ADSL, ADSL Interface, and ADSL Settings in ScreenOS Devices
The following are the topics of ADSL Interface:
About ADSL
Traditional telephone lines use analog signals to carry voice service through twisted-pair copper wires. However, when using analog transmission, the service provider can use only a small portion of the available bandwidth. To work around this limitation, the service provider can use digital transmission to access a wider bandwidth on the same media, at the same time. Because the service provider separates analog and digital transmissions, you can use your telephone and connect the Internet with your computer at the same time on the same line.
At the service provider’s central office, the digital subscriber line access multiplexer (DSLAM) connects many DSL lines to a high-speed network such as an Asynchronous Transfer Mode (ATM) network. ADSL transmission is asymmetric because the rate at which you can send data (the upstream rate) is considerably less than the rate at which you can receive data (the downstream rate). ADSL is ideal for Internet access because most messages sent to the Internet are small and do not require much upstream bandwidth, while most data received from the Internet require greater downstream bandwidth.
You can use the ADSL port on the NetScreen-5GT ADSL security device to enable Internet access for a network—without adding additional phone lines, and without using an additional ADSL modem. For details on connecting and cabling the NetScreen-5GT ADSL, see the NetScreen-5GT ADSL User’s Guide.
About the ADSL Interface
The ADSL interface on the NetScreen-5GT ADSL security device uses ATM as its Transport Layer. The interface supports multiple permanent virtual circuits (PVCs), which are continuously available logical connections to the network, on a single physical line (the adsl1 interface). You can configure additional virtual circuits on the device by creating subinterfaces (such as adsl1.1, adsl1.2).
Before you can configure the adsl1 interface, however, you must obtain the DSLAM configuration details for the ADSL connection from the service provider, as detailed in ADSL Settings from the Service Provider.
ADSL Settings from the Service Provider
The service provider for ADSL Internet access must provide you with some details about the ADSL connection so you can configure the security device to connect to their servers. Not all service providers use the same implementation of ADSL; you might be given any combination of the ADSL parameters as described in Table 1.
Table 1: ADSL Settings
ADSL Parameters |
Description |
|---|---|
Virtual Path Identifier and Virtual Channel Identifier (VPI/VCI) |
The service provider identifies the virtual circuit on the DSLAM. |
ATM encapsulation method (Multiplexing mode) |
The ADSL interface on the security device supports the following ATM Adaptation Layer 5 (AAL5) encapsulations:
|
Point-to-Point Protocol (PPP) |
A standard protocol for transmitting IP packets over serial point-to-point links, such as an ATM PVC. The security device supports the following methods of transporting PPP packets:
|
IP addresses |
The service provider might give the network a static IP address or a range of IP addresses. The service provider should also give you the address of the DNS server to use for DNS name and address resolution. |
Discrete multitone (DMT) |
A method for encoding digital data in an analog signal. By default, the ADSL interface uses Auto Detect mode, in which it automatically negotiates the DMT operating mode with the service provider DSLAM. You can change the mode on the adsl1 interface to force the interface to use only one of the following DMT standards:
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