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Network design
802.3af specifications) that provides centralized power over pins 7 and 8 using a special cord
with over-current protection, and alarm LEDs for each output. The 1145B uses a locking station
cord to guard against damage, compared to the signature detection method of the IEEE Draft
802.3af specifications.
WAN
Because of the high costs and lower bandwidths available, there are some fundamental
differences in running IP Telephony over a WAN versus a LAN. Because of the resource
scarcity, it is important to consider network optimizations and proper network design, because
problems are more likely to manifest themselves in a WAN environment.
Topics covered include:
Overview
Frame Relay
Overview
The overview section covers:
QoS
Codec selection and compression
Serialization delay
Network design
QoS
In particular, QoS becomes more important in a WAN environment than in a LAN. In many
cases, transitioning from the LAN to the WAN reduces bandwidth by approximately 99%.
Because of this severe bandwidth crunch, strong queuing, buffering, and packet loss
management techniques have been developed. These are covered in more detail in the
of Service guidelines
Recommendations for QOS
In general, for the WAN, Avaya recommends tagging IP Telephony bearer and signaling
packets with DiffServ Code Point (DSCP) 46 (Expedited Forwarding). This tagging can be
administered in Avaya IP Telephones, Communication Manager, and circuit packs. At the
routers, Avaya recommends using strict priority queuing for voice packets, and weighted-fair
queuing for data packets. Voice packets should always get priority over non-network-control
data packets. This type of queuing is called Class-Based Queuing (CBQ) on Avaya data
networking products, or Low-Latency Queuing (LLQ) on Cisco routers.
302 Avaya Application Solutions IP Telephony Deployment Guide
chapter.
Quality
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