16 - Understanding Wireless Roaming and Location Services

Question 1

Moving from one access point to another is called ____.

Answer 1

roaming

Question 2

What are common situations that typically cause roaming?

Answer 2

• Maximum data retry count is exceeded – excessive numbers of data retries
• Low RSSI – when the received signal strength drops below a threshold
• Low SNR – when the difference between the received signal strength and noise floor drops below a threshold
• Proprietary load-balancing schemes – schemes in which clients roam to more evenly balanced client traffic across multiple APs

Question 3

This occurs when a client changes it’s 802.11 radio to the channel that is being scanned, broadcasts a probe request, then waits to hear any probe responses from AP’s on that channel.

Answer 3

active scan

Question 4

A client sends probe request to specific destination SSID, only APs with a matching SSID reply with a probe response.

Answer 4

directed probe

Question 5

A client sends a broadcast SSID (actually a null SSID) in the probe request, all APs receiving the probe request respond with a response

Answer 5

broadcast probe

Question 6

This is performed by changing to 802.11 radio of the client to the channel that is being scanned and waiting for a periodic beacon from any ap’s on that channel. By default, APs send beacons approx. every 100 ms

Answer 6

passive scan

Question 7

During a channel scan, the client is unable to transmit or receive client data traffic. Clients take various approaches to minimise this impact to their data traffic. What are these approaches?

Answer 7

• Background scanning

* On-roam scanning

Question 8

Clients can scan available channels before they need to roam. This scan builds on the knowledge of the RF environment and available APs so clients can roam faster if necessary

Answer 8

background scanning

Question 9

In contract to background scanning, ___ occurs when a roam is necessary. Each vendor/ device can implement its own algorithms to minimise the roam latency and the impact on data traffic.

Answer 9

on-roam scanning

Question 10

A ___ is a collection of mobility controllers (MCs) across which roaming needs to be supported. A ___ can consist of up to 24 WLCs that share the context and state of client devices and WLC loading information. The WLCs of a ___ forward data traffic among the group, which enables intercontroller WLAN roaming and WLC redundancy.

Answer 10

mobility group

Question 11

A wireless client can roam between any AP in a mobility group without being required to ___ to the network.

Answer 11

re-authenticate

Question 12

A controller can recognise controllers that belong to another mobility group. When this occurs, the controllers are said to be in the same ___.

Answer 12

mobility domain

Question 13

For two controllers to be in the same mobility domain, they must know each other, which means that the built in ______of each controller must be entered in to the other controller.

Answer 13

mac address and management IP address

Question 14

If a client moves from one controller to another in a different mobility domain (that is, to a controller that is not known by the controller that the client leaves), the client will have to ___, ___ and ___.

Answer 14

re-authenticate, re-associate and get new IP information

Question 15

To ensure fast secure roaming, all controllers between which roaming should occur should be in the same ___.

Answer 15

mobility group

Question 16

Controllers in a MG must all have these characteristics in common:

Answer 16

• Mobility domain name
• Version of controller code
• CAPWAP mode
• ACLs
• WLANs (SSIDs)

Question 17

There are two types of roaming…

Answer 17

• Layer 2 roaming

* Layer 3 roaming

Question 18

__ roaming occurs when the client moves from one AP to another and is maintained in the same client subnet/VLAN.

Answer 18

L2

Question 19

L2 roaming occurs in two ways:

Answer 19

• Intracontroller roaming

* Intercontroller roaming (layer 2)

Question 20

• ___ roaming
o when a client moves from location t1 to t2, it asks for reauthentication on a new AP.
o this authentication is done by a query that is sent to the controller to which the AP is connected.
o If the controller is the same one to which the AP that the client is leaving was associated, the controller simply updates the client database with the newly associated AP.

Answer 20

intracontroller roaming

Question 21

• ___ roaming
o In this process, a client roams from an AP that is joined to one controller and roams to an AP that is joined to a different controller
o When a client at location t2 moves to t3, it associates to an AP that is joined to the new controller, the new controller exchanges mobility messages with the original controller and the client database entry is copied to the new controller.

