Allied Telesyn International CentreCOM MAC Layer Bridge Models AT-6870 AT-6875 User Manual PN 613-10450-00
Copyright 1996 Allied Telesyn International Corp. All rights reserved. No part of this publication may be reproduced without prior written permission from Allied Telesyn International. Allied Telesyn reserves the right to make changes in specifications and other information contained in this document without prior written notice. The information provided herein is subject to change without notice.
Statement U.S. Federal Communications Warning: This equipment has been tested and found to comply with the limits for a Class A digital device pursuant to Part 15 of FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment.
Statement die Berschtigung zur Uberprufung der Serie auf Einhaltung der Bestimmungen eingeraumt. Von benutzer zusammengestellte Systeme, die dieses Gerat beihalten, mussen den Bestimmungen von Vfg 243 entsprechen. Notes The following are examples of special notices used throughout this manual. They are Notes, Cautions, and Warnings. They are defined as follows: Note: This indicates a note of specific interest related to the immediate text in which it is found.
Table of Contents Statement ...................................................................................................................... iii U.S. Federal Communications ............................................................................................................... Canadian Department of Communications .......................................................................................... Electrical Notice .........................................................................
Table of Contents IEEE 802.3/10BASE2 (Thin Ethernet)............................................................................................... IEEE 802.3/10BASE5 (Thick Ethernet)............................................................................................. Propagation.............................................................................................................................................. IEEE 802.3 Four Repeater Rule...................................................
Chapter 1 Overview CentreCOM MAC Layer Bridge ❑ ❑ AT-6870 AT-6875 Learning Bridge SNMP Manageable Learning Bridge IEEE 8023 Compliant Ethernet Compatible The CentreCOM Bridges allow two IEEE 802.3 sub-networks to be connected into a single network. Each sub-network may be IEEE 802.3 Ethernet or thin Ethernet. The CentreCOM Bridges transparently forward packets between both networks.
Overview The TCP/IP SNMP is supported by the AT-6875. The bridge can be monitored and manipulated by many SNMP compatible management stations. Several parameters of the AT 6875 can be managed under SNMP including custom filtering, static forwarding entries, and STP.
AT-30xxTR Multiport Repeater Light Function RX1 Channel 1 Receiving TX2 Channel 2 Transmitting RX2 Channel 2 Receiving Table 1: AT-6870 Front Panel Back Panel The back panel contains the following elements, shown in Figure 2: ❑ ❑ ❑ ❑ ❑ ❑ ❑ IEC-320/CEE-22 compatible power connector. Channel 1 connector for Ethernet or IEEE 802.3 10BASE5. Channel 1 thin Ethernet coaxial connector. Channel 2 connector for Ethernet or IEEE 802.3 10BASE5. Channel 2 thin Ethernet coaxial connector. Fan vent.
Overview Application Guidelines Overcoming Physical Limitations This section shows how bridges can be used to overcome common physical limitations. The next section shows how to do this in such a way that network performance is improved. Maximum Network Length A bridge can be used to link several networks serially (see Figure 3) in the same way as a repeater is used. The maximum network length only applies to individual networks, so that the overall network length is not bound by any limit.
AT-30xxTR Multiport Repeater Placement of Bridges in a Network The key to effective use of a bridge is to find the Work Groups within your organization and to place bridges between the networks in different groups. Network traffic within each Work Group is isolated by a bridge and has no effect on the overall network. When computers from different groups need to communicate, bridges allow them to do so transparently, as if there were just one big network. Simple Bridged Network .
Overview From To Frames/Second (Average) 1 2 9000 1 2 1000 1 4 1000 2 3 1000 2 4 1000 3 4 9000 Table 2: Traffic Between Nodes In this case there are two clusters. The first contains nodes 1 and 2, and the second contains nodes 3 and 4. Within each cluster, the traffic levels are around 13000 frames per second, while the traffic between the groups is around 4000 per second. A bridge could be placed between nodes 2 and 3.
AT-30xxTR Multiport Repeater 2. As long as the backbone network is operating correctly, any fault within a Work Group has no effect on other Work Groups. 3. Network faults are isolated to a single Work Group and are therefore easier to find. Figure 7: A Backbone Network Mixing Media The AT-6870/ AT-6875 MAC layer bridge can also be used to interconnect networks that use different media. You may use Thin Ethernet on one channel, and Ethernet on the other channel.
Overview Fault Tolerance and Isolation A single large network has several problems relating to faults. Two are listed below: 1. If the network fails all users lose connectivity. 2. Because of the network size, it may take a long time to find the fault. Figure 9 shows the failure of a simple network. Figure 9: Failure on a Simple Network When bridges are used, a network becomes much more fault tolerant. This is especially true if a backbone network topology is used.
AT-30xxTR Multiport Repeater Figure 11: Failure of a Backbone Network A bridged network is therefore inherently more fault tolerant, providing service to many users even when network components fail. This has the side effect of making it much easier to isolate the cause of the network fault. Since only a small part of the bridged network fails, this provides a much smaller area within which to search for a problem. Using Backup Bridges The CentreCOM MAC Layer Bridge uses the IEEE 802.
Overview The network depicted in Figure 12 would continue to operate if one of the bridges was turned off accidentally, or if a cable between one of the bridges and a network was unplugged. Figure 13: Advanced Use of Backup Bridges By using backup (or redundant) bridges, it is possible to design a network topology that is extremely resilient to failure.
