Date post: | 02-Jun-2018 |
Category: |
Documents |
Upload: | jarrett-mathews |
View: | 218 times |
Download: | 0 times |
of 21
8/10/2019 Cte 10106
1/21
Note: The source of the technical material in this volume is the Professional
Engineering Development Program (PEDP) of Engineering Services.
Warning: The material contained in this document was developed for Saudi
Aramco and is intended for the exclusive use of Saudi Aramcos
employees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,
or disclosed to third parties, or otherwise used in whole, or in part,
without the written permission of the Vice President, Engineering
Services, Saudi Aramco.
Chapter : Communications For additional information on this subject, contact
File Reference: CTE10106 J.S. Phillips on 873-0228
Engineering EncyclopediaSaudi Aramco DeskTop Standards
Network Considerations
8/10/2019 Cte 10106
2/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards
CONTENTS PAGES
Network Plans .................................................................................................1
Calculate Community Of Interest ..................................................................18
8/10/2019 Cte 10106
3/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 1
NETWORK PLANS
Except for the discussion on signaling, prior modules have focussed on very local aspects of
telephone service: station, loop, and switching. This module discusses the planning andconstruction necessary to interconnect these local devices and systems into an inter-area
network.
Telephone
Set
Loop
TelephoneSwitch
Network
Support Services
Trunking Plan Routing Plan Numbering Plan
SynchronizationPlan
Service Plan Emergency
Restoration Plan
FIGURE 1
Six plans are discussed in this module:
Trunking Plan
Routing Plan
Numbering
Plan
Synchronization
Plan
Service Plan
Emergency
Restoration Plan
Interconnection arrangements between switches. Trunking plans depend on the
amount of traffic and the cost of facilities between the two points.
Actual path(s) taken by calls traveling between two locations within a network. Paths
depend on traffic volume, economics, and government directives.
Numbers assigned to switches or groups of users within a switch. Number
assignments affect routing, switch translation, and general network administration.
Timing arrangements for digital switches and transmission facilities. Synchronization
involves very accurate master clocks and a hierarchy of control if those clocks fail.
Network access privileges. Services are controlled by charging plans or by limiting
access.
Methods used during crises to provide emergency telephone service. Alternate or
reduced telephone services are provided.
Plan Plan Description
FIGURE 2
8/10/2019 Cte 10106
4/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 2
Trunking Plan
The efficient interconnection of telephone switches depends on the amount of traffic between
the switches and the cost of providing the circuits between them.
Fully-Meshed and Demand-Meshed Networks
An example of a fully meshed network is shown in Figure 3. Each of the eight switches in the
network is connected to all other switches. Such an arrangement is unnecessarily complex in
real telephone networks. In many cases there is very little traffic between some switches,
resulting in long idle periods on interconnecting trunks if such were provided. In these cases it
is more economical to combine that small amount of calling traffic with other traffic and send
it through an intermediate switch. This process is called tandeming the traffic and the
intermediate switch is called a tandem switch.
The result of this simplifying process is the demand-meshed network shown in Figure 4.
Economic criteria (e.g., cost/call, calls/trunk) have been applied to each of the traffic paths in
the fully meshed network to determine which of the paths are economical. A call that must be
tandemed (e.g., a call from switch 4 to switch 8) must pass through a minimum of three
switches and two trunks to reach its destination (e.g., 4-2-8 or 4-3-8). The economic decision
to tandem or not to tandem must include the cost of switching as well as the cost of using two
trunks instead of one. These calculations will be covered in the next module on traffic
engineering.
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Demand-Meshed NetworkFully-Meshed Network
FIGURE 3 FIGURE 4
8/10/2019 Cte 10106
5/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 3
Saudi Aramco Trunking Plan
The Saudi Aramco trunking plan for both the internal and external (MOPTT) switches is
shown in Figures 5 and 6. Each of the central offices in the Saudi Aramco network functionsas a tandem switch for a group of smaller switches, usually PABXs. Saudi Aramco traffic
completing within the Saudi Aramco network is referred to as on-net traffic, whereas the calls
terminating in the Saudi Telecom public network is referred to as off-net traffic. In the
trunking arrangements with Saudi Telecom, Saudi Aramco avoids toll diversion, the use of a
private network to bypass toll (long-distance) charges on off-net calls.
A detailed drawing for the Saudi Aramco trunking plan is given in Drawing DA-478462.
