MDS213 Datasheet, PDF (26/120 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps + 1Gbps Ethernet Switch

MDS213
Data Sheet
3.8.1 Collision-Based Flow Control
Collision-based Flow Control, also referred to as Backpressure Flow Control, inhibits frame reception for ports
operating in half-duplex mode by "jamming" the link. When the free buffer space drops below a user-defined buffer
memory threshold, the MDS213 sends a jam sequence to all non transmitting ports, after approximately eight bytes
of payload data has been received, to generate a collision. The jam sequence is a predefined serial data stream
sent to all ports to indicate that there has been a collision on the network. These ports will delay (defer) the
transmission of data onto the network until the sequence has been completed.
3.8.2 IEEE 802.3x Flow Control
IEEE 802.3x Flow Control reduces network congestion on ports that are operating in full duplex mode using MAC
Control PAUSE frames and is managed by the Flow Control Management Registers. The full-duplex PAUSE
operation instructs the MAC to enable the reception of frames with a destination address equal to a globally
assigned 48-bit reserved multicast address of 01-80-C2-00-00-01. These PAUSE frames are subsets of MAC
Control frames with an opcode field of 0x0001 and are used by the MAC Control to request that the recipient stops
transmitting non-control frames for a specific period. The PAUSE Timer is loaded from the PAUSE frame and is
started upon the reception of a PAUSE frame. It will request a length of time for which it wishes to inhibit data frame
transmission.
In general, the IEEE standard allows pause frames longer than 64 bytes to be discarded or interpreted as valid. The
MDS213 recognizes all MAC Control frames (PAUSE frames) between 64 and 1518 bytes long. Any PAUSE
frames presented to the MAC outside of these parameters are discarded.
Preamble
SFD
DA
SA DATA PAD
FCS Carrier Extension
Mll Frame Size: 512 bits
Slot Time: 4096 bits
FCS Coverage
Late Collision Threshold:
Slot Time - Header Size
= 4032 bits
GMAC Frame with Carrier Extension
Mac Frame with Extension InterFrame Mac Frame Inter Frame
Burst Limit
65,536 bits
Carrier Event Duration
GMAC Frame Bursting
Mac Frame
Figure 3 - Frame with Carrier Extension and Frame Bursting
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