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  • Updated On : . ISN: Free Numbers Fast. Dennis Baron, MIT Ben Teitelbaum, Internet2 John Todd, Loligo September 13 th , 2006 Fall VON, Boston, MA. …. …. PSTN. …. …. Internet. …. …. VoIP Service Provider. …. …. VoIP brought to you by….

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Isn free numbers fast

ISN: Free Numbers Fast

Dennis Baron, MITBen Teitelbaum, Internet2John Todd, Loligo

September 13th, 2006Fall VON, Boston, MA



VoIP ServiceProvider

VoIP brought to you by…

RTC brought to you by…

Old world new world
Old World / New World

Radically new devices / services


[email protected]

Deep bureaucratic hierarchy

The world is flat (almost)

Telco provider control

Be your own provider

Sip edu

  • Email address as RTC handle

  • 250k .edu users

sip:[email protected]

Unfortunately, it’s hard to enteralphanumeric addresses on this:

Isn numbers
ISN Numbers…


Domain-local(you allocate)

ITAD(IANA allocates)[RFC3219]

Itad subscriber numbers
ITAD Subscriber Numbers

  • Defined by Telephony Routing over IP (TRIP) [RFC3219]

  • Globally unique

  • Lots of them (256 through 232-1)

  • IANA is already set up to allocate

  • ISN resolution works just like ENUM

Corporate Enterprises

  • Sterling National Bank

  • Apple Computer

ISN Trial Participation

  • 67 domains from 14 countries


  • Internet2

  • Hofstra University

  • UCLA

  • MIT

  • Stanford

  • University of Alaska Fairbanks

  • University of California, Berkeley

  • Florida State University

  • University of Manitoba (Canada)

  • University of Oregon

  • Royal Institute of Technology (Sweden)

  • NE Worcestershire College (England)

  • Trent University (Canada)

  • University of North Carolina

  • University of Texas, Austin

  • Columbia University

  • UCSD

  • Taiwan Academic Network

ITAD Assignments

  • 153 domains from 17 countries

VoIP Solution Providers

  • Tello

  • Iotum

  • Digium

  • Nokia

VoIP Service Providers

  • Free World Dialup

  • Stealth Communications


  • RCN Corporation

  • VoIPteq

  • SIP Broker

  • TellMe

  • PhoneGnome


  • BizFu

  • Manitoba New Democratic Party

  • Packet Clearing House


  • State of Oregon


  • ITAD Subscription: Free

  • License restrictions: None

  • Monthly recurring: None

  • Tech time: Small

  • User instruction: Medium

Benefits 1 2

  • Free VoIP calling (expected zero-cost)

  • Future-proof numbering

  • Does not require change of equipment

  • Easy user memorization

  • Unique format makes routing and CDRs obvious

Benefits 2 2

  • Incremental deployment of dialing plan

  • Even works with most SIP-only iPBX systems

  • Does not require VPNs, Switch fabrics, or contracts

  • No question of "ownership" of number space

  • No contradictory routes possible

  • Low technology hurdles to jump (standards-based!)

Isn vs enum vs sip aor

Enum in a nutshell

sip:[email protected]

mailto:[email protected]

sip:[email protected]

ENUM in a Nutshell

  • Take an E.164 number

  • Convert it to FQDN

  • Query DNS for NAPTRs

  • Apply resulting regexs to get list of URIs:


Isn in a nutshell

sip:[email protected]

mailto:[email protected]

sip:[email protected]

ISN in a Nutshell

  • Take an ISN

  • Convert it to FQDN

  • Query DNS for NAPTRs

  • Apply resulting regexs to get list of URIs:


Note: We are working to ensure that the ISN root zone will be administered on behalf of the ISN user community by a neutral, non-profit organization. Following the trial, the root may or may not be “”.

3 easy steps
3 Easy Steps

  • Request an ITAD from IANA

  • Publish your ITAD/ISN information in DNS

    • Option1: Put full NAPTR in root zone* IN NAPTR 100 10 "u" "E2U+sip” "!^\\+*([^\\*]*)!sip:\\[email protected]!" .

    • Option2: Have root zone delegate to your own nameservers

  • Enable inbound / outbound ISN calling

    • Recipes for SER and Asterisk available

Asterisk implementation
Asterisk Implementation

  • Outbound dialplan (one line!):Exten => _012.,1,Dial(SIP/${ENUMLOOKUP(${EXTEN},sip,i,})

  • Inbound:

    • No changes if your system supports inbound SIP extension calls

Ser implementation 1 2
SER Implementation1/2

  • Inbound:

    • No changes if your system supports inbound SIP extension calls

    • Otherwise, can alias ISNs to URIs and resolve (see ISN Cookbook for example)

Ser implementation 2 2
SER Implementation2/2

  • Outbound:route[3] { # Assert that uri is in proper format if (! (uri =~"^sip:[0-9]+\*[0-9][email protected]")) { xlog("L_CRIT", "%Tf: route[3] called with improper ISN\n"); break; }; if (!exec_dset("/usr/local/bin/")) { sl_send_reply("404", "Not Found"); break; } else { xlog("L_INFO", "%Tf: Routing outbound ISN Call %ru(From [%fu], To [%tu])\n"); # Relay the message if (!t_relay()) { sl_reply_error();}; };} # end of ISN route block

Dumb ipbx implementation
“Dumb” iPBX Implementation

  • Pseudocode using public helpers:

    if $DIALEDNUMBER starts with "012" then strip off "012" from $DIALEDNUMBER send SIP INVITE to [email protected] dial-as-normal

Mit deployment
MIT Deployment

  • Motivation

    • Evolution of our SIP infrastructure

    • Advancing support of early technology adopters

    • While maintaining interoperability with legacy technologies

    • Support for innovation on the “experimental campus”

    • Broaden our federation options

    • But still encourage the migration to full URI support!

Mit deployment1
MIT Deployment

  • Use Cases

    • Student can be called in her dorm room from friends and family using non-MIT VoIP services that use SIP analog terminal adapters

    • MIT press editor can collaborate with authors using his traditional PBX ISDN phone

    • MIT researchers can reach experimental voice recognition servers at a remote research lab from any campus phone

Mit deployment2
MIT Deployment

  • Issues

    • Easy to implement “native” ISN dialing on our SER based SIP proxies (but we haven’t done this yet)

    • Legacy PBX (Lucent 5ESS) couldn’t seem to cope with the “*”

    • Implemented Asterisk server to collect digits and route ISN calls

Mit deployment3

DNS lookup for 262

FWD phone rings

MIT SIP Proxy Servers

Campus Network


MIT Asterisk Server




Server prompts for number:

User dials 248911*

Server prompts for domain:

User dials 262#

MIT PBX user dials *0

MIT Deployment

Self demo

  • Call: +1-712-432-7935

  • Listen to the IVR

  • Enter an ISN

    • 87225*270 - MIT Shuttle Track

    • 2425*259 - Tello “success” message

    • 1234*256 - Recorded monkeys, echo test

For more information
For More Information