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Document Contents Executive Summary Introduction Background Recommendations for a MOREnet Dialing Plan Conclusion Related Documents References Appendix: Private Numbers Glossary Endnotes Illustrations The Connectivity Picture Tables Call Type Table MOREnet Dialing Plan FAQ Frequently asked questions about MOREnet's dialing plan. Research Feedback Form Submit this form to suggest research topics or ask research-related questions.

MOREnet Dialing Plan: PSTN and IP Network Integration for H.323, H.320 VoIP and Public Voice Networks

Executive Summary

Migrating voice and video services from the PSTN to IP-based networks brings as many challenges as opportunities. Although cost-efficiency, scalability, ease of deployment and other factors drive organizations towards converged voice, video and data networks, interoperability between the PSTN and IP networks remains an issue.

The rapid rise of voice-over-IP (VoIP) systems as replacements for traditional PBX systems as well as the explosion of H.323 as a tool for both educational and business applications calls for a better way to manage the interoperability issues. There will continue to be H.320-based video systems, PBXs and the PSTN for many years to come, but these systems should not be isolated from the IP-based network using VoIP and H.323. While gateways have improved and are able to handle many devices, the idea of a universal calling schema has recently become a hot topic.

In the PSTN, E.164 is the global standard for dialing systems and is technology-independent. An E.164 address may connect to a analog device, such as a phone, modem or fax machine, or to a digital device, such as an ISDN modem or video terminal. In the Internet, the IP address is the unique identifier and represents a device, regardless of the connection type (Ethernet, ATM, etc.) or device type (PC, printer, router, etc.).

A new standard, ENUM, has been proposed by the ITU (which is responsible for the E.164 standard) and the IETF (which is responsible for IP) that marries E.164 addressing and DNS, a tool used to located an IP address based on a device name and domain identifier.

This paper explores the issues related to a universal dialing system for both PSTN voice and IP-based voice and video systems. Although there are several dialing plans in existence, none of them are standards-based. After careful consideration, the recommendation made is that MOREnet use the E.164 dialing system in preparation for ENUM as the unified dialing system. This maintains interoperability, is standards-based, and will be the least disruptive to operations over the next few years.

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Introduction

Although voice, video and data are converging onto a single network, there is no current solution for an integrated dialing plan. Traditional phones use E.164¹ addresses (we call them "phone numbers"), and IP phones and video codecs use IP addresses. However, the two systems need to be unified so that a caller can reach a destination regardless of the device type. In other words, calling an IP phone from a PSTN phone should just work.

Today, an enterprise that wants to map a phone number to an IP address has to have a gateway-a device that translates an IP address to a phone number and vice versa. These devices are controlled by the organization, so there is no central system or hierarchy to use to find a gatekeeper in order to make a connection.

One proposed system, called ENUM², might rectify this situation. By extending the functionality of the DNS system and adding some hierarchical structure, a scalable system to map phone numbers to IP addresses can be built. However, ENUM is still in draft form, with no current date for approval, although there are several vendors with trial implementations.

MOREnet and its customers need a dialing plan that can co-exist with E.164 as well as IP (using the gateway structure in place today, as well as ENUM or related services in the future). The continual readdressing of terminals as convergence occurs creates a support load that is unnecessary if proper planning is undertaken. Call routing issues for both the PSTN and IP networks demand a solution that can scale and interoperate within the various standards.

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Background

In the public network, the North American Numbering Plan is used to make phone calls (in the U.S.A., Canada and Mexico). Phone numbers are in the format NPA-NNX-XXXX, where:

NPA - Numbering Plan Area ("area code") [in the format NXX]

NNX - Office Code [in the format NNX]

XXXX - Phone number (subscriber's "address") [in the format XXXX]

where N = a number between 2 and 9 and X = any number (0-9)

NPA-NNX combinations are generally geographically specific, such as 573-874 being an office serving Columbia, MO, while 408-526 is an office serving San Jose, CA. Exceptions to this include 800/888/877 toll-free numbers, which are not geographically specific (although the area codes that they can be called from can be controlled).

