HPE6-A47 Exam Dumps : Designing Aruba Solutions

 A collision domain is a logical area of the network where devices share the same wireless medium and may interfere with each other’s transmissions. In a WLAN, a collision domain is defined by the channel and the coverage area of an AP or a client. Devices that operate on the same channel and are within range of each other belong to the same collision domain and must contend for access to the medium using the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. Devices that operate on different channels or are out of range of each other belong to different collision domains and do not interfere with each other.

In this scenario, the architect plans 12 APs for an auditorium that is 325 square meters (3,498 square feet). Each AP has one 2.4 GHz radio and one 5 GHz radio. Both types of radios use 20 MHz channels. Assuming that DFS channels can be used in this design, the question is how many 5 GHz collision domains does this design provide.

To answer this question, we need to consider the following factors:

• The number of available 5 GHz channels in the regulatory domain of the auditorium. Different countries have different regulations on the use of the 5 GHz band, which affects the number and availability of channels for WLANs. For example, in the United States, there are 25 non-overlapping 20 MHz channels in the 5 GHz band, but some of them are subject to Dynamic Frequency Selection (DFS) requirements, which means that they must avoid interfering with radar systems by detecting and switching to another channel if radar signals are present. In other countries, such as Japan, there are 19 non-overlapping 20 MHz channels in the 5 GHz band, but some of them are restricted to indoor use only. Therefore, the number of available 5 GHz channels for the design depends on the regulatory domain of the auditorium.
• The channel assignment and distribution of the 12 APs in the auditorium. The channel assignment and distribution of the APs affect the number and size of the collision domains in the WLAN. Ideally, the APs should be assigned to non-overlapping channels and distributed evenly across the auditorium to provide optimal coverage and capacity, while minimizing co-channelinterference and adjacent channel interference. Co-channel interference occurs when devices on the same channel interfere with each other, while adjacent channel interference occurs when devices on nearby channels interfere with each other. Both types of interference degrade the performance and quality of the WLAN. Therefore, the channel assignment and distribution of the APs should follow the best practices of RF design, such as using a channel reuse plan, avoiding channel overlap, and adjusting the transmit power and antenna gain of the APs to match the coverage and capacity requirements of the auditorium.
• The coverage and capacity requirements of the auditorium. The coverage and capacity requirements of the auditorium affect the number and placement of the APs and the transmit power and antenna gain settings of the radios. The coverage requirement refers to the minimum signal strength and signal-to-noise ratio (SNR) that the APs and clients need to maintain a reliable wireless connection. The capacity requirement refers to the maximum number of clients and the minimum throughput and quality of service (QoS) that the APs and clients need to support the applications and services of the auditorium. The coverage and capacity requirements of the auditorium depend on the size and shape of the space, the density and distribution of the clients, the types and characteristics of the applications and services, and the performance and capabilities of the devices. Therefore, the coverage and capacity requirements of the auditorium should be determined by conducting a site survey and a network analysis, and then used to guide the design and configuration of the APs and radios.

Based on these factors, we can estimate the number of 5 GHz collision domains in the design as follows:

• Assuming that the auditorium is located in the United States and that DFS channels can be used in the design, there are 25 non-overlapping 20 MHz channels in the 5 GHz band. However, not all of them may be available or suitable for the design, depending on the presence and activity of radar systems in the area, the compatibility and support of the APs and clients, and the interference and noise level of the environment. Therefore, we will use a conservative estimate of 15 available 20 MHz channels in the 5 GHz band for the design.
• Assuming that the 12 APs are assigned to non-overlapping channels and distributed evenly across the auditorium, each AP will have its own 5 GHz collision domain, as there will be no co-channel interference or adjacent channel interference among the APs. Therefore, there will be 12 5 GHz collision domains in the design, corresponding to the 12 APs.
• Assuming that the coverage and capacity requirements of the auditorium are moderate and that the transmit power and antenna gain settings of the radios are adjusted accordingly, each AP will cover an area of about 27 square meters (290 square feet), which is roughly the size of a small classroom. This means that the APs will provide adequate signal strength and SNR for the clients, while avoiding excessive overlap and interference among the APs. Therefore, there will be no need to further divide or merge the 5 GHz collision domains in the design, as they will match the coverage and capacity requirements of the auditorium.

Hence, the number of 5 GHz collision domains in the design is 12, which is the answer option C. References:

• RF Design | Validated Solution Guide - Aruba
• Configuring 2.4 Ghz and 5 Ghz Radios - Aruba
• Chapter T-5: Understanding RF Collision Domains - Aruba
• [Aruba Certified Design Professional Official Certification Study Guide (HPE6-A47)]

In the event of an MM outage, MCs continue to use their existing licenses for 30 days, and the network remains up. However, you cannot change the configuration items in the controller network. In addition, the MM manages many of the higher level functions that can cause issues in the network if the MM fails. Aruba recommends a backup MM for these situations. From an economic point of view, a backup MM for a VMM is free. If a customer has a hardware MM, the customer must purchase a backup hardware MM.

Jitter is the variation in the delay of packets arriving at the destination. It is caused by network congestion, routing changes, or other factors that affect the transmission quality. Jitter can affect the quality of VoIP calls, as it can cause gaps, distortion, or echo in the audio. According to the Aruba Validated Reference Design for Voice and Video over Wi-Fi, the recommended maximum jitter for VoIP calls is 30 ms. Therefore, a jitter of 100 ms would typically cause a poor experience for users.

The other options are incorrect because:

• A. The packet loss is the percentage of packets that are lost or discarded during transmission. Packet loss can affect the quality of VoIP calls, as it can cause missing or corrupted audio. However, according to the Aruba Validated Reference Design for Voice and Video over Wi-Fi, the recommended maximum packet loss for VoIP calls is 1 percent. Therefore, a packet loss of 0.3 percent would not typically cause a poor experience for users.
• B. The throughput is the amount of data that can be transferred per unit of time. Throughput can affect the quality of VoIP calls, as it determines the bandwidth available for the audio. However, according to the Aruba Validated Reference Design for Voice and Video over Wi-Fi, the typical throughput for VoIP calls is 64 Kbps. Therefore, a throughput of 67 Kbps would not typically cause a poor experience for users.
• C. The latency is the delay between the sender and the receiver of packets. Latency can affect the quality of VoIP calls, as it can cause delays or out-of-sync audio. However, according to the Aruba Validated Reference Design for Voice and Video over Wi-Fi, the recommended maximum latency for VoIP calls is 150 ms. Therefore, a latency of 100 ms would not typically cause a poor experience for users.

References:

• Aruba Validated Reference Design: Voice and Video over Wi-Fi - Chapter 2)
• Aruba Certified Design Professional Official Certification Study Guide (HPE6-A47) - Chapter 7)