Transcript Document

Cabling for 802.11n
Scott D. Thompson
President,
Oberon, Inc.
3/4/2009
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IEEE 802.11n DEFINITION
•
“n” is a proposed amendment to the IEEE 802.11 Standard
• Uses advanced signal processing (Multiple Input/Multiple
Output and beamforming) and advanced over the air
modulation and coding methods to achieve unprecedented
wireless data rates
• Many client devices and access points from leading vendors
are “n” ready
• May operate in the 2.4 GHz band and 5 GHz band
• In mixed mode deployments, 802.11n performance will be
degraded somewhat by 802.11 a/b/g clients, but may improve
connectivity performance of 802.11 a/b/g clients
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“SIGNALING” DATA RATE
vs.
DATA THROUGHPUT
“Signaling” data rate: Over the air modulation rate
commonly used to specify the product
Data throughput: effective Ethernet throughput at the
connector
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“SIGNALING” DATA RATE
vs.
DATA THROUGHPUT
In Practice
Technology
3/4/2009
“Signaling” data
rate
nominal data
throughput
100Base-T wired
Ethernet
100 Mb/s
>90 Mb/s
802.11 b wireless
11 Mb/s
~ 5-6 Mb/s
802.11 g wireless
54 Mb/s
~ 20-25 Mb/s
802.11 n wireless
300 Mb/s
~ 90 - 150 Mb/s
Or
6 x performance
.
“SIGNALING” DATA RATE
vs.
DATA THROUGHPUT
The difference is that the wireless connection has more
packet overhead and lower bit density in the signaling
And remember-
Wireless access points are (somewhat) like Ethernet hubs
- They share a collision domain, and they are half duplex.
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TYPICAL PRODUCT DATA RATE
Vendors Claim >100Mb/s data throughput rates per radio,
> 200 Mb/s for two radios.
SO….
requires cabling for 1000Base-T (Gigabit Ethernet) versus
100Base-TX (Fast Ethernet).
CAT5e or better, & will be less tolerant of cabling errors
Is the AP, switch, and/or controller port 1000Base-T (gigabit)
capable?
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INFRASTRUCTURE BANDWIDTH
What is the uplink bandwidth required when aggregating multiple
APs? (using an over-subscription factor of 20, for example)
960 Mb/s ea.
48 port switch
48 X (200 Mb/s) = 480 Mb/s
20 (over-subscription factor)
Controller A
480 Mb/s
Controller B
200 Mb/s ea.
peak
AP 1
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AP 2
AP 3
. 4
AP
AP 48
TIA GUIDELINES FOR CABLING
Telecommunications Systems Bulletin TSB-162
Telecommunications Cabling Guidelines for Wireless Access
Points (APs) provides guidelines on the topology, design,
installation, and testing of cabling infrastructure for
supporting wireless local area networks (WLANs) in
compliance with the ANSI/TIA/EIA-568-B.2 and TIA-569-B
standards for supporting wireless LAN in customer
premises.
TSB-162 was created by the TIA TR-42 engineering
committee and released in March of 2006. TSB-162 is not a
standard, but rather contains technical material that may
be useful to industry and users.
*Cabling Installation & Maintenance March, 2006
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TIA GUIDELINES FOR CABLING
TSB-162 states that cabling should be installed and
performance tested per existing 568-B.2 standards.
Determination of exact cell size and placement of the AP is
outside the scope of the TSB (perform a site survey or
simulation)
TSB-162 include wall-mount above the drop ceiling, wallmount below the drop ceiling, and in-grid ceiling mount.
Telecommunications Enclosures (TEs) can be mounted in a
ceiling panel to provide locked security or aesthetics for APs
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CELL SIZE
The TSB includes an example of a 60-foot by 60-foot
square cell structure
This agrees reasonably well with vendor recommendations for
3,000 sq. ft. “cell” sizes to support wireless voice over IP
AP
Lmax=13 m
(42 ft)
Hmax=80 m
(262 ft)
TR
X=18.3 m
(60 ft)
TO
r=13m
(42 ft)
Patch=6m
(20 ft)
3,600 sq.ft. square cell
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EQUIPMENT
(switch)
TIA 569-B Telecommunications Pathways
Telecommunications Enclosure (TE) may be used to enclose APs
The use of suspended ceiling space for horizontal connection points
may be acceptable, provided that the space is accessible without
moving building fixtures, equipment or heavy furniture
Access to the TE shall be controlled against unauthorized access
Cables that enter the TE shall be protected from sheath abrasion
and conductor deformation by means of grommets, bushings and
suitable cable management hardware
A TE should serve an area not greater than 3,600 sq. ft.
A minimum of 3” clear vertical space shall be available above the
ceiling tiles for horizontal cabling and pathway
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POWER OVER ETHERNET
•
Most vendor wireless access points can be powered by
IEEE 802.3af PoE. There are some exceptions, requiring
802.3at (PoE Plus)
• 802.11n products typically require close to 12.95 W if
both radios used
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OTHER CONSIDERATIONS
- Although 802.11n is capable of providing coverage over
large areas, recommend using the same density of access
points used in 802.11 a/b/g network
- This is consistent with TIA standards, vendor
recommendations, and anticipates applications requiring a
higher signal to noise ratio than data
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COAX CABLING TO ANTENNAS
- 802.11n access points may require three to six antennas
- Some access points have non-detachable or integrated antennas
- Ideally, antennas are unobstructed by ceiling tiles and other
objects
- Antennas should be spaced about
4” apart (2.4 GHz), and 2” apart
(5GHz) or greater. Beyond that,
there is not a need to “space
in increments of a wavelength”
- Use suitably rated coax such as
UL Type CL2P
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INSTALLING IN THE “PLENUM”
vs. THE AIR HANDLING SPACE
- Ideal location for access point is in the ceiling, but……
National Electric Code (NEC) regarding the plenum used for
environmental air…….
- Article 300.22(b) “Equipment and devices shall be permitted within
such ducts or plenum chambers only if necessary for their direct
action upon, or sensing of, the contained air”
-NEC Article 100 defines plenum as “A compartment or chamber to
which one or more air ducts are connected and that forms part of
the air distribution system”.
- NEC article 300.22(c) “The space over a hung ceiling used for
environmental air-handling purposes is an example of the type of
other space to which this section applies”, (Air-handling space as
opposed to a plenum space)
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N.E.C. COMPLIANCE
- NEC article 300.22(C)(2) “Electrical
equipment with a metal enclosure, (or
otherwise listed) shall be permitted to
be installed in such other space
unless prohibited elsewhere in this
Code”.
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- NEC article 300.23 “cables, raceways and equipment installed behind
panels, including suspended ceiling
tiles, shall be arranged and secured
so as to allow removal of panels and
access to the equipment.”
PREPARING FOR THE FUTURE
- Cable for the future. Faster wireless standards in the works, but nothing
eminent
- Gigabit Ethernet to the AP probably adequate for some time into the
future
- In Healthcare, the Joint Commission has established rules for mitigating
the spread of infectious disease and contaminants- limiting access to the
air-handling space. TIA tech. committee TR-42 Health care facility cabling
task group.
- Department of defense installations, & other government agencies may
require access point to be locked up
- Consider other RF services such as RFID, asset location, cellular, etc.
- RF cables- 802.11n has provisions for up to 8 antennas!
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www.oberonwireless.com
3/4/2009
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