Cisco CP-6851-3PCC-K9 Full English Product Description

Listing Title

Cisco CP-6851-3PCC-K9 Multiplatform (3PCC) 4-Line Expandable Gigabit PoE VoIP Desk Phone, 3.5-inch 396×162 Backlit Grayscale LCD with XML Application Support, Dual 10/100/1000BASE-T Gigabit Switched Ethernet Ports with PC Pass-Through, IEEE 802.3af Class 2 PoE Powered, Full-Duplex HD Wideband Echo-Canceling Speakerphone, Dedicated RJ-9 Wideband Headset Port, Supports One Cisco 6800 Key Expansion Module (KEM) for 28 Additional Programmable Buttons, Open-Standard SIP MPP Third-Party Call Control Firmware, SRTP/TLS Encrypted Secure Voice, Desktop & Wall Mountable, End-of-Sale Announced April 29, 2026, Ideal for Office Receptionists, Administrative Managers, Multi-Line High-Productivity Staff, Small-to-Mid Business SIP PBX and UCaaS Deployments

Full Commercial Overview

The Cisco CP-6851-3PCC-K9 is a high-productivity expandable mid-tier multiplatform (MPP) VoIP desk phone within Cisco’s IP Phone 6800 Series product lineup. The suffix3PCCdenotes Third-Party Call Control, meaning the unit runs pure open-standard SIP firmware independent of Cisco CUCM enterprise call managers, fully interoperable with Webex Calling, Broadsoft, Asterisk, and all industry-standard hosted SIP PBX and UCaaS platforms.

This model differentiates itself from the CP-6841 (non-expandable 4-line model) by supporting one dedicated Cisco 6800 Key Expansion Module (KEM). The KEM adds 14 physical programmable keys plus an additional 14 keys accessible via page toggle buttons, delivering a total of 28 extra BLF (Busy Lamp Field) monitoring, speed dial, or feature control buttons for receptionists and busy administrative staffCisco.

Equipped with four independent SIP registrations, Gigabit Ethernet switching ports, a high-resolution 3.5-inch grayscale backlit display, native IEEE 802.3af PoE, and enterprise-grade HD wideband audio, the CP-6851 balances multi-line call handling, expandable productivity controls, and secure encrypted SIP communications for mid-volume business telephony deployments. Cisco issued an official End-of-Life announcement for the IP Phone 6851 on April 29, 2026, with the End-of-Sale cutoff date set for October 28, 2026; it remains fully supported by firmware updates and Cisco technical support until the scheduled end-of-support milestonesCisco.

All device provisioning, dial plan configuration, unattended bulk firmware upgrades and remote diagnostics are supported via TFTP, HTTP and HTTPS secure auto-provisioning. Basic local configuration adjustments can be completed directly through the backlit graphical LCD menu navigation without requiring a PC web portal, and the display supports customizable XML enterprise applications for corporate LDAP directories, internal announcements and custom business workflow toolsCisco Russ....

Hardware, Display & Audio Architecture

1. Four Independent Programmable SIP Line Buttons

Four physical tricolor LED illuminated line keys on the left side of the display support up to four unique SIP registrations. Each line key enables multi-call-per-line appearance functionality to manage multiple concurrent calls, shared line monitoring and BLF extension status tracking. LED color coding indicates call state: solid green for idle line, solid red for active/held calls, flashing red for incoming ringing calls.

2. Graphical LCD Display & Physical Control Layout

• Display Panel: 3.5-inch (9cm) white backlit grayscale LCD screen with 396 × 162 pixel high resolution. The screen renders caller ID name/number, real-time call duration timestamps, local call history logs, system menu navigation prompts, network time/date, XML corporate directory and application content, plus status icons for active headset, mute and DND modes.
• Hard Key Layout & Navigation: Standard 12-key tactile numeric dial pad; dedicated fixed-function illuminated hard keys: Mute, Headset, Speakerphone, Volume Toggle, Central Four-Way Navigation Cluster with Select Button, Directory, Applications, Hold, Transfer, Conference and three context-sensitive LCD softkeys for dynamic call control workflows.
• LED Status Indicators: Backlight status LEDs on all line and function keys; dedicated vertical red Message Waiting Indicator (MWI) LED integrated on the handset cradle to notify users of unheard voicemail messages (solid red = new voicemail, flashing red = incoming call alert).

