XRT75R12D_06 Datasheet, PDF (128/134 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET

XRT75R12D
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER REV. 1.0.1
FIGURE 70. ILLUSTRATION OF THE SUPER PATTERN WHICH IS OUTPUT VIA THE "OC-N TO DS3" MAPPER IC
PATTERN A
PATTERN A
PATTERN B
CROSS-CHECKING OUR DATA
• Each SUPER PATTERN consists of (621 + 621 + 622) = 1864 clock pulses.
• The total amount of time, which is required for the "DS3 to OC-N Mapper" IC to transmit this SUPER
PATTERN is (720 + 720 + 720) = 2160 "STS-1" clock periods.
• This amount to a period of (2160/51.84MHz) = 41,667ns.
• In a period of 41, 667ns, the LIU (when configured to operate in the DS3 Mode), will output a total (41,667ns
x 44,736,000) = 1864 uniformly spaced DS3 clock pulses.
• Hence, the number of clock pulses match.
APPLYING THE SUPER PATTERN TO THE LIU
Whenever the LIU is configured to operate in a "SONET De-Sync" application, the device will accept a
continuous string of the above-defined SUPER PATTERN, via the TCLK input pin (along with the
corresponding data). The channel within the LIU (which will be configured to operate in the "DS3" Mode) will
output a DS3 line signal (to the DS3 facility) that complies with the "Category I Intrinsic Jitter Requirements -
per Telcordia GR-253-CORE (for DS3 applications). This scheme is illustrated below in Figure 71.
FIGURE 71. SIMPLE ILLUSTRATION OF THE LIU BEING USED IN A SONET DE-SYNCHRONIZER" APPLICATION
STS-N Signal
De-Mapped (Gapped)
DS3 Data and Clock
DDSS33totoSSTTSS-N-N
MMaappppeerr//
DDeemmaappppeerr
IICC
TPDATA_n input pin
LLIIUU
TCLK_n input
8.8.3 How does the LIU permit the user to comply with the SONET APS Recovery Time
requirements of 50ms (per Telcordia GR-253-CORE)?
Telcordia GR-253-CORE, Section 5.3.3.3 mandates that the "APS Completion" (or Recovery) time be 50ms or
less. Many of our customers interpret this particular requirement as follows.
123