What are possible reasons for wireless network issues?

In a no-interference environment with perfect conditions (which I'm sure you don't have), Cisco LAP access points are spec'd for 25-50 users each for acceptable performance with a "well....you can do it" maximum of 100 users per AP. Other top tier brands are going to come in right around the same figure. SOHO equipment will be much less, usually about 10-15 connections before things start getting ugly.

It sounds to me like you just have highly congested access points. I'd consider adding more, and also doing what you can to push users to 5GHz to cut down on interference.

Edit: Just as an anecdote, I deployed 2 Cisco LAP1142s to the lecture rooms at $LastJob, because they were 90+ seat rooms. This was our standard lecture room spec. The coverage was not the issue at all, but the potential clients per AP was a deal breaker, causing me to throw almost $1500 per lecture room at it.

It's not just the number of APs you have, it's how they're distributed and how the clients are connected to them. Look to see if some are over-subscribed while others are idle. Look to see if there are issues with interference, etc. You may need to look at managed APs if these current ones are unmanaged. And of course if they are currently managed then much of what we're suggesting to you should be suggested already from the managment interface's reporting metrics.

Also, as to the connection itself - is that bandwidth guaranteed or is this essentially like the usual home or small business "best efforts" SLA? And what use is it being put to? 200 people all hammering the living snot out of youtube, facebook, skype and spotify all at once with a dozen other random websites open for each one is obviously not the same as 200 people checking your local news website and their webmail every hour or so.

"who is regularly experiencing issues with their internet connection"

Others have already looked at your wireless issues, but you specifically point out the internet connection, so is it the wifi or the internet connection?

Things to look at on the internet connection can include:

• Type of firewall (is it rated to handle that kind of throughput, number of sessions, etc.)
• firewall logs (session count, I/O, etc.)
• router logs (if applicable)
• What are they accessing? Are the servers/apps they need local or across the internet connection?
• What is "expected" by the client? Maybe 100/50 is awesome for some, but crap for this client.
• Are there bottlenecks limiting that bandwidth? Are you truly getting that kind of bandwidth at the client level (remember like others have said, if they are all sharing g radios they are probably not getting anywhere near that 100/50)
• Have you opened any support calls with Sonicwall or other hardware OEMs for troubleshooting?
• Have you done internal customer service such as interviewing end-users, isolating where the issue is (broad or narrow scope), ruling out factors and variables, etc.

Hope that helps.

In that environment (usually called high density) high interference is inevitable. To reduce it 5 Ghz mode should be preferred if your hardware supports that frequency. I also know that some top AP-s of Cisco and ArubaNetworks (3600 series and AP 130 respectively) theoretically could provide stable WiFi connection in such conditions, of course if deployed in right way.

But before you will know your hardware making some solutions is useless.