. . how would you do that? , from inside or from outside your network), then it will be at best half assed. Here you surely need a proxy, unfortunately Asterisk is not that beast (yet).

True, vitelity at al. can do that, but in effect all their calls are stateless in origination, your 800 seats under asterisk are, unfortunately stateful.

regards

dicko
 

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