# Calculating file name with field calculator

Is it possible to calculate the file name in an attribute table?

My shapefile has a name like "cities.shp". In this shapefile I want to have a attribute "cities").

Sorry for that stupid question! I did find an very easy way to do what I aked in this thread. Just use the QGis processing tool and the SAGA "merge vector layers" tool. The merged shape file has a column (called "Layer") filled with the shape file names.

You can copy the following script to your QGIS (Processing Toolbox > Scripts > Tools > Create new script). This script takes shapefiles from one folder, uses the Field Calculator algorithm to add the filename as an attribute (with Null values but you can edit this to another expression) and outputs the shapefiles into another folder:

##Test=name import os import glob from os.path import expanduser home = expanduser("~") # Change to match your folder path for shapefiles path_dir = home + "DesktopTest" path_res = path_dir + "Results" def run(): # Set directory and search for all shapefiles then run algorithm os.chdir(path_dir + "Shapefiles") for fname in glob.glob("*.shp"): processing.runalg("qgis:fieldcalculator", fname, fname, 2, 99, 0, True, 'NULL' , path_res + "/"+ fname) # Paths of the shapefiles in the Result folder with list comprehension output = [shp for shp in glob.glob(path_res + "*.shp")] run()

There are ways to write attributes to existing shapefiles but I don't have that knowledge yet. Hope this helps!

From your comment I would assume that you just want to add a new field?

Open the attribute table of the file, start an edit session, and then use this button:

In your case you would have to opt for Text:

## Magnetic field in two conducting parallel plates. (stripline) [closed]

Want to improve this question? Update the question so it's on-topic for Physics Stack Exchange.

Studying Poynting Vector power density I found a geometry that I really can't figure it out and is nowhere to be found on the internet.

I have two conducting parallel plates with opposite surface current density but they are joined to be a ring. How would I go about getting its magnetic field? or inductance, I'm trying to later calculate the total magnetic energy but can't see how to set the Maxwell equations in differential or integral forms for getting the magnetic field

Io is given and it assumes $h ll b-a$ $hll a$ $hll b$

the total magnetic energy is:

I tried using boundary conditions, I think the field must be on the $z$ direction, but I think I need to make some assumptions about the dimensions to solve it and can't figure out what it is.

## SB 1383 Organics Capacity Calculator

SB 1383 requires California counties and each city, regional agency, and special district that provides solid waste collection services within each county, to plan for adequate capacity for recycling organic waste. CalRecycle is providing this optional calculator to assist jurisdictions with this organics recycling planning requirement.

This guidance tool was developed by CalRecycle as a courtesy for informational and example purposes only. Use of this tool is optional and is not a regulatory requirement. In the event of any conflict with this guidance tool or information herein, applicable statutory and regulatory provisions shall control. This tool and information herein are based on known facts and legal authority as understood by CalRecycle at the time of release. Any analysis, guidance, or other information herein may be subject to change based on changed facts or legal authority, actual or understood, subsequent to the time of this communication. The provision of this guidance tool and any analysis, guidance, or other information herein shall not be construed as a waiver of any rights or remedies available to CalRecycle. Recipients of this communication are encouraged to seek the assistance of legal counsel to comply with applicable state law based on their pertinent facts and circumstances. CalRecycle makes no representation that use of this tool will ensure compliance with regulatory requirements. The user assumes all risk and CalRecycle accepts no responsibility or liability to any person because of the use of, or reliance upon, this tool or the information herein.

Each county is responsible for leading this collaborative effort among all cities, regional agencies, and special districts that provide solid waste collection services within the county.

Each jurisdiction is responsible for:

• Estimating the amount of all organic waste in tons that will be disposed by organic waste generators.
• For capacity planning purposes, organic waste includes food scraps, landscape and pruning waste, wood, paper products, digestate, and biosolids. Each type of organic material included in the 2014 organic waste disposal baseline and Statewide Waste Characterization Studies (WCS) is included in the calculator below, except for carpet and textiles.
• “Verifiably available” means that each jurisdiction can demonstrate the available capacity through a contract, franchise agreement, or other documentation of existing, new, or expanded capacity at a facility, activity, operation, or property that recovers organic waste. A facility permit alone is not an indication of the amount of capacity available to a jurisdiction and, therefore, does not satisfy this requirement.

