Improvement of Stability and Performance

Features listed below contribute a lot to the stability improvement of ADSL2/2+:

• Mandatory support of trellis coding;
• Mandatory one bit constellations;
• Receiver determined tone ordering;
• Receiver determined pilot tone;
• Channel discovery;
• On-line reconfiguration capabilities such as bit swaps and seamless rate adaptation (SRA);
• Frame structure with optimized use of RS coding gain;
• Parameters allowing enhanced configuration of the overhead channel.

Trellis coding and one-bit constellations are optional items in G.992.1 (ADSL), but they become mandatory options in G.992.3 (ADSL2) and G.992.5 (ADSL2+) now.

ITU-T G.992.3 provides for improved robustness against bridged taps and noise with a receiver determined pilot tone in the downstream direction. This adaptable pilot tone location, compared to G.992.1 which forces the pilot tone on carrier # 64, results in better clocking.

Improvement in Power Management

G.992.1 defined two types of power management states in the first generation ADSL, which are L0 (with full power on) and L3 (idle with no power consuming). Relative to the first generation of ADSL, G.992.3 added another power management state to ZTE´s ADSL2/2+, named L2 state.

The L2 power mode is one of the most important innovations of the ADSL2 standard.

In this state, the ADSL link is active but a low power signal conveying background data is sent from the ATU-C to the ATU-R. That is to say, when the traffic is low, ATU-C can lower the transmit power; this means not only power saving but also the decrease of crosstalk.

This mode enables statistical power savings at the ADSL transceiver unit in the central office (ATU-C) by rapidly entering and exiting low power mode based on Internet traffic running over the ADSL connection. The L2 entry/exit mechanisms and resulting data rate adaptations are accomplished without any service interruption or bit errors so that the user does not notice it.

Improvement in OAM

ZTE´s ADSL2/2+ has provided enhanced OAM protocol to retrieve more detailed performance monitoring information as well as new line diagnostics procedures. Determining the cause of problems in consumer, ADSL service has at times been a challenging obstacle in ADSL deployments. To tackle the problem, ZTE´s ADSL2 transceivers have been enhanced with extensive diagnostic capabilities. These diagnostic capabilities provide tools for trouble resolution during and after installation, performance monitoring while in service, and upgrade qualification.

In order to diagnose and fix problems, ZTE´s ADSL2 transceivers provide for measurements of line noise, loop attenuation, and signal-to-noise ratio (SNR) at both ends of the line. These measurements can be collected using a special diagnostic testing mode even when line quality is too poor to actually complete the ADSL connection.

Additionally, ZTE´s ADSL2 includes real-time performance monitoring capabilities that provide information on line quality and noise conditions at both ends of the line. This information is interpreted by software and then used by the service provider to monitor the quality of the ADSL connection and prevent future service failures. It can also be used to determine if a customer can be offered higher data rate services.

Bonding For Higher Data Rates

A common requirement among carriers is the ability to provide different service level agreements (SLAs) to different customers. Bonding multiple phone lines together can significantly increase data rates to homes and businesses. To enable bonding, ZTE´s ADSL2 supports the ATM Forum´s inverse multiplexing for ATM (IMA) standard (af-phy-0086.001) developed for traditional ATM architectures.

Through IMA, ZTE´s ADSL2 can bind two or more copper pairs in an ADSL link. The result is of far greater flexibility with downstream data rates. The IMA standard specifies a new sub-layer that resides between the ADSL physical layer (PHY) and the ATM layer. At the transmitter side, this sub-layer, called the IMA sub-layer, takes in a single ATM stream from the ATM layer and distributes this stream to multiple ADSL PHYs. At the receiver side, the IMA sub-layer takes in ATM cells from multiple ADSL PHYs and reconstructs the original ATM stream.

The IMA sub-layer specifies IMA framing, protocols and management functions that are used to perform these operations when the PHYs are lossy (bit errors), asynchronous, and have different delays. In order to work under these conditions, the IMA standard also requires modifications to some of the standard ADSL PHY functions such as the discarding of idle cells and erroneous cells at the receiver. ZTE´s ADSL2 includes an IMA operation mode to provide the necessary PHY modifications for IMA to work in combination with ADSL.

