MGT 302 Exam 2

design of service blueprint flowhart

- each activity that makes up a typical service encounter is mapped into the flowchart - there are levels: top level consists of activities that are under control of the customer - second: those activities preformed by the service manager in handling the customer third level: the repair activities preformed in the garage lowest: the internal accounting activity

2 viewpoints when observing arrivals at service facility

1) analyze the time b/w successive arrivals - any statistical distribution? usually we can assume time b/w arrivals is exponentially distributed 2) set some time length (T) and try to determine how many arrivals might enter system w/i T. we assume number of arrivals per time unit is Poisson distributed

inventory costs that must be considered when making any decision that affects inventory size (4)

1) holding (or carrying) costs - cost of storing / handling it in facilities where breakage can occur and u need to buy big space. it can depreciate, u r paying taxes 2) setup (or production change) costs 3) ordering costs 4) shortage costs *establishing the correct quan to order from vendors involves search for the min total cost resulting from the combined effects of 4 individual costs: holding costs, setup costs, ordering costs, and shortage costs

2 categories of contact

1) pure virtual customer contact (companies such as ebay and second life enable customers to interact w one another in an open enviro 2) mixed virtual and actual customer contact (customers interact with one another in a server moderated enviro such as product discussion groups, youtube, wiki)- operations mang challenge is to keep the tech functioning and up to date and to provide a policing function through monitoring the encounters that take place

all firms keep a supply of inventory for the following reasons (purpose of inventory): (6)

1) to maintain indepdence from operations 2) to meet variation in product demand 3) to allow flexibility in production schdling 4) to provide a safeguard for variation in raw material delivery time 5) to take adv of economic purchase order size 6) many other domain specific reasons overall: - inventory is costly and large amounts are undesirable. long cycle times are caused by large amounts of inventory and that is undesirable (detail pg 356)

purpose of inventory analysis, whether in manufacturing, distribution, retail, or services is to specify 1) and 2) ??

1) when items should be ordered 2) how large the order should be

2 basic inv decisions that need to be made

1) when should an item be ordered 2) how large should the order be

3 models used with upper echelon inventories in a make-to-stock enviro (retail store inventories, warehouse inventories)

1. The single-period model - Used hen making a one time purchase of an item. Ex: purchasing t-shirts to sell at a one time sporting event 2. Fixed-order quantity model - Used when we want to maintain an item "in stock" and when we resupply the item, a certain # of units must be ordered each time. - Inventory for item is monitored until gets to a level where risk of stocking out is great enough we are compelled to order more 3. Fixed-time period model - Similar to ^ . Used when item should be in stock and ready to use - Rather than monitoring inventory level and ordering more when level gets down to a critical quantity, the item is ordered at certain intervals of time ie every friday - Convenient for groups of items ordered together ie dif types of bread to a grocery store - rather than delivering the 10 dif types at dif times, more efficient to deliver all 10 at same time on same schd

2 types of multiperiod inventory systems

1. fixed-order quantity model (economic order quantity, EOQ, Q-model) 2. fixed-time period models (periodic system, periodic review system, fixed-order interval sustem, P-model)

5 main inv costs relevant to models

1. the cost of the item itself 2. the cost to hold an item in inv 3. setup costs 4. order costs 5. costs incurred when an item runs short

mixed (line structure)

2 categories under this: 1) multiple-to-single channel structures, 2) alternative path structures. 1 ex: lanes that merge into one for single phase service ie bridge crossing where 2 lanes merge into one. or there can be lines that merge into one for multiphase service such as subassembly lines feeling into a main line 2 ex: think diagram of 9 boxes and can switch from one to another randomly

solutions for tasks that have longer task times than the workstation cycle time required to meet a certain output

Split the task Share the task Use parallel workstations Use a more skilled worker Work overtime Redesign

For our purposes, think of a process and define inventory as

WIP(work in process) = throughput rate * flow rate • WIP = # of units

Every service has a service package: what are the 5 features?

