Any network condition that can affect the flow of encoded audio
packets between client devices or computers, between clients and
Office Communications Server, or between a client and the IP/PSTN
gateway can impair voice quality. The audio signal that is
transmitted across a network is digitally encoded and encapsulated
in RTP packets, which are not subject to the type of interference
that typically affects analog audio streams.
The most common network-related issue areas are caused by the
loss of audio packets or delays in the transmission of the packets
(that is, jitter), which can produce unwanted audio artifacts (that
is, distortions) or silence when the Office Communicator client
receives and processes the audio packets. In the case of receipt of
an incomplete RTP packet stream that cannot be adequately corrected
(that is, healed), the audio can be poor or even unintelligible.
Network issues can also be caused by high latency (that is, long
round-trip times) or low bandwidth. In some cases, transmission
packets that are out of order can cause network issues. The
following table describes network-related voice quality issues.
Table 2. Network-related
voice quality issues
||Potential Symptoms and Causes
- Wi-Fi networks are often a source of packet loss, generally
ranging from a low level of loss (< .5% of packets) to extremely
high levels (> 50% of packets). This loss can occur in public
Wi-Fi hotspots, home networks, and enterprise Wi-Fi deployments.
Typical sources of interference include other wireless devices and
phones, competing Wi-Fi networks, low density of access points, and
- Wireless wide area networks (WANs) are vulnerable to connection
issues caused by devices that operate on similar frequencies and
use the same infrastructure.
- High network traffic can cause the allocated bandwidth to be
consumed, which can prevent packet transmission and cause packet
loss. This can happen because of insufficient capacity of IP/PSTN
gateways, edge servers, home office network components, or other
- Internet Protocol security (IPSec) key negotiations can
increase the time required to set up a call, which can result in
dropped packets if negotiations exceed network thresholds.
- Policies that are applied by software or hardware firewalls,
proxy servers, routers, and gateways can affect the VoIP traffic.
Such policies can result in dropping of VoIP traffic or routing of
network traffic to paths or queues that might be overloaded.
- Hardware failures or configuration errors can cause packet
loss. These failures can be hardware issues or half-duplex
configuration settings that cause premature link saturation.
- High packet delays or a sudden increase in delays can cause
packets to be dropped by the receiving client’s audio processing
component, even if they eventually arrive at the network layers.
- Wi-Fi and wireless WANs often cause high jitter among network
- The quality of home broadband connections can vary. The use of
queuing algorithms to control the bandwidth or even the design of
the transmission medium can affect the amount of jitter on the
- Jitter in received RTP packets can increase one-way audio delay
at the receiver.
- Satellite networks have high latency because of the distances
that the signal must travel.
- The distance between client computers can significantly
increase one-way and round-trip latencies. The distance to be
travelled includes the route that network traffic takes between two
Office Communicator clients and between an Office Communicator
client and the Mediation Server. High latency can be the result of
significant geographic distances, of inefficient deployment of
Office Communications Servers, or of the underlying network
- Public Wi-Fi hotspots that are designed for Web browsing and
e-mail may not have sufficient bandwidth for audio communication.
The available bandwidth at a hotspot at any given time depends on
many factors, including the bandwidth usage of all users.
- Wireless WAN bandwidth can vary depending on the location of
the user relative to the transmission tower.
- WANs and home broadband networks are often shared by multiple
users, which can saturate one or more links.