We provide here an overview of both SMTP and EMSD, to
compare and contrast their features and to lay the groundwork for
analysis of the experimental results in Sections ![[*]](file:/usr/local/lib/latex2html/icons/crossref.gif){kind=icon}
and
.
According to RFC 821[79], the objective of Simple Mail Transfer Protocol (SMTP) is to transfer mail reliably and efficiently. The SMTP design is based on the following model of communication:
As the result of a user mail request, the sender-SMTP establishes a two-way transmission channel to a receiver-SMTP, which may be either the ultimate destination or an intermediate.
Following this, the sender-SMTP sends a MAIL command indicating the sender of the mail. If the receiver-SMTP can accept mail it responds with an OK reply. The sender-SMTP then sends a RCPT command identifying a recipient of the mail. If the receiver-SMTP can accept mail for that recipient it responds with an OK reply; if not, it responds with a reply rejecting that recipient (but not the whole mail transaction). The sender-SMTP and receiver-SMTP may negotiate several recipients. When the recipients have been negotiated, the sender-SMTP sends the mail data, terminating with a special sequence. If the receiver-SMTP successfully processes the mail data it responds with an OK reply. Note that the dialog is purposely lock-step, one-at-a-time.
SMTP provides two mechanisms for the transmission of mail: directly from the sending user's host to the receiving user's host when the two host are connected to the same transport service, or via one or more relay SMTP-servers when the source and destination hosts are not connected to the same transport service. The mail commands and replies have a rigid syntax. Replies also have a numeric code.
Thus it can be seen that for the exchange of any one message with SMTP, a number of transactions must be completed. EMSD attempts to improve efficiency by cutting down on this number and simplifying the process for the case of short messages.
The EMSD specifications define the protocols between an EMSD Device and an EMSD Server. EMSD requires ESROS (Efficient Short - Remote Operation Services) [91]. The EMSD-P&FS consist of two independent components: Efficient Mail Submission & Delivery Protocol (EMSD-P) and EMSD Format Standards (EMSD-FS).
EMSD-FS is responsible for defining the format of a limited size interpersonal message. It defines the "Content" encoding (Header + Body) and the end-to-end envelope. It relies on EMSD-P for the transfer of the content to its recipients.
EMSD-P is responsible for wrapping a limited size message in a point-to-point envelope and submitting or delivering it. EMSD-P performs the envelope encoding and relies on the services of ESROS for transporting the envelope. Some of the services of EMSD-P include message originator authentication and optional message segmentation and re-assembly. The Efficient Mail Submission & Delivery Protocols are designed with three high level goals:
These goals will prevent, whenever possible, the expense and associated problems of "re-inventing the wheel." The EMSD Protocols make heavy use of existing technology:
These technologies have been thoroughly tested and have proven to be reliable solutions for the problems they address (e.g. message format, reliable message delivery, encoding and compacting). The EMSD Specifications allow for users who enjoy the advantages of this new technology and at the same time want be connected to the rest of the existing messaging world.