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X.400, Makint eMessage

By Carl Malamud

ent programs-word praces ors, mailprograms, databases-will want to usethis service, hence the need for many dif­ferent user interfaces.

So ho doeslDe.'s e HandlingIB 's S ADistribution ~,.,... ( ADS),or Digital Equipment Corp.'s MelSS3,lEeRouter and Mailbus relate to 1.400? Su-perficially, all of these t addrthe same issues as the 1.400 staIlldarlaThey allo a program to submit a mes­sage with a standard format that betransferred to the destiDatioo .

It' important to realize all threeproprietary message-bandling tandardsaddr issues pecific to the environ­ments they serve. Action Technologies'MHS, for instance, bas specific supportfor DOS file formats. More important, Ho­veIl bundles it in with its network operat­ing system--meaning that the MTA is in­eluded in the price of the network.

SNADS handles the issue of routingmessages in the fairly complex SNA envi­ronment, using a large IBM QIainframeboth an MTA and the u er interface.SNADS i actually the MTA for a programcaDed OISOSS (Distributed Office SupportSy tern). DlSOSS is the user iDterface forahbrary ystem (indudiDg . OIl

the MVS operatinl ystem.PROFS i the other large ~ssq~

The second part of the standard, themessaging component itself, identifiesstandard services that an X.4OO-basedsystem provides. These are manifestedas fields in the header or eaveindicate handling and details such theaddress to u for replies, date ofmessage, or a request for a receipt upondelivery. The interpersonal messagingcomponent also identifie the type of data

in the message-­plain text, say, or acolor image.

Actually,there' a thirdpiece to a me ­sagHaodJiag ys­tem, the user inter­face, an applicationthat' used to com­

pose and read The UTA getsthe message to the destiDation, and themessaging component defmes what amessage looks like. The user program,called a u agent, acceSses these ser­vices through a rnessqing applicationprogram interface and pr t the uwith a menu of options, directory of mailuser names, aod other utilities.

1.400 is very careful DOt to pecifywhat a user interface looks like. It oo1ybandies delivery of the andtheir format while en route. Many differ-

ome say that when X.400 ta­bilize , all our messagingproblems will vanish. AndX.400 and its X.500 kin arecertainly being touted as theultimate approach to mes­

sage exchange. So network managersno have to answer the big question:"How does X.400 fit into existing mes­sage- ystem architectures?"

Like the white knights that came be­fore it (remember X.25, Ethernet, A,SM, and Unix?), X.400 will fill a gap. Butit's not going to be the final answer toanything. Instead, it'll be an importanttool in an arsenal consi ting of many soft­ware sy terns.

One way to better understand therole of X.400 is by comparing it with oth­er backbone technologies like Fiber Dis­tributed Data Interface. FOOl is an ex­tremely fast (100 'Mbitls) data link layerprotocol that's particularly suitable forbackbones interconnecting maller net­works-multiple Ethernets and tokenrings, for in-stance-on a largesite. But FOOl willby no mean re­place Ethernet, to­ken rlni, ARCne~and other local orspecialized LANprotocols. X.400,like FOOl, is firstand foremo t an interconnection proto­col, a great leveler of proprietary and defacto approaches.

1.400 can be divided into t 0 pieces.The message-transfer part of the stan­dard specifies how two computers can ex­change a message-some arbitrary blockof data (usually text) with an "envelope"that signifies ho hould receive it Pro­grams that implement these message for­mat are Me sage Tran fer Agent(MTAs), which may have to forward am e to yet another MTA for delivery.

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e.t i a writer and consultantbased in San Francisco. He is the authorof three boo , including the forthcomingAul"i", Nop,ll Net,,",s (Van os­trand Reinhold, 1990).

Second, the gate ay ha to take theme5i1age and actually modify the formatof the contents. In the DEC environment,messages u the ASCII character t; in

ADS, the EBCDIC character is used.The job of converting every mes­

sage format to every other message for­mat is enormou . What X.400 doe is toprovide a common gateway method. Aingle type of gateway can replace the

patch line required for the mix-and­match y tem combinations in an organi­zation. If every me sage- y tem vendorbuild a gate ay to X.400 (see th figurefor an example of a Unix X.400 gate ay),then the job of connecting multiple, dis­similar me age systems is infinitelyimplified.. .

sy tem sold by 18 . Running under the change m sag with AIl-in-OneVMlC S operating y tern, PROFS use a All three environmen also havenetwork-based job-entry facility in S A gate ay to others. For example, Soft­called NIE rather than ADS. PROFS and S 'tch make gate ays that will allowDlSOSS users can communicate with each DEC, MHS, and ADS to connect to ODe

other u ing a PROFS bridge built into DI- another and to 1.400. The gate ay opoSOSS. Thu , two technically different erate much the same as DEC Me1ssa.1remessage-handling y tern appear to the Router gateway , tran lating the addressu r as though they were integrated. and document content to conform to the

DEc's Message Router take advan- tandards of the receiving environment.tage of the architectural feature of DEC- The gateway' job is to receive anet that provide seamles acce to file message and translate it into a form thataero a DEC network. MAILbus proto. the next message-handling service cancol establi h the connection to the - understand. In an aD-OEC environment,sage Router software. MAILbus is a com- this is a imple matter of changing themon interface to the DEC messaging header of the envelope to re6ect the De

environment. DEC's All-in-One office addr ing method.automation ystem i an example of a na- In the case of the DEC etive application that u the MAILbus Router gate y to the IB ADS envi-interface. rooment, ho ever, more b'allSIaltioo

sage Router bas other user inter- needed. rll'St of all, addrfaces. The old VMS mail utility, for exam- quite different. The gate ay m t keep apie, has a gate ay to sage Router. It directory that map DECnet-style ad­alIo users in the VMS Mail utility to ex- dresse to S ADS- tyle addr

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MODATACOMMU ICATIONS0 MAACH 1990