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Telecom operators will carry more VoIP calls over satellite links
even in poor weather—using WTL’s Dynamic Trunk Capacity (DTC) for
DVB-S2
Brussels, Belgium, August 31, 2009, WTL have today announced an improved
solution for operators carrying VoIP traffic over DVB-S2 satellite
links. By using major enhancements in the latest DVB-S2 terminals
WTL have produced a highly efficient package for telecom operators
who route multiple VoIP calls. WTL have worked closely with DVB-S2
transmission equipment to bring a new dimension to the solution by
developing Dynamic Trunk Capacity (DTC) and including it in a range
of VoIP SoftSwitches that react intelligently to changes in link
conditions.
DVB-S2 products offer Low Density Parity Check (LDPC), a new error
correction code, and also new modulation schemes: Variable Coding
and Modulation (VCM), and Adaptive Coding and Modulation (ACM). All
combine to increase the available throughput of a given satellite
channel by up to 130%.
WTL have taken advantage of new DVB-S2 features like Newtec’s
implementation of ”Flex ACM” which allows the satellite terminal to
renegotiate the coding/modulation scheme being used “on-the-fly,”
according to atmospheric conditions. This means that the most
effective modulation is used at any given time ensuring maximum
throughput for the prevailing conditions is always achieved. Tests
show that changing modulation and coding can give additional
bandwidth efficiency of more than 50%.
The Problem of
“Rain-Fade”
Adverse weather can affect satellite performance. For example,
torrential rain in tropical regions can reduce bandwidth by 5 – 20%,
depending on the frequencies and encoding involved. This leads to a
difficult trade-off when setting link capacity between the clear-sky
performance and the worst case.
To account for this the WTL software samples the link quality every
few seconds and dynamically adapts to any changes. For example, when
weather changes mean the link performance is reduced, ACM will come
into operation and down-shift the modulation scheme to a lower
throughput; the WTL SoftSwitch will detect this, and reduce the
number of calls allowed over this route. Of course, the reverse is
also true: as conditions improve and the link performance recovers,
the SoftSwitch will detect this and open up the connection to more
calls. WTL already help operators to use satellite trunks
efficiently by using the patented NOP bandwidth saving technique.
This typically saves at least half the bandwidth consumed by
standard VoIP calls. NOP also protects voice quality from problems
caused by packet loss and jitter in shared satellite links.
Variable bandwidth availability over satellite links can lead to
quality problems for VoIP equipment, and this happens particularly
in a shared link environment, where the bandwidth available for VoIP
compared to data can change. If an IP link is only capable of
carrying 10 VoIP calls, adding an 11th will overload the
link and degrade the quality of all 11 calls: not just the extra
call. On the other hand, avoiding this problem by intentionally
under-provisioning the link wastes valuable bandwidth.
WTL’s new development also overcomes the problem of variable
bandwidth by allowing the switch to detect bandwidth saturation
conditions, and to quickly adapt the capacity of the link so that
the packet error rate stays under control. The capacity of the link
is controlled under 2 conditions:
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Slight link degradation. In
this case there is no need for extreme measures, and a graceful
reduction occurs: the WTL switch will not route new calls over the
degraded link; calls complete and are not replaced by new ones
until the link capacity has reduced to the desired level.
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Severe link degradation.
Rapid reduction in link usage is needed in order to preserve the
quality of active calls: the WTL switch selectively closes calls
and rejects new call attempts until the traffic reduces to the
link’s current capacity.
Simon Pearson, WTL’s Business Development Director, commented, “WTL
NOP and DTC both offer major efficiency benefits to help customers
get the most out of their satellite channels. The DVB-S2 terminals
do this at the coding and transmission layer, whilst we do it at the
VoIP or payload layer. It made sense that we should combine these
two approaches to offer the best efficiencies in the market for
telecom operators carrying VoIP over satellite.”
WTL’s DTC is now available following testing with pilot customers.
It is suitable for fixed or mobile operators with a call capacity
from 10 to 10,000 simultaneous calls.
About WTL
World Telecom Labs is a Belgium-based company which has long been a
leader in the provision of VoIP switches, Pre-Paid applications, and
signaling gateways for emerging carriers and telecom service
operators. WTL has an installed base of 100,000s of voice ports with
service providers worldwide switching billions of minutes of VoIP
traffic using WTL equipment.
For more details Email:
sales@wtl.be or Check our
Web Site:
www.wtl.be
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