ANSI SCTE 25-1-2017 pdf free download – Hybrid Fiber Coax Outside Plant Status Monitoring – Physical (PHY) Layer Specification v1.
1.1 Scope
This specification describes the PHY layer requirements that must be implemented by all Type 2 and Type 3 compliant OSP HMS transponders on the HFC plant and the controlling equipment in the headend. Any exceptions to compliance with this specification will be specifically noted in this document as necessary. Refer to Table 1 for a full definition of the Type Classifications. Note Electromagnetic Compatibility (EMC) is not specified in this standard and is left to the vendor to ensure compliance with local EMC regulatory requirements. Other than operating temperature, physical parameters such as shock, vibration, humidity, etc., are also not specified and left to the vendor’s discretion.
1.2 Transponder Type Classifications Transponder type classifications referenced within the HMS suite of specifications are defined in Table 1.
1.5 Functional Assumptions
1.5.1 Forward and Return Spectrum The forward spectrum in HFC cable systems refers to the passband of frequencies with a lower edge of between 48 MHz and 87.5 MHz, depending on the particular geographical area, and an upper edge that is typically in the range of 300 MHz to 860 MHz depending on implementation. Analog television signals in 6-MHz or 8-MHz channels are assumed to be present on the forward spectrum as well as other narrowband and wideband digital signals.
The return spectrum in HFC cable systems refers to the passband of frequencies with a lower edge of 5 MHz and an upper edge that is typically in the range of 42 MHz to 65 MHz depending on the particular geographical area. Narrowband and wideband digital signals may be present on the return spectrum as well as analog television signals in 6-MHz or 8-MHz channels. The full spectrum in HFC cable systems refers to the combined forward and return spectrums and excludes any guard band. The guard band refers to the unused frequency band between the upper edge of the usable return spectrum and the lower edge of the usable forward spectrum. Specific limits on forward and return spectrum for various geographical areas are detailed in Table 3.
1.5.2 Transmission Levels
The nominal level of the forward spectrum HMS carrier(s) is targeted to be no higher than –10 dBc relative to analog video nominal carrier levels. The nominal power level of the return spectrum HMS carrier(s) will be as low as possible to achieve the required margin above noise and interference. Uniform power loading per unit bandwidth is commonly followed in setting signal levels on the return spectrum, with specific levels established by the cable network operator to achieve the required carrier-to-noise and carrier-to-interference ratios.
2 Physical Layer Specification
This section describes version 1.0 of the HMS PHY layer specification. The PHY layerdescribes rules that govern the transmission of bytes from one device to another. The specificrequirements of the HMS PHY layer are detailed in this section.
2.1 Separate Forward and Return ChannelsThe one-way communication channel from the HE to a managed OSP NE is referred to as theforward channel. The one-way communication channel from a managed OSP NE to the HE isreferred to as the return channel. Both the forward and the return channels are placed on specificcenter frequencies. The forward and return channels’ center frequencies are different. Since theNEs only listen to the forward channel, they cannot listen to return channel transmissions fromother NEs. This channel separation is a result of the sub-band split between the forward andreturn portions of the typical HFC plant spectrum.
2.2 Single Forward and Return Path ChannelsTo keep management of carrier frequencies simple, each HMS-based status monitoring systemhas a single forward channel and a single return channel. This does not preclude the use ofmultiple monitoring systems, each with its own individual forward and return RF channels.
2.3 Byte-Based TransmissionThe physical layer provides byte-based communications in both directions, between a managedNE and the headend. It delivers bytes from one end of the channel to the other end of thechannel.2.4 Byte Formats and Transmission OrderBytes on both forward and return channels are ten bits in length. They contain one start bit, eightbits of data, and one stop bit. The start bit has binary value ‘0’, and the stop bit has binary value‘1.’Throughout this document, bits labeled ‘0’ are the least significant bits (LSBs). The LSB of asingle byte is always transmitted first following the start bit. Bits labeled ‘7’ are the mostsignificant bits (MSBs). The MSB of a single byte is always transmitted last followed by thestop bit. The transmission order is summarized in Figure 2.ANSI SCTE 25-1 pdf download.