This document provides design considerations and deployment guidelines
for the implementation of the Vocera® Badge Voice over WLAN (VoWLAN) technology
on the Cisco Unified Wireless Network infrastructure.
Note: Support for Vocera products should be obtained directly from Vocera
support channels. Cisco Technical Support is not trained to support
This guide is a supplement to the Cisco Wireless LAN Controller
Deployment Guide and only addresses the configuration parameters that are
particular to Vocera VoWLAN devices in a lightweight architecture. Refer to
Cisco 440X Series Wireless LAN Controllers for more information.
It is assumed that readers are familiar with the terms and concepts
presented in the Cisco IP Telephony SRND and the Cisco Wireless LAN SRND. .
Wireless UC Design guide—
Cisco Unified Communications SRND Based on Cisco Unified Communications
This document is not restricted to specific software and hardware
Technical Tips Conventions for more information on document
This table summarizes the four key functions and how they behave within
a Cisco Unified Wireless network.
Layer 2 Roaming
Layer 3 Roaming
No special configuration
No special configuration
No special configuration
No special configuration
No special configuration
No special configuration
Enable Controller Multicast
Enable Controller Multicast
Disable Vocera VLAN IGMP-Snooping or run 22.214.171.124 or later
126.96.36.199 or later
No special configuration
No special configuration
No special configuration
The communication badges allow a wearer instant communication with any
other badge wearer as well a Private Branch Exchange (PBX) integration and
badge location tracking. The utilization of an 802.11b/g wireless network
requires the use of multicast and UDP unicast packet delivery with limited
requirements for Quality of Service (QoS) as of Vocera Server Software release
3.1 (Build 1081). The encryption capabilities are 64/128 bit Wired Equivalent
Privacy (WEP), Temporal Key Integrity Protocol (TKIP), Message Integrity Check
(MIC), and Cisco Temporal Key Integrity Protocol (CKIP) combined with the
authentication capabilities of Open, Wi-Fi Protected Access-Pre-shared Key
(WPA-PSK), WPA-Protected Extensible Authentication Protocol (PEAP) and
Lightweight Extensible Authentication Protocol (LEAP).
With the push of a button, the Vocera server responds with
Vocera, which is a prompt to issue commands such
as record, where (am I)
messages, and so forth. The Vocera server provides
the necessary services and/or call setup to complete the request.
Vocera's 802.11b capable Communication System makes use of proprietary
voice compression and the use of a UDP port range. The Vocera System software
runs on a Windows server that manages call set up, call connection and user
profiles. They have partnered with Nuance 8.5 Speech Recognition and Voiceprint
software in order to enable badge voice communications. Vocera recommends a
separate Windows server to run the Vocera Telephony Solutions Software to
enable Plain Old Telephone Service (POTS) connectivity with the badges.
See the Network Sizing section of this
document for further details.
Refer to the
Vocera Communications System Specifications
information on Vocera Server sizing matrix.
The Vocera Badge utilizes both unicast and multicast packet delivery to
provide several key features that make up this complete solution. Here are four
of the essential features that rely on proper packet delivery. Also provided is
a basic understanding of how each feature uses the underlying network for
delivery and functionality.
Badge to Badge Communications—When one Vocera user calls another
user, the badge first contacts the Vocera server, which looks up the IP address
of the badge of the callee and contacts the badge user to ask the user if they
can take a call. If the callee accepts the call, the Vocera server notifies the
calling badge of the IP address of the callee badge to setup direct
communication between the badges with no further server intervention. All
communication with the Vocera server uses the G.711 codec and all
badge-to-badge communication uses a Vocera proprietary codec.
Badge Telephony Communication—When a Vocera Telephony server is
installed and setup with a connection to a PBX, a user is able to call internal
extensions off of the PBX or outside telephone lines. Vocera allows users to
make calls by either saying the numbers (five, six, three, two) or by creating
an address book entry in the Vocera database for the person or function at that
number (for example, pharmacy, home, pizza) the Vocera server determines the
number that is being called, either by intercepting the numbers in the
extension or by looking the name up in the database and selecting the number.
The Vocera server then passes that information to the Vocera Telephony server
which connects to the PBX and generates the appropriate telephony signaling
(for example, DTMF). All communication between the badge and Vocera server and
Vocera server and Vocera Telephony server use the G.711 codec over unicast
Vocera Broadcast—A Vocera Badge user can call and communicate to a
group of Vocera badge wearers at the same time by using the Broadcast command.
When a user broadcasts to a group, the user's badge sends the command to the
Vocera server who then looks up the members of a group, determines which
members of the group are active, assigns a multicast address to use for this
broadcast session, and sends a message to each active user’s badge instructing
it to join the multicast group with the assigned multicast
Badge Location Function—The Vocera server keeps track of the access
point to which each active badge is associated as each badge sends a 30 second
keep alive to the server with the associated BSSID. This allows the Vocera
system to roughly estimate the location of a badge user. This function has a
relatively low degree of accuracy because a Badge might not be associated to
the access point to which it is closest.
The Vocera whitepaper
Vocera Infrastructure Planning Guide
, describes the site
survey minimum requirements that show that the badge should have a receive
signal strength minimum of -65 dBm, a signal-to-noise ratio greater than 25 db
and proper access point overlap and channel separation. Although the badges use
a similar omni directional antenna as a notebook that is used for a site
survey, it does not mimic the behavior of the badge very well, given the
wearers' affects on signal strength. Given this unique requirement and this
behavior of the transmitting device, the use of the Cisco Architecture and
Radio Resource Management is ideal in order to make sure there is a lack of
unusual radio frequency (RF) site characteristics.