Routing Plan
The routing plan for a network is a series of rules defining how calls are completed across the
network. In a fully-meshed network, the routing plan is simple: each call has a direct path to
its destination switch. In the case of a demand meshed network, routing becomes a very
important issue. Let us examine the demand-meshed network once again. For a call from
switch 4 to switch 8, a number of paths are possible: 4-2-8; 4-3-8; 4-3-2-8; etc. A routing plan
would consider the economics of each route and select the route that would yield the lowest
capital cost on a per-call basis.
8/10/2019 Cte 10106
6/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 4
Tanajib
DCO
(Future)
Ras Tanura
Fetex 150
DCO
Dhahran
No. 2 EAX
Dhahran
Fetex 150
DCO
Abqaiq
Fetex 150
DCO
Udhailliyah
C1 EAX
(present)
DCO
(Future)
Tanajib Community PABX
Tanajib Marine RSUSafaniya PABX
RT Terminal PABX
RT ITC PABX
Abu Ali PABX
SCECO Ghazlan
Berri DCO
Ju'aymah DCO
Turaif PABX
Badanah PABX
Rafha PABX
Qaysumah PABX
IPSA IPS-3
IPSA IPS-4
SCECO Headquarters
Dammam Powerplant
Transformer Yard
Qurayyah PABX
Pager Terminal
LIP Training PABX
Yanbu NGL PABXYanbu Crude PABX
E/W MC-1
E/W MC-2
E/W MC-3
IPSA IPS-6
IPSA IPS-7
IPSA IPS-8
Uthmaniyah
Shedgum
Shedgum Powerplant
Faras Powerplant
Mubarraz Svc Ctr
Tanajib Plant RSU
IPSA IPS-5
Tanajib
Clinic
(Future)
Ras Tanura
Clinic
Dhahran
Clinic
840 PABX
(Ind. Sec,
TOPS,
School,
Steineke)
Abqaiq
Clinic
Al Hasa
Clinic
SCECO
Clinic/ISD
Subnetwork
(Future)
FIGURE 5
8/10/2019 Cte 10106
7/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 5
MFC
MFC
MFC
DP
MFC
MFC
MFC
MFC
MFC
Hi-Usage - PCMMFC
DP
MFC - microwave
MFC - PCM cable
Operator Calls - PCM cable
Eastern Province Overflow Final - PCM
NSD/ISD - microwave
MFC - PCM
Local - PCM
MFC - PCM
PCM
MFC
High Usage
MFC
MFC
MFC
MFC
MFC
MFC
MFC
Rahima PRX
Doha PRX
Khobar AXE
Civil AviationSXS
MFC
Future
Future
Future
Madinat
PRX
Mahasin
PRX
Al Hasa
Local Tandem
AXE
Ras
Tanura
Fetex
150
DCO
DhahranNo.2
EAX
Tanajib
Fetex
150
(Future)
Kafji
Dhahran
EOB
Fetex
DCO
Abqaiq
EOB
Fetex
DCO
Udhailiyah
DCO
(future)
Al-Hasa
PABX
Dammam
Local
Tandem
Dammam
Secon-
dary
DSX
Toll
Office
Reference:Saudi AramcoDrawing No..
D-478462
FIGURE 6
8/10/2019 Cte 10106
8/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 6
Alternate Routing
Another aspect of a routing plan is the definition of alternate routes within the network. In the
example shown in Figure 7, suppose the primary route from switch 4 to switch 8 is throughswitch 2 (4-2-8). If all circuits on route 2-4 are busy, it is possible to alternate route the call
through switch 3. Care must be taken to avoid an alternate routing strategy that would result
in circular routing, i.e., routing rules that would result in traffic leaving a switch and returning
to the same switch before arriving at its destination.
1
2
3
4
5
6
7
8
Demand-Meshed Network
2-4
Alternate
Route
is
2-3-4
Dhahran
Abqajq
Ras Tanura
Udhailiyah
Ju'aymah
Ras Tanajib
Safaniya
Shedgum
FIGURE 7
One-Way Versus Two-Way Trunking
The previous examples of fully-meshed and demand-meshed networks showed all trunk
groups as two-way, that is, each trunk could be accessed (seized) from either end. This
arrangement allows greater efficiency in the network, but can result in a problem if a circuit is
simultaneously seized from each end. A simultaneous seizure of this type is called glare in the
network, and usually results in two lost calls and customer complaints. Some software
adjustments can be made to reduce the likelihood of glare, such as ordered- (1-2-3-4-5-etc.)
and reverse-ordered (-10-9-8-7-etc.) trunk access from opposite ends of the trunk group. In
most cases, the decision to implement one-way versus two-way trunk groups is a matter of
efficiency versus the possibility of glare.
