Specifications

Network Requirements and Preparation
9 – 2 ShoreTel, Inc.
Overview
The ShoreTel 6.1 system is an IP-based voice solution deployed across your IP network.
This allows the components of the system to be located anywhere on your IP network,
resulting in a single system for all your voice applications at all locations. This single
system approach significantly reduces the complexity associated with legacy systems
that consist of multiple PBXs, multiple voice mail systems, multiple auto-attendants,
and multiple automatic call distribution systems, each with their unique management
interfaces.
Since the ShoreTel 6.1 system becomes another application on your IP network, it is
important to understand how the system integrates with your data network. As you
migrate your network to include voice as another application across your wide area
network, it becomes necessary for your IP LAN and WAN to provide a network that
meets the requirements for toll-quality voice. The ability of your network to deliver this
performance will vary based on the number of simultaneous calls between locations,
the voice quality required, and the other application traffic on the network. Some of the
key considerations are:
• Bandwidth
• Service levels
• Addressing
Advantages of Voice Over IP
Going back to the basics of voice, consider a traditional call over the Public Switched
Telephone Network (PSTN). The PSTN is a circuit-switched network. A telephone call
reserves an end-to-end physical circuit for the duration of the call. This circuit consists
of many subsegments within the PSTN, and a subsequent call between the same two
endpoints may follow a different path. However, for the duration of the call, the circuit
is fully available to that single call.
Packet-switched networks, such as the Internet, do not reserve a circuit between
endpoints. Instead, messages or files are broken into many small packets. These
packets may take different routes from source to destination, traveling along network
circuits that are shared with packets from other sources. These packets travel to the
final destination, where they are reconstructed into the original message or file.
One analogy between circuit-switched and packet-switched networks is that of railway
versus roadway transportation systems. A railway is similar to a circuit-switched
network. The path of the train is essentially reserved, and the whole train travels intact
from source to destination. A roadway, on the other hand, is shared among many
smaller units, each having the intelligence to find its destination. The railway provides
a clear end-to-end path, relatively immune to delays, but at a high overhead cost. The
roadway can be used more efficiently, but it is vulnerable to congestion.
The advantage of circuit-switched networks is that they provide dedicated bandwidth
between endpoints and therefore can easily guarantee a known, consistent quality of
service. Their disadvantage is their poor utilization of network resources, since they
demand a dedicated, separate network relative to the packet-switched network.
Conversely, the advantage of packet-switched networks is that they provide better
utilization of network resources, enable flexible traffic routing, provide a single
network to manage, allow for standard voice and data monitoring tools to be used,
allow applications to be shared over a common network, and enable applications to
become more portable—and this is just the beginning.