Introduction
In this article, we perform a complete teardown and technical analysis of the Cisco Systems 7900 Series IP Phone, specifically the CP-7960G model. This enterprise-grade VoIP device, introduced in the early 2000s and widely deployed in corporate environments, represents a key milestone in IP telephony. The unit examined was manufactured in 2003, during a period when Cisco dominated the market for business communication systems. Our goal is to explore its internal architecture, hardware components, and design choices that enabled reliable SIP and SCCP protocol support, as well as integration with Cisco Unified Communications Manager.
Background
Before the rise of IP telephony, office communication relied on analog and ISDN lines, which required extensive cabling and dedicated PBX systems (private telephone systems used inside a company to manage internal calls between employees and route external calls to and from the public telephone network). These private branch exchanges were costly, occupied entire rooms, and demanded specialized maintenance. Proprietary protocols and hardware further complicated scalability and integration.
The late 1990s marked a shift with the advent of VoIP (Voice over IP) technology, leveraging existing LAN infrastructure to transmit voice data over IP networks. This innovation drastically reduced hardware requirements and operational costs, enabling centralized management and easier deployment of advanced features.
Cisco Systems, already a leader in networking equipment, capitalized on the transition to IP telephony by introducing the 7900 Series IP Phones, designed for enterprise environments. These devices supported SCCP (Skinny Client Control Protocol), Cisco’s proprietary signaling protocol used to control IP phones, and later also supported SIP (Session Initiation Protocol), the open standard for managing real-time communication sessions. Both protocols allowed the phones to integrate with Cisco Unified Communications Manager (CUCM), Cisco’s widely used call‑processing platform.
Today, while IP phones remain in use, the trend is moving toward softphones and collaboration platforms such as Webex and Microsoft Teams, which integrate voice, video, and screen sharing directly into the user’s computer, reducing reliance on dedicated desk phones.
Teardown
The Cisco CP-7960G is relatively straightforward to disassemble. The top and bottom housings are secured by several screws, which can be removed with a standard Phillips screwdriver. Once the outer shell is detached, the Main PCB Assembly is mounted to the upper housing using nine Phillips screws.
A notable issue during disassembly is the brittleness of the plastic. The casing is made from a Polycarbonate/ABS blend, which tends to degrade over time. As a result, screw posts often fracture when torque is applied, causing the shafts to detach from the main structure. This phenomenon appears common across older Cisco IP phones, likely due to some additive of the plastic, though the exact cause remains unclear.
Main Printed Circuit Board Assembly
After removing the screws, the internal layout reveals a single Main PCB as the core component, with the plastic housings serving primarily as protective and aesthetic covers. The board is labeled:
PCB ASSY: 73-8158-05 Rev A0
This PCB integrates all critical subsystems, including the Ethernet interface, DSP (Digital Signal Processor), audio codec, and power regulation circuits.
Main Board and Architecture
The Cisco CP-7960G features a single main PCB that integrates all critical subsystems. Unlike modular designs, this board hosts the display interface, keypad circuitry, and connectors for the handset and network ports. The keypad is implemented directly on the PCB using carbon contact pads, which interface with the conductive rubber domes embedded in the top housing. When a key is pressed, the rubber dome closes the circuit on the PCB, registering the input.
Expected Electronic Components
Given the phone’s role as an enterprise-grade VoIP device, the architecture includes:
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- Ethernet Controller – Provides 10/100 Mbps network connectivity for VoIP traffic.
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- Main MCU / DSP – Handles call processing, audio encoding/decoding, and protocol management (SIP/SCCP).
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- Flash Memory – Stores firmware and configuration data.
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- RAM – Temporary storage for call handling and buffering.
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- Audio Codec ICs – Convert between analog audio signals and digital streams.
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- Power Regulation Circuitry – Supports Power over Ethernet (PoE) and local DC input, supplied from an external Power Supply.
The board also includes connectors for:
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- RJ-45 Ethernet ports (LAN and PC passthrough)
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- Handset and headset jacks
This integrated design reflects the cost and complexity of early IP phones, which were considered high-end technology in the early 2000s, as it is reflected by the quantity of electronic components.