The Vocera badge is a low powered device, worn next to the body with
limited signal error correction capabilities. The Vocera requirements in this
document can be easily achieved. However, it can become overwhelmed if there
are too many SSIDs for it to process and allow the badge to work
Figure 1—General Multicast Forward and Prune with Lightweight
Access Point Protocol (LWAPP) Wireless
Understanding multicast within an LWAPP deployment is necessary to
deploy the Vocera broadcast function. This document later covers the essential
steps to enable multicast within the controller-based solution. There are
currently two delivery methods that the LWAPP controller uses to deliver
multicast to the clients:
The unicast-multicast delivery method creates a copy of every multicast
packet and forwards it to every access-point. When a client sends a multicast
join to the wireless LAN, the access point forwards this join through the LWAPP
tunnel to the controller. The controller bridges this multicast join onto it's
directly connected local area network connection that is the default VLAN for
the associated WLAN of the client. When an IP multicast packet arrives from the
network to the controller, the controller replicates this packet with an LWAPP
header for each access point that has a client within the wireless domain who
has joined this specific group. When the source of the multicast is also a
receiver within the wireless domain, this packet is also duplicated and
forwarded back to the same client who sent this packet. For Vocera badges, this
is not the preferred method of multicast delivery within the LWAPP controller
solution. The unicast delivery method works with small deployments. However,
due to the considerable overhead on the Wireless LAN Controller (WLC), this is
never the recommended multicast delivery method.
Figure 2—LWAPP Multicast-Unicast
Note: If AP Group VLANs are configured, and an IGMP join is sent from a
client through the controller, it is placed on the default VLAN of the WLAN
that the client is on. Therefore, the client might not receive this multicast
traffic unless the client is a member of this default broadcast domain.
The multicast-multicast delivery method does not require the controller
to replicate each multicast packet received. The controller is configured for
an un-used multicast group address that each access point becomes a member of.
With Figure 3, the multicast group defined from the WLC to the access point is
188.8.131.52. When a client sends a multicast join to the WLAN, the access point
forwards this join through the LWAPP tunnel to the controller. The controller
forwards this link-layer protocol onto it's directly connected local area
network connection that is the default VLAN for the associated WLAN of the
client. The router that is local to the controller then adds this multicast
group address to that interface for forwarding ((*,G)) entry. With Figure 3,
the example multicast join was sent to the multicast group 184.108.40.206. When the
network now forwards multicast traffic, the multicast address of 220.127.116.11 is
forwarded to the controller. The controller then encapsulates the multicast
packet into an LWAPP multicast packet addressed to the multicast group address
(example here is 18.104.22.168) that is configured on the controller and forwarded
to the network. Each access point on the controller receives this packet as a
member of the controllers multicast group. The access point then forwards the
clients/servers multicast packet (example here is 22.214.171.124) as a broadcast to
the WLAN/SSID identified within the LWAPP multicast packet.
Note: If you improperly configure your multicast network, you could end up
receiving another controller's access point multicast packets. If the first
controller has to fragment this multicast packet, the fragment is forwarded to
the network and each access point must spend time to drop this fragment. If you
allow all traffic such as anything from the 224.0.0.x multicast range, this is
also encapsulated and subsequently forwarded by each access point.
Figure 3—LWAPP Multicast-Multicast
This document is not a network multicast configuration guide. Refer to
Multicast Routing for a complete implementation story. This document
covers the basics to enable multicast within your network environment.
IP multicast routing allows the Cisco IOS® software to forward
multicast packets. The ip multicast-routing global
configuration command is required to allow multicast to function in any
multicast enabled network. The ip multicast-routing
command should be enabled on all routers within your network between the WLC(s)
and their respective access points.
This enables the routing interface for Internet Group Management
Protocol (IGMP) operation. The Protocol Independent Multicast (PIM) mode
determines how the router populates its multicast routing table. The example
provided here does not require the rendezvous point (RP) to be known for the
multicast group and therefore sparse-dense-mode is the most desirable given the
unknown nature of your multicast environment. This is not a multicast
recommendation to be configured to work although the Layer 3 interface directly
connected to your controller should be PIM enabled for multicast to function.
All interfaces between your WLC(s) and their respective access points should be
Router(config-if)#ip pim sparse-dense-mode
IGMP snooping allows a switched network with multicast enabled to limit
traffic to those switchports that have users who want multicast to be seen
while pruning the multicast packets from switchports that do not wish to see
the multicast stream. In a Vocera deployment, it can be undesirable to enable
CGMP or IGMP snooping on the upstream switchport to the controller with
software releases earlier than 126.96.36.199.
Roaming and multicast are not defined with a set of requirements to
verify that multicast traffic can follow a subscribed user. Although the client
badge is aware that it has roamed, it does not forward another IGMP join to
make sure that the network infrastructure continues to deliver the multicast
(Vocera broadcast) traffic to the badge. At the same time, the LWAPP access
point does not send a general multicast query to the roamed client to prompt
for this IGMP join. With a Layer 2 Vocera network design, disabling IGMP
snooping allows traffic to be forwarded to all members of the Vocera network no
matter where they roam. This ensures that the Vocera broadcast feature works
irrespective of where the client roams. Disabling IGMP snooping globally is a
very undesirable task. It is recommended that IGMP snooping only be disabled on
the Vocera VLAN that is directly connected to each WLC.
IGMP Snooping for more information.
Router(config)#interface vlan 150
Router(config-if)#no ip igmp snooping
With the release of 188.8.131.52, Cisco introduces an IGMP query to allow
users to roam at Layer 2 by sending a general IGMP query when this occurs. The
client then responds with the IGMP group that they are a member of and this is
bridged to the wired network as described earlier in this document. When a
client roams to a controller that does not have Layer 2 connectivity, or a
Layer 3 roam, synchronous routing is added for multicast source packets. When a
client, who has completed a Layer 3 roam sources a multicast packet from the
wireless network, the foreign controller encapsulates this packet in the
Ethernet over IP (EoIP) in IP tunnel to the anchor controller. The anchor
controller then forwards that to the wireless clients locally associated as
well as bridge this back to the wired network where it is routed using normal
multicast routing methods.
