LAN vs. WAN Bandwidth
time. If there is sufficient bandwidth in the network compared to the payload of the
devices connected to the network, the VoIP system will probably meet the definition of
mission-critical success on that network.
LAN vs. WAN Bandwidth
It is fairly easy and inexpensive to create a high-bandwidth “internal” Local Area
Network (LAN) within a single building to help ensure that the bandwidth-to-payload
ratio stays high. However, it becomes more difficult once the traffic makes its way onto
some Wide Area Network (WAN) “external” bearer with limited or unpredictable
bandwidth. The bandwidth of various bearers is mostly a function of how much monthly
fee the user is willing to pay for service. DSL speeds of 100-200 kbps are fairly
inexpensive. Cable and WiMAX are often in the 0.5 to 5 Mbps range (speed may vary
depending on loading by other users). DSL and Cable are generally used for public
(internet) rather than private networks, where security can be an issue, and where
bandwidth can not generally be guaranteed. T1 and E1 are 1.5 or 2 Mbps respectively
which can have less bandwidth than Cable or WiMAX, but they do offer a guaranteed
bandwidth, and they can be used for a private (non internet) network. Fiber offers the best
bandwidth, but at a cost generally higher than other options.
Data vs. Voice Traffic
It is hard to quantify how much payload data-traffic uses unless intelligent network
equipment is configured to intentionally control the amount of payload allowed through.
Without such limits, data applications can briefly take up the entire available bandwidth
of a limited pipe such as a T1 or E1 circuit (e.g. during file downloads). Unlike VoIP
applications, where lost packets are audibly recognized, dropped data packets are usually
not recognized by the application user. This is because data packets have built-in retry
mechanisms – if one gets dropped, the same packet is sent again until it makes its way
through the network. However, with VoIP packets, there are generally no such retries –
lost packets are usually not recovered. Thus the most notable effect of lost data packets is
increased delay in getting the data (e.g. web pages take longer to load, etc.), but the
notable effect of lost voice packets is gaps in the received audio – missing syllables and
words. A sparse number of dropped packets is usually unnoticeable to a data user, while
still very noticeable to a voice user. For this reason a network that may have been
perfectly adequate for data-only applications, could be horrible for voice
applications.
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