255-700-447
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PacketStar
®
PSAX 2300 Multiservice Media Gateway User Guide
, Issue 1
Release 9.0.0
Chapter 3 System Features
PSAX System Software Features
The LANET protocol is designed to be active in the upper end of the physical
layer of the OSI seven-layer model. Within a byte-oriented serial data stream,
LANET provides a framing structure around ATM cells for transmission pur-
poses and regular frame-marker bit patterns for cell extraction. Each LANET
frame (2,400 bytes) is subdivided into 45 ATM cells (totaling 2,385 bytes)
with a 15-byte overhead. This structure permits a transmission rate scalable
according to the physical medium.
The 15-byte overhead, accounting for 0.63 percent of the bandwidth,
includes the LANET frame and subframe headers, which are used in conjunc-
tion with traditional cell header error-detection methods, such as header
error control (HEC), to enhance cell delineation for noisy environments. The
protocol thus becomes independent of the transmission rate while still natu-
rally synchronizing with an 8-kHz transmission clock via the 2,400-bytes-
per-frame structure.
Traditionally, block-error correction schemes, such as Reed Solomon coding,
have been used to protect the header. As a simple alternative, the PSAX sys-
tem software uses an error-tolerant addressing scheme (multiple redundancy
addressing) that establishes multiple virtual circuits to the same destination,
requiring no special hardware nor modification to the current standard. The
addresses for the circuits are within the error space of the principal address
used for actual transmission. The most probable error patterns occurring in
the address field will simply change the address to another valid address. This
approach maintains independence from the application layer because it
Figure 3-9. Relationship Between LANET and the OSI Model
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
LANET Protocol
Encryption
Error Correction
Bit Interleaf
Satellite
Radio
Land Lines
ATM
Voice
Video
Images
Data
SERVICE-INDEPENDENT ARCHITECTURE
Layer 1
From bits per second to megabits per second
CELL-BY-CELL ENCRYPTION