Hi Justin, Long ago, back in 1986, ASN.1 specification considered a wastage of octets to use 2 bytes for the first 2 roots. So they juxtaposed both into a single octet using the formula Root * 40 + Second root. This was due to the fact that there ar only 3 root nodes (ITU-T, ISO and Joint ISO-ITU). Since the values of OID are encoded in 7Bit encoded Integer. We can have only 128 values for this juxtaposed integer to be represented in a single octet. 128/3 is approx. 40. The first 40 is given to ITU-T, the next 40 to ISO and the rest to joint iso-itu. This also explains why the second level arc cannot have more than 40 siblings.
Hope this will clarify your doubt. regards, Sathya Narayanan S RPG Cellular Services Limited GSM : +91 98410 48051 > -----Original Message----- > From: Hwang, Justin > Sent: Thursday, November 15, 2001 10:13 PM > To: '[EMAIL PROTECTED]' > Subject: RE: [ASN.1] itu-t (0) recommendation (0) h (8) 245 version > (0) 2 > > Hi, > > I never decode OBJECT ID before, so please > help me with the following questions. > > > itu-t (0) recommendation (0) h (8) 245 version (0) 2 > > 1) 40 * 0 + 0 = 0 > > ===> Why 40? where 40 comes from? and why only 1 byte for both "itu-t (0) > recommendation (0)"? why not 2 bytes? 1 byte (0) for itu-t and other byte > (0) for recommendation? > > > 2) 8 > > 3+4) 245 = 11110101B => 1 0000001 0 1110101 = F1 75 > > ===> How "11110101B" is converted to "1 0000001 0 1110101"? > > > 5) 0 > > 6) 2 > > > Thanks! > > Justin > > > -----Original Message----- > From: Sathya[IT] [mailto:[EMAIL PROTECTED]] > Sent: Thursday, November 15, 2001 3:35 AM > To: [EMAIL PROTECTED] > Subject: RE: [ASN.1] itu-t (0) recommendation (0) h (8) 245 version (0) > 2 > > > Hi Bernd, > > While I encode this, the octets turn out to be 00 08 81 75 00 02 > > I dont understand how you arrived at f1 instead of 81. Is there a > significance > for the deviation? > > regards, > > Sathya Narayanan S > RPG Cellular Services Limited > GSM : +91 98410 48051 > > > -----Original Message----- > > From: Bernd Kunze > > Sent: Monday, November 05, 2001 9:15 PM > > To: '[EMAIL PROTECTED]' > > Subject: RE: [ASN.1] itu-t (0) recommendation (0) h (8) 245 version > > (0) 2 > > > > Hi, > > > > itu-t (0) recommendation (0) h (8) 245 version (0) 2 > > > > 1) 40 * 0 + 0 = 0 > > 2) 8 > > 3+4) 245 = 11110101B => 1 0000001 0 1110101 = F1 75 > > 5) 0 > > 6) 2 > > > > => 00 08 F1 75 00 02 > > > > Bernd
