Cisco Systems 8600 Series manual UBR Connection, UPC Overview

Traffic Policing Examples

Figure 7-21 UBR Connection, UPC Overview

UBR Traffic

Multiple PVCs

CPE

Cells per sec.

Time

Verify	To UPC for each
	individual PVC
VPIs,		Policing
VCIs

PCR

SCR=0 when CLP=Yes (UBR.2)

For UBR connections, the first bucket polices PCR compliance within the CDVT(0+1) limits. The second bucket, used when CLP is set to Yes, tags all CLP(0) cells.

Clumping

(Cells arriving early, i.e, at a higher than contracted rate)

Cells arriving late

(at a less than

contracted

cell rate)

TAT TAT TAT TAT TAT TAT TAT TAT

CLP(0+1) cells to Leaky Bkt 1

5	4	3		2	1
CLP=1	CLP=0	CLP=1	CLP=0		CLP=0
			5		3	CLP(1) cells compliant with Leaky Bkt 1, admit to network
		CLP=1			CLP=1
Time					4	2	1	4	2	1
interval				CLP=0		CLP=0	CLP=0	CLP=0	CLP=0	CLP=0
variations				CLP(0) cells					Admit to network
	+
CDVT(0+1)				compliant with				+
Leaky Bkt 1				Leaky Bkt 1,		BT+ CDVT
				applied to
						Leaky Bkt 2
PCR(0+1)				Leaky Bkt 2
Leaky Bkt 1						SCR=0
	discards							For CLP = No, (i.e., UBR.1),
	if depth >							Leaky Bkt 2 sees no traffic.
CDVT(0+1)

Note: The notation 0, 1, and 0+1 refers to the types of cell being specified: cells with CLP set to 0, CLP set to 1, or both types of cells, repectively. For example, CLP(0), CLP(1), and CLP(0+1)

For CLP = Yes, (i.e., UBR.2), CLP(0) cells that were compliant with Leaky Bkt 1 are sent to Leaky Bkt 2. Since SCR = 0 for Leaky Bkt 2, the bucket is essentially always full, and all cells are therefore tagged with CLP being set to 1. This allows the network to recognize these UBR cells as lower priority and available for discard in the event of network congestion.

S6351

7-36Cisco BPX 8600 Series Reference