Discover the difference between our sDSL
service and our aDSL service.
How does Signet Technologies sDSL differ from Signet Technologies aDSL?
First, a few definitions:	
ISDN Integrated Services Digital Network
iDSL ISDN Digital Subscriber Line
aDSL Asymmetric Digital Subscriber Line
sDSL Symmetric Digital Subscriber Line
T1 DS1 (1.55 Mbits/sec. clear channel leased line)
POTS Plain Old Telephone System
UPSTREAM From you, to the internet
DOWNSTREAM To you, from the internet
Loop Reach Distance from the Tel-Co central office to you
Signet Technologies has chosen Symmetric DSL to meet the demands of business customers. Many "push" and "pull" applications such as email, file transfer (ftp), multimedia, electronic commerce, and web hosting have brought about the requirement for high speed data transfer, upstream as well as downstream. aDSL provides fast data transfer in the downstream direction while the upstream is relatively slow. Because of this, aDSL seems more suited to a residential product where the casual web surfer has little need for high speed upstream to the Internet.

Signet Technologies sDSL utilizes 2B1Q line encoding which is based on the same technology that has been used for years in ISDN and some T1. This allows for multiple sDSL loops to be bundled with existing services such as ISDN, T1, and POTS lines. This spectral compatibility insures maximum DSL loop reach as well as data rates. aDSL utilizes DMT and CAP line encoding which has been shown to have spectral compatibility issues with existing services. When bundling aDSL with 2B1Q encoded services, the aDSL lines show speed degradation of up to 70% and, in cases of T1 adjacencies, fails completely (aDSL fails, or performance suffers, when bundled with other services).

Signet Technologies sDSL provides speeds that fill the gap between ISDN/Dial-up connections and leased line T1. An end-user can start at a low speed and upgrade in logical steps as their company grows.

With aDSL, most providers only support 3 grades of service:
Downstream Upstream
384 kbps 128 kbps
1.5 Mbps 384 kbps
7 Mbps 1.5 Mbps

Most of the time, these speeds are on a "best effort" basis and providers only guarantee about 50% of the bandwidth. aDSL can also be "Rate Adaptive" which means that the speed will fluctuate depending on back haul over subscription, line conditions, and distance.

With aDSL, END-USERS ARE NOT GUARANTEED A SPECIFIC DATA RATE. When these two technologies were first introduced, it seemed as though aDSL would have the better loop reach. As chip sets have improved, sDSL seems to be winning the loop reach battle. Signet Technologies sDSL outperforms some of the aDSL offerings by as much as 20% longer loop reach.

Symmetric bandwidth Asymmetric bandwidth
2B1Q line encoding DMT, CAP line encoding
Co-existence with T1, ISDN, HDSL, IDSL Spectral Compatibility Issues
Low Power requirements - 1W/line High Power requirements - 4-8W/line
Static Rate Adaptation - sensible Dynamic Rate Adaptation little upgrade path choice for upgrade
T1/FT1 competing at a higher price for business Cable modems competing at lower price for residents
ISDN to T1 speeds Up to 8M downstream, 1M upstream