8/10/2019 Cte 10106
9/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 7
Numbering Plan
In today's world it is possible for one station to directly dial over 98% of the other telephones
in the world without operator intervention. This requires each of these hundreds of millions oftelephones to have a unique number. As shown in Figure 8, coordination of telephone
numbering is divided among many organizations and agencies, including the ITU, Ministries,
Telephone Operating Companies and in some cases, such as Saudi Aramco, individual
companies.
Country Code 2 or 3 ITU/CCITT
Digits Responsible Agency Example
966-
Number Element
Area Code 1 to 3 MOPTT -3-
Exchange (NNX) 2 or 3 MOPTT -875-
Station Number 4 Saudi Aramco -6290
9 to 13
FIGURE 8
The full telephone number of a station is composed of four parts and may involve up to 13
digits. The numbering plan for a telephone network is closely associated with the routing and
trunking plan of the network, as well as the engineering of the telephone switch. The type ofsignaling, i.e., link-to-link or end-to-end (see previous module), is influenced by the number
of digits that must be transmitted; and any change in exchange codes must be reflected in the
routing tables of all switches with a "need to know" in order to complete the call. Within
Saudi Arabia, each area code is divided into Local Calling Areas (LCAs) corresponding to
areas of the same leading NXX (#xx exchange prefix) numbers. In general, there is no toll
charge associated with calls between switches within the same LCA boundary.
Dialing Plan
It is frequently necessary to implement local dialing arrangements to access local or long-distance networks or services, including vertical features on the serving switch. Dialing plans
may even vary from switch to switch in a network, depending on the capabilities of the switch
to provide translations such as digit addition, digit deletion, and digit absorbing. To the
greatest extent possible, however, an effort is always made to standardize dialing plans. This
avoids confusion and allows users to complete calls with a minimum of training,
inconvenience, and assistance.
8/10/2019 Cte 10106
10/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 8
Country
Codes
KSA Area
Codes
Eastern Province
LCAs
Saudi Aramco
Assigned NNXs
1
United States
44
United
Kingdom
92
Pakistan
961
Lebanon
962
Jordan
963Syria
964
Iraq
965
Kuwait
966
Saudi Arabia
967
Yemen North
Oman968
969
Yemen South
971
United Arab
Emirates
973
Bahrain
974
Qatar
-1
DilamDiriyah
Kharj
Riyadh
-2
Hawiyah
Jeddah
Makkah
Taif
-3
-4
Arar
DubaMadinah
Rafah
Tabuk
Turayf
Yanbu
-5
-6
Baqa
Buraydah
Ghat
Hail
Zilfi
-7
Abhah
Jizan
Khamis
Mushait
LCA (1)
King Khalid
City
LCA (2)
Khafji
Safaniya
Tanajib
Nariyah
LCA (3)
Jubail
LCA (4)
Khursaniyah
Abu Ali
Berri
Ghazlan
Juaymah
Ras Tanura
Rahimah
Dammam
Al-Khobar
Dhahran
LCA (5)
Abqaiq
Madinat
Abqaiq
LCA (6)
Shedgum
Faras
Mubarraz
Hofuf
Uthmaniyah
Udhailiyah
Khurais
378 - Tanajib
378 - Tanajib
67x - Ras Tanura
87x - Dhahran
572 - Abqaiq
574 - Abqaiq
577 - Shedgum
577 - Udhailiyah
378-0 to 378-8 Saf
378-3 to 378-4 Tan
378-5 to 378-6 Tan
378-9 Tan Marine
673-0 to 673-9 RT
678-1 RT Terminal
678-2 Abu Ali
678-3 RT
678-7 Berri
678-9 Ju'aymah
873- Dh EOB
874- Dh EOB
875- Dh EOB
876- Dh EOB
877- Dh No.2 Misc
878- Dh No.2 EAX
572- Abqaiq
574- Abqaiq Misc
577-1 Shedgum
577-2 Al Hasa
577-4 Shedgum
577-5 Uthmaniyah
577-7 to 577-8 Udh
* Not all switches
represented in this
list.
