Chapter 6 - Quality of Service
Best-effort model Integrated services (IntServ) Differentiated services (DiffServ)
The three models for implementing QoS are:
Queuing
QoS Sequence Classification and marking (Classifying/marking) -> Congestion Avoidance (Policing and Selective Dropping) -> Congestion Management (______________, Scheduling and Shaping)
High, Normal, Medium, Low
Priority Classification (4):
increase, bandwidth, buffer space, dropping
The following approaches can prevent drops in sensitive applications: - __________________ link capacity to ease or prevent congestion. - Guarantee enough ____________ and increase ___________ to accommodate bursts of traffic from fragile flows. There are several mechanisms available in Cisco IOS QoS software that can guarantee bandwidth and provide prioritized forwarding to drop-sensitive applications. Examples being WFQ, CBWFQ, and LLQ. - Prevent congestion by _____________ lower-priority packets before congestion occurs. Cisco IOS QoS provides queuing mechanisms that start dropping lower-priority packets before congestion occurs. An example being weighted random early detection (WRED).
Serialization Delay
The fixed amount of time it takes to transmit a frame from the NIC to the wire is known as what?
best-effort
Which model based on these drawbacks? There's no guarantees of delivery. Packets will arrive whether they can and in any order possible, if they arrive t all. No packets have preferential treatment. Critical data is treated the same as casual email is treated.
De-jitter Delay
Which type of delay? The fixed amount of time it takes to buffer a flow of packets and then send them out in evenly spaced intervals.
Code delay
Which type of delay? The fixed amount of time it takes to compress data at the source before transmitting to the first internetworking device, usually a switch.
Serialization Delay
Which type of delay? The fixed amount of time it takes to transmit a frame onto the wire.
Packetization Delay
Which type of delay? The fixed time it takes to encapsulate a packet with all the necessary header information.
Queuing Delay
Which type of delay? The variable amount of time a frame or packet waits to be transmitted on the link.
Propagation Delay
Which type of delay? The variable amount of time it takes for the frame to travel between the source and destination.
Quality of Service (QoS)
? is an ever increasing requirement of networks today. New applications available to users, such as voice and live video transmissions, create higher expectations for quality delivery.
Congestion
? occurs when multiple communication lines aggregate onto a single device such as a router, and then much of that data is placed on fewer outbound interfaces, or onto a slower interface. Congestion can also occur when large data packets prevent smaller packets from being transmitted in a timely manner.
First-In, First-Out (FIFO) Weighted Fair Queuing (WFQ) Class-Based Weighted Fair Queuing (CBWFQ) Low Latency Queuing (LLQ)
A number of queuing algorithms are available. For the purposes of this course, we will focus on the following (4):
Experience
Although data traffic is relatively insensitive to drops and delays compared to voice and video, a network administrator still needs to consider the quality of the user experience, sometimes referred to as Quality of ______________or QoE.
scalability
As a host forwards traffic to a router, the router classifies the flows into aggregates (classes) and provides the appropriate QoS policy for the classes. DiffServ enforces and applies QoS mechanisms on a hop-by-hop basis, uniformly applying global meaning to each traffic class to provide both flexibility and ______________. For example, DiffServ could be configured to group all TCP flows as a single class, and allocate bandwidth for that class, rather than for the individual flows as IntServ would do.
Best-effort model
Based on the description - which of the three models for implementing QoS is this? - Not really an implementation as QoS is no t explicitly configured. - Use when QoS is not required.
Differentiated services (DiffServ)
Based on the description - which of the three models for implementing QoS is this? - Provides high scalability and flexibility in implementing QoS. - Network devicews recognize traffic classes and provided different levels of QoS to different traffic classes.
Integrated services (IntServ)
Based on the description - which of the three models for implementing QoS is this? - Provides very high QoS to IP packets with guaranteed delivery. - It defines a signaling process for applications to signal to the network that they require special QoS for a period and that bandwidth should be reserved. - However, ______________ can severely limit the scalability of a network.
