VoIP

VoIP - ENUMVoIP - ENUM

CS 412

Presented by: ChunLok Mah

VoIP IntroductionVoIP Introduction

1) (VoIP) Voice over IP / IP Telephony Refers to the technology that supports two-way transmission of voice traffic over a packet-based IP network.

2) IP Phone, Web Set, or Soft Phone – new digital phone sets that utilize the VoIP technology. A Soft Phone typically does not include a traditional desktop phone, but instead uses the computer monitor of a local pc as the phone.

3) IP Telephony Gateway – device that translates IP telephone calls to the standard signal based telephone network, or vice versa. This allows users of IP phone systems to communicate with people using traditional phone systems.

4) Integrated Communication Platform (Gatekeeper)– device that combines all of a small businesses’ communication needs into one box. Serves as the hub/router for your local area network, connects with your DSL, cable, or T1 line as your gateway to the web, and provides your IP telephony services.

5) Multi-Service Networking – refers to putting all of the major communications services – voice, video, and data – onto a single IP based network.

Public switched telephone network (PSTN) Public switched telephone network (PSTN)

Building 1PBX

PBXinterconnect

Building 2PBX

Branch OfficePBX

PSTN network

TelephoneTelephone

TelephoneTelephone

TelephoneTelephone

Telephone

Telephone

voice

data

Voice Over IP (VoIP)Voice Over IP (VoIP)

IP network

Building 1H.323 terminal Gatekeeper


HighSpeeddata network

TelephoneH.323 terminal

ComputerH.323 terminal

TelephoneH.323 terminal Computer

H.323 terminal

Branch OfficeH.323 terminal Gatekeeper


H.323 terminal



H.323 = Packet-based multimedia communications systems

voice

data

VoIP PSTNVoIP PSTN

ISP network







H.323 terminal



H.323 terminal



Building 1PBX

PBXinterconnect

Building 2PBX

Branch OfficePBX

PSTN network

TelephoneTelephone

TelephoneTelephone

TelephoneTelephone

Telephone

Telephone

SIP Gateway

VOIP PSTN (continue)VOIP PSTN (continue)

Building 1PBX

PBXinterconnect

Building 2PBX

Branch OfficePBX

PSTN network

TelephoneTelephone

TelephoneTelephone

TelephoneTelephone

IP network






H.323 terminal



H.323 terminal

Telephone

TelephoneComputer

H.323 terminal



SIP Gateway

VoIP PSTN (continue)VoIP PSTN (continue)

PSTN networkIP network



Telephone

1) Alice dials Bob’s telephone number +61012345678

2) Telephone network routes the call request to the associate IP Gateway

3) Gateway looks up database with query +61012345678Gateway selects server 10.0.0.1

4) Gateway completes cal to SIP port on server 10.0.0.1

SIP Gateway

5) Bob IP telephone+6012345678

send corresponding telephone call code

VOIP PSTN (example)VOIP PSTN (example)

Consider an example. When Alice, on a normal telephone, wants to callBob, on an Internet phone.

1. All Alice needs to do is simply dial Bob’s telephone number, or his E.164 address.

2. Of course, because Bob’s phone is connected to the Internet and can’t directly receive Alice’s call request, a gateway is necessary. The telephone system should be able to map Alice’s call request to the Internet telephony gateway that is configured to act as Bob’s gateway agent.

3. The gateway then needs to translate Bob’s E.164 phone number into an IP address. Then the gateway has to map the telephone network signals associated with Alice’s call request to corresponding signals within an Internet session initiation protocol,

4. and then send these IP packets to Bob’s Internet phone. If Bob answers the call, the phone uses the same protocol to inform the gateway

5. The gateway then sends a corresponding telephone call code across the telephone network to Alice.

When Bob accepts the call, the gateway can then pass all data originating from Alice to Bob’s IP address, and all data received from Bob’s IP address across to the telephone connection to Alice for the duration of the call.

Alice never needs to know that Bob is using an Internet device. Alice dialed a phone number, heard it ring, and then heard Bob answer the call. For Alice, nothing has changed. Bob heard the phone ring, picked it up, and talked to Alice. For Bob, nothing has changed.

