If a new call is accepted without a particular limit , QoS for calls in progress may be degraded below an acceptable level, because total bandwidth required for the calls exceeds the network capacity .
Edge-to-edge measurement based admission control (EMBAC), 它使用了 edge-to-edge probe flow and QoS measurement to ensure spare capacity for the new flow. This method neither uses hop-by-hop signaling, nor requires any additional functionality for routers in the backbone network.
A VoIP network is designed to satisfy requirements such as allowed budget and voice quality objectives. While VoIP network is used, test calls are periodically generated between a set of PBX pairs, and voice quality and network-level QoS such as packet loss rates are measured for the test calls.
As the results, problems in voice level QoS as well as network level QoS are identified. These problems are, then, analyzed and fixed through admission control optimization, network optimization, or fault and error recovery, depending on the specific causes.
Each test call undergoes the same admission control as ordinary calls do
Once a test call is established, the artificial voice generation device attached to the call-originating PBX (Device A) sends artificial voice to the voice quality evaluation device attached to the call-terminating PBX (Device B) through the forward VoIP path.
Location-to-Location VoIP traffic demands are represented by traffic matrix a[i,j]
“ i” represents the source
“ j” represents the destination
Parameter Assuming Explain Parameter The number of the VoIP calls k The maximum transfer rate for a VoIP call w (average number of frozen out calls) / (average number of active calls) Freezeout fraction Represents the percentage of time during which speech is present P Edge-to-edge peak pocket loss rate is no more than a pre-determined value “F” F the edge-to-edge blocking probability is no more than this pre-determined value “B” B
 B. Li, M. Hamdi, D. Jiang. Y. T. Hou, and X. Cao, “QoS-enabled voice support in the next-generation Internet: Issues,, existing approaches and challenges,” IEEE Communications Magazine, Vol.38, No.4, April, 2000.
 L. Breslau, E. Q. Knightly, S. Shenker, I. Stoica, and H. Zhang, “Endpoint admission control: architectural issues and performance,” pp. 57-69, SIGCOMM’00, 2000.
 F. Borgonovo, A. Capone, L. Fratta, M. Marchese, and C. Petrioli, “PCP: A bandwidth guaranteed transport services for IP networks,” ICC’ 99, pp. 1999.
 G. Bianchi, A. Capone, C. Petrioli, “Throughput analysis of end-to-end measurement-based admission control in IP,” INFOCOM 2000, 2000.
 V. E.lek, G. Karlsson, and R. Ronngren, “Admission control based on end-to-end measurement,” INFOCOM 2000, 2000.
 M. Schwartz, K. Mase, and D. R. Smith, “Priority channel assignment in tandem DSI,” IEEE Trans. on Communications, Vol.Com-28. No.10, 1980.