Marking
Based on the description, which QoS Mechanism terminology is this? Adding a value to the packet header
802.1Q
Based on the description, which QoS Mechanism terminology is this? An IEEE specification for implementing VLANs in Layer 2 switched networks.
Classification
Based on the description, which QoS Mechanism terminology is this? Determines what class of traffic packets or traffic belong to.
WRED algorithm
Based on the description, which QoS Mechanism terminology is this? Provides buffer management and allows TCP traffic to throttle back before buffers are exhausted.
Congestion Management
Based on the description, which QoS Mechanism terminology is this? Queuing and scheduling methods where excess traffic is buffered while it waits to be sent on an egress interface.
Traffic Shaping
Based on the description, which QoS Mechanism terminology is this? Retains excess packets in a queue and then schedules the excess for later transmissions over increments of time.
CoS Bits
Based on the description, which QoS Mechanism terminology is this? Used to identify a Layer 2 QoS Marking
Traffic Policing
Based on the description, which QoS Mechanism terminology is this? When the traffic rates reaches the configured maximum rate, excess traffic is dropped.
Assured Forwarding (AF)
Based on the description, which category for 64 DSCP values? RFC 2597 defines AF to use the 5 most significant DSCP bits to indicate queues and drop preference. As shown in Figure 3, the first 3 most significant bits are used to designate the class. Class 4 is the best queue and Class 1 is the worst queue. The 4th and 5th most significant bits are used to designate the drop preference. The 6th most significant bit is set to zero. The AFxy formula shows how the AF values are calculated. For example, AF32 belongs to class 3 (binary 011) and has a medium drop preference (binary 10). The full DSCP value is 28 because you include the 6th 0 bit (binary 011100).
Expedited Forwarding (EF), voice
Based on the description, which category for 64 DSCP values? RFC 3246 defines EF as the DSCP decimal value 46 (binary 101110). The first 3 bits (101) map directly to the Layer 2 CoS value 5 used for voice traffic. At Layer 3, Cisco recommends that EF only be used to mark ___________ packets.
Best-Effort (BE)
Based on the description, which category for 64 DSCP values? This is the default for all IP packets. The DSCP value is 0. The per-hop behavior is normal routing. When a router experiences congestion, these packets will be dropped. No QoS plan is implemented.
3, Class Selector
Because the first __ most significant bits of the DSCP field indicate the class, these bits are also called the _________________ (CS) bits. As shown in Figure 4, these 3 bits map directly to the 3 bits of the CoS field and the IPP field to maintain compatibility with 802.1p and RFC 791.
mark
Before a packet can have a QoS policy applied to it, the packet has to be classified. Classification and marking allows us to identify or "___________" types of packets. Classification determines the class of traffic to which packets or frames belong. Only after traffic is marked can policies be applied to it.
30
Cisco products use the RTP port range 16384 to 32767 to prioritize voice traffic. Voice can tolerate a certain amount of latency, jitter, and loss without any noticeable effects. Latency should be no more than 150 milliseconds (ms). Jitter should be no more than 30 ms, and voice packet loss should be no more than 1%. Voice traffic requires at least ___ Kbps of bandwidth.
avoidance
Congestion management includes queuing and scheduling methods where excess traffic is buffered or queued (and sometimes dropped) while it waits to be sent on an egress interface. Congestion __________________ tools are simpler. They monitor network traffic loads in an effort to anticipate and avoid congestion at common network and internetwork bottlenecks before congestion becomes a problem.
Insensitive
Data - Smooth /Bursty - Benign/Greedy - Drop ____________ - Delay ___________ - TCP retransmits
Latency
Delay or ______________ refers to the time it takes for a packet to travel from the source to the destination. Two types of delays are fixed and variable. A fixed delay is a specific amount of time a specific process takes, such as how long it takes to place a bit on the transmission media. A variable delay take an unspecified amount of time and is affected by factors such as how much traffic is being processed.
