Optical Ethernet combines the flexibility and price performance of Ethernet with the reliability and scalability of optical systems.
By TONY RYBCZYNSKI
Nortel Networks
The convergence of enterprise networking on Internet Protocol (IP) and Optical Ethernet is about to make router networks much simpler, faster, and more reliable. Optical Ethernet combines the flexibility and price performance of Ethernet with the reliability and scalability of optical systems. With Optical Ethernet, the WAN looks more like an extension of the campus than the Internet, routing switches replace multiprotocol routers, and networks become less hierarchical.
Multi-protocol routers revisited
Multi-protocol routers are the workhorses of enterprise networking, but how does their value proposition change as the world moves to end-to-end IP and Ethernet? Routers route, and routing is a fundamental requirement of any packet network. Routing takes place at Layer 3--the level at which end-to-end addressing takes place. This addressing structure is hierarchical (much like telephone numbering), which makes routing tenable. Routing consists of two closely related functions: the act of determining routes to various destinations through routing protocols such as Open Shortest Path First (OSPF) and the act of forwarding packets to the next best hop (or hops in the case of multicast). Routers are required to provide routing between physical or logical LAN segments; within a given LAN, the broadcast nature of the LAN is leveraged to dynamically learn which IP addresses are locally reachable.
Routers also support traffic management functionality over the WAN with the dual (and somewhat conflicting) objectives of maximizing network utilization under various traffic and failure conditions, and meeting end user and application needs. These objectives are met through various queuing functions to ensure fair treatment of users and maximum aggregate throughput, and through various quality-of-service (QoS) mechanisms that provide unfair treatment of users and applications. Packet classification, shaping, and policing are some of the tools of the trade.
Router networks today present significant challenges to IT managers. This is largely driven by the heterogeneous nature of enterprise networking. Attracting, training, and retaining IT skills is an on-going concern. This heterogeneity is caused by multi-protocol operation, by multiple LAN technologies, and by the proliferation of WAN services.
It has been a multi-protocol world with enterprise networks required to support different protocols for different application environments: e.g., IBM's SNA for mainframe environments, IP for UNIX, IPX for Novell, and DECnet for legacy Digital Equipment (now Compaq) systems. Each of these had its own networking and routing protocols and idiosyncrasies (e.g., IPX is notoriously chatty).
It has been a multi-LAN technology world with enterprises having deployed Ethernet, token ring, FDDI (Fiber Data Distribution Interface), and ATM--and some sites having all of these. Routers not only had to support the physical LAN media which required a range of copper, coax, and fiber interfaces, but also had to support the Media Access Control (MAC) functionality specified for a specific type of LAN technology. In addition, they also supported higher level gateways to these LAN environments. For example, routers emulated Ethernet or token ring environments when interfacing to ATM campus backbones.
It has been a multi-WAN technology world. Routers encapsulate packets onto lower speed WAN services:
• Dedicated point-to-point circuits; e.g., running point-to-point protocol (PPP) over private lines.
• Virtual circuits; e.g., using multiprotocol encapsulation via RFC1490 over frame relay or RFC 1483 over ATM.
• Various VPN mechanisms over the Internet; e.g., using IPSec or Layer 2 transport protocol (L2TP).
• Circuit-switched connections; e.g., analog modems, ISDN.
It doesn't stop there. Routers also support protocols that allow aggregation of serial links for more scalable bandwidth, via mechanisms such as multilink PPP (over leased lines), multilink frame relay, and ATM Inverse Muxing. These mechanisms provide added resiliency and speeded recovery when individual links fail. Routers also provide WAN resiliency features. At medium and larger sites, multiple physical paths (in extreme cases over physically diverse access configurations, even from multiple carriers) are configured with dynamic routing provided by the router. At smaller sites, routers manage an on-demand backup via analog modems and ISDN. Routers also perform WAN data compression to use WAN links more efficiently. Using the Internet for site-to-site connectivity introduces yet more requirements in the area of IP virtual private network (VPN) tunneling support on the one hand, and firewalls on the other.
IP and Ethernet simplify your world
It is becoming a single protocol IP world. The industry is moving toward IP for everything, so the complexity of multi-protocol routing networking is decreasing dramatically. The reasons are numerous: IP is ubiquitous in enterprise networks and the Internet, more people understand IP than any other protocol, gateways for non-IP applications exist, and protocol stacks are readily available at both the IP and higher levels (e.g., TCP).
It is becoming a LAN technology Ethernet world. Ethernet has matured to become the LAN technology of choice with the best price/performance, with robust 100-plus Gbit/sec switching platforms and with link speeds heading to 10 Gbits/sec. There are compelling reasons to not only use Ethernet in new sites but to move to Ethernet as quickly as possible in existing sites.
It is becoming a simpler WAN world with emerging Ethernet MAN/WAN connectivity, combining the flexibility and price performance of Ethernet with the reliability and scalability of optical systems. WAN encapsulation (everything runs on Ethernet), WAN data compression (optics delivers scalable bandwidth), and configuring IP tunneling and firewalls (Virtual Private Ethernets are as secure as frame relay) are no longer relevant in an Ethernet WAN environment. The result is WAN interfaces that are just like campus links, including support of Ethernet-based link aggregation (through mechanisms such as split MultiLink Trunking).
So a simplifier, faster, and more reliable enterprise networking world is emerging with the convergence of Ethernet and IP. The key elements of this new world are QoS-enabled Ethernet switches in the wiring closets, IP and Ethernet-optimized routing switches in the campus cores, and private or managed Optical Ethernets across the MAN and WAN.
What does it mean for IT?
Enterprises need to complete their evolution toward an Ethernet-only switched LAN and IP-only routed environments. Many enterprises (particularly in the high-tech, utility, and education segments) have done this, leveraging intelligent Layer 2 switches in the wiring closets and routing switches in the campus backbones.
With end-to-end Optical Ethernet in the LAN/MAN/WAN, routing functionality is delivered through IP and Ethernet-optimized routing switches at the core of a logically extended metropolitan campus network with smaller metro sites being logical wiring closets within this network. The value proposition includes a substantial improvement in the total cost of ownership of enterprise networks, data distribution, and application processing, opening up new opportunities for outsourcing and freeing up budgets for strategic investments in e-business initiatives such multi-channel customer care and supply chain management. In the transition period, legacy routers serve as multiprotocol gateways encapsulating all traffic onto IP, non-Ethernet LAN gateways, and as legacy WAN gateways to virtual and physical circuit networks.
IT networking managers are on a treadmill of continuous upgrades, configuration and management complexity, and steep learning curves associated with today's enterprise networks. But there is a better way. Routing in an IP and Ethernet world can provide much higher price/performance, can be simpler to configure and manage, and can be more reliable through integration with optics. This, in turn, can open up new opportunities right across IT by allowing the rethinking of application and storage deployment and significantly improving IT user and application performance.
Tony Rybczynski is director of strategic enterprise technologies at Nortel Networks. He has over 30 years experience in the application of packet network technology.
