How to transparently transmit 10 Gb Ethernet signals on a fiber-optic network

10-Gbit Ethernet LAN technology is increasingly used in enterprises, which brings new challenges and opportunities to optical transmission network (OTN) suppliers. Similarly, for companies that serve businesses, governments, and other large organizations, the transparent transmission of 10-Gbit Ethernet signals is becoming a key competitive factor.

From the perspective of the end customer, the OTN should be a seamless extension of the existing 10-Gbit Ethernet LAN infrastructure without having to impose any constraints on the local protocol or propose specific processing requirements prior to transmission.

For example, if a customer organization or equipment vendor uses a 10-Gbit Ethernet preamble to track error messages or manage Interbox communication links, it is important to maintain the integrity of the preamble information throughout the transmission on the OTN.

Similarly, if the customer's LAN uses a jumbo packet to maximize the data load ratio in a 10-Gbit Ethernet LAN, the ability to transmit huge packets must also be seamlessly maintained on the OTN.

The inherent line rate differences between 10-Gbit Ethernet LANs and OTN networks make these goals difficult to implement. The 10-Gbit Ethernet LAN signal operates at a nominal line rate of 10.3125 Gbps (10 Gbps x 66/64), while the OPU2 load is rated at 9,995,276,963 bps (OC-192 x 238/237).

Therefore, it is impossible to maintain the 'bit transparency' while maintaining the 10-bit Ethernet LAN signal in the OPU-2 payload using the Universal Framing Procedure (GFP). Standard 10.7-GHz line rate.


However, it is possible to achieve the desired goals by using the 'information transparency' technique described in this article. The key is to use the digital flexibility inherent in the OTN standard, combined with intelligent signal mapping technology to convert 10-Gbit Ethernet signals into standard 10.7-GHz OTU-2 signals for transmission.

Many of the current standards are attributed to the OTN name. Since the focus of 'transparent information' technology is to adapt the first layer of standards to 10-Gbit Ethernet transmissions without changing the physical layer, optical layer or any other layer implemented in software. From an implementation point of view, this is also an advantage because all changes occur at the digital layer, so the mapping function can be effectively implemented in ASIC hardware.

The Optical Transport System (OTH) defined in ITU G.872 (Optical Transport Network Architecture) establishes the transport technology of OTN. The G.872 standard defines an architecture consisting of an optical channel (OCh), an optical multi-tasking segment (OMS), and an optical transport segment (OTS) that describes the functionality required for OTN operation.

It is worth noting that the development of G.872 is dedicated to the inherent flexibility of constructing digital solutions (described in Section 9.1 of G.872). This work allows Forward Error Correction (FEC) and also introduces two digital layer networks: Optical Data Unit (ODU) and Optical Transmission Unit (OTU). The goal is to map all client signals to the optical channel through the ODU and OUT layer networks.

As a result, OTN can provide key advantages over Sonet/SDH, including more powerful FEC capabilities, transparent transmission of local client signals, more levels of serial monitoring, and conversion scalability. The following section details how to use the flexibility in the OTN standard to transmit 10-Gbit Ethernet signals while maintaining information transparency.

The basic challenge is how to pass the preamble and process the jumbo frame without changing the standard 10.7-GHz OTU line rate. If you only want to pass the preamble, you might use GFP packets, and the 10-Gbit Ethernet signal can fit the 10.7 GHz ODU-2. However, if you also want to include jumbo frames and maintain the existing 10.7-GHz transmission rate, the 10-Gbit Ethernet signal is no longer suitable.

One way to solve this problem is to send both the preamble and the jumbo frame, but map it to the ODU-2 at a higher rate. All 10.3-GHz signals (10-Gbit Ethernet data and encoding) are encapsulated in a synchronous OTN wrapper, which results in an OTU signal output rate of 11.1 GHz instead of the industry standard 10.7 GHz.

Although the ITU has a large number of proposals for using this solution, this is not the best solution, because shifting to a higher line rate will cause many serious problems for manufacturers who set up infrastructure around the 10.7-GHz standard.

In addition, while for some vendors, the transition to 11.1 GHz seems to be a viable short-term solution, it is still a visionary solution because it cannot smoothly transition to the next 40 Gbps transmission environment. If some OTUs are at 10.7 GHz and other OTUs are at 11.1 GHz, it is not possible to combine multiple OTUs from different customers in a multitasking manner.

An alternative 'information transparency' approach allows seamless 10-Gbit Ethernet traffic (including data, control, preamble, and jumbo packets) to be seamlessly transmitted over standard OTN 10.7-GHz signals that are fully compatible with G.709. The only difference is the number of 'idle' in the signal.

The standard 10-Gbit Ethernet 64B/66B encoding specifies data, idle, and ordered sets. The solution acquires 10.3125 GHz (10-Gbps data x 66/64) 10-Gbit Ethernet signals and intelligently segments them, mapping all information onto the OTN signal while minimizing idle. By separating the 64B/66B encoding, GFP encapsulation of the packet with a payload type, and GFP encapsulation of the ordered set with a different payload type, all information can be effectively mapped to the standard. 10.7-GHz OTN signal.

This scheme maintains full compatibility with the 802.3 specification because it fully complies with the minimum instantaneous inter-packet interval (IPG) of 5 bytes and the specified average minimum IPG of approximately 10 bytes.

From the customer's point of view, due to this information transparency, there is no difference between the data stream transmitted in the customer's proprietary 10-Gbit Ethernet LAN and the data stream transmitted on its vendor's OTN network. This allows customers to make the best use of giant packets, as well as those with built-in preamble information to provide a carrier-class communications integrity platform.

This information transparency scheme can also be efficiently implemented as a complete unit in a hardware ASIC. High-performance digital processing technology enables tight mapping and enhanced FEC capabilities to be tightly integrated into a single component to provide maximum flexibility for mapping 10Gbit Ethernet signals to various OTN line rates.