What are the two categories of QoS that applications generally can bebroken into?
Applications generally can be broken into either latency-sensitive or latency-insensitive.
What term involves delaying the flow of data traffic designated as less important compared to other traffic streams?
Traffic shaping involves delaying the flow of data traffic designated as less important compared to other traffic streams.
QoS describes the strategies used to manage and increase the flow of networktraffic. QoS features enable administrators to predict bandwidth use, monitorthat use, and control it to ensure that bandwidth is available to the applicationsthat need it. These applications generally can be broken into two categories:
. Latency-sensitive: These applications need bandwidth for quick deliverywhere network lag time impacts their effectiveness. This includesvoice and video transfer. For example, voice over IP (VoIP) would bedifficult to use if there were a significant lag time in the conversation.
. Latency-insensitive: Controlling bandwidth also involves managinglatency-insensitive applications. This includes bulk data transfers such ashuge backup procedures and File Transfer Protocol (FTP) transfers.
Essentially what happensis that traffic is placed in order based on its importance on delivery time. Alldata is given access, but the more important and latency-sensitive data is givenhigher priority.
Traffic shaping is a QoS strategy designed to enforce prioritization policies on the transmission of data throughout the network. It is intended to reduce latency by controlling the amount of data that flows into and out of the network. Traffic is categorized, queued, and directed according to network policies.
Methods used for traffic shaping?
Shaping by application: Administrators can configure a traffic shaperby categorizing specific types of network traffic and assigning that category a bandwidth limit. For example, traffic can be categorized usingFTP. The rule can specify that no more than 4Mbps be dedicated for FTP traffic. This same principle can apply to Telnet sessions, streaming audio, or any other application coming through the network.
. Shaping network traffic per user: Every network has users who use more bandwidth than others. Some of this might be work-related, but more often than not, it is personal use. In such a case, you might need to establish traffic shaping on a per-user basis. Traffic shapers allow administrators to delegate a certain bandwidth to a user. For instance, Bob from accounting is allowed no more than 256Kbps. This doesn’t limit what the user can access, just the speed at which that content can be accessed.
. Priority shaping: One important consideration when looking at trafficshaping is determining which traffic is mission-critical and which is lessso. In addition to setting hard or burstable traffic limits on a per-applicationor per-user basis, traffic shaping devices can also be used to definethe relative importance, or priority, of different types of traffic. For example, in an academic network where teaching and research are most important, recreational uses of the network (such as network games orpeer-to-peer file-sharing application traffic) can be allowed bandwidth only when higher-priority applications don’t need it.
Remember that traffic shaping involves delaying the flow of data traffic that is designated as less important compared to other traffic streams.
Caching is an important consideration when optimizing network traffic. For example, as discussed in Chapter 4, “Components and Devices,” proxy servers use caching to limit the number of client requests that go to the Internet. Instead, the requests are filled from the proxy server’s cache. Recall from Chapter 4 that when a caching proxy server has answered a request for a webpage, the server makes a copy of all or part of that page in its cache. Then,when the page is requested again, the proxy server answers the request from the cache rather than going back out to the Internet. For example, if a client on a network requests the web page www.comptia.org, the proxy server can cache the contents of that web page. When a second client computer on the network attempts to access the same site, that client can grab it from theproxy server cache; accessing the Internet is not necessary. This greatly reduces the network traffic that has to be filtered to the Internet, a significant gain in terms of network optimization.
Rules that can be established to cache:
- . What websites to cache
- . How long the information is cached
- . When cached information is updated
- . The size of cached information
- . What type of content is cached
- . Who can access the cache
Advantages and disadvantage of caching?
The advantages of properly configured caching are clear—reduced bandwidth, and latency and increased throughput. One possible disadvantage of caching is receiving out of date files because you obtain content from the caching engine and not the website itself.
Caching improves network performance by caching content where?
❍ A. Locally.
❍ B. On a remote server.
❍ C. In archives.
❍ D. Caching does not improve network performance
A. Caching improves network performance by locally caching content, thereby limiting surges in traffic.
Which of the following would most likely use latency-sensitive QoS?
❍ A. FTP
❍ B. DNS
❍ C. SNMP
❍ D. VoIP
D. Latency-sensitive applications include those for voice and video transfer. For example, voice over IP (VoIP) would be difficult to use if there were a significant lag time in the conversation.