Avaya 555-245-600 Manual Do Utilizador

Some common negative practices that can severely impact network performance, especially 
when using IP Telephony, include:

●

A flat, non-hierarchical network, for example, cascading small workgroup switches 
together. This technique quickly results in bottlenecks, because all traffic must flow across 
the uplinks at a maximum of 10 Gbps, versus traversing switch fabric at speeds of 
256 Gbps or greater. The greater the number of small switches or layers, the greater the 
number of uplinks, and the lower the bandwidth for an individual connection. Under a 
network of this type, voice performance can quickly degrade to an unacceptable level.

●

Multiple subnets on a VLAN. A network of this type can have issues with broadcasts, 
multicasts, and routing protocol updates. This practice can have a significant negative 
impact on voice performance, and complicate troubleshooting.

●

A hub-based network. Hubs in a network create some interesting challenges for 
administrators. It is advisable not to link more than four 10baseT hubs or two 100baseT 
hubs together. Also, the collision domain, the number of ports that are connected by hubs 
without a switch or router in between, should be kept as low as possible. Finally, the 
effective (half-duplex) bandwidth that is available on a shared collision domain is 
approximately 35% of the total bandwidth that is available.

●

Too many access lists. Access lists slow down a router. While access lists are 
appropriate for voice networks, care must be taken not to apply them to unnecessary 
interfaces. Traffic should be modeled beforehand, and access lists applied only to the 
appropriate interface in the appropriate direction, not to all interfaces in all directions.

Avaya recommends caution when using the following:

●

Network Address Translation (NAT). IP Telephony may not work across Network 
Address Translation (NAT), because if private IP addresses are exchanged in signaling 
messages, these addresses are not reachable from the public side of the NAT and cannot 
be used for the media sessions. See 

on page 302 for more information on the 

problem and solutions for using NAT with IP Telephony. 

●

Analog dial-up. Be careful in using analog dial-up (56 K) to connect two locations. 
Upstream bandwidth is limited to a maximum of 33.6 K, and in most cases is less. This 
results in insufficient bandwidth to provide toll-quality voice. Some codecs and network 
parameters provide connections that are acceptable, but consider each connection 
individually.

●

Virtual Private Network (VPN). Large delays are inherent in some VPN software products 
due to encryption, decryption, and additional encapsulation. Some hardware-based 
products, including Avaya VPN products, encrypt at near wire speed, and can be used. In 
addition, if the VPN is run over the Internet, sufficient quality for voice cannot be 
guaranteed unless delay, jitter, and packet loss are contained within the parameters that 
are listed above. See 

 for more information.