American Fibertek SM24p-PoE Manuel d'instructions télécharger pdf (Page 40)

User Manual

Rev.A1

1-Mar-11

3-4. How does a switch work?

The switch is a layer 2 Ethernet Switch equipped with 24 Fast Ethernet ports

and 2 optional modules which support Gigabit Ethernet or 100M Ethernet. Each port

on it is an independent LAN segment and thus has 26 LAN segments and 26

collision domains, contrast to the traditional shared Ethernet HUB in which all ports

share the same media and use the same collision domain and thus limit the

bandwidth utilization. With switch’s separated collision domain, it can extend the

LAN diameter farther than the shared HUB does and highly improve the efficiency

of the traffic transmission.

Due to the architecture, the switch can provide full-duplex operation to

double the bandwidth per port and many other features, such as VLAN, bandwidth

aggregation and so on, not able to be supported in a shared hub.

Terminology

Separate Access Domains:

As per the description in the section of “What’s the Ethernet”, Ethernet

utilizes CSMA/CD to arbitrate who can transmit data to the station(s) attached in the

LAN. When more than one station transmits data within the same slot time, the

signals will collide, referred to as collision. The arbitrator will arbitrate who should

gain the media. The arbitrator is a distributed mechanism in which all stations

contend to gain the media. Please refer to “What’s the Ethernet” for more details.

In Fig.3-5, assumed in half duplex, you will see some ports of the switch are

linked to a shared HUB, which connects many hosts, and some ports just are

individually linked to a single host. The hosts attached to a shared hub will be in the

same collision domain, separated by the switch, and use CSMA/CD rule. For the

host directly attached to the switch, because no other host(s) joins the traffic

contention, hence it will not be affected by CSMA/CD. These LAN segments are

separated in different access domains by the switch.

Micro-segmentation:

To have a port of the switch connected to a single host is referred to as

micro-segmentation. It has the following interesting characteristics.

- There is no need the access contention (e.g.Collision). They

have their own access domain. But, collision still could happen

between the host and the switch port.

- When performing the full duplex, the collision vanishes.

- The host owns a dedicated bandwidth of the port.

The switch port can run at different speed, such as 10Mbps, 100Mbps or

1000Mbps. A shared hub cannot afford this.

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American Fibertek SM24p-PoE Manuel d'instructions Page 40