It was our regular client (an estate agent office) who was having problem with his business computers. There were 4 computers in total but internet connection was very unstable / intermittent. He tried to call the service provider but they were not helpful. They tested the line from their side and advised him that their line was OK and problem lied on his side. Our engineer went there the same day and conducted some line tests but everything seemed to be OK. The problem was the ethernet hub. Our engineer replaced the hub and the problem went away.