As the name implies, the purpose of this presentation is to provide a simplified tutorialon local area networks (LANs) and virtual local area networks (VLANs)…
The instructions and terminology used in this presentation attempt to comply with industry practices and written standards. They represent the generally accepted implementations of the written standards. It is important to understand that written standards are sometimes ambiguous, and are thus implemented differently among various vendors. This tutorial seeks to balance between the two and does not rely solely on written standards or specific implementations. All IP addresses and numbering schemes in this tutorial are hypothetical, and used for illustration purposes. Hub (a collision domain)
- A hub is a L1 (physical layer) multi-port repeater.
– It receives a signal on one port, regenerates it, and transmits it out all ports. – All devices connected to a hub receive any transmission on that hub, regardless of the intended recipient. – Note: Simple hubs have a single bus that is capable of operating at either 10Mbps or 100Mbps, but not both. These are pure L1 devices, no “smarter” than the original coax Ethernet bus they replaced. The very common 10/100 hubs actually have two buses, a 10M bus and a 100M bus, which are bridged. This bridging function is a L2 function, so technically speaking 10/100 hubs are not pure L1 devices.
- Two or more devices on a hub cannot transmit at the same time.
– When two or more devices simultaneously transmit, there is a collision. – The devices must back off and re-transmit at dispersed intervals, so that only one device is transmitting at any given time.
- Generally speaking, only four 10M hubs or two 100M hubs can be
- Because of these characteristics, a hub (or a group of hubs connected together) is known as a collision domain.
- Hubs operate only at half duplex; attached devices cannot transmit
LANs and VLANs A Simplified Tutorial.pdf