cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 171

• Manufacturer Part Number: cn8237
• Description: Atm Oc-12 Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

CN8237
ATM OC-12 ServiceSAR Plus with xBR Traffic Management
Figure 6-8. Introduction of CDV at the ATM/PHY Layer Interface
Figure 6-9. Schedule Table with Slot Conflicts at Different CBR Rates
28237-DSH-001-C
6.2.3.3 CBR Cell Delay
A
00 01
Variation (CDV)
Cell Scheduler
B
02 03 04 05 06
5
4
A
CBR connections are sensitive to CDV. (See ATM Forum UNI 3.1 or TM 4.1 for a
complete definition of CDV.) The CN8237’s Traffic Manager minimizes CDV by
basing all traffic management on the Scheduler clock frequency and providing the
user the ability to explicitly decide the transmit time for CBR traffic. However, no
system is without some CDV. In the case of terminals using the CN8237, the
dominant factor in CDV is the variation introduced between the segmentation
coprocessor and the PHY layer device at the Transmit FIFO buffer (TX_FIFO).
Line overhead created by the framer in the PHY layer device causes this variation.
Figure 6-8
contracts for different CBR rates on more than one CBR channel, causing
schedule slot conflicts in the Schedule table.
a linear representation of a Schedule table with 100 schedule slots. CBR channel
A has reserved bandwidth for a rate of 282.56 K cells/second or every fifth cell
slot. CBR channel B has reserved bandwidth for a rate of 353.2 K cells/second or
every fourth cell slot. In this case there is a schedule slot reservation conflict
between channels A and B every 20th cell slot, and one of the channel’s slots has
to be reserved one slot later.
B
A possible source of Schedule table-dependent CDV is created when the host
07 08 09 10
5
4
Mindspeed Technologies
illustrates this interface.
Segmentation
Coprocessor
Schedule Table
A
B
11 12
4
5
13 14 15 16
B
A
PHY Interface
4
™
6.2 xBR Cell Scheduler Functional Description
Cells are added at CBR rate
17 18 19
Figure 6-9
5
(Line rate — Line overhead)
B
(1-9 Cells)
TX_FIFO
Cells are removed at
illustrates an example of
4
A
20 21
6.0 Traffic Management
B
22
23
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