Numbering Plan

Numbering Plan

National Schemes• The objective of numbering plan is to uniquely identify

every subscriber connected to telecom network. In the early stages of development , a numbering scheme was confined to a single local exchange and exchanges were identified by the name of the town in which they were located.

• In order to establish a connection through a network , it is necessary for caller to inform the switching center the address of the customer being called i.e. the called customer directory number.

• This determine both the route for a call and charging rate. In the multi-exchange area linked numbering scheme was introduced .

Numbering Plan• In linked numbering scheme the local numbering scheme

covers a number of exchanges , so a call from any exchange in the area uses the same number to reach a particular customer .

• The part of directory number is an exchange code and remaining is customer number in that exchange.

• The subsequent introduction of Direct Distance Dialing (DDD) or Subscriber Trunk Dialing (STD) or National Wide Dialing (NWD) required the development of National Number Plan (NNP) .

• As per ITU-T maximum 11 digits for international number and max digits for national number is 11- N , where N is number of digits in country code in world numbering plan.

• National numbering plan contains:1. An area code2. An exchange code 3. Customer’s number in local exchange.

Numbering Plan• For a local call ,only the exchange code and the subscriber

number is normally dialed but full national number is needed for long distance call.

• In order to enable local exchange to differentiate between them a trunk prefix is dialed before national number. This enable the call to trunk exchange where a register translates the area code to determine the required trunk routing.

• An additional prefix following the trunk prefix denotes the international call and route the call from the trunk exchange to international gateway exchange.

• The international prefix is followed by international code for required country.

• In North American numbering plan has uniform numbering scheme , a 3 digit area code is followed by 3 digit office code and 4 digit customer number.

Numbering PlanInternational Numbering

• An introduction of International Subscriber Dialing (ISD ) made it necessary for every subscriber station in the world to have unique number.

• In the ITU-T world numbering plan each subscriber’s number consists of country code followed by the subscriber’s national number.

• For numbering purposes the world is divided into zones, each given a single digit code . Each country within a zone has zone number as the 1st digit of its country code as shown in table 10.1 .

• However the European numbering zone has been allocated two codes because of large number of country codes required within this code.

• Typical international numbers is shown in table 10.2

Numbering PlanTable 10.1 : World Numbering Zones

Zone Countries

1 North America

2 Africa

3 & 4 Europe

5 South America and Cuba

6 South Pacific (Australia )

7 USSR

8 North Pacific (Eastern Asia )

9 Far East and Middle East.

0 Spare code

Numbering Plan

Zone Country Country code

No of digits in NNP

Total digits

1 USA 1 10 11

1 Canada 1 10 11

2 Egypt 20 8 10

2 Liberia 231 6 9

3 France 33 8 10

3 Portugal 351 7 or 8 10 or 11

4 UK 44 8 or 9 10 or 11

4 Switzerland 41 8 10

5 Brazil 55 9 11

5 Ecuador 593 7 10

Table 10.2 : Examples of Typical International numbers

Numbering Plan• Within each zone every country has allocated a single two

digit or three digit code number. For example within zone 3 (Europe) Holland has the code 31 and Albania has 355.

• The three digit code is allocated to small countries , having fewer digits in their NNP to minimize the total number of digits in customers international number.

Numbering Plan

Country Code National Number

1- 3 Digits

12 Digits maximum

9- 11 Digits

Area code Exchange code Line number

(b) National telephone number

(a) International telephone number

Charging Plan• The cost of providing a telecommunication network

consist of capital cost and the current operating expenses. All of these costs must be met from income obtained by telecom operators from its customers.

• The charges paid by each customer should be related to the proportion of those costs incurred in providing services. The charges that are made to customer are levied in following way:

1. An initial charges for installing of customer’s line.2. Monthly line rent charges .3. Call charges.• The charging plan provide recovering both capital cost

and operating cost from subscribers. The cost of shared resources like the switching equipment is divided among a large number of subscribers over a period of time.

Charging Plan

• The cost of dedicated resources like telephone instrument and subscriber line must be recovered from individual customer.

• A subscriber’s share of capital cost of common resources is generally covered in initial connection charges and rental component .

• The rental may be levied on a monthly , quarterly, half yearly or annual basis.

• The part of the operating cost is incurred if network carries no traffic , so this should be recovered by rental charges.

• Those parts of the capital cost and operating cost which depend on traffic carried should be recovered from call charges .

• Some operators do not make separate charge for local call but include them in rental , this is known as flat rate tariff.

• Other charge a unit fee per call or fee proportional to call duration . This is known as message rate tariff.

• Local call charges are made on local meter basis and STD calls are charged on the basis of AMA (automatic message accounting) in which CDR of each call is made.

• The quantity of switching , junction and trunk transmission equipment provided in the network is based on the estimated busy hour traffic .A large part of this hardware remains idle during off-peak hours

• In order to restrict peak demand and encourage off-peak demand ,it is common to make the metering rate vary with time of day.

• Because of these relative cost and to restrict peak demands .it is common to make call charges vary with time of the day.

Charging Plan

Charging Plan• A charging plan for long distance calls should satisfy

following criteria :

1. The call revenue should recover the capital and operating cost , these are entirely traffic dependent.

2. Charges to and from customer who are geographically close should be made similar to give equal treatment and to avoid complaint.