AT-30xxTR Multiport Repeater Installation and Operation Unpacking Rough handling during shipping can damage electronic equipment. After you unpack the CentreCOM MAC Layer Bridge, check carefully for possible damage. If you notice any damage, contact the shipper.
Overview Settings Figure 14: Location of Headers and Transformers Thin Ethernet Transformer . Each channel has a transformer IC component that is only for thin Ethernet operation. This component must be moved to a spare socket if thin Ethernet is not used. The placement of these transformers is given below in Table 3 Network Type Channel 1 Channel 2 Ethernet T4A (Thick) T2A (Thick) IEEE 802.
AT-30xxTR Multiport Repeater 1. Remove any transformer in position T4. 2. Install the transformer into position T4A. Configuring Channel 2 Note: Channel 2 is set at the factory to operate with Ethernet or IEEE 803.2 10BASE5. Setting Channel 2 for Thin Ethernet Operation: 1. Remove any transformer in position T2A. 2. Install the transformer into position T2. Setting Channel 2 for Ethernet or IEEE 802.3 10BASE5 Operation: (Channel 2 Factory Setting) 1. Remove any transformer in position T2. 2.
Overview The network itself may be faulty. This can usually be checked independently of the bridge by establishing communication between two computers that are directly attached to the network. Finally, you should check that the bridge configuration matches the network attachments being used. Turn off the power and remove the power cord from the bridge. Remove the cover and inspect the intemal configuration.
Chapter 2 Specifications Software Features Hardware Features Compliant with IEEE 802.1 STP specification UDP/IP protocol support Dynamic forwarding table creation SNMP network management agent Power-on diagnostics Custom filtering criteria Networks Memory Performance Physical Characteristics Forwarding Rate Filtering Rate Dimensions Weight Temperature Operating Storage Relative Humidity IEEE 802.3 10BASE5 compliant Ethernet version 1.0 and 2.0 compatible IEEE 802.
Specifications Accessories 16 Part No. AT-RKMT-2 AT-RKMT-3 AT-1250 ATBRKT-13 Description Rackmount kit for 19 in. rack Rack mount “ears” kit for 19 in.
Appendix A IEEE 802.3 Quick Primer IEEE 802.3 AUI Drop Cables AUI or "drop cables" can be no longer than 50 meters (164 feet) each. Attachments may be made only to the cable ends at the 15 pin D-shell connector. AUI drop cables may have a maximum 257ns propagation delay for computing the worst case propagation delay of a cable system. AUI cable propagation delay is about 5.13 ns/meter.
IEEE 802.3 Quick Primer IEEE 802.3 Four Repeater Rule 18 No more than four repeaters may be linked to connect five segments and no other attachments may be on the linking segments. If attachments are present on the repeater coax link segments, then no more than two repeaters linking three segments may be configured. These limitations are set to keep propagation delay packet jitter, and signal attenuation to within acceptable standards.
Appendix B Network Frame Formats The Ethernet and IEEE 802.3 specifications define slightly different frame header formats. Both Ethernet and IEEE 802.3 use two 6 byte source and destination addresses, but the following two byte field is interpreted as a packet type by Ethernet and as a packet length by IEEE 802.3. Figure 15 shows the Ethernet and IEEE 802.3 frame formats. Figure 15: Ethernet and IEEE 802.
Network Frame Formats Note that this problem exists only at the MAC interface level, and is independent of the higher level protocols being used, such as TCP/IP. Therefore, systems which use Ethernet and IEEE 802.3, may not be able to communicate with each other even though they use the same higher level protocol. Many vendors’ interfaces can recognize both IEEE 802.3 and Ethernet frames on the same network. This is done by using Ethernet packet types that are greater than the maximum frame length.
Appendix C Power Cords and Plugs A standard power supply cord is shipped with all units sold in the United States. For units shipped internationally, the customer must supply a power cord that meets the regulations of the country where the bridge is operated.
Appendix D Glossary 10BASE5 - Also called thick Ethernet, 10BASE5 is a 10 Mhz, Baseband, 500 meter coaxial segment. The cable is also refered to as "yellow" cable. Cable impedance is 50Ω. Thick Ethernet cable is typically used as a trunk or backbone path of the network. 10BASE2 - Also called thin net or CheaperNet, 10BASE2 is a 10 Mhz, Baseband, 185 meter coaxial segment. Cable impedance is 50Ω.
Glossary THICK ETHERNET - see 10BASE5. THIN ETHERNET - see 10BASE2. LINK SEGMENT - The link segment of coaxial cable is a segment which has no MAU devices but links two Local Area Network (LAN) devices together such as repeaters. MAU - Media Attachment Unit or transceiver, provides an electrical attachment to a 10BASE2 or 10BASE5 coaxial cable segment. The MAU will convert the IEEE 802.
Appendix E Warranty and Service Information Allied Telesyn International Corp. (ATI) warrants to the original consumer/ purchaser that each of its products, and all components thereof will be free from defects in materials and/or workmanship for one year (two years on CentreCOM 100, 125, 126, 150, 200, 250, 270, 440, 470, and MX Series transceivers) from the original date of purchase. Any warranty hereunder is extended to the original consumer/purchaser and is not assignable.
Warranty and Service Information ATI makes no express or implied warranties including, but not limited to, any implied warranty of merchantability or fitness for a particular purpose, except as expressly set forth in this warranty. In no event shall ATI be liable for incidental or consequential damages, cost, or expenses arising out of or in connection with the use or performance of the product delivered hereunder.
