CommunicAsia2005

June 17, 2005
Optimising Ethernet traffic over SDH/SONET infrastructure

Motti Holler

ISRAEL -- Over the past few years carriers and service providers have invested heavily in new packet-switched backbone networks and more conventional SDH/SONET and ATM-based transport networks. Certainly, the rationale for building out disparate, and in some cases parallel, networks was sound at the time: Immediate support for traditional leased line services, voice and DSL required circuit switched or cell-based backbones with guaranteed quality of service (QoS). An IP-centric future, moreover, required implementation of IP/MPLS cores fed by a metro Ethernet transport layer.

However, the reality on the ground has changed. Business customers are much more demanding. Their networks are more complex; their applications are more bandwidth hungry; their purse strings even more tightly drawn. Fierce competition, on the other hand, is forcing carriers to become even more creative in their service delivery and pricing options. The bottom line: Customers want their service providers to deliver any service over any infrastructure.

Enabling customers to connect their LANs over SDH/SONET networks so that they utilise and pay only for the bandwidth they require is one of the major challenges service providers face today. This is due to the fact that SDH/SONET networks are optimised for digital voice, not for data. The problem is particularly acute when there is a need for existing SDH/SONET networks to transport LAN traffic at various transport rates that are not inherent to SDH/SONET.

Virtual concatenation
By provisioning additional bandwidth upon request at a low granularity of 2 or 1.5Mbps, however, SDH/SONET operators are able to offer customers next-generation services over networks, without any need for forklift upgrades. Utilising new virtual concatenation technology at the low granularity of VC-12 (2Mbps) or VT1.5 (1.5Mbps) allows multiplexing Ethernet streams in such a way that the SDH/SONET pipeline is optimised for Ethernet traffic.

RAD's FCD-155 Ethernet-over-SDH/SONET CLE (customer located equipment) uses virtual concatenation to map Ethernet traffic into SDH/SONET virtual containers in multiple increments of nx2Mbps (VC12) or nx1.5Mbps (VT1.5), up to full wire-speed Fast Ethernet. In addition to delivering Ethernet traffic across the SDH/SONET network, the FCD-155 transports additional TDM channels, up to a total of four E1/T1 lines, a single E3/T3 or a sub-STM-1 line. Virtual concatenation is just one example of the new technologies being introduced to leverage existing SDH/SONET transport infrastructure to deliver Ethernet services.

RAD Data Communications has introduced a unique set of Ethernet access solutions for service provisioning and carrier backhaul applications over low and high-speed SDH/SONET and PDH circuits. In addition to the FCD-155 Ethernet-over-SDH/SONET CLE, these products include Gigabit Ethernet over SDH/SONET and PDH converters, Ethernet-over SDH/SONET gateways, an Ethernet inverse multiplexer, and STM-1/OC-3 high capacity terminal multiplexers. These devices offer service providers and end users the ability to transport Ethernet services over any data rate -- from fractional E1/T1 to full E1/T1, up to nxE1/T1 and STM-1. The benefit is that the industry now has a single source supplier for a range of carrier and campus applications.

Gigabit Ethernet over SDH/SONET
RAD's high-speed RIC-155GE is a cost-competitive Gigabit Ethernet-over-STM-1 gateway, designed to efficiently deliver GbE traffic over SDH and PDH networks. A second converter, the RIC-155A, features two Fast Ethernet ports to dynamically convert two different flows of Fast Ethernet traffic over an STM-1 link. Both devices are designed to better utilise the SDH interface's full payload. This is an especially attractive alternative for ISPs and carrier backhaul applications, or for carriers seeking new ways to provide high bandwidth Ethernet services to customers. The RIC-155 GE will also support Jumbo Frames of up to 9,000 bytes for higher network efficiency of large file transfers and video streams.

Seamless LAN connectivity between remote locations
Egate is RAD's new family of affordable Ethernet-over-SDH/SONET gateways, which enable transparent, seamless LAN connectivity between remote locations over existing E1/T1 or fractional E1/T1 physical ports. Egate allows service providers to offer transparent Layer 2 services (VPNs and Internet access, for example) over E1/T1 lines, while reducing equipment costs and simplifying network maintenance. This provides a solution to service providers that need to map Ethernet over E1/T1 circuits and then hand the Ethernet traffic to the packet-switched backbone. These include ISPs, regional service providers and competitive city carriers, which typically transport their customers' Layer 2 LANs over an incumbent's SDH infrastructure. Major corporations that maintain their own networks can also benefit from this solution, since it will allow them to connect remote offices that are not currently reached due to an absence of Next Generation infrastructure in the field.

The Egate-20 has up to four 10/100BaseT ports connecting to the packet network and eight E1/T1 ports connecting remote subscribers to the service. The Egate-100 features Gigabit Ethernet ports on the network side and OC-3/STM-1 ports on the subscriber side. Ports can be configured to be clear channel (G.703) or channelised (G.703 and G.704), supporting up to 256 logical connections (on the Egate-20) and 512 (on the Egate-100). Both Egate devices map Ethernet traffic over E1/T1 or timeslot bundles to specific VLANs, interconnecting remote subscribers to the packet network. The VLAN stacking option transports user traffic transparently, keeping all the user LAN settings intact.

