QoS Policing & Shaping
Shaping and Policing is a Traffic Condition Technique comes under QoS PHB. Both is used to rate limit traffic on a interface or sub-interface to adhere to a traffic contract or to restrict further congestion of traffic down to the remaining network devices. The way shaping and policing rate-limit traffic is different in a way that shaping buffer the the traffic exceeding a certain bit-rate unlike policing drop the exceeding bit-rate. Shaping A network device buffer packet in it’s output queue to slow down the rate of transmission and decrease the bit-rate. It does so by sending some packets then hold on for some moments and then send some packets again, so on and so fourth. Device uses it’s processor clock rate to achieve the goal. The purpose of shaping is to provide a CIR(committed information rate) without dropping packets. For example a serial link has a 128Kbps of physical […]
Tags   burst phb policing qos shaping token-bucket 
QoS Classification & Marking
Classification & Marking are some technique to identify traffic types and segregate them by defining specific values in some additional fields of the IP/Frame Header. DSCP, Precedence(IP Header) DSCP and Precedence is a part of IP Header TOS field. There is a long story behind the development of DSCP and IP Precedence. So we will discuss long story in short. The TOS field of IP Header is a 8bits word. When using IP Precedence, we use first 3bits and while using DSCP, we use 6bits. In DSCP first 3 bytes called class-selector(CS), which is there to make DSCP compatible with IP Precedence and also to support PCP and MPLS Exp. Then the additional 3 fields in DSCP is called drop-precedence or drop-probability. Whether it’s a DSCP class-selector or Precedence, higher value always takes priority.IP Precedence has 8 values ranging from 0 to 7. Each of the values has special significance […]
Tags   acl class-map policy-map qos 
Quality of Service(QOS) Fundamentals
QOS is a technique to prioritize important traffic over less important traffic based on the class and characteristics of the traffic. For an example a VoIP traffic adheres to low latency and guaranteed delivery with a low amount of bandwidth unlike a FTP traffic adheres more BW. By default a network device treat all kind of traffic in a same manner and use best effort in terms of delivering the packets to the destination. A network device place the traffic in a FIFO(First in First Out) Queue of the Output Buffer to accomplish it. But when there is a Congestion(Queue is full), the packets are likely to be dropped. In this situation the QOS comes into picture to handle the congestion and condition the packet depending on their characteristics. Path Characteristics A packed is originated from a source and to be delivered to a destination, travels many hops and links. […]
Tags   cbwfq cos llq policing qos shaping tos WRED