Each county is responsible for:

• Collecting organic waste recycling capacity information from each of the jurisdictions.
• Identifying any jurisdiction, which includes the county, that does not have enough organic waste recycling capacity.
• Submitting an organic waste recycling capacity report to CalRecycle according to the following schedule:
• August 1, 2022: For the period January 1, 2022 - December 31, 2024.
• August 1, 2024: For the period January 1, 2025 - December 31, 2034.
• August 1, 2029: For the period January 1, 2030 - December 31, 2039.
• August 1, 2024: For the period January 1, 2035 - December 31, 2044.

Instructions

Please note that the calculator contains ToolTips ( ) with definitions, user input instructions, and additional guidance about the origin of predefined or calculated data. Select the ToolTip and a small graphic will appear with more information.

Fields in each step that require an entry to calculate data in related steps are noted with a red asterisk (*).

Please note that this calculator does not save any of the data that are entered. To save a record of your data please use the "export to excel" button located at the bottom of the calculator after completion.

This webpage has an “idle timer," that is set for 120 minutes, during which the webpage caches temporary data. After this initial 120 minute period, any further period of inactivity exceeding 15 minutes (e.g. not making any changes to records in Step E, or Step F, or Step G during the additional 15 minute timeframe) may result in a loss of all data entries and/or an inconsistent Excel export. Therefore, after this webpage has been open for 120 minutes, users may experience some issues in displaying or exporting data, if not continuously updating information within every 15 minutes, and may choose to refresh the webpage prior to the start of data entry to maximize the initial timeframe available.

## 3 Tariff Browser

### 3.1 Tariff Browsing

The following operation types can be carried out on the screen Browse tariff :

• Browse nomenclature tree
• Display duty rates and other measures

The way the criteria are entered is described in Display criteria.

#### 3.1.1 Browse nomenclature tree

The goods nomenclature is built as a hierarchically structured tree. After the button Browse nomenclature tree has been pressed, the Tariff Browser displays the Nomenclature tree screen with the section list. From that list, after clicking the section number, it is possible to go to the chapter list (two-digit code), then accordingly to the heading list (four-digit code), the sub-heading list (six-digit code), the combined nomenclature – CN list (eight-digit code), and the TARIC nomenclature list (ten-digit code), which is on the lowest tree level.

To all chapters two links are added: Legal Notes and ExplanatoryNotes . The first link allows user to go to legal notes of the chapter, and the second to explanatory notes of the chapter. This doesn't mean that each chapter has legal and explanatory notes attached. In fact, only certain chapters actually have such attachments. The links indicate however, that Legal Notes and ExplanatoryNotes can be attached to any chapter.

The layouts of the screens on chapter and position levels are related. The only difference is that only notes can be attached to positions.

Sometimes footnotes and BTI links are assigned to codes on given levels. Clicking on the BTI link redirects user to the BTI EU System.

Instead of scrolling the tree step by step, one can go directly to the searched code through entering the code into the Goods nomenclature code field and clicking the button Browse nomenclature tree . The browser displays the searched code in the context of adjacent codes.

From the Tariff tree screen it is possible go directly to the Duty rates screen. This is possible through clicking the nomenclature code on the lowest level, that is, the code which has no hierarchically lower codes. From that code one can go to the measures which are assigned to it.

Note: Entering a criterion in the additional information field when browsing nomenclature tree has no influence on the course of operation.

#### 3.1.2 Display duty rates and other measures

The measures are duty rates, taxes (VAT and excise tax), and non-tariff restrictions which are assigned to nomenclature codes.

The measures are always displayed for a particular nomenclature code. After the code has been entered the Tariff Browser displays all measures assigned to that code, for all the origin/destination countries. If, besides the code, also the origin/destination country criteria have been entered, the result will concern only those measures which are assigned simultaneously to the selected nomenclature code and origin/destination country.

Note: Entering the additional information as criterion has no influence on the course of measure display operation.

