3. MAN Access Network
3.4 Ethernet Challenges in Network Operations and Management
Although Gigabit Ethernet offers many unique capabilities and advantages which can satisfy business needs in a metropolitan network, there are challenging issues that need to be resolved with respect to inter-working with or replacing the existing SONET/SDH and ATM networks.
3.4.1 Can Gigabit Ethernet provide the equivalent QoS (quality of service) that is currently provided by SONET/SDH and ATM?
Providing quality service that meets customers’ requirements is a fundamental concern of telecom carriers. Enterprise customers demand guaranteed quality of service to ensure reliable business operations. Therefore, if telecom carriers were to apply Gigabit Ethernet technology to achieve bandwidth scalability and fast provisioning time for their business customers, it would be critical to maintain the existing level of QoS.
Unlike ATM, Gigabit Ethernet does not have admission control capability to regulate individual user’s traffic stream. Gigabit Ethernet can only rely on “policy-based” QoS to manage the aggregated traffic. The policy-based QoS always reserves additional bandwidth capacity (i.e., over engineering the bandwidth requirement) sufficient to meet the QoS objective at peak hour traffic demand. Since Gigabit Ethernet equipment has a cost advantage over SONET/SDH and ATM equipment, “over engineering” is a small price to pay to reap the benefit of bandwidth flexibility. In the future, the QoS capability may be provided at the IP layer (such as IP/MPLS protocol) once the IP QoS capability becomes mature.
3.4.2 Can Gigabit Ethernet provide the network performance monitoring capability that is currently provided by SONET/SDH and ATM?
There are several overhead bytes (e.g., the B1 byte) in the current SONET/SDH frame format designed for monitoring the network transmission performance (GR-253, 2000). By analyzing the network performance monitoring information, carriers can detect network degradation, localize faults, and take proper maintenance actions before service-affecting failures take place. In contrast, however, in the Gigabit Ethernet frame format there exists no overhead byte for performance monitoring. Gigabit Ethernet can only monitor whether the incoming packets are in error. Once an error occurs, Gigabit Ethernet will report error messages to the network management system through the standard SNMP interface. The error
reporting mechanism is much slower compared to the performance monitoring capability of SONET/SDH or ATM technologies.
The IEEE 802.3 standards committee is in the process of defining a WAN PHY layer protocol for the transmission of Gigabit Ethernet traffic via the existing SONET/SDH equipment. Having Gigabit Ethernet transported in the SONET/SDH payloads can leverage the existing performance monitoring capability of SONET/SDH equipment. This WAN PHY layer protocol provides a foundation for telecom carriers to monitor the transmission performance of Gigabit Ethernet (Information Technology, 2000).
The drawback of the lack of performance monitoring capability of Gigabit Ethernet is becoming less critical. Because most transmission networks are fiber-based with high performance and reliability, the majority of failures are event-driven (e.g., fiber cut) rather then caused by equipment or facility degradation. The existence of performance monitoring capability may not be as critical as in the past.
3.4.3 Can Gigabit Ethernet provide network protection switching and fault isolation capabilities that are currently provided by SONET/SDH and ATM?
SONET/SDH frame structure has signaling overhead bytes (e.g., the K1 and K2 bytes) that can be used to provide protection-switching functions within a 50ms interval (GR-253, 2000).
Furthermore, there are overhead bytes in the SONET/SDH format to provide fault isolation.
Gigabit Ethernet has no signaling capability to provide any protection switching or fault isolation functions. Alarms will be reported through the SNMP interface to the appropriate network management center. Although the Ethernet aggregate link capability can also provide a similar protection function within 1 second, it is incompatible with the 50 ms switching time of SONET/SDH. The WAN PHY layer protocol can leverage the protection switching and fault isolation functions built in the SONET/SDH frame format.
3.4.4 How can Gigabit Ethernet scale up in large carrier network?
Because Ethernet is traditionally used as a LAN in a private enterprise environment, the scale and size of any single Ethernet network is much smaller compared to a public telecom network. However, there will be multiple Gigabit Ethernets complementing the functions of SONET/SDH systems. The SNMP network management interface can be scaled up to manage clusters of Gigabit Ethernets. An end-to-end Ethernet connection (LAN, MAN to WAN) has the benefit of a homogenous layer-2 network management system that can simplify the operations management of a telecom network.
Ethernet technology has evolved into multi-gigabit bandwidth with applications extending from LAN, MAN, and even to WAN. Telecom carriers are faced with fast growing Internet data traffic that exceeds traditional voice traffic. Gigabit Ethernet technology holds the promise to relieve the critical bandwidth bottleneck in the access network.
The simple protocol of Ethernet can offer telecom carriers many advantages in terms of simplified network architecture and substantial equipment cost reduction. The dynamic bandwidth allocation flexibility makes many new business applications possible. This, in turn, will create new revenue opportunities while reducing capital investments for telecom carriers.
Compared with existing SONET/SDH and ATM infrastructure, Ethernet technology has some weaknesses in the areas of network
3.5 Summary
Ethernet technology has evolved into multi-gigabit bandwidth with applications extending from LAN, MAN, and even to WAN. Telecom carriers are faced with fast growing Internet data traffic that exceeds traditional voice traffic. Gigabit Ethernet technology holds the promise to relieve the critical bandwidth bottleneck in the access network.
The simple protocol of Ethernet can offer telecom carriers many advantages in terms of simplified network architecture and substantial equipment cost reduction. The dynamic
bandwidth allocation flexibility makes many new business applications possible. This, in turn, will create new revenue opportunities while reducing capital investments for telecom carriers.
Compared with existing SONET/SDH and ATM infrastructure, Ethernet technology has some weaknesses in the areas of network operations and management. As Gigabit Ethernet can be transported over the existing SONET/SDH and ATM infrastructure, the characteristics of both technologies can complement each other. For applications less concerned about QoS, the Gigabit Ethernet is already an ideal solution. As Ethernet technology and its communications protocols continue to evolve, its potential and impact as a broadband end-to-end architecture is emerging. When and how to leverage Gigabit Ethernet technology’s capabilities will remain a business challenge for telecom carriers.
In order to help telecom carriers to quantitatively select the best MAN access technology, we have employed the Fuzzy MCDM (Multi-Criteria Decision Making) method in the next section to further study the MAN access technology issue.