Unformatted text preview: 6 W 26 m 36 2 7 H 17 X 27 n 37 3 8 I 18 Y 28 o 38 4 file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/smtp_sim.htm (17 of 23) [12/09/2001 14.47.52] Chapter 28. SMTP: Simple Mail Transfer Protocol 9 J 19 Z 29 p 39 5 a K 1a a 2a q 3a 6 b L 1b b 2b r 3b 7 c M 1c c 2c s 3c 8 d N 1d d 2d t 3d 9 e O 1e e 2e u 3e + f P 1f f 2f v 3f / Figure 28.6 Encoding of 6-bit values (base-64 encoding).
When the number of characters to encode is not a multiple of three, equal signs are
used as the pad characters.
The following example of these two encodings is from RFC 1522:
From: =?US-ASCII?Q?Keith_Moore?= <[email protected]>
To: =?ISO-8859-l?Q?Kelcl_J=F8rn_Simonsen?= <[email protected]>
CC: =?ISO-8859-l?Q?Andr=E9_?= Pirard <[email protected]>
A user agent capable of handling these headers would output:
From: Keith Moore <[email protected]>
To: Keld J0rn Simonsen <[email protected]>
CC: Andre Pirard <[email protected]>
Subject: If you can read this you understand the example.
To see how base-64 encoding works, look at the first four encoded characters in the
subject line: SWYg. Write out the 6-bit values for these four characters from Figure 28.6
(S=0xl2,W=0xl6,Y=0xl8,and g=0x20) in binary:
010010 010110 011000 100000
Then regroup these 24 bits into three 8-bit bytes:
=0x20 which are the ASCII representations for I, f, and a space. file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/smtp_sim.htm (18 of 23) [12/09/2001 14.47.52] Chapter 28. SMTP: Simple Mail Transfer Protocol Body Changes: Multipurpose Internet Mail Extensions (MIME)
We've said that RFC 822 specifies the body as lines of NVT ASCII text, with no structure.
RFC 1521 [Borenstein and Freed 1993] defines extensions that allow structure in the
body. This is called MIME, for Multipurpose Internet Mail Extensi...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12