VOIP PSTN (problem) VOIP PSTN (problem)

ProblemThe simplest way to configure each gateway is to load each gateway with a configured

list of E.164 phone numbers and corresponding IP addresses. This approach is currently very common, but, like all statically configured approaches, has its weaknesses. But what happens when the IP device is numbered dynamically using the Dynamic Host Configuration Protocol (DHCP), or if it’s mobile, and moves from one service provider’s IP network to another, or when the end subscriber changes providers and that subscriber’s network is renumbered, or when the primary gateway fails and the providers want to switch to a secondary device? In other words, how can this mapping be dynamic rather than static?

SolutionThe way a dynamic domain name-to-IP address mapping can be maintained on the

Internet is through the Internet Domain Name System (DNS). The telephony gateway can use the E.164 address as the DNS query, and request the DNS to return the corresponding IP address. In our example, when Alice rings Bob, the gateway can use the DNS to obtain Bob’s current IP address. The gateway can then use the Session Initiation Protocol (SIP) to send to Bob’s Internet phone a call request, which then starts Bob’s phone ringing. If Bob changes IP address, then the corresponding change is a change in the DNS, not in the gateway itself. If the primary gateway fails and a secondary gateway is used, the secondary system can already access all necessary mappings through the DNS. The solution of this critical job fall to a little-known standard called Enum

What is ENUM?What is ENUM?

Short for “electronic numbering”. A protocol developed by the Internet Engineering Task Force

(IETF) Allows telephone numbers to be mapped to Internet Protocol (IP)

addresses. Through this mapping, a calling user can use the domain name system (DNS) to identify all communications services, such as facsimile, email, VoIP (voice over Internet Protocol) and a mobile phone service associated with the called user.

Internet telephony will benefit from this technology. It is being sought by federal agencies and other large organizations that see many potential benefits in the technology, such as big cuts in long-distance phone bills.

Telephone numbers used in ENUM would be E.164 numbers. These are telephone numbers defined and structured at the international level by the International Telecommunication Union (ITU) in its E.164 recommendation. E.164 describes the structure of the numbers used in the international telecommunication system and defines the general framework and criteria for assigning country codes (eg. 61 for Australia ).

How does ENUM work?How does ENUM work?

1) Once a telephone number is entered, it is translated into an Internet address using the following steps:

2) The phone number is translated into a fully qualified E.164 number by adding the city (or area) and country code. Example: 555-1234 dialed in Washington, DC becomes +1-202-555-1234, where the "1" represents the North American country code. The "+" indicates that the number is a fully qualified E.164 number.

3) All characters are removed except for the digits. Example: 12025551234

4) The order of the digits is reversed. Example: 43215552021 5) Dots are placed between each digit. Example: 4.3.2.1.5.5.5.2.0.2.1 6) The domain "e164.arpa" is appended to the end. Example:

4.3.2.1.5.5.5.2.0.2.1.e164.arpa 7) ENUM then issues a DNS query on this domain. Once the

authoritative name server is found, ENUM retrieves relevant NAPTR Resource records and will perform according to the user's registered services for that number.

Enum - arpaEnum - arpa

What is .arpa, and why is it the top level domain for ENUM? Why not create a new top-level domain specifically for ENUM?

The .arpa domain has been designated for Internet infrastructure purposes. It is managed by the Internet Assigned Numbers Authority (IANA) in cooperation with the Internet technical community under the guidance of the Internet Architecture Board (IAB). A new top-level domain (e.g., .e164) was not created because ENUM is an infrastructure application appropriate for designation within the previously established .arpa domain. ENUM is considered appropriate as an infrastructure application because it provides a set of DNS-based resource directories, referenced by phone number, for use by various ENUM-enabled application clients (such as telephones, SIP servers, and voice messaging systems).

Why is the number reversed? Why is the number reversed?

DNS names are structured from right to left. In the example used above (4.3.2.1.5.5.5.2.0.2.1.e164.arpa), DNS would first search for the top-level domain arpa, then search second-level domains for e164, then search the next level for the country code 1, etc.

Enum (example)Enum (example)

Let’s say Bob’s Internet telephone services are mapped to the E.164 address+61-0-12345678.

1) All Alice needs to do is simply dial Bob’s telephone number, or his E.164 address.

2) The telephone network routes the call request toward the Internet gateway that is the nominated service agent for this E.164 number.

