The RMON matrix group (20.14.1.5 Matrix) provides two tables with the same information, matrixSDTable and matrixDSTable. The matrix group allows an agent to collect information on traffic flow indexed by the source and destination addresses. The manager begins the process by supplying attributes for Status, Owner, the usual Index, the interface DataSource, and the maximum table size. Once the row is valid, the agent begins collecting, for every xsource,destinationy pair, counts of the number of packets, octets and errors. The record for (A,B) counts these things sent by A; the corresponding record for (B,A) counts the reverse direction. The actual matrixSDTable is indexed by the manager-supplied Index value and the source and destination Ethernet addresses in that order. A companion table (or view) is also maintained called matrixDSTable, that lists the same information but indexed by destination first and then source. This view is not present to supply information about the reverse direction; that would be obtained by reversing source and destination in the matrixSDTable. Rather, the matrixDSTable allows a manager to extract all information about a single destination D in a single SNMP tree-walk operation of the prefix matrixDSTable.Index.D.

a. Suppose we want all the table data about a given destination D, and have only the matrixSDTable. Explain why every row of matrixSDTable would need to be examined.

b. Now suppose we repeat the investigation of (a), but this time the manager has previously downloaded the complete list of all hosts on the LAN by using the RMON hosts tables. If N is the number of hosts on the LAN, explain how to nd all hosts that communicated with D using only N retrieval requests.

c. Explain how to nd all hosts S that sent packets to D even more quickly using the matrixDSTable. If MN is the number of such S, your answer should involve N+1 retrieval requests.