Telecom formulas
ATM
service categories:
CBR |
Constant Bit Rate |
rt-VBR |
Realtime Variable Bit Rate |
nrt-VBR |
Nonrealtime Variable Bit
Rate |
ABR |
Available Bit Rate |
UBR |
Unspecified Bit Rate |
GFR |
Guaranteed Frame Rate |
Traffic
parameters
PCR/SCR/MCR
Peak/Sustained/Minimum
Cell Rate
CDVT
Cell
Delay Variation Tolerance
BT
Burst
Tolerance
Qos
Parameters
CLR
Cell
Loss Ration
CDV
Cell
Delay Variation
CTD
Cell
Transfer Delay (Max, Mean)
CER
Cell
error ratio
ATM header (total Virtual Circuit ID = virtual path ID +
virtual channel ID)
virtual path ID |
|
virtual path
ID
|
virtual channel ID |
Virtual Channel ID | |
Virtual Channel ID | Payload type(3) / CLP(1) |
crc-8 checksum |
realtime | non-realtime;
no delay requirements |
||||
Attribute | CBR | rt-VBR | nrt-VBR | ABR | UBR |
CLR | specified | specified | specified | specified | no |
CDV/CTD MaxCTD |
CDV + maxCTD |
CDV + maxCTD |
MeanCTD [?], larger than for rt |
no | no |
PCR, CDVT | specified | specified | specified | specified | specified |
SCR, BT |
N/A |
specified |
specified, larger BT than rt-VBR |
N/A |
N/A |
MCR | N/A |
N/A |
N/A |
specified |
N/A |
Congestion control |
no |
no |
no |
yes |
no |
Effective bandwidth requirement (in cells per unit time) for a connection with average cell spacing T, maximum acceptable delay D and maximum queue M:
max(1/T, M/D).
The bandwidth of 1/T is needed to keep up with the average cell spacing, and the bandwidth of M/D is needed to process a burst of size M within the time constraint D.