High Speed LAN Technology

High speed is a relative concept, faster than fast is high-speed. Therefore, based on the current local area network (LAN) using Fast Ethernet is 100M, transmission rate is greater than 100M can be considered a high-speed LAN. The technologies that have been used in this regard are gigabit Ethernet and ATM, which are being tested with Gigabit Ethernet. Because Gigabit Ethernet has the advantages of low cost, good interconnection and many supporting manufacturers, it has become the mainstream technology of high-speed local area network.

The technology of constructing high-speed LAN

Wiring Technology

Most of the currently installed network cabling is unshielded twisted pair, the standard is generally Eia/tia and ISO published "Super Five" standard (of course, the earliest wiring is not satisfied). These performance standards can meet the requirements of Gigabit Ethernet and asynchronous transfer mode with speeds above 1.2Gbps. The predetermined six-class cabling frequency limit is 200MHz, so it is hard to say how high the future coding system will be at 200MHz. Therefore, in the LAN construction, the data rate is not the decisive factor of the steering fiber. (Computer science)

The cost comparison also shows that the unshielded twisted pair continues to be the main reason for media selection in the horizontal channel connected to the workstation. Clearly, the cost of fibre to desktop is much higher than that of unshielded twisted-pair wires. In general, the cost of passive parts in the former is more than three times times that of the latter, and if the cost of an active device, such as a hub and network interface card (NIC), is added, the cost variance is further increased.

However, the distance limit is the inevitable choice of the floor connection and the interconnection of the park. In addition, the explosive growth in bandwidth requirements requires that network cabling be considered for future smoothing upgrades. Therefore, in the structured wiring, because the backbone installation conditions are generally very difficult, network planners must consider the use of the highest capacity of the cable, in the campus network construction, the general requirements of fiber to the community, fiber to the building.

On the other hand, the cost of fiber cabling is dropping significantly. This makes multimode fiber, Single-mode fiber has a high cost performance. Composite cables are now being installed in many buildings, using multimode fiber and single-mode fiber. This represents a new trend of development and is well worth the reference.

Link Layer Technology

Gigabit Ethernet can provide 1Gbps of communication bandwidth, and has the simplicity of Ethernet. It uses the same CSMA/CD protocol, the same frame format and the same frame length, and also supports Full-duplex and EtherChannel. For a vast network of users, this means that existing investments can be extended to gigabit Ethernet at a reasonable initial cost. In this way, gigabit Ethernet on the basis of the current Ethernet can be smooth transition, comprehensive balance of the existing endpoint workstation, management tools and training base and other factors, resulting in a very low overall cost, is currently the preferred technology in the LAN construction.

The physical layer of Gigabit Ethernet, like Ethernet and Fast Ethernet, defines only the physical layer and the media access control layer. On the implementation, the physical layer is the key component of Gigabit Ethernet, three kinds of transmission media are defined in ieee802.3z: multimode fiber, Single-mode fiber, coaxial cable. IEEE802.3AB is defined as a unshielded twisted-pair-wire medium. In addition to the above several transmission media, there is a multi-vendor definition of the standard 1000BASE-LH, it is also a optical fiber standard, transmission distance of up to 100 kilometers. Another feature of the Gigabit Ethernet physical layer is the use of 8B/10B encoding, which is the same as Fibre Channel technology (Fiber Channel), with the same benefits that network device vendors can use existing 8B/10B encoding/decoding chips, which will undoubtedly shorten the product development cycle, and can reduce costs.

Multi-layer switching technology

The exchange technology can be divided into the second layer exchange and multilayer exchange, but strictly speaking, the exchange means the connection between the source and the destination address, any technology above the second level can not be said to be the exchange technology. Load balancing has largely replaced the fourth-tier exchange term, just as the term "cognitive" has largely replaced the seventh-tier exchange.

The second layer Exchange is the exchange of the second layer of OSI or the MAC layer. This is our usual switch, technically very mature, it works on the second layer of the OSI 7-layer model, the data link layer, and the exchange is based on the MAC address.

The third layer Exchange, or network layer Exchange, is in the third layer of the OSI protocol, which provides higher level services, such as routing functions. Traditionally, routers are interconnected by software, but routers are expensive and slow to transmit, becoming a bottleneck in the network. Third-tier exchange is the use of wire-speed switching technology to integrate routing functions into the switch, which is called a routing switch or a third-tier switch. The third layer Exchange can realize the line speed exchange at each network level, the performance has greatly improved. At the same time, it retains the network topology and services on the third tier. These structures and services have great advantages in terms of network segmentation, security, manageability, and suppression of broadcasts. The goal of the third tier switch is to replace the existing router, which provides communication of information between subnets, increasing the speed of communication from hundreds of packets per second to millions of packets per second. The third tier exchange is designed to forward multiple protocols at high speed, or to provide firewalls to protect network resources or to achieve bandwidth reservation. The LAN backbone switch will be the third tier switch.

Layer Fourth Exchange technology utilizes the information in the third and fourth layer headers to identify the application data flow session. With this information, layer fourth switches can make intelligent decisions about where to forward the session transport stream. As a result of this, the user's request can be forwarded to the "best" server based on different rules. Therefore, layer fourth switching technology is the ideal mechanism for data transmission and load balancing among multiple servers.

At present, there are many products to support multi-layer exchange, such as Cisco Catalyst 5509/6509, Extreme Diamond Series, Foundry Bigiron series and Alteon ace-180e and so on.

Multilayer switching technology has now been described as an integrated, complete solution that supports a wide range of LAN architectures, combining exchange technology and routing technology intelligently. Multi-layer switching technology combines the optimal characteristics of local area network switching technology and routing technology, and has higher performance price ratio than traditional router based LAN backbone, as well as more powerful flexibility, which is the foundation of High speed LAN implementation.

Issues to consider

High-speed LAN networking mode is now very simple, there is no other better choice: basically is Gigabit Ethernet for the backbone, the use of high-performance two or three-layer switch as the core; network cabling, the backbone and switch between the connection recommended multimode or Single-mode fiber, horizontal wiring can be used in the Super five type of unshielded twisted pair. As mentioned earlier, this structure is easy to expand and upgrade. Switch products are Cisco 6509/6509 OSR, Foundry bigiron 8000/4000, Extreme black Diamond 6816/6808, Alcatel powerrail 5200/2200, Lucent Cajun P880, Riverstone rs32000/rs8600, Huawei MD5500, Dragon rs6006g/rs6004g, creative AR8000 and so on.

However, the success of a network construction must also consider the following issues:

The scalability of the business

Whether the business can be carried out or not, is the main criterion of various technical evaluation. Now, the construction of high-speed information networks are required for the integrated services including voice, video and data, therefore, whether to support a variety of VLANs, whether or not to support IP multicast, product selection must be considered when the problem.

Mature Technology

The network technology of gigabit LAN and high speed router has the problem of imperfect control domain, there will be many insurmountable obstacles in the process of key data service or continuous media information communication. Whose product solves good and bad, must have the case proof, cannot at the product itself the document or the factory boast. Immature network technology is not easy to use, this is the establishment of key business high-speed LAN basic criteria.

Interoperability of networks

Network interoperability is the most important performance of network value. Network interoperability is manifested not only in geographical coverage area, but also in interconnection with other networks. High-speed LAN interoperability is mainly reflected in the exchange with the original network, and a higher level of network interoperability.

Network reliability

Network reliability must be supported by network protocol, device backup and routing backup, especially the control and management system of network protocol is very important.