After the criterion (criteria) has been entered and the operation initialized, the browser displays the Duty Rates screen, where the information is presented in following order: the goods code with the goods description, measurement unit, restrictions concerning import and/or export of goods (with relevant footnotes, legal acts, and additional codes), and duty rates for particular countries or for a specific country (with relevant footnotes, legal acts, and additional codes as well).

Clicking the footnote code, legal act and additional code button opens the screen with detailed information. On the screen presenting the additional code description text sometimes the link to the footnote text of this code is displayed.

Some rates include a link to so-called agricultural component (Meursing code). After clicking that link (“Composition of goods Meursing code”) the Meursing calculator screen is displayed where, after entering used values, it is possible to calculate an additional duty for certain agricultural commodities.

Sometimes applicability of a measure or the amount of duty rate depends on the certain conditions. In such a case the link Conditions is displayed below the measure. After clicking that link the screen presenting the information regarding conditions is displayed.

If the measure is assigned to the country group, it happens that some countries from that group are excluded from the application of the measure – then beside the country group code the abbreviation excl. is displayed with link(s) to excluded country (countries) id.

Duty rates are displayed in the alphabetical order according to the geographical areas to which they are assigned, but in the beginning measures assigned to all the countries ( Erga Omnes ) are always displayed.

By clicking the code of the country or country group one will receive the related information on the Geographical areas screen.

There is also displayed a list of links which represent the Nomenclature Groups connected with current nomenclature code or code above in hierarchy. User can click on those links and can see the group description and its start date.

The additional information covers: Legal Notes, Explanatory Notes, Binding Tariff Information, Lists of Goods, Classification Regulations, Explanatory Notes for CN, Classification Rulings of European Commission, Adjudications of European Court of Justice, Pronouncements of Customs Code Committee, Compendium of Classification Opinions and Decisions of Harmonised Code Comittee.

The display of additional information is carried out by displaying all information (within one of the mentioned above areas) which is assigned to the nomenclature code entered as a criterion. When, for example, code 0101 00 00 00 has been entered and additional information area "Legal notes" selected, the browser displays all legal notes assigned to the code 0101 00 00 00. Only the additional information valid for the entered validity date is displayed. If for example user inserted in the nomenclature code field Chapter “5002” and selects Explanatory notes in the additional information and clicks the button “Search additional information” then system displays a link “Uwaga do pozycji 5002 ” and if user clicks on that link system displays the content of explanatory notes of chapter 5002.

Independent from whether one or more information is assigned to the entered code, the found information is displayed in the beginning as a list of identifiers. After clicking the proper identifier the complete additional information is displayed in the Tariff Browser.

When no additional information is assigned to the entered code, the browser displays the message “No search results”.

##### Display criteria for Browse Tariff
###### Country of origin/destination (only for measures)

For each country, the line contains the country code and the country name.

Beside the country, also the goods nomenclature code indicating the commodity must be entered. If no code has been entered, the browser displays no measures.

If no code has been entered, the browser displays the message “Goods nomenclature code cannot be empty”.

### 3.2 Text search

The text search is searching for additional information with nomenclature codes descriptions added, according to text expression. When, for example, the word "saltpeter" has been entered and additional information area "Legal Notes" selected, the Tariff Browser displays all legal notes containing the word "saltpeter". Only the additional information valid for the set reference validity date is searched.

Independent from whether one or more occurrence of the entered expression is found in the selected search area, the found information is displayed in the beginning as a list of identifiers. After clicking the proper identifier the complete additional information with the occurrences of the entered expression highlighted is displayed in the browser.

#### 3.2.1 Textual search tips

On the Text expression screen the searched word or other search pattern (a fragment of a word, sentence, eventually with special signs or operators) should be entered.

To search for a tariff information based upon a fragment of a word, the star wildcard character ( * ) should be used. For example, when searching for "pac*", all information containing "pac_" such as "packs", "packings", packages" etc. is obtained.

Several text expressions can be entered as well. To get the information containing all expressions, the expressions should be connected by AND operator. To get information containing at least one expression, the expressions should be connected by OR operator.

The browser does not distinguish different sizes of letters. The same results will be obtained after entering “Meat”, “MEAT”or “meat”.

