You work as a network technician at Company.com. Your boss is interested in the QoS
technology in the context of video traffic. What can be said of application of this technology
in this type of network? (Select three)
A.
The access layer is the initial point at which traffic enters the network. Traffic is
marked (or remarked) at Layers 2 and 3 by the access switch as it enters the network, or is
“trusted” that it is entering the network with the appropriate tag.
B.
No traffic marking occurs at the core layer. Layer 2/3 QoS tags are trusted from
distribution layer switches and used to prioritize and queue the traffic as it traverses the core.
C.
Traffic inbound from the access layer to the distribution layer can be trusted or reset
depending upon the ability of the access layer switches. Priority access into the core is
provided based on Layer 3 QoS tags.
D.
IP precedence, DSCP, QoS group, IP address, and ingress interface are Layer 2
characteristics that are set by the access layer as it passes traffic to the distribution layer.
The distribution layer, once it has made a switching decision to the core layer, strips these
off.
E.
MAC address, Multiprotocol Label Switching (MPLS); the ATM cell loss priority (CLP)
bit, the Frame Relay discard eligible (DE) bit, and ingress interface are established by the
voice submodule (distribution layer) as traffic passes to the core layer.
F.
The distribution layer inspects a frame to see if it has exceeded a predefined rate of
traffic within a certain time frame, which is typically a fixed number internal to the switch. If a
frame is determined to be in excess of the predefined rate limit, the CoS value can be
marked up in a way that results in the packet being dropped.
Explanation:
Three main types of QoS policies are required within the Campus:
1)Classification and Marking
2)Policing and Markdown
3)Queuing
Classification, marking, and policing should be performed as close to the traffic-sources as
possible, specifically at the Campus Access-Edge. Queuing, on the other hand, needs to be
provisioned at all Campus Layers (Access, Distribution, Core) due to oversubscription ratios.
Distribution and edge switches can be configured to trust the COS markings of incoming
traffic, rest the COS value to 0, or reset the COS value to a different value. These switches
also perform the necessary functions to map the layer 2 COS values to a layer 3 TOS or
DSCP value when sending traffic into the cloud.