Chapter 4: Backbone Topology

Chapter 4: Backbone Topology

Addressing

The topology of a mail backbone may be represented by the addressing scheme it uses. However, this is not a necessary component of the addressing mechanism. In fact, it is rarely desirable to have the address linked to the topology; it simplifies the task of routing but creates a dependency on the backbone, which the user should not directly see.

It may be easiest to illustrate this with an example of paper mail. If I send a message to my sister in California, I address the letter to ?Sharon Rhoton, street address, Ventura, CA, postal code, U.S.A.? I do not need to attempt to determine which route the letter will follow and include all the intermediate destinations, as in ?local post office -> Central Vienna post office -> New York -> Los Angeles -> Ventura -> Sharon Rhoton.? And yet that is the way many electronic mailing systems used to work. With Digital?s Message Router, you need to enter all the intermediate message routers if your recipient is not directly accessible to yours. So you may require an address of the format

John Rhoton @ A1MBX @ NODE1[JR1] @ NODE2[JR2] @ NODE3[JR3] @ NODE4[JR4]

but if you were already on node four you would require only

John Rhoton @ A1MBX @ NODE1[JR5] @ NODE2[JR6] @ NODE3[JR7]

and if you were on node one you could get away with

John Rhoton @ A1MBX

so the address was not universal.

With X.400, my address will always...

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