Power supply
The Cisco CP-7960G receives power through a 48V DC supply, which is standard for IEEE 802.3af Power over Ethernet (PoE) devices. This voltage is delivered via an external power adapter. The input stage includes a reverse polarity protection diode, ensuring the device is safeguarded against incorrect wiring.
Power enters the main assembly through a daughterboard labeled:
PCB ASSY: 73-8521-01 Rev A0
This board acts as the power interface, routing the 48V input to the main PCB, where it is stepped down by DC-DC converters to lower voltages required by the system (typically 3.3V and 5V for logic and peripherals). These converters supply the MCU/DSP, Ethernet controller, audio circuits, and the LCD display.
The simplicity of the input stage—just a diode for polarity protection—reflects reliance on PoE standards for upstream regulation and safety. The main PCB handles all subsequent voltage regulation internally.
Main Board
The main board, labeled:
ASSY#: 73-8158-05 Rev A0
includes a barcode sticker, likely identifying the PCB Assembly part number. No additional part numbers were found on the copper layers or silkscreen of either side of the PCB.
Key Components Identified
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- IDT 74FCT3573AQ High-speed octal D-type flip-flop with 3-state outputs, commonly used for bus interfacing.
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- ADR73311LARS Analog Devices audio codec, supporting voice-band signal processing for VoIP applications.
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- 74VHC4053 Triple 2-channel analog multiplexer/demultiplexer, used for audio signal routing.
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- Cisco-labeled IC (P/N 17-7167-02) Internally marked as M29W800AB, an 8 Mbit Flash memory (by STMicroelectronics), likely storing firmware and configuration data.
Under the RF shield, the main logic ICs are found.
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- Cisco ASICs
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- F731891PDV (08-0312-01)
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- F731532APGE (08-0338-03) These are custom Cisco chips, likely handling VoIP protocol processing, audio DSP, and system control.
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- Cisco ASICs
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- Broadcom BCM5912A2KQM A PoE power management IC, responsible for negotiating and regulating IEEE 802.3af power delivery to the board.
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- Two IDT71V416S10PH 4 Mbit SRAM chips, providing volatile memory for call handling and buffering.
I created a spreadsheet with the main components found on the board
PCB Technology
The main board is a 4-layer stack with a standard 1.6 mm thickness. It features mostly SMD components, with some through-hole connectors and headers. Components are placed on the top side (component layer), while the bottom side only shows solder joints for THT parts. SMD components were soldered using an IR reflow oven after pick-and-place assembly and stencil-applied solder paste. Through-hole components were inserted and soldered manually, as indicated by flux residues, likely because their low pin count did not justify wave soldering. After this, elements such as the display and power daughterboard were manually mounted for final assembly.
The smallest SMD components use 0603 packaging, and all reference designators are clearly marked on the silkscreen. This process reflects early 2000s telecom manufacturing standards: mixed technology assembly, reflow for SMD, and manual soldering for THT parts.
Display
The display appears to be an LCD dot-matrix panel, although it has not been powered for verification. It is connected to the main PCB via a flat Kapton flex tab, which presses against the board for electrical contact. The module is manufactured by U.R.T. (UNITED RADIANT TECHNOLOGY CORPORATION) and marked:
The module is manufactured by U.R.T. (United Radiant Technology Corporation) and marked:
UMSH-7093AN-12FIt is mounted on a plastic frame labeled 700-05023-01, likely a Cisco Systems part number. Searches for these identifiers return results tied to Cisco IP phones, suggesting the display was custom-made for this model.
Final Thoughts
The Cisco CP-7960G represents a snapshot of early 2000s enterprise VoIP technology—robust, feature-rich, and built with a level of complexity that justified its premium cost at the time. The teardown reveals a mixed-technology PCB with custom Cisco ASICs, discrete audio codecs, dedicated PoE management, and separate memory chips, all integrated into a design optimized for reliability rather than miniaturization.
Compared to modern IP phones or softphone solutions, this architecture feels over-engineered, yet it highlights the evolution from hardware-centric telephony to software-driven collaboration platforms like Webex and Microsoft Teams. For engineers and enthusiasts, examining these legacy devices provides valuable insight into design practices, manufacturing processes, and the technological priorities of that era.
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