From its origin more than 25 years ago, Ethernet has evolved to meet the increasing demands of packet-switched networks. Due to its proven low implementation cost, its known reliability, and relative simplicity of installation and maintenance, its popularity has grown to the point that today nearly all traffic on the Internet originates or ends with an Ethernet connection. Further, as the demand for ever-faster network speeds has grown, Ethernet has been adapted to handle these higher speeds and the concomitant surges in volume demand that accompany them.
The One Gigabit Ethernet standard is already being deployed in large numbers in both corporate and public data networks, and has begun to move Ethernet from the realm of the local area network out to encompass the metro area network. Meanwhile, an even faster 10 Gigabit Ethernet standard is nearing completion. This latest standard is being driven not only by the increase in normal data traffic but also by the proliferation of new, bandwidth-intensive applications.
The draft standard for 10 Gigabit Ethernet is significantly different in some respects from earlier Ethernet standards, primarily in that it will only function over optical fiber, and only operate in full-duplex mode, meaning that collision detection protocols are unnecessary. Ethernet can now step up to 10 gigabits per second, however, it remains Ethernet, including the packet format, and the current capabilities are easily transferable to the new draft standard.
In addition, 10 Gigabit Ethernet does not obsolete current investments in network infrastructure. The task force heading the standards effort has taken steps to ensure that 10 Gigabit Ethernet is interoperable with other networking technologies such as SONET. The standard enables Ethernet packets to travel across SONET links with very little inefficiency.
Ethernet’s expansion for use in metro area networks can now be expanded yet again onto wide area networks, both in concert with SONET and also end-to-end Ethernet. With the current balance of network traffic today heavily favoring packet-switched data over voice, it is expected that the new 10 Gigabit Ethernet standard will help to create a convergence between networks designed primarily for voice, and the new data centric networks.
10 GIGABIT ETHERNET TECHNOLOGY OVERVIEW
The 10 Gigabit Ethernet Alliance (10GEA) was established in order to promote standards-based 10 Gigabit Ethernet technology and to encourage the use and implementation of 10 Gigabit Ethernet as a key networking technology for connecting various computing, data and telecommunications devices. The charter of the 10 Gigabit Ethernet Alliance includes:
- Supporting the 10 Gigabit Ethernet standards effort conducted in the IEEE 802.3 working group
- Contributing resources to facilitate convergence and consensus on technical specifications
- Promoting industry awareness, acceptance, and advancement of the 10 Gigabit Ethernet standard
- Accelerating the adoption and usage of 10 Gigabit Ethernet products and services
- Providing resources to establish and demonstrate multi-vendor interoperability and generally encourage and promote interoperability and interoperability events
- Fostering communications between suppliers and users of 10 Gigabit Ethernet technology and products
The 10 Gigabit Ethernet Alliance
The purpose of the 10 Gigabit Ethernet proposed standard is to extend the 802.3 protocols to an operating speed of 10 Gbps and to expand the Ethernet application space to include WAN links. This will provide for a significant increase in bandwidth while maintaining maximum compatibility with the installed base of 802.3 interfaces, previous investment in research and development, and principles of network operation and management.
In order to be adopted as a standard, the IEEE’s 802.3ae Task Force has established five criteria that the new 10 Gigabit Ethernet P (proposed) standard must meet:
- It must have broad market potential, supporting a broad set of applications, with multiple vendors supporting it, and multiple classes of customers.
- It must be compatible with other existing 802.3 protocol standards, as well as with both Open Systems Interconnection (OSI) and Simple Network Management Protocol (SNMP) management specifications.
- It must be substantially different from other 802.3 standards, making it a unique solution for a problem rather than an alternative solution.
- It must have demonstrated technical feasibility prior to final ratification.
- It must be economically feasible for customers to deploy, providing reasonable cost, including all installation and management costs, for the expected performance increase.
The 10 Gigabit Ethernet Standard
Under the International Standards Organization’s Open Systems Interconnection (OSI) model, Ethernet is fundamentally a Layer 2 protocol. 10 Gigabit Ethernet uses the IEEE 802.3 Ethernet Media Access Control (MAC) protocol, the IEEE 802.3 Ethernet frame format, and the minimum and maximum IEEE 802.3 frame size.
