当一个子网或者子网的一部分中出现太多分组的时候，网络的性能开始下降。这样的情况称为(55)。

(73)

(72)

(71)

(70)

For　each　blank,　choose　the　best　answer　from　the　four　choices　and　write　down　on　the　answer　sheet.

(71)is　a　channel'　s　capacity　which　directly　reflects　the　data　transfer　rate　of　the　channel.

(72)functions　in　a　NetWare　network　which　is　used　to　define　addressing　schemes.

(73)is　a　network　layer　device　that　supports　multiple　LAN　interfaces　and　segments　LANs　into　smaller　collision　and　broadcast　domains.

(74)is　the　popular　LAN　developed　under　the　direction　of　the　IEEE802.3.

(75)is　a　device　which　enables　digital　microcomputers　to　communicate　across　analog　telephone　lines.

(68)

(67)

(66)

In　the　following　essay,　each　blank　has　four　choices.　Choose　the　most　suitable　one　from　the　four　choices　and　write　down　in　the　answer　sheet.　Heterogeneous　network　environments　consist　of　computer　systems　from(66)vendors　that　run(67)operating　systems　and　communication　protocols.　An　organization　that(68)its　computer　resources　is　usually(69)the　task　of　integrating　its　heterogeneous　systems.　Typically,　each　deparlment　or　division　has　defined　its　own　network　needs(70)OS,　LAN　topology,　communication　protocols,　applications,　and　other　components.

(65)