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參數(shù)資料
| 型號： | MB86976PF-G |
| 元件分類： | 微控制器/微處理器 |
| 英文描述： | 2 CHANNEL(S), 10M bps, LOCAL AREA NETWORK CONTROLLER, PQFP144 |
| 封裝： | PLASTIC, QFP-144 |
| 文件頁數(shù)： | 13/46頁 |
| 文件大?。?/td> | 212K |
| 代理商： | MB86976PF-G |
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xDSL WAN Ethernet Bridge Controller
20
Fujitsu Microelectronics, Inc.
Advanced 11/5/98
steps are performed automatically:
1.
A 10-bit hash value is calculated from the 48-bit Source Address
and is used as the pointer to one of 1024 database “buckets”.
2.
The corresponding “bucket” is linearly searched until an entry
containing an identical, valid 48-bit address is found or the end of
the “bucket” is reached.
3.
If a valid matching entry is found, the timestamp field in the
header of the matching entry is set to 1.
If no matching entry is found, and at least one empty location
exists, the Source Address is written into the database, setting
both the timestamp and valid fields to 1. If an empty location
does not exist, then exit.
Note that ethernet frames with errors (CRC, illegally large or
small) do not update the SADB.
Purging Outdated Entries
To allow the MB86976 to operate in the “auto-learning” mode, a
purging routine must be periodically executed to maintain a
Source Address Database of the most recent entries. Not purging
the Source Address Database may cause it to fill up and prevent
learning of new addresses.
The default aging period is set (upon power-up) to 300 seconds
with a resolution of 1 second in accordance with the 802.1d
specification. This value may be overwritten by the processor at any
time with any 9-bit unsigned value in SADB_Aging representing
the aging period in seconds.
Every aging period (default 300 seconds), the following steps are
performed:
1.
Read the header word of the first entry in the Source Address
Database.
2.
If the dynamic bit is 0, proceed to the next entry.
3.
If the value contained in the timestamp field is non-zero, then reset
the timestamp bit to 0.
If the value contained in the timestamp field is 0 and the valid bit
is non-zero, then reset the valid bit to 0.
If neither case exists, do nothing.
4.
Repeat steps 2 and 3 for all header words in the Source Address
Database.
It should be noted that due to the implementation of the packet
aging function, there will exist situations where source address
database entries may remain in the database for up to twice the
specified aging period before being purged.
Hashing Algorithm
An exclusive-or polynomial function generates the 10-bit hash
value used to index entries in the source address database. The hash
value is as follows where n is for 0 through 9 for each one of the 10
bits:
hash(n) = a(n)
⊕ a(n+10)⊕ a(n+20) ⊕ a(n+30) ⊕ a(n+40)
Bits 8 and 9 of the hash value are a function of 4 bits of the source
address. All other bits are a function of 5 bits.
User-Defined Look-up Table Filtering
The user-defined look-up table filtering process enables generic
filtering capabilities. By configuring the 24 16-bit user-defined
table entries, a user is able to search for any sequence of bits within
the first 32 bytes of a frame.
Through judicious partitioning of the 24 available table entries,
up to 8 multiple filters can be constructed.
Note that unlike the Source Address Database filtering process,
multiple filters will require multiple filtering operations per frame.
Look-up Table Format
Each table entry is comprised of three 16-bit words-header, data,
and mask—as shown in table below. The header controls the word
offset of the frame word to be matched, the id value of the filter
string that this match relates to, the logic operation of the match,
and the destination that the frame should receive if total matching
occurs, as well as flags for validity, the beginning and end of the
string.
Examples of UDLT lookup table entries are given in “UDLT
Programming Examples” on page 40.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MB86977 | 制造商:FUJITSU 制造商全稱:Fujitsu Component Limited. 功能描述:IP PACKET FORWARDING ENGINE |
| MB86977PFV-G-BND | 制造商:FUJITSU 制造商全稱:Fujitsu Component Limited. 功能描述:IP PACKET FORWARDING ENGINE |
| MB86A21PMC-G-BNDE1 | 制造商:FUJITSU 功能描述: |
| MB86A21PMC-G-JNE1 | 制造商:FUJITSU 功能描述: |
| MB86A22PMC-ES-BNDE1 | 制造商:FUJITSU 功能描述: |
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