i. Transmission Group (10): This group does not have any variables but is a place holder for MIB mod- ules. Some of the modules covered in the transmission group are FDDI (15), RS-232 (33), LDAP (16), X.25 (38), and SONET (39). Fundamentals of EMS, NMS and OSS/BSS CCITT Joint Standard Registration Member body Organization authority Internet Directory Management Experimental Private MIB-2 System (1) SNMP (11) Interfaces (2) AT (3) ICMP (5) UDP (7) Transmission (10) IP (4) TCP (6) EGP (8) Figure 16.3 MIB-II tree. j. SNMP Group (11) This group is for the simple network management protocol (SNMP). It has a lot of counters to capture information on the PDUs (packet data units). The various kinds of PDUs, the number of PDUs received, the number of PDUs transmitted, and the PDU errors are all captured using counters. It is also possible to enable and disable authentication traps. Being the MIB for the most popular network management pro- tocol, SNMP MIB is handled in more detail in the next section. SNMP has three popular version and the MIB changes associated with each of these versions are discussed under SNMPv1 MIB, SNMPv2 MIB, and SNMPv3 MIB. Management Information Base (MIB) 16.4 SNMPv1 MIB SNMP uses ASN.1 for defining objects and PDUs exchanged by the management protocol. Only a subset of ASN.1 data types is used. They are INTEGER, OCTET STRING, OBJECT IDENTIFIER, SEQUENCE, SEQUENCE OF, and NULL. RFC 1155 states how objects are defined. In MIB, object types have an OBJECT DESCRIPTOR that is a textual name and an OBJECT IDENTIFIER. A representation bladeLocation {blade 10}, has bladeLocation as the OBJECT DESCRIPTOR, and {blade 6} as the OBJECT IDENTIFIER. The OBJECT IDENTIFIER for the SNMP subtree is 1.3.6.1.2.1.11. Objects can be added to the tree for data collection. For example a count of SNMP input messages can be maintained in snmpInMsgs using the OBJECT IDENTIFIER is 1.3.6.1.2.1.11.8, where 8 is the subidentifier for this new object. Each scalar object of the input message object has only one instance and it