flowspec - Sockets 2 Reference

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flowspec

typedef struct _flowspec

{

int32 TokenRate; /* In Bytes/sec */

int32 TokenBucketSize; /* In Bytes */

int32 PeakBandwidth; /* In Bytes/sec */

int32 Latency; /* In microseconds */

int32 DelayVariation; /* In microseconds */

GUARANTEE LevelOfGuarantee; /* Guaranteed, Predictive, */

/* Best Effort, etc. */

int32 CostOfCall; /* Reserved for future use, */

/* must be set to 0 now */

int32 NetworkAvailability; /* read-only: */

/* 1 if accessible, */

/* 0 if not */

} FLOWSPEC, FAR * LPFLOWSPEC;

Members
TokenRate
A token bucket model is used to specify the rate at which permission to send traffic (or credits) accrues. In the model, the token bucket has a maximum volume, TokenBucketSize, and continuously fills at a certain rate TokenRate. If the bucket contains sufficient credit, the application can send data and reduce the available credit by that amount. If sufficient credits are not available, the application must wait or discard the extra traffic.

A value of -1 in the members TokenRate and TokenBucketSize indicates that no rate-limiting is in force. The TokenRate is expressed in bytes per second.

If an application has been sending at a low rate for a period of time, it can send a large burst of data all at once until it runs out of credit. Having done so, it must limit itself to sending at TokenRate until its data burst is exhausted.

In video applications, the TokenRate is typically the average bit rate peak to peak. In constant rate applications, the TokenRate is equal to the PeakBandwidth.

TokenBucketSize

The TokenBucketSize is expressed in bytes.

The TokenBucketSize is the largest typical frame size in video applications. In constant rate applications, the TokenBucketSize is chosen to accommodate small variations.

PeakBandwidth
This member, expressed in bytes/second, limits how fast packets may be sent back to back from the application. Some intermediate systems can take advantage of this information resulting in a more efficient resource allocation.

Latency

Latency is the maximum acceptable delay between transmission of a bit by the sender and its receipt by the intended receiver(s), expressed in microseconds. The precise interpretation of this number depends on the level of guarantee specified in the QOS request.

DelayVariation
This the difference, in microseconds, between the maximum and minimum possible delay that a packet will experience. This value is used by applications to determine the amount of buffer space needed at the receiving side in order to restore the original data transmission pattern.

LevelOfGuarantee

This is the level of service being negotiated for. The GUARANTEE type is enumerated below. Four levels of service are defined: Guaranteed, Guaranteed Delay, Predictive, Controlled Load and Best Effort.

The reason for defining both predictive and guaranteed service is that predictive services may achieve substantially better performance given the same level of network resource usage, while guaranteed service provides the mathematical level of certainty needed by selected applications. Specific providers may implement none, one, or both of these services.

Best effort service is just a hint to the service provider and should be always supported.

CostOfCall
This is just a place holder for now and should always be set to 0 until we can come up with a meaningful cost metric.

NetworkAvailability
Network Availability - This is a read-only field for the transport provider to use in indicating to the application whether or not the underlying media is currently accessible or temporarily unavailable. The typical example for a temporarily inaccessible network would be a wireless interface that has lost contact with the base station (due, for example to terrain interference). Any change in this value should result in an FD_QOS indication to applications that have registered interest in same.

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