Just as 1000BASE-X and 1000BASE-T (Gigabit Ethernet) remained true to the Ethernet model, 10 Gigabit Ethernet continues the natural evolution of Ethernet in speed and distance. Since it is a full-duplex only and fiber-only technology, it does not need the carrier-sensing multiple-access with collision detection (CSMA/CD) protocol that defines slower, half-duplex Ethernet technologies. In every other respect, 10 Gigabit Ethernet remains true to the original Ethernet model.
An Ethernet PHYsical layer device (PHY), which corresponds to Layer 1 of the OSI model, connects the media (optical or copper) to the MAC layer, which corresponds to OSI Layer 2. Ethernet architecture further divides the PHY (Layer 1) into a Physical Media Dependent (PMD) and a Physical Coding Sublayer (PCS). Optical transceivers, for example, are PMDs. The PCS is made up of coding (e.g., 64/66b) and a serializer or multiplexing functions.
The 802.3ae specification defines two PHY types: the LAN PHY and the WAN PHY (discussed below). The WAN PHY has an extended feature set added onto the functions of a LAN PHY. These PHYs are solely distinguished by the PCS. There will also be a number of PMD types.
10 Gigabit Ethernet in the Marketplace
The accelerating growth of worldwide network traffic is forcing service providers, enterprise network managers and architects to look to ever higher-speed network technologies in order to solve the bandwidth demand crunch. Today, these administrators typically use Ethernet as their backbone technology. Although networks face many different issues, 10 Gigabit Ethernet meets several key criteria for efficient and effective high-speed networks:
- Easy, straightforward migration to higher performance levels without disruption,
- Lower cost of ownership vs. current alternative technologies – including both acquisition and support costs
- Familiar management tools and common skills base
- Ability to support new applications and data types
- Flexibility in network design
- Multiple vendor sourcing and proven interoperability
Managers of enterprise and service provider networks have to make many choices when they design networks. They have multiple media, technologies, and interfaces to choose from to build campus and metro connections: Ethernet (100, 1000,and 10,000 Mbps), OC-12 (622 Mbps) and OC-48 (2.488 Gbps), SONET or equivalent SDH network, packet over SONET/SDH (POS), and the newly authorized IEEE 802 Task Force (802.17) titled Resilient Packet Ring.
Network topological design and operation has been transformed by the advent of intelligent Gigabit Ethernet multi-layer switches. In LANs, core network technology is rapidly shifting to Gigabit Ethernet and there is a growing trend towards Gigabit Ethernet networks that can operate over metropolitan area distances.
The next step for enterprise and service provider networks is the combination of multi-gigabit bandwidth with intelligent services, leading to scaled, intelligent, multi-gigabit networks with backbone and server connections ranging up to 10 Gbps.
In response to market trends, Gigabit Ethernet is currently being deployed over tens of kilometers in private networks. With 10 Gigabit Ethernet, the industry has developed a way to not only increase the speed of Ethernet to 10 Gbps but also to extend its operating distance and interconnectivity. In the future, network managers will be able to use 10 Gigabit Ethernet as a cornerstone for network architectures that encompass LANs, MANs and WANs using Ethernet as the end-to-end, Layer 2 transport method.
Ethernet bandwidth can then be scaled from 10 Mbps to 10 Gbps – a ratio of 1 to 1000 — without compromising intelligent network services such as Layer 3 routing and layer 4 to layer 7 intelligence, including quality of service (QoS), class of service (CoS), caching, server load balancing, security, and policy based networking capabilities. Because of the uniform nature of Ethernet across all environments when IEEE 802.3ae is deployed, these services can be delivered at line rates over the network and supported over all network physical infrastructures in the LAN, MAN, and WAN. At that point, convergence of voice and data networks, both running over Ethernet, becomes a very real option. And, as TCP/IP incorporates enhanced services and features, such as packetized voice and video, the underlying Ethernet can also carry these services without modification.
