To summerise a firewall typically works on layer 3, 4 and sometimes partially on 7 (e.g. FTP / limited SIP awareness)
A SBC works on layer 7 and can fully understand VOIP traffic, meaning that it can:
- Block denial of service attacks
- Detect spoofed / malicious SIP packets
- Close and open RTP ports as nesacasery
- Transcode between different media protocols
The major seeling point of an SBC is used to provide interopability between different SIP solutions, since SIP implmentations quite often devaite from each other.
SIP utilizes RTP (Real-time traffic protocol) that unfortuanely typically requires UDP ports 6000 - 40000 to be available (much like the downfalls of FTP) - a traditional firewall will not be able to protect the SIP traffic.
They can be placed behind a firewall (that works properly with NAT an SIP) or simply presented directly to the router.
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