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9/25/2011 1 CIRCUIT SWITCHING - TELETRAFFIC Routing
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CIRCUIT SWITCHING -TELETRAFFIC
Routing
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RoutingConcepts
A route is a path to particular destination
An exchanges determines the call destination by analyzing the called number and then selects an outgoing trunk in a route to destination
2 types of destination
A final destination (FDEST) is a call is the local exchange that serves the called party
An intermediate destination (IDEST) is an exchange where the call path enters another network, on its way to the destination
Digit analysis is the process that produces a FDEST and IDEST from called subscriber number (EC-LN), national number (AC-EC-LN), or international number (CC-AC-EC-LN)
RoutingConcepts
In LATA exchanges, calls with subscriber and national numbers can have IDEST or FDEST destination
Called with international called number always have an IDEST
In IC exchanges, all calls have IDEST destinations
In calls with national called number, IDEST is an exchange in the LATA network determined by combination of AC-EC
For calls with international called numbers, the IDEST depends on whether the IC exchange is an ISC exchange If the exchange is no an ISC, the call destination is an ISC in the IC
network determined by the country code (CC) in the number
At the ISC, the destination is an ISC in the country identified by CC
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Routing
Routing
Alternate routing is the procedure by which an exchange selects an outgoing trunk for a call when there are several routes to a destination
In this procedure, the order in which the routes are listed specifies the sequences in which an exchange checks the outgoing trunk groups for available trunks.
In alternate routing, the TG to destination are ordered:
The 1st choice route is the most direct one
The 2nd choice is the most direct one among the remain routes
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Routing
Automatic rerouting (crankback) is a refinement of alternate routing Automatic rerouting depends on ability of an exchange to
signal the preceding exchange that is not able to extend the setup
Traffic EngineeringObjectives
To determine relationship between 3 components What’s the quality of service experienced by a users in a
given system with the given traffic load
How the system has to be dimensioned in order to achieve a given QoS with given traffic
How big can the traffic load be without deteriorating the QoS
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Traffic EngineeringObjectives
Traffic theory describes the dependencies between different factors by means of mathematical models QoS
Offered traffic
The capacity of the system
The quantities considered are often stochastic Distribution of the number of connections in progress
Queue length distribution in a buffer
Traffic EngineeringSystem and Traffic Models
Model are needed both for system and the traffic offered to it
In the system model, the most central functionalities of the system are described by means of simple basic elements Servers
Queue
Traffic model describes behavior of the offered traffic Traffic process
Base on measurement
Aims at an economical, parsimonious description with as few parameters as possible
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Traffic EngineeringTraffic Models
Traffic EngineeringThe use of Traffic Theory
Design of networks and its elements
Dimensioning
Optimization
Performance evaluation
Control action
Efficient operation of the networks
Traffic control
Routing
Charging
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Traffic EngineeringConcepts
Dimensioning – determine the number of trunks required on a route or connection between exchanges Calling rate – the number of times a route or traffic path is
used per unit period, or more properly defined “ the call intensity per traffic path during the busy hours”
Holding time – the duration of occupancy of one or more paths per call, or sometimes “the average call duration of occupancy of one or more paths per call”
Traffic path – a channel, time slot, etc.
Carried traffic – the volume of traffic actually carried by a switch
Offered traffic – the volume of traffic offered to a switch
Traffic EngineeringConcepts
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Traffic EngineeringConcepts
Traffic EngineeringConcepts
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Traffic EngineeringConcepts
Traffic EngineeringConcepts
Preferred unit of traffic intensity is Erlang (Erl) erlang is dimensionless unit
One erlang represents a circuit occupied for 1 hour
Consider a group of circuits, traffic intensity in erlang is number of call-seconds per second or number of call-hours per hour
Example: a group of 10 circuits had a call intensity 5 erlangs 5 circuits is busy at the time of measurement
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Traffic EngineeringConcepts
Example In a local switch, the number of calls in an hour is 1800
The mean holding time of a call is 3 minutes
A = 1800 x 3 / 60 = 90 erlang
Traffic EngineeringConcepts
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Traffic EngineeringConcepts
Traffic EngineeringTraffic Modelling
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Traffic EngineeringTraffic Flow
Offered traffic, Ao
Traffic, which would be carried were there no constrain in the system
A theory concept
Carried traffic, Ac Traffic that is usually being carried
Blocked (lost) traffic, Al Difference between the offered and carried traffic
Traffic EngineeringConcepts
Lost call / blocked calls
Grade of service (GOS) or Quality of Service (QoS) Expresses probability of meeting blockage during the BH
Expressed by letter p
Defined as probability of blockage in term of erlang formula
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Traffic EngineeringConcepts
GOS depends on number of factors The distribution in time and duration of offered traffic
(random or periodic arrival, constant or exponential holding time)
Number of traffic sources (limited or infinite)
The availability of trunks in a group to traffic sources (full or restricted availability)
The manner in which lost calls are handled Lost call clear (LCL)
Lost call held (LCH)
Lost call delayed (LCD)
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Traffic EngineeringConcepts – Erlang B
Traffic EngineeringConcepts – Erlang B
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Traffic EngineeringConcepts – Erlang C
Traffic EngineeringConcepts – Erlang C
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Traffic EngineeringConcepts
Traffic EngineeringDimensioning
Efficiency
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Traffic EngineeringOverflow Traffic
The system consists of 2 parts Primary system: m1 servers
Secondary system: m2 servers
The arriving traffic is first offered to primary system
If all servers of the primary system are occupied, the call is directed to the secondary group The traffic directed from the primary group to the secondary
group is called overflow traffic
If all servers of the secondary group are also occupied, the arriving calls is blocked
Traffic EngineeringOverflow Traffic
Alternate Route
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Traffic EngineeringOverflow Traffic
Traffic EngineeringOverflow Traffic
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Traffic EngineeringBlocking of Overflow Traffic
Traffic EngineeringBlocking of Overflow Traffic
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Traffic EngineeringDimensioning – Overflow Traffic
