# AWS RTB Fabric Glossary
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## Application
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A customer-built software system that connects to RTB Fabric [gateways](#gateway-definition) to send or receive real-time bidding requests. Applications are external to RTB Fabric and can be [requester applications](#requester-definition) that send bid requests or [responder applications](#responder-definition) that receive and process bid requests. Applications connect to RTB Fabric through gateways, which handle the routing and processing of requests between applications.

## Availability Zone (AZ)
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Distinct locations within an AWS Region that are engineered to be isolated from failures in other AZs.

## Customer
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User of the service. Includes [Demand-Side Platforms (DSPs)](#dsp-definition) and [Supply-Side Platforms (SSPs)](#ssp-definition).

## Demand-Side Platform (DSP)
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An adtech system that allows advertisers to buy ad inventory from multiple ad exchanges through one interface. Also known as a buyer. The service helps DSPs to participate effectively in real-time bidding auctions with a high-performance, low-latency infrastructure.

## Flow
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Part of a [link](#link-definition) configuration that defines how RTB requests are processed. Created with the `UpdateLinkModuleFlow`. Flows can include [RTB modules](#module-definition) configured for specific behaviors such as additional filtering and enrichment actions. Default flows are created with links, but you can update a flow with additional modules.

## Gateway
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RTB Fabric infrastructure components that serve as connection points for customer [applications](#application-definition). *Requester gateways* receive requests from requester applications and forward them through [links](#link-definition) to responder gateways. *Responder gateways* receive requests from requester gateways and forward them to responder applications, then return responses through the same pathway.

## Link
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The core component of RTB Fabric that establishes secure, bidirectional communication channels between [gateways](#gateway-definition). Links provide authenticated communication, traffic routing and load balancing, performance monitoring, and security controls. Links can include processing logic through [modules](#module-definition).

## Requester
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A customer [application](#application-definition) that sends bid requests to RTB Fabric through a requester [gateway](#gateway-definition).

## Resources
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[Gateways](#gateway-definition), [links](#link-definition), [flows](#flow-definition), and [RTB modules](#module-definition) that comprise the RTB Fabric infrastructure. Customer [applications](#application-definition) are external to RTB Fabric and connect to these infrastructure resources.

## Responder
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A customer [application](#application-definition) that receives bid requests from RTB Fabric through a responder [gateway](#gateway-definition) and returns bid responses.

## RTB module
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A component that performs specific operations on RTB requests, such as filtering or enrichment. RTB modules can be configured by [Supply-Side Platforms (SSPs)](#ssp-definition) or [Demand-Side Platforms (DSPs)](#dsp-definition) in their [flows](#flow-definition), although they are not required to configure a flow. RTB Fabric provides built-in modules (QPS rate limiter, OpenRTB filter, error masker) available at no additional charge. Modules are configured using the `UpdateLinkModuleFlow` API operation.

## Supply-Side Platform (SSP)
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An adtech system that helps publishers manage and sell their ad inventory through programmatic auctions to [Demand-Side Platforms (DSPs)](#dsp-definition) and advertising agencies. Also known as a seller. The service helps SSPs with very low latency requirements process high volumes of real-time bid requests and responses.

## Virtual private cloud (VPC)
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A logically isolated network in the AWS Cloud. This virtual network resembles a traditional network that you'd operate in your own data center, with the benefits of using the scalable infrastructure of AWS. For more information, see [Amazon Virtual Private Cloud (Amazon VPC).](http://aws.amazon.com/vpc/)