1. Internet Telephony (VoIP) Henning Schulzrinne Dept. of Computer Science Columbia University Fall 2003

2. Overview new Internet services: “telephone”, “radio”, “television” why Internet telephony? why not already? Internet telephony modalities components needed: – audio coding – data transport – quality of service – resource reservation – signaling – PSTN interworking: gateway location, number translation

3. Name confusion Commonly used interchangeably: – Internet telephony – Voice-over-IP (VoIP) – IP telephony (IPtel) Also: VoP (any of ATM, IP, MPLS) Some reserve Internet telephony for transmission across the (public) Internet Transmission of telephone services over IP-based packet switched networks Also includes video and other media, not just voice

4. New Internet services tougher: replacing dedicated electronic media vs. new modes (web, email) distribution media (radio, TV): hard to beat one antenna tower for millions of $30 receivers typewriter model of development radio, TV, telephone: a (protocol) convergence?

5. The phone works – why bother with VoIP user perspectivecarrier perspective variable compression: tin can to broadcast quality  no need for dedicated lines better codecs + silence suppression – packet header overhead = maybe reduced bandwidth security through encryptionshared facilities simplify management, redundancy caller & talker identificationadvanced services better user interface (more than 12 keys, visual feedback, semantic rather than stimulus) cheaper bit switching no local access fees (but dropping to 1c/min for PSTN) fax as data rather than voiceband data (14.4 kb/s) adding video, application sharing is easy

6. Emergency Calling 911 in North America, 112 in Europe, others elsewhere First implemented 1968 in US, now roughly 95% of US population Basic 911 service: route emergency call to nearest emergency call center (public safety answering point – PSAP) Later, enhanced 911 (E-9-1-1) for selective routing and conveying caller location information to PSAP Roughly, 150 million 911 calls per year (2000) – 45 million wireless For wireless: Phase I and Phase II – Phase I conveys call back number + Pseudo-ANI (cell face identifier) to PSAP – Phase II provides caller location (e.g., via GPS or TOA)

7. Wireless 911 Phase II - TDOA BellSouth

8. Wireless 911 Phase II - EOTD BellSouth

9. Wireless 911 Phase II Example: Sprint PCS and Nextel use GPS Implementation just starting VolP has similar problems as wireless: – devices change “network attachment point” Accuracy67%95% Handset-based50m150m Network-based100m300m

10. E9-1-1 Tandem w/SRDB PSAP End office Loop Acces s Contr ol ie DLC Syste m Update Links The Local Loop EM TrunksES Trunks Public Safety Answering Point PSAP ALI Data Links Recent Change Links DBMS Service Providers ALI Database Elements SCP GATEWAY (Firewall) E9-1-1 Call flow elements - wireline ALI

11. ALI/SR DBASE PSAP Public Safety Answering Point MSC MPC PDE E2 E9-1-1 Tandem w/SRDB 1 2 3 4 5 6 7 8 E9-1-1 CALL FLOW ELEMENTS - WIRELESS TDL’s 9 #9 is only applicable in a CAS-Hybrid architecture, such as BellSouth’s WLS911 Solution