presentation - heanet, ireland's national education
TRANSCRIPT
VoIP in ContextNiall O’Reilly, University College Dublin IT Services
HEAnet National Networking Conference 2006
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
VoIP in Context
• Strategic issues
• How VoIP works
• Interoperation
Strategic options
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
VoIP: Strategic Issues
• Global or local scope?
• Build, buy, or leave it to the users?
• Proprietary or standards-based?
• Branding?
First, see how it works ...
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
How VoIP works
• Different flavours:Standards: SIP, H.323, Services: Skype, IP-TSPs
• Similar requirements:Find called partySet up call
Look at SIP ...
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
SIP — direct call
192.168.19.7610.17.243.34
INVITE sip:10.17.243.34100 Trying -
ACK
RTP session (voice, video, etc)
Artificially simple case:caller knows where my phone is
Caller’s
phoneMy
phone
200 OK180 Ringing -
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
SIP — where did he go?
10.17.243.34
Usual case:my phone is nomadic
Caller’s
phoneMy
phone
10.97.1.5
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
SIP servers keep track
10.17.243.34
SIP Registrar:tracks last REGISTER event
Caller’s
phoneMy
phone
10.97.1.5
SIP Registrar serversip.example.netCaller’s SIP server
(if any)
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
SIP — using servers
INVITE sip:[email protected]
ACK
RTP session (voice, video, etc)
Servers broker call using SIPPayload is carried peer-to-peer
INVITE
INVITE
200 OK
ControlTransport
Data
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
VoIP compared to e-mail
Submit
Difference:mail servers carry payload
Forward
Retrieve
Control & DataTransport
Messagequeue
Messagestore
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
VoIP compared to POTS
Place call
Difference:Payload travels over provider’s resources
Set upcircuit
Terminate call
Voice trafficover circuit
Vertically integrated:no separation of Control, Data,
and Transport
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
Interoperation
• Technology: gateways, mapping
• Service management
• Business model
POTS is centre-stage
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
POTS Interoperation
• Dial planwhat can be dialled (DTMF-12)
• Numbering planwhat can be reached (E.164)
• Interconnectionspecific number ranges — routing
codes
• Cascaded chargesterminating operator in control
• Fewer hops best for business
Originating Operator
TerminatingOperator
TransitOperator
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
• POTS uses [*#0-9]— VoIP side must accommodate
• Customer aliases facilitate this— Real POTS phone number
(E.164)— Two-stage dialling to
“extension”— [email protected]— [email protected]
VoIP/POTS Address Mapping
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
VoIP Interoperation
• Technology open — just like e-mail
• Operator business model varies— “walled garden” vs “public
park”
• Obstacles may be significant — NAT, firewall
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
VoIP Interoperation• Static routes support bilateral
agreements
• VoIP “islands” may need to route via POTS
— involving duration charges, double transcoding
• ENUM maps numbers to URLs— but not yet widely (enough) deployed
Not unlike e-mail before MX records
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
• Example
• [Remember “!” and “%” for e-mail]
• *8 *4yy 8972xxxx
• sip:[email protected]
Address Mapping
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
• Encodes E.164 numbers as domain names
— no “short codes” or “operator-specific”
• Standard algorithm to determine URL
— DDDS: RFC 3401ff
Not yet generally deployed
ENUM
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
Strategic options
• Global or local scope?
• Build, buy, or leave it to the users?
• Proprietary or standards-based?
Branding?
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
Local or global scope
• Technology substitution
• “Free” long-distance phone-calls
• Extend footprint of internal PBX— teleworkers, conference-
goers
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
Build, buy, or step aside
• In-house like e-maillinked to other administrative processes
• Outsource to existing IP-TSPestablished expertise
• Skype — just workswalled garden with gates (charged
Skype-in, -out)
Gizmo — has free SIP-out
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
Standard or proprietary
• Cisco, Nortel, ...
• Skype
• StandardInteroperabilityExploits DNS for provisioningOpen Source: SER, Asterisk
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
Branding• What goes on the stationery?
• Skype: joe_user
• IP-TSP: sip:[email protected]
• Own-brand: sip:[email protected]
E.164: +353-1-716-xxxx
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
Strategic options
• Global or local scope?
• Build, buy, or leave it to the users?
• Proprietary or standards-based?
• Branding?
• Know what you require, then decide
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
VoIP Resources
• Terena VoIP Cookbook (2004)
• Richard Stastny’s Bloghttp://voipandenum.blogspot.com
iptel.org
Niall O’Reilly — UCD IT ServicesVoIP in Context — HEAnet NNC 2006
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