Telos' Exclusive Agile Connection Technology - IP Audio Your Way
As we all know, there are no quality of service guarantees with the Internet. Bandwidth guarantee is only one of many problems that you can encounter with IP audio transmission. Other issues include packet loss, jitter, NATs and firewalls, not to mention dynamic IP addresses getting changed on you. Not to worry though, the Zephyr/IP has you covered.
When networks become congested, routers can begin to drop packets. A number of solutions have been proposed: retransmission, forward error correction and concealment.
Retransmission works great for an email or a data file, but not for audio transmissions. It introduces an unacceptable amount of delay because the audio stream needs to wait for the lost packets.
Forward error correction (FEC) is a clever approach because extra data is sent allowing the receiver to recover lost audio packets. The problem is that it requires additional bandwidth at a time when packets are being dropped due to lack of bandwidth. This, in fact, can make the problem worse. It also introduces additional delay.
Concealment, on the other hand, requires no additional bandwidth and it does not introduce additional delay. It works by reproducing dropped packets based on neighboring packets. Developed by Fraunhofer Institute, it is not detectable up to 5% loss and still usable to about 20% loss. Being the best solution, this is how the Zephyr/IP overcomes packet loss.
Jitter is the unpredictable arrival of audio packets. Although they are produced at a regular interval, some packets may get delayed, may take a different path or may arrive out of order. To overcome jitter you need to buffer a certain amount of audio at the receiver. If the buffer is too small, you lose audio data. If it is too large you have too much delay. Setting the buffer manually is ineffective since jitter can continually change. The Z/IP constantly measures the jitter and adjusts itself dynamically to the optimum level.
Even if you have enough bandwidth from your ISP, it is possible that your audio packets will pass through congested routers along the transmission path. You could send your audio at very low bitrates to improve your chances, but you’d be sacrificing quality. The Z/IP gives you a better solution. It constantly monitors the available bandwidth and adjusts bitrate on the fly. You always get the best possible audio quality for network conditions at the moment. MPEG AAC-ELD is capable of switching bitrate inaudibly, and the Z/IP takes advantage of this by sending a control signal from the receiver to control the transmitter's rate.
During an incoming call, Firewalls and NATs (Network Address Translation) devices often prevent data from reaching your IP devices. Traditionally, this meant that you had to manually configure your firewall or NAT for the call. This is no simple task if you don’t have direct control over the firewall or NAT. The Z/IP overcomes this by using Telos' free Z/IP Server. The Z/IP Server works as a switchboard and allows your Z/IP to be reachable by others. If both Z/IPs are behind especially troublesome NATs or Firewalls, the Z/IP Server can act as a media relay station to complete the transmission. The Z/IP Server also provides a directory service. This allows you to browse for the Z/IP you want to call, if you can't remember the exact name. The directory lookup supports wildcards and phonetic (soundex) searches.
Remembering and entering IP addresses can be confusing for operators. Especially at remote sites, where the number changes with each new location. Dynamic IP numbers are another source of confusion. The Z/IP offers an easier way. You assign your Z/IP a text name one time. Each time a Z/IP is connected to the network, it communicates with the Z/IP Server, which then learns its IP number automatically. Others connect by 'dialing' this name. Yet easier, you can make a group using an identifier such as your call letters. Any Z/IP that is joined to the group will see a list of all other available units, and you simply select one of them to connect.