Why does manual installation of Red Hat Enterprise Linux 7.2 not letting select CDROM as Source of Installation probe?

Issue

• Why does manual installation of Red Hat Enterprise Linux 7.2 not letting select CDROM as Source of Installation probe?
• Can't see cdrom or /dev/sr0 in the options to be selected for Source of installation during installation of Red Hat Enterprise Linux 7.2.
• The anaconda.log shows messages as follows.

07:56:00,525 INFO anaconda: setting <pyanaconda.ui.gui.spokes.software.SoftwareSelectionSpoke object at 0x7f449a57fe10> status to: Downloading package metadata...
07:56:00,580 INFO anaconda: Thread Done: AnaPayloadThread (139932677220096)
07:56:00,630 INFO anaconda: setting <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0> status to: Downloading package metadata...
07:56:00,630 INFO anaconda: setting <pyanaconda.ui.gui.spokes.software.SoftwareSelectionSpoke object at 0x7f449a57fe10> status to: Downloading group metadata...
07:56:00,631 INFO anaconda: setting <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0> status to: Error downloading package metadata
07:56:00,643 INFO anaconda: spoke is ready: <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0>
07:56:00,643 INFO anaconda: setting <pyanaconda.ui.gui.spokes.software.SoftwareSelectionSpoke object at 0x7f449a57fe10> status to: Error downloading package metadata
08:00:43,043 DEBUG anaconda: Entered spoke: SourceSpoke
08:00:43,085 DEBUG anaconda: Setting up repos: []
08:01:20,706 INFO anaconda: Running Thread: AnaPayloadRestartThread (139932677220096)
08:01:20,707 DEBUG anaconda: Left spoke: SourceSpoke
08:01:20,708 INFO anaconda: Running Thread: AnaPayloadThread (139932668827392)
08:01:20,709 INFO anaconda: Thread Done: AnaPayloadRestartThread (139932677220096)
08:01:20,984 INFO anaconda: spoke is not ready: <pyanaconda.ui.gui.spokes.software.SoftwareSelectionSpoke object at 0x7f449a57fe10>
08:01:20,994 INFO anaconda: spoke is not ready: <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0>
08:01:20,995 INFO anaconda: setting <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0> status to: Setting up installation source...
08:01:21,776 INFO anaconda: Thread Done: AnaPayloadThread (139932668827392)
08:01:21,786 INFO anaconda: setting <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0> status to: Probing storage...
08:01:21,787 INFO anaconda: setting <pyanaconda.ui.gui.spokes.software.SoftwareSelectionSpoke object at 0x7f449a57fe10> status to: Downloading package metadata...
08:01:21,787 INFO anaconda: setting <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0> status to: Downloading package metadata...
08:01:21,788 INFO anaconda: setting <pyanaconda.ui.gui.spokes.software.SoftwareSelectionSpoke object at 0x7f449a57fe10> status to: Downloading group metadata...
08:01:21,788 INFO anaconda: setting <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0> status to: Error downloading package metadata
08:01:21,799 INFO anaconda: spoke is ready: <pyanaconda.ui.gui.spokes.source.SourceSpoke object at 0x7f449a57fbd0>
08:01:21,799 INFO anaconda: setting <pyanaconda.ui.gui.spokes.software.SoftwareSelectionSpoke object at 0x7f449a57fe10> status to: Error downloading package metadata