3. Key Expansion Module (KEM) Compatibility

The CP-6851 uniquely supports installation of one Cisco IP Phone 6800 Key Expansion Module (KEM), a separate accessory sold individually (SKU: CP-68KEM-3PCC). The KEM features dual grayscale LCD panels, 14 physical programmable PLK (Programmable Line Keys), and two page buttons that unlock an additional 14 programmable keys, for a total of 28 expandable control buttons. These keys can be configured for BLF extension monitoring, speed dial, call park, pickup or custom feature shortcuts, though the KEM does not support independent SIP line registrations for outbound calling initiationCisco. When the base phone enters power-save mode, the connected KEM also activates low-power standby state; pressing the phone’s central select key wakes both devices simultaneouslyCisco.

4. Complete Wideband HD Audio Subsystem

• Ergonomic wired analog handset with noise isolation and native G.722 HD wideband audio support, connected via a standard RJ-9 modular port.
• Built-in full-duplex hands-free speakerphone with advanced acoustic echo cancellation, enabling simultaneous talk-and-listen conference-style calling without audio cut-off; automatic DTMF tone privacy masking activates during speakerphone operation.
• Dedicated RJ-9 wideband headset audio port fully compatible with Cisco 500 Series wired headsets and mainstream industry-standard office wired headsets.
• Supported Voice Codecs: G.711 A-law / µ-law, G.726, G.729A/B/AB, G.722 HD wideband voice, G.722.2, iSAC, ILBC, OPUS wideband audio codecs.
• Audio Optimization Technologies: Adaptive dynamic jitter buffer, Voice Activity Detection (VAD) silence suppression, Comfort Noise Generation (CNG); DTMF signaling transmitted via in-band audio or RFC 2833 out-of-band SIP INFO signaling.

5. Chassis & Mounting Specifications

Compact matte charcoal gray ABS plastic desktop chassis with a removable single-position foldable rear foot stand for stable desk or countertop placement. The foot stand can be fully detached to enable wall mounting, with pre-drilled standardized mounting holes located on the rear panel of the phone.

• Physical Dimensions (W × D × H): 207 × 265 × 33 mm
• Unit Weight: 615 g
• Power Save Mode Support: Configurable low-power standby to reduce idle energy consumption, compatible with connected KEM expansion module.

Network, Power & Hardware Interfaces

1. Dual Switched 10/100/1000BASE-T Gigabit Ethernet RJ45 Ports

Two auto-sensing Gigabit Ethernet ports with an integrated mini network switch, a core deployment advantage for office workstations with attached desktop PCs, laptops or POS terminals:

• Primary WAN Port: Connects the IP phone directly to corporate LAN switches, VoIP gateways or SIP PBX appliances for SIP control signaling and RTP voice media traffic.
• Secondary PC Pass-Through Port: Enables direct connection of downstream Ethernet devices to the corporate network through the phone, eliminating the requirement for extra wall-mounted network jacks and cutting office cabling infrastructure costs.

Supported networking standards: Full IPv4 RFC compliance suite, DHCP client for automatic IP addressing, DNS A/SRV record lookup, ARP, ICMP, TCP/UDP, RTP/RTCP voice media quality reporting, Layer 2 802.1p QoS traffic marking, voice VLAN tagging (802.1Q), STUN NAT traversal for remote/home office NAT network environments, SNTP network time synchronization, CDP and LLDP network device discovery protocolsCisco Russ....

2. Dual Power Supply Options

1. Native IEEE 802.3af Class 2 PoE Support (Primary Deployment Method): The phone draws electrical power directly from PoE-enabled network switches via Ethernet cabling, eliminating separate AC power adapters for standard office workstation deployments.
2. Auxiliary AC Power Supply Backup: Optional country-specific universal AC-to-DC power adapter (Cisco 6800 series 5V power cube, sold separately), rated for 100–240 VAC 50/60Hz input, output 5V DC / 2.0A for phone operation in non-PoE network environments.