a bundle of goods and services that is provided in some enviro. 1) supporting facility - physical resources that must be in place before service can be offered (golf course, ski lift, airline) 2) facilitating goods: material purchased or consumed by the buyer or the items provided to the customer (golf clubs, skis) 3) Information: operations data or info that is provided to customer to enable efficient / customized services (tee-off time, seat preferences, medical records) 4)explicit services: benefits readily observable by the sense and that consist of the essential or intrinsic features of the service (response time of ambulance, air conditioning in hotel room) 5) Implicit services: psychological benefits that the customer may sense only vaguely, or the extrinsic features of the service (worry-free auto repair, status of a degree from an Ivy, privacy of a loan office)

high and low degree of customer contact

a concept that relates to the physical presence of the customer in the system - service systems with high degree are more difficult to control than more difficult to rationalize than those with a low degree - in high the customer can affect the time of demand, exact nature of service, and quality or perceived quality of service bc the customer is more involved in the process - in high there can be a lot of diversity of customer influence and system variability

product-process matrix

a framework depicting when the dif production process types are typically used, depending on prod volume and how standardized the prod is (see graph in google docs)

inventory turn

a measure of the expected number of times inv is replaced over a year

days of supply

a measure of the number of days of supply of an item (inverse of inventory turn scaled to days) ex: if a firms inventory turn is 6 times per year, a days supply is one-sixth times per year --> 1/6 * 365 = 60.8 days

exponential distribution

a probability distribution associated w the time b/w arrivals - when arrivals at a service facility occur in a random way, a plot of the interarrival times yields an exponential dist.

queuing system waiting line (or queuing) systems 3 parts:

a process where customers wait in line for service 3 major components: 1) the source population and the way customers arrive at the system 2) the servicing system 3) the condition of the customer exiting the system

make-to-order environment

a prod enviro where the product is built directly from raw materials and components in response to a specific order - make customers prod from raw materials (decoupling point closer to where product is being made) (ex: boeings process for making commercial aircraft) emphasis: not on inventory, rather managing the capacity of critical resources (such as engineering and construction crews)

assemble-to-order environment

a production enviro where pre-assembled components, subassemblies, and modules are put together in response to a specific custom order (exs: dell desktop computers) - firm that combines a number of pre-assembled modules to meet a customer specifications (decoupling point closer to where product is being made) - primary task: define a customers order IN TERMS OF alternative components and options SINCE it is these components and options that are carried in inventory needs for success: engineering design that enables flexibility in combining components/ options/ modules into finished products - apply principle of lean manufact. to decrease time required to assemble finished goods --> by doing so delivering customers orders so quickly they appear as if they are a make to stock firm from perspective of customer

make-to-stock environment

a production enviro where the customer is served "on-demand from finished goods inventory (exs: TVS, clothes, packaged food products) - firm is serving customers from finished good inventory (decoupling point closer to finished good being delivered) issues seen: balancing the level of finished inventory against the level of service to the customer (having a lot of inventory is costly and hard to store etc) - more inventory = more cost. --> trade-off b/w the costs of the inventory and the level of customer service must be made --> can be improved by better estimates or knowledge of customer demand, rapid transportation alternatives, speedier production, more flexible manufacturing - invest in lean manufac. FOCUS: proving finished goods where and when the customers want

number of components vs finished goods (adv of assemble to order vs make to stock)

advantage of the assemble to order over the make to stock: moving decoupling point from finished goods to components the number of finished products = way more than the number of components that are combined to produce the finished product there are xxxxxxx number of components possible to make x item (think comp ex), --> if all combinations of these xxxxxx components are valid, they can be combined into a total of XXXXXXXXX dif final configurations Ni = # of alterntatives for component i. n = total # of combinations of components (given all are viable) formula: total number of combinations = N1 X N2 X N3..... X Nn IN SUMMARY: it is much easier to manage and forecast the demand for xxxx number of components than XXXXXXXX dif final configurations

assumptions to know with waiting line model formulas

all models we assume are steady-state formulas derived on assumption that the process under study is ongoing. thus, they provide inaccurate results when applied to processes where the arrival rates and/or service rates change over time

fixed-time period model aka P-model

an inventory control model that specified inventory is ordered at the end of a predetermined time period. the interval of time b/w orders is fixed and the order quantity varies TIME TRIGGERED - limited to placing orders at the end of a predetermined time period, only the passage of time triggers the model - counting takes place at a review period - larger avg inv bc it must also protect against stock outs during the review period, T

