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Module 9: QoS Concepts - Coggle Diagram

- - - - Pcket loss
        
        Without any QoS mechanisms in place, packets are processed in the order in which they are received. When congestion occurs, network devices such as routers and switches can drop packets. This means that time-sensitive packets, such as real-time video and voice, will be dropped with the same frequency as data that is not time-sensitive, such as email and web browsing.
      - Network bandwidth is measured in the number of bits that can be transmitted in a single second, or bits per second (bps). For example, a network device may be described as having the capability to perform at 10 gigabits per second (Gbps).
- - - - Video
        
        Data
        
        Most applications use either TCP or UDP. Unlike UDP, TCP performs error recovery. Data applications that have no tolerance for data loss, such as email and web pages, use TCP to ensure that, if packets are lost in transit, they will be resent. Data traffic can be smooth or bursty. Network control traffic is usually smooth and predictable. When there is a topology change, the network control traffic may burst for a few seconds. But the capacity of today’s networks can easily handle the increase in network control traffic as the network converges.
        
        Without QoS and a significant amount of extra bandwidth capacity, video quality typically degrades. The picture appears blurry, jagged, or in slow motion. The audio portion of the feed may become unsynchronized with the video.
      - Voice traffic is predictable and smooth, as shown in the figure. However, voice is very sensitive to delays and dropped packets. It makes no sense to re-transmit voice if packets are lost; therefore, voice packets must receive a higher priority than other types of traffic. For example, Cisco products use the RTP port range 16384 to 32767 to prioritize voice traffic
- - - - Weighed Fair Queuing
        
        Class-Based Weighted Fair Queuing (CBWFQ)
        
        Low Latency Queuing (LLQ)
        
        The Low Latency Queuing (LLQ) feature brings strict priority queuing (PQ) to CBWFQ. Strict PQ allows delay-sensitive packets such as voice to be sent before packets in other queues. LLQ provides strict priority queuing for CBWFQ, reducing jitter in voice conversations, as shown in the figure.
        
        Class-Based Weighted Fair Queuing (CBWFQ) extends the standard WFQ functionality to provide support for user-defined traffic classes. With CBWFQ, you define traffic classes based on match criteria including protocols, access control lists (ACLs), and input interfaces. Packets satisfying the match criteria for a class constitute the traffic for that class. A FIFO queue is reserved for each class, and traffic belonging to a class is directed to the queue for that class.
        
        Weighted Fair Queuing (WFQ) is an automated scheduling method that provides fair bandwidth allocation to all network traffic. WFQ does not allow classification options to be configured. WFQ applies priority, or weights, to identified traffic and classifies it into conversations or flows, as shown in the figure.
      - FIFO has no concept of priority or classes of traffic and consequently, makes no decision about packet priority. There is only one queue, and all packets are treated equally. Packets are sent out an interface in the order in which they arrive, as shown in the figure. Although some traffic may be more important or time-sensitive based on the priority classification, notice that the traffic is sent out in the order it is received.
- - - - Integrated Services
        
        Differentieted Services
        
        The differentiated services (DiffServ) QoS model specifies a simple and scalable mechanism for classifying and managing network traffic. For example, DiffServ can provide low-latency guaranteed service to critical network traffic such as voice or video, while providing simple best-effort traffic guarantees to non-critical services such as web traffic or file transfers.
        
        The IntServ architecture model (RFC 1633, 2211, and 2212) was developed in 1994 to meet the needs of real-time applications, such as remote video, multimedia conferencing, data visualization applications, and virtual reality. IntServ is a multiple-service model that can accommodate many QoS requirements.
      - The basic design of the internet is best-effort packet delivery and provides no guarantees. This approach is still predominant on the internet today and remains appropriate for most purposes. The best-effort model treats all network packets in the same way, so an emergency voice message is treated the same way that a digital photograph attached to an email is treated. Without QoS, the network cannot tell the difference between packets and, as a result, cannot treat packets preferentially.
- - - - Classification and Marketing
        
        Marketing an Layer 2
        
        Marketing and Layer 3
        
        Type of Service and Traffic Class Field
        
        DSCP Values
        
        Class Selector Bits
        
        1 more item...
        
        4 more items...
        
        The Type of Service (IPv4) and Traffic Class (IPv6) carry the packet marking as assigned by the QoS classification tools. The field is then referred to by receiving devices which forward the packets based on the appropriate assigned QoS policy.
        
        IPv4 and IPv6 specify an 8-bit field in their packet headers to mark packets. As shown in the figure, both IPv4 and IPv6 support an 8-bit field for marking: the Type of Service (ToS) field for IPv4 and the Traffic Class field for IPv6.
        
        802.1Q is the IEEE standard that supports VLAN tagging at Layer 2 on Ethernet networks. When 802.1Q is implemented, two fields are added to the Ethernet Frame. As shown in the figure, these two fields are inserted into the Ethernet frame following the source MAC address field.
        
        How a packet is classified depends on the QoS implementation. Methods of classifying traffic flows at Layer 2 and 3 include using interfaces, ACLs, and class maps. Traffic can also be classified at Layers 4 to 7 using Network Based Application Recognition (NBAR).
      - There are three categories of QoS tools, as described in the table: Classification and marking tools Congestion avoidance tools Congestion management tools