CSS: A Simple and Efficient Network Solution

　　Foreword:

　　After being developed for decades, Ethernet technology, which is flexible and simple to deploy, has become the primary local area network technology. All-in-IP is now a current trend in the communications industry.

　　As the network scale continues to expand and more applications emerge, the Ethernet is becoming more complex as it evolves from a bus topology to a Mesh topology and from a small-scale single plane network to a large-scale hierarchical network. The industry is facing a great challenge. How does it ensure efficient packet forwarding while maintaining network simplicity? Various technologies and standards have been developed to achieve this goal; the Cluster Switch System (CSS) is one of these technologies. CSS virtualizes multiple switches into one logical switch to simplify the network architecture and improve network efficiency.

　　Conflict Between Simplicity and Efficiency

　　With the increasing popularity of the Internet, the Ethernet has been gaining more and more attention, quickly earning worldwide recognition and becoming an inevitable choice because of its simplicity, flexibility, and easy expandability.

　　However, with the growth of the Ethernet, many issues arise. The first issue is how to improve forwarding performance without making the network more complex. Simplicity and efficiency contradict one another.

　　1. Simple but inefficient at the initial stage: Initially, the Ethernet uses a bus network topology and the carrier sense technology to control packet forwarding. Although the network is simply constructed, its efficiency is low. Only one host at a time is permitted to send packets.

　　2. Highly efficient but complex in later stages: When the network scale expands, the Ethernet's low forwarding performance cannot meet the needs of increasing numbers of customers. Ethernet switches have been developed, and full mesh topology is now being used to improve forwarding efficiency and enhance network reliability. Although network performance has improved, a new problem emerges: network loops. To prevent this issue, the Spanning Tree Protocol (STP) has been developed. STP prevents network loops by blocking links, but this method deteriorates network performance. Another protocol, the Multiple Spanning Tree Protocol (MSTP), has been developed to overcome this defect. MSTP ensures high network performance, but it is difficult to deploy and maintain. When MPLS is deployed, the construction of the Ethernet is no longer simple.

　　Network designers are facing a dilemma: If the network is simple, its efficiency is low. If the network is highly efficient, it is complex. Is there a technology that can improve network forwarding performance while keeping the network construction simple?

　　CSS: A Simple and Efficient Network Solution

　　CSS virtualizes multiple switches into a single, high-performing logical switch.

　　CSS offers the following features:

　　1. Many-to-one virtualization: CSS virtualizes multiple switches into one logical switch that has a unified control plane and provides unified management.

　　2. Unified forwarding plane: CSS uses a unified forwarding plane that shares and synchronizes forwarding information.

　　3. Inter-chassis link aggregation: CSS aggregates links between member switches to one trunk link.

　　Figure 1 Physical and logical form of a CSS and a CSS network

　　Figure 1 shows the physical and logical form of a CSS and a CSS network. CSS virtualizes multiple switches into one logical device and supports inter-chassis link aggregation. CSS simplifies network topology and greatly improves network performance by offering the following features:

　　1. Simplified operation and maintenance: A CSS functions as one logical switch, simplifying operation and maintenance and reducing OPEX.

　　2. High reliability: When one switch in a CSS fails, another switch in the CSS takes over the control and forwarding of packets to prevent services from being influenced by single-point failures.

　　3. Loop-free network: CSS supports inter-chassis link aggregation to prevent loops. Therefore, the deployment of complicated protocols, such as MSTP, is unnecessary.

　　4. Load balancing: CSS supports equal cost multiple path (ECMP) across switches, making full use of network links and bandwidths.

　　CSS simplifies network architecture and improves forwarding performance while maintaining network functions. CSS has all the functions of physical switches in the cluster but provides better performance, gaining wide customer recognition and becoming the preferred solution for simple and efficient network deployment.

　　CSS Evolution

　　CSS has undergone two development stages.

　　At the early stage, switches, which are interconnected by dedicated cables, set up a CSS using dedicated line cards. Because the dedicated line cards do not occupy the slots for service line cards, they do not deteriorate the system’s forwarding performance. Meanwhile, the interfaces on dedicated line cards have a higher transmission rate than the interfaces on service line cards, which improves the bandwidth for CSS interconnection.

　　In the later stages, physical switches, which are interconnected by standard cables, establish a CSS using service line cards. Although several service interfaces are used for this interconnection, this mode has a slight impact on the forwarding performance of the entire system because the forwarding capability of the switches is greatly improved. The use of standard service interfaces and standard cables allows switches that are located a great distance from one another to form a cluster, making CSS deployment flexible. Moreover, the interconnected interfaces support link aggregation, which allows for the flexible expansion of interconnection bandwidth.

　　Huawei Next-Generation Switches Construct High-Performance CSS

　　Huawei next-generation CE12800 switches support CSS technology and allow for flexible and efficient CSS deployment in the following ways:

　　1. Flexible combination of models: Different CE12800 models can form a CSS. For example, a CE12812 and a CE12808 can form a CSS.

　　2. Various available interface bandwidth: The CSS interconnection interfaces can be 10GE or 40GE interfaces. In the future, these will evolve into100GE interfaces.

　　3. High-speed interconnection: CSS allows a maximum of 16 interfaces to be bundled into a trunk interface, providing 640 Gbit/s of unidirectional forwarding bandwidth.

　　4. Long-distance deployment: CSS uses service line cards for interconnection, and CSS switches are connected by standard optical fibers. These features allow switches that are located a great distance from each other to form a cluster.

　　CE12800 switches provide superior networking capabilities because they have line cards with high-density interfaces and high levels of forwarding performance. Figure 2 and 3 illustrate two possible configurations on networks with CE12800 switches.

　　Figure 2 High-density 10GE access provided by CE12800 CSS

　　Figure 2 shows an application of CE12800 CSS. Two CE12812s form a CSS and connect to downstream CE6800s through 40GE interfaces. The CE6800s are configured in stacks. The CE12800s and CE6800s establish a full mesh topology and are interconnected through trunk links. The entire network provides a maximum of 5,805 x 10GE interfaces for downstream devices.

　　Figure 3 High-density GE access provided by CE12800 CSS

　　Figure 3 shows an application of high-density GE access provided by CE12800s and CE5800s. Two CE12812s form a CSS and connect to downstream CE5800s through 10GE interfaces. The CE5800s are configured in stacks. The entire network provides a maximum of 25,344 x GE interfaces for downstream devices.

　　Because CE12800 switches offer high levels of forwarding performance, the networking capability of CSS formed by CE12800s is greatly improved, which allows for deployment on networks of different scales.

　　Summary

　　After years of development, CSS has gained acceptance by more and more customers. CSS simplifies network architecture and improves network performance. CSS deployment is simple, and CSS technology does not deteriorate network functions. Because CSS is so simple to deploy, customers are not required to learn new technologies, and their operating costs are reduced. CSS will definitely offer wider applications as its development continues.