Added new FAQ entry

See work item https://fuselabs.visualstudio.com/BotFramework/_workitems/edit/43642

Author: Michael Miele

articles/bot-service-resources-bot-framework-faq.md

@@ -43,6 +43,8 @@ In case you don't find the answer you're looking for, you can post your question
 - [What are the rate limits?](bot-service-resources-faq-general.md#what-are-the-rate-limits)
 - [How will I know if I'm impacted by rate limiting?](bot-service-resources-faq-general.md#how-will-i-know-if-im-impacted-by-rate-limiting)
 - [How to implement human handoff?](bot-service-resources-faq-general.md#how-to-implement-human-handoff)
+- [What is the size limit of a file transferred using a channel?](bot-service-resources-faq-general.md#what-is-the-size-limit-of-a-file-transferred-using-channels)
+
 
 <!-- Retired, re: https://github.com/MicrosoftDocs/bot-docs/issues/1698
 - [What are some community-authored dialogs?](bot-service-resources-faq-general.md#what-are-some-community-authored-dialogs)

articles/bot-service-resources-faq-general.md

@@ -85,6 +85,12 @@ The Bot Framework service must protect itself and its customers against abusive
 
 We're continuously tuning the rate limits to make them as lenient as possible while at the same time protecting our service and our users. Because thresholds will occasionally change, we aren't publishing the numbers at this time.  Finally, if you are hosting your bot on an App Service, the bot is bound to the limitations of the App Service. For more information, see [SLA summary for Azure services](https://azure.microsoft.com/support/legal/sla/summary/) If you are impacted by rate limiting, feel free to reach out to us at [[email protected]](mailto://[email protected]).
 
+## What is the size limit of a file transferred using channels?
+
+A size limit of 262144 bytes exists when transferring a file, a PDF for example, using channels such as Direct Line and Facebook. The size cannot be increased. If the limit is exceeded the following error is issued: *The request content length exceeded limit of 262144 bytes*. The only alternative is to provide a secure URL (HTTPS) in the **ContentUrl** attribute and pointing to the file stored in a secure location.
+
+Notice that if you use the Bot Emulator to test your bot, you will not have the size limitation. If you use the Teams channel, the limitation appears to be greater than 262144 bytes. But the Teams channel can't handle PDF files but pictures with a format such as like PNG.
+
 ## How will I know if I'm impacted by rate limiting?
 
 It is unlikely you'll experience rate limiting, even at high volume. Most rate limiting would only occur due to bulk sending of activities (from a bot or from a client), extreme load testing, or a bug. When a request is throttled, an HTTP 429 (Too Many Requests) response is returned along with a Retry-After header indicating the amount of time (in seconds) to wait before retrying the request would succeed. You can collect this information by enabling analytics for your bot via Azure Application Insights. Or, you can add code in your bot to log messages.
@@ -97,7 +103,6 @@ Rate limiting is caused by any of the following conditions:
 * A client of a bot sends messages too frequently
 * Direct Line clients request a new Web Socket too frequently
 
-
 ## How to implement human handoff?
 
 At times it is necessary to transfer (handoff) a conversation from a bot to a human being. This happens for example if the bot does not understand the user, or if the request cannot be automated. In these cases, the bot provides a transition to humans.
@@ -139,3 +144,4 @@ In the case of channels that do not handle the handoff, the middleware is used t
 
     **Q2: Do we need to refer to this?**: [HandoffMiddleware.cs](https://github.com/microsoft/BotBuilder-Samples/blob/master/experimental/handoff-library/csharp_dotnetcore/samples/LivePersonAgentBot/Middleware/HandoffMiddleware.cs).
 >
+