3. Additional Physical Interfaces

• RJ-9 modular wired handset connector
• Dedicated RJ-9 wideband headset audio jack
• Recessed pinhole password-protected factory reset button for restoring default device configurations.

Core Business Telephony Feature Set

All calling functions can be configured via auto-provisioning templates, on-device LCD menu or triggered through standard SIP star feature access codes:

1. Four-Line Multi-Call Handling: Multi-call-per-line appearance support, per-line call waiting, call hold, music-on-hold, attended & blind call transfer, local three-way ad-hoc audio conferencing, call swap between active lines, automatic last number redial, on-hook dialing, global Do Not Disturb (DND) mode to suppress incoming ring alerts, call park and unpark functionality, shared line appearance monitoring and BLF extension busy lamp field status tracking (supported via base phone line keys or attached KEM expansion module).
2. Caller ID & Personalization: Caller ID name and number display on LCD, outbound caller ID blocking, anonymous call rejection, customizable distinctive ringtones configurable per line, programmable speed dial assignments and local stored personal phone directory with BLF extension monitoring support; LDAP corporate directory lookup via XML application framework.
3. Utility & Group Calling Features: One-touch intercom calling with auto-answer speakerphone mode, selective and group call pickup, call back on busy, system broadcast paging support.
4. Local Call Log Storage: Onboard storage for dialed, received and missed call records with timestamps and call duration data, fully viewable on the phone’s LCD screen or embedded web management portal.
5. Voicemail Integration: Native MWI voicemail notification via SIP SUBSCRIBE/NOTIFY messaging, dedicated one-touch Messages hard key for instant voicemail retrieval.

Security & Remote Management Capabilities

1. Voice & Signaling Encryption: SRTP (Secure Real-time Transport Protocol) up to 256-bit AES encryption for VoIP voice media streams, TLS encrypted SIP control signaling to prevent network call eavesdropping and malicious signaling interception.
2. Multi-Tier Device Access Security: Separate administrator and end-user permission levels protected by unique passwords; password-locked factory reset function to block unauthorized full configuration erasure.
3. Automated Provisioning & System Monitoring: Secure unattended remote firmware upgrades without interrupting active voice calls, centralized syslog event logging, built-in network diagnostic tools for IT administrators and small business telecom service providers; customizable XML enterprise application support for corporate directories and internal business services; RTCP-XR voice quality statistics reporting for network telephony performance auditing.

Environmental & Regulatory Specifications

• Regulatory Compliance Certifications: FCC Part 15 Class B electromagnetic interference compliance, UL / C-UL electrical safety certification, CE marking for European Union market compliance, A-Tick Australian telecommunications certification, HAC hearing aid compatibility certification.
• Operating Environment: Indoor use only Operating Temperature: 0°C ~ +40°C (32°F ~ 104°F) Storage Temperature: -10°C ~ +60°C (14°F ~ 140°F) Operating Humidity: 10% – 90%, non-condensing Storage Humidity: 10% – 95%, non-condensing
• Memory Architecture: Onboard flash memory for persistent firmware and configuration storage, dedicated SDRAM runtime memory for real-time multi-line call processing, LCD menu rendering and embedded web server operation.
• Lifecycle Status: Announced End-of-Life April 29, 2026; End-of-Sale cutoff October 28, 2026; fully supported active MPP multi-platform VoIP hardware with ongoing firmware maintenance until scheduled end-of-support milestonesCisco.
• Warranty: Standard one-year limited Cisco hardware warranty for commercial business end-user deployments.

