RFDOCSIS Architecture Explained: Network Elements & Functions
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This page describes the DOCSIS architecture and its network elements along with their functions.
The DOCSIS network architecture is divided into customer-side components, cable operator-side components, and the HFC network.
What is DOCSIS?
DOCSIS helps cable operators provide internet services to consumers over existing cable TV systems. It requires a DOCSIS-compatible cable modem at the customer’s premises to access the services provided by the cable operator. The DOCSIS standard is managed by CableLabs.
The full form of “DOCSIS” is “Data Over Cable Service Interface Specification.” Other contributing companies include Cisco, Broadcom, Intel, Netgear, ARRIS, and Texas Instruments, among others.
It allows the transmission and reception of high-bandwidth data over an existing cable TV network or HFC (Hybrid Fiber Coaxial) network. The first DOCSIS standard, version 1.0, was developed in 1997, followed by other DOCSIS standards as mentioned in the following table.
| Standard version | Features | Downstream data rate | Upstream data rate |
|---|---|---|---|
| DOCSIS 1.0 | Initial cable broadband technology | 40 Mbps | 10 Mbps |
| DOCSIS 1.1 | Added Voice over IP service | 40 Mbps | 10 Mbps |
| DOCSIS 2.0 | Higher upstream speed | 40 Mbps | 30 Mbps |
| DOCSIS 3.0 | Greatly enhances capacity | 1 Gbps | 100-200 Mbps |
| DOCSIS 3.1 | Capacity and efficiency progression | 10 Gbps | 1-2 Gbps |
| DOCSIS 4.0 | Symmetrical streaming and increased upload speeds | 10 Gbps | 6 Gbps |
DOCSIS Architecture Explained
The figure depicts the DOCSIS architecture. Let’s understand the functions of each of its elements.
There are three major elements of a DOCSIS system:
- Cable modem (CM)
- HFC network or cable TV network
- CMTS (Cable Modem Termination System)
The DOCSIS network offers a bi-directional flow of IP data between the CM and CMTS over the existing cable network. The cable network can be either all coaxial cable or a Hybrid-Fiber/Coax (HFC) cable network.
Cable Modem (CM)
The cable modem is the main interface between the HFC network and the home network, bridging packets flowing between them. It allows connections with different customer premise equipment (CPEs) intending to access the internet.
Typical CPEs used at home or office premises are gateways, VoIP telephones, WiFi modems or routers, personal computers, and set-top boxes (STBs). CPEs can either be embedded with the CM in a single device, or both can be separated into standalone devices.
WiFi modems or routers handle providing simultaneous internet access to desktops, mobiles, laptops, tablets, etc., using WiFi signals. CPEs support IPv4, IPv6, or both.
CMTS (Cable Modem Termination System)
CMTS stands for Cable Modem Termination System. It is the main element located at the cable operator’s side. The DOCSIS standard defines messages and data types exchanged between the CMTS and the CM.
The CMTS connects the cable operator’s back office and core network to the HFC network. The main function of the CMTS is to forward packets between the HFC and the back office. It also forwards packets between upstream and downstream channels on the HFC network.
Here, “downstream” refers to the data flow from the cable company to the customer premises equipment, whereas “upstream” refers to the data flow from the CM (i.e., cable modem) to the cable company (i.e., CMTS side).
The CMTS is connected with a DHCP server, switch, and router to provide backbone internet connectivity. The DHCP server provides the cable modem with initial configuration information, such as IP address assignment, etc.
Other provisioning systems handle software downloads to the cable modem, configurations of the cable modem, and so on. An SNMP manager allows the cable operator to configure and monitor the cable modem and CMTS.
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