ZL50408GDC ZARLINK [Zarlink Semiconductor Inc], ZL50408GDC Datasheet - Page 45

• Manufacturer Part Number: ZL50408GDC
• Description: Managed 8-Port 10/100M 1-Port 10/100/1000M Ethernet Switch
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

7.9
The ZL50408 implements a hardware assisted link failure detection mechanism utilizing a Link Heart Beat (LHB)
packet. The LHB packet format is defined as a 64-byte MAC control frame with a user defined opcode. The packet
format is illustrated below:
Where “xx-xx-...” is the source port MAC address and “yy-yy” is the special opcode defined by register setup
(LHBReg0,1). The opcode “00-01” is reserved for the flow control packet. We recommend opcode “00-12” for the
LHB packet.
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 ZL50408 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, all of the ports in a group can be in the same ZL50408 or
in multiple ZL50408 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.
If a VLAN includes any of the ports in a trunk group, all the ports in that trunk group should be in the same VLAN
member map.
The ZL50408 also provides a safe fail-over mode for port trunking automatically. If one of the ports in the trunking
group goes down, the ZL50408 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.
Failover Backplane Feature
Features and Restrictions
Unicast Packet Forwarding
Port Trunking
01-80-c2-00-00-01
xx-xx-xx-xx-xx-xx
Zarlink Semiconductor Inc.
ZL50408
45
88-08
yy-yy
00-00-...
CRC
Data Sheet