# Bandwidth Guarantee
A network management feature that ensures a minimum amount of bandwidth is always available to a specific application, user, or traffic class. It prevents network congestion from degrading the performance of critical services by reserving a portion of the total available bandwidth for their exclusive use.
**Pronunciation:** /ˈbændˌwɪdθ ˌɡærənˈtiː/
**Difficulty:** Intermediate
**Synonyms:** Bandwidth Reservation, Guaranteed Rate, Committed Information Rate (CIR)
**Categories:** Network Management, Quality of Service
**Tags:** Networking, QoS, Traffic Shaping, Bandwidth Management, Performance
Canonical: https://scaleengineer.com/glossaries/bandwidth-guarantee
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## Definitions

- **In Network Quality of Service (QoS):** In the context of Quality of Service (QoS), a **Bandwidth Guarantee** is a policy that reserves a minimum amount of network capacity for a specific traffic flow, application, or user. This reserved capacity is often referred to as the **Committed Information Rate (CIR)**.

The primary goal is to provide predictable performance for critical or delay-sensitive applications. For example, a video conferencing stream requires a consistent amount of bandwidth to avoid freezing or pixelation. A **Bandwidth Guarantee** ensures that even if other users start large downloads, the video stream's performance is not affected.

**How it works:**
* **Classification:** Network traffic is first identified and classified based on criteria like application type (e.g., VoIP, HTTP), source/destination IP address, or port number.
* **Queuing:** Classified traffic is placed into different queues. High-priority queues, which have a **Bandwidth Guarantee**, are serviced before lower-priority queues.
* **Scheduling:** A scheduling algorithm (like Weighted Fair Queuing) ensures that the high-priority queue gets its guaranteed share of the bandwidth.

It's important to note that a **Bandwidth Guarantee** is a *minimum*. If the network is not congested, the application may be able to use more bandwidth than its guaranteed amount, a concept often called "bursting." This differs from bandwidth limiting or rate limiting, which sets a *maximum* data rate. The concept of **Bandwidth Reservation** is central to this process.

## Etymology

The term combines "Bandwidth," referring to the data transfer rate of a network, and "Guarantee," meaning a formal promise or assurance. It literally means a promise of a certain data transfer rate.

## First used

Late 1980s

## Historical context

The concept of **Bandwidth Guarantee** emerged alongside the development of Quality of Service (QoS) mechanisms in computer networking, primarily during the late 1980s and early 1990s.

Early networks, like those based on the original Ethernet standards, treated all traffic equally. As networks began to carry more diverse types of traffic, including real-time voice and video alongside data, the need for traffic prioritization became apparent.

Technologies like Asynchronous Transfer Mode (ATM) in the early 1990s were among the first to offer sophisticated QoS features, including the ability to reserve bandwidth for specific connections. Later, protocols like Integrated Services (IntServ) with its Resource Reservation Protocol (RSVP) and Differentiated Services (DiffServ) were developed for IP networks to provide similar capabilities. DiffServ, in particular, became the more scalable and widely adopted approach, allowing network administrators to classify traffic and apply policies, including setting a **Committed Information Rate (CIR)**, which is a form of **Bandwidth Reservation**.

## Q&A

- **What is the primary purpose of a Bandwidth Guarantee in a network?:** The primary purpose is to ensure that critical applications or services receive a consistent and predictable level of network performance, even during periods of high network congestion. By reserving a minimum amount of bandwidth, it prevents less important traffic from consuming all available resources and degrading the performance of essential services like VoIP, video conferencing, or critical business applications. This is a core concept of **Bandwidth Reservation**.

## Usage examples

- To ensure our VoIP calls remain clear and jitter-free, the network administrator configured a **Bandwidth Guarantee** for all voice traffic.
- The service level agreement (SLA) includes a **Bandwidth Guarantee** of 100 Mbps, ensuring our cloud backups have a **Guaranteed Rate** even during peak business hours.
- For our video conferencing system, we set a **Committed Information Rate (CIR)**, which acts as a **Bandwidth Guarantee** to prevent lag and dropped frames.

## Related terms

- Quality of Service (QoS)
- Traffic Shaping
- Latency
- Jitter
- Packet Loss

## Popular related terms

- Quality of Service (QoS)
- Traffic Shaping
- Latency
- Jitter