DOCSIS Provisioning of EPON, Passport to the Future!
By Steven Harris
Our networks are evolving to meet the ever-increasing thirst for bandwidth, whether that is with DOCSIS, fiber deep (FD), or passive optical network (PON) technology. A protocol that is well known in the cable network is Ethernet, supporting a coexistence approach for operators with the very familiar DOCSIS. Operators are now able to deploy Ethernet over the access network or optical distribution network (ODN) to reach the customer premises with triple play services and beyond. Ethernet is widely used in cell backhaul controllers, multiple dwelling units (MDU), and business services (e.g., point to point or hosted PBX). For many of our technology deployments, provisioning is a necessary requirement for device enablement, whether that is Ethernet or DOCSIS. For an access network with Ethernet, provisioning of Layer 2 (L2) optical network units (ONUs) via an optical network terminal (OLT) is deployed. The OLT resides at a headend or hub site (with options for remote OLT in the ODN), similar to a CMTS, and is a key component of the Ethernet provisioning process.
Here we will build on my previous Broadband Library article on 1 gigabit (IEEE 802.3ah) and 10 gigabit (IEEE 802.3av) Ethernet passive optical network (EPON) technology, as Ethernet supports an option for next generation capacity. For other readers, my future articles will focus on the extensive progress being made in parallel with gigabit passive optical networks (GPON) and 10 gigabit-capable symmetric passive optical networks, more commonly known as XGS-PON (ITU-T G.9807.1). XGS-PON addresses the costly time and wavelength division multiplexing (TWDM) optics used in next generation PON version 2 (NG-PON2). For now, EPON provisioning is the topic at hand.
DOCSIS provisioning of EPON, or DPoE, is a scalable operational support system interface (OSSI) used by operators to provision EPONs. DPoE builds on the service interoperability in EPON (SIEPON) working group standard. DPoE additionally leverages the foundation of a well proven DOCSIS back office system while promoting multivendor interoperability, lowering the cost of ownership, leveraging the workforce knowledgebase, and supporting metro Ethernet services.
DPoE was developed and is supported by the cable operator, SCTE·ISBE, vendor, supplier, and CableLabs communities, with two specifications for this virtualized framework known as DPoEv1 and DPoEv2. DPoEv1 specified a virtual cable modem (vCM) structure (see figure 1.0), along with how this virtualized component is used to communicate with an ONU at the subscriber premises. In addition, DPoEv1 called for a layer known as the DOCSIS mediation layer (DML), communicating with the existing DOCSIS OSSI. DPoEv2, built upon v1, is focused on more complex services, including quality of service (QoS) capabilities. Additional requirements for features found DPoEv2 such as Internet protocol version 6 (IPv6), multicast, and Ethernet operation, administration, and maintenance (eOAM) were added into this specification. Even support for multi-point-to-multi-point architectures or Metro Ethernet Forum (MEF) Ethernet local area network (E-LAN) architectures were included. DPoE with EPON technology leverages the DOCSIS infrastructure and service platform our industry has deployed, similar to how DOCSIS provisioning of GPON (DPoG) also leverages the DOCSIS back office. The DPoE network operates similar to a DOCSIS centralized scheduler via logical link identifiers (LLID), comparable to DOCSIS service identifiers (SIDs). All these components need to be verified for interoperability, and CableLabs is the entity that reviews DPoE components and alignment to the specifications. CableLabs fully tests and certifies DPoE compliant products to ensure industry interoperability.
Figure 1.0 DOCSIS HFC coexistence with Ethernet FTTH (EPON)
EPON leverages an all fiber optic transport system and signaling architecture over ODN. The ODN is the access portion, similar to our DOCSIS HFC network. For control of the cable modems the DOCSIS network uses the CMTS. While the main component of the EPON/DPoE system here is the OLT, where the vCM software component resides for control of the ONUs, the OLT is the interface between the ODN and the operator’s back office / core IP network (Figure 1). At the premises where traditional DOCSIS cable modems have resided, now is a DPoE/EPON system known as a DOCSIS optical network unit, or D-ONU, used for service connectivity. There are two forms of a D-ONU, one that is bridge pluggable, known as a B-ONU. Another form of D-ONU known as a B-ONU that has a baseband IEEE Ethernet interface, also called a bridge baseband ONU (BB-ONU). The B-ONU and BB-ONU define interfaces for small form-factor pluggable (SFP) modules, adding additional flexibility for different variants of Ethernet.
Figure 2.0 Service interoperability in EPON
The vCM is the software element of the OLT, or interface between the D-ONU (often referred to as just an ONU) and DOCSIS provisioning system. The vCM allows the ONU to communicate with a DOCSIS network via translation from Ethernet into DOCSIS. The function of the vCM is to obtain IP addressing via the dynamic host configuration protocol (DHCP), download configuration from a trivial file transfer protocol (TFTP) server, and parse type length value (TLV) configuration code. The vCM is also a simple network management protocol (SNMP) agent acting on behalf of the ONU to provide information (e.g., status) to the operator. In addition to SNMP, a DPoE system v2 utilizes eOAM for installing, monitoring, and troubleshooting metropolitan-area networks (MANs) and wide area networks (WANs). The major function for eOAM is to configure a ONU to behave as required by a modem configuration file. The DML on the other hand is the entity or process in the DPoE system that translates all DOCSIS specific management tools into EPON language, such as the DOCSIS management information base (MIB) interpretation, vCM creation, eOAM messages, or keeping the software load up to date via a DOCSIS secure software download (SSD).
Figure 3.0 ONU service identifiers (LLID), service flows and classification via ports
The access network will undergo a major uplift over the next few years, so stay connected with SCTE·ISBE. Our technologies and architectures such as EPON, GPON, fiber deep and distributed access architecture (DAA) will be major components of this uplift. The important take away here is to understand where the industry is going and keeping current with our industry as a society member. SCTE·ISBE is now approaching 20,000 minutes of archived webinar content, a full database called “Knowledge Resource Collection” that offers access Expo papers, training with 800+ modules of content, and chapter activities affiliated to future operator strategies. We now offer MEF carrier Ethernet certification opportunities, core fiber optic skills for deploying EPON with broadband fiber installer (SCTE.org/BFI) and opportunities in transport with broadband transport specialist (SCTE.org/BTS).
Education is the passport to the future, for tomorrow belongs to those who prepare for it today! — Malcolm X.
Figure 4.0 Remote OLT and headend OLT
Figure 5.0 eOAM
Steven Harris
Senior Director, Advanced Network Technology and Instruction, Learning and Development, SCTE•ISBE
Steve Harris is the Executive Director of Technical Education and Sales at SCTE·ISBE. He is a respected international telecommunications subject matter expert, sought-after presenter, and principle instructor. He responsible for the tremendous growth of SCTE·ISBE training curriculum, learning paths and certifications for 100,000+ telecommunication professionals. He also has responsibility for the client partnerships for the SCTE·ISBE Corporate Alliance Program (CAP) MSOs and vendors community.
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