Saudi Aramco
Switch Codes *
Coordinated by ITU Administered by Saudi MOPTT Administered by Saudi Aramco
FIGURE 9
8/10/2019 Cte 10106
11/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 9
Synchronization Plan
To a growing extent, the telephone network is becoming an integrated digital network
involving digital switches, digital links, and even digital (common channel) signaling. Themethod of digitizing voice is standardized, so that interfacing between switches and
transmission systems (digital fiber optics, microwave) is simple and efficient.
PCM Hierarchy
There are two main formats used for digitizing voice, one (T-1) developed in the United
States, and the other (CCITT) developed for European use. Both systems involve 8-bit
sampling at 8 kHz intervals, with pulse-code modulation (PCM) of a carrier signal. This
introductory course does not have time to detail the operation of PCM systems; however, the
European PCM hierarchy, as used by Saudi Aramco, is illustrated in Figure 10.
1
2
3
4
5
6
7
28
29
30
64
kb/s
2.048
mb/s
2.048
mb/s
8.448
mb/s
8.448mb/s
8.448
mb/s
8.448
mb/s
2.048
mb/s
2.048
mb/s
2.048
mb/s
34.368
mb/s
34.368
mb/s
34.368
mb/s
34.368
mb/s
139.264
mb/s
30 ch
120 ch
480 ch
1920 ch
FIGURE 10
Saudi Aramco Wideband Network
The Saudi Aramco wideband network, comprised of fiber optics and microwave systems, are
a combination of digital and analog systems. The systems north and south of the wideband
hub, Dhahran, are shown in Figures 11 and 12. This wideband network is used for voice
trunking as well as other voice and data services not directly associated with the telephone
network.
8/10/2019 Cte 10106
12/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 10
FIGURE 11
8/10/2019 Cte 10106
13/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 11
FIGURE 12
8/10/2019 Cte 10106
14/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 12
Digital Trunking
It is possible, in the digital exchanges utilized by Saudi Aramco, to interface two ways with
digital transmission systems: at the 64 kb/s (vf) level, or at the 2.048 mb/s with blocks of 30trunks. The advantage of the former is that small trunk groups are efficiently served.
However, each trunk working on the switch must be terminated individually, requiring much
more interface equipment on the switch. The latter alternative provides 30 trunks with only
one switch/transmission interface, greatly decreasing the cost of trunking.
Synchronization Clocks
This strong interaction between switching and transmission requires a common clocking
arrangement, so that the digital pulses, including digital signaling links, are coordinated
properly. A fault in synchronization results in "slips" timing mismatches and a loss ofinformation. This slip may not affect voice quality much, but can be a serious problem in
signaling and other data communications.
There are several methods for synchronizing a complex digital network. The most common
method, and the one used by Saudi Aramco, is a master-slave arrangement as shown in Figure
13. The method is based on the principle of designating one clock as the master clock and
locking (slaving) all other clocks to it. The master clock for the Saudi Aramco network has
been installed in the Dhahran EOB digital central office and is based on an atomic (Cesium)
standard with a lifetime stability of one part in 1012. Three clocks are installed together and
outputs are constantly analyzed on a two-out-of-three comparison algorithm. A caution alarmis generated when the frequency difference is over 1 x 1011, and a frequency alarm when the
frequency difference is over 1 x 109. Other clocks (crystal oscillators) are installed in each of
the other digital central offices, and provide backup synchronization with an accuracy of three
parts in 107 . Clocking signals from the Dhahran EOB are imposed on the digital microwave
and fiber optics facilities, which in turn synchronize the other digital telephone switches. If
these digital links (or the Dhahran clocks) were lost, the telephone switches would provide
local synchrony until the master clocks could be reconnected.
