I’ve worked with a couple of organizations in the past several months that have had… inconsistent configuration on their AudioCodes gateways and SBCs for proper connectivity to multiple (or in some cases single) SfB pools. For simplicity, I’ll use the term “SBC” to mean both the SBC and Gateway, unless there’s a particular need to call out one versus the other.
In an AudioCodes SBC, you can route traffic to/from your SfB system using a variety of uncivilized methods, including specifying IP addresses. Yuck. Do yourself – and those who’ll look at your config after you’re done – a favor and use Proxy Sets. You’ll find those under “Signaling & Media”, then “Core Entities”, then “Proxy Sets”.
A Proxy Set lets you specify a number of characteristics for a system that you want your SBC to communicate with, allowing for much less clumsy and random configuration. Here’s a Proxy Set configured for one simple SfB server:
This could be a standalone mediation server, a Standard Edition server, or a solo Enterprise Edition Server. Let’s have a more detailed look at the configuration.
The General section is pretty straight forward. You need to give your Proxy Set a name. There aren’t any particular requirements here, so use something that make sense to you. The first part of your SfB pool name is a good choice “LAXSfBPool”, for example. The name of your telco provider is a good choice for connections to the PSTN. For the rest of this post, I’ll assume you’re connecting to an SfB Standard Edition server.
Next you need to specify the SIP interface that your SfB server will connect on. A SIP interface is a network interface plus a few other characteristics, like what port and protocol the SBC will listen on. The TLS context is the group of TLS settings that you’ll use to talk to your SfB server.
SfB uses SIP OPTIONS (yeah, it’s capitalized, I’m not yelling) for two purposes. One is to advertise capabilities (“options”) and the other is as a heart-beat or keep alive mechanism. For connecting an SBC to SfB, you’ll want to set the Proxy Keep-Alive to Using Options. There’s a timer for how often you want these sent – the default is every 60 seconds, and you can leave that in place. The remainder of the variables here are for tuning the specific behavior of your connection if OPTIONS aren’t received, and what criteria need to be met for the connection to be “up” again. Generally, you can leave these alone – I’ve never had to tweak them in a couple decades of doing this stuff.
The advanced section has only two settings. Classification Input determines whether the SBC will listen to anything from the specified IP addresses (we’ll see that part later) or if the port and transport type – TCP,UDP.TLS must match too. Go ahead and change this to include Port & Transport Type if you’re super security aware, otherwise leave it at IP address. For DNS resolve method, you can leave this blank to use the global parameter “Proxy DNS Query Type”. You can do some funky things here, but I’ll talk about FQDNs and IPs later when we specify those.
This section is where I see the most misconfiguration. For a Standard Edition server, however, you don’t need any settings here, so leave them at their defaults (having them set won’t affect anything, but sure is confusing to look at when troubleshooting).
This is the spot where you add the FQDN or IP address, port, and transport type for you SfB servers. You can use server FQDNs if you like, especially for more advanced configurations that use the various DNS Resolve Methods in the Advanced section… However, for SfB, most everyone that I know uses the IP addresses of the servers – they’re unlikely to ever change, and using IPs means you’re not dependent on DNS infrastructure. This also guards against changes or deletions of DNS records, though you have other problems if that happens! I always specify the port and transport type, to prevent any gotchas should the system defaults ever be changed.
Next post, we’ll have a look at the changes that need to be made when you have an Enterprise Edition pool with multiple front-ends, as well as multiple pools. Just for fun, there are some differences in configuration here if you have a gateway or an SBC.