363-206-285
Technical Specifications
Issue 3 June 2001
10-7
— Buffering .5 MByte for each direction
— See Table 10-2 for optical characteristics.
â– Format Specification:
The LAN interface converts incoming MAC frames to an ATM cell format
using ATM adaptation layer 5 (AAL5) encapsulation as specified in IETF
RFC-1483. ATM cells are distributed in round robin order on 1 to 8 ESF
formatted DS1 signals using the ATM forum IMA Specification Version 1.1
for inverse multiplexing. The DS1 signals are mapped into asynchronous
VT1.5 signals for transport through a SONET network. The circuit pack can
compensate for up to 50 ms of differential delay among the 8 DS1s and
uses a single IMA group with one ATM virtual channel (VC). The following
provisioning options are provided:
— AAL5 Protocol - VC multiplex or LLC encapsulation (Bridged)
— MAC Frame Check Sequence (FCS) Preservation - enable or
disable
— ATM Virtual Path ID and Virtual Channel ID
— IMA group ID
— IMA Frame Length - 32, 64, 128, 256
— ATM scrambler - on/off
— ATM polynomial - on/off.
The IMA link IDs are assigned automatically by the system in the range 0 to
7. The IMA protocol operates in symmetric configuration with common
clock.
â– Alarms:
Local LAN port failures are detected by monitoring for the presence of
either MAC frames or Link Pulses per IEEE 802.3. From the SONET
direction, failures are detected by monitoring for VT1.5 (AIS, LOP), DS1
LOF, Loss of IMA frame, Loss of IMA Delay Synchronization (LODS), Loss
of Cell Delineation (LCD) and excessive AAL5 CRC errors. The alarm level
for a local LAN port failure is user provisionable (Major, Minor, Not
Alarmed).
â– Performance Monitoring:
In addition to DS1 path and VT1.5 path performance monitoring, the BBF9
circuit pack supports performance monitoring of data flow in both
directions. The parameters supported are:
— Transmit MAC packets forwarded (towards the WAN)
— Transmit MAC packets discarded
— Receive MAC packets forwarded (towards the LAN)
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