These three deployment scenarios cover best practices and design
parameters to help with a successful Vocera Badge deployment:
Understanding how the Vocera Badge features interact within an LWAPP
split MAC environment is essential. With all deployment scenarios, multicast
should be enabled and aggressive load balancing should be disabled. All badge
WLANs should be contained within the same broadcast domain across your entire
This is the most straight forward deployment scenario. It allows you to
deploy the Vocera Badge solution with little deployment concerns. Your network
must be enabled for IP multicast routing only to allow the access points to
receive the LWAPP multicast packets. If required, you can limit network
multicast complexity by configuring all routers and switches with the
controllers multicast group.
With multicast configured globally on the controller, the proper SSID,
security settings, and all the access points registered the Vocera Badge
solution and all its functions operates as expected. With the Vocera Broadcast
function, a user roams and the multicast traffic follows as expected. There are
no extra settings required to be configured to allow this solution to function
When a Vocera Badge sends a multicast message, as it does with the
Vocera Broadcast, it is forwarded to the controller. The controller then
encapsulates this multicast packet within an LWAPP multicast packet. The
network infrastructure forwards this packet to every access point that is
connected to this controller. When the access point receives this packet, it
then looks at the LWAPP multicast header to determine which WLAN/SSID it then
broadcasts this packet to.
Figure 5—Single Controller in Multicast-Multicast
Multiple controllers must all have connectivity to each other via the
same Layer 2 broadcast domain. Both controllers are configured for multicast as
shown, using the identical access point multicast groups on each controller to
limit fragmentation. With the assumption that this Layer 2 broadcast domain is
connected via a common switch or a common set of switches, CGMP/IGMP snooping
on these switches must be disabled for this single VLAN or run 184.108.40.206 or
later WLC software. With the Vocera Broadcast function and a user roam from an
access point on one controller to an access point on a different controller,
there is no mechanism for IGMP joins to be forwarded to the new Layer 2 port
for IGMP snooping to work. Without an IGMP packet reaching the upstream CGMP or
IGMP capable switch, the specified multicast group is not forwarded to the
controller and therefore is not received by the client. In some cases this
might work, if a client that is part of the same Vocera Broadcast group has
already sent this IGMP packet before the roaming client roams onto the new
controller With the advantages of version 220.127.116.11, a client who roams to
another controller as a Layer 2 roam receives a general IGMP query immediately
after authentication. The client should then respond with the interested groups
and the new controller is then bridged this to the locally connected switch.
This allows the advantages of IGMP and CGMP on your upstream switches.
You can create additional badge SSIDs and Layer 2 domains for separate
badge networks as long as your network is configured to pass multicast traffic
appropriately. Also, each Vocera Layer 2 broadcast domain created must exist
everywhere a controller is connected to the network so as not to break
Figure 6—Multiple Controller Layer 2
The Layer 3 roaming deployment strategy should only be used with
controller-to-controller roaming with WLC software release 18.104.22.168 or later.
If a client that has been connected to the Vocera broadcast group and receives
the appropriate multicast stream and roams to another controller as a Layer 3
roam with the LWAPP Layer 3 roaming configured, it is queried for interested
multicast groups. The client, when sourcing to the same Vocera broadcast group,
has these packets delivered to the anchor controller through the EoIP tunnel
and has these packets routed through normal multicast routing methods.
Figure 7—Multiple Controller Layer 3
Wireless IP Telephony networks require careful RF planning. A thorough
voice site survey is often required to determine the proper levels of wireless
coverage and to identify sources of interference. Access point placement and
antenna selection choices can be greatly eased with the help of the results of
a valid voice site survey. The most important consideration is the transmit
power of the wireless phone. Ideally the phone learns the transmit power of the
access point and adjust its transmit power to that of the access point.
Although the majority of the wireless networks today are deployed after
an extensive RF site survey, they are done with keeping data service in mind as
well. VoWLAN phones are likely to have different roaming characteristics and
different coverage requirements than those of a typical WLAN adapter for a
mobile client such as a laptop. Therefore, an additional site survey for voice
is often recommended to prepare for the performance requirements of multiple
VoWLAN clients. This additional survey gives the opportunity to tune the access
points to ensure that the VoWLAN phones have enough RF coverage and bandwidth
to provide proper voice quality.
For additional information on RF design considerations, refer to the
chapter on WLAN Radio Frequency (RF) Design Considerations in the Cisco
Wireless LAN Design Guide, available at
Consider the factors listed in this section when you survey multi-floor
buildings, hospitals, and warehouses.
Construction Methods and Materials
Many aspects of the building construction are unknown or hidden from
the site survey, so you might have to acquire that information from other
sources (such as architectural drawings). Some examples of typical construction
methods and materials that affect the range and coverage area of access points
include metallic film on window glass, leaded glass, steel-studded walls,
cement floors and walls with steel reinforcement, foil-backed insulation,
stairwells and elevator shafts, plumbing pipes and fixtures, and many
Various types of inventory can affect RF range, particularly those with
high steel or water content. Some items to watch for include cardboard boxes,
pet food, paint, petroleum products, engine parts, and so forth.
