GarrettCom 4K16 User Manual

Page 27

Magnum 4K16 Switches Installation and User Guide

(12/05)

www GarrettCom com

There are no collision-domain restrictions or limitations.

The Magnum 4K-Series Switches perform half- or full-duplex mode auto-

negotiation independently on all switched ports. If the device or node on the other end of

a port’s attached cable supports auto-negotiation or is set to operate as full-duplex, the

Magnum 4K16 Switch will negotiate to run full-duplex. If the attached device or node

doesn’t support F/H mode or fixed at Full or Half duplex (for example, if it is a 10 Mb

repeater or a standard 10 Mb hub or older Switch with Fixed full duplex mode), the

4K16-Switch’s RJ-45 ports will default to operate at half-duplex.

4.6

Flow-control, IEEE 802.3x standard

Magnum 4K- Series Switches incorporate a flow-control mechanism for Full-

Duplex mode. The purpose of flow-control is to reduce the risk of data loss if a long

burst of activity causes the switch to save frames until its buffer memory is full. This is

most likely to occur when data is moving from a 100Mb port to a 10 Mb port, and the

speed difference makes the 10Mb port unable to keep up. It can also occur when multiple

100Mb ports are attempting to transmit to one 100Mb port, and in other protracted heavy

traffic situations.

Magnum 4K-Series Fiber Switches implement the 802.3x flow control (non-

blocking) on Full-Duplex ports, which provides for a “PAUSE” packet to be transmitted

to the sender when the packet buffer is nearly filled and there is danger of lost packets.

The transmitting device is commanded to stop transmitting into the switched port for

sufficient time to let the Switch reduce the buffer space used. When the available free-

buffer queue increases, the Switch will send a “RESUME" packet to indicate the

transmitter to start sending the packets. Of course, the transmitting device must also

support the 802.3x flow control standard in order to communicate properly during

normal operation.

Note:

When in Half-Duplex mode, the 4K16-switch implements a back-

pressure algorithm on 10/100 Mb ports for flow control. That is, the switch prevents
frames from entering the device by forcing a collision indication on the half-duplex ports
that are receiving. This temporary “collision” delay allows the available buffer space to
improve, as the switch catches up with the traffic flow.

4.7

Power Budget Calculations for 4K-Series FKM’s with Fiber Media

Receiver Sensitivity and Transmitter Power are the parameters necessary to

compute the power budget. To calculate the power budget of different fiber media
installations using Magnum products, the following equations should be used:
OPB (Optical Power Budget) = P

(min) - P

(min)

where P

= Transmitter Output Power, and P

= Receiver Sensitivity