IEEE 802.1Qbu-2016 pdf free.IEEE Standard for Local and metropolitan area networks- Bridges and Bridged Networks- Amendment 26: Frame Preemption.
In a port of a Bridge or station that supports frame preemption, a frame of priority n is not available for transmission if that priority is identified in the frame preemption status table (6.7.2) as prccmptablc and cithcr the holdRequcst object ( is set to the value hold, or the transmission of a prior preemptablc frame has yet to completc because it has been intcrruptcd to allow the transmission of an express frame. Credit-based shaper algorithm
(hange the text of list items e) andj,), and insert new NOTEs, renumbering subsequent NOTEs, as follows:
e) transmit. Takes the value TRUE for the duration of a frame transmission from the queue: FALSE when any frame transmission from the queue has completed. lithe credit-based shaper aloriihm A used in cornhinion with franie.preemption (6.7.2Liransmit only akes.thalue TRUE while the frame is actually being transmjncd by the MA. If the frame transmission is delayed or interrupted (e.g.. the frame is a preemptable frame and its transmission is intermpted to allow the transmission of an express frame from a difterent queue. or the franie is an express frame and there is a delay before transmission can start because a preemptable frame was being transminedjjrwismit takes the i1Me FALSE until transmission of the frame commetics QrjLlesumed, Traimmit also takesjhc value FALSE during the transmission of any overhead that is a consequence of frame preemption:
i.e.. any additional frame overhead that is added to the preemptable frame when preemption occurs.
NOTE I—The conseuCnce of this is that any overhead associated with preemption does not come out of the reservctl bandwidthfjhc credit-based shaper.
f) credit. The transmission credit, in bits, that is currently available to the queue. If. at any time, there are no frames in the queue, and the trans,nhl parameter is FALSE, and the transmission gate for thc queue is open (, and credit is positive, and there is no precniptahle frame from this queue for which transmission is in pmgress hut has bccn interrupted, then credit is set to zero.
r’OTh. 2 The £.ondilion that the jwnrnjf paranwier j&fAl..Landjprceniptablc frame Qr pan-frame j vaitjng in the MAC’ tbr transmission can only occur if the credit-based shaper alorithni is used in combination with Preemption. Enhancements for scheduled traffic
Change the second paragraph of as follows:2
A gale control list associated with each Port contains an ordered list of gate operations. Each gate operation changes the transmission gate state for the gate associated with each of the Port’s traffic class queucsui allows associated control operations to be scheduled. In an implementation that does not support enhancements for scheduled traffic, all gates are assumed to be permanently in the open state. Table 8-6 identifies the gate operation types. their parameters. and the actions that result from their execution. The state machines that control the execution of the gate control list, along with their variables and procedures, are specified in 8.6.9.IEEE 802.1Qbu pdf free download.