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Do We Really Needthe 100-meter Limit?
Igor G. Smirnov, RCDDSignamax, Inc.
Dr. Andrey B. SemenovIT Co.
Preface• Statistical data and calculations in this
presentation
– based on information collected by:
IT Co.
AESP East Europe
Signamax, Inc.
– from warranted installations
over a 10-year period
500,000 cabling links/channels analyzed
100-meter Limit Background• Bell System Practices, SECTION 518-010-101 (1976)• Forerunner of structured cabling standards, it defined:
– Cabling topology– Telecom spaces:
Terminal Room Equipment Room Apparatus Closet Riser Closet Satellite Closet
– Cross-connections and interconnections– Administration, and…
Bell System Practices
…and
– Cabling distances:
“3. PLANNING
3.03 For optimum working conditions, one
closet should be provided for each 10,000
square feet of usable floor space. The cabling
should be laid out so that all cable runs between the
apparatus closet and the key equipment
are as short as possible…”
Bell System Practices“…Loop resistance should not exceed 50 ohms or
approximately 1000 feet of 24-gauge cable.”
ApparatusCloset
SatelliteLocation
EquipmentRoom
ApparatusCloset
2,500 ft2 2,500 ft2
10,000 ft2 10,000 ft2
SatelliteCloset
SatelliteCloset
SatelliteLocation
SatelliteLocation
SatelliteLocation
Bell System Practices“…Loop… should not exceed …approximately 1000 feet…”That means that technically it was possible to service an area up to 1000 ft in diameter or 500 ft x 500 ft (250,000 ft2)
AC
500 f
t
500 f
t
AC
250 ft
250 ft
250
ft
250
ft
KSU
KSU
Bell System Practices• AT&T Cabling Systems Engineering Group,
building its verdict on its vast research data, showed that:
– 98 % of all phone sets in commercial buildings were located no more than:
150 ft (45 m) away from switchboards dimensionally, or
300 ft (about 100 m) in terms of cable length
Bell System Practices• Elegant explanation was suggested by Donna
Ballast in CI&M (August 2006):200 ft: worst-case ceiling pathway from TC to WA
45 ft: drop from ceiling in TC and Work Area
33 ft: Work Area and equipment cords
10 ft: slack in the TC
10 ft: slack in the Work Area
30 ft: de-rating for TP to undercarpet cabling
328 ft (100 m)
+++++
New Trends
TDMM
Bell System Practices 10BASE-T
ANSI/EIA/TIA-568
100-Meter Impact• Canonic “generic cabling” principle is often used
in complete isolation of immediate networking infrastructure
• Template approach to structured cabling design does not allow to implement it in almost 100% situations
• Structured cabling component selection is done empirically
100-Meter Impact• The following conceptions are absent:
– Integrated system approach to providing high efficiency of structured cabling
– Transmission media selection
– Administration subsystem architecture
– Evaluation of horizontal cable consumptionas the key element of structured cabling
100-Meter Impact• 20 years ago:
– TIA-568(Commercial Building Telecommunications Cabling)
• Today:– TIA-568-C (Commercial Buildings)
– TIA-758 (Campus)
– TIA-862 (Building Automation)
– TIA-942 (Data Centers)
– TIA-1005 (Industrial)
Transmission Limitations
• The Shannon-Hartley noisy channel theorem
– The theorem establishes channel capacity for a
communication path, a limit for the maximum amount
of error-free digital data that can be transmitted with a
specified bandwidth in the presence of the noise
interference
Tx RxTransmission Channel
Transmission Limitations
• The Shannon-Hartley noisy channel theorem
where
C channel capacity, bit/s
B bandwidth of the channel, Hz
S total received signal power over the bandwidth, W or V2
