Chapter 3 System Features
AC 60 Software Features
3-26
255-700-025
PacketStar
™
Access Concentrator 60 User Guide
, Issue 1
Release 6.3.0
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
purposes and thus regular frame-marker bit patterns for cell extraction. Each
LANET frame (2400 bytes) is subdivided into 45 ATM cells (totaling 2385
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 conjunction with traditional cell-header
error-detection methods, such as header error correction (HEC), to enhance
cell delineation for noisy environments. The protocol thus becomes
independent of the transmission rate while still naturally synchronizing with
an 8-kHz transmission clock via the 2400 bytes-per-frame structure.
Traditionally, block-error correction schemes, such as Reed Solomon (RS)
coding, have been used to protect the header. As a simple alternative, the
Access Concentrator system software uses an error-tolerant addressing
scheme (multiple redundancy addressing) that establishes multiple virtual
circuits to the same destination, thus requiring no special hardware and no
modification to the current standard. The addresses for the circuits are within
the error space of the principal address used for actual transmission. Thus,
the most probable error patterns occurring in the address field will simply
change the address to another valid one. This approach maintains
independence from the application layer because it encodes the header
Figure 3-6. The 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
Содержание PacketStar AC 60
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