The Cisco 2921 router is designed for small offices, supporting up to 100 IP phones. It has 3 Gigabit Ethernet WAN ports, 4 EHWIC slots, 3 DSP slots, 1 service module slot, 512MB DRAM, and 256MB compact flash. The router has a maximum power output of 370 Watts with an AC power supply or 280 Watts with PoE.

1. Cisco 2921 Specs
The Cisco 2921 router, supporting voice module, is designed for small offices.
Cisco 2921 Specs
Release Date: 13-OCT-2009
AC Input Voltage: 100 to 240 VAC auto ranging
Compact Flash (External) - Default: slot 0: 256 MB; slot 1: none
Maximum End-Point PoE Power Capacity with PoE Boost (Watts): 750
Airflow: Back and Side to Front
Temperature: 9,843 feet (3,000m ) Maximum Altitude : 32 to 77 F (0 to 25 C)
ISM Slots: 1
Modular LAN Switchports (with optional PoE): 50
Altitude: 10,000 ft (3,000m)
DC Input Voltage:
24 to 60 Vdc, autoranging positive or
negative
Compact Flash (External) - Maximum: slot 0: 4 GB; slot 1: 4 GB
Temperature: 13,123 feet (4,000m) Maximum Altitude : 32 to 86 F (0 to 30 C)
Cisco Unified SRST Sessions: 100
SFP-based ports (use of SFP port disables the corresponding RJ-45 port): 1
Memory DDR2 ECC DRAM - Maximum: 2 GB
Onboard DSP (PVDM) Slots: 3
Wall-Mount (refer to installation guide for approved orientation): No
Double-Wide Service Module Slots: 1
Power Supply: AC; PoE; and DC
Serial console port: 1
Acoustic: Sound Pressure (Typical/Maximum): 54.4/67.4 dBA
USB Console port (Type B) (up to 115.2 kbps) 1: 1
Maximum Power with PoE Power Supply (Platform Only) (Watts): 370
AC Input Current: 3.4 to 1.4A range (max AC power supply)
Maximum Power with DC-PoE Power Supply (Platform Only) (Watts): n/a
Dimensions (H x W x D):
3.5 x 17.25 x 18.5 in. (88.9 x 438.2 x 469.9
mm)
Rack Mounting Kit: Included
Weight with AC PoE Power Supply (No Modules): 30 lb (13.6 kg)
RPS Support (External): Cisco RPS 2300
EHWIC Slots: 4
Short-Term (per NEBS) Humidity : N/A
Cisco Unified CCME Sessions: 100
Typical Weight Fully Configured : 34 lb (15.5 kg)
External USB 2.0 Flash Memory Slots (Type A): 2

2. AC Input Surge Current: < 50A
Integrated WAN Ports: 3 GE; (1 SFP)
Non-Operating Temperature: -40 to 158 F (-40 to 70 C)
Relative Humidity: 10 to 85%
Acoustic: Sound Power (Typical/Maximum): 62.6/74.5 dBA
Temperature: Short-Term (per NEBS) 5906 feet (1,800m) Maximum
Altitude:
n/a
Temperature: 5,906 feet (1,800m) Maximum Altitude : 32 to 104 F (0 to 40 C)
Non-Operating Relative Humidity: 5 to 95%
Maximum End-Point PoE Power Available from DC PoE Power Supply
(Watts):
n/a
Weight with AC Power Supply (No Modules): 29 lb (13.2 kg)
Serial auxiliary port: 1
Embedded Hardware-Based Cryptography and Acceleration: Yes
RJ-45-based ports: 3
Optional Airflow Kit: n/a
Memory DDR2 ECC DRAM - Default: 512 MB
Typical Power (No Modules) (Watts): 60
DC Input Current: (MAX) 12A (24V); 5A (60V)
Total onboard WAN 10-100-1000 Ports: 3
Rack-Mount 19 in. (48.3 cm) EIA: Optional
AC Input Frequency: 47 to 63 Hz
Double-Wide EHWIC Slots: 2
Service Module Slots: 1
Rack Units: 2 RU
Non-Operating Altitude: 15,000 ft (4,570m)
Maximum End-Point PoE Power Available from AC PoE Power Supply
(Watts):
280
Maximum Power with AC Power Supply (Watts): 320
Cisco 2921/K9 supports expansion functions with modules and cards
① Compact flash 0 and 1 (0, right) ⑦ 10/100/1000 Ethernet port (GE 0/1 and GE 0/2)
② EHWIC 0,1,2 and 3 (0, far right) ⑧ 10/100/1000 Ethernet port GE 0/0
③ USB serial port ⑨ Ground
④ RJ-45 serial console port ⑩ USB 0 and 1 (1, top)
⑤ AUX port ⑪ Service module slots
⑥ SFP

3. Cisco 2921 VS Huawei
Vendor Product Description Huawei Advantages
CISCO CISCO2921
Cisco 2921 w/3 GE,4 EHWIC,3 DSP,1 SM,256MB CF,512MB
DRAM,IPB
HUAWEIAR2220
3GE WAN(1GE Combo), 2 USB, 4 SIC, 2 WSIC, 1 DSP Slot,
150W Power
Forwarding performance：1Mpps vs.
479Kpps
IO Slots: 2 WSIC vs. 1 SM
hot-swappable interface card
Source:http://www.cisco.com/c/en/us/products/routers/2921-integrated-services-router-isr/index.html
From https://howcisco.wordpress.com/