fixed-order quantity model aka Q-model

an inventory control model where the amount requisitioned is fixed and the actual ordering is triggered by inventory dropping to a specified level of inventory EVENT TRIGGERED - initiated order when the event of reaching a specified reorder level occurs - places an order when the remaining inv drops to predetermined order point, R. - the inv remaining must be continually monitored - every time withdrawal or addition to/from inv is made, records must be updated to reflect whether reorder point has been reached - no review period - model is favored for more expensive items bc avg inv is lower - better for items of importance such as critical repair parts bc there is closer monitoring and quicker response to potential stock outs - requires more time to maintain bc every additional or withdrawal is logged

reorder point

an order is placed when the inv position drops to this level. re order point is set to cover the expected demand during the lead time, plus a safety stock determined by the desired service level

single period inventory model problem

answers the question of how much to order when an item is purchased only one time and it is expected that is will be used and then not reordered ex: deciding how many daily newspapers to put in a stand. only can sell that one day and if you print more than they purchase its a loss, and if you dont print enough its a loss of profit associated with sales. ex: selling tshirts for championship bball game, airline flights

assembly line

area where an item is produced through fixed sequence of workstations, designed to achieve a specific production rate (ex toys and cars) items used in high volume - bottom right of product process matrix = high product volume, high standardized commodity product [not one of a kind]

managing inventory is not only about mathematics, it is also an ___

art

inventory turn

better measure in evaluating the performance of a process than the total avg value of inventory an efficiency measure where the cost of goods sold is divided by the total avg value of inventory - this makes it easier to compare across similar firms (YOU WANT TO TURN INVENTORY MORE TIMES PER YEAR THAN A DIF MANUFACTURER)

model 2

constant service system single channel layout single service phase infinite source pop poisson arrival pattern constant service pattern unlimited permissible queue length ex: roller coaster rides in amusement park dif b/w 1: multiple options - deciding which ride to ride or which equip to purchase out of a choice of 3

most inv control systems are too big that it is not practical to model and give thurough treatment to each item. in these cases, it is useful to ?

ctegorize items according to their yearly dollar value -- ABC categorization

going from model 1 to model 2 waiting lines?

cut in half bc service is changing from expoential to constant and have another line system metrics also shorter

ways to lower inv

decrease lead (substaintially lower SS needed) lowering variability -> level production schds decrease set up cost lower servce level

manufacturing cell

dedicated area where a group of similar prods are produced. cells dedicated/designed to perform specific processes on a limited range of prods - typically schd to produce only as requested in response to current customer demand - middle huge cell in product process matrix = medium product volume, medium standardized commodity product

ABC inventory classification

divides inv into dollar volume categories that map into strategies appropriate for the category 3 groupings: 1. high dollars volume (A) - roughly top 15% of the items and represent 80% of yearly dollar value 2. moderate dollar volume (B) - roughly top 35% of the items and represent 15% of yearly dollar value 3. low dollar volume (C) - roughly top 50% of the items and represent 5% of yearly dollar value generally the smaller # of items account for large dollar vol and large # of items account for small dollar vol. both cases can be more imp than the other.

take care of your _____ and they will take care of you back - ? loyal ____ are assets not liabilities. they are your most valuable resource

employees - branson employees

according to bawany should put who first and who second?

employees first and customers second

multiperiod inv models are designed to

ensure an item will be available on an ongoing basis throughout the year

probability approach to safety stock

ex: "set the safety stock level so that there will be only 5% chance of stocking out if demand exceeds 300 units" - considers only the prob of running out of stock, not how many units we are short

fixed order quan models attempt to determined the specific point, ___, at which an order will be placed and the size of that order, ____. The order point, ____, is always a specified number of units. An order size of, ____, is placed when the inv available reaches point ____

fixed order quan models attempt to determined the specific point, R, at which an order will be placed and the size of that order, Q. The order point, R, is always a specified number of units. An order size of, Q, is placed when the inv available reaches point R

2 line layouts that are better for helping each other, efficiency, and possibly more output

flexible and U-shaped line layouts

just as is the case w manuf process design, the standard tool for service process design is a ?

flowchart

project layout

for large/massive products. They are produced in specific location, labor, material, and equipment are moved to the product rather than vise versa. the product (by virtue of its big weight or bulk) remains in a fixed location and manuf equip is moved to the product exs: construction sites (houses, bridges), movie shooting lots areas on site designated for various purposes - most top left of product process matrix = low product volume, low (one of a kind) product standardization

retail sites carry inventory for what purposes?

immediate sale to customer

in distribution, inventory is classified as _____ meaning that it is being moved in the system.

