Monday, March 09, 2009

Other Flavors of Packet Voice

When we think of telephone service these days it's in terms of two battling technologies. There's circuit switched telephony that has been the standard for over a hundred years versus VoIP, the emerging standard. But, actually, VoIP is just the best known example of technologies to transmit voice by packet over networks.

The real technology battle is the shift from switched circuit networks to packet networks. But that's been going on forever. Aren't we there yet? No, not really. But that's the direction we're headed until something else is invented.

Circuit switched networks have their advantages. Once you establish a path or circuit between two points, you have exclusive use of that connection until you are done with it. The advantage is that a continuous connection usually has little latency since there are no routing decisions to be made once the circuit is set up. The same is true for jitter, although signal quality is only as good as the connection quality. Analog has crosstalk issues and noisy lines can drop out portions of a digital bitstream.

The big disadvantage with circuit switched networks is that they tie up an expensive resource whether it's being used or not. That's the efficiency improvement that packet switched networks offer. By breaking up data into bite size (or is that byte size?) packages, routers can act as traffic controllers to keep the network busy but not overloaded.

Packet switched networks are a natural for data communications. The Internet protocol, TCP/IP handles breaking large data files into packets and reassembling them on the other end. It also ensures accurate delivery by forcing a retransmission of damaged packets. What VoIP does is mimic computer data by breaking the continuous voice signal into IP compatible packets and sending them down the same network with data file packets. But the TCP or Transmission Control Protocol that ensures accurate delivery doesn't work so well with VoIP. Since a conversation is continuous, retransmitting a broken packet and delivering it later would only cause confusing interference.

VoIP's popularity can be traced to the fact that IP is so popular and nearly ubiquitous in corporate LANs as well as the Internet. But beyond the internal corporate network, there are other types of packet switched networks for WAN or Wide Area Network transmission.

VoATM or Voice over ATM networks also breaks a continuous speech signal into packets. But ATM (Asynchronous Transfer Mode) breaks the signal into 53-byte packets known as cells. The small cells reduce the effect of jitter or variable time delay and one lost or damaged cell doesn't markedly degrade the quality of the voice stream.

VoFR or Voice over Frame Relay networks use frames that transmit large packets of data that vary in size but can be up to a 1,000 or more bytes in length. Frame Relay networks have been very popular for connecting multiple business locations together, but are giving way to the newer MPLS or Multi-Protocol Label Switching networks that provide the same service and more.

Both Frame Relay and ATM networks are private network technologies. They pre-date the massive popularity of the Internet and don't use Internet Protocol. But they do support voice, data and video using their own proprietary protocols.

What about MPLS networks? Being multi-protocol, as the name says, a private MPLS network can easily support VoIP traffic. Since this is also a private networking arrangement, the service quality variabilties of the public Internet are avoided. When VoIP is transmitted on an MPLS network it is known as VoIPoMPLS. But there's a way to directly implement voice on an MPLS network that is known as VoMPLS. This is a fairly new technology that is designed to work in on converged network carrying voice, video and data simultaneously over the same paths. MegaPath, a leading competitive carrier, has just announced a VoMPLS service for its network that combines manged voice, data and security for business-grade users.

Even wireless is not immune to the move from circuit to packet switching. Right now cellular services offer switched voice connections on one set of channels and packet switched data on another. But this may be changing with the emergence of WiMAX and LTE as wireless broadband services. A new forum has started up to develop VoLGA or Voice over LTE via General Access.

Is your company looking at options to reduce telephony costs or make better use of the network resources you already have? A reduced cost digital trunking service or some form of packet voice service may be the answer.

Click to check pricing and features or get support from a Telarus product specialist.

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