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Scalable VoIP Communication Using ITU-T Recommendation H.323 for Global Networking

This document outlines the key features of H.323, a globally scalable VoIP communication framework. It emphasizes the role of intelligent H.323 terminals and Gatekeepers in establishing peer-to-peer calls while facilitating routing and address resolution. Gatekeepers manage call routing, handle NAT/firewall traversal, and provide necessary network services, allowing for efficient call accounting and presence information exchange. The globally decentralized nature of H.323 enables enterprises and service providers to efficiently manage their communication infrastructure across different regions.

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Scalable VoIP Communication Using ITU-T Recommendation H.323 for Global Networking

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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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