3-3. Flow Control

Flow control is a mechanism to tell the source device stop sending frames for a specified period of time designated by target device until the PAUSE time expires. This is accomplished by sending a PAUSE frame from target device to source device. When the target is not busy and the PAUSE time is expired, it will send another PAUSE frame with zero time-to-wait to source device. After the source device receives the PAUSE frame, it will again transmit frames immediately. PAUSE frame is identical in the form of the MAC frame with a pause-time value and with a special destination MAC address 01-80-C2-00-00-01. As per the specification, PAUSE operation can not be used to inhibit the transmission of MAC control frame.

Normally, in 10Mbps and 100Mbps Ethernet, only symmetric flow control is supported. However, some switches (e.g. 24-Port GbE Web Smart Switch) support not only symmetric but also asymmetric flow controls for special applications. In Gigabit Ethernet, both symmetric flow control and asymmetric flow control are supported. Asymmetric flow control only allows transmitting PAUSE frame in direction way from one side, the other side does not but only receive and discard the flow control information. Symmetric flow control allows both two ports to transmit PASUE frames to each other simultaneously.

Inter-frame Gap time

After the end of a transmission, if a network node is ready to transmit data out and if there is no carrier signal on the medium at that time, the device will wait for a period of time known as an inter-frame gap time to have the medium clear and stabilized as well as to have the jobs ready, such as adjusting buffer counter, updating counter and so on, at the receiver site. Once the inter-frame gap time expires after the de-assertion of carrier sense, the MAC transmits data. In IEEE802.3 specification, this is 96-bit time or more.

Collision

Collision happens only in half-duplex operation. When two or more network nodes transmit frames at approximately the same time, a collision will always occur and interfere with each other. This results the carrier signal distorted and un- discriminated. When a collision is detected during a frame transmission, the transmission will not stop immediately but, instead, continue transmitting until the rest bits specified by jamSize are completely transmitted. This guarantees the duration of collision to be enough to have all involved devices able to detect the collision. This is referred to as Jamming. After jamming pattern is sent, MAC stops transmitting the rest data queued in the buffer and waits for a random period of time, known as backoff time with the following formula. When backoff time expires, the device goes back to the state of attempting to transmit frames. The backoff time is determined by the formula below. When the times of collision is increased, the backoff time is getting longer until the collision times excess 16. If this happens, the frame will be discarded and backoff time will also be reset.

where

k = min (n, 10)

31

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Edimax Technology ES-5240G+ user manual Flow Control
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ES-5240G+ specifications

Edimax Technology ES-5240G+ is a highly versatile and efficient Ethernet switch designed to cater to the networking needs of small to medium-sized businesses and home offices. With its robust features and reliable performance, this switch is an essential component for a seamless network infrastructure.

One of the standout features of the ES-5240G+ is its 24 10/100/1000Mbps Gigabit Ethernet ports. This allows for high-speed connectivity, enabling users to transfer large files quickly and efficiently. The switch is equipped with a non-blocking architecture, ensuring that all ports can be utilized simultaneously without any reduction in bandwidth. This is particularly beneficial for businesses that rely on high-speed internet and internal networks for their daily operations.

The ES-5240G+ supports advanced Layer 2 switching features, including VLAN (Virtual Local Area Network) support, port mirroring, and link aggregation. These features enhance network management and optimization, making it easier to segment network traffic and improve security. With VLAN support, users can create separate networks within the same switch, leading to improved performance and reduced broadcast traffic.

Moreover, the ES-5240G+ incorporates IEEE 802.3x Flow Control, which helps to prevent data loss during heavy traffic periods. This technology allows for effective communication between devices and ensures smooth data transmission, even in congested network environments. Additionally, the switch is equipped with Automatic MDI/MDI-X detection, eliminating the need for crossover cables and simplifying installation.

From a security perspective, Edimax has included features such as address filtering and port security, which help to protect the network from unauthorized access. The switch can restrict access to specific MAC addresses, providing an added layer of security for sensitive data.

In terms of energy efficiency, the ES-5240G+ is designed to comply with IEEE 802.3az Energy Efficient Ethernet standards. This technology helps to reduce power consumption during low-traffic periods, making it an eco-friendly choice for businesses looking to minimize their carbon footprint.

Overall, Edimax Technology ES-5240G+ stands out as a reliable and efficient Ethernet switch, equipped with a range of features that enhance network performance and security. Its capabilities make it an ideal choice for businesses seeking to streamline their networking infrastructure and improve operational efficiency.
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