By Shaun McFallVP of MarketingHarris Stratex Networks Inc.

Telecom leaders are finally realiz-ing the benefits of carrier Ethernet globally, especially in many Asian economies, as network operators migrate to multiservice microwave systems to support backhaul and fiber extension services.

The dividends of implement-ing carrier-class Ethernet are clearEthernet is highly reliable, easy to implement and use, and highly interoperable. It is also eas-ily configured and provisioned. Ethernet carries voice, data and multimedia traffic, which are now vital as applications con-verge in business, residential and mobile market sectors. For mobile operators, this results in reduced backhaul cost and the ability to serve higher-speed backhaul requirements, provid-ing more bandwidth and higher throughput to serve multimedia applications.

Ethernet is far more scalable than SONET, ATM or frame relay technologies. Moreover, there are good reasons for moving to Ethernet. The technology is also attractive for providers moving toward IP- and packet-based networks. Many of these service providers are already deploying Ethernet in the access and ag-gregation parts of their network to serve IPTV, storage and similar applications as efficiently as possible.

Carrier Ethernet is now playing a significant new role in metro, edge and core networks as part of a mixed-technology solu-tion, as Asias mobile operators increase their focus on HSDPA technologies. Common hardware platforms are emergingthey use multiple access and trunking products to address standard plesiochronous digital hierarchy (PDH), Super PDH, SONET/syn-

chronous digital hierarchy (SDH) and Ethernet.

This doesnt imply that the move to Ethernet is simple and directintegration and opera-tional challenges remain, includ-ing operations, administration and maintenance. Furthermore, to avoid cost-inefficient imple-mentations, the methods used to transport Ethernet data must also be considered.

Operators and vendors have to adapt Ethernet, long a best-ef-fort transport technology, to pro-vide the carrier-class performance they have experienced with time division multiplex (TDM) technologies such as PDH and SDH/SONET. The Metro Ethernet Forum and other organizations are addressing these challenges through new initiatives with the help of vendors and operators.

Ideal setupAn ideal carrier-class wireless transmission equipment supports various schemes to protect traffic

against link or network impairment. The equipment must be pro-tected against device failure using monitored hot-standby terminals with redundant transmitters and receivers. The online transceiver is protected with a redundant set to automatically switch online in case of failure. Space and frequency diversity, in accord with other mechanisms, protect against link failure or disruption caused by path impairment.

Another more cost-effective network-protection scheme is self-healing switching of traf-fic around a point of failure, by switching traffic through another route in the network. This pro-tection can take the form of a simple ring, or the operator can opt for a more complex mesh architecture.

Typically, Ethernet ring and mesh network protection is im-plemented via Ethernet switch-es using Rapid Spanning Tree Protocol (RSTP). However, the switching or convergence times

supported by this method are unpredictable and can exceed several seconds, which does not meet the carrier-class standards demanded by network operators. The ideal GbE switch solution supports advanced RSTP through a Resilient Wireless Packet Ring capability that can deliver car-rier-grade convergence times for Ethernet ring and mesh networks of less than 100ms.

Carrier Ethernet meets the throughput, speed, latency and reliability metrics required for todays high-bandwidth services. Throughput is a critical metric, since it defines the maximum amount of data that can be trans-ported over an Ethernet connec-tion or link. A microwave link has a total data capacity determined by the bandwidth and modula-tion setting applied to its modem. The amount available for payload traffic is the Ethernet throughput; it is equal to total data capacity minus the overhead for auxiliary data channels, FEC and network management, including manage-ment telemetry. For wireless sys-tems operating on the licensed bands, this throughput is dedi-cated or guaranteed. If the link is installed correctly, variable path conditions or interference dont affect the link throughput.

Transport technology is also critical. A simple mapping of data into the framing of PDH (NxE1/DS1) or SDH/SONET ra-dio systems will not workthis would waste bandwidth, and increase jitter and delay. The best solution doesnt distinguish between Ethernet and TDM data, but provides native support for both kindswith data mapped into byte-wide frames that pro-vide efficient and flexible wireless transport. When configured for Ethernet data and/or TDM, the configured capacity is fully avail-able. An optimal solution should be configurable for full-duplex

Figure 1: The optimal wireless carrier Ethernet transport solution incorporates link aggregation inside the radio, using an embedded L2 Ethernet switch.