The text expression is a word or part of the word. For example: “meat”, “beef meat”, “fresh beef meat”, etc.

If there is need to search in all areas one should select “All” in additional information drop down list. As a result of search there will be presented a list of all available areas with number of matches in each. Every item of this list is a link to search in particular area.

More precise ways of searching are described in the examples below.

#### 3.2.2 Search examples

When using text search, special operators, which define the range of searched expressions, can be used. The following list presents examples of possible operators to be used. The examples concern nomenclature code descriptions in English. The main purpose of the list is to present the principles of search, so it may happen, that due to modifications of the Master Tariff the real search results will look a bit different.

Example: when searching for "live AND animals", the results are: “LIVE ANIMALS”, "Live bovine animals" and "Other live animals".

Example: when searching for "potatoes OR meat", the results contain word "potatoes" or "meat" or both of them.

Note: when using AND in combination with OR:
The AND operator takes precedence to the OR operator. However, this precedence can be altered by putting parentheses. When searching for "meat OR fruits AND fresh", the results are all expressions containing word "meat" and all containing both words "fruits" and "fresh". When searching for "(meat OR fruits)" AND fresh" the results are all descriptions containing the word "fresh" and at least one of the words "meat" or "fruits".

Example: When searching for “pack*”, the results include "packs", "packings", packer", "packed" etc. next to "packages".

Example: when searching for “processe?” the results include "processes" and "processed".

Example: When searching for “\$live”, the results include "Liver" and "living" next to "live".

operator expands search to include all expressions spelling in a way similar to the searched for expression. It may only appear at the end of a word.

Example: When searching for “packs

”, the results include "backs", "parkas", "parks" and "padlocks" next to "packs".

#### 3.2.3 Search criteria for text search

The text expression is a text or its fragment. After the text expression has been entered, the Tariff Browser finds it within the selected additional information category. The default search area is Nomenclature Codes Descriptions.

Information, within the entered expression is searched for. Additional information covers: Nomenclature Codes Descriptions, Legal Notes, Explanatory Notes, REG, INF ( do zmiany ).

After the expression and the selected area have been entered, the browser displays additional information containing entered expression. When in the selected area there is no expression entered as a criterion, the browser displays an adequate message.

### 3.3 Correlation Table

Changes can be performed to TARIC Nomenclature codes (10 –Digit codes). Correlation table is a tool that helps traders to find out which of the nomenclature codes are affected by those changes.

This process concerns Importing or Exporting of good

The Correlation type shows the type of the displayed results (New commodity codes / Expired codes). After the code has been entered, the Tariff Browser displays the new commodity codes with the expired codes and the start date of replacement and in other case systems shows the expired commodity codes the codes which replace them and the start date of replacement.

This is the goods nomenclature code. After the code has been entered, the Tariff Browser finds goods nomenclature if it is expired or if it is replaced another code.

This is the start date for the correlation table search.

This is the end date for the correlation table search.

### 3.4 Geographical area search

Searching for the geographical area consists of searching for the country or country group.

The country is searched for by entering the ISO country code (for example, “PL”). The obtained result includes, beside the ISO country code and the country name, also the codes of all the country groups, to which the searched country belongs.

The country group is searched for by entering the code of this group (for example, „1011”). The obtained result includes the list of all the countries which belong to this group. Besides, at each country the list of all the groups to which the country belongs is presented.

### 3.4.1 Search criteria for geographical area

This is the country code given by the International Standard Organization (ISO) under the number 3166-2 Alpha code. After the code has been entered, the Tariff Browser finds the country name, codes of country groups to which the country belongs.

This is the name of the country. After the name has been entered, the Tariff Browser finds the ISO country code, codes of country groups to which the country belongs.

This is the code of the country group to which two or more countries belong. After the code has been entered, the Tariff Browser finds the ISO country codes, country names.

### 3.5 Preliminary information

Information covers information contained in the first volume of Master Tariff. The Tariff Browser displays the complete information, for a previously set reference validity date.

### 3.6 Preliminary Information HS

Information covers information contained in the first volume of Master Tariff. The Tariff Browser displays the complete information, for a previously set reference validity date.

### 3.7 Certificates

Certificate identifies licences, certificates and similar documents required to be produced for import/export declarations. Certificates are not integrated as separate measure types, but as conditions of the various measure types, for example surveillance, preferences etc. Here user can search and view details of certificates.

This is the code of the certificate. After the code has been entered, the Tariff Browser finds the certificate together with its description.

This is the description of the certificate. After the description has been entered, the Tariff Browser finds the certificate together with its code.

Additional code is used optionally for creation of measures.

This is the additional code. After the code has been entered, the Tariff Browser finds the code with its description.

This is the description of the additional code. After the description has been entered, the Tariff Browser finds the additional code.

### 3.9 Quota search

This function allows to search and view Quotas defined in system. One can search quotas by quota number, country code, critical status and status.

After search, on the screen will be presented a list of found quotas. To view full information about particular quota one should use “Details” link placed on the right side of screen.

#### 3.9.1 Browse quota

The quota number that identifies the quota.

The critical state indicator provides information that the quota is in the critical state i.e. the quota has reached the quota critical threshold and it is close to being exhausted.

The geographical area of origin the quota applies for. The quota can be associated with the geographical area or group of countries. In the latter case it is applicable to all the geographical areas that belong to the group of countries in the quota validity period. As a search criterion a geographical area can be specified.

Status displays the status of quota. If quota is e.g. open, blocked, unblocked etc.

Detailed information related to status, balance, associated nomenclature codes and associated subquotas

This function allows users who intend to load into their own IT systems and databases the Tariff data maintained by Tariff system. The XML extractions include collections of hierarchical Tariff objects, the links between different Tariff objects and reference attributes that allows unambiguous identification of the object in the XML extractions. The extracted data includes all EU-TARIC and National Tariff objects.

The user must acknowledge the rights of the customs authority and then he can download the .zip file.

### 3.11 Goods Index Alphabetical

The purpose of the Alphabetical Commodity Index (AIT) is to support the classification of goods. The Alphabetical Commodity Index contains the names of goods which are not included in the goods nomenclature and are therefore often classified as "others", or have trade names which are different from those in the Goods Nomenclature.

The user must enter a text phrase to which he wants to search for a link to the nomenclature code.

## How to Capture and Categorize Expense Receipt in QuickBooks Online?

Let us now discuss capturing the expense receipt image through your mobile device in QuickBooks Online through a step-wise step process:

### Capturing the Expense Receipt in QuickBooks Online

First of all, you should ensure that the QuickBooks Online mobile app is already installed on your iOS or Android device. After that, you can follow the below simple steps for capturing the receipt in QuickBooks Online:

Step 1. At first, open the QuickBooks Online mobile app and click on the menu icon.

Step 2. Now you need to click on the Receipt snap button.

Step 3. Once you have clicked on the receipt snap button, click on the receipt camera icon and click the picture of your expense receipt.

Step 4. After that, click on ‘Use this photo’ and then click on Done. Now, the QuickBooks will start a transaction on the basis of the captured receipt, you will have to categorize it later.

Now since we have already entered our expense receipt in QuickBooks Online with the help of capturing expense receipt process, a transaction has already been started by the QuickBooks on the basis of the captured receipt, let us now see how to categorize the expense receipt in QuickBooks Online:

### Categorizing the Expense Receipts in QuickBooks Online

Once you have entered the expense receipt in QBO, you need to review, edit and categorize them. You can follow the below-sequenced steps to accomplish this:

Step 1. First of all, open QBO and go to the Banking or Transactions menu.

Step 2. Now you need to go to the receipt tab and choose the expense receipt to view its further details.

Step 3. In case the Action column against the expense receipt reflects the ‘review’ status, choose the expense receipt to make corrections if any and add missing info (if any).

Step 4. Now for categorizing the receipt, you will see there’s match status reflecting in Action column, which tells us that QuickBooks has recognized a transaction that matches the expense receipt.

Step 5. In that case, you should review the linked record and if you are satisfied that it is correct, you need to click on match to connect the expense receipt with the transaction.

