ANSI SCTE 25-2-2017 pdf free download – Hybrid Fiber Coax Outside Plant Status Monitoring – Media Access Control (MAC) Layer Specification v1.0.
2.1.2 Definitions and Conventions
2.1.2.1 Separate Forward and Return Channels
The one-way communication channel from the HE to a managed OSP NE is referred to as the forward channel. The one-way communication channel from a managed OSP NE to the HE is referred to as the return channel. Both the forward and the return channels are placed on specific center frequencies. The forward and return channels’ center frequencies are different. Since the NEs only listen to the forward channel, they cannot listen to return channel transmissions from other NEs. This channel separation is a result of the sub-band split between the forward and return portions of the typical HFC plant spectrum.
2.1.2.2 Single Forward and Return Path Channels per MAC Layer Domain
To keep management of carrier frequencies simple, each HMS-based status monitoring system has a single forward channel and a single return channel. This does not preclude the use of multiple monitoring systems, each with its own individual forward and return RF channels.
A MAC layer domain consists of a single forward RF channel and a single return RF channel over which a single HMS MAC layer bandwidth allocation and management protocol operates. It includes a centralized HE and multiple HMS-compliant transponders interfacing to managed OSP NEs. The centralized HE may support multiple HMS-based status monitoring systems, i.e.: multiple MAC layer domains. Each OSP NE must only access a single forward channel and its associated single return channel; i.e.: it must only operate within a single HMS MAC layer domain.
2.1.2.3 Network Element (NE) Term Usage
The HMS MAC layer supports bandwidth management and reliable communications between a HE and multiple HMS-compliant transponders that interface to managed OSP NEs. Throughout this document, the terms “HMS-compliant transponder”, “transponder”, and “NE” are used interchangeably when describing the MAC processes that support the exchange of data or other information between two or more entities at the DLL.
2.1.2.4 Packet
A packet is a unit of data exchanged between the HE and any of a number of managed OSP NEs at the DLL. Packets are strings of bytes that can be sent contiguously or be separated by periods of silence. Document SCTE 25-1 HMS Outside Plant Status Monitoring – Physical (PHY) Layer Specification v1.0 describes specific byte transmission modes that must be implemented in both forward and return channels. A MAC packet consists of a MAC header, a variable-length payload, and a frame check sequence (see Section 2.3).
|2.1.2.5 Most Significant
Byte Unless otherwise specified, it is assumed throughout this document that the left-most entry in any numeric value is the most significant, i.e.: for the address represented as 12-34-56-78-9A-BC the left-most entry ‘12’ is the most significant value.
2.1.2.6 Byte Number Representation
Throughout this document, bits labeled ‘0’ are the least significant bits (LSBs) and bits labeled ‘7’ are the most significant bits (MSBs). The bits in a given byte will be described with bit 7 (MSB) at the left and bit 0 (LSB) at the right. This convention has been adopted for presentation purposes only and has no effect on the actual bit transmission order. Bit transmission order details are provided in Section 2.2 of this specification.ANSI SCTE 25-2 pdf download