Premisys 600, Reference Manual

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Server Cards 7-1
IMUX Card Introduction
Chapter 7
IMUX Card
7.1 Introduction
The ISDN card supports B channel bandwidth of 56K, 64K, 384K, 1536K and MultiRate
(MRate). Normally, the MRate option will allow users to select any combination of 64K B
channels needed for the call request, but in areas where rates greater than 64Kbps are not
supported by the local ISDN switch, B channels must be aggregated to support calls at
MultiRate speeds.
The solution to this problem is the Inverse Multiplexer card that works with the ISDN card to
provide the exact B channel bandwidth needed in 56Kbps, 64Kbps and H0 (384Kbps)
increments. Since the IMUX card does not support NFAS (see ISDN chapter for further
information), the maximum 56Kbps or 64Kbps B channel allocation is 23 for T1 systems and
30 for E1 systems. The maximum B channel allocation for H0 (384Kbps) is 3 for both T1 and
E1 systems.
Figure 7-1 shows a typical IMUX application. The DTE located at System Unit "A" needs a
128Kbps circuit to connect to the DTE at System Unit "B." The user selects one of the IMUX
engines (ports) to dial two B channels (64Kbps each) that multiplex the data to the IMUX card
located at System Unit "B."
The system will dial the IMUX Primary or Hunt Number and establish the connection with
the IMUX Card at the other end of the circuit (dark line on diagram). Once completed, it will
call the IMUX Additional Number to set up the rest of the bandwidth needed, organize the
data "pipe" and complete the call.
It is strongly suggested that the user obtain an Additional Number from the ISDN carrier
because other incoming calls to the Primary Number or Hunt Number could accidentally be
included in the IMUX call that you are trying to establish. Since all B channel bonding
happens on the Additional Number, if it is available, this call collision could be averted.
Figure 7-1.Typical IMUX Application
DTE
ISDN
Network
DTE
HSU
IMUX
ISDN
System Unit A
HSU
IMUX
ISDN
System Unit B