RS8234 Mindspeed Technologies, RS8234 Datasheet - Page 176

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

6.0 Traffic Management
6.2 xBR Cell Scheduler Functional Description
6.2.4 VBR Traffic
6-16
VBR Service Categories
6.2.4.2 Rate-Shaping
6.2.4.3 Single Leaky
Categories to TM 4.1
RS8234 VBR Service
6.2.4.4 Dual Leaky
6.2.4.1 Mapping
vs. Policing
Bucket
Bucket
The RS8234 Cell Scheduler also supports multiple priority levels for VBR traffic.
The VBR service class takes advantage of the asynchronous nature of ATM by
reserving bandwidth for VBR channels at average cell transmission rates without
hardcoding time slots, as with CBR traffic. This dynamic scheduling allows VBR
traffic to be statistically multiplexed onto the ATM line, resulting in better use of
the shared bandwidth resources.
The ATM Forum TM 4.1 Specification describes the different categories of VBR
service in a different manner than is employed in the RS8234 device. These
relationships are described here:
Table 6-3. RS8234 VBR to TM 4.1 VBR Mapping
The Cell Scheduler rate-shapes the segmentation traffic for up to 64 K
connections. The outgoing cell stream for each VCC is scheduled according to
the GCRA algorithm. This guarantees compliance to policing algorithms applied
at the network ingress point. Channels can be rate-shaped as VCs or VPs,
according to one of three leaky bucket paradigms, set by the SCH_MODE bit in
the channel’s segmentation VCC Table entry.
The first and simplest bucket scheme is single leaky bucket. The user defines a
single set of GCRA parameters — I (Interval) and L (Limit). I is used to control
the per-VCC PCR and L is used to control the CDVT of the outgoing cell stream.
The user enables this scheme by setting the SCH_MODE bits to “100” (VBR1).
The user can also select, on a per-VCC basis, to apply two leaky buckets to a
single connection. The user enables this scheme by setting the SCH_MODE bits
to “101”(VBR2).
L2 parameters. These parameters are stored as bucket table entries. (See
Table 6-15
with regard to using these 256 values to specify SCR or PCR. In VBR2, I1 and L1
can specify either PCR and CVDT, or SCR and Burst Tolerance (BT), with I2 and
L2 used to specify the parameters not assigned to I1 and L1.
VBR1
VBR2
VBR3 (or VBRC)
RS8234 VBR
When using VBR2 SCH_MODE, you are limited to 256 values for the I2 and
For example, you can configure:
I1 = PCR, L1 = CDVT, I2 = SCR, L2 = BT
or
I1 = SCR, L1 = BT, I2 = PCR, L2 = CDVT
Mindspeed Technologies
for the definition of a bucket table entry.) There is complete flexibility
(None)
VBR.1
VBR.2 /VBR.3
TM 4.1 VBR
ATM ServiceSAR Plus with xBR Traffic Management
TM 4.1 does not employ single
Double leaky bucket.
TM 4.1 defines two conformance standards for
CLP(0+1).
™
Comments
leaky bucket.
28234-DSH-001-B
RS8234