Some of our customers have misconceptions about what session border controllers (SBCs) are. People who ask for an SBC often actually need a softswitch instead.
SBCs, along with firewalls and intrusion prevention systems, are often used by corporations to enable VoIP calls to and from a protected enterprise network.
Most SBCs provide firewall features for VoIP traffic (such as a denial of service protection, call filtering, and bandwidth management).
Some years ago, SBCs and softswitches had more distinct sets of functions, and it was easy to tell which was which. Currently, modern SBCs and softswitches are very similar, with a significant overlap in functionality.
The differences between SBCs and softswitches mainly relate to security and quality of service functions.
Simply, an SBC for voice is a firewall for a network and a softswitch for voice is a router for a network.
From the table below, we can see that the functionality of modern softswitches overlaps that of the SBCs:
| Security | ||
|---|---|---|
| Topology Hiding | + | + |
| Malicious attacks such as a denial-of-service attack (DoS) or distributed DoS | + | + |
| Toll fraud via rogue media streams | + | |
| Malformed packet protection | + | + |
| Encryption of signaling (via TLS and IPSec) and media (SRTP) | + | + |
| Connectivity | ||
| NAT traversal | + | + |
| SIP normalization via SIP message and header manipulation | + | + |
| IPv4 to IPv6 interworking | + | + |
| VPN connectivity | + | + |
| Protocol translations between SIP, SIP-I, H.323 | + | + |
| Regulatory | ||
| Emergency calls prioritization and | + | + |
| Lawful interception | + | + |
| Media services | ||
| DTMF relay and interworking | + | + |
| Media transcoding | + | + |
| Tones and announcements | + | + |
| Data and fax interworking | + | + |
| Support for voice and video calls | + | + |
| Other | ||
| Statistics and billing information (CDRs) | + | + |
| Call Accounting | + | + |
| WebRTC implementations | + | + |
| Quality of service | ||
| Traffic policing | + | |
| Resource allocation | + | |
| Rate limiting | + | |
| Call admission control | + | |
| ToS/DSCP bit setting | + | |
| Softswitch Functions | ||
| Authorization | + | |
| Registration | + | |
| Switching | + | |
| Routing | + | |
| Billing | + |
Not all SBCs have all the functionality outlined in the table for them, and similarly for softswitches. This table merely illustrates the range of functionality for SBCs and softswitches. There are many SBC and softswitch manufacturers, who add all kinds of functions into their products. Thus, the differences between SBCs and softswitches is often unclear.
As we can see, SBCs and softswitches usually cover most of the functionality, but their core functions are quite different. SBCs are more like firewalls for voice traffic, while softswitches are a central part of a voice network infrastructure. They are used for switching and routing voice traffic and very often have billing and accounting functions.
Another important distinction is that softswitches provide infrastructure for a business environment. They allow an organization to establish and operate some business model, while SBCs are only network components that provide security (along with other functions) for the network.
- Photo by Liks Digital on Unsplash