Cisco 1751 Full Product Description

1. Short Overview

Suffix & Naming Breakdown

• 1751: Mid-tier multiservice modular router in the 1700 lineup
• -V: Optional voice variant with preinstalled DSP modules for native VoIP, fax relay, and voice termination

Core Differentiators vs Cisco 1721

1. Three modular shared slots (2 universal WIC/VIC + 1 dedicated voice/NIM slot) vs only 2 WIC slots on the 1721; supports VIC voice cards for analog/digital telephony
2. Native multiservice voice gateway capability (FXS/FXO/E&M voice ports) – entirely absent on the data-only 1721
3. Larger default DRAM (64MB base vs 32MB on 1721), same max 96MB DRAM and 16MB Flash ceiling
4. Higher overall multiservice throughput optimized for concurrent voice + data traffic
5. Supports DSP modules for voice compression (G.711, G.729a) and fax relay; 1721 has no voice DSP expansion
6. Retains all 1721 strengths: 802.1Q VLAN routing, hardware VPN accelerator slot, cross-compatible WIC library

2. Hardware Interface & Performance Specifications

Modular Expansion Architecture (3 Shared Slots Total)

1. 2 Universal WIC/VIC Slots: Accept interchangeable WAN Interface Cards (WICs) or Voice Interface Cards (VICs), cross-compatible with Cisco 1600, 2600, 3600 Series:
   • WIC options: ISDN BRI, T1/FT1 integrated DSU/CSU, synchronous/asynchronous serial, ADSL/G.SHDSL/G.FAST broadband, 4-port Ethernet switch WIC (WIC-4ESW), analog modem WICs
   • VIC voice cards: VIC-2FXS, VIC-4FXS, VIC-2FXO, VIC-2E/M for analog PBX, PSTN, and trunk telephony connections
2. 1 Dedicated Voice/DSP/NIM Slot: Accommodates DSP modules for voice compression/fax relay or compact network interface modules; the C1751-V ships with preloaded DSP resources for multi-line voice deployments
3. Internal crypto accelerator slot: Supports MOD1700-VPN module for hardware-offloaded IPsec DES/3DES encryption to reduce CPU overhead for multi-site VPN tunnels

Fixed Built-in Ports

1. 1 × 10/100BASE-TX autosensing Fast Ethernet LAN (RJ45): Auto 10/100 Mbps full/half duplex, fully supports IEEE 802.1Q VLAN trunking and inter-VLAN routing for segmented office subnetsCisco
2. RJ45 Console port (blue): Local out-of-band CLI management, up to 115.2 kbps baud rate
3. RJ45 AUX port (black): Remote out-of-band management via external analog PSTN modem, asynchronous up to 115.2 kbps
4. Kensington security lock slot for physical desktop anti-theft mounting

Memory & Performance Benchmarks

• Default DRAM: 64MB; maximum expandable DRAM: 96MB
• Default Flash memory: 32MB; maximum supported Flash: 16MB dual-bank Flash for primary/backup IOS image redundancy
• IP forwarding throughput: Up to 12,000 packets per second (pps), optimized for mixed voice/data multiservice loads
• Maximum concurrent IPsec site-to-site VPN tunnels: Up to 100 (varies by IOS feature set, memory, and crypto accelerator module)
• Supported IOS releases: Cisco IOS 12.2 XM / 12.4T multiservice trains (last official maintenance firmware branches)
• Voice capacity (C1751-V): Supports up to 8 concurrent VoIP calls with standard DSP modules, G.729a low-bitrate compression for WAN bandwidth savings

Physical & Power Parameters

• Form factor: Fanless compact metal desktop chassis; optional third-party 19-inch rack-mount brackets available
• Power input: External 12V DC wall-mount AC-DC power adapter (not included with base chassis)
• Front panel LEDs: System power, slot status for all three modular bays, Fast Ethernet link/activity, crypto module health, DSP voice status
• Operating environment: Dry indoor office use only; operating temperature range 0°C to +40°C, non-condensing relative humidity 10–85% RH
• No native PoE power output; all IP cameras, wireless APs, and PoE endpoints require external PoE injectors

3. Cisco IOS Software Multiservice Feature Suite

Routing & WAN Connectivity

• IPv4 core routing protocols: Static routes, RIP v1/v2, OSPF, EIGRP, BGP (IP Plus feature set)
• WAN encapsulations: PPP, HDLC, Frame Relay, ISDN, PPPoE (DSL broadband), Dial-on-Demand Routing (DDR) for redundant backup links
• HSRP for router failover redundancy; NHRP for DMVPN hub-spoke multi-site VPN architectures
• Network Address Translation (NAT): Static NAT, dynamic NAT, PAT overloading for multi-user Internet access
• IEEE 802.1Q VLAN trunking and inter-VLAN routing for segmented internal office LANs

