Cisco IP Phone 7905G Administration Guide for H.323
Cisco IP Phone 7905G for H.323 Overview

Table Of Contents

Cisco IP Phone 7905G for H.323 Overview


Hardware Overview

Software Features


Basic Services

Supplemental Services

H.323 Overview

Components of H.323

H.323 Terminals

H.323 Gateways

H.323 Gatekeepers

H.323 MCUs

H.323 Proxy Server

Cisco IP Phone 7905G for H.323 Overview

This chapter describes the hardware and software features of Cisco IP Phone 7905G and provides a brief overview of H.323 protocol. It contains the following sections:


Hardware Overview

Software Features

H.323 Overview


The Cisco IP Phone 7905G is a cost-effective, entry-level, single-line telephone that operates on IP-based telephony networks. It provides access to IP telephony applications and makes use of broadband bandwidth that are available with digital subscriber line (DSL), fixed wireless, cable modems, and other Ethernet connections. The Cisco IP Phone 7905G is easily installed by an end user.

Hardware Overview

The Cisco IP Phone 7905G is a compact, easy-to-install device that can function as a desk unit or be mounted on a wall. Figure 1-1 shows the Cisco IP Phone 7905G.

Figure 1-1 Cisco IP Phone 7905G


LCD screen to provide status messages.


Hold button.


Signaling protocol: H.323.


Dial pad.


Softkeys. These keys vary, depending on current phone activity.


Volume button for handset or speaker (depending on which is active). Also controls the ring volume when the handset is on-hook.


Navigation button to scroll through text and navigate the LCD display.


Handset with indicator light that blinks for incoming calls.


Menu button to provide access to phone services.



The unit provides the following connectors and indicators:


Switch hook

Ringer with LED

12-key dial pad


Volume toggle

Vertical scroll navigation toggle

2 backlit LED hard keys, for Hold and Services

4 soft-key buttons

Monochrome (black/white) 192x64 resolution LCD display

RJ-45 10BASE-T Ethernet port—To connect the phone to a 10/100BASE-T hub or another Ethernet device

Software Features

The Cisco IP Phone 7905G supports the following software features:


Basic Services

Supplemental Services


The Cisco IP Phone 7905G supports the following protocols:

Cisco Discovery Protocol (CDP)

Domain Name System (DNS)

Dynamic Host Configuration Protocol (DHCP)


Internet Control Message Protocol (ICMP)

Internet Protocol (IP)

Real-Time Transport Protocol (RTP)

Simple Network Time Protocol (SNTP)

Transmission Control Protocol (TCP)

Trivial File Transfer Protocol (TFTP)

User Datagram Protocol (UDP)

Basic Services

The Cisco IP Phone 7905G supports the following basic services.

Provisioning through LCD screen menus, TFTP server, or web browser

IP address assignment—DHCP or manual static IP address

Configurable Type of Service (ToS) bit for Quality of Service (QoS)

Configurable ring

Configurable tone (dial tone, ringback tone, busy tone, alert tone, reorder tone)

G.711 u-law and A-law support

Voice-activity-detection (VAD) and comfort-noise-generation (CNG) support for G.711 u-law and G.711 A-law, and support for G.729 Annex B

Out-of-band dual-tone multifrequency (DTMF) relay support

Dynamic jitter buffer for voice packets

Supplemental Services

The Cisco IP Phone 7905G supports the following supplemental services:

Call waiting support

Calling line ID presentation/rejection (CLIP/CLIR) support

Three-way calling support

Call hold support

H.323 Overview

H.323 is the International Telecommunication Union (ITU) standard for transmitting voice, video, and data across an IP network. Like other VoIP protocols, the H.323 standard is designed to address the functions of signaling and session management within a packet telephony network. Signaling allows call information to be carried across network boundaries. Session management provides the ability to control the attributes of an end-to-end call. The H.323 standard includes support for call signaling and control, multimedia transport and control, and bandwidth control for both point-to-point and point-to-multipoint conferences.

The H.323 standard consists of the following components and protocols:

Call signaling using the H.225 protocol

Media control using the H.245 protocol

G.711, G.722, G.723, G.728, and G.729 audio codecs

H.261 and H.263 video codecs

Data sharing using the T.120 protocol

Real-time transport protocol (RTP) and RTP Control Protocol (RTCP) for media transport

Components of H.323

The H.323 standard employs a system of interconnected voice terminals, gateways, gatekeepers, multipoint control units (MCUs), and proxy servers.

Voice terminals provide point-to-point and point-to-multipoint conference capability for audio, video, and data. Voice gateways interconnect the packetized IP network to the PSTN or ISDN network. Gatekeepers provide admission control and address translation services for H.323 voice terminals and gateways. MCUs enable two or more gateways to engage in point-to-point or point-to-multipoint audio or video conferences. Figure 1-2 shows the components in a H.323 system.

Note The term conference refers to an established session (or call) between two or more endpoints (terminals). In this document, the terms conference and call are used interchangeably.

Figure 1-2 H.323 Architecture

H.323 Terminals

In the context of an H.323 network, voice terminals must feature system control units, media transmission capabilities, audio codecs, and network interfaces suitable for transmitting and receiving packetized data.

H.323 Gateways

H.323 gateways have characteristics of both standard Switched Circuit Network (SCN) access points and H.323 access points. Gateways handle the translation of audio, video, and data transmission formats as well as communications systems and protocols. The primary responsibility of H.323 gateway is to perform call setup and teardown operations between packetized IP networks and standard switched networks.

Note Gateways are only necessary in H.323 systems where calls must connect over both packetized IP networks and switched circuit networks like the PSTN.

H.323 Gatekeepers

Gatekeepers are primarily responsible for pre-call and call-level control services for H.323 gateways. Gatekeepers are optional components in H.323 systems, When gatekeepers are used in a system, they perform the following call setup and management services:

Address translation for IP addresses originating from H.323 aliases (, for example) or E.164 addresses (e.g., standard telephone numbers)

Admissions control for authorizing or rejecting access to a H.323 zone.

Bandwidth control for gateway bandwidth requirements

Zone management for registered voice terminals, gateways and MCUs

Gatekeepers can also provide the following optional functionality:

Call control signaling using the gatekeeper Routed Call Signaling model

Call authorization to restrict access to certain voice terminals or gateways or to restrict access based on time-of-day criteria

Bandwidth management for the H.323 system that will enable the gateway to restrict access when requested bandwidth is unavailable

Call management including maintaining a list of active calls you can use to indicate available and unavailable voice terminals and gateways

H.323 MCUs

MCUs are endpoints in H.323 networks that support point-to-multipoint conferences. Each MCU consists of a multipoint controller and at least one multipoint processor responsible for receiving voice, video, and data streams. These streams are distributed to access points participating in a point-to-multipoint conference.

H.323 Proxy Server

An H.323 proxy server is a proxy specifically designed for the H.323 protocol that examines packets between two communicating applications. Proxies are able to determine the destination of a call and perform call-connection steps, if necessary.

H.323 proxies perform the following key functions:

Voice terminals that do not support Resource Reservation Protocol (RSVP) can connect through remote access or local area networks (LANs) with relatively reliable quality of service (QoS) to the proxy. Pairs of proxies can then be employed to develop tunnels across the IP network.

Proxies support routing H.323 traffic separately from ordinary data traffic using application-specific routing (ASR).

Proxies are compatible with network address translation functions in gateways or gatekeepers, enabling H.323 to be deployed in networks using private address space.

You can use an H.323 proxy to help ensure network security by configuring the proxy server to allow only H.323 traffic over the network.