Practical TCP/IP and Ethernet Networking- P35: The transmitter encodes the information into a suitable form to be transmitted over the communications channel. The communications channel moves this signal as electromagnetic energy from the source to one or more destination receivers. The channel may convert this energy from one form to another, such as electrical to optical signals, whilst maintaining the integrity of the information so the recipient can understand the message sent by the transmitter | 152 Practical TCP IP and Ethernet Networking object that contains a single object instance the integer value that indicates the total number of input Novell Netware packets on a router interface. An object identifier or object ID uniquely identifies a managed object in the MIB hierarchy. The MIB hierarchy can be depicted as a tree with a nameless root the levels of which are assigned by different organizations. Figure MIB tree The top-level MIB object Ids belong to different standards organizations while lower-level object Ids are allocated by associated organizations. Vendors can define private branches that include managed objects for their own products. MIBs that have not been standardized typically are positioned in the experimental branch. The managed object at Input can be uniquely identified either by the object name - . . .temporary - or by the equivalent object descriptor . SNMPv2 protocol operations SNMP is a simple request-response protocol. The network-management system issues a request and managed devices return responses. This behavior is implemented by using one of four protocol operations Get GetNext Set and Trap The Get operation is used by the NMS to retrieve the value of one or more object instances from an agent. If the agent responding to the Get operation Application layer protocols 153 cannot provide values for all the object instances in a list it does not provide any values The GetNext operation is used by the NMS to retrieve the value of the next object instance in a table or list within an agent The Set operation is used by the NMS to set the values of object instances within an agent The Trap operation is used by agents to asynchronously inform the NMS of a significant event The Get GetNext and Set operations used in SNMPv2 are exactly the same as that used in SNMPv1. SNMPv2 however adds and enhances some operations. The
