In this section:

Overview

Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service and voice calls at the same time. ADSL can generally only be distributed over short distances from the telephone exchange (the last mile), typically less than 4 kilometers (2 mi), but has been known to exceed 8 kilo meters (5 mi) if the originally laid wire gauge allows for further distribution.

At the telephone exchange the line generally terminates at a digital subscriber line access multiplexer (DSLAM) where another frequency splitter separates the voice band signal for the conventional phone network. Data carried by the ADSL are typically routed over the telephone company's data network and eventually reach a conventional Internet Protocol network.

Most ADSL communication is full-duplex. Full-duplex ADSL communication is usually achieved on a wire pair by either frequency-division duplex (FDD), echo-cancelling duplex (ECD), or time-division duplex (TDD). FDD uses two separate frequency bands, referred to as the upstream and downstream bands. The upstream band is used for communication from the end user to the telephone central office. The downstream band is used for communicating from the central office to the end user.

Configuring ADSL

  1. Choose Network from the Configuration Menu.

  2. Scroll to WAN Interface IPv4 Settings and select the ADSL radio button.

  3. Click Submit.

  4. Choose Network > ADSL Configuration.

  5. Configure settings using the information in the table below as a guide. When you have finished configuring settings, click Submit to make your changes take effect.

    ADSL Parameters

    ParameterDescription

    ADSL Interface IPv4 Settings

    Creates a WAN connection through the ADSL interface. Select the type of IP4v ADSL interface to use:

    ADSL-PPPoATM

    Establishes a WAN connection using a PPP session over ATM. If you choose ADSL-PPPoATM, enter the username and password given to you by your network provider in the User Name and Password fields.

    ADSL-PPPoE  

    Establishes a WAN connection using a PPP session over Ethernet over ATM. If you choose ADSL-PPPoE, enter the username and password given to you by your network provider in the User Name and Password fields.

    ADSL-Static IP

    Establishes a static IP address over ATM. RFC 2684 is used to bridge IP over ATM.

    Note: This setting requires you to return to the Network Configuration page and manually enter the IP address, Netmask, and Gateway IP given by your service provider.

    See Configuring ADSL for Static IP.

    Keepalive Ping         

    Select the Keepalive Ping check-box to periodically send pings to the specified host to monitor the status of the Primary interface.

    PPP Link Status

    Verify the status of your PPP link. The PPP link should be up. To manage PPP settings, refer to Configure WAN Interface Settings.

    ATM Encapsulation Method

    Provides a way to encapsulate various protocols over ATM. Select the ATM encapsulation method used by your service provider. Choose the ATM encapsulation method used by your service provider:

    Logical Link Control (default)

    		Multiplexes multiple protocols over a single ATM VC. The protocol of a carried protocol data unit (PDU) is identified by prefixing the PDU with a Logical Link Control (LLC) header.

    VC based Multiplexing

    Defines one permanent virtual circuit (PVC) per protocol. This uses more VCs than LLC encapsulation but reduces overhead because a header is not necessary.

    For example, to forward IP and IPX over ATM, two dedicated PVCs must be defined. One PVC carries the IP address and another carries Internetwork Packet Exchange (IPX). As the number of protocols increase, PVC also increase.

    Primary PVC Settings

    Set the Permanent Virtual Circuit setting to either autodetect or manual:

    Autodetect VC (default)

    Identifies encapsulation automatically to dynamically create higher protocol layers.

    Manually set VC 

    The following fields become active:

    VPI: Enter the Virtual Path Identifier (VPI)

    VCI: Enter the Virtual Channel Identifier (VCI) Specifies the Virtual Path Identifier (VPI) and

    Virtual Channel Identifier (VCI) values for the Data PVC. If unknown, request this information from your service provider.

    VCI, used in conjunction with the VPI, indicates where an ATM cell is to travel over a network. ATM, or asynchronous transfer mode, is a method that many Internet Service Providers (ISPs) use to transfer data to client computers. Because ATM sends packets over fixed channels, the data is easier to track than information sent over the standard TCP/IP protocol.

