Transcript SIP Basics - Massachusetts Institute of Technology

Internet Peering and
PSTN Access
Merit VoIP Seminar
Dennis Baron
April 3, 2008
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Dennis Baron, April 3, 2008
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Outline
• It’s all SIP!
• SIP.edu
• ISN
• PSTN Access
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Dennis Baron, April 3, 2008
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Well You Are Using SIP Anyway
• What is SIP
– IETF Standard defined by RFC 3261
– “The Session Initiation Protocol (SIP) is an application-layer
control (signaling) protocol for creating, modifying and
terminating sessions with one or more participants.”
• Can be used for voice, video, instant messaging, gaming,
etc., etc., etc.
• Uses URIs for addressing – single communications identity
–
mailto:[email protected] for email
–
xmpp:[email protected] for instant messaging
–
sip:[email protected] for voice and video
• Usernames just replaced by numbers for telephone
applications
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Soft and Hard SIP Clients
• “Hard phones”
• “Soft phones”
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Why Phone NUMBERS?
• Users should not be burdened with device addresses, when it’s
people they really care about
• Addresses should be mnemonic and empower enterprises to
manage the identities of their users
sip:[email protected]
• It’s time to put E.164 phone
numbers behind us!
• A.G. Bell did not say:
“+1-617-252-1232, come
here. I need you!”
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Architecture (Phase 1)
SIP User Agent
DNS SRV query
sip.udp.bigu.edu
INVITE
(sip:[email protected])
bigu.edu
SIP
Proxy
DNS
INVITE
(sip:[email protected])
SIP-PBX
Gateway
PRI / CAS
PBX
telephoneNumber
where mail=”bob”
Campus
Directory
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Bob's Phone
Dennis Baron, April 3, 2008
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Architecture (Phase 2)
SIP User Agent
DNS SRV query
sip.udp.bigu.edu
INVITE
(sip:[email protected])
If Bob has registered, ring his SIP phone;
Else, call his extension through the PBX.
bigu.edu
DNS
location
DB
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SIP
Proxy
INVITE
(sip:[email protected])
SIP
Registrar
REGISTER
(Contact: 207.75.164.131)
Bob's SIP Phone
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How to SIP from a 12-key phone?
Old World*
Emerging
New World
IP Desk
Phones
Cell Phones
Legacy Desk
Phones
PSTN
* Transitional period during which we have to
Solution:
numeric aliases
support these devices will last a long time!
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ITAD Subscriber Numbers (ISN)
• 21232*270
locally
assigned
IP Telephony Administrative Domain (ITAD)
• ITADs
–Defined by Telephony Routing over IP (TRIP)
[IETF RFC3219]
–Globally unique
–Lots of them (232 - 256)
–IANA is already set up to allocate
• ISN resolution works just like ENUM
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Assigned ITADs (as of 3/15/06)
Academic
Corporate Enterprises
–
Internet2
–
Hofstra University
–
UCLA
–
MIT
–
Stanford
–
University of Alaska Fairbanks
–
University of California, Berkeley
–
Florida State University
–
University of Manitoba
–
University of Oregon
–
Royal Institute of Technology
–
Tello
–
NE Worcestershire College
–
Iotum
–
Trent University
–
Digium
–
University of North Carolina
–
University of Texas, Austin
–
Columbia University
–
BizFu (web hosting)
–
UCSD
–
Manitoba New Democratic Party
–
Taiwan Academic Network
–
Packet Clearing House
–
+36 others
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–
Sterling National Bank
–
Apple Computer
VoIP Service Providers
Government
–
State of Oregon
–
Free World Dialup
–
Stealth Communications
–
SIPcall.com
–
RCN Corporation
–
VoIPteq
–
SIP Broker
VoIP Solution Providers
Other
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How Does Peering Work?
Public
Internet
Transit
Transit
ISP #1
ISP #2
Your
Network
Your
Partner
Workstation
Web Server
Peering
diagrams courtesy of Stealth Communications
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Options for PSTN Termination
• May be an evolution or combination of different interconnect
options
– Transit via gateway to campus PBX
– Direct IP connection to carriers
– Access via regional or national networks
– Access via commodity Internet
– Brokers for peering and PSTN termination
• PSTN-to-VoIP and VoIP-to-PSTN traffic can use different
options
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Types of Peering Connections
• Direct interconnection at
a carrier hotel (“private
peering”).
ISP 1
Your
Network
ISP 2
ISP 3
ISP 1
Your
Network
IX
ISP 2
• Peering typically done
over Layer-2 Fabrics
(also known as a NAP or
IX)
ISP 3
diagrams courtesy of Stealth Communications
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ENUM for Peering
+1-212-232-2020
sip: [email protected]
•
IETF RFC 3761
h323: [email protected]
•
Single number for
multiple services
h323: [email protected]
http: www.stealth.net
...
diagrams courtesy of Stealth Communications
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ENUM for Peering (cont.)
Query-Response technology
1. User initiates phone call
2. Query sent to ENUM database
3. Routing information (URL) returned
4. If “true”, call established between the
organizations
ENUM
database
2
3
Carrier/
Enterprise
“1”
4
WAN
4
Carrier/
Enterprise
“2”
4
1
Originating
IP Phone
Terminating
IP Phone
Initiate calls using telephone numbers
diagrams courtesy of Stealth Communications
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Broker Example (Arbinet)
Independent non-profit
company
Download
Numbers
Peer
with
partner
University
ENUM
Server
Import Numbers
Route call
Over Internet2
diagram courtesy of Arbinet
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Considerations for Peering
• Things to think about
– Signaling and media can take separate routes
– Diversity of paths – failover
– Quality of service issues
– Options for flexible services
• And opportunities to consider
– Disaster recovery options
– Flexibility in choosing carriers
– Control routing yourself in real-time
– Trade minutes like a carrier
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Questions?
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