Quality of Service (QoS) Congestion Management Notes
Of all the tools within the QoS toolset, congestion management tools, also known as queuing tools, provide the biggest impact on application service levels. Whenever packets enter a device faster than can exit it, congestion exists and this is where queuing tools come into play. Queuing tools are only engaged when congestion exists, otherwise packets are sent as soon as they arrive. When congestion does exist, packets must be buffered, or queued, to mitigate dropping.
Packet markings, or lack thereof, affect queuing policies, so queuing policies are complementary and have a dependence on classification and marking policies.
Scheduling vs. Queuing
These two terms are often incorrectly used interchangeably – they are two different things. Scheduling determines how a frame or packet exits a device. Whenever packets enter a device faster than they can exit it, as is the case with speed mismatches (ex. Gigabit Ethernet traffic heading to a WAN interface), congestion can occur. Devices have buffers that allow the temporary storing and subsequent scheduling of these backed-up packets, and this process is called queuing.
Inbound traffic > Queuing (During congestion) > Scheduling > Outbound traffic
- Queuing – orders packets in linked output buffers. Only Continue reading
