Signamax
™
065-7921PoE 12-Port 10/100/1000BaseT/TX Web Smart PoE Switch
36
The maximum length of the extension is equal to the quantity (slotTime -
minFrameSize). The MAC continues to monitor the medium for collisions while it is transmitting
extension bits, and it will treat any collision that occurs after the threshold (slotTime) as a late
collision.
3-4. How does a switch work?
The switch is 10-Port 10/100/1000Mbps TP and 2-Port Gigabit TP/SFP Fiber Web
Smart Ethernet Switch.
Each port on it is an independent LAN segment and thus has 12 LAN
segments and 12 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.