Step 6. If in case, you don’t think that there is a matching transaction against the expense receipt, you can create an entirely new one by going to the Expense menu> Expense tab and then clicking on a ‘New’ transaction and then expense again.

Step 7. Once you have created a new expense, attach the receipt image to it.

## SB 1383 Organics Capacity Calculator

SB 1383 requires California counties and each city, regional agency, and special district that provides solid waste collection services within each county, to plan for adequate capacity for recycling organic waste. CalRecycle is providing this optional calculator to assist jurisdictions with this organics recycling planning requirement.

This guidance tool was developed by CalRecycle as a courtesy for informational and example purposes only. Use of this tool is optional and is not a regulatory requirement. In the event of any conflict with this guidance tool or information herein, applicable statutory and regulatory provisions shall control. This tool and information herein are based on known facts and legal authority as understood by CalRecycle at the time of release. Any analysis, guidance, or other information herein may be subject to change based on changed facts or legal authority, actual or understood, subsequent to the time of this communication. The provision of this guidance tool and any analysis, guidance, or other information herein shall not be construed as a waiver of any rights or remedies available to CalRecycle. Recipients of this communication are encouraged to seek the assistance of legal counsel to comply with applicable state law based on their pertinent facts and circumstances. CalRecycle makes no representation that use of this tool will ensure compliance with regulatory requirements. The user assumes all risk and CalRecycle accepts no responsibility or liability to any person because of the use of, or reliance upon, this tool or the information herein.

Each county is responsible for leading this collaborative effort among all cities, regional agencies, and special districts that provide solid waste collection services within the county.

Each jurisdiction is responsible for:

• Estimating the amount of all organic waste in tons that will be disposed by organic waste generators.
• For capacity planning purposes, organic waste includes food scraps, landscape and pruning waste, wood, paper products, digestate, and biosolids. Each type of organic material included in the 2014 organic waste disposal baseline and Statewide Waste Characterization Studies (WCS) is included in the calculator below, except for carpet and textiles.
• “Verifiably available” means that each jurisdiction can demonstrate the available capacity through a contract, franchise agreement, or other documentation of existing, new, or expanded capacity at a facility, activity, operation, or property that recovers organic waste. A facility permit alone is not an indication of the amount of capacity available to a jurisdiction and, therefore, does not satisfy this requirement.

Each county is responsible for:

• Collecting organic waste recycling capacity information from each of the jurisdictions.
• Identifying any jurisdiction, which includes the county, that does not have enough organic waste recycling capacity.
• Submitting an organic waste recycling capacity report to CalRecycle according to the following schedule:
• August 1, 2022: For the period January 1, 2022 - December 31, 2024.
• August 1, 2024: For the period January 1, 2025 - December 31, 2034.
• August 1, 2029: For the period January 1, 2030 - December 31, 2039.
• August 1, 2024: For the period January 1, 2035 - December 31, 2044.

Instructions

Please note that the calculator contains ToolTips ( ) with definitions, user input instructions, and additional guidance about the origin of predefined or calculated data. Select the ToolTip and a small graphic will appear with more information.

Fields in each step that require an entry to calculate data in related steps are noted with a red asterisk (*).

Please note that this calculator does not save any of the data that are entered. To save a record of your data please use the "export to excel" button located at the bottom of the calculator after completion.

This webpage has an “idle timer," that is set for 120 minutes, during which the webpage caches temporary data. After this initial 120 minute period, any further period of inactivity exceeding 15 minutes (e.g. not making any changes to records in Step E, or Step F, or Step G during the additional 15 minute timeframe) may result in a loss of all data entries and/or an inconsistent Excel export. Therefore, after this webpage has been open for 120 minutes, users may experience some issues in displaying or exporting data, if not continuously updating information within every 15 minutes, and may choose to refresh the webpage prior to the start of data entry to maximize the initial timeframe available.

## How to calculate network bandwidth requirements

Bandwidth requirements vary from one network to another, and how to calculate bandwidth properly is vital to building and maintaining a fast, functional network.

