Tài liệu Ethernet over VDSL docx

Ethernet over VDSL White Pape r 1. Introduction VDSL (Very high data rate Digital Subscriber Line) is a broadband transport technology for twisted copper pairs operating at data rates of up to 52.8 Mbit/s with corresponding maximum reach ranging from 1000 feet (300 meters) to 4500 feet (1500 meters) of 24 gauge wire. VDSL offers tremendous promise as a means to provide the next generation of high-speed networking technology over copper telephone lines. VDSL is referred to as a last-mile technology, as it is used for inter-connections between a telephone switching station and a home or office, and is not used for interconnecting switching stations. 2. VDSL Benefits • Highest-rate DSL technology available • Support for Symmetric and Asymmetric modes of operation • Up to 52 Mbit/s downstream over single copper twisted-pair loop • Coexistence with Voice • Home networking or LAN over regular telephone lines • The dominant physical access medium based on copper loop for MTU (Multi Tenant Unit) and residential applications 3. VDSL Applications • Digital Video broadcast • Video-on-demand • Video conferencing and Voice over IP • LAN to LAN connection over the existing telephone wires 4. VDSL Deployment Scenarios • Possible deployment scenarios for VDSL are Fiber to the Exchange (FTTEX), Fiber to the Neighborhood (FTTN), Fiber to the Cabinet (FTTCab) and Fiber to the Building (FTTB). In FTTEX, all subscribers are within close range of the Central Office (CO). FTTN and FTTCab are appropriate for VDSL termination in DLCs and NGDLCs. FTTB can bring fiber directly into buildings, such as MDU and MTU, where VDSL is terminated. July 04 • Ethernet over VDSL Figure 1. VDSL Deployment Scenario As demonstrated in Figure 1, VDSL technology enables transmission of high-speed traffic between the Network, the ONU, and end user premises over the existing telephone lines. The VDSL CPE on the user side is connected to VDSL ONU over a twisted copper pair. The connection of the the user’s home network to the public network is smoothly achieved by a native Ethernet interface between the VDSL CPE interface and the LAN on the user’s side. 5. Ethernet Over VDSL Technology Using Ethernet Over VDSL technology enables the existing public copper network and the user LAN networks to be used for migration to new emerging services. It also has the following advantages: • No need for new wiring • Meeting consumer price and performance needs • Cost effective high speed access - up to 20 Mbit/s or more • Simple, easy to install; true plug-and-play • Near-zero configuration • Enables simultaneous delivery of additional services such as voice Ethernet framing ensures compatibility with existing Ethernet LAN • MAN/WAN compatible • Eliminates protocol conversions Figure 2 describes the components involved in the connection between user premises equipment and the Ethernet core. July 04 • Ethernet over VDSL Figure 2. VDSL Deployment Scenario In Figure 2, the traffic from the user equipment to the CPE is transmitted over LAN media using a native Ethernet frame. The Ethernet frame is transmitted from the CPE to the IMAP or DSLAM over VDSL using a twisted copper pair. The connection between the IMAP or DSLAM and the Ethernet core can be applied over any transmission media, and the Ethernet frame can be mapped to any destination over the public network using standard layer 2 MAC algorithms. 6. Ethernet over VDSL (EoVDSL) Frame Encapsulation 6.1 VDSL Frame Format The Ethernet frame is encapsulated in the following VDSL frame format: July 04 • Ethernet over VDSL Figure 3. VDSL Ethernet Frame The payload is divided into two equal parts: fast channel for latency sensitive services, and slow channel (mandatory). The slow and fast channel alternate as shown in Figure 3. To apply the mandatory Transport Class 1 (single latency) the values F=0, S=200 should be set to remove the fast channel fields from the transmitted frame. 6.1.1. Fast Channel Figure 4. Fast Channel Fast channel is optional, and defined for latency-sensitivity applications such as Voice. The Fast Codeword should be <= 180 octets. The number of Fast FEC octets can get the values 2,4,16 octets. 6.1.2. Slow Channel July 04 • Ethernet over VDSL Figure 5. Slow Channel The Slow channel is mandatory and defined for data transmission. The Slow codeword consists of 3-octet Operation Channel (OC) field, a Slow Payload field and a slow FEC field of 16 octets. The length of the Slow Codeword is ≤ 200 octets. The slow codewords are protected by an Interleaver before transmission into the lines; it carries both payload and in-band control channel. 6.1.2.1 Operational Channel Figure 6. Operational Channel The Operational Channel contains 3 octets per frame: one Op-code octet and two data octets. It is used as transport media for VOC (VDSL Overhead Control) and EOC (Embedded Operation Channel), while VOC used for control of the modem layers (VDSL chipset), and EOC is used for management applications. 6.2 Ethernet Frame July 04 • Ethernet over VDSL Figure 7. Ethernet Frame • The Ethernet frame must be transferred transparently, without manipulating the frame content. • The encapsulation method is a store & forward mechanism. It is not data dependant (no bit stuffing) • EoVDSL is a PHY. • Prioritization is performed by higher layer devices and packets are transferred in the order they are received. • The Ethernet packet is preceded by an IPG of 9.6 usec/0.96 usec for 10/100Mbit/s links. • The preamble (0x55) is not used by MAC. The SFD (0x5D) is required by the MAC layer. The Data in Figure 7 refers to the Ethernet frame from the destination address to the FCS, Destination Address, Source Address ,Type/ Length, DATA, FCS. 6.3 EoVDSL Encapsulation July 04 • Ethernet over VDSL Figure 8. EoVDSL Encapsulation The Ethernet frame (without preamble, SFD and EFD {Ethernet frame data}) is encapsulated by a new preamble. Idle bytes are filled with flags. • The preamble includes a length field. • Ethernet Frame Data from destination address to FCS. 7. Conclusion Ethernet over VDSL is an excellent solution for high speed applications. The media is highly available, and cheap compared to other solutions. It is also simple to connect to, from any type of equipment supporting Ethernet LAN, and no protocol conversion is required. Teledata Networks Website: www.teledata-networks.com Specifications published here are current as of the date of publication of this document. Teledata Networks reserves the right to change specifications without prior notice. The information contained herein is Teledata Networks proprietary information. Products or features contained herein may be covered by patents in one or more countries. Copyright © 2004 Teledata Networks. All rights reserved. P/N 760-000544 Rev A. Original. File Name: Ethernet over VDSL WP.doc . native Ethernet interface between the VDSL CPE interface and the LAN on the user’s side. 5. Ethernet Over VDSL Technology Using Ethernet Over VDSL technology. 6. Ethernet over VDSL (EoVDSL) Frame Encapsulation 6.1 VDSL Frame Format The Ethernet frame is encapsulated in the following VDSL frame format: