IP Centrex CPE

Customer Gateways, Terminal Adapters, and Integrated Access Devices (IADs)
IP Phones and LAN Phones
Softphones and Firmphones
Ethernet Switches for LAN

Customer Gateways, Terminal Adapters, and Integrated Access Devices (IADs)

A Customer Gateway allows existing analog and/or ISDN station equipment to be used on IP Centrex lines. The Customer Gateway has an Ethernet interface for connecting to the LAN. It also provides jacks to connect analog devices (telephones, fax machines) and/or ISDN telephone sets. On behalf of the analog devices it serves, the customer gateway performs voice digitization & packetization and converts analog signaling into IP telephony messages. On behalf of the ISDN telephones it serves, the Customer Gateway performs voice packetization and converts Q.931 messages into IP telephony messages. The customer gateway sends the IP telephony messages across the LAN, over the broadband access facility, and through the managed backbone network to the Network Gateway (for Class 5 switch architectures) or to the Softswitch (for Softswitch architectures.)

A Customer Gateway serves a number of stations and would typically be located in a telephone closet where it connects to the building's telephone wiring. A Terminal Adapter is similar to a Customer Gateway in its function. However, the Terminal Adapter can only support one or several stations and would typically be located near a user's desk. A common use a Terminal Adapter is to allow a conventional fax machine to be part of an IP Centrex group.

The term Integrated Access Device (IAD) is used when a Customer Gateway or Terminal Adapter is combined with an IP Router, Ethernet hub/switch, and broadband service device (e.g., DSL modem, cable modem) into a single piece of CPE.

IP Phones and LAN Phones

The IP Phone (also known as a LAN Phone or Ethernet Phone) combines the Customer Gateway functionality and telephone set functionality into one device. The IP Phone has an Ethernet interface to the LAN. It digitizes and packetizes the user's speech and also generates the appropriate IP Telephony signaling messages. An IP Phone is typically a multi-button device with an LCD screen; it often can support advanced call control capabilities. Some IP Phones contain an integrated passive hub or Ethernet switch. The passive hub allows the Ethernet connection from the user's PC to be plugged into the IP Phone, and the IP Phone is subsequently plugged into the LAN. This passive hub allows the two devices to use the same LAN connection and avoids the need for additional wiring to the desktop for the IP Phone. An integrated Ethernet switch also minimizes the wiring requirements to the desktop but it also can support QoS mechanisms to prevent the PC's data traffic from impairing voice quality during calls.

Softphones and Firmphones

When a PC is equipped with microphones and speakers (or a headset), the PC can be used as a telephone. In this configuration, known as a softphone, the PC is loaded with a software application that performs the functions of an IP Phone. Because the same processors are used to support the softphone application as well as other applications, a call's quality can degrade when the Operating System seizes the PC's resources. This problem is resolved by the firmphone. A firmphone is a softphone where a new hardware card is added to the PC. This card provides dedicated hardware resources for Voice over Packet, so call quality does not degrade when the OS is busy.

Ethernet Switches for LAN

Ethernet LANs for data applications can be built using Ethernet hubs or switches. Depending on a number of factors, including the number of PCs, the number of Centrex stations, the pre-existing data traffic, and the LAN's pre-existing capacity, it may be necessary to upgrade a hub-based LAN to Ethernet switches before adding IP Centrex service. In some instances, it may be desirable to build a separate LAN (or portion of a LAN) just for IP Centrex service; in this approach, it is easier to address reliability and quality of service concerns.