in-transit

independent demand vs dependent demand

ind: the demands for various items are unrelated to each other (demand for a car) dept: the need for any one item is a direct result of the need for some other item, usually an item of which is it part (wheels / tires for the car)

characteristics of service processes: a service is the output of a process that is _____ services ____ patented services can be classified according to ? --> in some processes the customer need not be ? for ex when a customer order s processed from an online transaction. but sometimes in other processes the customer is directly involved. for ex when a tooth is removed at dentist office how do service systems differ from manufact systems the service-system design matrix explores? virtual services offered through the internet often enable?

intangible cannot the degree of "contact" or physical presence of the customer in the system need not be present at all service systems differ from manufact systems in that typically services cannot be placed in inventory for later use. the process is the product. explores the trade-offs b/w sales opportunity, efficiency, and charactertitics of the workers in service processes enable customers to interact directly w one another in an open or moderated enviro

Factors to consider with waiting lines:

line length, number of lines, queue discipline

what is a manufacturing process

manufacturing processes are used to make tangible items. at a high level, these processes can be divided into 3 steps (1. sourcing the parts needed. 2. making the item. 3. sending the item to the customer) to allow parts of the process to operate independently, inventory is strategically positioned in the process at places called decoupling points. positioning the decoupling points has an impact on how fast a customer can be served, the flexibility the firm has in responding to specific customer requests, and many other trade-offs

littles law

mathematically relates inventory, throughput, and flow time. A relationship between units produced and time. littles law says there is a long term relationship b/w the inventory, throughput, and flow time of a production system in steady rate the relationship is (inventory=throughput rate X flow time) - you can change around these things to get the other components if given 2 - this makes it helpful to diagnose a plants performance

simplified way to think about material in a process is the 2 states it is in:

matieral in a process is in one of two states: 1) state where the material is moving or "in-transit" (ie the material is b/w the vendor and the raw material inventory at the manufacturer) 2) material is sitting in inventory and acting as a "buffer" waiting to be used until needed (allows dif entities in the process to operate independently

model 3

multichannel system multi-channel, single line layout single service phase infinite source pop poisson arrival pattern exponnential service pattern unlimited permissible queue length ex: parts counter in auto agency dif: multi-channels (multiple clerks at bank or checkout lines at store)

exiting the queue system

once a customer is served, two exit fates: 1) customer may return to source pop and immediately become a competing candidate for service again. 2) may be low prob of reservice

multichannel, single phase (line structure)

only one thing happens, but there is several lines to do it in (ex: checking out at a store or grocery, there is multiple lines to do the same thing) prob: uneven service time given to each customer results in unequal speed or flow among the lines which results in people being served in their line before people in others who got there first.

Poisson distribution

probability distribution for the number of arrivals during each time period - where one is interested in the number of arrivals during some time period, T. Distribution obtained by finding the prob of exactly n arrivals during T. if the arrival process is random, the dist is the Poisson - poisson is discrete dist (curve becomes smoother as your test size becomes larger)

poke yokes "avoid mistakes"

procedures that prevent mistakes from becoming defects basic blueprinting describes the features of the service design but does not provide any direct guidance on how to make the process conform to that design --.> apply poke yokes - common in factories and consist of things such as fixtures to ensure parts can attach only in the right way, switches that automatically turn off equip after certain period of time or if a mistake was made etc - also applied to fail-safing actions of the customer as well: height bars at amusement parks etc

continuous process

process that converts raw materials into finished product in one contiguous flow - similar to assembly line in that the production follows a predetermined sequence of steps, but the flow is continuous such as with liquids rather than discrete - such structures usually highly automated and in one integrated machine that can operate 24/7 (ex: undifferentiated materials such as petroleum, chemicals, drugs) - most bottom right of product process matrix = high product volume, high standardized commodity product [not one of a kind]

workcenter (ie job shop)

process w great flexibility to produce a variety of products, typically at lower volume levels - similar equip or functions grouped together. a [art being worked on travels according to the sequence of operations from workcenter to workcenter where proper machines located for each operation - top left of product process matrix = low product volume, low (one of a kind) product standardization

5 basic structures of formats facilities are arranged

project, workcenter, manufacturing cell, assembly line, continuous flow

inventory records usually differ from the actual physical count; inventory accuracy refers to how well the 2 agree another way to ensure accuracy is to count inventory freq and match this against records - this is a method called?