The local PSTN switch routes the call if the call destination is local, or hands the call to an IXC if the call is long distance. Call information, such as calling number, called number, billing number, etc. is passed from switch to switch using SS7.³

Outside the PSTN, however (such as IP-based H.323 video or VoIP), we either need to know the IP address, the DNS name, or the gateway and the codec id of a remote video codec (the same is true of a VoIP phone).

IP numbers are in the format of A. B.C. D, where each digit is a number between 0 and 255. There are complex rules to IP assignments, and properly assigned numbers are necessary to connect to the global Internet. Currently, IP version 4 is in use, but a new version of IP has been developed, called IP v6, which will eventually replace version four.

With an IP address of 209.12.36.92, for example, a user can locate a device on the Internet. However, these numbers are hard to remember, may change often, and aren't as stable as phone numbers, as individual sites can renumber IP devices at will (or may use DHCP,⁴ which assigns a new number each time a device is connected to the network). DNS helps, as it assigns a name to the IP address that is easier to remember (such as www.more.net), and then gives the IP address that matches. With this system, users do not care what the IP address is as long as the DNS system knows.

An example of this type of locating system can be found in the cellular networks today. Each cell phone has a unique Electronic Serial Number (ESN), When a cell phone is programmed, it is told what its E.164 address is, and the cellular carrier's database is given the ESN - E.164 match also. When someone calls the E.164 address, the carrier looks up the phone's ESN in its database, locates it in the network and forwards the call. The caller does not know which cellular carrier he or she is calling, which network the phone is on (home or roaming), where it is, what kind of phone (CDMA, TDMA, GSM, PCS), etc. They know that for a voice call they can call a particular E.164 number and the phone will ring.

Imagine trying to do this by having to keep track of the various carriers, whose phone is from which carrier and what the phone's ESN is. If you get a new phone, your ESN changes-which means all your friends and family need to be updated with the new number, or they can't call you! The use of the E.164 number to mask the technical implementation issues makes the system easy to use.

Directory Services

In the IP world, there are no directory services, although LDAP and DNS are being used to attempt to build such a system.

Ideally, knowing a person's DNS "name," e-mail address, or phone number should allow a user to access to the database to find out other service addresses, such as their H.323 video address, VoIP phone address, etc. This is the goal of ENUM. Once a users knows one identifier, he or she can query the database to find the correct addressing information; for example, knowing an e-mail address (fred@more.net) will allow an ENUM query to return the IP address of Fred's SIP⁵ phone for a VoIP call or the E.164 address of his PSTN or cell phone for a standard voice call.

Transition

Moving between the rigid hierarchical structure of the PSTN and the looser IP network is difficult, but increasingly necessary, as we move through the "transition time" from multiple networks to a single, converged network. This transition will take months to even begin, as ENUM is not yet ratified and accepted, although there are several companies with offerings and implementations based on the draft.

Numbering Systems

In the PSTN, an international standard known as E.164 is used in the assignment of numbers. This standard is administered by the ITU-T and is used worldwide to assign telephone numbers. In North America, the ITU-T's E.164 addressing scheme is administered by the North American Numbering Plan Administrator (NANPA), which is an agency charged with managing the address space. The NANPA manages the allocation of numbers to providers, works with regulatory bodies and ensures global connectivity of devices.

In the IP world, addresses are assigned by the IANA to Tier 1 ISPs, who in turn distribute them to their connected networks, and so on. Addresses are not assigned in a geographic fashion like telephone numbers, and without any directory services, finding out what's at a number is difficult to impossible. There are no US-wide or global rules on how IP addresses should be allocated, so each organization has come up with its own plan. In addition, technologies such as DHCP and Network Address Translation (NAT) complicate the IP network.

