Jan 20, 2010

Asymmetric DSL vs. Symmetric DSL

Asymmetric DSL vs. Symmetric DSL
xDSL is a new digital service that uses high-bandwidth to bring voice, video and data to your business. It is also used for fast, "always on" access to the Internet. It has many useful applications for SMBs. xDSL is the acronym for the general category of Digital Subscriber Line service, with its many flavors. Each flavor of xDSL has its own characteristics and special features.

Asymmetric Digital Subscriber Line (ADSL) and Symmetric Digital Subscriber Line (SDSL) are two of the many flavors of xDSL. ADSL is sometimes referred to as Asynchronous, or full-rate DSL. SDSL is sometimes referred to as Synchronous DSL. Both ADSL and SDSL offer unique features that can provide an excellent telecom solution for your business. Choosing one over the other will depend upon the particular needs of your business. Look below to determine which service is most suitable for your small to medium sized business.

What is ADSL?
Asymmetric Digital Subscriber Line (ADSL) is currently the most popular flavor of DSL. It is widely deployed and used by many home consumers and SMBs. ADSL is called "asymmetric" because most of its two-way bandwidth is devoted to the downstream direction that sends data to the user. Only a small portion of bandwidth is available for upstreaming. Most Internet users, and especially those who use graphics- or multi-media intensive Web data, need lots of downstream bandwidth. For these applications, user requests and responses are small and require little upstream bandwidth. Using ADSL, up to 8 Mbps of data can be sent downstream and up to 640 Kbps are available for upstreaming. The high downstream bandwidth means that your telephone line will be able to bring large data files, video, audio, and 3-D images to your computer or hooked-in TV set. And, since it supports Plain Old Telephone Service (POTS), a small portion of the downstream bandwidth can be devoted to voice, rather than data, so you can make phone calls without having to use another separate line.


What is SDSL?
Single-Line, or Synchronous, Digital Subscriber Line (SDSL) supports symmetric service. A single line can carry anywhere from 160 Kbps to as much as 1.5 Mbps in each direction equally. SDSL is often used in wideband digital transmissions for carrying large amounts of data in both directions within a business site.

SDSL is symmetrical (upstreaming and downstreaming). For this reason, the maximum data rate is lower than that for ADSL. It can carry large amounts of data in both directions. SDSL does not support POTS. It is data-intensive, rather than being voice-intensive.


G-Lite ADSL is a "lighter " version of full-rate ADSL. It can deliver up to 1.5 Mbps downstream and up to 384 kbps upstream. A splitter is not required for installation. It is intended for home consumers, small businesses and remote offices.

How ADSL and SDSL Work
The terms "downstreaming" and "upstreaming" are key to understanding what ADSL and SDSL can do for your business. . Downstreaming denotes downloading ( such as downloading large files), while upstreaming denotes uploading (such as uploading large files). Both of these terms refer to the direction, or destination, of data flow, flowing either from the Internet to your computer or network (downstreaming), or from your computer or network to the Internet (upstreaming). Downstream data rate refers to the speed this data travels from the Internet (or other remote network) to your local computer or network. Upstream data rate refers to the speed this data travels from your local computer or network to the Internet or other remote network.

ADSL service works quite differently from SDSL.The downstreaming data rates for ADSL are much faster than the upstreaming data rates. What this means is that the path used for downloading files can carry more data than the path used for upstreaming, and it can carry this data at a much faster rate.

Using ADSL technology, you may be able to download a file as fast as you can when using a premium service such as T-1. However, since the upstreaming rates are much slower, the service cannot accommodate uploading large files with the same quickness. For SMBs that frequently download large files but have minimal need for downstreaming, ADSL is an excellent telecom solution.

SDSL is an excellent solution for businesses that require fast speeds for both upstreaming and downstreaming, but do not need voice service. It uses both paths for data capacity and data rates for both directions are equally fast. Speeds are less than those of ADSL, but both uploading and downloading large files can be accomplished with the same speed.

