IBM SG24-4817-00 - Manual (Page 117)

This soft copy for use by IBM employees only.
Notes:
1 Any two combinations of token-ring (IEEE 802.5) and Ethernet /
IEEE802.3 LAN Emulation.
2 Sum of the LECs when two sets of LES/BUS configured.
3
Average value based on the performance test.
6.2.1.4 SSI Connection (TRS Capacity)
The IBM 8285 implements a dynamic routing mechanism between ATM switches.
This mechanism, called the
switch-to-switch interface (SSI) protocol, was
developed by IBM based on the ATM Forum PNNI Phase 1 specification, and is
an IBM exclusive. SSI provides many benefits, such as reducing the workload of
route definition, enabling link aggregation between switches, and enabling
automatic route backup should the primary route fail. However, as with any
dynamic routing protocol, the need to exchange information between nodes can
consume bandwidth and processing resources. The IBM 8285 has the following
capacity limitations for SSI connection:
• Maximum number of ATM switches per cluster
• Maximum number of ATM switch hops in a cluster
Call setup and cell transmit time are proportional to the number of hops.
• Parallel / Multiple SSI link
Parallel SSI links between two hubs are supported but the bandwidth cannot
be shared. This means a data path between two switches is assigned to a
specific SSI link even if you have parallel SSI links. But parallel SSI links
increase the total bandwidth available between switches. There is no limit
for the number of the parallel SSI links but excessive links provide little
additional benefit.
Multiple SSI links which provide alternate paths are supported. There is no
limit to the number of multiple SSI links allowed as long as the network is
designed within the restrictions of the maximum number of ATM switches
and ATM switch hops in a cluster.
Table 25 shows the summary of the TRS capacity of the IBM 8285 and IBM 8260.
Table 25. TRS Capacity of the I B M 8285 Nways A T M Workgroup Switch and I B M 8260
Nways Multiprotocol Switching Hub
Description Value
Maximum number of the ATM switches per a cluster 25
Maximum number of the ATM switch hops in a cluster 5
6.2.1.5 NNI Connection
The IBM 8285 implements static routing mechanism between ATM switches as
well. It is called NNI and is fully-compliant with the IISP specification of The ATM
Forum. The NNI connection may be established on a physical link (direct
connection) or over a permanent VP (PVP) connection via the ATM WAN module.
As of today, IISP is the only protocol that can be used to interconnect an IBM
campus ATM switch to another vendor
′
s switch. On the NNI connection, the
following capacity limitations should be considered:
• Maximum number of static route definitions
Chapter 6. IBM 8285 Planning and Installing
101