When deciding on the best bandwidth configuration to run your video conferencing on...you may think you have endless choices. Sometimes it appears that way when you may actually be limited to just a few. Here's a comparison when your only choices are between ISDN and ADSL. So the question than becomes this. Which is better in the sense of connection speed and for Video conferencing between ISDN PRI (1.544Mbps) to ADSL (1.544Mbps)? PRI ISDN T1 is the industrial strength flavor of ISDN, and is intended for users with much greater capacity requirements. PRI has 23 B channels plus one 64 Kbps D channel. Each channel has a 64Kbps capacity, enabling a total transmission speed of up to 1.536Mbps. With PRI ISDN, you can pre-define the number of channels used for specific types of calls or data delivery. What this means is that you can use the various channels for accomplishing different things on different channels simultaneously. In other words, PRI ISDN offers much greater flexibility than that provided by BRI ISDN. Additionally, the D channel is used as the switching channel that communicates with the Central Office for Call Management. It is used to carry local and long distance traffic. An ADSL circuit connects an ADSL modem on each end of a twisted-pair telephone line, creating three information channels -- a high speed downstream channel, a medium speed duplex channel, depending on the implementation of the ADSL architecture, and a POTS (Plain Old Telephone Service) or an ISDN channel. The POTS/ISDN channel is split off from the digital modem by filters, thus guaranteeing uninterrupted POTS/ISDN, even if ADSL fails. The high speed channel ranges from 1.5 to 6.1 Mbps, while duplex rates range from 16 to 832 kbps. Each channel can be submultiplexed to form multiple, lower rate channels, depending on the system. ADSL modems provide data rates consistent with North American and European digital hierarchies and can be purchased with various speed ranges and capabilities. The minimum configuration provides 1.5 or 2.0 Mbps downstream and a 16 kbps duplex channel; others provide rates of 6.1 Mbps and 64 kbps duplex. Products with downstream rates up to 8 Mbps and duplex rates up to 640 kbps are available today. ADSL modems will accommodate ATM transport with variable rates and compensation for ATM overhead, as well as IP protocols. Downstream data rates depend on a number of factors, including the length of the copper line, its wire gauge, presence of bridged taps, and cross-coupled interference. Line attenuation increases with line length and frequency, and decreases as wire diameter increases. They are completely different technologies used for different things. With ADSL you are generally given Internet access and with a PRI you get 1472 kbps of usable bandwidth to be used in a combination of various ways. The key difference is that with a PRI, you never actually have to connect to the Internet as you do with DSL. Therefore, a video call doesn't have to use IP as it most likely would with DSL. Therefore things that affect call quality like latency are generally not as a big a factor with ISDN. Many companies still use ISDN PRIs for video conferencing to power multiple video calls simultaneously. A lot of people are now using both ISDN and Internet access via DSL/T1/T3/Cable/etc. for their video needs. Generally ADSL is far cheaper but the quality isn't necessarily as good because the customer has little control over the path an IP call takes through the Internet, but that my friend is another conversation for another time. |
