DP-9851-L-K9 Cisco 9851 6-Line Enterprise PoE IP Desk Phone

Cisco DP-9851-L-K9 Enterprise IP Phone Overview

The Cisco DP-9851-L-K9 is a high-performance, 6-line enterprise VoIP desk phone designed to deliver crystal-clear HD audio, advanced connectivity, and seamless compatibility with leading communication platforms. Built for modern workplaces, it features dual PoE support and a durable carbon-black finish.

General Product Details

Brand & Identification

• Brand: Cisco
• Model: DP-9851-L-K9
• Category: VoIP Desktop Phone

Key Functional Attributes

Platform Compatibility

• Cisco BroadWorks
• Cisco Webex Calling
• Cisco Webex Dedicated Instance (DI)
• Asterisk Systems

Integrated Security Components

• Trusted Platform Module (TPM) 2.0

Build & Design

• Color: Carbon Black
• Material: ABS Polycarbonate (74% post-consumer recycled plastic)

Advanced Phone Capabilities

Wireless & Connectivity Features

• Built-in NFC Wireless Interface

Call Handling Services

• Voicemail
• Caller Identification
• Call Waiting, Hold, Transfer & Forward
• Call Park / Pickup
• Conference Calling

User Controls & Indicators

• Six Programmable Keys
• Speakerphone with Indicator
• Mute, Headset & Status Indicators
• Calendar and Line Status LEDs
• Busy Lamp Field (BLF)

Additional Convenience Tools

• One-Button-to-Join (OBTJ)
• QR Code Access
• Music on Hold
• Call Recording Support
• Do Not Disturb Mode
• Kensington Security Slot
• Sleep Mode Function

IP Telephony & VoIP Specifications

Core VoIP Capabilities

• Integrated Ethernet Switch
• Supports SIP, SDP, RTCP, RTP & SRTP Protocols
• Up to 46 SIP Lines

Supported Audio Codecs

• Opus, G.722, G.722.2
• iSAC, G.711 A-law/U-law
• G.729a/b, iLBC

Quality of Service & Network Control

• IEEE 802.1Q VLAN Tagging
• DHCP & Static IP Assignment
• IEEE 802.1X, EAP-FAST, EAP-TLS Security
• FIPS 140-2, TLS 1.3, SRTP Encryption

Networking Protocol Support

• IPv4 / IPv6
• DHCP, DNS, TFTP, HTTPS
• GARP, RTP, RTCP
• Cisco Discovery Protocol (CDP)
• LLDP & LLDP-MED

Connectivity Ports

• 2 × Ethernet 10/100/1000 (RJ-45)
• PoE Class 3 Support

Compatible Software Suites

• Cisco Webex
• Cisco Unified Communications Manager

Voice & Audio Enhancements

• Acoustic Echo Cancellation (AEC)
• Forward Error Correction (FEC)
• Automatic Gain Control (AGC)
• Comfort Noise Generation (CNG)
• Voice Activity Detection (VAD)
• Packet Loss Concealment (PLC)
• Silence Suppression
• Acoustic Shock Protection
• Adaptive Jitter Buffer (AJB)
• Dual Tone Multi-Frequency (DTMF)
• HD Audio & Ultrasonic Support

Display Features

Screen Specifications

• Type: Color LCD
• Location: Base
• Size: 3.7 Inches
• Resolution: 240 × 480 Pixels
• Backlit: Yes

Supported Interface Languages

• English (US/UK), French, German, Spanish, Italian, Portuguese
• Dutch, Danish, Swedish, Norwegian, Finnish
• Russian, Ukrainian, Turkish, Greek, Polish, Czech, Hungarian
• Japanese, Korean
• Chinese (Simplified & Traditional)
• Brazilian Portuguese, Catalan, French Canadian, Spanish (Colombia)

Miscellaneous Specifications

Connectivity & Ports

• RJ-9 Headset Port
• 2 × RJ-45 Network Ports
• USB Type-A (4-pin)
• USB Type-C (24-pin)

Core Communication Capabilities

At its heart, the 9851 is engineered for efficiency and clarity. The six programmable line keys support multiple concurrent calls, allowing users to manage conversations, hold calls, and initiate transfers with ease. This multi-line capacity is essential for roles that require constant accessibility and call handling.

HD Voice Audio Quality

The phone's standout feature is its certified HD audio. Utilizing wideband codecs, it captures and reproduces sound with exceptional fidelity, making conversations feel natural and lifelike. This reduces listener fatigue and minimizes misunderstandings, a critical advantage in detailed technical or client discussions.

Acoustic Components

Superior audio is achieved through a combination of a high-quality handset, built-in speakerphone with full-duplex acoustics, and advanced audio algorithms that suppress echo and background noise. Whether in a private office or a bustling cubicle, call clarity remains consistently high.

Intuitive User Interface

Navigating the phone's features is straightforward thanks to a crisp, pixel-based grayscale display and a logical key layout. The dedicated buttons for hold, transfer, conference, and speakerphone provide one-touch access to the most common telephony functions, streamlining daily workflows.