soft
DiffServ is not an end-to-end QoS strategy because it cannot enforce end-to-end guarantees. However, DiffServ QoS is a more scalable approach to implementing QoS. Unlike IntServ and hard QoS in which the end-hosts signal their QoS needs to the network, DiffServ does not use signaling. Instead, DiffServ uses a " _______ QoS" approach. It works on the provisioned-QoS model, where network elements are set up to service multiple classes of traffic each with varying QoS requirements.
priority
FIFO has no concept of ___________ or classes of traffic and consequently, makes no decision about packet priority. There is only one queue, and all packets are treated equally. Packets are sent out an interface in the order in which they arrive, as shown in the figure. Although some traffic is more important or time-sensitive based on the priority classification, notice that the traffic is sent out in the order it is received.
fastest
FIFO, which is the __________ method of queuing, is effective for large links that have little delay and minimal congestion. If your link has very little congestion, FIFO queuing may be the only queuing you need to use.
bandwidth, queue, discards
For CBWFQ: To characterize a class, you also specify the queue limit for that class, which is the maximum number of packets allowed to accumulate in the queue for the class. Packets belonging to a class are subject to the ____________ and ____________ limits that characterize the class. After a queue has reached its configured queue limit, adding more packets to the class causes tail drop or packet drop to take effect, depending on how class policy is configured. Tail drop means a router simply ____________ any packet that arrives at the tail end of a queue that has completely used up its packet-holding resources. This is the default queuing response to congestion. Tail drop treats all traffic equally and does not differentiate between classes of service.
bandwidth
For CBWFQ: When a class has been defined according to its match criteria, you can assign it characteristics. To characterize a class, you assign it ____________, weight, and maximum packet limit. The bandwidth assigned to a class is the guaranteed bandwidth delivered to the class during congestion.
all
For Congestion Avoidance: When the queue is below the minimum threshold, there are no drops. As the queue fills up to the maximum threshold, a small percentage of packets are dropped. When the maximum threshold is passed, ____ packets are dropped.
jitter
For example, when a router receives a Real-Time Protocol (RTP) digital audio stream for Voice over IP (VoIP), it must compensate for the _________ that is encountered. The mechanism that handles this function is the playout delay buffer. The playout delay buffer must buffer these packets and then play them out in a steady stream as shown in Figure 1. The digital packets are later converted back to an analog audio stream.
digital signal processor
For losses as small as one packet, the _______________________ (DSP) interpolates (inserts) what it thinks the audio should be and no problem is audible to the user. However, when jitter exceeds what the DSP can do to make up for the missing packets, audio problems are heard.
Queue
Holds packets in memory until resources become available to transmit them is known as what?
Network Based Application Recognition
How a packet is classified depends on the QoS implementation. Methods of classifying traffic flows at Layer 2 and 3 include using interfaces, ACLs, and class maps. Traffic can also be classified at Layers 4 to 7 using ____________________________ (NBAR). Note: NBAR is a classification and protocol discovery feature of Cisco IOS software that works with QoS features. NBAR is out of scope for this course.
non, end-to-end
How traffic is marked usually depends on the technology. The decision of whether to mark traffic at Layers 2 or 3 (or both) is not trivial and should be made after consideration of the following points: Layer 2 marking of frames can be performed for __________-IP traffic. Layer 2 marking of frames is the only QoS option available for switches that are not "IP aware". Layer 3 marking will carry the QoS information __________________.
Type of Service (TOS), Traffic Class
IPv4 and IPv6 specify an 8-bit field in their packet headers to mark packets. As shown in Figure 1, both IPv4 and IPv6 support an 8-bit field for marking, the ____________________ (ToS) field for IPv4 and the _______________ field for IPv6. These fields are used to carry the packet marking as assigned by the QoS classification tools. The field is then referred to by receiving devices to forward the packets based on the appropriate assigned QoS policy.
discarded
If the jitter is so large that it causes packets to be received out of the range of this buffer, the out-of-range packets are ______________ and dropouts are heard in the audio.
First-In, First-Out (FIFO)
In its simplest form, _________ queuing, also known as first-come, first-served (FCFS) queuing, involves buffering and forwarding of packets in the order of arrival.