### What went wrong, and what we learned

As most network administrators can attest, bandwidth is one of the more important factors in the design and maintenance of a functional LAN or WAN. Unlike a server, which can be configured and reconfigured throughout the life of the network, bandwidth is one of those elements of network design that is usually optimized by figuring out the correct bandwidth formula for your network from the outset.

Wondering how to calculate bandwidth requirements when designing the network? What specific considerations apply? These are some of the questions we’ll answer in this tip.

### Understanding bandwidth

Bandwidth refers to the data rate that is supported by the network connection or the interfaces that connect to the network. It represents both volume and time, representing the amount of data that can be transmitted between two points in a set period of time. It is usually expressed in terms of bits per second (bps), or sometimes in bytes per second (Bps).

Network bandwidth represents the capacity of the network connection, though it’s important to understand the distinction between theoretical throughput and real-world results when figuring out the right bandwidth formula for your network. For example, a 1000BASE-T — which uses unshielded twisted-pair cables — Gigabit Ethernet (GbE) network can theoretically support 1,000 megabits per second (Mbps), but this level can never really be achieved in practice because of hardware and systems software overhead.

One point to consider when thinking about how to calculate bandwidth needs on your network is this: Bandwidth should not be confused with throughput, which refers to speed. While high-bandwidth networks are often fast, that is not always the case. A helpful metaphor when thinking about bandwidth is cars on a highway. A high-bandwidth network is like a six-lane highway that can fit hundreds of cars at any given moment. A low-bandwidth network is like a single-lane road in which one car queues directly behind another.

Although the large highway is likely to move vehicles faster, rush-hour traffic can easily bring cars and trucks to a standstill. Or, perhaps, the cars cannot get onto the highway quickly because it’s clogged with large delivery trucks that take up a lot of space on the road. Similarly, even a high-bandwidth network can run slowly in the face of problems, such as congestion and bandwidth-hungry applications.

These very points make calculating bandwidth requirements a challenge, yet the consequences of getting the bandwidth formula wrong are considerable. If you don’t procure enough bandwidth, you all but guarantee the network will run slowly. However, significantly overprovisioning bandwidth can be cost-prohibitive for most enterprises.

So, how do you determine the right formula that will meet your bandwidth requirements? The process begins with asking the right questions: What applications are users running, and what is the performance service-level agreement for these applications? I know some network managers who are only concerned with how many users are on a virtual LAN. What you really need to know is what the users will be doing on the network. It’s possible that 200 users will cause less of a bottleneck than a group of three users that really beats the heck out of the network because of some funky client-server application or extensive use of a bandwidth-heavy service, like high-definition video conferencing.

### Coming up a formula for how to calculate bandwidth

There are two basic steps to calculating bandwidth requirements:

1. Determine the amount of available network bandwidth.
2. Determine the average utilization required by the specific application.

Both of these figures should be expressed in bytes per second. Consider the following formula: A GbE network has 125,000,000 Bps of available bandwidth. This is computed by taking the amount of bits — in a Gigabit network, that would be 1 billion — and dividing that by eight to determine the bytes:

1,000,000,000 bps / 8 = 125,000,000 Bps.

After determining the network’s bandwidth, you’ll have to see how much bandwidth each application is using. Use a network analyzer to detect the number of bytes per second the application sends across the network. To do this, first enable the Cumulative Bytes column of your network analyzer. The next steps in the bandwidth formula are:

1. Capture traffic to and from a test workstation running the application.
2. In the decode summary window, mark the packets at the beginning of the file transfer.
3. Follow the timestamp down to one second later, and then look at the cumulative byte field.

If you determine that your application is transferring data at 200,000 Bps, then you have the information to perform the calculation: 125,000,000 Bps ÷ 200,000 = 625 concurrent users. In this case, the network will be fine even if there are several hundred concurrent users.

Look what would happen, though, if you had a 100 Mbps network: 13,102,000 Bps ÷ 200,000. You would then have a network that could not support more than approximately 60 users running the application concurrently. Knowing how to calculate bandwidth formula is, therefore, very important to network administrators.

A final recommendation: Capture the data in 10-second spurts and then do the division. It’s also a good idea to check multiple workstations to ensure the number is reflective of the general population. It’s also important to determine how many concurrent users you will have.