1. © 2007 AT&T Knowledge Ventures. All rights reserved. AT&T and the AT&T logo are trademarks of AT&T Knowledge Ventures. Interconnection and Interoperability in a VOIP World Challenges facing the industry Richard N. Clarke Assistant Vice President Regulatory Planning and Policy rnclarke@att.com Committee on Telecommunications NARUC – Winter Committee Meetings Washington, DC 19-Feb-08

2. Page 2 Overview of the issues  Currently, default for voice traffic exchange is TDM/SS7  Technology is very reliable and interoperable  Operational systems are highly developed  Business/financial models are reasonably well-known  IP-originated voice traffic is expanding rapidly  In the future, default for voice traffic exchange is likely to evolve to IP/SIP technology BUT EXACT ARCHITECTURES ARE STILL UNCLEAR

3. Page 3 Current TDM-TDM call flow Tandem Orig Class 5 Originating phone Call Direction Terminating phone Tandem Term Class 5 LERG TDM protocol transport links Analog/TDM access lines Circuit switch with routing table (simple) LERG STP SS7 protocol signaling links Signal transfer point

4. Page 4 Future VoIP call flows Originating Computer Terminating Computer IP protocol transport links Analog inside wire Infrastructure-Based Orig Softswitch Term Softswitch IP-IP network interconnection (peering or transit) SIP signaling packets ENUM Electronic number mapping database (complex) Peer-to-Peer

5. Page 5 Transition challenges  Full transition to IP-based VoIP interconnection still requires:  Technology to be standardized  Reliability to be proven  Operational systems developed and disseminated  Business/financial models become clearer  VoIP regulatory mandates seem unlikely to be needed  20,000+ IP networks already interconnect for best-effort data traffic exchange on an unregulated contractual basis  Negotiated prices for such IP data exchange are very cheap  Until IP transition progresses more fully, TDM interconnection must be the “lingua franca”

6. Page 6 Current VoIP-TDM call flow SIP signaling packets Originating Computer Call Direction Terminating Phone TDM protocol transport links IP protocol transport links Orig Softswitch SS7 protocol signaling links Tandem Term Class 5 STP LERG Gateway translating IP/SIP into TDM/SS7 LERG IP-TDM Gateway STP LERG