 plementors, and this may mean that it will not become a popular TCP/IP, as illustrated graphically in Figure 16.26. SNMP protocol migration path from SNMP to CMIP. In the meantime expect many runs over TCP/IP transport mechanism and CMIP over OSI based more acronyms! For example iBM and 3Com Corp proposed CMOL, the transport of CMIP over Logical Link Control, the idea being to save memory by transporting OSI based messages over a (PROTOCOL) (PROTOCOL) shortened protocol stack. SNMP has many similarities with CMIP and also many dif- ferences. The similarities are as follows. SNMP/OSI MANAGEMENT SYSTEM 1. At level 3, the IP layer used by SNMP is connectionless and it cannot be operated in a connection oriented mode. The Connec- tion-Less Interworking Protocol (CLIP) of OSI is very close to CMOT MANAGEMENT SYSTEM IP, both acting as routers to send datagrams up and down the stack. At level 4 the TCP service and protocol are similar to Class 4 of the OSI layer. Both use positive acknowledgement schemes with timer driven retries; both can reorder data if it is out of sequence on arrival; and both can use check-sums to protect against data corruption. At layer 7 the TCP/IP applications look like subsets of the OSI TCP/IP applications. Therefore, for example, FTP performs services (TRANSPORT) (TRANSPORT) similar to that obtained from FTAM. 4. Both SNMP and CMIP use the concept of protocol data units Figure 16.26 Alternatives for mixed SNMP/CMIP systems (PDUs) which are messages exchanged between systems at the same layer. They also both use ASN.1 to specify the PDUs and the managed objects. However, SNMP uses a subset of ASN.1, 16/24 Network management and although this reduces the amount of code, and memory, it that new objects can be added without affecting the agent's does restrict the encoding of complex items, such as lists. code. The structure of the MIB used in SNMP is similar to that within CMIP uses the concept of inheritance whilst SNMP does not. Therefore in CMIP it is possible to define an object and then to