8/10/2019 Cte 10106
15/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 13
Synchronization Clocks
Tanajib
DCO
(future)
Berri
DCO
Ju'ay-
mah
DCO
Ras
Tanura
DCO
Abqaiq
DCO
PTT
Dam-
mam
Udh
DCO
(future)
Atomic
Reference
Clocks1 x 10-12
Crystal
Oscillator
1 x 10-7
Master Synchronization
Through PCM System
Slave Synchronization
Through PCM System
Dhahran
EOB
DCO
Crystal
Oscillator-71 x 10
FIGURE 13
Service Plan
The service plan for a telephone network outlines all regular and special telephone services
provided by the telephone agency, their access privileges and arrangements, and any charging
rates to be applied. At Saudi Aramco, the telephone service plan is outlined in the following
General Instructions:
GI 1602.001 Residential Telephone Service
GI 1602.002 Business Telephone Service Inside Aramco
GI 1602.003 Business Telephone Service Outside Aramco
Telephone service is provided in six levels of service, as indicated in Figure 14. Each level
requires a specified level of authorization, as outlined in the applicable GI. Long-distance
charges for residential telephones are paid through direct payroll deduction, or by local
collection at call cabin stations. There is no departmental charge-back for long-distance
business calls; however, a summary of departmental calls is developed and sent to department
managers for their review and verification.
8/10/2019 Cte 10106
16/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 14
Level No. 1:
Aramco local service only.
Level No. 2:
Level No. 1 plus MOPTT LCA access.
Level No. 3:
Level No. 2 plus MOPTT Eastern Province access.
Level No. 4:Level 3 plus MOPTT national subscriber dialing.
Level No. 5:Level 4 plus international subscriber dialing.
Level No. 6:
Level 5 plus leased international voice circuit access.
FIGURE 14
The overall service plan for voice services, as outlined in GI 1602, also covers some special
voice services that are directly and indirectly associated with the telephone network.
FX and OPX
Most telephone service is provided through the local serving exchange, i.e., a Dhahran user is
connected to a Dhahran switch, Abqaiq to Abqaiq, etc. In some cases, however, it is desirableto provide telephone service from a distant switch rather than from the local switch. This
service is referred to as foreign exchange (FX) service. FX service requires special circuit
equipment to provide supervision and alerting (ringing) over long-haul facilities such as
microwave and fiber optics. A similar service involves off-premises extensions (OPX), in
which an extension from a main station is located at a distant location. FX and OPX services
are illustrated in Figure 15.
FX and OPX allow a user to bypass the local switch and receive a "dial tone" from a distant
switch. This is desirable if there are unique features in the distant switch that are required, or
if there is a necessity for continued service in the case of a local switching failure.
8/10/2019 Cte 10106
17/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 15
Ras Tanura DCO
(673-xxxx)
Dhahran DCO
(875-xxxx)
875-1234
Foreign
Exchange
(FX) from
Dhahran
Ras Tanura DCO
(673-xxxx)
Dhahran DCO
(875-xxxx)
Off Premises
Extension
(OPX) to
875-1234
Main Station
875-1234
FIGURE 15
Conference Bridges
On many occasions, e.g., management reporting and emergency coordination, it is necessary
to simultaneously interconnect many users in a shared conversation arrangement. This is
accomplished by special equipment known as a conference bridge. A conference bridge
(Figure 16) can be designed to accommodate a variable number of users, and provides the
important functions of simultaneous interconnection and volume control. Conference bridges
are accessed by dialing a single specified number, with the switch providing connection pathsup to the capacity of the bridge.
Dhahran DCO
(875-xxxx)
Conference
Bridge
875-1234
FIGURE 16
8/10/2019 Cte 10106
18/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 16
Mobile Telephone
Mobile telephone was originally a operator-assisted service. It is now integrated with
telephone switching and is known as Improved Mobile Telephone Service (IMTS). [TheSaudi Telecom public network mobile telephone service is called Advanced Mobile
Telephone Service (AMTS).] The Saudi Aramco mobile telephone networks are shown in
Figure 17.
North VHF Frequencies
Ch 1
Ch 2
Ch 3
Ch 4
South VHF Frequencies
Ch 1
Ch 2
Ch 3
Ch 4
Xmit
152.27
152.30
152.33
152.36
Xmit
152.39
152.42
152.45
152.48
Receive
157.53
157.56
157.59
157.62
Receive
157.65
157.68
157.71
157.74
UHF IMTS Freqencies
Ch 1
Ch 2
Ch 3
Ch 4
Ch 5
Ch 6
Ch 7
Ch 8
Note: All frequencies are
for base stations. Tx/Rx
reversed for mobile units.