Resource Reservation Protocol
In the IntServ model, the application requests a specific kind of service from the network before sending data. The application informs the network of its traffic profile and requests a particular kind of service that can encompass its bandwidth and delay requirements. IntServ uses the _______________________ (RSVP) to signal the QoS needs of an application's traffic along devices in the end-to-end path through the network. If network devices along the path can reserve the necessary bandwidth, the originating application can begin transmitting. If the requested reservation fails along the path, the originating application does not send any data.
admission control
In the IntServ model, the edge router performs ______________________ based on information from the application and available network resources. The network commits to meeting the QoS requirements of the application as long as the traffic remains within the profile specifications. The network fulfills its commitment by maintaining the per-flow state and then performing packet classification, policing, and intelligent queuing based on that state.
voice, data
In the early 2000s, the predominant types of IP traffic were __________ and ____________. Voice traffic has a predictable bandwidth need and known packet arrival times. Data traffic is not real-time and has unpredictable bandwidth need. Data traffic can temporarily burst, as when a large file is being downloaded. This bursting can consume the entire bandwidth of a link.
microflows
IntServ provides a way to deliver the end-to-end QoS that real-time applications require by explicitly managing network resources to provide QoS to specific user packet streams, sometimes called ____________________. It uses resource reservation and admission-control mechanisms as building blocks to establish and maintain QoS. This practice is similar to a concept known as "hard QoS." Hard QoS guarantees traffic characteristics, such as bandwidth, delay, and packet-loss rates, from end to end. Hard QoS ensures both predictable and guaranteed service levels for mission-critical applications.
share
Low-bandwidth traffic streams, which comprise the majority of traffic, receive preferential service, allowing their entire offered loads to be sent in a timely fashion. High-volume traffic streams ___________ the remaining capacity proportionally among themselves.
packet header
Marking means that we are adding a value to the ___________________. Devices receiving the packet look at this field to see if it matches a defined policy. Marking should be done as close to the source device as possible. This establishes the trust boundary.
error
Most applications use either TCP or UDP. Unlike UDP, TCP performs __________ recovery. Data applications that have no tolerance for data loss, such as email and web pages, use TCP to ensure that, if packets are lost in transit, they will be resent. Data traffic can be smooth or bursty. Network control traffic is usually smooth and predictable. When there is a topology change, the network control traffic may burst for a few seconds. But the capacity of today's networks can easily handle the increase in network control traffic as the network converges.
Aggregation, Speed Mismatch (1000 Mbps to 100 mbps or vice versa), LAN to WAN (also a change in BPS)
Name 3 examples of Congestion Points:
Code Delay Packetization Delay Queuing Delay Serialization Delay Propagation Delay De-jitter Delay
Name 6 different sources of Delay:
bits
Network bandwidth is measured in the number of ? that can be transmitted in a single second, or bits per second (bps). For example, a network device may be described as having the capability to perform at 10 gigabits per second (Gbps).
delay
Network congestion causes ?. An interface experiences congestion when it is presented with more traffic than it can handle. Network congestion points are strong candidates for QoS mechanisms.
QoS
Note: A device implements ? only when it is experiencing some type of congestion.
DiffServ
Note: Modern networks primarily use the ____________ model. However, due to the increasing volumes of delay- and jitter-sensitive traffic, IntServ and RSVP are sometimes co-deployed.
Classification and marking
Note: ________________________ can be done on ingress or egress, whereas other QoS actions such queuing and shaping are usually done on egress.
200, 30
One way Requirement for Video Latency < or equal to _______-400 ms Jitter < or equal to _______-50 ms Loss < or equal to 0.1-1% Bandwidth (384 Kb/s - 20+ Mb/s)
150, 30
One-Way Requirements for Voice Latency < or equal to _______ ms Jitter < or equal to _______ ms Loss < or equal to 1% Bandwidth ( 30 - 129 Kb/s)
Bandwidth
Packet loss is a very common cause of voice quality problems on an IP network. In a properly designed network, packet loss should be near zero. The voice codecs used by the DSP can tolerate some degree of packet loss without a dramatic effect on voice quality. Network engineers use QoS mechanisms to classify voice packets for zero packet loss. _______________ is guaranteed for the voice calls by giving priority to voice traffic over traffic that is not time-sensitive.