Levels of Inventory
Make sure you perform a site survey at peak inventory levels or at
times of highest activity. A warehouse at a 50% stocking level has a very
different RF footprint than the same warehouse at an inventory level of
Similarly, an office area after hours (without people) has a different
RF footprint than the same area full of people during the day. Although many
parts of the site survey can be conducted without full occupation, it is
essential to conduct the site survey verification and tweak key values during a
time when the location is occupied. The higher the utilization requirements and
the density of users, the more important it is to have a well designed
diversity solution. When more users are present, more signals are received on
each user's device. Additional signals cause more contention, more null points,
and more multipath distortion. Diversity on the access point (antennas) helps
minimize these conditions.
Keep in mind these guidelines when you conduct a site survey for a
typical office building:
Elevator shafts block and reflect RF signals.
Supply rooms with inventory absorb signals.
Interior offices with hard walls absorb RF signals.
Break rooms (kitchens) can produce 2.4 GHz interference through the
use of microwave ovens.
Test labs can produce 2.4 GHz or 5 GHz interference, creating
multipath distortion and RF shadows.
Cubicles tend to absorb and block signals.
Conference rooms require high access point coverage because they are
areas of high utilization.
Extra precaution must be administered when you survey multi-floor
facilities. Access points on different floors can interfere with each other as
easily as access points located on the same floor. It is possible to use this
behavior to your advantage during a survey. Using higher-gain antennas, it
might be possible to penetrate floors and ceilings and provide coverage to
floors above as well as below the floor where the access point is mounted. Be
careful not to overlap channels between access points on different floors or
access points on the same floor. In multi-tenant buildings, there might be
security concerns that require the use of lower transmission powers and lower
gain antennas to keep signals out of neighboring offices.
The survey process for a hospital is much the same as that for an
enterprise, but the layout of a hospital facility tends to differ in these
Hospital buildings tend to go through many reconstruction projects
and additions. Each additional construction is likely to have different
construction materials with different levels of attenuation.
Signal penetration through walls and floors in the patient areas is
typically minimal, which helps create micro-cells and multipath
The need for bandwidth increases with the increasing use of WLAN
ultrasound equipment and other portable imaging applications. The need for
bandwidth increases with the addition of wireless voice as
Healthcare cells are small, and seamless roaming is essential,
especially with voice applications.
Cell overlap can be high, and so can channel reuse.
Hospitals can have several types of wireless networks installed. This
includes 2.4 GHz non-802.11 equipment. This equipment can cause contention with
other 2.4 GHz networks.
Wall-mounted diversity patch antennas and ceiling-mounted diversity
omni-directional antennas are popular, but keep in mind that diversity is
Warehouses have large open areas that often contain high storage racks.
Many times, these racks reach almost to the ceiling, where access points are
typically placed. Such storage racks can limit the area that the access point
can cover. In these cases, consider placing access points on other locations
besides the ceiling, such as side walls and cement pillars. Also consider these
factors when you survey a warehouse:
Inventory levels affect the number of access points needed. Test
coverage with two or three access points in estimated placement
Unexpected cell overlaps are likely because of multipath variations.
The quality of the signal varies more than the strength of that signal. Clients
might associate and operate better with access points farther away than with
nearby access points.
During a survey, access points and antennas usually do not have an
antenna cable connecting them. But in a production environment, the access
point and antenna might require antenna cables. All antenna cables introduce
signal loss. The most accurate survey includes the type of antenna to be
installed and the length of cable to be installed. A good tool to use to
simulate the cable and its loss is an attenuator in a survey
Surveying a manufacturing facility is similar to surveying a warehouse,
except that there might be many more sources of RF interference in a
manufacturing facility. In addition, the applications in a manufacturing
facility usually require more bandwidth than those of a warehouse. These
applications can include video imaging and wireless voice. Multipath distortion
is likely to be the greatest performance problem in a manufacturing
In addition to static WEP and Cisco LEAP for authentication and data
encryption, the Vocera Badges also support WPA-PEAP (MS-CHAP v2)/WPA2-PSK.
LEAP allows devices to be authenticated mutually (badge-to-access point
and access point-to-badge) based on a user name and password. Upon
authentication, a dynamic key is used between the phone and the access point to
encrypt traffic. However, the ASLEAP dictionary attack should be considered
when you decide to use LEAP as your security solution:
Attack on Cisco LEAP Vulnerability for more information.
If LEAP is used, a LEAP-compliant RADIUS server, such as the Cisco
Access Control Server (ACS), is required to provide access to the user
database. The Cisco ACS can either store the user name and password database
locally, or it can access that information from an external Microsoft Windows
NT directory. When using LEAP, ensure that strong passwords are used on all
wireless devices. Strong passwords are defined as being between 10 and 12
characters long and can include both uppercase and lowercase characters as well
as the special characters.
Because all the badges use the same password and it is stored within
the badge, Cisco recommends that you use different user names and passwords on
data clients and wireless voice clients. This practice helps with tracking and
troubleshooting as well as security. Although it is a valid configuration
option to use an external (off-ACS) database to store the user names and
passwords for the badges, Cisco does not recommend this practice. Because the
ACS must be queried whenever the badge roams between access points, the
unpredictable delay to access an off-ACS database could cause excessive delay
and poor voice quality.
The wireless IP Telephony network, just like a wired IP Telephony
network, requires careful planning for VLAN configuration, network sizing,
multicast transport, and equipment choices. For both wired and wireless IP
Telephony networks, separate voice and data VLANs is often the most effective
way of suggested deployment to ensure sufficient network bandwidth and ease of
VLANs provide a mechanism for segmenting networks into one or more
broadcast domains. VLANs are especially important for IP Telephony networks,
where the typical recommendation is to separate voice and data traffic into
different Layer 2 domains. Cisco recommends that you configure separate VLANs
for the Vocera Badges from other voice and data traffic: a native VLAN for
access point management traffic, data VLAN for data traffic, a voice or
auxiliary VLAN for voice traffic, and a VLAN for the Vocera Badges. A separate
voice VLAN enables the network to take advantage of Layer 2 marking and
provides priority queuing at the Layer 2 access switch port. This ensures that
appropriate QoS is provided for various classes of traffic and helps to resolve
addressing issues such as IP addressing, security, and network dimensioning.