    The VCI within each ATM cell defines the fixed channel on which the packet of information should be sent. It is a 16-bit field, compared to the VPI, which is only 8 bits. Because this numerical tag specifies the virtual channel that each packet belongs to, it prevents interference with other data being sent across the network.

    Secondary PVC Settings

    (Optional) If your service provider supports multiple PVCs, you can enable a second PVC to use as a secondary WAN link. This can be used in a WAN failover (WAN Link Redundancy, or WLR) configuration to achieve WAN redundancy or load balancing data and voice traffic between the two virtual links.

    Configure Secondary PVC Settings:

    Select the Enable Secondary PVC check-box to enable a second PVC to use as a secondary WAN link.

    Choose Network > WAN Failover to open the WAN Link Redundancy page and refer to Configuring WAN Failover.

    Select the Enable WAN Link Redundancy check-box and configure settings on the page as needed. Click Submit to save your settings.

    Choose Network > WAN Failover > Secondary WAN to open the Secondary WAN Interface Settings page and select the Virtual Link for the WAN Interface Setting. Click Submit to save your settings.

  6. Configure the following settings on the ADSL Configuration Page:

Configuring ADSL for Static IP

 

  1. Choose Network > ADSL Configuration.
  2. Configure settings using the information in the ADSL Parameters table.

  3. In ADSL Interface IPv4 Settings, select ADSL-Static IP.

  4. Choose the ATM encapsulation method used by your service provider:
    • Logical Link Control (default)
    • VC based Multiplexing
  5. Select one of the following Primary PVC Settings:
    • Autodetect VC (default)
    • Manually set VC—The following fields become active:
      1. VPI—Enter the Virtual Path Identifier (VPI)
      2. VCI—Enter the Virtual Channel Identifier (VCI)
  6. Select Apply Later.

  7. Choose Network from the Configuration Menu.

  8. Scroll to WAN Interface IPv4 Settings and enter the IP Address and Subnet Mask given to you by your service provider.
  9. Scroll to Network Settings and enter the Default Gateway IP address given to you by your service provider.
  10. At the top of the Network Configuration page, click Submit All.
    ADSL for Static IP is now configured on your system.

Viewing ADSL Line Status

The ADSL Line Status page describes ADSL modem status. If the modem is in “Showtime,” rate and statistical information are also provided.

  1. Choose Network > ADSL Status.

  2. View ADSL status using the information below.

    ADSL Parameters

    ParameterDescription

    Status

    Describes ADSL line status.

    Modern Status

    The status of the training process with the digital subscriber line access multiplexer (DSLAM).

    DSLAM connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital communications channel using multiplexing techniques.

    “Showtime” indicates that the modem and DSLAM are in sync.

    Mode SelectedDisplays the ITU standard for the operating modem. For example:

    G.992.1 A is ADSL Annex A. Annex A is ADSL over PSTN. PSTN refers to the standard analogue circuits originally designed for voice with a data rate limit of 56k. Annex A provides a maximum speed of 24Mbps download and 1.4Mbps upload.

    G.992.5 is ADSL2+ Annex M. ADSL2+ Annex M allows dramatic increases in upstream data speed, with real-world upload speeds typically around 1.6 to 2.2Mb/s - sometimes twice as fast as “standard” with a maximum 3.3Mbps. The standard maximum download speed is 24 Mbit/s.

    (Annex A) upstream speeds.

    Trellis-Coded Modulation

    Indicates whether Trellis Coded Modulation (TCM) is enabled or disabled. TCM is a modulation scheme that allows highly efficient information transmission over band-limited channels such as telephone lines.

    Latency Type

    Indicates the modem latency type:


    Interleave—Increases resistance to noise bursts on a line. Increases latency on the line. 
    If during transit more than a certain amount of data has been lost, the data cannot be correctly decoded by your router. Short bursts of noise on the line can cause these data packets to become corrupt and the modem has to re-request data, which in turn can slow down the overall rate at which data is transmitted.

