Trapeze Networks MX-2XX-VOICE-LIC Fiche De Données
Dynamic Call Admission Control
Another challenge with large-scale voice
deployments, is how to manage AP resources
so they are neither wasted nor oversubscribed.
Specifically, the objective is to allow new calls
when the AP is idle, and prevent too many
concurrent calls degrading performance once
a threshold has been reached. The mechanism
for achieving this is known as Call Admission
Control (CAC).
deployments, is how to manage AP resources
so they are neither wasted nor oversubscribed.
Specifically, the objective is to allow new calls
when the AP is idle, and prevent too many
concurrent calls degrading performance once
a threshold has been reached. The mechanism
for achieving this is known as Call Admission
Control (CAC).
Without the ability to detect all voice calls
regardless of which SSID or device they origi-
nate from and which protocol is used, it is vir-
tually impossible to manage AP resources to
match demand. In fact, most vendors’ CAC is
little more than an arbitrary cap on the number
of devices that can associate with an AP, with
no awareness of active calls.
regardless of which SSID or device they origi-
nate from and which protocol is used, it is vir-
tually impossible to manage AP resources to
match demand. In fact, most vendors’ CAC is
little more than an arbitrary cap on the number
of devices that can associate with an AP, with
no awareness of active calls.
What matters to voice networks is active calls,
not associated devices. Hence, these simplistic
CAC implementations suffer from two common
problems: New callers being denied service even
though the AP could easily handle the call; and
active calls roaming from another AP, being
dropped.
not associated devices. Hence, these simplistic
CAC implementations suffer from two common
problems: New callers being denied service even
though the AP could easily handle the call; and
active calls roaming from another AP, being
dropped.
To avoid these errors, many wireless administra-
tors resort to disabling CAC altogether. But with
no CAC enforcement at all, there is nothing to
prevent over-subscription - thus as utilization
increases, they run the risk of degraded voice
quality by allowing too many simultaneous calls
on the same AP. Neither alternative is good -
one starves voice users from available resources,
the other allows too many calls without having
adequate capacity for peak demand.
tors resort to disabling CAC altogether. But with
no CAC enforcement at all, there is nothing to
prevent over-subscription - thus as utilization
increases, they run the risk of degraded voice
quality by allowing too many simultaneous calls
on the same AP. Neither alternative is good -
one starves voice users from available resources,
the other allows too many calls without having
adequate capacity for peak demand.
In contrast Trapeze Networks’ dynamic CAC
mechanism is stateful - it leverages stateful SIP
awareness in conjunction with other standards
such as WMM and TSPEC to recognizes active
calls regardless of origin. This maximizes avail-
ability of AP resources for voice services, and
preserves voice quality for active calls, by block-
ing new calls from starting, once the Active Call
Limit is reached. Even if the Active Call Limit is
reached, roaming calls will be accepted, but new
calls cannot be initiated until the Active Call
number falls below the threshold.
mechanism is stateful - it leverages stateful SIP
awareness in conjunction with other standards
such as WMM and TSPEC to recognizes active
calls regardless of origin. This maximizes avail-
ability of AP resources for voice services, and
preserves voice quality for active calls, by block-
ing new calls from starting, once the Active Call
Limit is reached. Even if the Active Call Limit is
reached, roaming calls will be accepted, but new
calls cannot be initiated until the Active Call
number falls below the threshold.
TSPEC and SIP Integration
Given that various standards, legacy protocols
and signaling methods are used for voice, a
holistic approach is needed to ensure that
mixed environments are properly supported
and managed. While many voice vendors have
used proprietary protocols, most handsets use
the WMM TSPEC signaling mechanism to indi-
cate their bandwidth and QoS requirements to
the AP by way of Add Traffic Stream (ADDTS)
messages. If the AP is not able to service those
requirements the client cannot set up a call.
Similarly, roaming clients that are already in a
call, also send an ADDTS message to a new AP
during the association process to ensure band-
width is available before completing the roam,
and will seek out an alternative AP if not. With
Dynamic CAC, Trapeze APs monitor the ADDTS
messages so it can adjust the Active Call count
based on WMM TSPEC state. This way, both SIP
clients and TSPEC compliant clients are taken
into account when evaluating the committed
AP resources.
and signaling methods are used for voice, a
holistic approach is needed to ensure that
mixed environments are properly supported
and managed. While many voice vendors have
used proprietary protocols, most handsets use
the WMM TSPEC signaling mechanism to indi-
cate their bandwidth and QoS requirements to
the AP by way of Add Traffic Stream (ADDTS)
messages. If the AP is not able to service those
requirements the client cannot set up a call.
Similarly, roaming clients that are already in a
call, also send an ADDTS message to a new AP
during the association process to ensure band-
width is available before completing the roam,
and will seek out an alternative AP if not. With
Dynamic CAC, Trapeze APs monitor the ADDTS
messages so it can adjust the Active Call count
based on WMM TSPEC state. This way, both SIP
clients and TSPEC compliant clients are taken
into account when evaluating the committed
AP resources.
Call Detail Records
The ability to distinguish between voice capable
devices and actual calls, gives rise to a wealth of
new reporting, analytics and accounting capa-
bilities around the ulitization of voice services.
devices and actual calls, gives rise to a wealth of
new reporting, analytics and accounting capa-
bilities around the ulitization of voice services.
This has important benefits for wireless capac-
ity planning too. Since the AP is now able to
detect a call being initiated and ended, it can
produce call detail records (CDRs) which are
send as standards compliant RADIUS messages
that may be stored in any RADIUS server. In
addition to call-start and call-end information,
the CDR also contains voice quality attributes,
source and destination caller IDs, SSID, AP,
duration and much more. These CDRs can be
used for accounting purposes and many other
applications by different stakeholders. The CDRs
are collected from the access points by the
WLAN controller and may be passed upstream
to RingMaster and SmartPass where they can
be used by IT management for a number of
applications, including monitoring voice roam-
ing patterns, voice quality analysis, capacity
planning and so on.
ity planning too. Since the AP is now able to
detect a call being initiated and ended, it can
produce call detail records (CDRs) which are
send as standards compliant RADIUS messages
that may be stored in any RADIUS server. In
addition to call-start and call-end information,
the CDR also contains voice quality attributes,
source and destination caller IDs, SSID, AP,
duration and much more. These CDRs can be
used for accounting purposes and many other
applications by different stakeholders. The CDRs
are collected from the access points by the
WLAN controller and may be passed upstream
to RingMaster and SmartPass where they can
be used by IT management for a number of
applications, including monitoring voice roam-
ing patterns, voice quality analysis, capacity
planning and so on.
When used in conjunction with Trapeze Location
Services, this information can also be used
to detect emergency calls and to direct first
responders to the exact location of the caller.
Services, this information can also be used
to detect emergency calls and to direct first
responders to the exact location of the caller.
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