Staying Connected in Israel

Phone Services in Israel

...and how they work.         

By: Yair Hakak

How does regular phone service work?

Regular phone service (also called POTS - plain old telephone service) has been around for about 100 years, and really hasn't changed much in that period. Your phone company has a copper wire running from your home to the local switch (local exchange), which is reserved for your use. When you pick up the telephone and dial, your conversation is converted by the telephone into audio waves, which are carried along the wire to the local exchange. If you're calling another person who is connected to the same exchange, the exchange basically "glues" your wire to the other person's wire and the call is connected - audio flows along the wire from your phone to its destination. To point out an interesting historical note, you may have seen old movies or pictures in which "telephone girls" would physically plug wires together using a "switchboard" to connect calls. Today, of course, the exchange does all this automatically, but the principle is the same, and many of these words, like "switchboard", "operator", and others, have survived.

The phone company connects all its exchanges to each other using larger wires, either large copper wires or fiber-optic cables, so that you can call a subscriber on another exchange (i.e. in another city). Additionally, the phone company is connected to other phone companies along the same lines, just as Bezeq is connected to HOT, Pelephone, Cellcom, Orange ...etc, so that your calls can be forwarded to another network or even to another country.

The key point is that each small segment of the network can be used for one phone call at any given time. For example, if there's one copper wire which connects you to the local exchange, you can make 1 phone call at a time, or use the modem, or the fax machine - but you can't do two of these things simultaneously, because your "circuit" is in use.

Similarly, if the phone company has connected 2 exchanges with a wire that can carry 50 conversations, if 50 people are on the phone and one more person wants to call from one exchange to the other, the call will not go through - because, as the phone company would say, "all circuits are busy."

Regular phone service: 3 exchanges connected

How does broadband phone service (VoB) work?

In order to understand how broadband phone service (or "voice over broadband") works, we first need to understand a little about how the internet works.

The internet is based on a protocol (a language computers use to talk to each other) called "TCP/IP", which stands for "transmission control protocol/internet protocol". TCP/IP allows data to be chopped up into "packets", small bundles of information, and sent out over a wire, but not necessarily take up the whole wire. So, for example, if a user sends two emails at a time, both emails will be chopped into packets and sent out over the wire, but content from both emails might be mixed up, i.e. a packet from email #1, a packet from email #2, then another packet from email #1, etc. The computer at the other end reassembles the packets so all the content is usable.

In addition to being "packet" based, the internet is also based on "distributed routing". Basically this means that while in the regular phone model we discussed above, a call from point A to point B will always follow the same route, on the internet, a packet from point A to point B might take any number of routes, because no one entity controls the whole network. This has advantages and disadvantages: the main disadvantage is that because the route is not known in advance, it might be slow or fast, depending on network conditions. The advantage is that the network can heal itself; if one route is broken, other routes will still work.

So really, how does broadband phone service work?

Instead of a regular phone, broadband phone service uses either an internet phone or a device known as an ATA (analog terminal adaptor), which plugs into a regular phone and turns it into an IP phone. This turns the conversation into packets, which can be transmitted over the internet. The ATA is in contact with the telephony server, which is a computer which may be located anywhere on the internet (unlike in regular telephony, where the phone and the exchange must be connected by a physical wire). Since the contact between the ATA and the telephony server is packet-based and over the internet, the route might be slow or fast (as we discussed above) and quality might suffer if the route is slow.

An ATA (analog terminal adaptor)

If one user of broadband phone calls another broadband phone user, the telephony server just sends the packets from the caller to the destination. At the destination, another ATA converts the packets back to audio, and the users can talk between them.

If a broadband phone user calls a regular telephone number, the telephony server passes the packets along to a "gateway server" - which basically converts packets back to regular audio, and then sends the audio to the regular phone network. When a broadband phone user receives a call from a regular telephone, the process is similar, but in reverse.

Broadband phone service

What other models are there?

In Israel, there are two main hybrid models which have some of the characteristics of broadband phone service (VoB) and some characteristics of regular phone service.

The first model is HOT telecom's VOIP service. In this service, HOT telecom, which has a copper wire into the user's home (the wire used to provide cable television service), has decided that instead of converting the conversation into audio and moving it along the wire (as in POTS service), HOT will provide each user with an ATA, convert all the conversations to packets, and use IP technology over their own wires.

HOT does this because IP technology is more efficient (as we discussed, the same wire can be used to move more packets and more content at a time), but, since HOT owns the wire, they can ensure that packets take a specific route through the network and therefore the speed of the route is known in advance. This means (theoretically, at least) that HOT can ensure a given level of quality on calls.

For these reasons, we can say that HOT's service is voice-over-IP (VOIP) but not broadband phone (VOB).

The second hybrid model is offered by some of the internet service providers (mainly 012 Golden Lines). This service is basically broadband phone, but since the phone provider is also the internet provider, they can ensure that the route between the user's ATA and the telephony server is known in advance, which means that quality can be improved.