zl50400 Zarlink Semiconductor, zl50400 Datasheet - Page 41

• Manufacturer Part Number: zl50400
• Description: Lightly Managed/unmanaged 9-port 10/100 M Ethernet Switch
• Manufacturer: Zarlink Semiconductor

Xon is triggered when a port is currently being flow controlled, and all of that port’s reserved FDB slots have been
released.
Note that the ZL50400’s per-source-port FDB reservations assure that a source port that sends a single frame to a
congested destination will not be flow controlled.
7.7.2
Flow control for multicast frames is triggered by a global buffer counter. When the system exceeds a programmable
threshold of multicast packets, Xoff is triggered. Xon is triggered when the system returns below this threshold.
Note:
7.8
The mapping between priority classes discussed in this chapter and elsewhere is shown below.
As the table illustrates, the classes of Table 9 are merged in pairs— P3 is used for network management (NM) and
expedited forwarding service (EF) frames. Classes P2 and P1 correspond to an assured forwarding (AF) group of
size 2. Finally, P0 is for best effort (BE) class.
Features of the ZL50400 that correspond to the requirements of their associated IETF classes are summarized in
the table below.
7.9
The ZL50400 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-xx-xx-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.
Network management (NM) and
Expedited forwarding (EF)
Assured forwarding (AF)
Best effort (BE)
If per-port flow control is on, QoS performance will be affected.
Mapping to IETF Diffserv Classes
Failover Backplane Feature
Multicast Flow Control
01-80-C2-00-00-01
Table 9 - Mapping to IETF Diffserv Classes for MMAC & CPU Ports
Table 10 - ZL50400 Features Enabling IETF Diffserv Standards
ZL50400
IETF
xx-xx-xx-xx-xx-xx
Global buffer reservation for NM and EF
Shaper for traffic on uplink port
No dropping if admission controlled
Global buffer reservation for two AF classes
Shaper for traffic on uplink port
Random early discard, with programmable levels
Service only when other queues are idle means that QoS not
adversely affected
Shaper for traffic on uplink port
Random early discard, with programmable levels
Traffic from flow control enabled ports automatically classified as BE
NM+EF
P3
Zarlink Semiconductor Inc.
ZL50400
41
AF0
P2
88-08
AF1
P1
yy-yy
00-00-...
BE
P0
CRC
Data Sheet