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CHAPTER 5 SAR FUNCTION
207
5.7 LAN EMULATION FUNCTION
The
μ
PD98405 supports several types of LAN emulation function in order to reduce the load related to LAN
emulation on the host system. The
μ
PD98405's LAN emulation assist function is valid only for type AAL-5
packets. The
μ
PD98405 supports flexible frame formats such as Ethernet and token-ring frame formats. The
Ethernet and token-ring frame formats are shown below.
Figure 5-45. Ethernet and Token Ring Frame Formats
LECID
AC Pad
S.A.
Destination Address
Source Address
Payload
0
4
8
12
16
FC
Routing Information Field
20
D.A.
LECID
IEEE802.3/Ethernet
IEEE802.5/Token-Ring
D.A.
S.A.
Type/Length
Destination Address
Source Address
Payload
0
4
8
12
16
(1) Storing the receive LECID in the receive indication
The
μ
PD98405 can store the receive LECID (LAN Emulation Client Identifier) for each receive VC in a
separate receive indication. If the RLI bit of the receive VC table is set to 1, the
μ
PD98405 loads the first
two bytes of the receive packet with an LECID to report it in the receive indication. The receive LECID is
indicated in the UINFO/LECID field of the receive indication. Upon receiving this indication, the host can
start processing of the LECID. The LECID is also stored into the receive buffer.
Remark
Enabling this function (RLI = 1) prevents the host from using the "user information (UINFO)."
The
μ
PD98405 stores the receive LECID into the UINFO/LECID field of the VC table, and
indicates such in the UINFO/LECID field of the indication.
(2) Automatically inserting the transmit LECID into the transmit packet
The
μ
PD98405 can automatically insert its LECID at the beginning of the transmit packet. The LECID for
each VC can be set separately in the LOCAL LECID field of the transmit VC table. This enables
connection to more than one emulated LAN.
If the LIE bit of the transmit VC table is set to 1, the
μ
PD98405 treats the value in the LOCAL LECID field of
the VC table as an LECID, and inserts it at the beginning of the VC transmit packet. The first two bytes of
the first buffer of the packet will not be overwritten with the LECID. The
μ
PD98405 creates a transmit
packet by adding the LECID to the contents of the transmit buffer.