xDSL Family

ADSL - Asymmetric Digital Subscriber Line

RADSL - Rate adaptive Digital Subscriber Line

VDSL - Very high Bit rate Digital Subscriber Line

HDSL - High Bit rate Digital Subscriber Line

SDSL – Symmetric Digital Subscriber Line

There are some characteristics included in all of the DSL technologies. When we consider the bandwidths of these DSL technologies are depends on the length of the loop (distance to the central office from the user end). 

ADSL

In ADSL there are many versions. They are ADSL, ADSL2, ADSL2+, The Downlink and Uplink will depend on this versions. The data transfer rates downstream are much faster than the upstream data rates in ADSL.

The data rate of ADSL is highly dependent upon the distance from the Central Office (CO) to the Consumer Premises (CPE). At a distance of 9000 ft we can achieve 8 Mbps downstream and while at 18000 ft we can only get 1.544 Mbps downstream. ADSL operates at frequencies above 4 kHz, typically from 30 kHz to 1.1 MHz (Upstream is in the range from 30 kHz to 138 kHz, downstream ranges from 138 kHz, to ~1.1 MHz).

Applications

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 reasonable rate. We can download large data files, streaming video, audio, and multimedia from the Internet fast. But, generally, cannot upload much more than e-mail messages.

 RADSL

RADSL stands for Rate Adaptive Digital Subscriber Line. Rate Adaptive simply means that the speed of the connection is adjusted to meet the line conditions that each transmit and receive unit sees. And the upstream is 128kbps – 1Mbps and downstream 600kbps – 7Mbps.RADSL same as ADSL but the distance will increase due to adjustment of streams.

Applications

RADSL is used by home consumers and many small business owners who mainly want to download files and small uploads. It is used for carrying voice, data and video at reasonable rate.

VDSL

This is the fastest DSL technology. VDSL stand for Very high bit-rate Digital Subscriber Line. Not like other DSL technologies the capacity of the link depends on the service offering and spectrum regulations. It has 55.2 Mbps of download speed and 16 Mbps Upstream over single twisted pair. And it has 34 Mbps of download speed and upstream if the link is symmetric. It uses much wider bandwidth than ADSL IT also depends on loop condition.

Applications

VDSL is capable of supporting high bandwidth applications such as HDTV as well as telephone services (VOIP) and high quality video conferencing.

HDSL

HDSL stands for High-bit-rate Digital Subscriber Line. The main characteristic of HDSL is that it is symmetrical. That means an equal amount of bandwidth is available in both directions. HDSL can carry as much on a single wire of twisted-pair cable as can be carried on a T1 line (up to 1.544 Mbps) in North America or an E1 line (up to 2.048 Mbps) in Europe over a somewhat longer range and is considered an alternative to a T1 or E1 connection.

The primary disadvantage of HDSL is that it requires two twisted pairs of wires to operate, which increases the deployment cost for service providers. Also, HDSL does not support Plain Old Telephone Service (POTS) on the same lines as the data.

Applications

It uses for business applications, server access in large organizations and traditional T1 roles.

SDSL

SDSL Broadband provides a high-speed internet access service, with matching upstream and downstream data rates ranging from several speeds from 128kbit/s to 2Mbit/s. Unlike ADSL, it cannot co-exist with a conventional voice service on the same pair as it takes over the entire bandwidth. So using your phone line and the SDSL simultaneously is impossible. It typically falls in price between ADSL and T-1, and it is mainly targeted at small and medium businesses who may host a server on site.

Applications

Medium businesses who need to host a server on site, high quality video conferencing and multiple voice lines.

Characteristics of broadband technologies

• Speed or capacity
• Latency and jitter
• Always on
• Bandwidth symmetry
• Addressability

Speed or capacity - That means the capacity of the network link between the user and the broadband service provider. It is the one of the crucial factor of broadband every one considered. There are many kinds of broadband technologies either wired or wireless. This characteristic is in every broadband technology. When user wants to download high capacity files, streaming, or video calls, and the user should have a better capacity of down link.

Latency and jitter – This characteristic is very much crucial in applications that depends on real time information or interaction, such as telephone calls (VOIP) and interactive game playing. In simple words, Latency is an expression of how much time it takes for a packet of data to get from one designated point to another. And jitter is the variation in the time between packets arriving. This characteristic is very much important when we are in VOIP calls and playing online games.

Always on – this characteristic is specially occurs when people wants to connect with the world in 24 hours. Some internet applications need this characteristic vastly. For an example when we are using SKYPE (VOIP applications) we fully open to the world. We need the attention of all-time. To get the maximum benefit always on is must. And also it provides the chance for new applications like health monitoring, security, live updates and the like instant messaging.

Bandwidth symmetry – today telecommunication services, especially broadband do not necessary provide the same capacity up and down stream. This characteristic depends on the requirement of a broadband connection. When a user interest on web browsing; low bandwidth can be sufficient for upstream. That means up link can use for only send the request to serves. To do a request user need very few bandwidths and the higher down stream connection returns the contents. When we transfer peer to peer bulky files we have to request higher downstream and upstream.

Addressability – Addressability also enables such functionality as a user being able to run a server that other internet user can access. Residential customers are provided dynamically assigned addresses, and even if they have static address, they are very few. Addressability with out inbound control increases the chance of attacks to a computer. Then the security of home computers depends in large part on the security of the gateways installed within the home or devices such as firewalls.