Allied Telesis Converteon AT-CV5000- User Manual
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Chapter 1: Overview

A Few Basics about Media Converters

MAC Address


Duplex Mode

An Ethernet media converter can interconnect network devices over large distances by transferring Ethernet traffic between twisted pair ports and fiber optic cabling.

A Converteon™ media converter line card has a MAC address table that can store up to 2K to 32 K MAC addresses, depending on the line card model. Refer to the Converteon™ Media Converter Line Cards Reference Guide for the number of MAC addresses that each line card can store. The line card uses the table to store the MAC addresses of the network end nodes connected to the ports, along with the port number on which each address was learned.

A line card learns the MAC addresses of the end nodes by examining the source address of each packet received on a port. It adds the address and port on which the packet was received to the MAC table if the address had not already been entered in the table. The result is a table that contains all the MAC addresses of the devices that are connected to the line card’s ports, and the port number where each address was learned.

When the line card receives a packet, it also examines the destination address and, by referring to its MAC address table, determines the port on which the destination end node is connected. It then forwards the packet to the appropriate port and on to the end node.

If the line card receives a packet with a destination address that is on the same port on which the packet was received, it discards the packet without forwarding it on to any port. Because both the source end node and the destination end node for the packet are located on the same port on the line card, there is no reason for the line card to forward the packet.

Duplex mode refers to the manner in which an end node receives and transmits data. If an end node can receive or transmit data, but not both simultaneously, the end node is operating in half-duplexmode. If an end node can both receive and transmit data simultaneously, the end node is operating infull-duplexmode. An end node capable of operating in fullduplex can handle data much faster than an end node that can only operate inhalf-duplexmode.

The twisted pair ports on the Converteon™ line cards can operate in either halfor full-duplexmode. The twisted pair ports are IEEE 802.3ucompliant and willAuto-Negotiatethe duplex mode setting for you.

You can disable Auto-Negotiationon the line card ports so that you can set the duplex mode manually through the management software.

In order for a line card port to successfully Auto-Negotiateits duplex mode





AT-CV5000Media Converter Chassis Installation Guide

with an end node, the end node should also be using Auto-Negotiation.Otherwise, a duplex mode mismatch can occur. A line card port, usingAuto-Negotiation,defaults tohalf-duplexif it detects that the end node is not usingAuto-Negotiation.This results in a mismatch if the end node is operating at a fixed duplex mode offull-duplex.

Consequently, when you connect an end node with a fixed duplex mode of full-duplexto a line card port, you should use theAT-S70management software to disableAuto-Negotiationon the port and set the port speed and duplex mode manually.

The bridging media converter line cards, for example the AT-CM202,AT-CM2K0S,and CM212x/1 Series line cards, usestore-and-forwardas the method for receiving and transmitting frames. When an Ethernet frame is received on a line card port, the line card does not retransmit the frame out the destination port until it has received the entire frame and has stored the frame in a port buffer. It then examines the frame to determine if it is a valid frame. The line card discards invalid frames, such as fragments or runts. This ensures that only valid frames are transmitted out the line card ports and that damaged frames are not propagated on your network.

The non-bridgingmedia converter line cards, for example theAT-CV102andAT-CV1KSS,usepass-throughas the method for receiving and transmitting frames. The line cards can support any frame size. They only support one speed on the copper and fiber ports. These line cards do not support the filtering feature and do not learn any MAC addresses.