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Recommendations for a MOREnet Dialing Plan

In order for devices to communicate with the PSTN as well as the IP network, a uniform addressing schema needs to be adopted. In the past, systems were devised to uniquely identify the codec, such as combinations of the ZIP code and MAC address⁶ of the codec, or ViDeNet's dialing plan⁷ based on a complex identifier.

These systems do not truly integrate with the E.164 addressing standards, and therefore pose issues in attempting to build a transparent network. Ideally, users don't need to know whether the traffic is carried via IP or the PSTN-they just need to know the destination terminal address (phone number).

One of the more promising implementations is ENUM,⁸ which would provide a DNS-type lookup for E.164 addresses. This system, when implemented, would remove the barriers between the IP and PSTN, as the record could identify the network type as well as the network and destination address.

The goal of a MOREnet dialing plan is to provide a numbering system that:

• Will properly identify the end stations
• Will not have to be changed in the foreseeable future
• Will interoperate with existing systems (E.164 and IP/DNS)
• Is easy to use (no major shifts in user skill set)

To accomplish this, the MOREnet dialing plan recommends the use of E.164 public numbers as the identifying terminal numbers for all devices, regardless of type (voice, video) or network (PSTN, Internet).

The advantages of using E.164 (and eventually ENUM) include:

• Stable end station addressing - end stations can be addressed once. Whether ENUM or a gateway is used to manage connectivity is irrelevant. The E.164 address is a unique identifier that will not need to be changed.
• Unique addresses - Since each E.164 address can be used only once, each address will be globally unique, just as phone numbers are today.
• Global connectivity - Since E.164 addresses are routed by the PSTN today, calls made to PSTN-connected devices (whether directly connected or via a gateway) can be made seamlessly, with no additional digits or information required to complete the call.
• Standards-based solution - Uses ITU (E.164) and IETF (DNS) standards, so vendor implementations will be readily available. ENUM is a combination of the E.164 and DNS systems.
• Easily understood - Users are very familiar with phone numbers (a.k.a. E.164 addresses), and will not have any problems relating to the use of E.164 addresses for video terminals as well as voice (PSTN or VoIP) terminals.
• Technology-independent - E.164 addressing doesn't care about the device--voice, video, or data. Today, a modem can be given an E.164 address and data transmitted, or a phone could have the same E.164 address and be used for a voice conversation. The network and devices are responsible for the transmission type, and there is no need for network routing or device type information to be embedded in the station address.
• With ENUM, a user can specify one or more methods and devices as connectivity options, further removing the issue of technology type.

These advantages exist regardless of what future standard may come to join E.164 and DNS together, whether it's ENUM or something else. The key issue is to choose something that is scalable and will be likely to interoperate with future standards.

MOREnet's use of E.164 addressing as outlined above does not preclude interoperability with ViDe, as the E.164 address will fit within the ViDe dialing scheme. However, the use of E.164 addressing allows global connectivity, while ViDe addressing limits the user to the ViDe network of devices.

E.164 Public Numbers

In North America, the NANP defines a 10-digit number in the format NPA-NNX-XXXX. If we add the country code of 1, we end up with +1-NPA-NNX-XXXX, which uniquely defines a device (the + means this is the complete number). This number is all we need to address a device.

To get a publicly addressable number, the codec owner must contact either the campus telephone department or the local phone company for an assignment of numbers. The assigned numbers then need to be routed to a suitable gateway device, such as an MCU, codec or voice bridge to actually terminate the call, or to a voice recording to tell callers that the number dialed is a video number and give contact information for further assistance.

The number can then be placed into the gatekeeper to provide address translation from the E.164 address to the IP address. Since it is a publicly dialable number, someone with an ISDN-based codec can dial into the codec or MCU and join a conference, even though they are not on the IP network. Customers would be responsible for assigning the numbers, keeping local gatekeepers up-to-date and notifying MOREnet of new or changed assignments.

