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2007 © MDS Version 1.0
ENUM overview
Introduction, Usage scenarios,
B. Höneisen, Switch
Goran Radoji_i_
2006 © MDS 2Version 1.0
Content
Part I: Introduction to ENUM
Part II: The ENUM forest
2006 © MDS 3Version 1.0
Content (part I)
• What is ENUM?
• How does it work
• What can you do with ENUM
• Interworking examples with SIP and ENUM
2006 © MDS 4Version 1.0
What is ENUM?
• ENUM: E.164 Number Mapping
• Idea: Make different numbers, addresses and URLsavailable under one single telephone number
• ENUM uses the DNS (Domain Name System) tomap telephone numbers into internet addresses
PSTN IP networkVoiceGateway
Alice
Bob
ENUM
DNS server
E.164
number
IP address
2006 © MDS 5Version 1.0
ENUM and Identifiers
• Internet identifiers typically look as follows:– mailto:[email protected]
– sip:[email protected]:5060
– msn:[email protected]
• Legacy telephony systems use the E.164 numbering:– +41 44 268 15 15
– +358 50 369 95 02
• To combine these two addressing schemes, the ENUMhas been standardized
– The “Common denominator”: Numbers
– E.164 numbers are mapped to Internet Identifiersor other communication parameters
– IETF protocol
2006 © MDS 6Version 1.0
How does ENUM work?
• E.164 numbers can be inserted into the DNS using ENUM
• Example for: +41-1-268 15 15– Remove everything but numbers: 4112681515
– Reverse it and put dots in between the digits: 5.1.5.1.8.6.2.1.1.4
– Add the suffix “.e164.arpa”: 5.1.5.1.8.6.2.1.1.4.e164.arpa
---> This is the DNS zone
– Fill this DNS zone with NAPTR records such as:» IN NAPTR 100 1 "u" "E2U+sip" "!^.*$!sip:[email protected]!” .
• When a E.164 number is dialed:– Devices look up the corresponding DNS zone for NAPTR records
– Replace the phone number (here: sip:[email protected])
2006 © MDS 7Version 1.0
Possibilities with ENUM
2006 © MDS 8Version 1.0
PSTN to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
A's SIPServer
2006 © MDS 9Version 1.0
PSTN to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
1
1) Call is routed to a PSTN-IP Gateway (GW)
A's SIPServer
2006 © MDS 10Version 1.0
PSTN to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
2
2) GW looks up in ENUM (DNS) and gets User B’s SIP address as answer
1
1) Call is routed to a PSTN-IP Gateway (GW)
A's SIPServer
2006 © MDS 11Version 1.0
PSTN to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
2
2) GW looks up in ENUM (DNS) and gets User B’s SIP address as answer
1
1) Call is routed to a PSTN-IP Gateway (GW) 3
3) GW routes call to B's SIP Server (BSS) (SIP address in ENUM answer points to BSS)
A's SIPServer
2006 © MDS 12Version 1.0
PSTN to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
4
4) BSS consults its database for the current location(s) of User B
2
2) GW looks up in ENUM (DNS) and gets User B’s SIP address as answer
1
1) Call is routed to a PSTN-IP Gateway (GW) 3
3) GW routes call to B's SIP Server (BSS) (SIP address in ENUM answer points to BSS)
A's SIPServer
2006 © MDS 13Version 1.0
PSTN to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
4
4) BSS consults its database for the current location(s) of User B
2
2) GW looks up in ENUM (DNS) and gets User B’s SIP address as answer
1
1) Call is routed to a PSTN-IP Gateway (GW) 3
3) GW routes call to B's SIP Server (BSS) (SIP address in ENUM answer points to BSS)
5
5) Call is routed to SIP phone of user B, and the phone rings
A's SIPServer
2006 © MDS 14Version 1.0
SIP to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
A's SIPServer
2006 © MDS 15Version 1.0
SIP to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
A's SIPServer
1
1) Call is routed to A's default outbound proxy (ADOP)
2006 © MDS 16Version 1.0
SIP to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
A's SIPServer
2
2) ADOP looks up in ENUM (DNS) and gets the SIP address for user B as answer
