Definitions of Protocol and Managed Objects for TN3270E Response Time Collection Using SMIv2 (TN3270E-RT-MIB)
Extracted elements (26)
Printer sessions (LU Type 1 or LU Type 3) are explicitly excluded from response time data collection. This mirrors historical SNA/MS RTM behavior and is not considered a problem since printer sessions are not the primary target for response time monitoring.
Sliding-window averages are used instead of straight interval-based averages because they are less susceptible to notification thrashing when response times oscillate near a threshold. The effective averaging period is approximately 2*SPMult*SPeriod due to the exponential decay, giving each transaction a half-life of SPMult*SPeriod.
The MIB uses SNA definite responses (DR) to timestamp flows rather than the SNA/MS Response Time Monitoring (RTM) method, because not all TN3270E server implementations have access to their underlying SNA stacks. RTM concepts (response time buckets, interval-based collection) are preserved.
The statistical significance test for tn3270eRtExceeded notifications uses the formula AvgCountTrans * ((AvgRt/ThreshHigh - 1)^2) >= IdleCount, making the required sample size inversely proportional to how far the average exceeds the threshold. This prevents a few very-slow transactions from being masked as statistically insignificant.
The tn3270eRtDataDiscontinuityTime object (TimeStamp) is provided so management applications can detect counter resets caused by TN3270E server restarts or other discontinuities. All wrappable Counter32 objects in tn3270eRtDataEntry should be monitored in conjunction with this timestamp.
TN3270 clients and TN3270E clients that do not support the RESPONSES function can be accommodated by substituting TIMING-MARK request/response flows for definite responses when approximating IP network transit time. The client must not have the NOP option enabled for TIMING-MARK to work in this role.
When a collection includes both clients that can and cannot calculate an IP-network component, data is aggregated differently based on the excludeIpComponent(1) bit. Mixing capable and incapable clients in an IP-inclusive collection silently drops the incapable clients' transactions from aggregation.
When a TN3270E server forwards a multi-RU chain from the SNA host, it may not know whether DR is requested until the LIC RU arrives. Because the TN3270E header (and thus DR specification) can only be included with the FIC RU, some servers routinely specify DR on all FIC RUs.
When correlating TN3270E server response time data with SNA host monitoring, management applications must use tn3270eResMapTable or tn3270eTcpConnTable for resource-to-client address mappings. tn3270eClientGroupTable, tn3270eResPoolTable, and tn3270eClientResMapTable cannot be used for correlation because their mappings may overlap and are not one-to-one.
A client SHOULD respond to a definite response request when it completes processing the transaction, not immediately upon receipt. Clients that respond immediately will be attributed lower total response times than actually occurred.
A server MAY reuse the interval from a recently completed TIMING-MARK flow as its approximation for IP network transit time (the F'-E' value) rather than sending a duplicate request shortly after.
A TN3270E server MUST integrate its normal TIMING-MARK processing with its use of TIMING-MARKs for computing response times, and MUST NOT send a second TIMING-MARK request to a client while waiting for the first to return, as this is prohibited by the TIMING-MARK protocol itself.
All transactions contributing response times to an aggregated value MUST make the same contribution: if IP-network component is required, transactions lacking it are excluded entirely; if IP-network is excluded, only the SNA-network component is used even for capable clients.
Either the average(3) or buckets(4) bit MUST be set to 1 in tn3270eRtCollCtlType for response time data collection to occur; both bits MAY be set to 1 simultaneously.
If an entry in tn3270eRtCollCtlTable has RowStatus active(1), an implementation SHALL NOT allow Set operations for any objects in the entry except tn3270eRtCollCtlThreshHigh, tn3270eRtCollCtlThreshLow, and tn3270eRtCollCtlRowStatus.
In order to generate timestamp F, a TN3270E server MUST ensure that each measured transaction specifies DR and that the TN3270E RESPONSES function has been negotiated with the client. If the SNA host did not request DR, the server adds its own DR request to enable timestamp F.
Management applications SHOULD use tn3270eRtSpinLock (an advisory TestAndIncr lock) to serialize creation or alteration of tn3270eRtCollCtlTable entries. Agents MUST implement this object but SHALL NOT enforce its use by management applications.
Timestamp E SHOULD be taken as close as possible to the TN3270E server's 'Telnet edge' when forwarding the Last-in-Chain (LIC) RU to the client, since this timestamp is used for calculating IP-network transit time.
To calculate sliding-window averages, a TN3270E server MUST maintain internal per-sample-period counters (T, TotalRts, TotalIpRts) and sliding counters (AvgCountTrans, TotalRtsSliding, TotalIpRtsSliding), updating them at each sample period end using the specified exponential-decay formula.
Four notifications are defined: tn3270eRtExceeded (average exceeds high threshold with statistical significance), tn3270eRtOkay (average falls below low threshold after an exceeded event), tn3270eRtCollStart (collection entry created), and tn3270eRtCollEnd (collection entry deleted or TCP session terminated). All require traps(5) bit set.
tn3270eRtCollCtlTable is indexed by tn3270eSrvrConfIndex and tn3270eClientGroupName (imported from TN3270E-MIB). Each entry controls collection type (aggregate/per-client), IP component inclusion, dynamic DRs, sliding-window parameters, bucket boundaries, and notification thresholds.
tn3270eRtCollCtlType is a BITS-syntax object with six flags: aggregate(0), excludeIpComponent(1), ddr(2), average(3), buckets(4), and traps(5). It controls all behavioral aspects of a response time collection entry.
tn3270eRtDataTable holds per-collection or per-client response time measurements. It is indexed by tn3270eSrvrConfIndex, tn3270eClientGroupName, tn3270eRtDataClientAddrType, tn3270eRtDataClientAddress, and tn3270eRtDataClientPort. Aggregate entries use address type unknown(0) and a zero-length address.
The TN3270E-RT-MIB is registered under the snanauMIB arc at { snanauMIB 9 }, where snanauMIB ::= { mib-2 34 }. The MIB module OID is tn3270eRtMIB, with sub-arcs for notifications (0), objects (1), and conformance (3).
The TN3270E-RT-MIB provides read-create access to collection control objects, meaning unauthorized Set operations could alter or disrupt response time data collection for TN3270/TN3270E sessions. Implementations should apply SNMPv3 view-based access control (RFC 2275) to restrict write access to the tn3270eRtCollCtlTable.
Tn3270eRtDataEntry contains: Gauge32 AvgRt and AvgIpRt (tenths of seconds), Gauge32 AvgCountTrans (transactions), DateAndTime IntTimeStamp, Counter32 TotalRts/TotalIpRts/CountTrans/CountDrs (all wrappable), Unsigned32 ElapsRndTrpSq/ElapsIpRtSq (tenths-of-seconds squared for variance), Counter32 Bucket1–5Rts, INTEGER RtMethod, and TimeStamp DiscontinuityTime.