Once numbers are acquired and configured on a device, the E.164 address can remain static, even if the IP address changes. This configuration is equivalent to giving a device a DNS name (such as fred.video.net) to map to an IP address; as long as the DNS system knows that fred.video.net is at the IP address 10.1.2.3, the call goes through. Tomorrow, if fred.video.net is at 10.4.7.93, as long as DNS is updated, the call will still complete. With an E.164 address, the caller can call 573-999-0000 to get to the device--whether it's at the 10.1.2.3 or the 10.4.7.93 IP address, making the E.164 address similar in nature to the DNS name.

The Connectivity Picture

In Fig. 1, the following calls can occur:

From \ To	Codec A	Codec B	Codec C	Codec D
Codec A		IP (a) or PSTN	IP (b) only	PSTN only
Codec B	IP (a) or PSTN		IP (c) only	PSTN only
Codec C	IP (a) only	IP only		PSTN via gateway (d)
Codec D	PSTN only	PSTN only	Cannot call

(a) Can use an IP address, DNS name, or PSTN number-to-IP lookup via public GK.

(b) Can use an IP address or DNS name only.

(c) Can use an IP address, DNS name, or private number-to-IP lookup via MOREnet GK.

(d) Must use IP to PSTN gateway (not shown).

Figure 1

In Fig. 1, it is apparent that sites A and B are better connected, as they have both IP and PSTN connectivity. For sites that do not want or need PSTN connectivity, an IP-only connection such as C will work. Note that codec C can still call a PSTN device through a gateway; this service could be local or MOREnet-provided. For a remote/off-net site such as D, the only option is a PSTN number.

Note that if there is a gateway capable of H.320 to H.323 conversion between the PSTN and the IP network that can take an E.164 address and map it to an IP address, then any PSTN-based device can call an IP device (i.e. site D can call site B, but only within the MOREnet network; if C had a PSTN-assigned E.164 address it could be called from anywhere via the gateway).

Number Allocation

The mapping of E.164 numbers based on locale is recommended based primarily on current convention-we all know that an area code refers to a specific geographic area. By having individual organizations acquire E.164 addresses from the local telephone company, geographic assignments can continue to be honored within the current NANP system. Most local telephone companies sell numbers for $1/month per number or $35/month for a block of 100 numbers. If the organization has its own PBX or purchases Centrex services, then it's likely that the organization's telecom personnel can assign some numbers from the block(s) already purchased from the telephone company.

MOREnet should not acquire E.164 numbers on behalf of its customers. Generally, any number assignment requires at least one physical voice line, which MOREnet does not have, but the customer does. This arrangement keeps MOREnet out of billing issues and leaves the negotiation of NNX and numbers between the local telephone company and the customer. Managing the numbers, allocations and the orders to assign them to customers would be difficult at best, and some phone companies may have reuse policies that prohibit the movement of the numbers from MOREnet to a customer.

Making Calls

Making calls using an E.164 number versus an arbitrary number (or name) is done in the same fashion as the user-supplied number or name. The gatekeeper (or DNS server) makes the translation between the dialed number (e.g., 573-999-0000) and the appropriate IP address and completes the call. Devices such as phones and codecs will likely have only one number, while gateways and MCUs may have multiple numbers, or a "pilot number" tagged to multiple numbers to allow several users access to the resource simultaneously. For a point-to-point call, a user only needs to dial the other user's number to be connected. For a multipoint call, each participant will need to dial the number for the MCU conference, just like they do today.

Other Dialing Plans

Other organizations, such as ViDeNet, have proposed dialing plans to solve the issue of uniquely identifying a codec. Having been offered to the Internet2 community, ViDe's dialing plan is the current proposed standard for the Internet2 Commons⁹ initiative and is the current "leader" for adoption. Other plans and recommendations have been made by Cisco, Indiana Higher Education Consortium (IHEC) and private plans (such as MOREnet's current system of Customer ZIP + last 2 octets of endpoint IP address¹⁰).