1
1) Call is routed to A's default outbound proxy (ADOP)
2006 © MDS 17Version 1.0
SIP to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
A's SIPServer
2
2) ADOP looks up in ENUM (DNS) and gets the SIP address for user B as answer
1
1) Call is routed to A's default outbound proxy (ADOP) 3
3) ADOP routes call to B's SIP Server (BSS) (SIP address in ENUM answer points to BSS)
2006 © MDS 18Version 1.0
SIP to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
4
4) BSS consults its database for the current location(s) of User B
A's SIPServer
2
2) ADOP looks up in ENUM (DNS) and gets the SIP address for user B as answer
1
1) Call is routed to A's default outbound proxy (ADOP) 3
3) ADOP routes call to B's SIP Server (BSS) (SIP address in ENUM answer points to BSS)
2006 © MDS 19Version 1.0
SIP to SIP terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
4
4) BSS consults its database for the current location(s) of User B 5
5) Call is routed to SIP phone of user B, and the phone rings
A's SIPServer
2
2) ADOP looks up in ENUM (DNS) and gets the SIP address for user B as answer
1
1) Call is routed to A's default outbound proxy (ADOP) 3
3) ADOP routes call to B's SIP Server (BSS) (SIP address in ENUM answer points to BSS)
2006 © MDS 20Version 1.0
SIP to PSTN terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
A's SIPProxy
2006 © MDS 21Version 1.0
SIP to PSTN terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
1
1) Call is routed to A's default outbound proxy (ADOP)
A's SIPProxy
2006 © MDS 22Version 1.0
SIP to PSTN terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
2
2) ADOP looks up in ENUM (DNS) and does not get any SIP address for user B as answer
1
1) Call is routed to A's default outbound proxy (ADOP)
A's SIPProxy
2006 © MDS 23Version 1.0
SIP to PSTN terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
2
2) ADOP looks up in ENUM (DNS) and does not get any SIP address for user B as answer
1
1) Call is routed to A's default outbound proxy (ADOP)
3
3) ADOP routes call to the PSTN-IP Gateway (GW)
A's SIPProxy
2006 © MDS 24Version 1.0
SIP to PSTN terminal
PSTN IP
A
SIP-A
PSTNIPGateway
ENUM(DNS)
B's SIPServer
B SIP-B
2
2) ADOP looks up in ENUM (DNS) and does not get any SIP address for user B as answer
1
1) Call is routed to A's default outbound proxy (ADOP)
3
3) ADOP routes call to the PSTN-IP Gateway (GW)
4) GW routes the call (within the PSTN) to B, and the PSTN phone of B rings.
4
A's SIPProxy
2006 © MDS 25Version 1.0
Content (part II: The ENUM forest)
• Two dimensions of ENUM
• Public vs. private ENUM trees
2006 © MDS 26Version 1.0
The ENUM forest...
• ENUM technology used in two “dimensions”:– public vs. private– User vs. Infrastructure
– User ENUM:» Assignee of E.164 numbers (e.g. university) control ENUM entries
– Infrastructure ENUM:» Carrier/Service Provider control ENUM entries
• For NRENs User ENUM is of interest
• Only e164.arpa is real ENUM as standardized by the IETF
User ENUM Infrastructure ENUM public ENUM e164.arpa private ENUM e164.info, ...
ie164.arpa e164.org, nrenum.net, ...
2006 © MDS 27Version 1.0
Public vs. private ENUM
Public ENUM (e164.arpa)• Advantages:
– Trust (national regulators have the final word on delegation)– Global solution (standardized in IETF with ITU involvement)– High availability
• Disadvantages:– Not available for every Country Code (often due to political reasons)
Private ENUM (e.g. e164.org)• Advantages:
– Available everywhere
• Disadvantages:– Holder of superordinate domain name has the sole power to rule, e.g.:
» Impose restrictions or costs (without any kind of control)– Continuity not guaranteed
» Sell the superordinate domain name / shut the tree down
2006 © MDS 28Version 1.0
Conclusion
• Private ENUM trees to be considered with care!• ENUM services can be missused by spamers!
