Subject: Re: bridges,switch
To: Erik E. Fair <>
From: Paul Goyette <>
List: tech-net
Date: 04/19/1999 16:10:34
On Mon, 19 Apr 1999, Erik E. Fair wrote:

> Oh, dear me. Terminology definitions required:
> repeater - only does signal regeneration for distance, i.e. bit level copy.
> No filtering capability at all (not even collisions), since it doesn't even
> store&forward. All 10base-T hubs are repeaters. An Ethernet with repeaters
> in it is still subject to the Ethernet maximum cable length limits.

Except some repeaters for Ethernet do "store-and-forward" at the
bit/byte level, performing signal retiming.  So, with 10Base5 cable and
a couple repeaters, you can easily exceed the 500M limitation.

> bridge - packet store&forward device; can retransmit for a collision.
> "learning bridges" collect up station addresses on a per port basis, and do
> not forward packets involved in "local conversations" to other ports. These
> can be used to extend an Ethernet beyond its length limit (as can routers).
> switch - same as a "learning bridge" (marketing-speak)

Except most "bridges" did what they did in software, while modern
"switches" do most of their work in silicon.

> router - protocol dependent packet store&forward device; only forwards
> packets directed to it, according to its routing tables for that protocol
> (e.g. IP, AppleTalk, DECNET, XNS).
> gateway - old Internet community term for "router", now more commonly used
> for Application Specific translation functions (e.g. an SMTP-to-cc:Mail
> "gateway"). Some Old Network Boys (and old RFCs) use the old definition.

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