Specifications

Bandwidth, Codecs and Compression

179

Redundant WAN links and load sharing

The usable bandwidth to be counted on such links (by number of calls using the link) must be

considered and may be set according to business requirements. A standby link may provide

the same, or reduced, bandwidth as compared to the main link that has failed. In this case, the

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

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.