N total noise or interference power over the bandwidth, W
or V2
S/N signal-to-noise ratio (SNR)
)1(log2 N
SBC
1.0E-16
1.0E-15
1.0E-14
1.0E-13
1.0E-12
1.0E-11
1.0E-10
1.0E-09
1.0E-08
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Permanent Link Length, m
Bit
Ero
r R
ate
10GBASE-T 10GBASE-T 10GBASE-T 10GBASE-T
1000BASE-T 1000BASE-T
100BASE-T
10BASE-T
Transmission Limitations
Cat. 5e
Cat. 6
Cat. 6ACat. 7A
Transmission Limitations
50
100
150
200
250
300
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
Nominal Velocity of Propagation (NVP)
Ch
an
ne
l Le
ng
th,
m
10BASE-T
100BASE-T
1000BASE-T
10GBASE-T
Segment Length Distribution• Two-point estimation
• Expansion of φ(х) into a Gram-Charlier series
XkLL
L gk
2
)( minmax
...])36(!4
)3(!3
1[2
1)( 244332
2
xxxxexx
u
2
)1()( 11*0
uux
Segment Length Distribution
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Segment length, m
Fre
que
ncy
of o
ccur
ence
45
Segment Length Distribution• In order to increase accuracy of calculations it is
recommended to use a “12/70” rule:
– Cabling links shorter than 12 m are not taken into consideration
– Cabling links beyond 70 m are calculated separately
– Accuracy increase – about 5 %
– Cable laying unevenness can be neglected
– Design raw error probability decrease – 5 to 7 times
10GE Capabilities vs. Category
Cabling category Link length Cabling utilization
Category 5e 25 m 13 %
Category 6 55 m 60 %
Category 6A 100 m 100 %
Category 7A 155 m 100 %
Category 8 40-100 Gbit/s
Capabilities vs. Category
0
1
2
3
4
5
6
50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Link length, m
Re
lativ
e c
ost
Category 6Category 6ACategory 7AOptical Fiber
130 140 150
Interconnect vs. Cross-connect • Interconnection vs. cross-connection
– Link/channel configuration gives 3- to 5-time reduction in bit error rate (BER)
• 98 % of all today’s installations/applications use interconnection scheme
• Channel models– Two-connector link (typical, approx. > 98 %)
– Three-connector link (uncommon, approx. < 1 %)
– Four-connector link (rare, approx. < 0.5 %)
10BASE-TToken Ring
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
“Generic” Cabling100 Gbit/s
10 Gbit/s
1 Gbit/s
100 Mbit/s
10 Mb/s
1 Mb/s
100 kbit/s
Token Ring
ARCnet
AppleTalk
ATM
TP-PMD100BASE-TX 100BASE-T4
ATM10BASE-T
100BASE-T2Demand Priority
1000BASE-T
1000BASE-TX
ATM
10GBASE-T
Voice-Grade
Category 3
Category 5
Category 5e
Category 6
Category 6A
Category 7A
“Generic cabling” turned out to benot so generic
Statistically cabling lives 5 to 7 years
Application-Dependent PHY
• CONCLUSIONS:
– Cabling links:
Majority (70 %) are within 45 meters, another 25 %
do not exceed 70 meters
Majority can support all applications up to 10GE,
and 10GE with certain limitations
Application-Dependent PHY
• CONCLUSIONS:
– Lifespan of an average structured cabling system
does not exceed 5–7 years
Choice of transmission media can be based on the best
cable meeting the networking needs rather than administered
by the standards
– 85 % of cabling systems are characterized by only
one parameter – number of work areas/outlets
Application-Dependent PHY• Attempts to strike a compromise between
physical level and application limitations
– ISO/IEC 11801 and CENELEC EN 50173engineering approach Flexible approach to distance limits
Basic estimation methods provided
– Anixter Levels Program (now obsolete) 7 levels of transmission performance
Flexible approach to component selection
Application-oriented approach
Other Distance Issues• There are other distance-dependent issues
influencing cabling design:
– Service area size
– Equipment and patch cord lengths
– Spare cable ratio
