21 - Introducing QoS Flashcards
Applications such as FTP and TFTP are considered __ applications. Both are used to send and receive files. Typically, a user selects a group of files that need to be retrieved and then starts the transfer. Once the download starts, no additional human interaction is required. Even with low bandwidth, the download will complete eventually.
batch
__ applications are applications in which the user waits for a response. Because these applications require human interaction, response times are more important than batch applications, but still are not critical.
Interactive
__ applications such as voice and video applications also involve human interaction. Because of the amount of information that is transmitted, bandwidth is critical. In additional, because these applications are time-critical, a delay on the network can cause a problem.
Real-time
What are the characteristics of data traffic?
- Smooth/bursty
- Benign/greedy
- Drop-insensitive
- Delay-insensitive
- TCP retransmits
What are the characteristics of voice traffic?
• Smooth • Benign • Drop-sensitive • Delay-sensitive • UDP priority • One-way requirements o Latency < 150ms o Jitter < 30ms o Loss <1% o Bandwidth 30-128 kbps
What are the characteristics of video traffic?
• Smooth • Benign • Drop-sensitive • Delay-sensitive • UDP priority • One-way requirements o Latency < 150ms o Jitter < 30ms o Loss < 0.1-1% o Bandwidth 384 kbps – 20+ Mbps
The fundamental purpose of __ is to manage contention for network resource to maximise the end-user experience of a session. Because not all packets are equal, you should not treat them equally.
QoS
When there is __ on a link, less important traffic is delayed or dropped in favour of delay-sensitive, business-important traffic.
contention
QoS gives priority to some sessions over other sessions. Packets of __-sensitive sessions bypass queues of packets belonging to __-sensitive sessions. When queue buffers overflow, packets are dropped on the session that can recover from the loss or those sessions that can be eliminated with minimal business impact.
delay, non-delay
Generally, you can place QoS tools into these different categories:
Classification and marking .
Policing, shaping and re-marking tools –
Congestion management or scheduling tools
Link specific tools
These tools analyse sessions to determine which traffic class they belong to and therefore which treatment the packets in the session should receive. Classification should happen as few times as possible because it takes time and uses resources. For that reason, packets are marked after classification.
Classification and marking
These tools assign different classes of traffic to certain portions of network resources. When traffic exceeds available resources, some traffic might be dropped, delayed, or re-marked to avoid congestion on a link.
Policing, shaping and re-marking tools
With these tools, when traffic exceeds network resources that are available, traffic is queued. Queued traffic will await available resources. Traffic classes that do not handle delay well are better off being dropped unless there is a guarantee delay-free bandwidth for that traffic class.
Congestion management or scheduling tools
With these tools, there are certain types of connections, such as WAN links, that can be provisioned with special traffic handling tools. One such example is fragmentation
Link specific tools
The ___ is a point in the network where packet markings are not necessarily trusted. You can create, remove, or rewrite markings at that point. The borders of a trust domain are the network locations where packet markings are accepted and acted upon.
trust boundary
A __ is a tool that inspects packets within a field to identify the type of traffic that the packet is carrying. Traffic is then directed to a policy enforcement mechanism for that type of traffic.
classifier
___ mechanisms include marking, queue, policing, shaping or any combination of those mechanisms.
Policy enforcement
A __ is a tool that writes a value in the header of the packet, frame, cell, tag, or label. The aim of ___ is to preserve the classification decision that the classifier tool reached. Devices that follow the device where __ was performed do not have to do classification and analysis to determine how to treat the packet.
marker, marking
