You kind of have to see this on a monitor to appreciate it. We have run the Capture File Viewer program (which comes with each version of VCS) twice (two instances of it) and we're looking at subsequent frames in the opening part of a dial-up Async PPP session. The link is negotiating Line Control Protocol options. The frame on the left is number 6, an LCP Configure Request from the DTE. In the Frame View on the right we've selected frame 7 of the same captured session; this is a Configure Ack from the DCE. The ISP we're dialing has accepted the set of LCP options we requested.

It's not always this clear-cut. Often you'll encounter situations among the myriad Internet protocols where things fail. The objective of this use of VCS is to be able to see just about any aspect of captured data in as much detail as you like.

Consider, for a moment, that the PPP connection just "died." Why did it die? You have several options with VCS. Here are a few:

• Print all or selected frames from a capture file. You will find an amazing array of print options; you can print things pretty much the way you prefer. For instance, you could just print the Decode panes, or you could print the decodes and the binary content of the frame. The possibilities are vast.
• Use VCS to view one frame and Capture File Viewer to look at a separate one...or a different view of the same frame.
• Without a multi-instance license you can only run a single instance of VCS, but as many instances of Capture File Viewer as you wish. In multi-link PPP, for example, packets may not appear in the "intended" order due to the whims of multi-link connections. This means you could arrange to see (to continue our simple example of the LCP option negotiation phase of a PPP session) Configure Request 3 and the reply to it, a Configure Ack, Reject, etc. from the other end.
• If you can imagine it, it can probably be done with the VCS suite of software.