The following table lists terms and definitions used in this Quality of Service configuration discussion.
Quality of Service Configuration Terms and Definitions
| Term | Definition |
|---|---|
| Class of Service (CoS) | The grouping of priority and forwarding behaviors that collectively determine packet bandwidth behavior as it transits the link, including: 802.1p, IP ToS rewrite, priority Transmit Queue (TxQ), Inbound and/or outbound Rate Limiter (IRL) and outbound rate shaper. |
| DSCP | Differentiated Services Code Point. The lower 6 bits of the ToS field defined by RFC 2474. |
| Flows | In a QoS context, a sequence of IP packets that share a common class of service and forwarding treatment as they transit the interface. |
| Forwarding Treatment | Queue behavior during the packet egress stage (strict priority, weighted fair, hybrid). |
| Jitter | The change in a flow‘s packet spacing on the link due to the bursty and congestive nature of the IP network. This irregular spacing - jitter - can severely degrade the quality of voice calls or multimedia presentations. |
| Port Group | The grouping of ports based upon the same CoS features and port type. |
| Port Type | The differentiation of ports based upon TxQ, IRL, ORL, and flood control resource capabilities. |
| Priority | The preference of one packet (classification) or queue (packet forwarding) over another. |
| Quality of Service (QoS) | A bandwidth management mechanism able to preferentially treat packets based upon packet classification and forwarding treatment. |
| Rate Limiting | The bounding of bandwidth used by a QoS packet flow such that excess packets are dropped/clipped. |
| Rate Shaping | The rescheduling of bursty traffic while in the queue based upon packet buffering such that traffic beyond the configured bandwidth threshold is delayed until bandwidth usage falls below the configured threshold. |
| Type of Service (ToS) | An 8-bit field defined by RFC 1349 used for the prioritization of packets within a QoS context. |
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