Differences between IP PBX – Softswitch and Analog/Mixed type PBX
What is an Analog/Mixed PBX:
An analog only PBX is one that supports analog phones and trunk lines. While this type of PBX is not very common now, we could look at the Mixed type EPABX which are quite common today. These type of PBX basically have a cabinet, processor, power supply and Slots to insert various cards to enable various functionalities. Note that all the above components (Including the software and the CLI interface to manage the system) are all manufactured by one vendor.
Mixed type of EPABX supports all types of trunks (Analog trunks, ISDN, PRI trunks and even IP Trunks) and all types of extensions (Analog, Digital, IP) through the various cards that could be inserted into the slots of the EPABX. So, the capacity of the EPABX is determined by the number of cabinets the PBX has and the number of Cards it can accommodate in the empty slots.
How Mixed EPABX enables analog and digital trunks and extensions:
You have separate cards called Analog trunk cards (4 Port, 8 Port, 16 Port, 24 Port) etc. depending on the manufacturer to connect the analog trunks with the EPABX. (Analog trunks are the lines from the telephone company which allow the user to make outgoing calls). Similarly there are Digital Trunk Cards (ISDN line connectivity, PRI line connectivity). An ISDN line is a two channel digital line that can carry upto two calls simultaneously per line. A PRI line is a digital trunk line which can carry upto 30 Channels in a single line (This is possible by multiplexing and de-multiplexing at either sides).
You have separate cards called Analog extension cards (4 Port, 8 Port, 16 Port, 24 Port) etc. depending on the manufacturer to connect normal analog telephones (The same that we have at our homes). There are similar cards for connecting Digital extensions or digital phones (Digital phones are different from the analog phones – they are proprietary to the manufacturer, they have more features like certain keys holding certain numbers and the user could call those numbers by dialling the respective key etc). Digital phones also enable some level of CTI (Computer Telephony Integration) where the users could just click the contacts in their outlook to call from their digital phones and some other basic computer interactivity.
What is a Soft switch – IP PBX:
An IP PBX – Soft switch in particular is a software which acts as a Switch between all your trunks and extensions. It is a full fledged PBX but the software is the heart of the system. It controls all the actions of the PBX. So, is a soft switch devoid of hardware? No. A soft switch uses any standard server or PC to do its job. So, it can be downloaded into your server and uses the processor, memory etc. of your server. Another thing: It uses the switching capacity of your network IP switches too.
IP PBX – Soft switches support all extensions (Analog, IP) and all trunks (Analog, Digital and IP). You may have noticed that they don’t support digital phones as the digital phones use proprietary technology of the mixed PBX vendors. There are some PCI based cards/ analog telephony interface cards which enable the IP PBX to support analog extensions and analog and digital trunks.
How Soft switch – IP PBX enables analog and digital extensions and trunks:
IP PBX (Soft switch) use the standard server hardware. Hence they use the PCI/ PCI Express interfaces available with the PC/ Server to connect the analog trunks through analog telephony cards. There are various type of analog trunk cards like 4 port, 8 port and common models up to 24 ports to connect to the trunk lines from your telephone service provider to make external calls. There are also digital cards (ISDN, PRI) from one port to up to 4 ports in the common models to connect to ISDN and PRI trunk lines from your service provider to the IP PBX. These cards may also come with echo cancellation modules to suppress the echo which arises when the analog and digital signals are converted to IP. Yes, all the signals are converted to IP and then forwarded or processed.
IP PBX (Soft switch) use similar PCI/ PCI Express interfaces to connect analog extension cards which enables the user to connect analog phones with the IP PBX. They come in similar variants like 4-ports… up to 24 ports in various combinations for common models. (The combination cards contain both analog trunk interfaces and extension interfaces – like 2 Ports for connecting analog trunks and 2 ports for connecting analog extensions).
How IP Extensions (IP Phones) and IP Trunks are handled by Mixed type of PBX:
So, essentially since mixed PBX are slot based system, they have separate cards for connecting IP Phones. Each card has a maximum capacity of IP Phones that could be registered with them and they also have a maximum number of concurrent connections that they support for IP Calls. For IP Trunks on the other hand, they have a separate IP Trunking card which enables them to connect to other mixed type of PBX with similar cards via SIP Trunking.
Here there is one more point to be noted: SIP is the open standard protocol for connecting IP Phones. That means, if you buy the EPABX from a vendor, you may not necessarily buy the SIP phones from the same vendor. You can buy it from any vendor and integrate them with the above system (If the IP Extension card supports SIP). There is also a proprietary IP Protocol common with many major vendors where you need to buy the IP Cards in the PBX and IP phones from the same vendor in order for the system to work. This could support more features than the SIP based ones.
How IP Extensions (IP Phones) and IP Trunks are handled by Soft switch (IP PBX):
Since this is a software based system sitting on any general server (with some minimum specifications specified by the vendor), you just need to add licenses to enable the extensions (The number of such extensions that can be supported depends on the IP PBX model and also the hardware configuration – generally this is also specified by the number of concurrent calls). These systems generally support any SIP phone.
IP Trunks can directly be terminated on your network and the route specified in the soft switch for the extensions to seize them when required. In fact, you could also connect multiple such IP PBX and trunk them together by adjusting the settings in the respective soft switch. There is no extra hardware required to do these things.
Thanks for this explanation. It’s very useful for my studies
good article
We have an office where we have a NEC EPABX & model is IP1E-8KSU-A1.
Now we are connecting our new office at 500 mts from our old office with a Point to Point Laser Connection.
we would like to use the present system at our old office to give extensions to the new office . the number of extensions would be 30 to 40 extensions. The EPABX is in the capacity to do that.
But how can we get the extension from the old office to the new office. Please know that cabling cannot be done as it requires civil work. The Point to point laser beam is the only means of transport.
can we use cards ? suggest
You can do two things. You can install a VOIP (IP Extension) Card on this PBX and have IP Phones on the other end (the IP phones can connect to the PBX over the optical laser network).
Or, you can install another (smaller) PBX that has IP Trunking capability on the other side and connect that PBX with this one over IP Network (Optical Laser). The advantage of this method is, you can use analog phones, digital phones or IP phones at the other end.