SNMP and Unicode?

[janzen]

christel.sohnemann____philips.com wrote:

> I am just wondering if SNMP is able to transport Unicode strings?
> So for example, if I have a SNMP Agent Application, which works with ASCII strings and there is  - let's say - a SNMP Management Application with chinese fonts (UTF8 for example), what happens to the transported strings?
> More precisely: can the SNMP Agent send UTF8 strings or does SNMP only transport ASCII strings?

No, SNMP is not limited to ASCII strings; and yes, you can use UTF-8. 
See the description of the SnmpAdminString TC, defined in the
SNMP-FRAMEWORK-MIB (RFC 2571):


SnmpAdminString ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "255a"
    STATUS       current
    DESCRIPTION "An octet string containing administrative
                 information, preferably in human-readable form.

                 To facilitate internationalization, this
                 information is represented using the ISO/IEC
                 IS 10646-1 character set, encoded as an octet
                 string using the UTF-8 transformation format
                 described in [RFC2279].

                 Since additional code points are added by
                 amendments to the 10646 standard from time
                 to time, implementations must be prepared to
                 encounter any code point from 0x00000000 to
                 0x7fffffff.  Byte sequences that do not
                 correspond to the valid UTF-8 encoding of a
                 code point or are outside this range are
                 prohibited.

                 The use of control codes should be avoided.

                 When it is necessary to represent a newline,
                 the control code sequence CR LF should be used.

                 The use of leading or trailing white space should
                 be avoided.

                 For code points not directly supported by user
                 interface hardware or software, an alternative
                 means of entry and display, such as hexadecimal,
                 may be provided.

                 For information encoded in 7-bit US-ASCII,
                 the UTF-8 encoding is identical to the
                 US-ASCII encoding.

                 UTF-8 may require multiple bytes to represent a
                 single character / code point; thus the length
                 of this object in octets may be different from
                 the number of characters encoded.  Similarly,
                 size constraints refer to the number of encoded
                 octets, not the number of characters represented
                 by an encoding.

                 Note that when this TC is used for an object that
                 is used or envisioned to be used as an index, then
                 a SIZE restriction MUST be specified so that the
                 number of sub-identifiers for any object instance
                 does not exceed the limit of 128, as defined by
                 [RFC1905].

                 Note that the size of an SnmpAdminString object is
                 measured in octets, not characters.
                "
    SYNTAX       OCTET STRING (SIZE (0..255))


> And if it would be possible to send UTF8 strings by the SNMP Agent and the SNMP Manager only processes ASCII strings, what happens then?

Depends entirely on the implementation of the particular SNMP manager
you're using; specifically, on how it deals with characters in the range
0x80..0xff.  Most likely it will either throw them away, display them in
some kind of hex or escaped format (eg. '\xFC'), or display junk (eg.
treat them as if they were ISO 8859-1 characters).  

--
Martin Janzen
janzen at pixelmetrix.com