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What is Burstable Bandwidth?

Burstable refers to a type of bandwidth allocation that allows a network connection to exceed its committed rate for brief periods of time.

Burstable bandwidth is often used in situations where the amount of data being transmitted is highly variable, such as with web applications or online gaming. This type of bandwidth allocation is typically more expensive than fixed-rate plans, as it requires ISPs to have extra capacity available to handle sudden spikes in traffic.

It is worth noting that burstable bandwidth is not the same as unlimited bandwidth. Customers with burstable bandwidth are still subject to data caps and other limitations, and the amount of additional bandwidth they can use is typically limited to a certain percentage of their committed rate.

Dissecting Burstable

The term "burstable" originated in the telecommunications industry, specifically in the context of T-carrier and E-carrier digital circuits. Burstable was coined to describe a type of bandwidth allocation that allowed a circuit to exceed its fixed rate for short periods of time, typically to accommodate bursts of data traffic that exceeded the normal usage patterns of the circuit.

Burstable bandwidth was invented to address the limitations of fixed bandwidth allocations, which resulted in lost packets and degraded performance when network traffic exceeded connection capacity. Burstable bandwidth provides a flexible and scalable solution for handling variable network traffic, especially for web applications, by allowing users to temporarily exceed their committed rate when additional capacity is available during a burst.

The duration of bursts in burstable bandwidth can vary widely depending on the specific application and network conditions. The duration of a burst is typically determined by the amount of data that needs to be transmitted and the available bandwidth at the time of the burst.

The interval between bursts can also affect the duration of bursts. If the interval between bursts is short, users may be able to sustain high bandwidth transmissions for longer periods of time, but this may also increase the risk of network congestion or other issues.

How Burstable Bandwidth is Used

Burstable bandwidth allocates two types of bandwidth to users - committed and burstable bandwidth. Committed bandwidth is a guaranteed amount of bandwidth that is always available to the user. The user's connection is limited to this committed rate under normal usage patterns.

On the other hand, burstable bandwidth is an additional amount of bandwidth that can be used when available. When the user's network connection has extra capacity available, such as during a lull in traffic, the user can temporarily exceed the committed rate and use the burstable bandwidth. The amount of additional bandwidth a user can use during a burst is typically limited to a certain percentage of their committed rate.

Additionally, the amount of committed and burstable bandwidth allocated to each user may vary based on their service plan or subscription level. The ISP may also define a burst size, which represents the maximum amount of data that can be transmitted during a burst. Here’s the typical process for ISPs when activating burstable bandwidth for users:

Step 1: Bandwidth Allocation

The ISP allocates a certain amount of bandwidth to the user, typically divided into a committed rate and a burstable rate. ISPs offer users a percentage of the committed bandwidth as burstable bandwidth. 

Step 2: Traffic Monitoring

The ISP monitors the user's network traffic to determine when burstable bandwidth can be used. This typically involves using specialized equipment, such as routers or switches, that are capable of tracking and analyzing network traffic in real-time.

Step 3: Burst Mode Activation

When the user's network traffic exceeds their committed rate, the ISP may activate burst mode, which allows the user to temporarily use additional burstable bandwidth.

When a user's network traffic exceeds their burstable rate or if they exceed their burst size limit, the traffic monitoring equipment may apply traffic shaping or other QoS techniques to limit or delay the traffic.

Components of Burstable Bandwidth

Burstable bandwidth is made up of several components, each of which plays a critical role in determining how the bandwidth is allocated to users.

Committed Rate

The committed rate is the minimum amount of bandwidth that the user is entitled to, regardless of the amount of traffic on the network.

The average committed rate for internet connections can vary widely depending on the type of connection and the specific service plan. For residential internet connections, the average committed rate typically ranges from 25 Mbps to 500 Mbps, with higher speeds available in some areas. For business internet connections, the average committed rate may be even higher, ranging from 100 Mbps to 10 Gbps or more, depending on the specific needs of the business.

Burstable Rate

The burstable rate shows how much extra bandwidth is available for the user to access when the network has extra capacity. The specific percentage of burstable bandwidth that is offered can vary depending on the ISP and the user's subscription plan. ISPs may offer different percentages based on factors such as network capacity, overall usage patterns, and the type of internet connection being used.

Burst Size

The burst size is a key parameter in burstable bandwidth allocation, and it determines the maximum amount of data that can be transmitted during a burst. To compute the burst size, a formula is typically used that takes into account the user's committed rate and the interval between bursts. The burst size is calculated as follows:

burst = (rate [bps]) * 0.00025 [sec/interval]) or (maximum packet size [bits]), whichever is greater.

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