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)]

 To ensure that wireless voice traffic is properly prioritized for Microsoft Skype for Business, the architect should set up firewall policies and SDN to mark voice on the MCs or MM. Firewall policies are used to classify and prioritize traffic based on the application, user role, device type, and location. SDN is used to integrate with the Skype for Business SDN API, which provides real-time information about voice and video sessions, such as source and destination IP addresses, ports, codecs, and quality metrics. By using firewall policies and SDN, the MCs or MM can dynamically mark voice traffic with the appropriate DSCP values and queue them in the highest priority queue on the wireless and wired network12.

The other options are not sufficient or relevant for ensuring wireless voice traffic prioritization for Skype for Business. Broadcast suppression combined with AirGroup is used to reduce the network overhead and improve the user experience for wireless devices that use multicast or broadcast protocols, such as Apple Bonjour or Microsoft UPnP3. Airtime Fairness set to fair-access is used to balance the airtime usage among clients with different capabilities and data rates, such as 802.11ac and 802.11n4. Voice-aware Layer 3 roaming is used to enable seamless handoff of voice sessions across different subnets without dropping the call5. While these features may enhance the overall wireless performance and reliability, they do not directly prioritize voice traffic for Skype for Business.

References:

• Aruba Validated Reference Design: 802.11ac Networks
• Aruba Validated Reference Design: Skype for Business
• Aruba Validated Reference Design: AirGroup
• Aruba Validated Reference Design: Adaptive Radio Management
• Aruba Validated Reference Design: Voice over Wireless LAN

The specifications for the AP models are in the format of Tx:Rx:SU-MIMO:MU-MIMO:MU-MIMO clients, where Tx is the number of transmit antennas, Rx is the number of receive antennas, SU-MIMO is the number of spatial streams supported in single-user MIMO mode, MU-MIMO is the number of spatial streams supported in multi-user MIMO mode, and MU-MIMO clients is the number of MU-MIMO clients that can be served simultaneously.

The customer requirements are:

• Support for MU-MIMO: This means the AP must have a MU-MIMO value greater than 1, as MU-MIMO is a technique that allows multiple spatial streams to be transmitted to different clients at the same time.
• Support for up to four spatial streams, both when MU-MIMO is used and when it is not used: This means the AP must have a SU-MIMO value and a MU-MIMO value of 4, as spatial streams are independent data streams that can be transmitted or received by an antenna.
• Support for transmissions to up to three MU-MIMO clients at the same time: This means the AP must have a MU-MIMO clients value of 3, as this indicates the maximum number of clients that can receive MU-MIMO transmissions from the AP at the same time.

Based on these criteria, only the AP 335 meets the customer requirements, as it has a specification of 4x4:4:4:4:3, which means it has 4 transmit and receive antennas, 4 spatial streams in both SU-MIMO and MU-MIMO modes, and can serve 3 MU-MIMO clients simultaneously. The AP 325 does not meet the customer requirements, as it has a specification of 4x4:4:4:3:3, which means it has only 3 spatial streams in MU-MIMO mode, and can only serve 2 MU-MIMO clients simultaneously.

References:

• Aruba AP-335 Wireless Access Point | Aruba
• Aruba AP-325 Wireless Access Point | Aruba
• Multi-User MIMO in WiFi 6 - Arista Networks