Cisco 2921 User Manual

281
Cisco 3900 Series, Cisco 2900 Series, and Cisco 1900 Series Integrated Services Routers Generation 2 Software Configuration Guide
Chapter Configuring Radio Settings
Disabling and Enabling Short Radio Preambles
Disabling and Enabling Short Radio Preambles
The radio preamble (sometimes called a header) is a section of data at the head of a packet that contains
information that the wireless device and client devices need when sending and receiving packets. You
can set the radio preamble to long or short:
• Short—A short preamble improves throughput performance.
• Long—A long preamble ensures compatibility between the wireless device and all early models of
Cisco Aironet Wireless LAN Adapters. If these client devices do not associate to the wireless
devices, you should use short preambles.
You cannot configure short or long radio preambles on the 5-GHz radio.
To disable short radio preambles, follow these steps, beginning in privileged EXEC mode:
SUMMARY STEPS
1. configure terminal
2. interface dot11radio {0| 1}
3. no preamble-short
4. end
5. copy running-config startup-config
DETAILED STEPS
Short preambles are enabled by default. Use the preamble-short command to enable short preambles if
they are disabled.
Command Purpose
Step 1
configure terminal Enters global configuration mode.
Step 2
interface dot11radio {0| 1} Enters interface configuration mode for the 2.4-GHz radio
interface.
Step 3
no preamble-short Disables short preambles and enable long preambles.
Step 4
end Returns to privileged EXEC mode.
Step 5
copy running-config startup-config (Optional) Saves your entries in the configuration file.

Cisco 2921 Specifications

General

Ethernet LAN	Yes
Cabling technology	10/100/1000Base-T(X)
Networking standards	IEEE 802.1Q, IEEE 802.1ag, IEEE 802.3, IEEE 802.3ab, IEEE 802.3af, IEEE 802.3ah, IEEE 802.3u
Ethernet LAN data rates	10, 100, 1000 Mbit/s
Ethernet interface type	Gigabit Ethernet
Product color	Black
Rack capacity	2U
USB version	2.0
RS-232 ports	1
USB ports quantity	2
Ethernet LAN (RJ-45) ports	3
DHCP client	-
Routing protocols	BGP, EIGRP, OSPF
Supported protocols	IPv4, IPv6, IS-IS, IGMPv3, PIM SM, SSM, DVMRP, IPSec, GRE, BVD, MPLS, L2TPv3, PPP, MLPPP, MLFR, HDLC, RS-232, RS-449, X.21, V.35, EIA-530, PPPoE, ATM
Firewall security	Cisco IOS
Operating altitude	0 - 3000 m
Non-operating altitude	0 - 4570 m
Storage temperature (T-T)	-40 - 70 °C
Operating temperature (T-T)	0 - 40 °C
Storage relative humidity (H-H)	5 - 95 %
Operating relative humidity (H-H)	10 - 85 %
AC input voltage	100 - 240 V
Power source type	AC
AC input frequency	47 - 63 Hz
Safety	UL 60950-1, CAN/CSA C22.2 No. 60950-1, EN 60950-1, AS/NZS 60950-1, IEC 60950-1
Electromagnetic compatibility	47 CFR, ICES-003, EN55022, CISPR22, AS/NZS 3548, VCCI V-3, EN 300-386, EN 61000, EN 55024, CISPR 24EN50082-1

Weight and Dimensions

Depth	469.9 mm
Width	438.2 mm
Height	88.9 mm
Weight	13200 g