Integrated services (IntServ), Differentiated services (DiffServ)
QoS is really implemented in a network using either IntServ or DiffServ. While __________ provides the highest guarantee of QoS, it is very resource-intensive and therefore, limited in scalability. In contrast, _____________ is less resource-intensive and more scalable. The two are sometimes co-deployed in network QoS implementations.
64
RFC 2474 supersedes RFC 791 and redefines the ToS field by renaming and extending the IPP field. The new field has 6-bits allocated for QoS. Called the Differentiated Services Code Point (DSCP) field, these six bits offer a maximum of ___ possible classes of service. The remaining two IP Extended Congestion Notification (ECN) bits can be used by ECN-aware routers to mark packets instead of dropping them. The ECN marking informs downstream routers that there is congestion in the packet flow.
outbound
Shaping is an _____________ concept; packets going out an interface get queued and can be shaped. In contrast, policing is applied to inbound traffic on an interface. When the traffic rate reaches the configured maximum rate, excess traffic is dropped (or remarked).
voice
Similar to ____________, video can tolerate a certain amount of latency, jitter, and loss without any noticeable affects. Latency should be no more than 400 milliseconds (ms). Jitter should be no more than 50 ms, and video packet loss should be no more than 1%. Video traffic requires at least 384 Kbps of bandwidth.
FTP
Some TCP applications can be very greedy, consuming a large portion of network capacity. ________ will consume as much bandwidth as it can get when you download a large file, such as a movie or game.
weighted random early detection (WRED), no
Some congestion avoidance techniques provide preferential treatment for which packets will get dropped. For example, Cisco IOS QoS includes __________________________________ (WRED) as a possible congestion avoidance solution. The WRED algorithm allows for congestion avoidance on network interfaces by providing buffer management and allowing TCP traffic to decrease, or throttle back, before buffers are exhausted. Using WRED helps avoid tail drops and maximizes network use and TCP-based application performance. There is ____ congestion avoidance for User Datagram Protocol (UDP)-based traffic, such as voice traffic. In case of UDP-based traffic, methods such as queuing and compression techniques help to reduce and even prevent UDP packet loss.
classes
Specifically, DiffServ divides network traffic into _________________ based on business requirements. Each of the classes can then be assigned a different level of service. As the packets traverse a network, each of the network devices identifies the packet class and services the packet according to that class. It is possible to choose many levels of service with DiffServ. For example, voice traffic from IP phones is usually given preferential treatment over all other application traffic, email is generally given best-effort service, and nonbusiness traffic can either be given very poor service or blocked entirely.
Best-Effort (BE) Expedited Forwarding (EF) Assured Forwarding (AF)
The 64 DSCP values are organized into three categories:
802.1p
The 802.1Q standard also includes the QoS prioritization scheme known as IEEE _____________. This standard uses the first three bits in the Tag Control Information (TCI) field. Known as the Priority (PRI) field, this 3-bit field identifies the Class of Service (CoS) markings. Three bits means that a Layer 2 Ethernet frame can be marked with one of eight levels of priority (values 0-7) as displayed in Figure 2.
scalable
The DiffServ design overcomes the limitations of both the best-effort and IntServ models. The DiffServ model is described in RFCs 2474, 2597, 2598, 3246, 4594. DiffServ can provide an "almost guaranteed" QoS while still being cost-effective and _____________.
DiffServ
The _________________ model is similar in concept to sending a package using a delivery service. You request (and pay for) a level of service when you send a package. Throughout the package network, the level of service you paid for is recognized and your package is given either preferential or normal service, depending on what you requested.
differentiated services (DiffServ)
The ___________________ QoS model specifies a simple and scalable mechanism for classifying and managing network traffic and providing QoS guarantees on modern IP networks. For example, DiffServ can provide low-latency guaranteed service to critical network traffic such as voice or video while providing simple best-effort traffic guarantees to non-critical services such as web traffic or file transfers.