– System redundancy options
– Prospects for cables with higher impedance
– 15-meter problem
… and others
Service Area Size• Six-around-one model
2a
TRTR11
TRTR22
TRTR33
TRTR44
TRTR55
TRTR66
TRTR77
Service Area Size• Linear programming problem
• Problem simplification
min)MG(R
0k
n
1iikii
m90VerYyXx kiki
constay )1(
constYX
yx kk
2
))((
N
i
R
k
N
jkjki lMlGlG
1 1
7/
1
)]()([)(
Service Area Size
0.96
0.98
1
1.02
1.04
1.06
1.08
40 44 48 52 56 60 64 68 72 76 80
Service area diameter, m
Cost
opt
imiza
tion
inde
x
70
Service Area Size• CONCLUSIONS:
– Service area diameter should not exceed 70–75 m
– Horizontal subsystem requires 85 % of all resources during installation (element #1 for optimization)
– Horizontal subsystem cable length does not exceed 70 m (approx. 95 %)
Patch Cord Length Allocation• Equipment and patch cord routes
• φk(x) requires usage of certain connecting field layout rules and cable management panels
j
j
x
x
kajk dxxNkn1
)(
Patch Cord Length AllocationInterconnection
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
48 72 96 120 144 168 192 216 240 264
Number of Work Areas
Patc
h co
rd le
ngth
sha
re
1.0 m (3 ft)1.5 m (5 ft)2.0 m (7 ft)3.0 m (10 ft)
Patch Cord Length AllocationCross-Connection
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
48 72 96 120 144 168 192 216 240
Number of Work Areas
Patc
h co
rd le
ngth
sha
re
1.0 m (3 ft)1.5 m (5 ft)2.0 m (7 ft)
Patch Cord Length Allocation• CONCLUSIONS:
– Patch cord length dependency on the Work Area number (N) is very complex and should be tabulated
– Four influencing variables:
1. Number of Work Areas/Telecommunications Outlets
2. Cord type
3. Number of racks/cabinets in the cross-connect
4. Connecting hardware layout
Patch Cord Length Allocation• CONCLUSIONS:
– Average “data” cord length –1.5 м (5 ft)
– Average “phone” cord length – 1 m (3 ft)
– Overall channel length reduction – about 5 m (17 ft)
Patch Cord Length Allocation• CONCLUSIONS:
Reduction in 20 m in horizontal cable length
+5-meter reduction in equipment and patch cord lengths (5 m * 1.2 (1.5) = 6–7.5 m equivalent)
=up to 28-meter reduction of channel length, which guarantees 100% application functioning(the rule of 80 m)
Spare Cable Ratio• Calculation of spare cable ratio can be done
with the help of Fokker-Plank equation:
• Initial and boundary conditions:
• Average cable excess:
x
fl
x
f
t
f
2
22
2
0)0,(' tf 0),( Ltf)(),0( xxf
1 01 00
]),(1[/}),()(]),(1[{t
L
t
LL
dxxtfdxxtfxLdxxtfl
Spare Cable Ratio
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0 25 50 75 100 125 150 175 200 225 250 275 300
Consumed cable length (m)
Pro
ba
bili
ty 1 drop2 drops4 drops6 drops7 drops
Spare Cable Ratio
Standarddeviation
Cable reel length
250 m(820 ft)
305 m(1,000 ft)
500 m(1,640 ft)
1,000 m(3,280 ft)
19 m(62 ft)
11.5 % 9.8 % 9.0 % 7.6 %
17 m(56 ft)
10.0 % 8.4 % 6.9 % 5.3 %
15 m(49 ft)
9.3 % 7.9 % 6.6 % 4.9 %
Spare Cable Ratio• CONCLUSIONS:
– Spare cable ratio advantage for larger cable reels is insignificant – ~ 1–5 %
– Recommended spare cable ratio – 10 %
– 500-meter and 1,000-meter cable reels are impractical due to unhandiness during installation (size and weight)
Overall Conclusions• Application-dependent cabling is inevitable
• Current “generic” concept can be used only as a foundation in creating up-to-date, flexible cabling systems
• Wanted concepts and methods:
– More flexible and precise transmission media selection/categorization
– Administration subsystem architecture (equipment/patch cord) principles and guidelines
Igor G. Smirnov, RCDDSignamax, Inc.
Dr. Andrey B. SemenovIT Co.
Thank you for your attention!