    Interleaving is a method of taking data packets, chopping them up into smaller bits and rearranging them so that contiguous data is spaced further apart into a non-continuous stream. Data packets are re-assembled by your modem.

    Fast Path—Improves (lowers) latency and lowers noise margin dB, which can lower line stability. Fast Path is identified on the system by its Depth of Interleaving (D Value) of 1. Fast Path sends one packet at a time.

    ATM Virtual Circuit Information

    Detected: Displays system virtual channel information:

    VPI: Virtual Path Identifier

    VCI: Virtual Channel Identifier

    Rate
    Displays ADSL System Data Rates

    Data RateDisplays the data rate in kilobits per second. The EdgeMarc supports several versions of ADSL (ADSL, ADSL2, ADSL2+, and so on) and associated annex versions.

    Max Attainable Data Rate

    Describes maximum downstream and upstream data rate or speed that the DSLAM negotiates with your ADSL modem. For a given service, the service provider may mandate a given maximum data rate.

    Information

    Displays ADSL system details

    Interleaver Depth

    Displays the downstream and upstream Depth of Interleaving (D Value). Interleaving helps maintain tolerance against noise on longer length lines.

    Various depths of interleaving may be applied by the DSLAM. A depth of 1 indicates the line is on Fast Path with no interleaving applied.

    Line Attenuation

    Displays downstream and upstream signal loss over the line in decibels. Typical values for line attenuation on an ADSL connection are between

    5 dB and 50 dB (lower values are better).

    Signal Attenuation

    		Displays downstream and upstream reduction of signal strength during transmission; when a signal is attenuated so much that the destination cannot interpret the signal or the signal fails en route. Attenuation in both signal frequency and the range between the endpoints of the medium affect the amount of signal reduction.
    Signal-to-Noise-Ratio

    Displays system downstream and upstream

    signal-to-noise ratio (SNR) information. The higher the noise margin, the stronger the ADSL signal is compared to noise on the line. A ratio between 15 and 18 is good, indicating that your signal is very strong, and/or there is very little noise.

    Actual Aggregate Transmit Power

    Measures downstream and upstream ADSL transmission power spectrum density (PSD). These calculations can help in designing over-voltage protection circuits for ADSL and in debugging ADSL analog circuitry.

    Superframe

    Displays the number of downstream and upstream superframes received with an error. A superframe consists of 68 ADSL frames plus a synchronization frame. The ADSL modem generates 4000 frames per second. The global duration of an ADSL superframe is 17 ms.

    CRC

    Displays the number of downstream and upstream Cyclic Redundancy Check (CRC) errors. CRC is an error detection code used to verify packet transmission between the sender and the receiving end. A CRC error indicates that part of the data packet is corrupt and requires retransmission.

    Forward Error Corrections

    Displays the number of downstream and upstream Forward Error Correction (FEC) errors that have been corrected with error correction applied to the line.

    Error correction is turned on at the same time as Interleaving. It's normal to see FEC errors on an Interleaved line, indicating that the Interleaving and error correction process is working.

     Errored

    Displays the number of downstream and upstream Errored Seconds (ES). An ES is a one-second period of time in which one or more coding violations occurred or at least one Loss of Signal events occurred. It is not unusual to see occasional ES.

     Severely Errored

    Displays the number of downstream and upstream

    Severely Errored Seconds (SES). An SES is a one-second period that contains 30% or more errored blocks or other events.

    Unavailable

    Displays the number of downstream and upstream Unavailable Seconds (UAS). Ten consecutive Severely Errored Seconds (SES) triggers a UAS event that removes the path from use. The path becomes usable again after 10 consecutive seconds with no SES events.

    HEC Error

    Displays the number of downstream and upstream Header Error Check/Correction (HEC) errors. HEC is a type of CRC error check which has been performed on the header of an ATM cell. This count is usually where HECs have been uncorrected and have been discarded.

    If these errors are too high, throughput is slowed and can lead to connection instability.