选出应填入下面一段英语中______内的正确答案。 Astute service providers realize that the continued sup
选出应填入下面一段英语中______内的正确答案。
Astute service providers realize that the continued support oflegacy X.25 and asynchronous network elements using separate operations network is cost(1). For example, the maintenance of multiple networks can require additional staff. Often, this staff must be trained on multiple vendor technologies, sometimes requiring parallel groups specializing in each(2). Hence, additional maintenance procedures must be maintained and administrative records are(3). The duplication oftransport facilities to carry(4)network traffic is an inefficient use of resources. And not surprisingly, more technologies installed in a central office mean the necessity for more physical space, and an increase in power connections and power consumption. Migration ofthese(5)network elements to IP-based DCns is alogical strategy.