– Handles byte transfer between transmit front-end buffers and the FESH RAM.
The transmit byte layer which:
– Handles NCP buffer prefixes for transmission.
– Interconnects with the CSP layer (external registers and control words).
– Handles chaining thru NCP buffers for SDLC transmits.
– Handles chaining thru NCP buffers for each frame relay frame and chaining between frames to
transmit.
Receive Layers
The receive layers are composed of:
The front-end circuits which perform the following functions:
– Deserialization of data
– Zero deletion
– Flag detection
– Early flag detection
– Abort detection
– Idle detection
– Overrun detection
– CRC calculation error detection
– Address compare/satellite echo suppression
– Interconnection with receive queue buffer.
Receive bit layer:
– Handles byte transfer between receive front-end buffer and FESH RAM.
Receive byte layer:
– Handles NCP buffer prefixes for receive
– Interconnects with CSP layer (external registers and control words).
– Handles chaining thru NCP buffers for SDLC receives.
– Handles chaining thru NCP buffers for frame relay frame receives. Also, use the SNAP header
format table to determine the offset and maximum counts to use for the first two buffers in the
receive chain for frame relay. Provide the actual count used in the receive buffer prefix.
Modem-Out Layer
The modem-out layer:
Interconnects with the CSP layer control word (CW).
Activates output modem control leads according to the modem-out CW prepared by the CSP micro-
code.
Modem-In Layer
The modem-in layer:
Interconnects with the CSP layer (control word and external registers).
Performs input modem control lead status confirmation.
Reports input modem control lead changes and X.21 steady states according to the modem-in CW
prepared by the microcode and stored in the FESH RAM.
Chapter 5. High Performance Transmission Subsystem (HPTSS)
5-13
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