MDS212 Datasheet, PDF (31/111 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps Ethernet Switch

MDS212
Data Sheet
6.0 Search Engine
The Search Engine is responsible for determining the destination information for all packet traffic that enters the
MDS212. 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. Either way, the result messages 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
EFD
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
Flg
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
UAPRSF
Window
Checksum
Urgent Pointer
Options + Padding
Data
64
Bytes
Figure 6 - Typical Packet Header Information
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