Multiservice Voice & Fax (Key Differentiator vs 1721)

1. VoIP call control: H.323, SIP, MGCP, RSVP bandwidth reservation for voice QoS
2. Analog telephony integration via VIC cards: Connect PBX, PSTN trunk lines, analog desk phones, and fax machines
3. Fax support: T.38 fax relay over IP, fax passthrough, store-and-forward fax
4. Voice compression codecs: G.711, G.729a, G.726, with DSP hardware acceleration to save WAN bandwidth
5. Call routing, dial plans, voice hunt groups, and toll bypass to cut long-distance PSTN charges

QoS & Bandwidth Management

• Base QoS: Weighted Fair Queuing (WFQ), traffic shaping
• Advanced QoS (IP Plus): Low Latency Queuing (LLQ), Frame Relay Traffic Shaping (FRTS), WRED, DiffServ DSCP marking, Link Fragmentation and Interleaving (LFI) to reduce voice delay on low-speed WAN links
• cRTP header compression for VoIP traffic over DSL/ISDN circuits

Integrated Enterprise Security Suite

1. IOS Context-Based Access Control (CBAC) stateful firewall: Dynamic deep packet inspection, application-layer filtering for HTTP, FTP, SIP, H.323
2. Optional IOS signature-based IDS for intrusion threat detection and mitigation
3. Full VPN stack:
   • Hardware-accelerated IPsec (DES / 3DES) site-to-site branch tunnels (with MOD1700-VPN module)
   • L2TP, L2F remote user VPN
   • Cisco Easy VPN Remote: Centralized security policy pull from headquarters VPN headends to simplify remote branch provisioning
4. AAA authentication: PAP/CHAP, RADIUS, TACACS+ for user access audit and control
5. Standard/extended ACLs for traffic filtering and access restriction

Management & Operations

• CLI command-line management via Console/AUX ports
• SNMP v1/v2c for network monitoring, RMON traffic statistics
• Cisco ConfigMaker graphical tool for simplified zero-touch deployment
• AutoInstall: Automated remote configuration download over WAN links
• Dual Flash bank storage for primary and backup IOS image disaster recovery
• Syslog event logging, NTP time synchronization for audit log consistency

4. Typical Deployment Scenarios

1. Small multi-line retail branch office: ADSL WIC primary broadband WAN, ISDN BRI WIC dial backup, VIC-4FXS for 4 store analog phones, 802.1Q VLANs to isolate POS payment terminals from employee Wi-Fi LAN, IPsec site-to-site VPN to corporate HQ, integrated firewall for PCI compliance security
2. Regional SME multiservice edge router: Dual T1 serial WIC redundant leased-line WANs, DSP module for 6 concurrent VoIP office calls, hardware VPN accelerator for multiple concurrent site-to-site tunnels, multi-VLAN routing for separate finance, HR, and engineering office subnets
3. Legacy DSL carrier voice/data CPE: G.SHDSL WIC copper access, VIC-2FXO trunk connection to local PSTN PBX, NAT for multi-user Internet sharing, CBAC firewall protection against external Internet threats
4. Remote industrial M2M site: Serial WIC for leased-line SCADA connectivity, FXS voice ports for site emergency phones, AUX-port modem remote out-of-band management, LTE USB dongle for emergency wireless failover

5. Standard Package Contents of C1751

Separately Sold Optional Accessories

• 12V DC external universal AC power supply
• WAN Interface Cards (WIC-1B-S/T, WIC-T1-DSU, WIC-ADSL, WIC-2SERIAL, WIC-4ESW, etc.)
• Voice Interface Cards (VIC-2FXS, VIC-4FXS, VIC-2FXO, VIC-2E/M)
• DSP voice compression modules (standard for C1751-V, optional for base C1751)
• MOD1700-VPN hardware IPsec encryption accelerator module
• CAT5e RJ45 Ethernet patch cords
• RJ11 DSL/ISDN telephone line cables
• CAT4/CAT6 USB LTE cellular dongles for secondary wireless backup WAN
• USB flash storage drives for offline configuration backups
• Third-party 19-inch rack-mount bracket kit
• External PoE injectors for IP cameras and wireless access points

Software Licensing Information

Short Commercial Catalog Summary