User's Manual

Network SupportChapter —4
124 700 Series Color Mobile Computer User’s Manual
Retrieval of Management Information
SNMP has the get-next primitive which permits the viewing of data
without requiring prior knowledge. If you know what you are looking for,
the get primitive will return it. When you want an entire table of
information, the get-next primitive will obtain it. However, unless
employed with care, the get-next primitive can be extremely
resource-intensive in real time, network bandwidth, and the agent’ s CPU
time. The simplest use of the get-next primitive is to start at the beginning
of a table, await the response and then issue another get-next with the
name returned. As an example, say you wanted the next-hop address,
next-hop interface, and route-type from a routing table containing 1000
entries. Using the simplest form of get-next, this would require 2x3x1000
or 6000 packets (get-next and get-response packets, columns, and rows).A
straight-forward optimization would be to request the three columns in a
single packet. This puts the number of packets at 2x1000 or 2000 packets.
In real time, it is the product of the round trip by the number of request.
In agent CPU time, this is still 6000 lookups in the routing table for both
cases.
An Early Approach to Getting More than One Item at a Time
The ability to retrieve only one piece or object at a time has been a
problem for SNMP. This is particularly an issue with the use of this
protocol in wireless environments where the wireless datapipe is small and
overhead due to network management it is considered overhead. One
approach creates multiple get-next requests running concurrently. A second
algorithm, reduces the packet count by combining the multiple concurrent
get-nexts into a single packet. Neither approach has been implemented
which makes network management in wireless environment, though
essential to the success of the operation, tenuous. The issue has been
resolved in SNMP V2 protocol where a get-bulk primitive has been
defined.
Conclusion
Software development moves forward by evolving the unknown into the
known and wireless environments are moving from vertical only
application to wide spread implementation. At the time of the SNMP
inception, it was not possible to conceive of a reliable transport based
network management protocol. Today’ s problems require more
sophisticated data to analyze a problem. This puts the burden back on the
protocol to send and receive data quickly and efficiently. Work continues
in subcommittees to improve SNMP and resolve the issues that are
developing with new applications and new network architectures.