🚀 go-pugleaf

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.

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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