The Vocera Badges use a broadcast feature that utilizes multicast to deliver.
This common VLAN ensures that when a badge roams between controllers, it
remains part of the multicast group. This last process is discussed in detail
when multicast is addressed later in this document.
IP Telephony network sizing is essential to ensure that adequate
bandwidth and resources are available to meet the demands presented by the
presence of voice traffic. In addition to the usual IP Telephony design
guidelines for sizing components such as PSTN gateway ports, transcoders, WAN
bandwidth, and so forth, also consider these 802.11b issues when you size your
wireless IP Telephony network. The Vocera Badges are a specialized application
that stretch the number of wired clients beyond our typical deployment
Number of 802.11b Devices per Access Point
Cisco recommends that you have no more than 15 to 25 802.11b devices
per access point.
Number of Active Calls per Access Point
Vocera uses two different codecs based on if it is a badge-to-badge
(proprietary low-bit rate codec) call or a badge-to-phone (G.711 codec) call.
This table shows a percentage of available bandwidth by data rates and gives
you a clearer picture of the expected throughput:
Badge-to-Badge (Proprietary Low-bit rate codec)
Note: If you use a Cisco Catalyst 4000 Series Switch as the main router in
the network, ensure that it contains, at a minimum, either a Supervisor Engine
2+ (SUP2+) or Supervisor Engine 3 (SUP3) module. The SUP1 or SUP2 module can
cause roaming delays, as can the Cisco Catalyst 2948G, 2980G, 2980G-A, 4912,
and 2948G-GE-TX switches.
You can create a switch port template for use when you configure any
switch port for connection to an access point. This template should add all the
baseline security and resiliency features of the standard desktop template. In
addition, when you attach the access point to a Cisco Catalyst 3750 Switch, you
can optimize the performance of the access point by using Multilayer Switching
(MLS) QoS commands to limit the port rate and to map Class of Service (CoS) to
Differentiated Services Code Point (DSCP) settings.
Any traffic that is not required by WLAN clients should not be sent to
an access point. A template should be designed in such a way that helps create
a secure and resilient network connection with these features:
Return Port Configurations to default— Prevents configuration
conflicts by clearing any pre-existing port configurations.
Disable Dynamic Trunking Protocol (DTP)— Disables dynamic trunking,
which is not needed for connection to an access point.
Disable Port Aggregation Protocol (PagP)— PagP is enabled by default
but is not needed for user-facing ports.
Enable Port Fast—Allows a switch to quickly resume forwarding traffic
if a spanning tree link goes down.
Configure Wireless VLAN—Creates a unique wireless VLAN that isolates
wireless traffic from other data, voice, and management VLANs. This isolates
traffic and ensures greater control of traffic.
Enable Quality of Service (QoS); do not trust port (mark down to
0)—Ensures appropriate treatment of high-priority traffic, including
softphones, and prevents users from consuming excessive bandwidth by
reconfiguring their PCs.
WS-C3750-48PS-S Inline Power Switches can be used to provide power to
access points that are capable of receiving inline power.
The Catalyst 6500 allows you to forward packets at line rate with all
the features described here as well as integrating numerous service modules.
The Wireless Service Module (WiSM) allows you to have two controllers each with
the capability to control 150 access points each. With up to five WiSMs per
chassis, this allows you to control over 1500 access points that support 50,000
clients within a single high performance switching architecture.
The Vocera Badge Configuration Utility (BCU) and the configuration of
the badge can introduce roaming and latency into your environment if done
incorrectly. Using the BCU and the Badge Properties Editor (BPE), verify these
settings (see Figure 8):
Figure 8—Vocera BCU Advanced Tab
Subnet Roaming is disabled.
Scan Default Channels (1,6,11) is
Broadcast Uses IGMP is enabled.
Roaming Policy is set to 2 or
When Subnet Roaming is checked, it instructs the badge
to request a new IP address after each roam. In the LWAPP environment, the
infrastructure helps maintain client connectivity at Layer 3. When a voice
client must wait for the DHCP server to respond before it is able to send or
receive packets, delay and jitter are introduced. If Scan Default
Channels (1,6,11) is not checked, the badge scans all 802.11b channels
when the badge looks to roam. This prevents the forwarding of packets and
As described in the Recommendations section
of this document, it is important to understand that each site has it's own RF
characteristics. AutoRF or Radio Resource Management (RRM) might need to be
tuned, with the understanding that each site is different and AutoRF/RRM should
be tuned for your environment.
Before you adjust AutoRF, refer to
Resource Management under Unified Wireless Networks for more
RRM allows you to adjust the transmit power of each access point, by
adjusting how strong each access point hears its third strongest neighbor. This
value can only be adjusted from the CLI using the config advanced
802.11b tx-power-thresh command as described in
Power Level Assignment Settings.
Before you adjust AutoRF, walk the deployment site using the Vocera
badge as worn by the end user and use a site survey tool in order to gain a
strong understanding of how the badge roams and at what power each access point
is seen. Once this is complete and it is determined that adjusting this value
is required, begin with a value of –71 dBm for the Transmit Power Control
algorithm. Use this CLI parameter:
config advanced 802.11b tx-power-thresh -71
Allow the network to work through this adjustment with a minimum of 30
minutes to an hour before you observe any changes. Once the network is given a
sufficient amount of time, walk the site using the same survey tool and badges
again. Observe the same roaming characteristics and access point power. The
goal here is to attempt to have the badges roam at or before the next access
point to get the best possible signal to noise ratio.