One obvious difference between MOREnet's proposed plan and the ViDe plan is the use of a Master Gatekeeper as a "root" authority, while stating "ViDe views numeric hierarchical dial plans as ultimately undesirable due to their inherent monopolistic tendencies."¹¹ The hierarchical dialing plans used for the PSTN/GSTN provide structure and authority for operations, just as DNS does for the IP world. While the structure of DNS is different than the PSTN, there are still root servers and name authorities, which provide the operational structure needed to build a global infrastructure.

A non-standard aspect of both the ViDe and IHEC systems include a format with variable-length addresses (which may lead to uncertainty regarding an address' completeness), and the lack of any identifier of the gateway or codec as part of the address (as occurred in the second version of ViDe's dialing plan, although it had different problems). Since the system is based on "zones," any mapping to geographical locations is impossible. The zone is organizational, much like a DNS space or IP address space assigned to the organization's IP network.

Both ViDe and IHEC identify the controller as part of the number. In the PSTN, the NPA and NNX identify the serving office, while in the IP world the gateway address tells a device how to find the world. For video devices, configuration needs to include the PSTN number, IP address and mask, the gateway and the IP address of the gatekeeper. Knowing which gatekeepers are responsible for which E.164 address space will help locate devices until ENUM removes the rigid PSTN structured hierarchy and allows for the more flexible DNS system (albeit still hierarchical in nature) to take its place. Other identifiers in some proposed dial plans include the technology type, exit discriminators and other things that should not be part of a "video phone number", just as the type of phone (analog, digital, cellular, ISDN, etc.) is not part of the E.164 address. These items should be handled by the ENUM system, negotiated during call setup, and (ideally) be transparent to the end users.

Other plans are focused on creating a video network with little to no interaction with the PSTN or voice networks, except through user-selected gateways. This type of plan is incongruent with intelligent networks and administratively controlled systems, which should choose the correct gateway based on the destination of the call (video or voice) and the bandwidth needed (among other factors).

Another significant drawback to any non-E.164 address system lies in social thinking. Everyone is accustomed to the NPA-NNX-XXXX system of dialing telephone calls, and the www.domain.tld or name@domain.tld formats on the Internet for websites and e-mail. Any changes to these or other customs must bring significant improvements while supplying a usable format. In contrast, the addition of services (i.e., video) while retaining the use of the existing dialing systems will only hasten the adoption and deployment of new offerings.

As an example of social (and technical issues) impacting these decisions, one of the options when the NANP was being revised in the early 1990s was to go to a four-digit NNX. Local dialing would be eight digits (NNXX-XXXX) and long distance 11 digits (NPA-NNXX-XXXX). This was rejected in favor of changing the digit restrictions in both the NPA and NNX numbers to NXX (N=2-9, X=0-9) from the former NZX-NNX (Z being 0 or 1). This change expanded the number of area codes from 100 to 800 and office codes (NNX) from 640 to 800, providing an additional 112,000 NPA-NNX combinations. While the eight-digit solution would have provided 576,000 new NPA-NNX combinations (464,000 more than the NPA-NNX change, or over five times as many new combinations), the social change in addition to the technical changes to accomplish it were deemed too significant at the time.

This social pressure will need to be overcome, as number exhaustion from cell, IP, video, and other phone devices will again be an issue in the next 50 years. Plans to extend the NANP from 10 to 12 digits (by adding 1 digit to the NPA and 1 digit to the NNX) have been presented (see the ATIS web site at http://www.atis.org/atis/clc/INC/Incdocs.htm for document INC 02-0107-029, "Industry Numbering Committee (INC) Recommended Plan for Expanding the Capacity of the North American Numbering Plan", December 2001).

Any proposed system should be:

• Scalable for the foreseeable future
• Standards-based and open
• Easily used and understood by the general public
• Extensible for future applications

E.164 and DNS combined via ENUM accomplish all of these goals.

