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Distributed, Globally Scalable VoIP Communication

Distributed, Globally Scalable VoIP Communication. Using ITU-T Recommendation H.323 May 1, 2006. Key H.323 Points. H.323 terminals are “intelligent” devices H.323 calls may be Peer to peer Routed through a Gatekeeper H.323 terminals or Gatekeepers may resolve address

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Distributed, Globally Scalable VoIP Communication

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  1. Distributed, Globally Scalable VoIP Communication Using ITU-T Recommendation H.323 May 1, 2006

  2. Key H.323 Points • H.323 terminals are “intelligent” devices • H.323 calls may be • Peer to peer • Routed through a Gatekeeper • H.323 terminals or Gatekeepers may resolve address • Gatekeepers are the more logical place • Gatekeepers can also facilitate exchange of presence information

  3. Designed to Scale • Gatekeepers may communicate with • Known peer Gatekeepers • Gatekeepers discovered through DNS • Routing a call is very “light-weight” • H.323 terminals ask “where is the called device”? • The Gatekeeper resolves the address and provides that to the endpoint

  4. Designed to Scale (cont) • Gatekeepers route calls when • It is necessary to traverse NAT/FW devices • The Gatekeeper is used for call accounting • The Gatekeeper is needed to provide network services • Otherwise, calls are placed peer to peer • In the worst case, calls are routed by • The calling terminal’s Gatekeeper • The called terminal’s Gatekeeper • Media flows directly between terminals, but may be routed to traverse NAT/FW devices

  5. Enterprise Enterprise Enterprise Enterprise Enterprise Enterprise Enterprise GK GK GK GK GK GK GK The “H.323 World” Internet

  6. Finding Remote Gatekeepers • Gatekeepers may send Location Request (LRQ) messages to peer gatekeepers • Useful for “internal” routing within an enterprise or service provider environment • Gatekeepers may “proxy” LRQ messages for other gatekeepers • Gatekeepers may query DNS to discover the location of a remote Gatekeeper • Globally scalable • Queries similar to finding a web site • Phone numbers work using ENUM

  7. Configuring DNS If you have a single Gatekeeper, tell the world to send it all calls: _h323cs._tcp IN SRV 0 0 1721 gk.packetizer.com. Larger enterprises may have multiple gatekeepers and may wish to optimize call routing: _h323ls._udp IN SRV 0 0 1719 gk.packetizer.com.

  8. Steps to Routing a Call • User enters “paulej@packetizer.com” • Terminal asks its gatekeeper, “how do I reach paulej@packetizer.com?” • The Gatekeeper queries DNS and learns that calls should be routed to gk.packetizer.com • The Gatekeeper returns the IP address of the remote Gatekeeper (or, optionally, it’s own address in order to facilitate NAT/FW traversal) • The call is established

  9. DNS GK GK Routing a Call 1. User enters “paulej@packetizer.com” 2. Where is “paulej@packetizer.com” 5. Send the call to gk.packetizer.com 3. What GK handles packetizer.com? 6. Call for “paulej@packetizer.com” 4. Answer: gk.packetizer.com does, and it accepts all inbound calls 7. Call for “paulej@packetizer.com”

  10. Globally Scalable • H.323 is globally scalable • System is entirely decentralized • Enterprises may manage their own communication infrastructure • Service providers may provide H.323 Gatekeeper functionality for customers spread around the globe

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