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Unread 05-04-2007, 06:46 AM   #3
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Various Internet telephone services (4)

SIP Broker,

This time we introduce SIP Broker, etc, as we once again look at overseas services.

This has come up several times in this series, but SIP peering services allow connections / affiliation between providers of Internet Telephony services (ITSP Internet Telephony Service Provider), and so apart from just a service for end users, also for VSPs.


Up until last time, we introduced services that were for, if you had to say one or the other, end users, however this time, we change viewpoint slightly, and look at services for VSPs.

Internet phone service, not just for calls between a VSP's own subscribers, but connecting across all VSPs is naturally convenient. The author thinks this, and has launched and runs the "SIP IX" site, however another site that is active, having the same philosophy, is "SIP Broker".

SIP Broker

SIP Broker (photograph 1) is run by Voxalot of Australia. Australia has surprisingly many VoIP-related businesses, and there are numerous Internet Telephony Service Providers. Even among these, this service is deeply interesting.

The contents are as follows:

- SIP domain to numeric Prefix mapping
- PSTN access numbers
- ENUM with automatic PSTN fallback

1. SIP domain to numeric prefix mapping

This is a SIP peering service. For each VSP, a prefix of the form *XXXX is provided, and connection can be done using that number. That is, you dial this prefix number, then the normal number, and you can connect to a user at another VSP just by dialing a number. The number of SIP servers registered is already around 1000 worldwide. Of those, around half are operational.

It is simple to register your own SIP server with SIP Broker. From the web site menu, select "NUMBER SEARCH". When you do this, the currently-registered SIP server list is displayed, and at the top, at "Add Proxy" (photograph 2), all you need to do is enter your SIP server's address. A prefix is automatically allocated. Currently, numbers in the 8200 range are being assigned.

At this point, the "Provider name", "Country", "Home page address", etc, currently, cannot be registered. You need to log in to the administration screen and register from there. For that, from "Register" at the top, access the "Member Registration" screen, enter the required information, and complete member registration. The SIP address domain-part that you enter here is allocated to your SIP server.

[page 2]
After logging in and selecting "Provider Details" from the menu, the provider name, etc, for the applicable SIP server can be edited. Incidently, you cannot change the prefix. If you really must change to a number you like, SIP Broker will assist you if you contact them direct.

The author has previously made contact, wanting to change to a number I liked. At the time, the "*7777" - a nice number with no breaks in it - was unassigned (in fact, I think, currently, it is still unassigned). I made contact saying "I want to change to *7777" but I was refused.

The reason for that was not because they couldn't give out such a good number, but because of a problem in the numbering plan. What the problem was, was that there was already a VSP to whom the number "*777" was assigned. Therefore, if a number "*7777" was assigned, it would become impossible to distinguish between the VSPs. The in-service (mid-way) change from the initial three-digits to four-digits was, I suppose, caused by the number of registered SIP servers exceeding expectations, breaking the original numbering plan. Anyway, as long as the number does not break the numbering plan, if it's available, they can change your number for you.

With this done, the preparations are now in order to receive calls with SIP Broker. Now, users under SIP servers throughout the world, via SIP Broker by dialing your number using the "*xxxx" prefix, will have their calls arrive at your SIP server. Conversely, to make outgoing calls using SIP Broker, just transfer the call in the form "*" (figure 1). The technical details of how to do this were introduced in article 4 in this series, so refer to that.

[Figure 1. Peering transfer using SIP Broker]

The author has also registered their SIP server with SIP Broker, "*7670" has been assigned. The number of the SIP terminal being used is "5303", so if you dial "*7670-5303" via SIP Broker, you will connect to the author, so if anyone's interested, call me.

I think it would be fantastic if VSPs positively made use of sites such as these, and made mutual connectivity possible. Currently, and this goes for both SIP Broker and SIP IX, there is no merit at all unless the person you want to call is at one of these registered servers. For this arrangement to be viable, the cooperation of many VSPs is vital. I hope to see that.

2. PSTN access numbers.

This is a service to connect to Internet phones via SIP Broker when calling from external (PSTN) lines such as fixed phones and mobile phones. There are over 150 access points set up in 21 countries around the world. See here (hyperlink) for the complete list. Make a phone call to any of the access points, then dial "prefix" + "number", and you'll be connected to the called party via the Internet. This is the type of familiar service already introduced in this series.

[page 3]

3. ENUM with automatic PSTN fallback

SIP Broker is actually closely connected with ENUM (Telephone Number Mapping). If the (dialed) number corresponds to the SIP peering service, it is processed that way. However, if the number is an unknown number, not corresponding (to the SIP peering service) the architecture anyhow tries ENUM. The ENUM service that is looked up is "".

Where the number can't be resolved even after checking ENUM, the response "300 Redirect" is returned. In this response is the instruction to redirect to "dialed number"@"your domain" . That is, SIP Broker could not resolve the number, so "have it dealt with by your own domain's SIP server" is what happens. (figure 2).

[Figure 2. number transfer using ENUM]
If an applicable (prefix) number is contained in (3), SIP Broker transfers it as is.

With this arrangement, even if a VSP's users are dialing what is clearly an outside line number, it is possible to initially try forwarding the call to SIP Broker. If the owner of that outside line number has it entered in ENUM, the SIP address can be retrieved using that numnber, making it possible to connect the call, as is, via the Internet. If there is no ENUM entry, the "300 Redirect" is returned, and then only after that, need the call be sent out to the external line (PSTN) via the VSP's gateway.

Even if it's a PSTN number, search out as much as possible the possibility of connecting via the Internet, and then only at the final stage, really connect to the PSTN - it could be said that this is a new way of thinking for LCR (Least Cost Routing). Further, I think you'd have to say this is a good concrete example of using ENUM. However, of course, it requires the (end-)user side to start positively making use of ENUM for this to work.

And on that note, I will now briefly introduce how to use "". The technical details are covered in detail in No. 5 in this series.

[translator's note: No. 5 was the October 2006 article on ENUM and ]


(the remainder of the article explains how to register your PSTN number with

Author's details:

Keiichi HONDA.

Started the company "IP Vision" in 2006, and is currently Managing Director.

Last edited by v164; 05-05-2007 at 01:00 AM. Reason: translation of remainder of article + typos
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