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Conclusion

The proposed ENUM system will marry E.164 and IP space in a single directory, able to find resources based on type. This system promises to be the beginning of a global directory structure, where users and resources can be matched up automatically to provide the services requested. Down the road, ENUM should be integrated with LDAP or a similar service, as well as Microsoft's Active Directory, Novell's NDS, and other similar resource directory systems to build a single directory repository system for authentication, accounting and resource locating network-wide for an organization.

Until ENUM services are widely deployed, interim systems will be used to help bridge the gap between the IP and PSTN worlds. Key to any solution is transparency, usability and the ability to easily migrate to the next iteration of services. As noted earlier, since ENUM is not yet ratified, any timetables for implementation, deployment and adoption would be wild guesses.

Any lasting solution needs to be global in nature, taking the whole E.164 addressing system into account as well as IPv4 and IPv6 network addresses. Using PSTN assignments of addresses keeps addressing unique, provides global connectivity and will likely ease migration to the next numbering system.

The recommendation outlined in this paper provides MOREnet with a standards-based solution to addressing IP devices for the E.164 world. Whether it is an H.323 codec, a H.323 to H.320 gateway or a VoIP phone, addressing can be done in a scalable, controlled manner that will not require renumbering when ENUM is adopted and implemented.

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Related Documents

Cisco Dialing Plan
http://www.cisco.sh/univercd/cc/td/doc/cisintwk/intsolns/voipsol/dp3_isd.htm

ViDeNet Dialing Plan
http://www.unc.edu/cavner/vide/videnet/documents/ViDeNet%20Architectural%20Bulletin%20June%2027%202001.doc

IHETS dialing plan
http://www.ihets.org/progserv/video/vidconf/ipvtf/08_dial_plan.html

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References

www.vide.net: ViDeNet - The Video Development Initiative

www.nanpa.com: NANPA - North American Numbering Plan Administrator

www.enumf.com: ENUM Forum

http://www.itu.int/osg/spu/enum/index.html: ITU ENUM site

http://www.ietf.org/html.charters/enum-charter.html: IETF ENUM site

http://www.atis.org/atis/clc/INC/Incdocs.htm: NPA Allocation Plan and Assignment Guidelines

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Appendix: Private Numbers

There are cases (and customers) that either do not want publicly addressable numbers or will likely never need or want them. In these cases, a private number can be used to address the device, similar to non-DID numbers on a PBX.

The NANP¹² has several blocks of reserved numbers (37X, 96X and N9X), which are reserved for future expansion. Also unassigned are the area codes with the second and third digits alike (i.e., 844, and including 222, 333, 444, 666, 777 and 999), and are reserved as Easily Recognizable Codes (ERC). It is unlikely that the NANP will put 444 into active service soon, as ERCs are difficult to get assigned, and 444 has traditionally been used in PBXs for private networks (like 10.x.x.x address in the IP world). See http://www.atis.org/atis/clc/INC/Incdocs.htm.

Since the 37X and 96X codes are reserved for "unanticipated purposes where it may be important to have a full range of 10 contiguous codes available," they are possibilities, as is 444, due to its popularity in private PBX networks. Calling any number with any of these area codes on the PSTN will get the caller a "Bleep…the number you have dialed…" message, so publishing the number won't connect you to someone else, although it may cause issues with outside parties believing it's a reachable codec over the PSTN.

Note that for calling outside the NANP area, the appropriate international codes need to be used; for calls from international locations to the NANP area, a country code of 1 is required (and presumed in the examples given).

By using the 444 NPA addresses, an organization can assign PSTN-like numbers to handle their codec needs. Note that organizations who chose private addresses can connect to codecs via IP regardless of the use of publicly-assigned or private (i.e., 444-xxx-xxxx) E.164 numbers. Organizations using private E.164 addressing (such as 444-xxx-xxxx) are restricted to making and receiving calls using the 444 prefix from within the organization's network using a private gatekeeper but could dial out to any PSTN number via a public gatekeeper.

