CHAP 1(GOS)

Introduction to Switching Systems Grade of Service (GoS): In telephone field busy hour traffic is used for planning purpose. Grade of service is measure of congestion , expressed as the probability that a call will be blocked or delayed. When dealing with GoS in traffic engineering , the clear understanding understanding of blocking criteria , delay criteria and congestion are essential. Blocking Criteria: If the design of system is based on the fraction of calls blocked (the blocking probability) then the system is said to be engineered on blocking basis. Blocking can occur when all devices are occupied , when demand of service is initiated.

•

•

•

•

The world's largest digital library

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.







Introduction to Switching Systems •

•

•

Blocking criteria are often used for dimensioning dimensioning of switching networks and interoffice trunk groups. Delay Criteria: If system is designed on the basis of fraction of calls delayed longer than the specified length of time , the system is said to be waiting system. Delay criteria is used in telephone system for dimensioning of registers. In waiting system a GoS objective could be either the percentage of calls which are delayed or percentage which are delayed more than certain length of time. Congestion :







Introduction to Switching Systems Measure of GoS: •

•

i.

GoS is expressed as a probability. The GoS 2%(o.o2) means that 98% calls will be connected and only 2% calls will be lost. The GoS is quoted as P.02 or P02 to represent a network busy probability of 0.02. GoS is applied to the terminal to terminal connections. For For th thee s stem stem con conne nect ctio ion n man man swit switch chin in ce cent nter erss th thee system is broken into following components: An int inter erna nall call call (ca (calli lling ng sub subsc scri ribe berr to swi switc tchi hing ng off office ice))

ii. An outg outgoin oing g call call to to trun trunk k netw network ork (sw (switc itchin hing g offic officee to







Introduction to Switching Systems Fundamentals For The Design Of Telecom Network: Network: •

•

•

The traffic analysis is the fundamental request for the design of cost effective and efficient configuration of networks. The effectiveness of a network can be evaluated in term of how much traffic it carries under normal or average load and how often the traffic volume exceeds the capacity of network. Fundamental problem in design of telecom network concerns the dimensioning of a route. Traffic: In telecom system , traffic is defined as the occupancy of a







Introduction to Switching Systems In a day 60 minute interval in which traffic is highest is called busy hour (BH).

•

Average Occupancy: If the number of calls to and from a terminal during a period of T seconds is n and average holding time is h second , the average occupancy is given by:

•

A =

•

nh T

The average occupancy is also referred to as traffic flow







Introduction to Switching Systems Centralized Switching System: •

Distributed Method: A simplest way of structuring the telecom switching is the terminal to terminal connection connection . This kind of switching is called distributed switching switching and applied to small telecom systems .

•

1.5, shows full interconnection of five terminals . Each terminal have two type of switches , one to make required link and other to connect to receive a call. . For N terminals the number of links are 1/2N (N-1).









Introduction to Switching Systems T2







Introduction to Switching Systems







Introduction to Switching Systems Centralized Model : The distributed system can not be extended to large terminal cases and the increased geographical separation of the terminals . A simple centralized system , which reduces the average

•

•







Introduction to Switching Systems Hierarchical System : •

Central offices may be interconnected interconnected by direct trunk groups or by intermediate office known as tandem ,toll or gateway office. The process of centralizing switching switching centers can occur at several levels leading to the







T1

Exch.































CHAP 1(GOS)

Recommend Documents