
IBM2520L8767
IBM Processor for ATM Resources
atmrm.chapt03.01
08/27/99
Packet Header
Page 47 of 553
alter_sched #
These encoding bits will alter the scheduling of cells on a Virtual Circuit (VC)
000 = Normal Scheduling
Scheduling is not altered.
001 = VC on VP
This VC is contained on a virtual path and will share the VP band-
width after one packet is sent. The scheduling parameters are con-
tained in the descriptor for the virtual path that is pointed to by the
Virtual Path Discriptor Address field in this LCD.
010 = MPEG-2 Scheduling
The cells being sent out on this connection are monitored for a Peak
Cell Rate (PCR). If a PCR is found, the AAL5 packet is terminated at
the end of the MPEG-2 frame and the last cell is scheduled to go out
at the time specified in the PCR.
011 = Packet-based scheduling Packets will be scheduled at the average interval and cells within the
packet will be scheduled at the peak interval. This is useful for send-
ing information where variably-sized packets need to be sent at regu-
lar intervals.
100 = ABR scheduling
This VC will send Resource Management cells and adjust its transmi-
sin rate according to the behaviors specified in the ATM Forum Traffic
Management Specification, Version 4.0.
101 = Fair VC on VP
This VC is contained on a virtual path and will share the VP band-
width after one cell is sent. The scheduling parameters are contained
in the descriptor for the virtual path which is pointed to by the Virtual
Path Descriptor Address field in this LCD.
110 = Reserved
For MPEG-2 scheduling.
111 = Reserved
transmit_priority #
This field specifies the priority of transmission on this connection. 0=high, 1=medium, 2=low.
max_resolution #
If this bit is set, the lower eight bits of the average interval and peak interval parameters contain a frac-
tional component. This allows a finer resolution for scheduling. For example, for a peak interval of 1.5
time units, the value written to the peak_interval field should be hex 0180. If this bit is set, the initial
value of timestamp should contain the current timeslot counter shifted 16 bits to the left.
max_burst_mult #
The values in this field and the next field are used to limit the number of cells that can be transferred at
the peak rate. The max_burst_value will be multiplied by 4 to the power of the value in this field to yield
the maximum credit time. This time is expressed in cell times and represents the time it would take to
acquire the maximum number of cell credits. This maximum credit time should equal the maximum
number of cells that can be transferred at the peak rate (MBS) times the difference between the aver-
age and intervals. Maximum credit time = MBS * (AI-PI) where MBS = maximum burst size, AI = aver-
age interval, and PI = peak interval. MBS must be at least 1 to transmit at peak rate. If MBS is not at
least 1 the peak interval should be set to the average interval.
max_burst_value #
The value in this field will be multiplied by 4 to the power of the value in the max_burst_mult field to
yield the maximum credit time.
head_packet_pointer
This field is used to chain buffers to LCDs.
tail_packet_pointer
This field is used to chain buffers to LCDs.
transmit_length
This field contains the length of the currently transmitted packet.
free_on_xmit
This bit is set if the header of the currently transmitted packet has specified that the packet is to be
freed after transmission.
queue_on_xmit
This bit is set if the header of the currently transmitted packet has specified that the packet is to be
queued after transmission.
dma_on_xmit
This bit is set if the header of the currently transmitted packet has specified that a DMA descriptor is to
be queued after transmission.
ABR Code Variables Definitions
(Page 2 of 7)
Field Name
Field Description