Note that this is not a recommended solution, as it does not provide for true PSTN to Internet interoperability and seamless dialing. However, there are applications where an organization may choose to keep the video network private, and in those cases, a private addressing schema is appropriate.

Allocation Methods

A system to allocate numbers from the 444 prefix will need to be developed. The solution for one network will not necessarily fit other networks wishing to model a dialing plan after this one; however, any system of assignment that allows for growth, management, and documentation would likely be sufficient. An example for MOREnet would be based on the existing NPA and NNX (office) codes of customers; Missouri has 7 area codes today, with 2 more on indefinite hold. So, one possibility is:

444-ABB-BCCC

where:

• 444 is the private NPA chosen
• A is a 1-digit identifier for the actual NPA (1=314, 2=417, 3=557*, 4=573, 5=636, 6=660, 7=816, 8=975¹³)
• BBB is the customers local NNX (central office code)
• CCC are the assignable numbers

A private network codec in Jefferson City, MO would be:

• 444-463-4001 if the customer is in the 634 exchange
• 444-475-1001 if the customer is in the 751 exchange

Jefferson City, MO has 16 exchanges: 522,526, 556, 619, 632, 634, 635, 636, 659, 680, 681, 690, 691, 751, 761, and 821.

Note that the customer is responsible for assigning numbers from the pool. Regardless of whether the numbers are private (444) or PSTN-supplied, the customer will need to either maintain a local gatekeeper or keep the gatekeeper provider (such as an upstream ISP) apprised of moves, additions and changes to the number-IP mapping.

The advantage to this system is simplicity; the customer (and any potential callers) knows where the codec is based on a well-known numbering system. The drawbacks include:

• More than 1 customer in an single central office (very likely)
• Missouri gets more than 10 area codes (not likely soon)
• A customer has more than 1000 codecs/endpoints (not likely soon)

Note: This is a private network or interim solution and is not interoperable now or in the future with ENUM or E.164 addressing. MOREnet does not recommend this implementation.

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Glossary

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Endnotes

1. E.164 is the international standard for telephone numbers, administered by the International Telecommunications Union (www.itu.int) globally and the North American Numbering Plan Administrator (www.nanpa.com) in the USA.
2. ENUM is a proposed standard for integrating E.164 numbers into the Internet's Domain Name Service (DNS) by the ITU and the Internet Engineering Task Force (IETF).
3. SS7, or Signaling System 7, is a definition of functions to be performed and a protocol to enable the performance of out-of-band signaling for call setup, billing, routing, and information exchange for the public switched telephone network (PSTN).
4. DHCP, or Dynamic Host Configuration Protocol, allows devices to poll a DHCP server to obtain an IP address and related information (mask, gateway, DNS, etc.) necessary to establish a connection on the network.
5. SIP, or Session Initiation Protocol, is a lightweight call setup protocol for VoIP and is replacing H.323 as a simpler, faster method to manage VoIP calls.
6. The combination of a 5-digit ZIP code + the last 5 digits of the MAC address create a 10-digit number, similar to a PSTN/E.164 address (i.e. ZIP=65201, MAC=03201, number is 652-010-3201). Note that there is no tie-back to a PSTN/E.164 number.
7. See http://www.unc.edu/video/videnet/faq/#Anchor-Wha-33913 or http://www.wvn.ac.uk/support/h323address.htm.
8. See www.enumf.org.
9. See commons.internet2.edu for more information about the Internet2 Commons:A Large-Scale, Distributed Collaborative Environment for the Research and Education Community
10. For example, 65202-133239 would be the address for a device with a 65202 ZIP code and an IP address ending in 133.239. Note that this results in an 11-digit number.
11. http://www.vide.net/workgroups/videnet/index.shtml
12. www.nanpa.com
13. Implementation of 557 as an overlay for 314 and 975 as an overlay for 816 have been suspended by the MO PSC as of 9/25/2001 (see NANPA planning letters PL-NANP-303 and PL-NANP-304 at http://www.nanpa.com/)

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