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Walkthrough Wednesdays

The Voice Federation Problem

Cisco Employee

IP-based communications has seen a meteoric rise within the boundaries of the enterprise. The majority of new product sales into enterprises are IP-based gear. Because of this, we are seeing lots of cases where enterprises communicate together, and though each has IP internally, the telephone network drives communications down to the least common denominator – a basic voice call.

In order to achieve real improvements in business-to-business productivity – through wideband voice and video combined with better voicemail, conferencing, contact center and telephony features – requires us to break past the landlock of the PSTN, and achieve true open federation.

Unfortunately, achieving open federation is no easy task. It requires overcoming four main technical hurdles: call routing, security, QoS, and fault management (aka troubleshooting).

The call routing problem is a simple one to understand. Given that the vast majority of calls are made to phone numbers, how does one determine a mapping from the number to the domain which owns it? Such a mapping needs to be global, openly available, and contain correct entries. Though attempts have been made to define such a global directory, none have succeeded.

Security is another challenge in open federation. There are many aspects to this problem, but the biggest by far is how to allow open connectivity while at the same time blocking VoIP Spam and Denial of Service attacks. Most organizations are fearful – with good reason – of just opening up a port on their firewall that would allow incoming SIP traffic to touch their call agents. What happens if someone sets up a cheap open source PBX on the Internet and starts spam-calling phones? Or what if they use the open pinhole to flood the corporate PBX with SIP traffic, causing it to fall over, disrupting normal voice traffic within the business? These are non-trivial risks. There are other aspects to the security problem. All traffic has to be encrypted as it flows between domains, and all intervening NATs and firewalls need to be traversed.

Quality of Service is another problem. Today, the Internet forms a global interconnection fabric that touches every enterprise. As such, it is a natural vehicle to use for open federation. However, the Internet provides no guarantees on Quality of Service. The resulting ‘best effort’ service is often good enough, but business-to-business federation demands something more. How can we achieve open federation with the level of call quality that each individual domain demands?

The final problem is an operational one – when calls transit between domains over the Internet, and things don’t work, how does each side of the call learn about the problems, and how are they diagnosed? The most important piece of this is to determine who is at fault. Is it the domains themselves? Is it the ISP of one domain or the other? Or was there a quality problem in one of the transit IP networks between?

And so, despite the great benefits of open federation, these four challenges – routing, security, QoS and troubleshooting – stand in the way of realizing it. Perhaps someday soon, these problems will be addressed.

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