User`s guide

Functional Overview
MS-4900, Rev. A 5–7
PAD Mode and
PVC Sessions
PAD mode ports output original news stories directly. For PVC sessions, the output
is straightforward: for any PVC session (of which only one is deliverable to any
PAD logical receiver), incoming stories are delivered to the logical receiver in proper
sequence from the head end, and the IDR V1000 delivers those stories exactly as
received.
PAD Mode and
TVC Sessions
For TVC sessions, however, multiple sessions can be delivered at the same time to
any given logical receiver. Since different TVC sessions contain different news
stories, displaying those stories in the order received would cause separate stories to
run together. Instead, to ensure that a TVC news story is delivered intact and that
news stories do not blend together, the IDR V1000 in PAD mode acts in a special
way: While any particular story of a logical receiver is being output, other stories
accumulate in the IDR V1000 buffer. At the same time each particular news story is
fully output, one next story is selected for continued output. The buffer of the IDR
V1000 is well utilized in these cases: if a story currently being output is quite slowly
delivered across the network multiple stories can fully accumulate, to completion, in
the buffer. This “accumulating” usually causes no trouble, because the buffer is
large.
Node Mode
The IDR V1000 does not need to buffer news stories in Node mode operation as it
does in PAD mode.
Node mode output is repacketized. The data originally received from the data
provider at the head end is output in specially formed “extract” packets (a protocol
proprietary to WavePhore Networks). Special “extracting” software running in the
output computer extracts the news stories from these Node mode packets. Each
“extract” packet is output in the order received and contains session identifiers and
control information. The advantage of Node mode is that the extract computer can
assemble simultaneous incoming stories in separate computer buffers, store them as
separate entities, format them in response to embedded commands, and display them
in preferred (and possibly user controlled) sequences.