3) The Internet gateway takes the call setup request with Bob’s number and first reverses the digits, then inserts a “.” between each digit, and finally appends e164.arpa. The resultant DNS string is the fully qualified domain name 8.7.6.5.4.3.2.1.0.1.6.e164.arpa. This name is then passed as a query to the Enum DNS.

4) The Enum DNS will reply with all associated NAPTR DNS resource records ORIGIN = 8.7.6.5.4.3.2.1.0.1.6.e164.arpa.

IN NAPTR = 100 10 "u" "sip+E2U" "!^.*$!sip:[email protected]!" 5) The Internet gateway will then query for the IP address for

sip:bob@server from DNS server6) The DNS will reply with the IP 10.0.0.17) Gateway will completes call to IP port on server 10.0.0.18) Bob picks up the phone. The gateway(10.0.0.1) then opens up a session

with UDP port 5060 on this SIP server to complete the call setup, requesting a voice session with the user Bob on this server.

Enum (example)Enum (example)

PSTN network

Telephone

IP networkBuilding 1

H.323 terminal Gatekeeper

Enum DNS Server

SIP Gateway

DNS Server

1) Alice dials Bob’s telephone number +61012345678

2) Telephone network routes the call request to the associate IP Gateway


3) Gateway queries 8.7.6.5.4.3.2.1.0.1.6.e164.arpa

4) Response sip+E2U sip:bob@server

5) Query IP address of server

6) Response 10.0.0.1

7) Gateway completes call to IP port on server 10.0.0.1

8) Bob IP telephone+6012345678

Enum - (NAPTR)Enum - (NAPTR)

100 10 "u" "sip+E2U" "!^.*$!sip:[email protected]!" 100 10 "u" "mailto+E2U" "!^.*$!mailto:[email protected]!"

(a) (b) (c) (d)

(a) Order Value - In this case the DNS entry uses an order value of 100 and apreference of 10.

(b) Rule - The “u” flag indicates that the rule is terminal and that the specified

URI is to be used. (c) Call request - the gateway picks the sip service

sip+E2U The gateway then opens up a session with UDP port 5060 on this

SIP server to complete the call setup, requesting a voice session

with the user Bob on this server.

"mailto+E2U" The gateway can complete the original text message delivery

request by opening a TCP session on port 25 of the mail server and

sending the message as mail addressed to user [email protected].

(d) URL - The operation of the regular expression produces the URI of the form

sip:[email protected]. The gateway then uses the DNS a second time

to translate the domain

ConclusionConclusion

1) Enum has the ability to make end-to-end phone calls using only regular data networks and avoiding the phone network entirely

2) "Enum standardizes the way in which you actually dial a phone number over the Internet without having to go to the PSTN for translation services" to an IP address, said David Fraley, principal analyst with Gartner Inc.'s Dataquest unit in San Jose, Calif. "Enum is a major step in helping to deliver voice-data convergence on an IP network."

3) That's the promise of Enum on a basic, though important, network plumbing level. From the users' perspective, Enum would let people give out a single telephone number, yet have it connect to multiple IP-enabled communications devices, such as their telephone, wireless phone, e-mail client, fax machine and wireless handheld computer.

4) "One thing Enum solves is the "business card' problem of too many addresses.... Over time you'll see people using a single telephone number as an address for a Web page or an e-mail address, or to receive a fax or an instant message," said Tom McGarry, chief of strategic technical initiatives at NeuStar Inc., Washington, D.C., one of three companies testing an Enum registry database.

NoteNote

Acronym1) (Enum) – Electronic Numbering2) (PBX) - Private branch exchange service3) (PSTN) - Public switched telephone network4) (SIP gateway) - Session Initiation Protocol gateway5) (NAPTR) - Naming Authority Pointers records.

Refernces1) http://www.cisco.com/warp/public/759/ipj_5-2.pdf2) http://www.tldp.org/HOWTO/VoIP-HOWTO-3.html#ss3.13) http://www.networkcomputing.com/918/918f1.html4) http://www.enum.org/5) http://www.epic.org/privacy/enum/default.html6) http://www.upgradepress.com/topstories/0602_voipterms.htm7) http://www.enum.org/information/faq.cfm

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