SBC vs. SIP Server – What is the difference?

by Alan Percy, Senior Director of Product Marketing at TelcoBridges

The question came early and often during our participation at Astricon 2018 in Orlando.  “What’s the difference between an SBC and a SIP Server like Kamailio or OpenSIPs?”   Reminding us that in our world of telecom jargon, sometimes we need to stop and explain what we are talking about.

Let’s step back for a moment to look at the big picture.  When deploying SIP-based applications like Asterisk or FreeSWITCH, at some point, there is a need to divide the call load amongst multiple servers (physical or virtual).  Possibly because of traffic or simply to hedge bets against outages from a server crash, spreading traffic across multiple physical servers is a wise strategy.  The next challenge is routing incoming traffic from one or more service providers to those SIP applications.  Both SIP servers and SBCs can route traffic based on a range of programmable criteria including: dialed number, originating number, randomly, round-robin, availability and more.

Both SIP Servers and SBCs can also handle some of the interoperability and security services, but this is where the differences start to be more apparent.

So, what is an SBC and how does it differ from a SIP Server like Kamailio or OpenSIPs?

The simplest explanation is – SIP Servers manipulate and route SIP messages, never touching the media path.   However, SBCs broker SIP messages and media, acting as an intermediary between two networks, applying complex manipulations, security and routing rules on both the signaling and media.

SIP Server Functional Architecture

SIP message and media brokering within an SBC is accomplished via a Back-to-Back User Agent (or B2BUA for short), essentially terminating the SIP session on one network and re-initiating a new session on another network.  This can be between a WAN and LAN, between two WANs or two LANs.   The most common use case for SBCs puts them in the DMZ, putting one side on the WAN and the other side on a private (and secure) LAN with SIP applications (Asterisk, FreeSWITCH or other) on the protected LAN.  In this role, the SBC protects and distributes the traffic load across the various SIP applications.

Session Border Controller Functional Architecture

Using a B2BUA is more resource intensive than a simple SIP Server, but this is balanced by the additional functionality and security provided.

Beyond greater control over security policies, SBC’s B2BUA capabilities have other benefits, including:

  • Real Topology Hiding – of both SIP messages and media, ensuring the internal network topology of your network is not exposed to the outside world.
  • DOS and DDOS Protection – Intelligent security that stops DOS attacks in their tracks before they can get into your network.
  • Registration Flood Detection and Protection – preventing “network probing” and attempts to overload Asterisk servers with bogus registration attempts.
  • Media conversion and transcoding
  • Advanced call routing and traffic management capabilities across multiple networks.
  • Multi-application support – distributing and adapting SIP traffic between dissimilar applications from different vendors.

Beyond that, there are many other reasons to use commercial SBCs like FreeSBC for scaling Asterisk and FreeSWITCH implementations:

  • Ease of configuration – with FreeSBC’s easy to use web portal, there are no cryptic script languages to learn!  Most configurations can be completed in a few minutes with a web browser.   Want to see how it’s done?  Take a tour of the web portal and learn how to configure FreeSBC for SIP Trunking on YouTube at:   https://youtu.be/GvfKSw1H6gU
  • Low cost subscription-based pricing that allows “pay as you grow” $1/session/year/server for FreeSBC Pro Edition
  • Carrier-grade – with scaling up to 60,000 sessions per server with 1+1 redundancy for High Availability
  • Platform choices – with versions for bare-metal, VMware, KVM and Amazon AWS
  • 24/7 Technical support availability
  • Regular software updates without having to wade through forum recommendations and Github branches

Understanding the difference between these two important network elements gives network designers the tools to build more efficient and secure solutions.

You can learn more by attending the upcoming webinar “What is an SBC?” at:  https://www2.telcobridges.com/WhatIsAnSBC

Download your free evaluation copy of FreeSBC TODAY at: www.FreeSBC.com