一个计算机网络系统通常由几个部分组成。其中，(42)对网络资源进行有效管理，提供基本的网络服务，网络操作界面，网络安全性和可靠性等措施。

(64)

(65)

(66)

In　low　-　speed　network　,it　is　usually　adequate　to　wait　for　congestion　to　occur　and　then　react　to　it　by　telling　the　source　of　packets　to　slow　down.　In　high　-　speed　networks,　this　approach　often　works　poorly,　because　in　the(71)between　sending　the　notification　and　notification　arriving　at　the　source,　thousands　of　additional(72)may　arrive.　In　ATM　network　,　a　major　tool　for　preventing(73)is(74)control.　　When　a　host　wants　a　new　virtual(75),it　must　describe　the　traffic　to　be　offered　and　the　service　expected.

(63)

(59)

(61)

(60)

(58)

The　Simple　Network　Management　Protocol(SNMP)is　an(66)protocol　that　facilitates　the　exchange　of　management　information　between(67).　It　is　part　of　the　Transmission　Control　Protocol/Internet　Protocol(TCP/IP)protocol　suite.　SNMP　enables　network(68)to　manage　network　performance,　find　and　sole　network　problems,　and　plan　for(69)An　　SNMP　-managed　network　consists　of　three　key　components:　managed　devices　,(70),and　network　-management　systems　.