| Title: | FDDI - The Next Generation |
| Moderator: | NETCAD::STEFANI |
| Created: | Thu Apr 27 1989 |
| Last Modified: | Thu Jun 05 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 2259 |
| Total number of notes: | 8590 |
About The different DECHUB 900 switch modules. How do they switch ? 1. When they take in a packet from the ethernet, do they hold the packet to check the crc before they put it out on the FDDI. ? 2. Do they only look at the first porsion af the packet, and then start to forward ? 3 Can switches be put in to a kind of "repeater mode" ? Jan.
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 1815.1 | store-and-forward algorithm used by switches900'serie | ULYSSE::YLOUPC::LOUIS | Thu Sep 28 1995 09:01 | 33 | |
<<< NETCAD::KALI$USER3:[NOTES$LIBRARY]HUB_MGNT.NOTE;1 >>>
-< DEChub/HUBwatch/PROBEwatch CONFERENCE >-
===============================================================================,
Note: 2806.1 Switching ? 1 of 1
ULYSSE::YLOUPC::LOUIS 24 lines 28-SEP-1995 08:44
-< 900's series switch support the "store-and-forward" algorithm >-
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>> About The different DECHUB 900 switches. How do they switch.
>>
>> 1. When they take in a packet from the ethernet, do they hold the packet
>> to check the crc before they put it out on the FDDI. ?
Yes - they use the store-and-forward algorithm. This means that the switch waits
to receive an entire packet, check the packet quality (runt, CRC, misaligned)
and if no error only forward it to the adequate LAN.
This algorythm garantees the integrity of the packet.
2. Do they only look at the first porsion af the packet, and then start
to forward ?
NO - But the Gigawitch/F supports this Cut-through algorithm and can be disable for
specific ports to allow store-and-forward feature.
The packet is transmitted as soon as it reads the destination address.
3 Can switches be put in to a kind of "repeater mode " ?
I don't think so.
I believe the Ethernet switching module (ESM) of Decswitch400 supports
this feature. I think it 's an automatic selection depending on the number
of station: 1 or more
yves
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| 1815.2 | Thanks ! | 51847::PALMANN | Jan Palmann C/S Comms. Copenhagen | Thu Sep 28 1995 11:18 | 1 |
| 1815.3 | Good and Bad | CHOWDA::FAHEY | Are we having 'FUN' yet? | Fri Sep 29 1995 13:35 | 16 |
To be clear... Cut Through Switching is only possible when switching
between identical technologies. (ie Ethernet to Ethernet or FDDI to
FDDI). You can't possibly cut through switch an Ethernet to FDDI
because 10Mbps can't fill a 100Mbps pipe.
Most people now agree that using cut through switching in Ethernet is a
bad idea. When an Ethernet LAN gets busy the number of collisions will
increase. It's possible that a collision can occur 'after' the
Destination Address field of the frame. Cut through switching on
Ethernet will pass 'bad packets'. On the other hand FDDI is not subject
to 'collisions' therefore it is reasonable to assume that if you start
receiving a packet that it will be a good packet hence with GIGAswitch
FDDI we support 'cut-through'
Jim
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