 checks the community string. Community name or community string is a set of octets used to identify a member in the community. An application can have more than one community name and only applications in the same community can interact. Hence commu- nity helps to pair two application entities. Data for sending Receive message Create PDU for management data in ASN. 1 form Parse message Generate Add source and (Optional) destination address Verify if version and authentication Discard data is correct message Check if source and destination can exchange message with SNMP Parse PDU and get data Add header and create SNMP Process data and generate response message Serialize SNMP message using Send the message to destination Figure 14.2 SNMPv1 message handling: (a) sending of SNMP message; (b) receiv- ing of SNMP message. The SNMP agent has a community profile that defines the access permissions to the MIB. The agent can view only a subset of managed objects in a network element and the agent can have read or write access to the visible objects. A generic "public" community usually offers read only access to objects. An agent can be associated with the public community to access the read only objects in the community. Let us describe the access policy shown in Figure 14.4. If "A" corresponds to the agent for managing a Cisco element and "B" corresponds to agent for managing a Fundamentals of EMS, NMS and OSS/BSS SNMP manager SNMP manager Authentication schema Authentication schema Authentication schema SNMP agent Figure 14.3 SNMPv1 security. Manager Community Agent A Agent B Profile A Profile B Figure 14.4 SNMPv1 access policy. Nortel element, then the manager has access to the community having both a Cisco and Nortel agent. Cisco agent and Nortel agent have a different community profile, which is "Profile A" and "Profile B." So the Cisco agent will be able to view only the managed objects defined by its profile and not Nortel managed objects that have a different profile, but the manager can view both Cisco and Nort