參數(shù)資料
型號: XRT75L00DIV
廠商: Exar Corporation
文件頁數(shù): 61/92頁
文件大?。?/td> 0K
描述: IC LIU E3/DS3/STS-1 SGL 52TQFP
標準包裝: 96
類型: 線路接口裝置(LIU)
驅(qū)動器/接收器數(shù): 1/1
規(guī)程: DS3,E3,STS-1,SONET
電源電壓: 3.135 V ~ 3.465 V
安裝類型: 表面貼裝
封裝/外殼: 52-LQFP
供應(yīng)商設(shè)備封裝: 52-TQFP(10x10)
包裝: 托盤
XRT75L00D
E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
REV. 1.0.2
59
What does this mean at the "Destination" PTE?
In this case, this DS3 signal (which has now been mapped into an STS-1 data-stream) will be transported
across the SONET network. As this STS-1 signal arrives at the "Destination" PTE, this PTE will extract (or de-
map) this DS3 data from each incoming STS-1 SPE. Now, in this case most (e.g., 177/178.8) of the incoming
STS-1 SPEs will contain 5592 DS3 data-bits. Therefore, the nominal data rate of the DS3 signal being de-
mapped from SONET will be 44.736Mbps. However, in approximately 1 out of every 178 incoming STS-1
SPEs, the SPE will carry 5593 DS3 data-bits. This means that (during these times) the data rate of the de-
mapped DS3 signal will have an instantaneous frequency that is greater than 44.736Mbps. These "excursion"
of the de-mapped DS3 data-rate, from the nominal DS3 frequency can be viewed as occurrences of "mapping/
de-mapping" jitter. Since each of these "bit-stuffing" events involve the insertion of one DS3 data bit, we can
say that the amplitude of this "mapping/de-mapping" jitter is approximately 1UI-pp. From this point on, we will
be referring to this type of jitter (e.g., that which is induced by the mapping and de-mapping process) as "de-
mapping" jitter.
Since this occurrence of "de-mapping" jitter is periodic and occurs once every 22.35ms, we can state that this
jitter has a frequency of 44.7Hz.
9.2.2.3
The 44.736Mbps - 1ppm Case
In this case, let us assume that a DS3 signal, with a bit-rate of 44.736Mbps - 1ppm is being mapped into an
STS-1 signal with a bit-rate of 51.84Mbps + 0ppm. In this case, the following this will occur.
In general, most of the STS-1 SPEs will each transport 5592 DS3 data bits.
However, within a "one-second" period a DS3 signal that has a bit-rate of 44.736Mbps - 1ppm will deliver
approximately 45 too few bits below that of a DS3 signal with a bit-rate of 44.736Mbps + 0ppm. This means
that this particular signal will need to "positive-stuff" or exclude a DS3 data bit from mapping every (1/44.736)
= 22.35ms.
In other words, we will need to avoid mapping this DS3 data-bit about one in every
(22.35ms*8000) = 178.8 STS-1 SPEs.
What does this mean at the "Source" PTE?
All of this means that as the "Source" PTE maps this DS3 signal, with a data rate of 44.736Mbps - 1ppm into
an STS-1 signal, most of the resulting "outbound" STS-1 SPEs will transport 5592 DS3 data bits (e.g., 3 Stuff
Opportunity bits will be carrying DS3 data bits, the remaining 6 Stuff Opportunity bits are "stuff" bits). However,
in approximately one out of 178.8 "outbound" STS-1 SPEs, there will be a need for a "positive-stuffing" event.
Whenever these "positive-stuffing" events occur then (for these particular STS-1 SPEs) the SPE will carry only
5591 DS3 data bits (e.g., in this case, only 2 Stuff Opportunity bits will be carrying DS3 data-bits, and the
remaining 7 Stuff Opportunity bits are "stuff" bits).
Figure 40 presents an illustration of the STS-1 SPE traffic that will be generated by the "Source" PTE, during
this condition.
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