Key Specification Bullet Points

• Model Number: Cisco CP-6851-3PCC-K9
• Device Type: Expandable Multiplatform 4-Line Open SIP VoIP Desk IP Phone (3PCC Third-Party Call Control MPP Firmware), Supports One Cisco 6800 KEM Expansion Module
• Supported Telephony Protocols: Industry Standard SIP v2 (RFC 3261 Suite), MPP Multiplatform Firmware for third-party PBX / UCaaS compatibility
• Supported Voice Codecs: G.711 A/µ, G.726, G.729A/B/AB, G.722 HD Wideband Voice, G.722.2, iSAC, ILBC, OPUS
• Display: 3.5-inch backlit grayscale LCD screen, 396 × 162 pixel resolution, XML corporate directory/application support
• Physical Buttons & Indicators: 4 programmable tricolor LED line keys, 12-key numeric dial pad, dedicated illuminated hard keys for Mute, Headset, Speakerphone, Volume, Navigation Cluster, Directory, Applications, Hold, Transfer, Conference; standalone red handset cradle MWI voicemail waiting LED
• Expansion Compatibility: Supports maximum one Cisco IP Phone 6800 Key Expansion Module (KEM), adding 28 total programmable BLF/speed dial/feature keys
• Physical Audio Interfaces: RJ-9 handset port, dedicated RJ-9 wideband headset jack, built-in full-duplex echo-canceling HD speakerphone, HAC hearing-aid compatible handset
• Ethernet Interfaces: Dual auto-sensing 10/100/1000BASE-T Gigabit switched LAN ports (WAN uplink + PC pass-through secondary port)
• Power: Native IEEE 802.3af Class 2 PoE support; Optional separate 5V DC AC power adapter sold individually
• Mounting Method: Removable foldable desktop foot stand as standard; wall-mount capable via rear chassis mounting holes
• Supported QoS & Networking: 802.1p Layer 2 QoS marking, voice VLAN 802.1Q tagging, DHCP client, STUN NAT traversal, SNTP time sync, CDP/LLDP network device discovery
• Security Features: TLS encrypted SIP signaling, SRTP AES encrypted voice media, dual-level admin/user password lock, HTTPS embedded web management, password-protected factory reset
• Core Call Features: 4-line multi-call-per-line concurrent call support, call waiting, hold, attended/blind transfer, three-way conference, BLF extension busy lamp field monitoring (base keys + KEM), caller ID blocking, anonymous call rejection, intercom, group call pickup, speed dial, LCD-accessible local call logs, DND silent mode, voicemail MWI notification, call park/unpark, shared line appearance, LDAP directory lookup via XML
• Management Tools: Embedded web admin interface, local LCD menu configuration, TFTP/HTTP/HTTPS auto remote provisioning, syslog event logging, unattended remote in-service firmware upgrades, customizable XML enterprise application support, RTCP-XR voice quality reporting
• Deployment Scenarios: Small/mid-sized business front reception desks, administrative manager workstations, multi-line high-productivity office staff, retail management counters, multi-line medium call-volume office deployments, remote home office telephony setups, third-party SIP PBX / Webex Calling / Broadworks UCaaS environments requiring expandable BLF monitoring keys
• Lifecycle Status: EOL announced April 29, 2026; EoS effective October 28, 2026, active supported MPP IP phone
• Warranty: One-year limited Cisco hardware warranty

Model Quick Reference

• CP-6851-3PCC-K9 is the expandable flagship 4-line multi-platform open SIP phone of Cisco 6800 MPP Series; the "3PCC" suffix denotes third-party open SIP firmware, fully separate from CUCM-locked SCCP enterprise variants.
• Core positioning: High-productivity expandable business VoIP endpoint built exclusively for open SIP PBX and hosted UCaaS platforms, offering four SIP registrations, Gigabit Ethernet, a large high-resolution LCD screen, and unique compatibility with a KEM expansion module for up to 28 additional programmable BLF monitoring and speed dial keys—its primary differentiator from the non-expandable CP-6841 model.
• Primary deployment advantage: Dual Gigabit switched Ethernet ports eliminate redundant wall network jacks for combined PC + phone workstation setups, native IEEE 802.3af PoE reduces separate power adapter cabling costs for mass office rollouts, and the KEM expansion capability delivers scalable extension monitoring for busy receptionists and administrative supervisors.
• Series internal comparison: CP-6821 (2-line entry, no Gigabit) < CP-6841 (4-line mid-tier, non-expandable) < CP-6851 (4-line expandable with KEM support, Gigabit Ethernet) < CP-6861 (4-line integrated Wi-Fi) < CP-6871 (6-line color LCD display).