Qos_Recommendation

QOS Parameters :---- Total Bandwidth consumption for different Traffic on a particular interface can be Capped to a particular limit .e.g Video Traffic has to be capped with 40% of the available bandwidth on an interface. To specify max. percentage of total bandwidth that a forwarding class can use , configure a transmit rate. [edit class-of-service] Schedulers { sched-assure { transmit-rate percent 40; This configuration sets the maximum transmission rate for assured forwarding class to 40% of the available bandwidth on interface.If the total throughput of the link is 1.5Mbps At most this class will consume 600kbps. This will help in case where High Priority & Strict Priority are consuming most of the available bandwidth in the Network.This is really helpful in preventing a single application or traffic flow from interface’s entire set of resources. The second most important resource to cap on an interface is Buffer Size. Buffer refers to available memory on an interface card before they are sent downstream. After Router performs the next-hop lookup , it sends the packets to the interface where they are served on the basis of relative priority of the Queue they belong to. While the Queue is serviced Packets being sent for transmission are stored up in Buffers. During periods of congestion When buffers begin to fill new packets being sent on interface can be dropped because there is no place to store them. However the larger the Buffer Size greater is the delay that is why it is recommended to put “Strict High Priority” traffic on least “Buffer Size” & all the other Traffic can be on a bit deeper Buffers. In the periods of congestion when “Rate of Queuing” exceeds the “Rate of Transmission” these Buffers begin to full .“Drop Profiles” can be configured to cater with the congestion of different Queue Buffers. Tail drop profile is a congestion management mechanism that allows switch to drop arriving packets when queue buffers become full or begin to overflow. Tail drop profiles define the meanings of the loss priorities. When you configure tail drop profiles you are essentially setting the value for queue fullness. The queue fullness represents a percentage of the memory used to store packets in relation to the total amount that has been allocated for that specific queue. The queue fullness defines the delay-buffer bandwidth, which provides packet buffer space to absorb burst traffic up to the specified duration of delay. Once the specified delay buffer becomes full, packets with specified drop probability are dropped from the tail of the buffer on the basis of the configured value. Tail Drop Profiles can be set for both Inbound/Outbound traffic :----- set class-of-service schedulers sched-best drop-profile-map loss-priority low protocol any drop-profile inprofile-best-effort set class-of-service schedulers sched-best drop-profile-map loss-priority high protocol any drop-profile outprofile- best-effort drop-profiles { inprofile-Best-effort { fill-level 70 drop-probability 5; fill-level 80 drop-probability 100; } } drop-profiles { Outprofile-Best-effort { fill-level 40 drop-probability 5; fill-level 50 drop-probability 25; fill-level 60 drop-probability 50; fill-level 70 drop-probability 100; } } drop-profiles { inprofile-assured-forwarding { fill-level 90 drop-probability 5; } } drop-profiles { outprofile-assured-forwarding { fill-level 60 drop-probability 5; fill-level 70 drop-probability 25; fill-level 80 drop-probability 50; fill-level 90 drop-probability 100; By default, if you do not configure any drop profile, tail drop profile is in effect and functions as the primary mechanism for managing congestion. In the default tail drop profile, when the fill level is 0 percent, the drop probability is 0 percent. When the fill level is 100 percent, the drop probability is 100 percent. Note :- The default drop profile associated with the packets whose loss priority is low cannot be modified. You can configure custom drop profile only for those packets whose loss priority is high.