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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

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Engineering Encyclopedia Communications


Saudi Aramco DeskTop Standards

CONTENTS PAGES

Network Plans .................................................................................................1

Calculate Community Of Interest ..................................................................18

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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

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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

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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.

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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

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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

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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.

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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.

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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

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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.

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FIGURE 11

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FIGURE 12

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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.

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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.

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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.

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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

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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

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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.

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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.

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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

Documents

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