3. The charging plan should easily understood by customers.

4. The charging plan should be suitable for implementation by automatic equipment . It should be compatible with numbering and routing plan

• The charges of long distance calls should be proportional to the distance x duration. The charge is based on the distance between originating and terminating transit exchanges.

Charging Plan• Trunk calls are charged on the basis of duration . In addition charges

also depend upon the radial distance between calling and the called station

Distance Km Meter pulse rate (pulses per minutes

25 To 50 (zone 2 ) 1.67

50 to 100 (zone 3 ) 5.00

100 to 200(zone 4 ) 7.50

200 to 500 (zone 5 ) 15.00

500 to 1000(zone 6 ) 20.00

More than 1000(zone 7 ) 30.00

• For international calls per minute based charging is made

ROUTING PLAN• Routing plan should be developed to determine which

exchange should be interconnected by direct route and which connection made via tandem exchange .

• Routing plan referred to the procedure that determines which path in a network are assigned to particular connections .

• This routing plan should be consistent with numbering, charging , transmission and signaling.

• If there is large traffic between two exchanges ,it is economical to provide a direct route between them.

• If there is little traffic between two exchanges , it is more economic to combine this with traffic to other destinations to produce a large amount of traffic over a common route to tandem switching center.

ROUTING PLAN• The correct solution depend on cost of circuits as well as

amount of traffic . If circuits are cheap , it is less expensive for them to lightly loaded route than to incur the cost of switching equipment in tandem exchange.

• Many direct routes are provided between local exchanges in small areas with high customers density but not to more distant exchanges.

• In some networks automatic alternate routing (AAR) is used. Direct routes are underprovided with circuits, when all circuits in the direct route are busy , traffic overflow to tandem route through switching center at higher level in hierarchy .

• A under provided direct route is called high usage route and indirect route to which its traffic finally overflows is called a final route.

ROUTING PLAN

• Only a small portion of calls use the final routes.

• The traffic level at which direct routes , automatic alternate routing should be used depend on relative cost of direct and alternate routing (including switching and signaling equipment) .

• Low traffic high cost direct route indicate tandem routing and high traffic low cost direct routes indicate direct connection.

• Modern networks have SPC exchanges , so their routing translation can be readily be changed . Using CCS7 enables the routing tables of exchanges to changed remotely .

ROUTING PLAN• The CCS7 networks can links the processors of exchanges

to control from network management centers (NMC).

• NMC can monitor the traffic on all the routes at frequent to enable its staff to change its routing in order to by pass failure and congestion.

• The ability to change routing table in exchanges permit direct routing whereby the preferred choices of routes are changed from time to time.

ROUTING PLAN• The function of tandem exchange is to interconnect those central

offices (local exchanges) within multi-exchange area having low traffic volume . Tandem exchange also provide alternate routes for different exchanges.

• To calculate whether a direct route is cheaper than tandem route , the cost ratio is defined as :

CR =

Cost of provision of direct circuits between two centers.

cost of provision of tandem connection between two centers

• Routing via tandem switch is always more economic if the cost is less than or equal to 1.

ROUTING PLAN

AUTOMATIC ALTERNATE ROUTING (AAR)• In alternate routing , connection should use direct route

(referred to as high usage route) , because direct route provides better transmission quality and use fewer network facilities .

• The use of AAR allows exchanges to avoid congestion and also to avoid link failure within the network.

• The use of this technique improves performance of the network , this not only cover operational cost but also the loss of revenue and consequences of not meeting service obligations to the customers (financial damages).

ROUTING PLAN• If all the direct trunks are busy calls are routed via

tandem exchanges or alternate routes maintain suitably low blocking probability. Thus the networks are designed to allocate a limited number of trunks in the direct route and provide alternate route for overflow.

• If high usage route consist of N trunks and offered traffic is A erlangs , the probability of all trunk busy is given by B formula .

ROUTING PLAN• The traffic carried on high usage AH route is :

AH = A (1-B) (N,A) erlangs The overflow traffic is :

AO = AB (N,A) erlangs • Erlang B formula is good representation of traffic on high

usage route ,because blocked calls are diverted to alternate route and does not reappear.

• The characteristic of traffic of high usage route is shown in fig 9.4. This figure shows that traffic offered to high usage route . The traffic carried by high usage routes are shown in fig 9.4 (b) and depicts that the traffic carried is equal traffic offered , if it is less than or equal to number of high usage trunks. If offered traffic is greater than number of high usage route , over flow occurs as shown in fig 9.4 ( c)

ROUTING PLAN• Fig 9.4 (b) shows that if traffic A(t) is offered to high usage group

of N trunks. The traffic carried is A(t) when A(t) ≤ N and is N when A(t) ≥ N .

• As shown in figure 9.4( c ) , the traffic which overflows to the final route is zero when A(t)≤ N and is A(t) –N when A(t)≥ N .

• If connection is required between exchange A and Exchange B and all circuits to the direct route A to B are busy , then exchange A attempts to route the call via exchange C .

• If there are free circuits from A to C . The attempt will be unsuccessful if there is congestion on route C to B . Exchange C signals this information back to A . On receipt of message exchange A releases the connection A to C and make new attempt , say over A to D to B.

ROUTING PLAN