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6.2.1.2 ATM Bandwidth Capacity
The ATM bandwidth should be considered in a large network, especially for
reserved bandwidth connections, such as the connections between switches.
This section describes the ATM bandwidth capacity of the 8285 switch and its
components:
•
Total Bandwidth
The total bandwidth available for each IBM 8285 Base Unit and ATM module
in the expansion unit is 212 Mbps/FDX. This is because, although the
switch-on-a-chip supports up to 256 Mbps for each module, the switch uses
64-byte cells internally to transport 53-byte ATM cells. Therefore, the
maximum external throughput per module is 256 Mbps x 53/64 or 212 bytes.
•
Total Reserved Bandwidth
The total reserved bandwidth available for each IBM 8285 base unit and for
each ATM module in the expansion unit is 85 percent of the total bandwidth
available and is 180 Mbps when the total bandwidth is 212 Mbps. In addition,
the maximum reserved bandwidth for an ATM port is 85 percent of the
physical port speed. For example, it becomes 85 Mbps for a 100 Mbps port
and 131 Mbps for a 155 Mbps port.
Table 23 shows the summary of the IBM 8285 ATM bandwidth capacity.
Table 23. Bandwidth Capacity of the IBM 8285 Nways ATM Workgroup Switch
Description Value
Total bandwidth for all ports in the base unit 212 Mbps (256
Mbps x 53/64)
Total bandwidth per an ATM module in the expansion unit 212 Mbps
Total reserved bandwidth for All ports in the base unit 180 Mbps (212
Mbps x 85%)
Total reserved bandwidth per an ATM module in the expansion
unit
180 Mbps
Maximum reserved bandwidth per an ATM port 85% of physical
port speed
6.2.1.3 Integrated LES/BUS Capacity
The IBM 8285 can integrate the LES/BUS server functions in the control point.
This section describes the capacity information when the function is configured:
•
Maximum Number of LES/BUS Instances
When the LAN Emulation protocol is used, each LES/BUS instance will define
an Emulated LAN (ELAN). The IBM 8285 can configure two LES/BUSs
instances, and therefore two ELANs. To interconnect these ELANs together
requires an ATM router, such as the IBM Multiprotocol Switched Services
Server.
•
Maximum Number of LECs
The number of LECs can impact LES performance, for example, during the
initial registration process and during the MAC-to-ATM address mapping
process.
Table 24 on page 100 shows the summary of the IBM 8285 integrated LES/BUS
capacity.
Chapter 6. IBM 8285 Planning and Installing 99