Low Latency Queuing (LLQ)
The _______________feature brings strict priority queuing (PQ) to CBWFQ. Strict PQ allows delay-sensitive data such as voice to be sent before packets in other queues. LLQ provides strict priority queuing for CBWFQ, reducing jitter in voice conversations.
best-effort
The basic design of the Internet provides for _________________ packet delivery and provides no guarantees. This approach is still predominant on the Internet today and remains appropriate for most purposes. The best-effort model treats all network packets in the same way, so an emergency voice message is treated the same way a digital photograph attached to an email is treated. Without QoS, the network cannot tell the difference between packets and, as a result, cannot treat packets preferentially.
best-effort
The best-effort model is similar in concept to sending a letter using standard postal mail. Your letter is treated exactly the same as every other letter. With the __________ model, the letter may never arrive, and, unless you have a separate notification arrangement with the letter recipient, you may never know that the letter did not arrive.
Integrated services (IntServ)
The needs of real-time applications, such as remote video, multimedia conferencing, visualization, and virtual reality, motivated the development of the ___________ architecture model in 1994 (RFC 1633, 2211, and 2212). ___________ is a multiple-service model that can accommodate multiple QoS requirements.
Interactive
The two main factors a network administrator needs to ask about the flow of data traffic are the following: Does the data come from an ____________ application? Is the data mission critical?
Classification and marking tools Congestion avoidance tools Congestion management tools
There are three categories of QoS tools:
Packet loss
This happens when congestion occurs.
Class of Service (CoS), IP Precedence
Traffic Marking for QoS QoS Tools Ethernet (802.1Q, 802.1p) - Layer 2 - Marking Field: _______________ (CoS) 802.11 (Wi-Fi) - Layer 2 - Marking field: Wi-Fi Traffic Identifier (TID) MPLS - Layer 2 - Experimental (EXP) IPv4 and IPv6 - Layer 3 - _________________ (IPP) IPv4 and IPv6 - Layer 3 - Differentitated Services Code Point (DSCP) - Only one with Width in Bits = 6, the rest above are 3.
shaping, policing
Traffic _____________ and traffic ______________ are two mechanisms provided by Cisco IOS QoS software to prevent congestion.
shaping, memory CBWFQ, LLQ
Traffic _______________ retains excess packets in a queue and then schedules the excess for later transmission over increments of time. The result of traffic shaping is a smoothed packet output rate. Shaping implies the existence of a queue and of sufficient memory to buffer delayed packets, while policing does not. Ensure that you have sufficient _____________ when enabling shaping. In addition, shaping requires a scheduling function for later transmission of any delayed packets. This scheduling function allows you to organize the shaping queue into different queues. Examples of scheduling functions are ________________ and _____________.
2,3
Trust Boundaries Trusted endpoints have the capabilities and intelligence to mark application traffic to the appropriate Layer ___ CoS and/or Layer ___ DSCP values. Examples of trusted endpoints include IP phones, wireless access points, videoconferencing gateways and systems, IP conferencing stations, and more. Secure endpoints can have traffic marked at the Layer 2 switch. Traffic can also be marked at Layer 3 switches / routers Re-marking of traffic is typically necessary. For example, re-marking CoS values to IP Precedent or DSCP values.
554
UDP ports, such as ______ used for the Real-Time Streaming Protocol (RSTP), should be given priority over other, less time-sensitive, network traffic.
Bursty
Video - ___________ - Greedy - Drop sensitive - Delay Sensitive - UDP priority
Smooth
Voice - __________ - Benign - Drop sensitive - Delay Sensitive - UDP priority
Type of Service (ToS)
WFQ classifies traffic into different flows based on packet header addressing, including such characteristics as source and destination IP addresses, MAC addresses, port numbers, protocol, and ___________________ (ToS) value. The ToS value in the IP header can be used to classify traffic. ToS will be discussed later in the chapter.
tunneling, encryption
WFQ is not supported with ______________ and _________________ because these features modify the packet content information required by WFQ for classification. Although WFQ automatically adapts to changing network traffic conditions, it does not offer the degree of precision control over bandwidth allocation that CBWFQ offers.
bandwidth
WFQ then determines how much ____________ each flow is allowed relative to other flows. The flow-based algorithm used by WFQ simultaneously schedules interactive traffic to the front of a queue to reduce response time. It then fairly shares the remaining bandwidth among high-bandwidth flows. WFQ allows you to give low-volume, interactive traffic, such as Telnet sessions and voice, priority over high-volume traffic, such as FTP sessions. When multiple file transfers flows are occurring simultaneously, the transfers are given comparable bandwidth.
