ZL50400GDC ZARLINK [Zarlink Semiconductor Inc], ZL50400GDC Datasheet - Page 42

• Manufacturer Part Number: ZL50400GDC
• Description: Lightly Managed/Unmanaged 9-Port 10/100 M Ethernet Switch
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

The LHB is done between two compatible MACs providing this function. A timer parameter will be set for both the
receiver and transmitter (LHBTimer).
On the transmission side, the MAC will monitor the transmission activities. If there is no activity for more than the
set period, a LHB packet will be sent to its link partner. Therefore, there should always be at least one packet
transmitted from the MAC for every period specified.
On the receiving side, the MAC will also monitor the activity. If there is no good packet received for more than 2X
the set period, an alarm will be raised to the CPU. The LHB packet is only used by the ZL50400 to reset the timeout
counter, it is ignored otherwise (i.e. not passed on within the system).
See the Failover Protection Application Note, ZLAN-43, for more information.
8.0
See Port Trunking application note, ZLAN-48, for more information.
8.1
A port group (i.e. trunk) can include up to 8 physical ports to form a fault tolerant link. There are eight trunk groups
total.
Load distribution among the ports in a trunk for unicast is performed using hashing based on source MAC address
and destination MAC address. Three other options include source MAC address only, destination MAC address
only, and source port (in bidirectional ring mode only). Load distribution for multicast is performed similarly.
The ZL50400 also provides a safe fail-over mode for port trunking automatically. If one of the ports in the trunking
group goes down, the ZL50400 can redistribute the traffic over to the remaining ports in the trunk with software
assistance.
8.2
The search engine finds the destination MCT entry, and if the status field says that the destination port found
belongs to a trunk, then the trunk group number is retrieved.
The source port of the packet is checked against the destination trunk group. If the source port belongs to the
destination trunk group, the packet is discarded.
A hash key, based on some combination of the source and destination MAC addresses for the current packet,
selects the appropriate forwarding port, as specified in the Trunk_Hash registers. Each trunk has eight trunk_hash
registers which selects one of the potential eight outgoing ports. The hash key provides a pseudo flow identifier
which force the same flow to the same destination flow. As a result, the packet will always arrive in order.
8.3
For multicast packet forwarding, the device must determine the proper set of ports from which to transmit the
packet based on the hash key.
Three functions are required in order to distribute multicast packets to the appropriate destination ports in a port
trunking environment.
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•
For example, port 0,1 and 2 belong to trunk group 0 and port 3 and 4 belong to trunk group 1. A single VLAN is
established in this system with port 0,1,2,3,4,5 and 6 as the members in the VLAN. When a multicast packet is sent
in from port 3, the ZL50400 select port 0,1,2,3,4,5 and 6 as potential destination based on the VLAN. Then port 3
and 4 are removed because they belong to the source port group (trunk group 1). Two ports from trunk group 0 will
The source port/group must be excluded from the forwarding.
Select one port per trunk group to forward the packet to. This selection is based on hash key described in
previous section.
Features and Restrictions
Unicast Packet Forwarding
Multicast Packet Forwarding
Port Trunking
Zarlink Semiconductor Inc.
ZL50400
42
Data Sheet