Bob Eager 16 th February 2015
Overview Scenario and infrastructure History The POTS era Home Highway Moving to ISDN and a PBX VoIP phase 1 VoIP phase 2 The current system Security Conclusion Questions
Scenario and Infrastructure the installation is in a nominally 5 bedroom house (2 floors) 4 bedrooms, one large office 3 reception rooms (one of which is a workshop!) kitchen, bathroom etc. family of two adults and two children the house is of an unusual layout and it is hard to hear people calling It s for you! when the phone has been answered in another part of the house much of this would apply to any office system too the system is very flexible
the house was completely rewired prior to developing the telephone system; this was to prove vital in the long run at least one analogue phone socket in each room (3 in living room, for possible Sky box etc.) all lines taken back to a wiring centre using a large Krone box: allows easy reconfiguration of extensions etc. 30cm at least one network socket (gigabit) in each room (3 in living room, 2 in workshop) all cables taken back to a rack for network switches
The POTS era POTS stands for Plain Old Telephone System a conventional landline initially, there was a single landline with one phone socket on each of the two floors one additional socket was fitted in an interim office (the spare room) this worked OK, but had some disadvantages: only one actual line answering the phone at night phone in office and not in bedrooms use of dial-up Internet precluded use of phone for incoming and outgoing calls and of course the data rate was slow typically about 40kb/sec
Home Highway this product was offered by BT for some years, and was used for a while a modified 2 channel ( basic rate ) ISDN allowing: two simultaneous voice calls or one voice call and one 64kb/s data call or one 128kb/s data call (charged as 2 calls) withdrawn by BT in 2005-2007 expensive, charged as dialup provided 3 phone numbers 2 analogue (including original) 1 data data analogue
Moving to ISDN and a PBX it was decided that an internal PBX would be nice, but these are generally expensive a cheaper alternative was an ISDN line, with a small ISDN PBX the one used was a CyberGear Gold (from ebay!) basically because it was adequate, and cheap 20cm
this provided: 6 internal analogue lines Ethernet connection via PPP and dialup, although this was soon replaced by ADSL on a separate POTS line the PBX was connected to the wiring centre (Krone box) so that various extensions could be paralleled up as required (e.g. all sockets in living room) this system worked well for some years but the ISDN was relatively expensive, and analogue ports on the PBX had a habit of dying (replacements from ebay!) it was thus decided to move to a hybrid analogue/voip solution
A little about Voice over IP VoIP uses a network (usually the Internet) to carry digitised conversations software or an IP phone is needed at the client end for calls to/from conventional numbers, an interface is needed to the normal telephone network; this is provided by an Internet Telephony Service Provider (ITSP) outgoing calls are sent to the provider, who charges for the call incoming calls come via the provider, and are handled by the software or phone the ITSP provides a phone number and calls to that number are routed to the client, who can choose to receive them anywhere on the Internet (e.g. on a laptop in the South of France!) this choice ( registration ) can be changed at any time (frequently)
VoIP phase 1 it was decided to set up a dedicated PC as a VoIP PBX the hardware used was a rack mounted, 1U Mini-ITX system, 800MHz Via C3 CPU, 512MB memory, hard disk the software was the open source Asterisk system, well proven and well documented the way this works is that Asterisk registers to receive calls from the ITSP, possibly on several different numbers it then routes calls to individual phones, which effectively register to Asterisk the way that they do this depends on how they are connected
how did this communicate with the analogue world? a PCI card to interface with the normal POTS line (needed anyway for ADSL) [for reasons, see later] supplied by Digium (the originators of Asterisk) a port to communicate with the external telephone network is called an FXO port (it communicates with the Central Office) Analogue Telephone Adaptors (ATAs) to interface with the internal telephones supplied by Sipura/Linksys/Cisco a port to communicate with a telephone is called an FXS port (it communicates with a Station)
a typical Digium PCI card (expandable) Cisco 8 port ATA:
VoIP phase 2 to reduce power consumption and noise, the PC was replaced by an HP Microserver: ample power and probably overkill, but at just over 100.!
