RS8234 Mindspeed Technologies, RS8234 Datasheet - Page 173

• Manufacturer Part Number: RS8234
• Description: Atm Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

RS8234
ATM 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
28234-DSH-001-B
6.2.3.3 CBR Cell Delay
A
00 01
Variation (CDV)
Cell Scheduler
B
02 03 04 05 06
5
4
A
By definition, CBR connections are sensitive to CDV. (See ATM Forum UNI 3.1
or TM 4.1 for a complete definition of CDV.) The RS8234’s Traffic Manager
minimizes CDV by basing all traffic management on the SYSCLK 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 RS8234, the dominant factor in CDV is the variation introduced between the
segmentation coprocessor and the PHY layer device at the Transmit FIFO
(TX_FIFO). Line overhead created by the framer in the PHY layer device causes
this variation.
contracts for different CBR rates on more than one CBR channel, causing
schedule slot conflicts in the Schedule Table.
this. Illustrated is a linear representation of a Schedule Table with 100 schedule
slots. CBR channel A has reserved bandwidth for a rate of 70. K cells/second, or
every fifth cell slot. CBR channel B has reserved bandwidth for a rate of 88.7 K
cells/second, or every fourth cell slot. In this case there will be a schedule slot
reservation conflict between channels A and B every 20th cell slot, and one of the
channel’s slots will have 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
Segmentation
Coprocessor
Schedule Table
Figure 6-8
A
B
11 12
4
illustrates this interface.
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
4
illustrates an example of
A
20 21
6.0 Traffic Management
B
22
23
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