question is how much error is acceptable. accuracy levels often recomended is .2+- for A 1+- for B and 5+- for C cycle counting. a physical inventory taking technique is counted on a freq basis rather than one or twice a year. useful method for schdling the audit of each item carried in inv. compaires audit inv at least yearly to ensure accuracy of records

bc finished goods inventory is more expensive than raw materials inventory, there is a trade off b/w?

quicker response to customer demand comes at the expense of greater inventory investment

manufacturing inventory

refers to items that contribute to or become part of a firms product output classified into raw materials, finished prods, component parts, supplies and work in processes

Customer contact: Extent of contact:

refers to the physical presence of the customer in the system the percentage of time the customer must be in the system relative to the total time it takes to perform the customer service (the greater the percentage of contact time b/w the service system and the customer

dif between a fixed order quan model where demand is known and one where demand is uncertain is in computing the ? the uncertainty element is taken into account in the ? R without safety stock is?

reorder point. the order quantity is the same in both cases, the uncertainty element is taken into account in the safety stock R without safety stock is simply the average demand during the lead time

EXs of types of make to stock enviro supply chain inventories

retail store inventory, warehouse inventory (single period, fixed order quantitity, fixed time period) also, manufac plant inventory, raw materials (material requirments planning)

service system design matrix

see notes on google doc - production efficiency decreases as the customer has more contact (influence) on the system - however, to off set this, it provides high sales opp to sell more products - low contact allows system to work more efficiently bc customer is unable to affect/disrupt system - however, little opp for additional prod sales

suggestions for managing queues based on research

segment the customers - if a group needs something that can be done very quickly give them a special line so they dont have to wait for the slower ones. (12 items or less etc) train your servers to be friendly - this can help if in long line inform your customers of what to expect - esp imp if waiting line longer tha norm try to divert attn when waiting - providing music, video etc encourage customers to come during slack periods

in services, the flowchart is called _____ which is (photo ex in google docs)

service blueprint: a flowchart of a process emphasizing what is visible to the customer - flowchart of a process emphasizing what is visible and not visible to customer unique feature: the distinction made b/w the high customer contact aspects of the service (parts of process customer sees) and those activities that the customer does not see with a line of visibility on the flowchart

multichannel, multi phase (line structure)

similar to multichannel, single phase but there are 2 or more services to be preformed in sequence. (ex: admission of patients in a hospital - many things to go through to get them admitted and several people are there to do that [channels])

model 1

simple system single channel layout single service phase infinite source pop poisson arrival pattern exponential service pattern unlimited permissible queue length ex: drive in teller at bank, one lane toll bridge

single channel, single phase (line structure)

simplest type of waiting line structure. ex: one person barber shop. there is a single phase you go through, just one task to be done with one person

single channel, multiphase phase (line structure)

single channel, but more than one phase to go through in that channel. ex: car wash (vacuum, then wash, then dry by this is a one line single channel process just multiple steps) -fairly uniform sequence - problem: build up between each service --> multiphase / separate washing lines

Track relay handoffs

splitting tasks exs

safety stock

the amount of inv carried in addition to the expected demand to provide protection against stock outs

inventory position

the amount on hand plus on order, minus backordered quantities. in the case where inv has been allocated for special purposes the inv position is reduced by these allocated amounts

how to design and analyze an assembly line: the assembly line design is centered on defining: ...... aka called? the workstations need to be defined so that?

the assembly line design is centered on defining the work content of workstations that are typically spaced along the line called ASSEMBLY LINE BALANCING the workstations need to be defined so that efficiency is maximized while meeting max cycle times and precedence constraints

throughput rate

the average rate (e.g. units/day) that items flow through a process • units completed per time period when using the process map, assuming the process is operating at a steady state, the throughput rate of the process is = to the avg demand and there is not excess or a shortage being produced

production process mapping is

the drawing of a diagram that depicts the material flow and inventory in a process

if safety stock is positive ? greater the safety stock, ___ the order is placed

the effect is to place a reorder sooner. greater the safety stock, sooner the order is placed

(single period) the optimal stocking level, using marginal analysis, occurs at the point when

the expected benefits derived from carrying the next unit are less than the expected costs for that unit

arrival rate constant arrival distribution variable arrival distributions

the expected number of customers that arrive each period (such as the avg of 1 every 6 minutes) constant arrival distribution is periodic, with exactly the same time b/w successive arrivals (usually just those controlled by a machine) much more common.