Answer 21

intercontroller roaming (L2)

Question 22

Intercontroller L2 roaming remains transparent to the user unless:

Answer 22

• Client sends a DHCP discover request

* The session timeout is exceeded

Question 23

__ roaming occurs when the client moves from an SSID on one AP (that is associated with one VLAN and respective IP subnet) to the same SSID on a different AP (that is associated with a different VLAN and IP subnet).

Answer 23

L3

Question 24

L3 roaming can occurring the following way:

Answer 24

Intercontroller Roaming (layer 3)

Question 25

• ___ Roaming
o Inter-subnet roaming is similar to intercontroller roaming in that the controllers exchange mobility messages on the client roam. However, instead of moving the client DB entry to the new controller, the original controller marks the client with an anchor entry in its own client DB. The DB entry is copied to the new controller client DB and marked with a foreign entry in the new controller. The roam remains transparent to the wireless client and maintains its original IP address.

Answer 25

Intercontroller Roaming (layer 3)

Question 26

___, also referred to as guest tunnelling, is a subset of a mobility group in which all the client traffic that belongs to a WLAN (typically the Guest WLAN) is tunnelled to a predefined WLC or set of controllers that are configured as an anchor for that specific WLAN. This feature helps to restrict clients to specific subnet and have more control over user traffic.

Answer 26

auto-anchor mobility

Question 27

What are the features of auto-anchor mobility?

Answer 27

• Limit guest access to corp network by first passing through the corporate firewall
• Implement a geographic access policy that can restrain client traffic to a specific subnetwork
• Change roaming characteristics if a firewall prevents L3 roaming from functioning properly.

Question 28

___ are used to perform network analytics, providing the ability to collect meaningful data about the wireless aspect of the network

Answer 28

Location-based services

Question 29

___ is about collecting data, correlating the collected data, and presenting it in a way that allows you to discover things that you might not have noticed. __ is also about extracting actionable data.

Answer 29

Analytics

Question 30

____ is a tool that provides leveraged analytics to understand mobile device patterns. ___ allows your wireless network to deliver dynamic and relevant content to mobile end users. Once the consumer connects to the network, the network provides the organisation with many different ways to engage the consumer.

Answer 30

Cisco Connected Mobile Experiences (CMX)

Question 31

There are 3 features of Cisco CMX:

Answer 31

Detect
o Can provide either a presence or location-based detection using the wifi signal.
o Presence is for smaller locations where you may only have one or two APs, however you still want to determine the number of vistors
Connect
o Provides a customised portal for guests to log in to the network
o Can be customised to provide splash screen when guests associate with the network
Engage
o Provide context to guests
o For example. If a guest enters the venue and is a recurring guest, you may send a coupon of some type.

Question 32

What are two Cisco CMX analytics tools?

Answer 32

Presence analytics
o Deals with counting devices.
o Number of guests can be counted by floor, or by building

Location Analytics
o Heatmaps provide a visual representation of total activity on a floor map in real time, but also can be views as a playback over time
o Useful to understand the space utilisation and popularity of different sections of a location.

Question 33

When you deploy APs to support location-based services, you need to consider the following guidelines.

Answer 33

• At least 3 APS must be used with no less that -75dBm signal strength on the same floor
• A good general principle is one AP per 2500 square feet
• APs should be installed along the perimeter walls. For high-density applications, it is recommended to add APs in the middle of dense areas
• Stagger the APs so you cover perimeter, and try and design so at least 4 APs are within line of sight
• There should be 20 percent cell overlap for optimised roaming and location calculations.

Question 34

How precise you are at locating your mobile devices depend upon the manner in which the devices are found. What are the 4 different methods of locating a mobile device?

Answer 34

o Presence (accurate to 20m)
o Basic location (accurate to 7 m)
o Enhanced location (accurate to 5m)
o Hyperlocation (accurate to 1m)