Chapter 9: Summing It Up

Chapter 9: Summing It Up

Similarities Between X.400 and SMTP

While X.400 and SMTP differ in many ways, it is important to realize that they perform the same function. That function is to route mail from one mail system to another through a wide area network. In order to do this, they employ different approaches, but the requirements laid on them are the same. As a result, there are many similarities between the two protocols.

Table 9-1 shows some analogies between X.400/OSI and SMTP/IP.

Table 9-1. Analogies Between X.400/OSI and SMTP/IP

X.400/OSI

SMTP/IP

CONS: Connection-oriented network service

TCP

CLNS: Connectionless network service

UDP

NSAP

IP address

TSEL

IP protocol number (TCP or UDP)

SSEL/PSEL

Socket

PSAP

Port

P2/P22

RFC 822 + RFCs 2045?2049 MIME

RFC 821 ? SMTP

POP3 / IMAP4

X.500

DNS

DAP

LDAP

In Favor of X.400

As we have seen, the designers at the CCITT/ITU and ISO were very fond of designing elegant architectures. They introduced structure to the design of networks and mail systems, which helped clarify the discussion of functionality and protocols.

From them we have the OSI network model and a clear definition of the components in a mail system or directory. They also designed a comprehensive mail and directory architecture, much of which has also found its way into the Internet?s mail paradigm.

In addition to the architectural specification, X.400 still has a few technical advantages over SMTP:


	?	X.400 offers a succinct message format.


	?	X.400 can restrict the...

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