GRF Overview Simple as UBR from end system view – End system does no policing or traffic shaping – May transmit at line rate of ATM adaptor Modest requirements on ATM network No guarantee of frame delivery Higher layer (e.g. TCP) react to congestion causing dropped frames User can reserve cell rate capacity for each VC – Application can send at min rate without loss Network must recognise frames as well as cells If congested, network discards entire frame All cells of a frame have same CLP setting – CLP=0 guaranteed delivery, CLP=1 best efforts 1

GFR Traffic Contract Peak cell rate PCR Minimum cell rate MCR Maximum burst size MBS Maximum frame size MFS Cell delay variation tolerance CDVT 2

Mechanisms for supporting Rate Guarantees Tagging and policing Buffer management Scheduling 3

Tagging and Policing Tagging identifies frames that conform to contract and those that don’t – CLP=1 for those that don’t Set by network element doing conformance check May be network element or source showing less important frames – Get lower QoS in buffer management and scheduling – Tagged cells can be discarded at ingress to ATM network or subsequent switch – Discarding is a policing function 4

Buffer Management Treatment of cells in buffers or when arriving and requiring buffering If congested (high buffer occupancy) tagged cells discarded in preference to untagged Discard tagged cell to make room for untagged cell May buffer per-VC Discards may be based on per queue thresholds 5

Scheduling Give preferential treatment to untagged cells Separate queues for each VC – Per VC scheduling decisions – E.g. FIFO modified to give CLP=0 cells higher priority Scheduling between queues controls outgoing rate of VCs – Individual cells get fair allocation while meeting traffic contract 6

Components of GFR Mechanism 7

GFR Conformance Definition UPC function – UPC monitors VC for traffic conformance – Tag or discard non-conforming cells Frame conforms if all cells in frame conform – Rate of cells within contract Generic cell rate algorithm PCR and CDVT specified for connection – All cells have same CLP – Within maximum frame size (MFS) 8

QoS Eligibility Test Test for contract conformance – Discard or tag non-conforming cells Looking at upper bound on traffic – Determine frames eligible for QoS guarantee Under GFR contract for VC Looking at lower bound for traffic Frames are one of: – Nonconforming: cells tagged or discarded – Conforming ineligible: best efforts – Conforming eligible: guaranteed delivery 9

Simplified Frame Based GCRA 10