Xmit
456.35
456.40
456.50
456.55
456.65
456.70
456.80
456.85
Receive
461.35
461.41
461.50
461.55
461.65
461.70
461.80
461.85
Dhahran
Ju'aymah
Terminal
Abu
Hadriyah
Safaniya
Berri
Abqaiq
Udhailiyah
Haradh
GOSP 1
Shedgum
Ju'aymah
Terminal
Abu
Hadriyah
SafaniyaZuluf
GOSP 2
Abqaiq
Udhailiyah
Haradh
GOSP 1
UHF
8 Channel
Duplex
VHF
4 Channel
Duplex
Dhahran
No.2 EAX
Telephone
Switch
877-04xx
877-05xx
877-45xx
877-46xxAbqaiq
No.2 EAX
(to be DCO)
Telephone
Switch
574-92xx
574-93xx
FIGURE 17
8/10/2019 Cte 10106
19/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 17
In IMTS, a mobile radio transmitting and receiving terminal is connected to a telephone
switch, and each individual mobile radio is assigned a specific number allocated to that
terminal. Radio carrier and radio signaling replace the normal loop and loop alerting of land-based telephone service. The number of channels in a network determine how many
simulaneous calls can be carried over the network. The radio channel must be repeatered
(amplified and retransmitted) at various points to provide coverage over the Saudi Aramco
operating area. Each idle mobile radio scans the channels for a transmitted code
corresponding to its listed number. As shown in Figure 16, Saudi Aramco operates two
mobile radio networks, one operating at VHF and another at UHF frequencies. A maximum
of eight simultaneous calls can be provided on each of these two networks.
Paging
Paging is a simplified form of radio alerting in which a telephone call to a paging telephone
number results in an alerting signal transmitted via radio to a small, mobile radio receiver
carried by the user. Some models of paging allow the transmission of a short message, or a
number to which a return call is requested.
Emergency Restoration Plan
Emergency restoration plans are still undergoing development within Saudi Aramco, but four
specific strategies are clearly indicated or in place:
The provision of dual routing for switches at all major industrial and administrative
centers
Duplicated "essential" service through separate switches, where possible
Parallel networking, as in the proposed Clinic/Industrial Security sub-networking
Stand-by restoration switching
In addition to emergency restoration, all switches have load control by which, under heavy
traffic overloads, non-essential calls are denied network access, or access is made "hard to
reach" through a high-blocking arrangement, in which only a small percentage of non-
essential calls are allowed to complete.
8/10/2019 Cte 10106
20/21
Engineering Encyclopedia Communications
Network Considerations
Saudi Aramco DeskTop Standards 18
CALCULATE COMMUNITY OF INTEREST
A term frequently encountered in trunking plans is community of interest. Community of
interest is a method of calculating the relative intensity of calling between two switchingcenters within a particular network. For two switches, A and B, the community of interest
between A and B is denoted by the letter K and is defined by the equation:
Originating traffic A to B Originating traffic at B
= KAB Total originating traffic at A Total network originating traffic
If all callers in the network tended to call all others equally (K=1), then the proportion of A-
calls from A to B would be equal to the proportion of all network calls originating at B. To
illustrate this [K=1] further, if switch B originates 10 percent of all traffic, then 10 percent ofthe traffic originating at switch A should terminate at switch B. But if only five percent of A's
traffic goes to B, then K= 0.05/0.10 = 0.5. Community of interest calculations are usually
performed when new switches are added to the network. All switch-to-switch community of
interest values are calculated, and the values are averaged for the area to be served by the new
switch. This procedure is only approximate, and may introduce some bias in traffic to/from
the new switch.
8/10/2019 Cte 10106
21/21
Engineering Encyclopedia Communications
Network Considerations
In-Class Example Calculation for Community of Interest
Calculate originating traffic for a new switch composed of 20% B and 40% C. In calculating
the Community of Interest for the new switch, use the traffic-weighted average for the valuescalculated to/from B and C.
to A: to B: to C: Total
Originating traffic from A to: 800 110 70 980
Originating traffic from B to: 50 500 80 630
Originating traffic from C to: 100 90 700 890
Total 950 700 850 2500
to A: to B: to C:
Comm. of interest from A to:
Comm. of interest from B to:
Comm. of interest from C to:
to A: to B: to New: to C:
Comm. of interest from A to:
Comm. of interest from B to:
Comm. of interest from New to:
Comm. of interest from C to:
to A: to B: to New: to C:
Originating traffic from A to:
Originating traffic from B to:
Originating traffic from New to:
Originating traffic from C to:
FIGURE 18