1. Towards Junking the PBX: Deploying IP Telephony
Wenyu Jiang, Jonathan Lennox, Henning Schulzrinne and Kundan Singh
Columbia University
We describe our departmental IP telephony installation

2. Columbia University, Deploying IP Telephony
What is a PBX ?
7040
External line
7041
Corporate/Campus
Telephone
switch
Private Branch
Exchange
Another
switch
7042
7043
Corporate/Campus LAN
Internet
March 12, 2001
Columbia University, Deploying IP Telephony

3. Columbia University, Deploying IP Telephony
What is IP Telephony ?
Corporate/Campus
Another campus
7040
8151
External line
8152
7041
PBX
PBX
7042
8153
8154
7043
Internet
LAN
LAN
March 12, 2001
Columbia University, Deploying IP Telephony

4. IP Telephony Protocols
Call
SIP
server
home.com
office.com
Contact “office.com” asking for “bob”
Session Initiation Protocol - SIP
Locate Bob’s current phone and ring
Bob picks up the ringing phone
Real time Transport Protocol - RTP
Send and receive audio packets
March 12, 2001
Columbia University, Deploying IP Telephony

5. Columbia University, Deploying IP Telephony
Architecture
rtspd
SIP/RTSP
Unified
messaging
RTSP media
server
sipum
Quicktime
RTSP clients
RTSP
T1/E1
RTP/SIP
Telephone
Cisco 2600 gateway
switch
SIP
conference
server
sipconf
Web based
configuration
Web server
SIP proxy,
redirect
server
SQL
database
sipd
e*phone
sipc
Software SIP
user agents
Hardware
Internet (SIP)
phones
SIPH.323
convertor
NetMeeting
sip323
H.323
March 12, 2001
Columbia University, Deploying IP Telephony

6. Columbia University, Deploying IP Telephony
Example Call
Bob signs up for the service from the web as
sipd canonicalizes the destination to
He registers from multiple phones
sipd rings both e*phone and sipc
Alice tries to reach Bob
INVITE
Bob accepts the call from sipc and starts talking
Web based
configuration
Web server
Call Bob
SIP proxy,
redirect
server
SQL
database
sipd
e*phone
sipc
Software SIP
user agents
Hardware
Internet (SIP)
phones
cs.columbia.edu
March 12, 2001
Columbia University, Deploying IP Telephony

7. Columbia University, Deploying IP Telephony
Other Services
Programmable servers
Time-of-day, caller identification
CPL, SIP CGI
Unified messaging
Centralized voice mail and answering machine
SIP, RTSP
Conferencing
Dial-in bridges; centralized audio mixing
Audio, video and chat
March 12, 2001
Columbia University, Deploying IP Telephony

8. Columbia University, Deploying IP Telephony
PSTN to IP Call
PBX
PSTN
External T1/CAS
Regular phone
(internal)
Call 1
Gateway
Internal T1/CAS
(Ext: )
Call 7134 2
713x is called a part of Coordinated Dial Plan (CDP) in a Nortel PBX
SIP server
sipd
Ethernet 3
sipc 5
Bob’s phone
SQL
database 4
7134 => bob
DID - direct and simple
No-DID - dial extension, supports more users
March 12, 2001
Columbia University, Deploying IP Telephony

9. Columbia University, Deploying IP Telephony
IP to PSTN Call
PBX
Internal T1/CAS
Call 4
Regular phone
(internal, 7054)
PSTN
External T1/CAS
Call 5
Gateway
( ) 3
Ethernet
SIP server
sipd
sipc 1
Bob calls
SQL
database 2
Use
March 12, 2001
Columbia University, Deploying IP Telephony

10. T1 Line Configuration (From the PBX Side)
Electrical/physical settings
T1 type: Channelized, PRI
Characteristics: line coding - AMI, B8ZS; framing - D4, ESF
Trunk type: DID, TIE
Channel type: Data, Voice-only, Data/Voice
Access permissions: adjust NCOS for internal T1 trunk and CDP routing entry (713x)
March 12, 2001
Columbia University, Deploying IP Telephony

11. Columbia University, Deploying IP Telephony
Security
Prevent unauthorized users from making certain (e.g., long-distance) calls
IOS access control
SIP authentication
Future:
PIN numbers for telephone users
Automated, electronic billing
March 12, 2001
Columbia University, Deploying IP Telephony

12. Conclusion and Future Work
Initial field test experience with deploying IP telephony in a campus environment
The architecture and installation experience can be used at other organizations
Future Work:
Additional services, e.g., instant messaging, VoiceXML
Performance and scalability: sipd, rtspd, sipconf
Firewall/NAT, SNMP
March 12, 2001
Columbia University, Deploying IP Telephony