Prom the viewpoint of keeping the level of reliability in telecommunication networks, the reliability management in operation phase has been more important than that in design phase. Typical measures for the reliability management are failure rate, unavailability, and maintainability. Failure rate and unavailability are usually used as evaluation criteria for network reliability. However, there are some problems in evaluating the maintainability because it depends on the various factors such as skill levels of maintainers, operation planning, and so on. In this paper, we focus on maintainability and analyze the characteristic of distribution of time to repair. Moreover, the relationship between maintainability and actual maintenance actions is also shown.%通信ネットワークの信頼性は，設計から運用段階における管理の重要性が高まっている．管理のための尺度としては，故障率，不稼働率，保全度などが代表的であり，特に故障率と不稼働率は多用される傾向にある．一方，保全度は様々な要因が含まれるため，評価が難しいという問題がある．本稿では通信ネットワークの保全度に着目し，そのための基礎検討として故障修理時間の分布特性をパラメトリック，ノンパラメトリックな方法の両面から評価する．更に実際の保全アクションとの対応についても論じる．
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