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Module 9: QoS Concepts, image, image, image - Coggle Diagram

- - - - Guarantee bandwidth and increase buffer space for fragile flows, using WFQ, CBWFQ, and LLQ for prioritized forwarding.
  - - - 9.5.11 Congestion Avoidance:
        Congestion management uses queuing and scheduling to buffer or drop excess traffic before transmission. Congestion avoidance proactively monitors traffic to prevent bottlenecks by selectively dropping packets as queues fill up. Cisco IOS QoS uses WRED to manage congestion by allowing TCP traffic to adjust before buffers overflow, preventing tail drops and optimizing performance. UDP traffic, like voice, relies on queuing and compression to minimize packet loss.
        
        9.5.12 Shaping and Policing:
        
        Traffic shaping and traffic policing prevent congestion in Cisco IOS QoS.
        
        Traffic shaping buffers excess packets and schedules them for later transmission, smoothing the output rate. It requires sufficient memory and a scheduling function like CBWFQ or LLQ. Shaping applies only to outbound traffic.
        
        Traffic policing is used for inbound traffic, dropping or remarking packets when the rate exceeds the configured limit. It is often used by service providers to enforce CIR, sometimes allowing bursts if the network permits.
- - - - 9.3.4 Weighted Fair Queuing (WFQ):
        Weighted Fair Queuing (WFQ) automatically allocates bandwidth fairly among traffic flows without manual classification. It prioritizes low-volume, interactive traffic (e.g., Telnet, voice) while sharing remaining bandwidth among high-bandwidth flows (e.g., FTP).
        
        the weighted fair queuing has limitations like:
        
        Not compatible with tunneling or encryption, as they alter packet data used for classification.
        Lacks the precise bandwidth control of CBWFQ.
        
        9.3.5 Class-Based Weighted Fair Queuing (CBWFQ):
        Class-Based Weighted Fair Queuing (CBWFQ) enhances WFQ by allowing user-defined traffic classes based on protocols, ACLs, and interfaces. Each class has a dedicated FIFO queue with assigned bandwidth and queue limits, ensuring guaranteed bandwidth during congestion.
        
        The class-based weighted fair queuing has also limitations like:
        Once a queue reaches its limit, excess packets are dropped (tail drop).
        Does not prioritize real-time traffic like LLQ.
        
        9.3.6 Low Latency Queuing (LLQ):
        Low Latency Queuing (LLQ) enhances CBWFQ by adding strict priority queuing (PQ), ensuring delay-sensitive traffic (e.g., voice) is sent first, reducing jitter. Without LLQ, CBWFQ treats all classes fairly, which can cause delays in real-time traffic.
        
        And also the low latency queuing has limitation:
        Prioritizing too much traffic in the PQ can starve other queues.
        Cisco recommends reserving the priority queue for voice traffic only.
- - - - Video traffic has unique characteristics and places greater demands on the network. Without QoS and additional bandwidth capacity, video quality can deteriorate, showing blurry images, audio desynchronization, and slow playback.
    - - Data traffic, which uses TCP or UDP, can be smooth or bursty, such as when using FTP to download large files, consuming all available bandwidth. While data traffic is less sensitive to drops and delays compared to voice or video, network administrators must ensure an adequate quality of experience (QoE). Additionally, network control traffic, generally predictable, may experience brief increases during topology changes, which modern networks can handle efficiently.
    - - Voice traffic is uniform and predictable, but highly sensitive to delays, jitter, and packet loss. Since retransmitting lost voice packets is not feasible, these packets must have high priority