Nortel Communication Server 1000 Fundamentals page 28

28 Description
Blocking
With the number of TNs greater than the number of T1 channels, calls
between the remoted line card and the switch may be blocked due to the
lack of an available timeslot. Normally, all signaling messages between the
RMI and the switch are passed through the MCR system, but not during
blocked situations.
Analog cards and digital cards handle blocking differently. For analog sets,
ringing messages destined for a remoted line card are dropped when
a time-slot allocation is attempted but a timeslot is not available. This
enables the caller to be forwarded to voice mail when no timeslots are
available. Also, when no timeslots are available, off-hook messages from
the remoted phones are not transported across the MCR. Instead, the
remote user receives re-order, or fast-busy (a fast busy signal) to indicate
that no timeslot is available.
With digital sets, ringing messages are not dropped when no timeslots
are available. If the user answers a ringing telephone when no timeslots
are available, the user receives a re-order signal to indicate the blocked
situation. The caller will hear silence, since the MCR system is out of
timeslots.
CardLAN
The local LMI and LMX act as a cardLAN slave to the XPEC or CPU card.
The RMI board sits in the CPU slot and therefore is the cardLAN master.
The local boards wait for the RMI to enable them to respond to their
cardLAN master. The RMI polls all 10 line card slots at the remote site in a
round-robin fashion and looks for newly inserted cards.
Upon LMX detection, the RMI queries the LMX with all known cardLAN
messages so that it can provide this information to the local card that is
emulating that LMX. Upon receiving the last message from the RMI, the
local board begins responding to polls normally. At each local cardLAN
query, the local card responds immediately, and it also sends that query to
the RMI. The RMI then queries the remoting LMX and sends the response
back to the local card. This method keeps the local site one poll behind,
but this is necessary to be able to respond to cardLAN fast enough at the
local site over long T1 distances.
If the RMI detects that an LMX has been removed or changed, it disables
or initializes the appropriate local card's cardLAN task. Also, if the local
card receives a cardLAN message that is undefined, no attempt is made
to answer that message. Should the existing Nortelline cards be updated
such that they operate on an expanded cardLAN message set, the MCR
system must also be updated.
Nortel Communication Server 1000
Mini-Carrier Remote Fundamentals
NN43001-557 04.01 4 June 2010
Copyright © 2003-2010 Nortel Networks. All Rights Reserved.