Specifications

Network Planning
August 08, 2000 68P81095E55 A-1
Appendix A
Network Planning
Nominal limitations for iDEN systems are based on the available hardware and the
localized traffic. Motorola iDEN provides documentation and tools to assist in the
planning of a network. The logical planning of network traffic is discussed in greater
detail in iDEN S.E.T.S Group Formulas for Traffic Analysis, MSO Timing System
(sysiu020 r12) and the MSC Subsystem General Planning and Expansion manual.
These documents are available on-line at the iDEN support website, AccessSecure.
The website also contains the DAP Tools capacity planning spreadsheet macros to
assist in the planning of dispatch calling.
Timing
The distributed nature of the iDEN system requires precise timing to assure the
proper processing of voice and data across the network. Two time models are
possible. (Please refer to MSO Timing System - sysiu020 r12).
Isochronous Timing
The synchronization of telecommunications systems is based on digital PCM
transport. In North America the standard is based on the T1s, operating at
1.544 Mbs, while most of the rest of world uses the ITU E1 format operating at
2.048 Mbs.
Since voice and data information could use different paths to travel across the
networks the data would have to be adjusted for time-delay based on the route the
data traveled. If control information takes a longer path than the data or voice
information, there would be a mismatch of information at the destination. This
requires adjusting the time for distance traveled. Historilcally, each network had a
single (isochronous) timing source with hardware and software to manage the time
differences. This requires a hierarchical, distributed method (Figure A-1).
Figure A-1 Isochronous Hierarchical Timing Distribution
The difficulty with isochronous hierarchical timing is that each element in the path
introduces a delay. There is also a delay introduced by the propagation time between
the elements. With digital switches, this creates a timing problem that requires more
hardware and software.
The different delay times causes the payload synchronization to be out of step
between source and destination elements. The result is that the payload (T1 or E1
frames) become unusable.
PSTN
Repeater
Isochronous
Timing Source
Switch B
(destination)
Switch A
(source)
PSTN
Repeater
PSTN
Repeater
PSTN
Repeater
PSTN
Repeater
PSTN
Repeater
PSTN
Repeater
PSTN
Repeater
Time A ≠ Time B
A
B
Traffic
Timing links
Timing Delay (link B) =
(link A time - link B time)
Multiple networks require multiple link hardare and links software offsets
Isochronous Timing Adjustment