The Relationship between ADSL and ADSL2/2+

ZTE´s ADSL2/2+ is backward-compatible with ADSL, such ability is called ADSL - ADSL2 - ADSL2+ Auto Fallback. It is the ability of the CO (Central Office) to connect in ADSL Annex A (G.dmt), ADSL2 or ADSL2+ mode, depending upon the standard support of the remote unit. It is accomplished by negotiation during initialization.

Through negotiation during initialization, the capability of equipment to support the G.992.3 and/or the G.992.1 Recommendations is identified. For reasons of interoperability, ZTE´s equipment chooses to support both Recommendations; for instamce, it is able to adapt to the operating mode supported by the far-end equipment.

Connector Types

	RJ-11 Broadband/Telephone Plug The US style RJ-11 plug is a 4 pin version of the RJ-45 pictured below. It is the smallest in size and is used in the UK for DSL/Broadband Internet connections (RJ-11 to RJ-11).
	USB Type A (Computer) Universal Serial Bus (USB) is the most popular way of connecting peripherals to your computer. To connect most devices, you'll require a type A to B cable (often supplied with the product).
	USB Type B (Peripherals) The other end of the USB wire features a square shape plug designed to connect to peripherals such as your USB DSL modem or router.
	RJ-45 Ethernet Network (Crimped Plug) The RJ-45 connector, featuring 8 pins, is the big brother of the RJ-11. It's used for data communications, specifically Local Area Networks (LANs). Cables can be either straight (for normal use between a hub and a computer) or crossed (for use between two hubs or switches). Each computer requires a Network Interface Card (NIC) to connect to the network.
	RJ-45 Ethernet Network (Moulded Plug) The moulded RJ-45 plug shown to the left performs exactly the same purpose as the crimped version above. Professionally constructed cables are usually moulded by a machine instead of crimped using a special device called a "crimping tool".

Wiring Diagrams

USB Modem

The easiest, and most popular way to get a single computer online with is via a USB modem. The process involves connecting the USB modem to the DSL side of your micro-filter, and your computer to the USB modem using a standard type A to B USB cable. Software installation procedure will vary depending upon the equipment purchased.

Many users choose to share their USB Broadband connection using software such as Microsoft Internet Connection Sharing (ICS). In this scenario, the computer will act as a gateway for other computers to access the Internet via a Local Area Network (LAN).

The same concept can be extended to wireless network cards instead of the more restrictive fixed approach above. This configuration is often referred to as "ad-hoc networking mode" with the sharing computer operating in "infrastructure mode". Most users will find that sharing their USB connection over a wired network is adequate.

Ethernet Router & Local Area Network

The following diagrams show sample configurations for Internet access via an Ethernet router/modem. Many routers feature a 2, 4 or 8 port inbuilt Ethernet hub or switch (a device used to connect computers together). In this scenario, computers can be connected directly to the router. Each computer is wired using a standard Ethernet cable with one end connected to a spare port on the inbuilt hub/switch and the other end connected to the computers network card.

If your Ethernet router only has 1 network port, or you want to connect more devices to the network than there are available ports, a Ethernet switch can be used in combination with a cross-over cable to extend the size of your network.

Micro-Filters and Additional Telephone Sockets

Micro-filters must be used to separate the two different frequency bands used over your telephone line (voice and data) and prevent your analogue devices from interfering with the Broadband frequency ranges used by your modem/router.

Simple method: Walk around your house and count how phones are plugged into a phone socket (on the same line) and order the same number of micro-filters. Simply unplug each phone, plug them into the splitter and reconnect to the phone line.

Cheaper method: Buy a single micro-filter and plug this into your master socket and run all the phone extensions off the phone side of the micro-filter. Finally, run an extension from the ADSL side of the splitter to where you want to use your ADSL modem.