How do I know if the tranmit power is too hot or too
Determining whether you have your transmit power threshold too high
or too low requires a good understanding of your environment. If you have
walked your entire deployment area (where you expect your Vocera badges to
function), you should know where your access points are located as well as
experience the roaming behavior of the badge.
What do I do if my transmit power is too hot?
The Vocera Badge roams based solely on the signal strength rather
than signal quality. If the Vocera Badge does not roam after it passes several
access points while engaged in the welcome tutorial or the test tone, the badge
is considered to be sticky. If this behavior is indicative of the entire campus
deployment area, then your transmit power threshold is too hot and should be
backed down. If only one or two isolated areas show this behavior and the rest
of the deployment area shows more idealistic roaming characteristics this is
not an indication that your network is running too hot.
What do I do if my transmit power is too cold?
The default transmit threshold should almost never provide you a
deployment area where your network runs too cold. If the transmit power
threshold is adjusted down, and walking the halls with the Vocera Badge
provides you with an environment where the badge roams well, but loses
connectivity and/or dead/spotty coverage, then your network might have been
tuned too low. If this is not characteristic of your entire network but
isolated to one or two areas, then it is more indicative of a coverage hole
rather than a network-wide problem.
If you find that in one or two areas, the badge sticks to an access
point rather than roaming in an idealistic manner, examine this area.
How is this area different from the rest of the campus?
If this/these areas are near building exits or areas under
construction, could coverage hole detection be forcing these access points to
raise the power?
Look at the WLC log file and access point neighbor lists to help
determine why such an anomaly could occur.
If you find that in one or more isolated areas, the badge experiences
dead or spotty coverage, then you need to examine these areas separately.
Is this area near an elevator shaft, radiology, or a break room?
These areas might be better suited by the installation or better
placement of an access point to allow for better voice coverage.
In both cases, it is always advisable to understand that you are
working in an unlicensed radio spectrum and idealistic behavior might not ever
be achievable. This could happen when you are situated next to a radio
transmission tower or device, a television transmitter or possibly a non-802.11
2.4 GHz repair facility (wireless phones, and so forth).
The Cisco Unified Wireless Network design and deployment guide should
be followed for the overall configuration of your WLC(s). This section provides
additional recommendations specific to Vocera® Communication Badges.
Note: Changes are left unsaved if you do not press the
Apply button before you move to the next step.
Complete these steps under the Controller top-level
Change Ethernet Multicast Mode to
Set the Multicast Group Address to 22.214.171.124 (or
some other unused multicast group address).
Set the Default Mobility Domain Name and RF-Network Name to your
Disable Aggressive Load Balancing.
Figure 9—General WLC Configuration
Click Controller > Interfaces.
Note: Your VLAN and IP address varies. The screen shots here provide sample
addressing which should not be directly followed.
Figure 10—List of WLC Interfaces
Complete these steps:
Enter a tag name representative of your Vocera VoWLAN network in
the Interface Name field.
Enter the VLAN number of that VoWLAN network in the VLAN ID field.
Click Apply and then click Edit
in order to edit the interface that you just created.
Enter the IP addressing for this interface that is in the range of
the VLAN and other related information.
For a WLAN that has only Vocera Badges, this configuration provides
sample settings that best support the Vocera Broadcast application.
Figure 11—802.11b/g Configuration
Complete these steps:
Update the Radio Policy field to a value that best fits you
Change Admin Status to
Set Session Timeout to 1800.
Set Quality of Service to
Set Broadcast SSID to
Set the Interface Name to the interface created for the Vocera
Set the security options to match your corporate
Figure 12—WLAN Configuration
Complete these steps:
Configure the AP Name.
Ensure that the access point is configured for
Ensure that Admin Status is
AP Mod” should be set to
Enter the location of the access point.
Enter the controller name that the access point belongs to. The
controller name can be found on the Monitor page.
Figure 13—AP Detail
Complete these steps:
Click Wireless located at the top of the WLC and
verify that all access points under Admin Status are set to
Click Network (located near 802.11b/g).
Use AutoRF to create a complete coverage with non-overlapping RF
channel and a transmit power. In order to do this, select
Automatic for both RF Channel Assignment and Tx Power Level
Click Save Configuration and see the
Tune AutoRF for Your Environment section of this
Choose Wireless > Access Points > 802.11b/g
After you conduct an RF site survey and configure the access points and
the phones, it is crucial to conduct verification tests to ensure that
everything works as desired. These tests should be performed at all of these
The primary area of each access point cell (where the badges are most
likely to connect to that particular access point).
Any location where there might be high call volume.
Locations where usage might be infrequent but coverage still has to
be certified (for example, stairwells, restrooms, and so
At the fringes of the access point's coverage area.
• These tests can be performed in parallel or series. If performed in
parallel, ensure that phones are powered off between testing points to test
full association, authentication, and registration at each location. Roaming
and load tests must be the final tests.
This section explains how to verify that the badge associates,
authenticates, and registers properly.
At multiple points throughout the environment, power-up the badges
and verify association with the access point. If the badge does not associate
with the access point, perform these checks:
Check the badge configuration to ensure proper SSID, authentication
type, and so forth.
Check the WLC configuration to ensure proper SSID, authentication
type, radio channels, and so forth.
Check your site survey to ensure the location has adequate RF
At multiple points throughout the environment, ensure that the phone
authenticates through the access point successfully. If the client does not
authenticate, check either the WEP key or the LEAP username and password on the
badges. Also, check the username and password on the AAA server by using a
wireless laptop with identical credentials.
