This document discusses key reliability, maintainability, and availability (RMA) requirements for systems. It defines metrics like MTBF, MTBCF, and MTTR that measure reliability, maintainability, and availability. Availability is calculated based on MTBF, MTBCF, and MTTR. Uptime and downtime are also important availability metrics measured over different time periods like percentage of hours in a week, month, or year. Developing RMA requirements also involves defining capacity needs like peak, minimum, and sustained data rates as well as considerations for operational suitability, supportability, and workforce needs.

1. DEVELOPING RMA REQUIREMENTS
UNIT – II

2. Developing RMA Requirements
RELIABILITY: (consistency" or "repeatability")
 the ability of a system or component to perform its
required functions under stated conditions for a
specified period of time.
MAINTAINABILITY:
 performing a successful repair action within a given
time.
 Used to Maintenance the operations.
 measures the easy and speed which a system
operational status after a failure occurs.
 to perform its required functions under stated
conditions for a specified period of time.

3.  AVAILABILITY:
 in the sense of available useful work.
 which a system, subsystem or equipment is in
a specified operable and committable state.

4.  MEASURE OF RELIABLILITY:
 Indicates the frequency of failure of the
network and its components.
 MTBF: MeanTime Between Failures
 MTBCF: MeanTime Between Mission-
Critical Failures

5. MTBF: Mean Time Between Failure.
 A basic measure of reliability.
 It is the predicted elapsed time(period
of time) between inherent failures of
a system during operation.
 MTBF is computing the failure rate,
which is estimated through testing or
analysis in terms of failures per hours
of operation.

6.  MTBCF : MeanTime Between Critical Failure.
 It is sometimes referred to as "mission reliability"
 It is a subset of MTBF because it only counts
those failures that result in a mission abort or
mission failure.
 It is a term used when redundancy exists in a
system.
 It is often used to differentiate system reliability
from series mean time between failure (MTBF).

7.  MEASURE OF MAINTAINABILITY:
 Statistical measure of the time to restore the
system fully operational status. Once it has
experienced a fault.(after repaired)
 MTTR: MeanTimeTo Repair: repairing a failure
system consists of detection, isolation
(separation) of the failure.

8.  MEASURE OF AVAILABILITY:
 Relationship between the MTBF, MTBCF, MTTR.
 A common measure of availability is expressed in
terms of percent of uptime or downtime.
 For example, a request for proposal (RFP) :
 from a potential customer may state a
required uptime of 99.999% (commonly
known as “five nines”).

9.  UP-TIME :
 Time during the computer is operational(ON).
 DOWN-TIME :
 Time during the computer is NOT
operational(OFF).
 Availability in terms of uptime and downtime
is measured Per week, per month, or per year
based on total amount of time for that
period.

10.  Analyzing a network’s availability gives us the
ability to schedule preventive maintenance and
replace.
Other measures of availability include
 uptime,
 downtime,
 error, and
 loss rates.

11.  The relationship shown as:
 A = (MTBCF) / (MTBCF + MTTR)
OR
 A = (MTBF) / (MTBF + MTTR)

13. UPTIME MEASURED OVER DIFFERENT TIME
PERIODES

14.  UPTIME:
 99% : system to be down quite a bit of time.
 99.9% : 10m applications stalling(enclose/stand)
for several seconds.
 99.99% : covers uptime requirements.
 9.999% : system being to push operational limits,
network is highly reliable.
 DOWNTIME :
 99% : considered as low performance.

15. Measuring uptime
 Services are measurable , configurable and
verifiable within the system.
 Measuring uptime divided into 3 parts:
 When should it be measured?
 Where should it be measured?
 How should it be measured?

17.  Developing DELAY requirements:
 Interaction Delay(INTD)
 Human ResponseTime(HRT)
 Network Propagation Delay(NPD)
 End –To – End delay
 Rountrip Delay
 Delay variations

18. Developing CAPACITY
requirements
 Estimates Data Rates:
 PDR – peak data rate.
 MDR – Minimum data rate.
 SDR – sustained data rate.
 Developing supplement :
 Operational suitability
 Supportability
 RMA
 Workforce