VDSL2 Interface Overview
This section includes the following topics:
- VDSL2 Systems
- VDSL2 Terms
- Implementation of a VDSL2 Network Using SRX Series Services Gateways
- VDSL2 Mini-PIM Support on SRX210 and SRX240 Services Gateways
- Supported Profiles
- Supported Features
VDSL2 Systems
Very-high-bit-rate digital subscriber line (VDSL) technology is part of the xDSL family of modem technologies that provide faster data transmission over a single flat untwisted or twisted pair of copper wires. The VDSL lines connect service provider networks and customer sites to provide high bandwidth applications (Triple Play services) such as high-speed Internet access, telephone services like voice over IP (VoIP), high-definition TV (HDTV), and interactive gaming services over a single connection. VDSL2 is an enhancement to VDSL and permits the transmission of asymmetric and symmetric (full-duplex) aggregate data rates up to 100 Mbps on short copper loops using a bandwidth up to 30 MHz.
The VDSL2 technology is based on the ITU-T G.993.2 standard. The VDSL2 uses Discrete Multitone (DMT) modulation . VDSL2 provides backward compatibility with ADSL, ADSL2, and ADSL2+ because this technology is based on both the VDSL1-DMT and ADSL2/ADSL2+ recommendations.
Packet Transfer Mode
VDSL2 interface supports Packet Transfer Mode (PTM). The PTM mode transports packets (IP, PPP, Ethernet, MPLS, and so on) over DSL links as an alternative to using Asynchronous Transfer Mode (ATM). PTM is based on the Ethernet in the First Mile (EFM) IEEE802.3ah standard.
Discrete Multitone Modulation
VDSL2 interface uses DMT modulation. Discrete multitone (DMT) is a method of separating a digital subscriber line signal so that the usable frequency range is separated into 256 frequency bands (or channels) of 4.3125 KHz each. The DMT uses the Fast Fourier Transform (FFT) algorithm for demodulation or modulation for increased speed.
VDSL2 Terms
Table 13 lists the terms related to VDSL2 technology.
Table 13: VDSL Terminology
Term | Definition |
|---|---|
ITU-T G.993.2 | International Telecommunication Union standard describing a data transmission method for VDSL2 transceivers. |
Packet Transfer Mode (PTM) | Transport of packet-based services method based on the EFM IEEE802.3ah standard. |
VDSL | VDSL is a DSL technology that provides data transmission over a single, flat, untwisted or twisted pair of copper wires at faster rate. |
VDSL2 | VDSL2 is an enhancement to G.993.1 (VDSL) that permits the transmission of asymmetric and symmetric (full duplex) aggregate data at faster rate. VDSL2 is based on ITU-T G.993.2 (VDSL2) standard. |
DMT | Discrete multitone (DMT) modulation is used by VDSL2. The DMT modulation is a method of separating a digital subscriber line signal so that the usable frequency range is separated into 256 frequency bands (or channels) of 4.3125 KHz each. |
Implementation of a VDSL2 Network Using SRX Series Services Gateways
In standard telephone cables of copper wires, voice signals use only a fraction of the available bandwidth. Like any other DSL technology, the VDSL2 technology utilizes the remaining capacity to carry the data and multimedia on the wire without interrupting the line's ability to carry voice signals.
The following example depicts the typical VDSL2 network topology deployed using SRX Series Services Gateways.
A VDSL2 link between network devices is set up as follows:
- Connect an end-user device such as a LAN, hub, or PC through an Ethernet interface to the customer premises equipment (CPE) (for example, an SRX Series device).
- Use an RJ-11 cable to connect the CPE to a DSLAM.
- The VDSL2 interface uses either Gigabit Ethernet or fiber as second mile to connect to the Broadband Remote Access Server (B-RAS) as shown in Figure 8.
- The ADSL interface uses either Gigabit Ethernet (in case of IP DSLAM] as the “second mile” to connect to the B-RAS or OC3/DS3 ATM as the second mile to connect the B-RAS as shown in Figure 9.
Note: The VDSL2 technology is backward compatible with ADSL. VDSL2 provides an ADSL interface in an ATM DSLAM topology and provides a VDSL2 interface in an IP or VDSL DSLAM topology.
The DSLAM accepts connections from many customers and aggregates them to a single, high-capacity connection to the Internet.
Figure 8 shows a typical VDSL2 network topology.
Figure 8: Typical VDSL2 End-to-End Connectivity and Topology Diagram
Figure 9 shows a backward-compatible ADSL topology using ATM DSLAM.
Figure 9: Backward-Compatible ADSL Topology (ATM DSLAM)
VDSL2 Mini-PIM Support on SRX210 and SRX240 Services Gateways
The SRX210 and SRX240 Services Gateways support the VDSL2 Mini-PIM (Annex A). The VDSL2 Mini-Physical Interface Module (Mini-PIM) carries the Ethernet backplane. When the Mini-PIM is plugged into the chassis, the Mini-PIM connects to one of the ports of the baseboard switch. The VDSL2 Mini-PIM on the SRX Series devices provides ADSL backward compatibility.
The VDSL2 Mini-PIM (Annex A) is compatible with ITU-T G.993.2 (VDSL2) standard.
Supported Profiles
A profile is a table that contains a list of preconfigured VDSL2 settings. Table 14 lists the different profiles supported on the VDSL2 Mini-PIM and their properties.
Table 14: Supported Profiles on the VDSL2 Mini-PIM
Profiles | Data Rate |
|---|---|
8a | 50 |
8b | 50 |
8c | 50 |
8d | 50 |
12a | 68 |
12b | 68 |
17a | 100 |
Auto | Auto mode (default) |
Supported Features
The following features are supported on the VDSL2 Mini-PIM:
- ADSL/ADSL2/ADSL2+ backward compatibility with Annex-A, Annex-M support
- PTM or EFM (802.3ah) support
- Operation, Administration, and Maintenance (OAM) support for ADSL/ADSL/ADSL2+ mode
- ATM quality of service (QoS) (supported only when the VDSL2 Mini-PIM is operating in ADSL2 mode)
- Multilink Point-to-Point Protocol (MLPPP) (supported only when the VDSL2 Mini-PIM is operating in ADSL2 mode)
- MTU size of 1500 bytes (maximum)
- Support for maximum of 10 permanent virtual connections (PVCs) (only in ADSL/ADSL2/ADSL2+ mode)
- Dying gasp support (ADSL and VDSL2 mode)