Voice over IP services

Configuring carriers

A carrier is a commercial VoIP provider connecting you to the public telephone network. Outgoing calls can be made via a carrier and incoming calls can be received from a carrier. You may need one or more carrier definitions, and may need a separate carrier definition for each number you have, depending on the how the carrier works. The FireBrick operates using SIP/2.0/UDP with PCMA/8000 audio and is compatible with most commercial VoIP carriers.

Outgoing registration

One of the simplest carrier configurations is where the FireBrick acts like a SIP phone, registering with the carrier.

You define the registrar which is the hostname or IP address of the carriers registration service. You will usually need to define username and password as well, and you may have to set a from address for the registration, depending on the carrier. The expires time defines the preferred re-registration time. The FireBrick will register at start up and periodically as needed.

For inbound calls, the carrier connects to the registered contact which the FireBrick provided. You will need to define extn as the internal extension number that is being called when a call comes from this carrier. This can, of course, be a ring group.

Authenticated inbound calls

Some carriers will not require or accept a registration from the FireBrick but will expect to send calls to the FireBrick on a pre defined IP address or host name that reaches the FireBrick. To allow such calls you set the toattribute which can be the complete To header value expected, or can simply be @hostname which is expected. In the latter case, the incoming-format can be used to define numbering that is presented before the '@' or set extn to send all incoming calls to a specific extension.

In some cases a carrier may be able to send authenticated calls, in which case define username and password which are checked when the calls come in.

If not authenticating calls, or even if you are, you may want to define allow to cover the IP addresses from which the call is permitted to arrive.

Direct inbound calls

You may want to publish a SIP URL to allow calls to you directly from anywhere on the Internet. This can be set up as above configuring a defined to address, and extn to which calls are sent. We recommend setting trust-cli to false in such cases as the call could claim to be from any number.

Outbound calls

When using a carrier for outbound calls, you can configure the proxy to use. If the username and password are defined then these will be used to authenticate outgoing calls. You can define the outgoing-format to use for numbering of external calls to the carrier. Each telephone user can be set to use a preferred carrier else one will be picked.

Carriers work in different ways for handling withheld numbers. If your are making a withheld call the default is not to send your number, and indicate that it is withheld in the headers. However, you carrier may know the number and send it anyway. If your carrier has a prefix to indicate withheld calls you can define withheld. E.g. in the UK some carriers use 141 as a prefix for this. In this case the number is sent in the headers but the prefix is used to tell the carrier it is withheld. We recommend you test withheld number calling with each new carrier you set up to ensure it works as you expect.

Configuring telephone users

Telephone users are internal extensions. They are typically locally connected SIP phones. They could be remote SIP phones. The SIP phone registers with the FireBrick. Do not use telephone definitions for calls from a carrier.

To define a user, set a name which is the part before the '@' in the registration or From header for calls. You can also define username and password to force authentication on calls and registrations from the phone.

You should define an extn which is the internal number for calls to and from the phone, and you may like to define a ddi which is the external public number to be used. See numbering section above.

By default SIP users must be on a local subnet, but for external users you can define local-only false. We recommend setting the allow IP range if you can to restrict login attempts to certain source IP addresses.

Allowing a remote user from the Internet can be dangerous, and you should always ensure a good password is used. Even with a good password, it is likely your FireBrick will come under attack if it allows registration attempts from anywhere in the Internet, so we strongly recommend using the allow restrictions if possible.

If the IP address of a phone is likely to change a lot, you may want to set a shorter expires time, but normally this does not need to be changed.

Pickup/steal

A prefix can be defined for telephones to pickup or steal a call, default is *.

• Using pickup with the extn of a ring group will take (pickup) the call ringing at the head of the queue.
• Using pickup with the extn of a telephone that has a call ringing will take (pickup) that call.
• Using pickup with the extn of a telephone that has a call in progress will steal that call.

To ensure this is not abused a telephone or ring group can have a list of extensions which are allowed to pick up. If not set then any extensions are allowed.

Busy Lamp

Some phones, e.g. SNOM, have busy lamp functions. Simply set BLF mode and the extension number to monitor. You can monitor a group extension number or a telephone extensions number. You can also monitor using the pickup prefix - this is useful as the button will usually dial the number you are monitoring, so this is ideal if monitoring a ring group as pressing the button picks up the ringing call.

Call groups

A call group allows one number to call multiple numbers, either all together or in a sequence, and allows queuing of calls. The simplest group is to ring a set of numbers all at once until one answers.

What numbers are rung

The initial set of numbers to call is defined in the ring attribute, but if a profile is defined and inactive then the out-of-hours attribute is used instead. If this initial set is empty then the group fails as busy.

After a defined period of time at the head of the queue the list of numbers is extended to include the overflow attribute as well.

Ring pattern

There are a number of options for how the numbers are rung. Each number is only tried once, but in the case of an internal number it is not tried if the telephone is known to have other calls or within its wrap-up time - but this only applies where the number is exactly the extn of a telephone. This means that if someone is on the phone, and then hangs up, they can then get a call from the ring group even if it is already ringing other phones.

All Ringing all numbers at once is the simplest to understand. This can create a two stage ringing process with the overflow being added after a defined delay. In this case the order attribute does not matter.

Sequence This means trying one phone at a time. After a configured progress-time the call is cancelled and the next phone tried, in order. Once all the phones in the initial set have been tried then the overflow set is tried even if not yet time.

Cascade This is the same as above except the existing calls are not cancelled as the cycle progressed, causing more and more phones to ring.

Ring order

Except when ringing all phones at once, the order the phones are rung can be important, and there are a number of options. The ordering only works for the first 64 numbers, once they are all tried the rest are rung together.

StrictThis is the simplest as it means the phones are tried in the order they are defined in the config, with overflow added to the end.CycleThis is the same as strict, but for each call the sequence continues from where it left off in the previous call.RandomThe order the phones are tried is random.OldestThe order the phones are tried is based on which phone has not had a call for the longest time. This only works where the number matches the extn of a telephone. Any that do not (e.g. external calls) are tried last.

Queued calls

Ring groups allow queuing. This means more calls can be waiting. As soon as a second call is queued the ring type of the first call changes to all so that it is answered more quickly and the second call can get to the front of the queue. You can limit how many calls are allowed in the queue.

The caller does not know they are in a queue, and if they are left ringing too long they may hang up, or their phone carrier may time out the call. To avoid this, if not answered after answer-time the call is answered anyway and a queue tone (different ringing tone by default) played.