engineer-to-order environment

the firm works w the customer to design the product, which is then made from purchases material, parts and components (decoupling point closer to where materials are sourced) (ex: lockheed martin's satellite division) emphasis: not on inventory, rather managing the capacity of critical resources (such as engineering and construction crews)

line structures

the flow of items to be serviced can go through single line, multiple lines, mix of the two etc

queuing theory is and assumes what

the mathematical analysis of the waiting line assumes customers arrive according to a poisson arrival distribution and are served according to an exponential service time distribution

explain how manufacturing processes are organized: manufacturing layouts are designed based on? trade-offs are depicted in the ____ matrix? this depicts what? _____ analysis is useful for understanding the cost trade-offs b/w alternative equip choices

the nature of the product, the volume needed to meet demand, and the cost of equipment product-process matrix. this depicts the type of layout relative to product volume and relative standardization of the product. break-even analysis

service rate

the number of customers a server can handle during a given time period

assembly line balancing

the prob of assigning tasks to a series of workstations so that the required cycle time is met and idle time is minimized

Closer the decoupling point is to the customer, ___?

the quicker the customer can be served If inventory very close to customer very short lead time.

Precedence relationship

the required order in which tasks must be performed in an assembly line. These relationships are what complicates the problem seen in the assembly line balancing problem

inventory define inventory system

the stock of any item or resource used in an org the set of policies and controls that monitor levels of inventory and determine what levels should be maintained, when stock should be replenished, and how large orders should be

in services, inventory generally refers to?

the tangible goods to be sold and the supplies necessary to administer the service

workstation cycle time (Takt time)

the time between successive units coming off the end of an assembly time - aka the time a prod passes through an assembly line workstation in uniform intervals

flow time

the time it takes one unit to completely flow through a process start to finish Time period must be the same (doesn't really matter which you use as long as consistent; ex: hour, shift, day, week, ...)

lead time

the time needed to respond to a customer order (amount of time from when you place order to when you have the product) (the time it takes to deign then build that custom airplane from a custom request) Key to cutting down lead time: strategically placing decoupling points - closer to customer. Decoupling times (where inventory builds up).

total average value of inventory

the total investment in inventory at the firm [the sum of the value/cost], of all the raw materials, work-in-processes (material that is in a manifct processes in a factory), and finished goods - not useful for evaluating the performance of a process

Optimal order quantity (Qopt)

this order size minimized total annual inv related costs unrealistic assumptions but a starting point: - demand is constant/uniform throughout period - lead time (time from ordering to receipt) is constant - price per unit is constant - inv holding costs is based on avg inv - ordering/set up costs constant - all demands for prod are satisfied, no backorders

dif between poisson and exponential

time between arrivals = exponentially distributed number of arrivals per specific period of time = poisson distributed

lean manufacturing

to achieve high customer service w minimum levels of inventory investment (focus on this in make to stock environment, applied in assemble to order also)

T/F: waiting lines are not a fixed condition

true. they can be controlled with system management and design (placing fast servers in high demand times, opening up fast food lines etc)

fixed order quan model formula this model assumes ?

use TC formula to find total annual cost, then the second step is to find the order quantity (Q / Qopt) at which the total cost is minimum. the total cost is mim at the point where the slope of the curve is zero. - find this point with bottom form on sheat constant demand and lead time, neither saety stock nor stock out cost is necessary and the reorder point, R, is simple R=dL

Queuing systems consists primarily of (2)

waiting lines and the available number of servers

(single period) expected marginal cost equation states that

we should continue to increase the size of the order, as long as the prob of selling what we order is equal to or less than the ratio on other side of eq

customer order decoupling point

where inventory is strategically positioned in the supply chain to allow processes on the supply chain to work independently

customer arrivals: infinite pops vs finite pops

whether the pop is finite or infinite effects a lot with the formulas of customer arrivals. finite: small pop. when a customer leaves its position as a member of the pop, the size of group is reduced by one, which reduced the probability of the next occurence. and when a customer is serviced and returns to the pop, the pop increases and probability of a user requiring service also increases bc there is more in the pop (think 6 machines being repaired) infinte: large pop. large enough pop that adding or subtracting 1 or 2 from it does not significantly affect the system probabilities. nor would the formulas for infinite queuing problems cause much error