20.2.2 Frame format

The following figure shows frame formats.

Figure 20-5: Frame format

<Structure of this section>

(1) MAC sublayer frame format

(a) Preamble and SFD

The Preamble and SFD field contains a 64-bit binary number. The first 62 bits are repetitions of 10, and the last two bits are 11 (1010...1011). Frames without this 64-bit pattern cannot be received.

(b) DA and SA

The DA and SA fields support a 48-bit format. They do not support 16-bit or local address formats.

(c) TYPE/LENGTH

The following table describes how the TYPE/LENGTH field is handled.

Table 20-14: Working with TYPE/LENGTH Fields
TYPE/LENGTH value	How the Switch handles the value
0x0000~0x05DC	IEEE 802.3 CSMA/CD frame length
0x05DD~	Ethernet V2.0 frame type

(d) FCS

The FCS field uses a 32-bit CRC.

(2) Handling of LLC

It is handled in the same way as Ethernet V2.

(3) Conditions for discarding received frames

Frames satisfying any of the following conditions are discarded:

The frame length is not a multiple of an octet.
Receive frame length (DA~FCS) is less than 64 octets or 1523 octets or more

If the use of jumbo frames is selected, the length of the received frame exceeds the specified size.
An FCS error has occurred.

(4) Handling Pads

If the length of a sent frame is less than 64 octets, padding is added immediately before the FCS field. The values to be padded are undefined.