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Combine Cellular Voice and Switched
Network Traffic
Combine Both Cellular Voice and Switched-Network "Back-Haul" Traffic
Over the Same T-Carrier (T1) Network
Problem
A plan is in place to deploy multiple cell sites to support six
rural service areas (RSAs) in Texas. Each cell site is initially
8-12 channels over a T1 facility, served by a single MTSO.
All calls to and from non-mobiles use the switched network.
To cover the RSAs without incurring significant long-distance
phone charges, a multiple T1 private network is envisioned
to extend from the MTSO to LEC central offices (CO) in each
of the six RSAs -- promising to result in a very costly overlay
network. What other options exist?
Solution
Coastcom's D/I Mux III can be used at the cell sites to "groom
and fill" the cellular service with the switched-network "back-haul" access,
making an overlay network unnecessary. The equipment consists
of D/I Mux III special T1 multiplexers at each cell site with
dual 4-Wire TO channel cards and TTU fractional T1 channel cards,
as needed, to connect locally to the T1 and to the LEC central
office (CO).
How Does It Work?
The D/I Mux III installed at the cell site has the flexibility
of multiplexing channels onto a network T1 to the MTSO location.
These channels can be allocated to voice and control data to
support the cellular service, or can be allocated as a partially
filled local-access T1 to the nearest CO to support back-haul
phone calls locally. This partially filled T1 is often referred
to as a fractional T1.
Figure c13. Cellular Service and "Back-Haul" Switched
Voice
By allocating the network channels to either the
cellular voice/data or the fractional T1 channel allocation,
the digital bandwidth can be shared between the various services.
This configuration is called "groom and fill". At the
MTSO location, the cellular and switched voice channels are connected
using the D/I Mux III or, alternatively, the Coastcom DXC II
mini-DACS. The mini-DACS can terminate up to 16 T1s in a 10 1/2-inch
chassis, reducing space, power, and overall cost of the solution.
What Actually Occurs?
The MTSO has voice tandem trunks that connect on a T1. These
trunks are connected to the mini-DACS together with the cellular
MBLT T1s. The T1s to each of the cell sites also connect to
the mini-DACS. The DXC II is programmed to allow any DS0 channel
originating from the MTSO to connect to any DS0 of the long-haul
T1 that is connected to the cell site. This grooms the network
at the MTSO, while the D/I Mux III redistributes the DS0 channels
at the cell site.
How Do You Set It Up?
An RSA cell site can, for example, be set up to support 12 DS0s
for cellular and 12 DS0s for "back-haul" switched-voice
access. At the MTSO, the mini-DACS programmed on a DS0 basis "fills" the
connecting long-haul T1 with channels connected to various
T1 trunks of the MTSO. The cellular base station trunks use
11 DS0s for cellular voice and one DS0 for cellular data control
to the base station. The remaining 12 DS0 channels are cross-connected
to a MTSO voice trunk T1. At the cell site, the D/I Mux III
is programmed to connect the 11 cellular voice channels to
six dual-channel 4-Wire VF channel cards, each connected to
cellular transceivers. One channel is available for cellular
data at 56/64 Kbps, which connects to a base station control
system. The remaining 12 channels are programmed to a TTU channel
card, providing T1 access to the local CO over a fractional
T1 facility.
What Information Do You Need?
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How many MVC voice channels do you have at
each cell site location?
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How many switched voice trunks do you need
at each cell site location?
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