I know SIP works, but why does it not work with _____________?

Ensuring InteroperabilitySean Rivers

2/1/2011

• Way for applications to setup sessions for exchanging data• SIP does not care about the contents of the session• SIP manages the attributes of the session until the session ends

What is SIP?

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What are the issues?

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• SIP can do both• TCP gives more control• UDP is faster and lighter

TCP vs UDP (the big rumble)

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Get him!

I am in control!

Three main options• In-band digits are sent through the audio and are

subject to the quality of the audio. – Everyone supports this, but it often does not work.– Does not work with compressed audio codecs

• RFC 2833 digits are sent digitally in the audio packets – Most common preferred method by carriers.– Works more often

• RFC 2976 SIP INFO – sends digits in SIP messaging via an INFO message.

– Pretty reliable and flexible for managing audio– Very few carriers support it.

DTMF (I can’t get in this darned conference?)

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Sometimes it feels like a rotary phone

Codecs

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G.711

G.729a G.722

AMR

DoD CELPGIPS

GSMiLBC

G.722.1

G.722.2

G.723.1

G.726G.728

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Speex

• 2 methods– Re-INVITE– UPDATE

• Why?– Optimize congestion– Join Conference

• What works best?– UPDATE

• What does everyone support?– Re-INVITE

Managing media

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• Options:– G.711 (wishful thinking)– T.38 (better)– Pass-through (Cisco only)

• Requires equipment• Call quality can still affect all

options

• New method in Store and Forward is interesting development.

Why is fax ALWAYS an issue?

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• REFER – RFC 3515– Removed the PBX from the call path completely.– Sometimes even removes the carrier– Carriers hate this.

• Re-INVITE – Standard SIP RFC– PBX stays in signaling path but audio is diverted– Carriers prefer this

Transfering Calls

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• Most carriers require registration• PBXs have very loose policies on registration

– 1 registration per PBX– 1 registration per carrier– 1 registration per trunk

• For simplicity most wholesale providers just do IP to IP Address

Do I need to REGISTER?

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• SIP over TLS (encrypt signaling)• IPSec (VPN tunnels)• SRTP (enrypt the audio)• Carriers fear the support of problematic certificate exchanges

Security Scuffle

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What are the main reasons we can’t get it together?

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Big companies vs. Little companies Carriers vs. ManufacturersBig companies see these issues and try to force change, but they are usually new entrants into the SIP world and are not able to push in the right direction to satisfy others.

Carriers are slow to change and manufacturers need to release new features.

Proprietary vs. Open

Established manufacturers have cultures of island development and internal standards. While many upstart Open Sourced developer want to make everything work.

• Hardware manufacturers test it at SIPit– Every 6 months– No carriers involved

• SIP Connect– Trunking standards for SIP providers and Manufacturers– Standard still in early adoption phase

What is being done about this?

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• You can get rid of most interoperability with Analog or PRI hand-off– Works– Quality can be an issue (too much conversion)– Price (IADs are not cheap)– Many SIP trunking benefits are lost and advanced PBX features as well

Chuck it and give them Analog (IAD)

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• Back to Back User Agent– Like an interpreter it listens to each party and speaks their language.– Can reside in the cloud and/or locally

What can I do about this now?

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What is the most common model?(What we do)

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• Carrier must have their SIP standard

• PBX will have their own• B2BUA will translate

Thank You…

Sean RiversDirector of Product Technology

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