MDS213 Datasheet, PDF (33/120 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps + 1Gbps Ethernet Switch

MDS213
Data Sheet
256K, 512K, 1024K Bytes depending on the application of the system designer. The MDS213 local memory
interface supports up to 2M bytes of SRAM.
6.0 Search Engine
The Search Engine is responsible for determining the destination information for all packet traffic that enters the
MDS213. The results from all address or VLAN searches are passed to the Frame Engine to be forwarded, or on to
the HISC block for further processing. The result messages to either the Frame Engine or the HISC provide all the
needed information to allow the destination block to process the packet.
The Search Engine has been optimized for high throughput searching, utilizing the integrated Switch Database
Memory (SDM). The internal SDM contains up to 2k MAC Control Table (MCT) entries. These MCT entries are
searched utilizing one of four Hashing algorithms that can be selected. This provides the capability of changing the
search hashing to optimize the hash tables based on the traffic patterns in a given network. For example, if a
company gets all their Network Interface Cards (NIC) from one vendor, then the source and destination MAC
addresses will have common fields. This can lead to inefficient search hashing. With 4 different hash selections that
utilize different parts of the address fields, and can be 8, 9, or 10 bits in length, the hashing algorithm that works
best for a user's network can be selected (by testing each hash algorithm).
Layer 1
Preamble SFD
DATA
FCS
Packet
Layer 2
ENET 2
Header
Layer 3 ^{IP Header}
Layer 4
TCP/IP
Header
Destination MAC Address
Destination MAC Address Source MAC Address
Source MAC Address
0x800
VLAN Tag
Ver IHL Typ of Serv
Total Length
Identifier
Fig Fragment Offset
Time to Live Protocol
Header Checksum
IP Source Address
IP Destination Address
Options + Padding
Source Port #
Destination Port #
Sequence Number
Acknowledgement Number
Offset Reserved U A P R S F
Window
Checksum
Urgent Pointer
Options + Padding
Data
.
.
.
64 Bytes
Figure 7 - Typical Packet Header Information
The search process begins when the Frame Engine transfers the first 64 bytes of a packet header to the Search
Engine. These bytes are parsed to extract the information needed to perform the search for the MCT entries that
match the source and destination MAC address, generate the search hash keys, lookup VLAN membership, and
other packet status information.
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Zarlink Semiconductor Inc.