EE Times-Asia | October 1-15, 2007 | eetasia.com

High-bandwidth services via carrier Ethernet

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connection capacities of up to 300Mbps or more on a single wireless link.

Latencydefined for wireless Ethernet as the delay that packets encounter as they move through a network of wireless links, rout-ers and other equipment from source to destinationis an-other key factor. Low latency is particularly important for voice callswhether traditional or VoIPand should not exceed 150ms across the network. One-way latency for live video should be under 1s. Carrier Ethernet solutions are now equipped to meet the latency requirements of emerging applications. Wire-less carrier Ethernet transport solutions support one-way link latency well below 50s for high-capacity applications and typi-cally less than 1ms per hop.

Transport methodsTodays wireless transmission radios must be able to support various transport methods (in-cluding Ethernet, STM1/OC3, E3/DS3 or E1/DS1) all using a single hardware/software platform and regardless of whether the traffic is uniform or mixed. The ability to alter throughput and payload mix and to select the RF channel bandwidth saves on upgrade costs. Moreover, it eliminates the need for many of the equipment change-outs required in the gen-erations before software-configu-rable radios. This enables users to mix and match network services and re-scale capacity as require-ments expand or change.

Redundancy is another key requirement. GbE provides ul-trahigh-speed links and link ag-gregation with cost-efficient redundancy. Link aggregation is used to achieve extremely high throughputs by combining the capacity of two or more physical links on a single virtual connec-tion. The aggregated capacity is the sum of the individual link capacities and is accessed on a single optical or electrical GbE interface. Implementing a single interface eliminates the need for

expensive external switches. If one link in the aggregated group fails, the data from the failed ra-dio is restored automatically on remaining links.

The optimal wireless carrier Ethernet transport solution incor-porates link aggregation inside the radio, using an embedded L2 Ethernet switch. This enables the aggregation of two, three or four physical links. Two or more 300Mbps links can be aggregated to provide 600Mbps, 900Mbps or 1.2Gbps throughput. Optional cross-polar interference cancel-lation can then be used to maxi-mize channel efficiency.

Channel eff iciency is the ability of a radio to send larger amounts of data over a single radio channel, compared with other radios in its class. Radio links achieve high efficiencies by using high modulation rates with an efficient modem design that can squeeze more payload into a given bandwidth and deliver bigger throughputs compared with less-efficient modems.

This method, however, has a trade-off. As modulation rates go up, system gain (a measure

of the usable signal that reaches a receiver from a transmitter) is reduced, and maximum hop distances are lowered. As a result, an efficient and flexible solution should offer the network op-erator two throughput choices: a system optimized for frequency efficiency or a system optimized for performance over longer path distances.

Ethernets proven QoS and integrated traffic-management capabilities are also essential for wireless transport solutions as long as they can be implemented without costly external switching devices for QoS or performance monitoring capabilities.

Radio systems have a fixed and finite bandwidth. Thus, they must be able to manage peak traffic flows by incorporating an embedded L2 switch to support industry-standard QoS proto-cols, enabling operators to seg-regate and prioritize Ethernet traffic based on service levels or traffic type for voice, data and video applications. A switch can also support remote monitoring transmission statistics to enable advanced troubleshooting and

packet network optimization.The most advanced wire-

less carrier Ethernet transport solutions incorporate multiport, wire-speed, Fast Ethernet or GbE L2 switches. QoS features include port priority, priority mapping for 802.1p/DiffServ and virtual LAN tagging including QinQ. Advanced remote network moni-toring diagnostics include data dashboards, and comprehensive remote monitoring stats per port and channel.

To maximize the use of Eth-ernet and to support efficient delivery of large amounts of data, wireless carrier Ethernet solutions should support jumbo frames greater than the standard 1,518/1,522bytes. Core network devices can typically handle more than 9,000byte frames. Edge network devices may sup-port smaller-sized jumbo frames. Currently, most major network operators require support for jumbo frames up to 4,000bytes. A 10/100/1,000Base-T/Lx GbE switch enables frame sizes from 64bytes to 9,600bytes, support-ing traffic at the network core or edge.

Figure 2: The ideal GbE switch solution supports advanced RSTP through RWPR capability, with the ability to deliver carrier-grade convergence times for Ethernet ring and mesh networks.

eetasia.com | October 1-15, 2007 | EE Times-Asia

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