Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: Notesfiles $Revision: 1.6.2.14 $; site siemens.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!princeton!siemens!fwb From: fwb@siemens.UUCP Newsgroups: net.lan Subject: Bridges, etc. Defined Message-ID: <29500002@siemens.UUCP> Date: Mon, 17-Feb-86 10:41:00 EST Article-I.D.: siemens.29500002 Posted: Mon Feb 17 10:41:00 1986 Date-Received: Wed, 19-Feb-86 00:53:33 EST Lines: 94 Nf-ID: #N:siemens:29500002:000:3620 Nf-From: siemens!fwb Feb 17 10:41:00 1986 The MAP 2.1 document from General Motors defines bridges, routers, and gateways (and repeaters in the bridge definition). I will quote from the document. There is no copyright notice on it, so I guess this is OK. Please try to imagine better graphics in the figures. ---------------------------------------------------------------------------- 3.3.2 _BRIDGES_ Bridges are transparent devices used to connect segments of a single LAN. The Data Link protocols of these segments are usually the same. A bridge can extend a network beyond the design specification of a single segment or physically isolate the segments from one another. By comparison to an (IEEE 802 baseband) repeater which provides transparent network expansion at the Physical Layer, the bridge provides network expansion at the Data Link Layer. ... Bridges may be used to provide connection of two identical network types such as two IEEE token bus implementations. A bridge may also be used in coupling dissimilar IEEE 802 networks. The architecture of a bridge is shown in Figure 3.3-1. User User 7 7 6 6 5 5 4 4 3 ----- 3 2 2 2 2 1 1 1 1 ^ ^ ^ ^ <___|_____| |_____|___> Segment A Segment B 3.3-1 BRIDGE ARCHITECTURE 3.3.3 _GATEWAYS_ Gateways are devices that connect different network architectures by performing protocol translation. The primary difference between a gateway and a bridge is that the gateway utilizes all seven OSI layers where a bridge is restricted to layers 1 and 2. ... Examples of gateway applications include connecting a MAP network to an Allen-Bradley Datahighway, a Modicon Modbus, a DEC Decnet, an IBM SNA, or an HP DS/1000 network. In terms of OSI architecture, a gateway can be illustrated as shown in Figure 3.3-2. User ----- User 7 7 7 7 6 6 6 6 5 5 5 5 4 4 4 4 3 3 3 3 2 2 2 2 1 1 1 1 ^ ^ ^ ^ <___|_____| |_____|___> Segment A Segment B 3.3-2 GATEWAY ARCHITECTURE 3.3.4 _ROUTERS_ Routers are commonly used to connect several networks together at a common point. In this configuration the Router provides path selection and alternate routing based on destination network layer addresses and status of connected networks, an illustration in OSI terms is as shown in Figure 3.3-3. A router has one common network address for all attached networks. ----INTERNET--- 3 3 3 2 2 2 1 1 1 ^ ^ ^ <_____| | |_____> NETWORK A | NETWORK C \ / NETWORK B 3.3-3 ROUTER ARCHITECTURE ----------------------------------------------------- Frederic W. Brehm (ihnp4!princeton!siemens!fwb) Siemens Research and Technology Laboratories 105 College Road East Princeton, NJ 08540 (609) 734-3336