At multiple points throughout the environment, ensure that the badges
register with the Vocera Communication Server. If the client does not register,
perform these checks:
Verify that the badge has the correct IP address, subnet mask,
primary gateway, primary TFTP, primary/secondary and
Stationary voice calls:
At multiple points throughout the environment, while you stand
still, make a call to another badge and conduct 60 to 120-second voice tests to
check voice quality. If the voice quality is unacceptable, move one badge to a
better location and test again. Is the voice quality acceptable? If not, check
your wireless coverage.
If the telephony server is configured, at multiple points
throughout the environment, stand still and make a call to a wired phone and
conduct 60 to 120-second voice tests to check voice quality. If the voice
quality is unacceptable, ask if you make a call using the wired phone. Is the
voice quality acceptable? If not, verify the wired network design against the
Use the site survey tools to verify that there is no more than one
access point per RF channel from that location with a signal strength (received
signal strength indicator [RSSI]) greater than 35. If there are two access
points present on the same channel, ensure that the signal-to-noise ratio (SNR)
is as high as possible to minimize interference. For instance, if the stronger
access point has an RSSI of 35, ideally the weaker access point should have an
RSSI of less than 20. In order to achieve this goal, you might have to reduce
one access point's transmit power or move the access point.
Check the QoS settings on the access point to confirm proper
Roaming badge calls:
If the telephony server is not available, initiate the Vocera
Tutorial with the command Begin Tutorial.
If the telephony server is available, initiate a call with a
stationary device to the badge.
Continually check voice quality while you traverse the total
wireless coverage area. If the voice quality is insufficient, perform these
Listen for all unacceptable changes in voice quality and take note
of the location and radio values on your laptop and CQ values from the
Watch and listen for the badge to roam to the next access
Note the other available access points in the site survey to check
coverage and interference.
Make adjustments to access point placement and settings to fine-tune
the WLAN, and perform these checks to ensure voice quality:
Use the site survey tools and verify that there is no more than one
access point per channel with an RSSI value greater than 35 in any given
location. Ideally, all other access points on the same channel should have RSSI
values as low as possible (preferably less than 20). At the border of the
coverage area where the RSSI is 35, the RSSI for all other access points on the
same channel should ideally be less than 20.
Use the site survey tools to verify that there are at least two
access points (total, on separate channels) visible in all location with
sufficient signal strength.
Check that the access points in a given roaming area are all on a
Layer 2 network.
These roaming issues can occur:
The badge does not roam when placed directly under the access
The badge is most likely not reaching the roaming differential
thresholds for the received signal strength indicator (RSSI) and channel
utilization (CU). Adjust the Transmit Power Threshold form the
The badge does not receive beacons or probe responses from the access
The badge roams too slowly.
Check authentication for a possible WEP mismatch.
The badge does not send out IGMP joins or the network sends IGMP
queries during a roam. Therefore, the Vocera broadcast function fails during a
Layer 2/Layer 3 roam.
The badge is capable of seamless Layer 2 roaming only (unless a Layer
3 mobility mechanism is configured). Ensure that the new WLC is not serving a
different IP subnet.
Verify that the associated access point/controller has IP
connectivity to the Vocera Communication Server.
Check the RF signal strength and badge CQ
Check for low RSSI on the destination access point.
Channel overlap might be insufficient. The badge must have time to
hand off the call smoothly before it loses its signal with the original access
The signal from the original access point might be
There are a few common configuration errors that can cause some easily
resolved audio issues. If possible, check audio problems against a stationary
(reference) badge to help narrow the problem to a wireless issue. Common audio
This problem can occur in the fringe areas of an access point, where
a signal might be too weak on either the badge side or the access point side.
Matching the power settings on the access point to the badge (20 mW), when
possible, can fix this problem. This problem is most common when the variation
between the access point setting and the badge setting is large (for example,
100 mW on the access point and 28 mW on the badge).
Check the gateway and IP routing for voice quality.
Check to see if a firewall or NAT is in the path of the proprietary
UDP packets. By default, firewalls and NATs cause one-way audio or no audio.
Cisco IOS® and PIX NATs and firewalls have the ability to modify those
connections so that two-way audio can flow.
One-way audio can occur if ARP caching is not configured on the
A common reason for choppy or robotic audio is when a microwave
operates nearby. Microwaves start at channel 9 and can extend from channels 6
Check for 2.4 Ghz wireless phones and other nurse call wireless
devices using tools like Cognio.
When you encounter problems with authentication, perform these
Check SSIDs to make sure they match on the badge and the access point
(or network). Also be sure the network has a route to the Vocera
Check the WEP keys to make sure they match. It is a good idea to
re-enter them on the Badge Configuration Utility (BCU) and reprogram the badge,
because it is easy to make a typing error when you enter a WEP key or
These messages or symptoms can occur:
Cannot Support All Requested Capabilities—This is most likely an
encryption mismatch between the access point and the client.
Authentication Failed / No AP Found—Ensure authentication types match
on the access point and the client.
No Service – IP Config Failed—If you use static WEP, ensure the keys
are configured correctly. Ensure other clients can receive DHCP using the same
De-authenticate all TKIP clients from AP—This problem happens when
the access point detects two MIC errors within 60 seconds. This countermeasure
keeps all TKIP clients from re-authenticating for 60 seconds.
Re-authentication / Session Timeout—If configured, a session timeout
triggers a re-authentication which causes gaps in the voice stream (300 ms +
WAN delay for 802.1x authentication).
This section gives examples of both proper and improper placement of
access points (APs) and antennas.