As we have seen with previous versions of Ethernet, the cost for 10 Gbps communications has the potential to drop significantly with the development of new technologies. In contrast to 10 Gbps telecommunications lasers, the 10 Gigabit Ethernet short links — less than 40km over single-mode (SM) fiber — will be capable of using lower cost, uncooled optics and, in some cases, vertical cavity surface emitting lasers (VCSEL), which have the potential to lower PMD costs. In addition, the industry is supported by an aggressive merchant chip market that provides highly integrated silicon solutions. Finally, the Ethernet market tends to spawn highly competitive start-ups with each new generation of technology to compete with established Ethernet vendors.
10 Gigabit Ethernet in the Metro
Vendors and users generally agree that Ethernet is inexpensive, well understood, widely deployed and backwards compatible from Gigabit switched down to 10 Megabit shared. Today a packet can leave a server on a short-haul optic Gigabit Ethernet port, move cross-country via a DWDM (dense wave division multiplexing) network, and find its way down to a PC attached to a “thin coax” BNC (Bayonet Neill Concelman) connector, all without any re-framing or protocol conversion. Ethernet is literally everywhere, and 10 Gigabit Ethernet maintains this seamless migration in functionality.
Gigabit Ethernet is already being deployed as a backbone technology for dark fiber metropolitan networks. With appropriate 10 Gigabit Ethernet interfaces, optical transceivers and single mode fiber, service providers will be able to build links reaching 40km or more. (See Figure 4.)
10 Gigabit Ethernet in Local Area Networks
Ethernet technology is already the most deployed technology for high performance LAN environments. With the extension of 10 Gigabit Ethernet into the family of Ethernet technologies, the LAN now can reach farther and support up coming bandwidth hungry applications. Similar to Gigabit Ethernet technology, the 10 Gigabit proposed standard supports both singlemode and multi-mode fiber mediums. However in 10 Gigabit Ethernet, the distance for single-mode fiber has expanded from the 5km that Gigabit Ethernet supports to 40km in 10 Gigabit Ethernet.
The advantage for the support of longer distances is that it gives companies who manage their own LAN environments the option of extending their data centers to more cost-effective locations up to 40km away from their campuses. This also allows them to support multiple campus locations within that 40km range. Within data centers, switch-to-switch applications, as well as switch to server applications, can also be deployed over a more cost effective multi-mode fiber medium to create 10 Gigabit Ethernet backbones that support the continuous growth of bandwidth hungry applications. (See Figure 5.)
With 10 Gigabit backbones installed, companies will have the capability to begin providing Gigabit Ethernet service to workstations and, eventually, to the desktop in order to support applications such as streaming video, medical imaging, centralized applications, and high-end graphics. 10 Gigabit Ethernet will also provide lower network latency due to the speed of the link and over-provisioning bandwidth to compensate for the bursty nature of data in enterprise applications.
10 Gigabit Ethernet in the Storage Area Network
Additionally, 10 Gigabit Ethernet will provide infrastructure for both network-attached storage (NAS) and storage area networks (SAN). Prior to the introduction of 10 Gigabit Ethernet, some industry observers maintained that Ethernet lacked sufficient horsepower to get the job done. Ethernet, they said, just doesn’t have what it takes to move “dump truck loads worth of data.” 10 Gigabit Ethernet, can now offer equivalent or superior data carrying capacity at similar latencies to many other storage networking technologies including 1 or 2 Gigabit Fiber Channel, Ultra160 or 320 SCSI, ATM OC-3, OC-12 & OC-192,and HIPPI (High Performance Parallel Interface). While Gigabit Ethernet storage servers, tape libraries and compute servers are already available, users should look for early availability of 10 Gigabit Ethernet end-point devices in the second half of 2001.
There are numerous applications for Gigabit Ethernet in storage networks today, which will seamlessly extend to 10 Gigabit Ethernet as it becomes available. (See Figure 6.) These include:
- Business continuance/disaster recovery
- Remote backup
- Storage on demand
- Streaming media
10 Gigabit Ethernet in Wide Area Networks
10 Gigabit Ethernet will enable Internet service providers (ISP) and network service providers (NSPs) to create very highspeed links at a very low cost, between co-located, carrier-class switches and routers and optical equipment that is directly attached to the SONET/SDH cloud. 10 Gigabit Ethernet with the WAN PHY will also allow the construction of WANs that connect geographically dispersed LANs between campuses or POPs (points of presence) over existing SONET/SDH/TDM networks. 10 Gigabit Ethernet links between a service provider’s switch and a DWDM (dense wave division multiplexing) device or LTE (line termination equipment) might in fact be very short — less than 300 meters. (See Figure 7.)
