Mitel mivoice business Engineering Manualline page 197

usable bandwidth is likely to drop when the backup link is activated. Each individual business
must consider if this is likely to cause problems and either set the limits to match, or accept
that, under failure conditions, some call issues may occur.
A load sharing link is similar to the standby link described above, since the overall bandwidth
is again likely to be reduced. Again, the business needs to determine what level of bandwidth
is acceptable.
Mitel recommends that you determine the minimum available bandwidth during the failure
condition, and use this as the normal limit. This will ensure that a failed WAN link has minimal
impact on the voice quality.
Routers that can deal with load sharing and hot standby links include protocols such as Virtual
Router Redundancy Protocol (VRRP) and/or Hot Standby Router Protocol (HSRP).
Example Hot Standby link
Suppose the business has two WAN links:
• 1.544Mbits/s
• 256kbits/s
Normally, the main 1.544 Mbit/s link is active and there is sufficient bandwidth for voice and
data. If this link fails, the backup is reduced to 256 kbit/s. To minimize voice issues during link
failure, the lower link rate should be used to determine available voice bandwidth. Nevertheless,
the business may be willing to handle the occasional outage and reduced voice quality to get
an increased number of voice channels.
Example load sharing link
Suppose the business has two WAN links that provide load sharing:
• 1.544Mbit/s
• 1.544Mbit/s
Together these two links can provide an aggregate bandwidth of around 3 Mbit/s, but during a
failure, this will drop to 1.544Mbit/s. Mitel recommends that the bandwidth allocation for voice
in this case be 1.544Mbit/s, but again, this is dependent on the requirements of the individual
business.
Additional information
For more details and for programming information refer to the Mitel System Administration Tool
Help for MiVoice Business.
Inter-zone bandwidth settings
As well as defining the zones and links between locations, the available bandwidth also needs
to be defined. Generally the available bandwidth on these links is also determined by the WAN
link protocol. This could be a dedicated link running cPPP, or may be a more general purpose
connection such as MPLS, or xDSL. Although the payload (IP) is common to these WAN
protocols, the bandwidth on the physical wire link may not be. The MiVoice Business system
considers the throughput, or payload bandwidth, with some minor overhead and is defined in
Table 54.
Bandwidth, Codecs and Compression
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