The State of SIP Application Development

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The State of SIP Application Development

• Brian Schwarz
• VP Engineering
• RedSky Technologies, Inc.

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Agenda

• What is a SIP Application?
• Survey of standards applying to presence and
  location
• Case study A SIP Application that supports
  NG911 (SIP calls with location)
• Challenges we encountered and how we resolved
  these

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What is a SIP Application?

• Leverages the capabilities of SIP, but provides
  value-added services beyond the delivery of the
  call
• Examples
• Call Recording
• Unified Communications (UC)
• UC with presence and location
• Call Center control

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RedSkys SIP Application

• Receives a SIP call without any location data
• Uses the content of the SIP INVITE to determine
  the location of the calling device
• Adds location information either by reference
  (through a URI) or by value (in a PIDF-LO) to the
  SIP INVITE
• Sends the call out, now with embedded location
  data that can be used to route the call to the
  appropriate PSAP (911 call center)

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Presence Standards

• SIMPLE (SIP Extensions for Presence)
• Supported by Microsoft (and others)
• http//www.ietf.org/html.charters/simple-charter.h
  tml
• Tight integration with SIP, so presence additions
  are seamless to the existing voice protocols
• XMPP (Jabber)
• Supported by Google (and others)
• http//www.xmpp.org
• Better for chat only messaging

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Location Standards

• MLP
• Mobile Location Protocol
• Widely used in existing mobile wireless
  infrastructure
• Supported by OMG (Object Management Group)
• XML-based, only allows geo-coded location
• HELD/PIDF-LO
• HTTP Enabled Location Delivery Presence
  Information Data Format-Location Object
• Supported by the IETF (Internet Engineering Task
  Force)
• Allows geo-located and civic addressing schemes

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Case Study NG911
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Challenges to SIP Apps B2BUA vs Proxy

• Proxy is simpler to develop and test than a B2BUA
• Real function of the RedSky LIS is as a proxy
  were not changing the original SIP content
• Only way to implement additions to the INVITE
  body is through a B2BUA
• The B2BUA takes on additional requirements in
  terms of callback routing
• Standards say that the FROM address out of the
  B2BUA should be the address of the B2BUA. How do
  we route a dropped call back to the originating
  device?

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Challenge Choosing the right SIP stack

• Roll your own
• Longer development time and interop requirements
• Flexibility in implementing the standards with
  regard to content
• Open Source (i.e. JAIN)
• Better development time, but still requires app
  infrastructure
• SipServlets (i.e. GlassFish, BEA)
• Fast development, focusing only on the
  application content
• Reduced control over the SIP content

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Challenge SIP capabilities abstract data

• SIP abstracts the actual device making the call
• Location Determination loss of MAC address
• Port-level discovery uses SNMP queries to the
  BRIDGE MIB on network switches, matching the MAC
  address to a port
• SIP doesnt communicate the MAC address how to
  do port-level discovery?
• Shared line
• Multiple devices can share the same SIP URI
• When dialing 911 which device made the call?

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Challenge SIP Data

• Even if SIP entities (i.e. clients, proxies and
  B2BUAs) can interoperate, the content of the SIP
  data can be crucial to an application
• Requires careful design of the data content
  within the SIP messaging to ensure the
  application will function properly

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Questions?