The 10 Gigabit Ethernet Technology 10GbE Chip Interfaces
Among the many technical innovations of the 10 Gigabit Ethernet Task Force is an interface called the XAUI (10 Gigabit Attachment Unit Interface). It is a MAC-PHY interface, serving as an alternative to the XGMII (10 Gigabit Media Independent Interface). XAUI is a low pin-count differential interfaces that enables lower design costs for system vendors.
The XAUI is designed as an interface extender for XGMII, the 10 Gigabit Media Independent Interface. The XGMII is a 74 signal wide interface (32-bit data paths for each of transmit and receive) that may be used to attach the Ethernet MAC to its PHY. The XAUI may be used in place of, or to extend, the XGMII in chip-to-chip applications typical of most Ethernet MAC to PHY interconnects. (See Figure 8.)
The XAUI is a low pin count, self-clocked serial bus that is directly evolved from the Gigabit Ethernet 1000BASE-X PHY. The XAUI interface speed is 2.5 times that of 1000BASE-X. By arranging four serial lanes, the 4-bit XAUI interface supports the ten-times data throughput required by 10 Gigabit Ethernet.
Physical Media Dependent (PMDs)
The IEEE 802.3ae Task Force has developed a draft standard that provides a physical layer that supports link distances for fiber optic media as shown in Table A.
To meet these distance objectives, four PMDs were selected. The task force selected a 1310 nanometer serial PMD to meet its 2km and 10km single-mode fiber (SMF) objectives. It also selected a 1550 nm serial solution to meet (or exceed) its 40km SMF objective. Support of the 40km PMD is an acknowledgement that Gigabit Ethernet is already being successfully deployed in metropolitan and private, long distance applications. An 850 nanometer PMD was specified to achieve a 65-meter objectiveover multimode fiber using serial 850 nm transceivers.
Additionally, the task force selected two versions of the wide wave division multiplexing (WWDM) PMD, a 1310 nanometer version over single-mode fiber to travel a distance of 10km and a 1310 nanometer PMD to meet its 300-meter-over-installedmultimode- fiber objective.
Physical Layer (PHYs)
The LAN PHY and the WAN PHY will operate over common PMDs and, therefore, will support the same distances. These PHYs are distinguished solely by the Physical Encoding Sublayer (PCS). (See Figure 7.) The 10 Gigabit LAN PHY is intended to support existing Gigabit Ethernet applications at ten times the bandwidth with the most cost-effective solution. Over time, it is expected that the LAN PHY will be used in pure optical switching environments extending over all WAN distances. However, for compatibility with the existing WAN network, the 10 Gigabit Ethernet WAN PHY supports connections to existing and future installations of SONET/SDH (Synchronous Optical Network/ Synchronous Digital Hierarchy) circuit-switched telephony access equipment.
The WAN PHY differs from the LAN PHY by including a simplified SONET/SDH framer in the WAN Interface Sublayer (WIS). Because the line rate of SONET OC-192/ SDH STM-64 is within a few percent of 10 Gbps, it is relatively simple to implement a MAC that can operate with a LAN PHY at 10 Gbps or with a WAN PHY payload rate of approximately 9.29 Gbps. (See Figure 9.). Appendix III provides a more in depth look at the WAN PHY.
As the Internet transforms longstanding business models and global economies, Ethernet has withstood the test of time to become the most widely adopted networking technology in the world. Much of the world’s data transfer begins and ends with an Ethernet connection. Today, we are in the midst of an Ethernet renaissance spurred on by surging E-Business and the demand for low cost IP services that have opened the door to questioning traditional networking dogma. Service providers are looking for higher capacity solutions that simplify and reduce the total cost of network connectivity, thus permitting profitable service differentiation, while maintaining very high levels of reliability.