Avaya 555-245-600 Manual Do Utilizador

In general, these concerns dictate a hierarchical network that consists of at most three layers 
(

●

Core

●

Distribution

●

Access 

Some smaller networks can collapse the functions of several layers into one device.

For IP Telephony to work well, WAN links must be properly sized with sufficient bandwidth for 
voice and data traffic. Each voice call uses 9.6 Kbps to 120 Kbps, depending on the desired 
codec, payload size, and header compression used. Additional bandwidth might be used if 
wideband audio or video is implemented. The G.729 compression algorithm, which uses about 
27 Kbps of bandwidth, is one of the most used standards today. Traditional telephone metrics, 
such as average call volume, peak volume, and average call length, can be used to size 
interoffice bandwidth demands. See 

 for more information.

Quality of Service (QoS) also becomes increasingly important with WAN circuits. In this case, 
QoS means the classification and the prioritization of voice traffic. Voice traffic must be given 
absolute priority through the WAN. If links are not properly sized or queuing strategies are not 
properly implemented, the quality and the timeliness of voice and data traffic will be less than 
optimal.

The core layer is the heart of the network. The purpose of the core 

layer is to forward packets as quickly as possible. The core layer 

must be designed with high availability in mind. Generally, these 

high-availability features include redundant devices, redundant power 

supplies, redundant processors, and redundant links. Today, core 

interconnections increasingly use Gigabit Ethernet or 10 Gigabit 

Ethernet.

The distribution layer links the access layer with the core. The 

distribution layer is where QoS feature and access lists are applied. 

Generally, Gigabit Ethernet connects to the core, and either Gigabit 

Ethernet or 100base-TX/FX links connect the access layer. 

Redundancy is important at this layer, but not as important as in the 

core. This layer is combined with the core in smaller networks.

The access layer connects servers and workstations. Switches at this 

layer are smaller, usually 24 to 48 ports. Desktop computers, 

workstations, and servers are usually connected at 100 Mbps or 

1 Gbps. Limited redundancy is used. Some QoS and security 

features can be implemented in the access layer.
Power over Ethernet (PoE) is included to power IP telephones and 

other access devices.