转自Q?A >http://www.mvista.com.cn/svu-www/index4/index4-9.htm
weidagang2046 2005-07-01 10:06 发表评论
]]>虚电路分ZU：一U永久虚电\QPVCQ；另一Uؓ交换虚电路（SVCQ?/P>
怹虚电路（PVCQ是指通信双方的电路在用户看来是永久连接的虚电路。PVC q预先定义。PVC 适用于通过路由器维持恒定连接，从而便于在动态网l环境下传输路由选择信息的电路。蝲波信号ؓ各用户分?PVCQ从而降低网l开销q提高网l性能?/P>
交换虚电路（SVCQ是指通信双方的电路在用户看来是由独立节点临时且动态连接的虚电路。一旦通信会话完成Q便取消虚电路?
转自Q?A >http://www.networkdictionary.com/chinese/networking/VirtualCircuits.php
weidagang2046 2005-06-30 13:43 发表评论
]]>I would like the group to reconsider the definition of spectrum efficiency in draft-ietf-rohc-rtp-01.txt and whatever other drafts may use this definition. I believe this definition is overly cellular specific and somewhat inaccurate.
?Spectrum efficiency
Radio resources are
used efficiently to
cellular systems this is achieved by maximizing the number of users
served within each cell, while the quality of the provided services
is kept at an acceptable level. A consequence of efficient spectrum
use is a high rate of errors (frame loss and residual bit errors),
even after channel coding with error correction.?
I suggest the following:
Spectrum Utilization (Cellular)
Radio resources are
used efficiently to
cellular systems this is achieved by maximizing the number of users
served within each cell, while the quality of the provided services
is kept at an acceptable level.
I suggest removing the following statement, as I believe this is more a statement of the way cellular system maximize the revenue producing aspects of spectral utilization.
?A consequence of efficient spectrum
use is a high rate of errors (frame loss and residual bit errors),
even after channel coding with error correction.?
I believe this may be a better definition for spectrum efficiency:
Spectrum efficiency
The amount of useful information that can be transmitted over a given spectrum (bandwidth) over a given period of time. For modem designers, spectrum efficiency is defined as the amount of bits per second per bandwidth. For packet communications systems, bandwidth efficiency can be defined as the amount of useful user packet transmitted per second per bandwidth excluding overhead. The difference being that one can have a network with good spectral efficiency at layer at two that results in a poor spectral efficiency when considering layer three. For a given BER, burst errors are more desirable than a binomial distribution of errors when considering packet communications.
Will Ivancic
from: http://www1.ietf.org/mail-archive/web/rohc/old-archive/msg00579.html
weidagang2046 2005-06-22 13:07 发表评论
]]>weidagang2046 2005-06-22 11:43 发表评论
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