On Nov 25, 2003, at 01:04 am, Clark Martin wrote:
At 8:09 AM +0000 11/24/03, Mark Benson wrote:On Nov 23, 2003, at 11:50 pm, Marten van de Kraats wrote:
And there-in lies the problem. Routers and Bridges are protocol level dependent and thus will not accept anything they are not set up to pass. TCP/IP routers that don't support AppleTalk will reject signals that are not routable, and may even just throw a panic fit (are these cheap routers or expensive ones?) Switches and Hubs however are packet level dependent and thus pass any packet that is designated to pass packets from one MAC address to another, regardless of what it contains.
Actually Hubs (originally known as repeaters) simply pass bits around and don't terribly much care if they are even Ethernet (oversimplification). Switches actually receive, hold and resend Ethernet packets but don't care about what is in them (if they do then they are kind of moving out of the definition of "Switch"). The problem often comes in the way marketing types tend to use "hub" for "switch" or the term "switching Hub". Also so called dual speed hubs muck it up more.
Yeh I remember this. Hubs take in packets and simply fire them at every machine on the network. Switches do it by MAC address. Hubs make a wet fish of multi-speed because quite often they confuse older 10Mbps NICs by firing 10Mbps and 100Mbps frequency packet signals at them which makes em go all wilty and shy, or something like that!
Hubs simply re-transmit the data literally bit by bit, they don't deal in packets. Switches receive a packet look at the destined MAC address and only send it out on the port they know is attached to that MAC address. If they don't know the port or if it's a broadcast address they send it back out to all the other ports.
Early 10/100 hardware has trouble with speed negotiation as the standards for negotiation weren't fully established at the time they were designed. Dual speed hubs tend to have this problem as they were some of the first 10/100 capable equipment and they quickly got superceded by switches.
Dual speed hubs seem to come in two flavors. The first switch all ports 10 or to 100BaseT depending on some criteria. I'm not even sure why such a beast ever got built. The second type switch individual ports to the appropriate speed of the attached device. All 10BaseT devices are connected to a 10BaseT hub which is linked through a 10BaseT to 100BaseT converter (basically a 2 port switch). All the 100BaseT devices are connected through a hub to the 100BaseT port of this switch. This means that all the 10BaseT devices share a single 10BaseT pipe to the faster network. This is why 10/100 switches quickly supplanted them. In a switch each 10BaseT port gets a full 10MBps connection to any other port, 10 or 100 speed).
--
Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
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