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

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

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

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?

The phone works – why bother with VoIP user perspective carrier 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 encryption shared facilities simplify management, redundancy caller & talker identification advanced 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

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)

Wireless 911 Phase II - TDOA BellSouth

Wireless 911 Phase II - EOTD BellSouth

Wireless 911 Phase II Example: Sprint PCS and Nextel use GPS Accuracy 67% 95% Handset-based 50m 150m Network-based 100m 300m Example: Sprint PCS and Nextel use GPS Implementation just starting VolP has similar problems as wireless: devices change “network attachment point”

E9-1-1 Call flow elements - wireline E9-1-1 Tandem w/SRDB End office Public Safety Answering Point ES Trunks EM Trunks Recent Change Links PSAP ALI Data Links PSAP Loop Access Control ie DLC System The Local Loop ALI Update Links SCP GATEWAY (Firewall) DBMS Service Providers ALI Database Elements

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