How many simultanoius calls can i manage in an asterisk server?

hi ,i have two asterisk systems,to be exact there are vicibox express installations ,i have 2 servers with params corei3 3.2 ghz 6 gb of ram .i am struglling sometimes because i get some service unavaiable on calls. how much calls can this server handle and does it affect that is a vicibox installation although i do no use vicidial exept ffor the carrier part where i write my voip information for the server to be connceted to voip.for the codex i use diallow=all allow g729 .PLease reply as soon as you can .thank u in advance

It’s impossible to determine what a server can handle without reviewing the dialplan and applications running as well as the calling patterns. There could be hard drive bottlenecks or network issues. When you use an app like vicidial or freepbx, there’s no telling what “extras” they’ve added that could slow things down. You might be able to get specific help if you post the logging when the “service unavailable” is occurring, plus show “core show channels” and “sip show channels” to see how many calls are running at that time.

A good testing tool is sipp, but that’s only going to help if you can simulate a typical load.

Related to Vicidia dialerl, ViciDial scales horizontally for all roles except the Database. For this reason, you will need to spend
extra time deciding on the hardware specifications of your Database server. The specifications it is
recommended for a database server up to 150 agents is as follows:
• Quad-Core CPU 2.0Ghz+
• 8GB ECC Ram
• 2-drive 240GB+ SSD (Intel 530, 730, etc) configured in RAID-1 on a Linux software RAID or
SSD-optimized raid card (LSI FastPath MegaRAID, etc)
• Redundant Power Supplies with each on a different battery back-up
To add to the above specification for handling up to 300 agents would be as follows:
• Two Quad-Core CPU 2.0Ghz+
• 16GB ECC Ram
• Two Separate 500GB enterprise-grade SATA drive for the OS in a RAID-1
For a 500 agent Database server, adding to the specification, would be as follows:
• Two Hex-Core CPU 2.0Ghz+
• 32GB+ ECC Ram
• 4-Drive 240GB+ RAID-10 on SSD (Intel 530, 730, etc) with SSD-optimized RAID card (LSI
FastPath MegaRAID, etc) or Linux software RAID
• Two Separate 500GB enterprise-grade SATA drive for the OS in a RAID-1
read the vicidial installation guide for more info

We have tested a good server with 800 concurrent calls succefully

What were the specs of the 800 call server?

Quad Core 3.2 GHZ , 8 GB RAM, SSD 256 , CentOS 7.x

The answer can vary by over an order of magnitude, depending on details that you haven’t provided , which is why the standard answer is that you need to benchmark with something representative of your actual application.

Also, if you are talking SIP (one of the missing details) Asterisk acts both a client and a server, and in certain outbound calling applications may actually be mainly client.

Big factors tend to be whether media passes through Asterisk, and the amount of transcoding needed.