PON主要包含如下配置。 (1)OLT OLT提供网络侧接口并连至一个或多个ODN,它通过ODN与用户侧的一个或多个ONU通信。OLT的任务是分离交换和非交换业务,管理来自ONU的信令和监控信息,为ONU和自身提供维护和指配功能等。 (2)ONU ONU提供用户侧接口并与ODN相连。在应用上,根据ONU到达的位置,可以将光纤接入网(OAN)分为光纤到路边(Fibe To The Curb,FTTC)、光纤到大楼(Fibe To The Building,FTTB)和光纤到户(Fibe To The Home,FTTH)或光纤到办公室(Fibe To The Office,FTTO)等。 1)FTTC:FTTC的ONU设置在路边的入孔、电线杆的分线盒处、交接箱等位置,从ONU到用户之间采用双绞线、同轴电缆等,是一种光缆/同缆混合系统。FTTC是所有应用方式的基础。 2)FTTB:FTTB中ONU直接放在楼内,再经过铜线将业务分送到各个用户。FTTB的光纤化程度比FTTC更进一步,适合与高密度用户区如写字楼等,通常采用点到多点结构。 3)FTTO:FTTO的ONU通常位于大企事业用户(公司、大学、研究所、政府机关等)终端设备处,由于这些用户业务量大,加上无源光网络的发展使得接入成本不断降低,因此这种结构发展很快,一般采用点对点或环型结构。 4)FTTH:FTTH的ONU位于用户家中,目前由于普通住宅用户业务量较小,经济的方式是采用点到多点结构。 另外有些地方会有FTTZ(Fiber To The Zone,光纤到小区)、FTTN(Fiber To The Node,光纤到节点)等说法。它们都属于FTTx系列。
58. 以下不属于无线接入技术的是______。
A.WLL
B.LMDS
C.DBS
D.PON
A B C D
D
[解析] PON是无源光网络,是光线接入网。 wireless local loop简称WLL,通过无线信号取代电缆线,连接用户和公共交换电话网络(PSTN)的一种技术。对于不具备线路架构条件的地方,如某些偏远地区或发展中国家而言,WLL 提供了一种既实用又经济的最后一英里(Last Mile 或最初一英里 First Mile)的解决方案。 在通信网发展的过程中,形成了多种接入网并存的状况。从广义上来讲,接入网可分为有线接入网和无线接入网。有线接入网包括双绞线铜缆接入网、光纤接入网和混合光纤/同轴电缆接入网;无线接入网包括固定无线接入网和移动无线接入网。如下表所示:
93. 802.lln is a WLAN standard approved by the______, which can be used ti support data rate up to 600Mbps.
A.IETF
B.IEEE
C.ITU
D.ISO
A B C D
B
[解析] 802.11n是由IEEE制定的一种无线局域网标准,可以支持最高速率达到600Mbps。
94. The VoIP gateway can perform the digitization, ______ and encapsulation required, and it controls the setup of VoIP calls between the calling device and the called device.
95. To maintain a telephone conversation over the Internet. The voice packets must arrive at their destination in______.
A.a continuous stream
B.a burst stream
C.a delayed stream
D.a burst mode
A B C D
A
[解析] 为了维持建立在互联网上的通话,声音数据包必须以连续流到达目的地。
A Next Generation Network(NGN)is a______network ,which is able to provide Telecommunication Services to users and to make use of multiple broadband, QoS enable transport technologies and in which service-related functions are______of the underlying transport-related technologies.
With the explosive popularity of mobile devices, we have witnessed a steady increase in demand for mobile date service. In addition mobile users also expect to connect to the Internet for communicate and access to services through the best suitable connection, anywhere and at anytime. Although the seamless roaming capability is well supported in conventional. Cellular communication networks, roaming and interworking technologies are still immature in heterogenous wireless networks. Seamless roaming over heterogenous wireless networks will be an ongoing and improved process, due to the requirements from both end users and network administrators. From the wireless access networks belonging to different administrative domains, mobile users cannot always identify at every instance which network is the best one to access for their service. It is highly demanded to establish a network architecture which can facilitate mobile terminals to access the appropriate network in a cost-effective way. If a mobile user wants to move from one network to another with continuous service, the terminals have to cope with network change to maintain service seamlessly. Quality of service is a major issue that the end users should be provided with the satisfying service, while the network workload and cost should not too much increased. In addition, since end users are provided with numerous service ranging from Voice-over-IP to Video-on-Demand services, it is expected that users can experience the same quality for all the different service. Therefore, the network architecture need to be designed in such a way that the quality mechanism is incorporated so that users are served according to their individual QoS requirements. Based on the paragraph above, at present, seamless roaming over heterogenous wireless network is ______ in conventional cellular communication networks, Because of ______, mobile users cannot always identify at every instance which network is the best one to access for their services. To satisfy the users QoS requirements, the network architecture design should include______.