Ethernet over low-speed networks
Much of the access to SDH/SONET networks, however, is over lower speed PDH tributaries. Few vendors offer carrier-class solutions for transporting Ethernet over fractional E1, E1/T1 or n x E1/T1. RAD's introduction of its new RICi-E1/T1 and RICi-E3/T3 Ethernet-to-PDH managed converters, therefore, is an important milestone, because they allow E1/T1 and E3/T3 lines with PDH interfaces to be fully utilised in transporting enterprise LAN traffic, alternative carrier services and cellular base station backhauling.

The state-of-the-art solution for transporting Ethernet services or connecting enterprise LANs at different locations over different rates PDH links usually requires the deployment of expensive WAN routers. Apart from the high capital expenses, however, this solution also obligates ongoing operating expenses for provisioning and upkeep. In contrast, RAD's new RICi devices are low cost and simple to install. Because they transport traffic transparently, irrespective of protocol, no changes in LAN configuration are required. This simplifies network planning and allows the different LANs connected to the network to function as if they are part of one, large single LAN. In addition, SNMP management support allows simple maintenance and monitoring of the entire network.

Intelligent inverse multiplexer
RAD's IMXi-4 intelligent inverse multiplexer transports LAN or high-speed data traffic across multiple, low cost TDM E1/T1 or SHDSL lines. By splitting traffic onto four E1/T1 or SHDSL links, the product enables transparent LAN services (TLS) or any other high-speed data stream to be transmitted over wide area networks. The IMXi-4 transfers Ethernet packets transparently, enabling service providers to use their next generation equipment in a TDM environment. Wireless providers, moreover, can plug their IP-based equipment into the device's Ethernet interface to connect to the Ethernet-based central site over the TDM network.

STM-1/OC-3 high capacity terminal multiplexers
RAD's Optimux-1551 and Optimux-1553 terminal multiplexers deliver traditional PDH services over existing SDH/SONET networks. They combine the high capacity associated with SDH/SONET add-drop multiplexers (ADMs) with the simplicity and low cost of a terminal multiplexer, significantly reducing operating and capital expenses (Opex and Capex). The 2U high Optimux-1551 provides connectivity for 63 E1 or 84 T1 lines, and the 1U high Optimux-1553 provides connectivity for three E3 or three T3 lines. The products comply with all SDH/SONET standards, and interface with existing SDH/SONET backbones through a single or redundant STM-1, OC-3 or STS-3 interface.

Designed for the rigorous requirements of carriers and service providers, the Optimux-1551 and Optimux-1553 offer a high level of reliability and manageability. Hardware redundancy is designed into the system without the need for custom Y-cables or external devices. This 1+1 redundancy is provided for all user interfaces through an optional, second, hotswappable multiplexer card. 1+1 redundancy is also available for the STM-1/OC-3 main link (uni-directional APS/MSP) and power supply modules. This reliable platform maximizes uptime for mission-critical applications.

Higher revenues at lower cost
The Optimux-155x devices allow service providers to extend their network towards remote customers, thereby enlarging customer reach and increasing revenues, without the expenses associated with deploying high-end ADMs, which add unnecessary cost and complexity in 'point to network' connections. Compared to the alternative of deploying PDH multiplexers at customer sites, the Optimux-155x devices interface directly with the existing SDH/SONET TDM infrastructures and consolidate traffic at the edge of the network. This enables service providers to save the cost of fiber deployment and of multiple ports on the ADM.

Differentiation of service for increased revenues
A unique feature of the Optimux-1551 is its optional 63 E1 redundancy module, which provides protection for the tributary channels, as is available for the uplink and the system. Since redundancy can be configured per individual E1/T1 tributary channel, a differential priority level can be assigned, so that, for example, link switching will be triggered only by failure of a higher priority line. Conversely, high priority channels will not be disrupted by failure of an individual low priority channel. This higher service level can be offered to customers at an added cost for increased revenue.

The Optimux-1553 is ideal for carriers or alternative service providers that need to fan out lower rate services from SDH/SONET backbones. Carriers can utilise their fiber optic lines much more efficiently by teaming the Optimux-1553 with a DS1 to DS3 mux such as the Optimux-T3, located at a small POP or customer premises to aggregate several individual E1/T1 lines and data onto a single E3/T3 line for transport to the regional SDH/SONET network. Additionally, higher rate E3/T3 services can also be offered directly to the customer. By combining the high capacity of SONET/SDH ADMs with the simplicity, low cost and small form factor of a terminal multiplexer, Optimux-1553 can dramatically reduce capital and operating expenditures.

Easy to install, maintain and operate, the Optimux-155x products require no training or expertise. As completely plug-and-play units, the products allow carriers to extend the benefits of SDH/SONET networks toward the customer premises or central office in a quick and inexpensive manner. Optimux-155x products are especially suitable for extending SDH/SONET network services toward remote and suburban locations such as industrial areas and business parks. An ideal choice for delivering multiple E1/T1 services, Optimux-155x units can be deployed in point-to-point applications, connecting two sites over fiber or copper to distances of up to 80km (50 miles).

A service provider can also use the Optimux-1551 and the FCD-155 to deliver E1/T1 services and Internet access to multiple customers, and the Optimux-1553 to provide E3/T3 lines to large enterprises with higher bandwidth requirements. Together with the Optimux-XLE1 (for E3) or the Optimux-T3/T3L (for T3), the Optimux-1553 can be used to combine E1/T1 and E3/T3 services over a single STM-1/OC-3 line.

(The author is sales director, India, RAD Data Communications)