Congestion
What is it called when the demand for bandwidth exceeds the amount available?
Jitter
What is it called when there is variations in delay?
Code Delay
What is the fixed amount of time it takes to compress data at the source before transmitting to the first inter-networking device.
Bandwidth
What is the number of bits that can be transmitted in a single second?
Propagation Delay
What is the variable amount of time it takes for the frame traverse the links between the source and destination?
dropped
When FIFO is used, important or time-sensitive traffic can be ____________ when congestion occurs on the router or switch interface. When no other queuing strategies are configured, all interfaces except serial interfaces at E1 (2.048 Mbps) and below use FIFO by default. (Serial interfaces at E1 and below use WFQ by default.)
Queuing
When the volume of traffic is greater than what can be transported across the network, devices queue, or hold, the packets in memory until resources become available to transmit them. ? packets causes delay because new packets cannot be transmitted until previous packets have been processed. If the number of packets to be queued continues to increase, the memory within the device fills up and packets are dropped. One QoS technique that can help with this problem is to classify data into multiple queues, as shown in the figure.
source
Where should markings occur? Traffic should be classified and marked as close to its ______________ as technically and administratively feasible.
IntServ (Integrated Services)
Which QoS Implementation model based on these Benefits? - Explicit end-to-end resource admission control - Per-request policy admission control - Signaling of dynamic port numbers
DiffServ (Differentiated Service)
Which QoS Implementation model based on these Benefits? - Highly Scalable - Provides many different levels of quality
IntServ (Integrated Services)
Which QoS Implementation model based on these drawbacks? - Resource intensive due to the stateful architecture requirement for continuous signaling. - Flow-based approach not scalable to large implementations such as the Internet.
DiffServ (Differentiated Service)
Which QoS Implementation model based on these drawbacks? - No Absolute Guarantee of Service Quality - Requires a set of complex mechanism to work in concert throughout the network.
IntServ (Integrated Services)
Which QoS Model? Signaling of dynamic port numbers such as H.323
Classification and marking tools
Which QoS tool based on the description? - Sessions, or flows, are analyzed to determine what traffic class they belong to. - Once determined, the packets are marked.
Congestion Avoidance Tools
Which QoS tool based on the description? - Traffic classes are allotted portions of network resources as defined by the QoS policy. - The QoS policy also identifies how some traffic may be selectively dropped, delayed, or re-marked top avoid congestion. - The primary data traffic in a bandwidth-efficient manner before tail drops caused by queue overflows occur.
Congestion Management Tools
Which QoS tool based on the description? - When traffic exceeds available network resources, traffic is queued to await availability of resources. - Common Cisco IOS-based congestion management tools include CBWFQ and LLQ algorithms.
Not Interactive
Which factor for data delay? Mission Critical: Delay can vary greatly as long as the necessary minimum bandwidth is supplied. Non Mission Critical: Gets any leftover bandwidth after voice, video and other data application needs are met.
