Essay On Pcb

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IEEE 802.1Qbb (PFC) is a Ethernet flow control mechanism proposed in 2008 \cite{barrass2008proposal}. PFC employs eight virtual channels with eight different priorities. For each priority, PFC uses IEEE 802.3 PAUSE frame \cite{barrass2007definition} to prevent packets loss, and the PAUSE action in a VC does not affect the flows with other priorities. As shown in Fig. \ref{PFC}, in the VC with priority-1, queue length exceeds the threshold, and the switch sends back a pause frame to the upstream switch. When receives a PAUSE frame, the P1 timer specifies how long the traffic should be paused, and the switch pauses the transmission of the flow of corresponding priority. there are eight timers controlling the pausing time for eight priority…show more content…
When receives the RM sell, the source starts to throttle the injection rate.\ b) BECN The Backward explicit congestion notification (BECN) \cite{newman1993backward}\cite{newman1994traffic} is different from FECN. Instead of returning RM cell by the destination-end, the congestion information is directly sent back to the source by the congested point (switch). As shown in Fig. \ref{BECN}, when the queue of a virtual channel exceeds a fixed threshold, the switch will directly send BECN cells to the source that contribute to the congestion. On each receiving of a BECN cell, the source reduces the sending rate of the specific virtual channel. If no BECN cell arrives on the throttled virtual channel for a time period, the sending rate will be gradually regained.\ c) TCP-ECN The ECN mechanism for TCP/IP protocol \cite{floyd1994tcp}\cite{ramakrishnan1998proposal}, TCP-ECN for short, is an end-to-end congestion control scheme deployed on layer 3 and layer 4. TCP-ECN employs Random Early Detection (RED) mechanism to mark the congested packet with \textit{Congestion Experienced} (CE) bit, which is carried in packet's IP header. And the end-host enables ECN-Capable TCP (ECT) bit in the packet header to support the ECN mechanism. Fig. \ref{TCP-ECN} illustrates the working process of TCP-ECN. When the queue length exceeds a fixed threshold, the router will use RED to set the CE bit in the packet header instead of dropping the packet, and
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