Distance Requirements
Both ADSL and SDSL are both distance sensitive. The closer your business is located from the CO, the faster your speed and the higher your bandwidth. For ADSL, your business must be located within 18,000 feet from the telephone company's central office (CO) to get service. For SDSL, you can be located as far away as approximately 23,000 feet.

Speed and Bandwidth
Speed and bandwidth are very important considerations when choosing a service. Speed refers to data transmission rate. Bandwidth is the capacity to carry data. Both are measured in bits per second. Speed and bandwidth determine the amount of data that can be transmitted, and how fast the data can be download and uploaded. Example: A 72 MB file downloaded at 128 Kbps will take about 10 minutes; if the same file is downloaded at 1.5 Mbps, it will only take about 48 seconds.

ADSL's data rates are 640 Kbps upstream and up to 8 Mbps downstream, depending upon your distance from the CO. At 9,000 feet from the CO, you can get as much as 8 Mbps; at 18,000 feet, you can get about 1.5 Mbps.

SDSL has more business bandwidth flexibility than ADSL. You can select the symmetric bandwidth that you desire from your service provider. The service can be packaged in a wide range of bandwidth configurations, including 144 Kbps, 160 Kbps, 192 Kbps, 384 Kbps, 416 Kbps, 768 Kbps, 1 Mbps, and 1.5 Mbps. Remember, the greater your distance from the CO, the lower the speed you can attain, regardless of its availability. Check with your service provider for the maximum speed you can get.

Installation: Wiring
ADSL and SDSL are easily installed on the ordinary twisted-pair copper wire currently behind the walls at your business. In some cases, the installation may require a different jack, a splitter and, occasionally, new wiring. The telephone company can complete the wiring for you, you can do it yourself, or you can hire an independent contractor.

Internet Access
Both ADSL and SDSL services provide an "always on" connection to the Internet. Once you install service, the connection is never interrupted.

If speedy access is very important to your business, and you don't require the bi-directional features associated with SDSL, ADSL is an excellent business solution. Using ADSL with its downstreaming speeds from 1.5 Mbps to 8 Mbps, data downloaded from the Internet will appear to pop-up almost instantly on your computer.

SDSL is also an excellent choice for Internet access. The downstreaming and upstreaming data rates of 144 Kbps to 1.5 are very good and yield good results.

ADSL is used by home consumers and many small business owners who mainly want to download files. It is used for carrying voice, data and video at fast rates. You can download large data files, streaming video, audio, and multimedia from the Internet very fast. But, generally, you cannot upload much more than e-mail messages.

SDSL is an excellent telecom solution for many SMBs. Using SDSL, you can upload and download large files equally fast. You can also run web and e-mail servers. It is also a cost-effective solution for connecting a small LAN to a LAN or a small LAN to a WAN.

Required Equipment
For both ADSL and SDSL, a POTS splitter is required. G-Lite ADSL does not require a splitter. A DSL modem and an Ethernet card are also required for installation.

Unlike your analog telephone line, your xDSL line does not draw its current from your local service provider central office. You'll need an Uninterruptible Power Supply (UPS) to ensure continuous service in the event of a power failure.

xDSL use requires that your computer have a Peripheral Component Interconnect (PCI) slot for installing the PCI. PCI adaptor cards may also be necessary to combine an Ethernet interface to your PC with DSL modem functions.

Cost and Value Considerations
ADSL and SDSL are very affordable and cost-effective services based upon a flat rate. Since cost is not based upon usage, you can use these services any time for as long as you want without incurring any usage charges. They are easily and inexpensively installed.

ADSL is generally best for SMBs where downloading files is most important. This is because of its larger data rate downstream. This means that the typical user will be able to download faster than they can send data.

SDSL is intended for businesses. The symmetrical features provide versatility and some options that are not available with ADSL. It also provides more flexibility than ADSL.

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Original Article here