Interactive
Which factor for data delay? Mission Critical: Prioritize for the lowest delay of all data traffic and strive for a 1 to 2 seconds response time. Not Critical Mission: Applications could benefit from lower delay.
best-effort
Which model based on these benefits? Model is most scalable Scalability is only limited by bandwidth limits, in which case all traffic is equally effected. No Special QoS mechanisms are required It is the easiest and quickest model to deploy
delay-sensitive
With LLQ, __________________ data is sent first, before packets in other queues are treated. LLQ allows delay-sensitive data such as voice to be sent first (before packets in other queues), giving delay-sensitive data preferential treatment over other traffic. Although it is possible to enqueue various types of real-time traffic to the strict priority queue, Cisco recommends that only voice traffic be directed to the priority queue.
voice
Without LLQ, CBWFQ provides WFQ based on defined classes with no strict priority queue available for real-time traffic. The weight for a packet belonging to a specific class is derived from the bandwidth you assigned to the class when you configured it. Therefore, the bandwidth assigned to the packets of a class determines the order in which packets are sent. All packets are serviced fairly based on weight; no class of packets may be granted strict priority. This scheme poses problems for _____________ traffic that is largely intolerant of delay, especially variation in delay. For voice traffic, variations in delay introduce irregularities of transmission manifesting as jitter in the heard conversation.
bandwidth
Without QoS and a significant amount of extra ____________ capacity, video quality typically degrades. The picture appears blurry, jagged, or in slow motion. The audio portion of the feed may become unsynchronized with the video.
drop
Without any QoS mechanisms in place, packets are processed in the order in which they are received. When congestion occurs, network devices such as routers and switches can _____ packets. This means that time-sensitive packets, such as real-time video and voice, will be dropped with the same frequency as data that is not time-sensitive, such as email and web browsing.
Jitter
___________ is the variation in the delay of received packets. At the sending side, packets are sent in a continuous stream with the packets spaced evenly apart. Due to network congestion, improper queuing, or configuration errors, the delay between each packet can vary instead of remaining constant. Both delay and jitter need to be controlled and minimized to support real-time and interactive traffic.
Voice
_____________ traffic is predictable and smooth, as shown in the figure. However, voice is very sensitive to delays and dropped packets; there is no reason to re-transmit voice if packets are lost. Therefore, voice packets must receive a higher priority than other types of traffic.
Video
______________ traffic tends to be unpredictable, inconsistent, and bursty compared to voice traffic. Compared to voice, video is less resilient to loss and has a higher volume of data per packet.
Policing
_______________ is commonly implemented by service providers to enforce a contracted customer information rate (CIR). However, the service provider may also allow bursting over the CIR if the service provider's network is not currently experiencing congestion. CIR or Committed Information Rate is a way of guaranteeing that, even though you share a bandwidth pool with many other users, you are assured that you will receive, at least a part of this, no matter how busy the link gets. According to Wikipedia - CIR is the bandwidth for a virtual circuit guaranteed by an internet service provider to work under normal conditions.
802.1Q
_______________ is the IEEE standard that supports VLAN tagging at layer 2 on Ethernet networks. When this particular standard is implemented, two fields are added to the Ethernet Frame. As shown in Figure 1, these two fields are inserted into the Ethernet frame following the source MAC address field.
Video
_______________ traffic has become the increasingly important to business communications and operations. According to the Cisco Visual Networking Index (VNI), video traffic represented 67% of all traffic in 2014. By 2019, video will represent 80% of all traffic. In addition, mobile video traffic will increase over 600% from 113,672 TB to 768,334 TB. The type of demands voice, video, and data traffic place on the network are very different.
Packet loss
____________________ is usually the result of congestion on an interface. Most applications that use TCP experience slowdown because TCP automatically adjusts to network congestion. Dropped TCP segments cause TCP sessions to reduce their window sizes. Some applications do not use TCP and cannot handle drops (fragile flows).
Class-Based Weighted Fair Queuing (CBWFQ)
_____________________ extends the standard WFQ functionality to provide support for user-defined traffic classes. For CBWFQ, you define traffic classes based on match criteria including protocols, access control lists (ACLs), and input interfaces. Packets satisfying the match criteria for a class constitute the traffic for that class. A FIFO queue is reserved for each class, and traffic belonging to a class is directed to the queue for that class. Example User-defined classes - Class 1, Class 2, Class 3.
Weighted Fair Queuing (WFQ)
_____________________ is an automated scheduling method that provides fair bandwidth allocation to all network traffic. WFQ applies priority, or weights, to identified traffic and classifies it into conversations or flows, as shown in the figure.