Dual PoE: Power and Connectivity

A defining technical feature of the DP-9851-L-K9 is its inclusion of dual Power over Ethernet (PoE) ports. This isn't just a redundancy feature; it's a connectivity hub that extends the value of your network infrastructure.

Primary PoE Port (Data + Power)

The primary network port connects to your LAN switch and receives both data and power (802.3af compliant). This eliminates the need for a separate power adapter, reducing cable clutter and simplifying installation. The phone becomes a networked device on your corporate VoIP system, ready to register with Cisco Unified Communications Manager (CUCM) or other compatible call controllers.

Secondary PoE Pass-Through Port

The secondary Ethernet port is a game-changer for workspace design. It can provide data connectivity and, crucially, *pass-through PoE power* to another device. This allows you to daisy-chain a device like a wireless access point, a video conferencing unit, or a desktop computer without needing a second cable run to the switch or a separate power outlet for that device. It maximizes the utility of a single network drop.

Deployment Scenarios for Pass-Through

Imagine a workstation with a desktop PC and the IP phone. Instead of two cables to the wall jack, only one is needed: it connects to the phone, and a short patch cable from the phone's PC port connects to the computer. This creates a cleaner, more organized desk environment and can significantly reduce wiring costs in new installations or reconfigurations.

Integration and Management in Enterprise Ecosystems

The Cisco 9851 is not a standalone device; it thrives as an integrated endpoint within a larger Cisco collaboration ecosystem. Its true potential is unlocked when deployed alongside Cisco's unified communications and networking solutions.

Cisco Unified Communications Manager (CUCM) Compatibility

The phone is designed as a "skinny client" (SCCP) or can operate using the SIP protocol, with firmware optimized for seamless registration and management via CUCM. Administrators can leverage CUCM's bulk administration tools to configure, update, and monitor hundreds or thousands of 9851 phones from a central interface.

Centralized Provisioning and Firmware

Phone settings, line appearances, speed dials, and services are pushed from CUCM. Firmware updates are delivered automatically, ensuring consistency, security, and access to new features across the entire phone fleet without touching a single physical device.

Feature Integration

When integrated with CUCM and presence servers, the 9851 can support extended features like extension mobility (logging into any phone), shared lines, and busy lamp fields (BLF) for monitoring colleague availability, though its display limitations mean BLF is managed via softkeys rather than a dedicated visual field.

Security and Network Resilience

Enterprise-grade security is built-in. The phone supports secure boot, image validation, and encrypted signaling (TLS) and media (SRTP) to protect against eavesdropping and tampering. It can use 802.1X authentication to ensure only authorized devices join the network.

Quality of Service (QoS) Marking

To maintain impeccable voice quality even on congested networks, the 9851 marks voice packets with the appropriate DSCP (Differentiated Services Code Point) values. This instructs network switches and routers to prioritize voice traffic over less time-sensitive data, preventing jitter, latency, and packet loss that degrade call quality.

Ideal Use Cases and Target Deployment Scenarios

Understanding where the Cisco 9851 excels helps in making informed procurement decisions. It is designed for specific environments and user profiles within the enterprise.

General Business and Administrative Staff

For employees who rely heavily on the phone for internal and external communication but may not require a color touchscreen for complex applications, the 9851 is an ideal, cost-effective workhorse. Its six lines are sufficient for most individual contributors, team leads, and administrative personnel.

Common Areas and Shared Workspaces

The phone's durability and straightforward interface make it perfect for lobbies, conference rooms (as a secondary phone), break rooms, or manufacturing floors. The PoE pass-through can even power a nearby wireless AP in such a shared space.

Hospitality and Front Desk Applications

In hotel front desks, clinic reception areas, or school offices, the 9851 provides reliable, clear communication for handling high call volumes. The ability to place calls on hold and transfer them is used frequently in these scenarios.

Remote and Branch Offices (ROBO)

For smaller satellite offices, the 9851 offers enterprise-quality features without the complexity or cost of higher-end models. Its PoE pass-through can simplify network setup in these locations by reducing the need for additional switches or power injectors.

Comparison and Positioning Within the Cisco IP Phone Portfolio

The DP-9851-L-K9 occupies a specific tier in Cisco's hierarchy, offering more than entry-level phones but without the advanced screen and application integration of the 8800 or 8900 series.

Vs. Entry-Level Models (e.g., 7800 Series)

Compared to the 2-line or 4-line 7800 series phones, the 9851 offers two additional line appearances and the critical dual PoE with pass-through functionality. It also typically features a slightly larger display and enhanced audio hardware, positioning it as a more capable solution for frequent phone users.

Vs. Advanced Models (8800/8900 Series)

The 8800 and 8900 series phones feature high-resolution color touchscreens, support for video (on some models), and greater programmability for XML-based applications. The 9851, with its grayscale display, is focused purely on superior voice communication and basic productivity features. It represents a significant cost savings while still delivering core enterprise telephony and HD voice.

Choosing the Right Model

The decision often comes down to user needs: if the primary requirement is excellent call handling, basic presence, and a simple interface, the 9851 is perfect. If users require deep integration with collaboration apps, visual voicemail, or a rich color interface for call history and contacts, a higher-tier model is more appropriate.