Information Technology Reference
In-Depth Information
When you specify that certain network traffic should go into the priority queue, the
router then not only guarantees that traffic bandwidth, it guarantees it the first band-
width. For example, using pure CBWFQ, Citrix traffic might be guaranteed 50 per-
cent of the bandwidth, but it may get that bandwidth after the router has fulfilled
some other traffic guarantees. When using LLQ, the priority traffic always gets sent
before any other guarantees are fulfilled. As you might guess, this works very well for
VoIP, making LLQ the preferred queuing algorithm for voice.
Although there are many other queuing algorithms available, these three encompass the
methods used by most modern networks.
Applying QoS
By nature, you can apply most of the QoS mechanisms discussed as the network traffic
leaves a router (because you cannot control the order the router receives traffic; it simply
arrives). Table 6-7 summarizes the QoS methods discussed and the direction you can ap-
ply them on your router.
Key
To p i c
Table 6-7
Applying QoS to Input and Output Interfaces of a Router
QoS Methods Applied as Traffic Enters
the Router (Input)
QoS Methods Applied as Traffic Leaves
the Router (Output)
Classification
Congestion Management
Marking
Marking
Policing
Congestion Avoidance
Shaping
Policing
Compression
Fragmentation and Interleaving
As you can see, you can apply some QoS methods (such as policing) in either direction.
Using Cisco AutoQoS
Deploying QoS can be complex (which is why there's a difficult CCNP Voice exam dedi-
cated just to the topic). To help ease the learning curve for QoS, Cisco created a mecha-
nism called AutoQoS, which allows you to enable a variety of QoS mechanisms with little
QoS knowledge. AutoQoS works so well out of the box that many network administrators
who have full knowledge of the QoS capabilities and configuration on Cisco devices use
it. AutoQoS moved to this acclaimed status because it deploys a template QoS configura-
tion in line with Cisco QoS best practices based on the bandwidth and encapsulation you
configured under each of your router or switch interfaces. This template-based QoS de-
ployment offers multiple advantages to manual QoS configuration:
Reduces the time of deployment: Entering a single command on a device is much
less time consuming than the potentially complex QoS configurations.
 
 
Search WWH ::




Custom Search