Voip
Content
Internet Telephony (VoIP)
Henning Schulzrinne Dept. of Computer Science Columbia University Fall 2003
Overview
new Internet services: ³telephone´, ³radio´, ³television´ 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
variable compression: tin can to broadcast quality no need for dedicated lines security through encryption caller & talker identification better user interface (more than 12 keys, visual feedback, semantic rather than stimulus) no local access fees (but dropping to 1c/min for PSTN) adding video, application sharing is easy
carrier perspective
better codecs + silence suppression ± packet header overhead = maybe reduced bandwidth shared facilities simplify management, redundancy advanced services cheaper bit switching fax as data rather than voiceband data (14.4 kb/s)
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 Phase I conveys call back number + Pseudo-ANI (cell face identifier) to PSAP Phase II provides caller location (e.g., via GPS or TOA)
For wireless: Phase I and Phase II
Wireless 911 Phase II - TDOA
BellSouth
Wireless 911 Phase II - EOTD
BellSouth
Wireless 911 Phase II
Accuracy Handset-based Network-based 67% 50m 100m 95% 150m 300m
Example: Sprint PCS and Nextel use GPS Implementation just starting VolP has similar problems as wireless:
±
devices change ³network attachment point´
E9-1-1 Call flow elements - wireline
End office ES Trunks
E9-1-1 Tandem w/SRDB
EM Trunks
Public Safety Answering Point
Loop Acces s Contr ol ie DLC Syste m
PSAP
The Local Loop Recent Change Links
PSAP ALI Data Links
ALI
SCP GATEWAY (Firewall)
DBMS
Update Links Service Providers
ALI Database Elements
E9-1-1 CALL FLOW ELEMENTS - WIRELESS
ALI/SR DBASE 9 6 2 5 E9-1-1 Tandem w/SRDB
Public Safety Answering Point
PDE 3 4 MPC E2
8
7
MSC
PSAP
#9 is only applicable in a CAS-Hybrid architecture, such as BellSouth¶s WLS911 Solution
1
Henning Schulzrinne Dept. of Computer Science Columbia University Fall 2003
Overview
new Internet services: ³telephone´, ³radio´, ³television´ 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
variable compression: tin can to broadcast quality no need for dedicated lines security through encryption caller & talker identification better user interface (more than 12 keys, visual feedback, semantic rather than stimulus) no local access fees (but dropping to 1c/min for PSTN) adding video, application sharing is easy
carrier perspective
better codecs + silence suppression ± packet header overhead = maybe reduced bandwidth shared facilities simplify management, redundancy advanced services cheaper bit switching fax as data rather than voiceband data (14.4 kb/s)
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 Phase I conveys call back number + Pseudo-ANI (cell face identifier) to PSAP Phase II provides caller location (e.g., via GPS or TOA)
For wireless: Phase I and Phase II
Wireless 911 Phase II - TDOA
BellSouth
Wireless 911 Phase II - EOTD
BellSouth
Wireless 911 Phase II
Accuracy Handset-based Network-based 67% 50m 100m 95% 150m 300m
Example: Sprint PCS and Nextel use GPS Implementation just starting VolP has similar problems as wireless:
±
devices change ³network attachment point´
E9-1-1 Call flow elements - wireline
End office ES Trunks
E9-1-1 Tandem w/SRDB
EM Trunks
Public Safety Answering Point
Loop Acces s Contr ol ie DLC Syste m
PSAP
The Local Loop Recent Change Links
PSAP ALI Data Links
ALI
SCP GATEWAY (Firewall)
DBMS
Update Links Service Providers
ALI Database Elements
E9-1-1 CALL FLOW ELEMENTS - WIRELESS
ALI/SR DBASE 9 6 2 5 E9-1-1 Tandem w/SRDB
Public Safety Answering Point
PDE 3 4 MPC E2
8
7
MSC
PSAP
#9 is only applicable in a CAS-Hybrid architecture, such as BellSouth¶s WLS911 Solution
1
