IP1000A LF
Preliminary Data Sheet
20/75
July 5, 2005
Copyright © 2005, IC Plus Corp.
IP1000A LF-DS-R08
Preamble and SFD generation
Preamble and SFD removal
Receive frame FCS checking and optional FCS stripping
Receive frame destination address matching
Support for multicast and broadcast frame reception or rejection (via filtering)
In addition, the MAC is responsible for generation of hardware signals to update the internal statistics
counters.
2.3.1
VLAN
Virtual Local Area Network (VLAN) technology is used to regulate broadcast and multicast traffic in
switched Ethernet networks. VLAN technology utilizes Ethernet frame tagging, providing Ethernet
switches a mechanism to correlate a specific Ethernet frame with a specific group of end stations. Using
this correlation, Ethernet switches in a network are able to regulate broadcast and multicast VLAN
tagged frames, forwarding such frames only to those nodes which are members of the same VLAN
(instead of to all nodes). In this way, broadcast and multicast network utilization is minimized.
The IEEE defines VLANs as follows:
VLANs facilitate easy administration of logical groups of stations that can communicate as if they
were on the same LAN. They also facilitate easier administration of moves, adds and changes in
members of these groups.
Traffic between VLANs is restricted. Bridges forward unicast, multicast and broadcast traffic only on
LAN segments that serve the VLAN to which the traffic belongs.
As far as possible, VLANs maintain compatibility with existing bridges and end-stations.
Detailed information on VLAN implementation is located in the following standards:
IEEE 802.1Q Virtual Bridged Local Area Networks (also now part of ISO/IEC 15802-3: 1998).
Specifies the operation of VLAN enabled Ethernet bridges, and defines the tagged frame format.
IEEE 802.3ac Frame Extensions for Virtual Bridged Local Area Networks (VLAN) Tagging on 802.3
Networks. Modifies the IEEE 802.3 specification to accommodate tagging for VLANs as specified in
IEEE 802.1Q.
The IP1000A LF supports VLANs with the following functions:
Transmission and reception of VLAN tagged frames, increasing the maximum frame size by four octets.
VLAN tags for transmit frames may be applied either by the host system prior to transfer of the frame
to the IP1000A LF via the transmit DMA process, or by the IP1000A LF via the VLAN tag information
specified in the TFC0 or the VLANTag register. The the TFC0 VLANTagInsert field, and MACCtrl
register AutoVLANtagging bit determines the source for VLAN frame tagging with the TFC0
VLANTagInsert having priority over the MACCtrl register AutoVLANtagging bit.
Any VLAN tagged frames received by the IP1000A LF may be transferred to the host system
unmodified, or stripped of all VLAN tags as determined by the MACCtrl register AutoVLANuntagging
bit. For any received frame which contains a VLAN tag, regardless of the state of the MACCtrl
register AutoVLANuntagging bit, the VLAN tag is copied to the RFS TCI field.
The priority of VLAN tagged frames received by the IP1000A LF may be detected and based on the
programmable PriorityThresh field of the RxDMAIntCtrl register, an interrupt asserted via the
RxDMAPriority field of the IntStatus or IntStatusAck register.
Using the ReceiveVLANMatch or ReceiveVLANHash fields of the ReceiveMode register, only VLAN
tagged frames with specified VLAN ID values are passed to the host system. All other VLAN tagged
frames and all un-tagged frames are dropped.
2.3.2
Layer 3/4 Checksums
The Ethernet Carrier Sense Multiple Access with Collision Detect (CSMA/CD) protocol comprises a portion
of Layer 2 within the Open Systems Interconnect (OSI) Seven Layer Model of network systems. Ethernet
incorporates a CRC capability (via the FCS field) in an attempt to check for errors during transmission.
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