On Fri, Mar 21, 2003 at 10:25:07PM +1200, Helmut Walle wrote: > On Fri, 21 Mar 2003, Gareth Williams wrote: > > identical, no? So... is then "hub" just another word for "bridge" > > (ie. they are essentially the same device) ? > > No, definitely not!
And I said yes :-) Well, it's a terminology difference that causes many confusions. Part of the problem is marketing-speak trying to invent a new name for an old product, and part of it is topology-descriptive, where the centre-point of a star network is the hub ... regardless of the actual unit's capabilities itself. However, once you get someone to explain just what the unit does, and you can get back on track :-) > A hub in the traditional sense (not modern stuff like switch hubs) is > only a signal regeneration and distribution device. It does not look > at the semantics of whatever layer. All traffic from all input ports > is copied to all other output ports. If you connect too many hosts to > one segment, network throughput will break down, because Ethernet uses > a CSMA/CD medium access. And, of course, the hub won't care what network protocols are being transmitted over Ethernet - it could be TCP/IP, NETBeui, SPX (Novell) or anything. But it still has to be Ethernet. Strictly speaking, it has to be the same _kind_ of Ethernet, but many of the UTP "hubs" you buy these days allow different speeds/duplex settings on each port, and therefore are not traditional hubs, they're more like gateways ... which are a step above bridges, equivalent to routers ... but basically they work so well that you can forget all about the details. > To build up larger networks, you have to keep local traffic local. > That is what bridges can do. They'll manage the Ethernet traffic for you, allow you to have networks larger than collision domains, and so on. > > A bridge receives and transmits protocol data units (PDUs) on the data > link layer, which are called Ethernet frames in Ethernet networks. A comment suggesting the Helmut is familiar with more network types that I am - I've pretty much only worked with Ethernets :-) -jim, brain hurting ...