Figure 17 shows improper placement of an access point and antennas
close to an I-beam, which creates distorted signal patterns. An RF null point
is created by the crossing of signal waves, and multipath distortion is created
when signal waves are reflected. This placement results in very little coverage
behind the access point and reduced signal quality in front of the access
Figure 17—Improper Placement of Antennas Near an
Figure 18 shows the signal propagation changes or distortions caused by
an I-beam. The I-beam creates many reflections from both received packets and
transmitted packets. The reflected signals result in very poor signal quality
because of null points and multipath interference. However, the signal strength
is high because the access point antennas are so close to the
Figure 18—Signal Distortions Caused by Placing the Antennas Too
Close to an I-Beam
The access point and antenna placement in Figure 19 is better because
it is away from the I-beams and there are fewer reflected signals, fewer null
points, and less multipath interference. This placement is still not perfect
because the Ethernet cable should not be coiled up so close to the antenna.
Also, the access point could be turned with the 2.4GHz antennas pointed to the
floor. This provides better coverage directly below the access point. There are
no users above the access point.
Figure 19—Access Point and Antennas Mounted on a Wall, Away from
Figure 20 shows the signal propagation caused by the wall on which the
access point is mounted.
Figure 20—Signal Reflection Caused by a Wall
The preceding examples also apply when you place access points and
antennas in or near the ceiling in a standard Enterprise environment. If there
are metal air ducts, elevator shafts, or other physical barriers that can cause
signal reflection or multipath interference, Cisco highly recommends that you
move the antennas away from those barriers. In the case of the elevator, move
the antenna a few feet away in order to help eliminate the signal reflection
and distortion. The same is true with air ducts in the ceiling.
A survey conducted without sending and receiving packets is not
sufficient. The I-beam example shows the creation of null points that can
result from packets that have CRC errors. Voice packets with CRC errors are
missed packets that adversely affect voice quality. In this example, those
packets could be above the noise floor measured by a survey tool. Therefore, it
is very important that the site survey not only measures signal levels but also
generates packets and then reports packet errors.
Figure 21 shows a Cisco AP1200 properly mounted to a ceiling T-bar,
with the antennas in an omni-directional position.
Figure 21—Cisco AP1200 Mounted to a Ceiling
Figure 22 shows a Cisco Aironet 5959 omni-directional diversity antenna
properly mounted to a ceiling T-bar. In this case, the Cisco AP1200 is mounted
above the ceiling tile.
Figure 22—Cisco Aironet 5959 Antenna Mounted to a
Figure 23 shows a Cisco AP1200 properly mounted to a wall.
Figure 23—Cisco AP1200 Mounted to a Wall
Figure 24 shows the Cisco Aironet 2012 diversity patch antenna mounted
to a wall. In this case, the Cisco AP1200 is mounted above the ceiling
Figure 24—Cisco Aironet 2012 Antenna Mounted to a
For areas where user traffic is high (such as office spaces, schools,
retail stores, and hospitals), Cisco recommends that you place the access point
out of sight and place unobtrusive antennas below the ceiling. Separation for
non-diversity antennas should not exceed 18 inches.
The throughput performance of the WLAN network is affected by unusable
signals. WLAN interference can be generated by microwave ovens, 2.4 GHz
cordless phones, Bluetooth devices, or other electronic equipment operating in
the 2.4 GHz band. Interference also typically comes from other access points
and client devices that belong in the WLAN but that are far enough away so that
their signal is weakened or has become corrupted. Access points that are not
part of the network infrastructure can also cause WLAN interference and are
identified as rogue access points.
Interference and multipath distortion cause the transmitted signal to
fluctuate. Interference decreases the signal-to-noise ratio (SNR) for a
particular data rate. Packet retry counts go up in an area where interference
and/or multipath distortion are high. Interference is also referred to as noise
level or noise floor. The strength of the received signal from its associated
access point must be high enough above the receiver's noise level to be decoded
correctly. This level of strength is referred to as the signal-to-noise ratio,
or SNR. The ideal SNR for the Vocera Badge is 25 dB. For example, if the noise
floor is 95 decibels per milliwatt (dBm) and the received signal at the phone
is 70 dBm, then the signal-to-noise ratio is 25 dB. (See Figure
Figure 25—Signal-to-Noise Ratio (SNR)
When you change the type and location of the antenna, it can reduce
multipath distortion and interference. Antenna gain adds to the system gain and
can reduce interference if the interfering transmitter is not directly in front
of the directional antenna.
While directional antennas can be of great value for certain indoor
applications, the vast majority of indoor installations use omni-directional
antennas. Directionality should be strictly determined by a correct and proper
site survey. Whether you use an omni-directional or patch antenna, indoor
environments require diversity antennas to mitigate multipath distortion. The
Cisco Aironet Series Access Point radios allow for diversity support.
Signal attenuation or signal loss occurs even as the signal passes
through air. The loss of signal strength is more pronounced as the signal
passes through different objects. A transmit power of 20 mW is equivalent to 13
dBm. Therefore, if the transmitted power at the entry point of a plasterboard
wall is at 13 dBm, the signal strength is reduced to 10 dBm when exiting that
wall. This table shows the likely loss in signal strength caused by various
types of objects.
Signal Attenuation Caused By Various Types of
Object in Signal Path
Signal Attenuation through Object
Glass wall with metal frame
Cinder block wall
Metal door in brick wall
Each site surveyed has different levels of multipath distortion, signal
loses, and signal noise. Hospitals are typically the most challenging
environment to survey due to high multipath distortion, signal losses and
signal noise. Hospitals take longer to survey, require a denser population of
access points, and require higher performance standards. Manufacturing and shop
floors are the next hardest to survey. These sites generally have metal siding
and many metal objects on the floor, which result in reflected signals that
recreate multipath distortion. Office buildings and hospitality sites generally
have high signal attenuation but a lesser degree of multipath