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what are session border controllers

Posted on 2014-12-08
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Last Modified: 2014-12-15
Hi,
I was reading about sip and rtp. But couldnt understand what a session border controller is. How they help in solving rtp firewall issue.
Also i read that they protect network from dos (denial of service attack) . whats a dos and how does sbc help prevent them

Thanks
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Question by:Rohit Bajaj
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Cliff Galiher earned 500 total points
ID: 40486846
Different vendors define SBCs differently, and not all have the same features.

But in general, one thing all SBCs have in common is that they sit at a network's edge (hence "border"), can read inside SIP packets and understand the SIP protocol...not just the port but actual SIP messages (hence "session"), and can modify IP addresses within the message, open ports dynamically as necessary for audio or video (such as those needed for RTP streams), close ports after a session ends, and filter unwanted SIP messages from ever reaching the SIP endpoint (hence "controller.")  

Some offer denial-of-service protection, QoS, and other advanced features, but not all SBCs do so. Some are written specifically for SIP while others can operate as a more generic firewall and/or router, but have SIP specific functionality. As I said, each vendor is different in this regard.

-Cliff
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by:Rohit Bajaj
ID: 40487564
Hi
What exactly is a dos and qos?
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Expert Comment

by:Cliff Galiher
ID: 40487880
DoS is the acronym for "denial of service."  That is *exactly* what it sounds like.  ANYTHING that denies service is a DoS attack. If I have a very fast internet connection and you have a very small one, I can literally just throw enough data at you that...unless you call your ISP and get them to block me at their end...I saturate your connection. That is one type of DoS.  Another type is if I see you are running apache and I know of a bug that can make your server crash. I am not flooding your network connection at all. I am just exploiting a bug with almost no data at all. But your server crashes and your service is now denied.

A DoS attack can take many many forms. There is no single quick answer here. But if an attacker can prevent you from getting service, or if they can block you from providing service, then it is...by definition...a DoS attack. And nobody is 100% immune. Just look at the recent Sony PlayStation and Xbox Live outages that the Lizard hacker group has claimed responsibility for. Those were (presumably) DoS attacks.

QoS stands for Quality of Service. And that usually comes in if you have a smaller pipe and want to make sure phone call traffic takes higher precedence than web browsing. Or if you  want to make sure any call to or from the boss's phone number takes precedence over other numbers. QoS is implemented a variety of ways, but it all boils down to a set of rules to decide whether a packet gets passed along or dropped in the event of conjestion...hence ensuring "quality" of the higher priority services.

-Cliff
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