the Digium card would not fit the Microserver, and was also rather unreliable (software wise) it was decided to replace this with another ATA; a Linksys/Cisco SPA3102 was used this has one FXO (phone line) and one FXS (phone) port, plus Ethernet and has the advantage of decoupling the phone connection from the actual server, simplifying changes of server SPA3102
VoIP phase 3 the previous system used three ATAs: 1. Cisco SPA8000-8 FXS ports for internal lines 2. Cisco SPA2000-2 FXS ports for internal lines (originally purchased for evaluation) 3. Cisco SPA3102-1 FXO/1 FXS port for external line/spare, respectively the first two of these were removed to reduce noise and power consumption, and to use more intelligent phones instead, all internal phones were replaced by IP phones (since the house was wired for Ethernet, this was not an issue) the last mentioned ATA was retained (and there is a plan for using the single FXS port for an external bell)
the phones chosen were once again Cisco products easy to configure via a web interface or an XML file on a server the SPA301 for two locations, and the more sophisticated SPA303 for the rest (a total of 9 phones) the SPA303 has a 2 port switch, so can be used alongside a PC; it can also use a wireless adaptor; it also has programmable softkeys SPA301 SPA303
The current system the system runs on an HP Microserver, running the FreeBSD operating system (most people use Linux ) it runs the Asterisk PBX software hardware: one SPA3102 FXS/FXO adaptor two SPA301 IP phones seven SPA303 IP phones one BT Bell 80D (right) for garden (not yet installed) one external POTS line (used for FTTC broadband) the existing gigabit network
a block of ten consecutive Canterbury numbers has been reserved from the ITSP, of which seven are in use: general house number personal numbers for each family member memo service (see later) remote door unlocking (see later) internal calls ring with a single ring cadence the house number rings with a normal cadence the personal numbers ring with a cadence corresponding to the Morse code for the individual s initial (sad but true) the other two never actually cause a phone to ring there is one more cadence used for another purpose (see later)
Asterisk is a very flexible system, very extensible with many useful features out of the box many of these are in use, and extra ones have been added through scripting; they include: textual caller ID (on the SPA303 phones, which have a screen) voicemail (with separate voicemail boxes ); waiting voicemail is indicated by a signal light on relevant phones shortcode dialling (avoids programming a directory on each phone and makes central maintenance of phone books easier) call recording selective ringing depending on number called, and time of day children s numbers ring their room only first, then rest of house if unanswered
caller blacklisting caller is just told you are blacklisted! caller greylisting (evil!) caller hears several rings, then is sent to voicemail; no phones actually ring every time this is for callers you d rather not speak to but don t want to offend outright call parking call can be parked, caller left on hold with hold music, but then picked up from another extension by dialling a specified number call pickup pick up ringing extension from another one internal paging (ring all phones with individual s own cadence, useful if their whereabouts is unknown) speaking clock (overrides the external 123 which is expensive)
Least cost routing the system does its best to minimise the cost of calls most calls are still routed via the POTS line at weekends, via BT (free, up to an hour, with automatic time limiting and warning messages) during the week, via the 18185 indirect carrier (5p per UK call) if the POTS line is in use, then the ITSP is used, so multiple calls are possible certain numbers are blocked completely e.g. 070xx, 09xx, etc special numbers (101, 111, 999 etc.) are routed via the POTS line too codes can be used to override the route used
Additional features the memo service one external number does not ring, but simply takes a message and emails it to a mailing list useful for memos when away from home, or even at home the voice file is emailed as an attachment the doorbell the bell push on the front door is connected to an Arduino microcontroller, which sends a message (via USB) to a listener process on the PBX the listener schedules an immediate call to all extensions with a special urgent cadence selected extensions can be hushed for a specified time (e.g. if someone is sleeping) by entering a code on any phone
the door lock the main front door lock is solenoid controlled it can be unlocked via a USB operated relay, controlled by the PBX an internal extension is reserved for unlocking the door the door can also be unlocked via an external call (using two factor authentication) useful if keys are lost and no-one is home call filtering anyone withholding caller ID is presented with a menu of options most just toy with the caller, while recording the call for future emailing! one option allows the caller through the menu is preceded by the Intercept Special Information Tone (tri-tone) indicating the equipment is disconnected, to fool auto diallers
alarm calls any extension can book an alarm call for any time in the next 24 hours, by dialling 125 and giving the time required at that time, the extension will ring for a fixed time or until answered if not answered, the call will be repeated twice more at one minute intervals alarm calls can also be set on any other extension (if one knows the privileged access code!) external bell (under development) connected to spare FXS port on SPA3102 called in parallel with other extensions for doorbell and incoming calls has to be enabled specifically, deactivates after a specified time
Security WARNING if the system is exposed to the outside world, it will be the target of hacking attempts these try to get free outgoing access which can cost you a lot of money the system needs to be properly secured
Fun bits there are scripts available that wait for caller silence, then say innocuous things these have been known to keep junk callers occupied for some time there are longer sound files that can also tie callers up, and these can be amusing: the menu system for withheld caller ID gives several options: if you are a telemarketer, press 1 if we have won a holiday, press 2 if you are conducting a survey, press 3 etc.
Conclusion it s really quite over the top for a house, but it s all useful stuff it s great fun and requires very little maintenance it may or may not save money a powerful system isn t necessary people do run it on a Raspberry Pi pretty well anything will support a few extensions it s easy to try it all out without compromising your existing telephone system; all you need is a number from an ITSP, and some hardware
Questions?