Router concept, function and development trend

Router concept, function and development trend


【Introduction】
In recent years, the development of routers has been ups and downs. In the mid-1990s, traditional routers became the bottleneck restricting the development of the Internet, replaced by ATM switches, and became the core of the IP backbone network, and routers became supporting roles. In the late 1990s, the scale of the Internet expanded further, and traffic doubled every six months. The ATM network became a bottleneck, and routers made a comeback. After the introduction of Gbps routing switches in 1997, people began to replace ATM switches with Gbps routing switches, and built a backbone network with routers as the core.


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In recent years, the development of routers has been ups and downs. In the mid-1990s, traditional routers became the bottleneck restricting the development of the Internet, replaced by ATM switches, and became the core of the IP backbone network, and routers became supporting roles. In the late 1990s, the scale of the Internet expanded further, and traffic doubled every six months. The ATM network became a bottleneck, and routers made a comeback. After the introduction of Gbps routing switches in 1997, people began to replace ATM switches with Gbps routing switches, and built a backbone network with routers as the core.

As the core device, the router is in a crucial position on the IP network. With the popularization of Internet applications, the rapid increase of network bandwidth and the improvement of users' requirements for service quality, the future of routers is also facing new changes.

Router concept

A router is a network device that connects multiple networks or network segments. It can "translate" data information between different networks or network segments, so that they can "read" each other's data to form a more Big network.

The router has two typical functions, namely the data channel function and the control function. Data channel functions include forwarding decision, forwarding, and output data link scheduling, etc., which are generally completed by hardware; control functions are generally implemented by software, including information exchange with neighboring routers, system configuration, and system management.

Router basic function introduction

Traditionally, routers work at layer 3 of the so-called network 7-layer protocol model. Their main task is to receive data packets from a network interface and decide which destination to forward to based on the destination address contained in them. Perhaps the router is also It may be the final destination and decide which network interface to forward from. This is the most basic function of the router-packet forwarding function.

According to the TCP / IP protocol, the specific packet forwarding process of the router is:

1. The different physical network media that the network interface receives the data packet determines different network interfaces, such as corresponding to 10Base-T Ethernet, the router has a 10Base-T Ethernet interface; corresponding to DDN, the router has a V.35 interface.

2. According to the network physical interface, the router calls the corresponding link layer to explain the link layer protocol in the processing data. This step is mainly to verify the integrity of the data.

3. After the link layer completes the integrity verification of the data frame, the router starts processing the IP layer of the data frame. Based on the destination IP address in the data frame, the router looks up the next IP address in the routing table and calculates a new checksum. If the type of the network interface that receives the data frame is different from the type of the network interface that forwards the data frame, the IP data packet may also be fragmented or reassembled due to the limitation of the maximum frame length.

4. According to the next IP address found in the routing table, IP data packets are sent to the corresponding output link layer, and finally sent out through the network physical output interface.

In order to maintain and use the router, the router also needs to have configuration or control functions.

The control function is provided by a series of rules, for example, it may be priority, denied access or provide accounting data. When a data packet enters the router, these related rules also apply to the data packet. In software-based routers, these rules are stored in a software database, and each data packet must be checked against the database when it passes.


Router development trend

The chip speed doubles every 18 months, while the Internet traffic doubles every 6 months. As the hub of the Internet, routers are developing in three directions: faster speed, better service quality and easier integrated management.

faster

Traditionally, routers are often regarded as the bottleneck of network speed. When the local area network speed has reached hundreds of megabytes, the processing speed of the router is at most tens of megabits. With the explosive growth of Internet users in recent years, everyone's research on routers is also focused on improving the processing speed of routers. From 1996 to 1997, a number of small innovative companies appeared in the United States, such as Nexabit, Juniper, and Avici, etc., which increased the processing speed of routers to the point where they reached their peak, and launched Gigabit routers one after another in a very short time. Even Cisco can only look beyond its speed. Since these high-speed routers all introduce the switching structure without exception, they are also called GSR-Gigabit Switch Routers. The optical interface speed of these routers also quickly increased from OC-12 (622 Mbps) to OC-48 (2.5 Gbps) and then to OC-192 (10 Gbps). This speed has already left ATM switches far behind. Since then, the irreplaceable position of ATM in the core network has completely shaken. The protracted battle between IP and ATM technology finally ended with the overwhelming advantage of IP. However, the increase in the speed of IP routers is directly due to the concept and technology of ATM. Many of the new concepts and new technologies proposed in the field of IP are also directly or indirectly derived from ATM. Two excellent technologies have gradually begun to merge. . In fact, the technical personnel of many companies engaged in the research and development of high-speed IP routers are the same as those who researched ATM technology in the past. Specifically, the rapid increase in the speed of IP routers comes from technological progress in the following four areas:

â‘ Hardware architecture

The hardware architecture of the router has undergone roughly six changes, from the earliest single-bus and single-CPU architectures to single-bus and multi-CPU to multi-bus and multi-CPU. Up to now, high-speed IP routers have drawn on the ATM method and adopted the crossbar switch method to achieve line-speed non-blocking interconnection between ports. The technology of high-speed crossbar has been very mature, and it has been widely used in ATM and high-speed parallel computers. The speed of high-speed crossbars that can be directly purchased on the market is as high as 50Gbps. With the introduction of high-speed crossbar switches, some corresponding technical problems have also been introduced, especially for IP multicast, broadcast, and quality of service (QoS). The use of mature scheduling strategies and algorithms has been well resolved. .

â‘¡ASIC technology

Over the years, due to cost and performance considerations, ASIC has become more and more widely used, almost ASIC. To greatly increase the speed in routers, the first thing that comes to mind is ASIC. Some use ASICs for packet forwarding, some use ASICs for routing, and ASIC chips for IPv4 routing are already on the market. In the booming trend of ASICs and a large number of applications, there is a trend worth noting. This is the emergence of so-called programmable ASICs. This is probably also a result of the rapid changes in the network itself. Due to the considerable investment in the design and production of ASICs, generally speaking, ASICs are only used in processes that have been completely standardized, and the structure and protocols of the network have changed quite quickly. Therefore, in the field of network equipment, a strange Programming ASIC ". Currently, there are two types of so-called "programmable ASICs". One is represented by 3COM's FIRE (Flexible Intelligent RouTIng Engine) chip. This ASIC chip has a CPU embedded in it, so it has certain flexibility; the other is represented by Vertex Networks' HISC dedicated chip. The chip is a CPU specially processed for communication protocols, and its architecture design is specially adapted to protocol processing. By rewriting the microcode, this dedicated chip can have the ability to handle different protocols to adapt to similar changes from IPv4 to IPv6.

â‘¢3 layer exchange

This is a revolutionary breakthrough in the protocol processing process, and is also the source of the GSR and TSR names. Since Ipsilon, a little-known company, introduced the IP Switch technology of "one-time routing, then switching" in 1994, major companies have launched their own proprietary 3-layer switching technology. Such as Cisco's Tag Switch, 3Com's Label Switch, etc. Combining the advantages of these proprietary technologies, IETF finally launched the Multi-Protocol Label Switching (MPLS) with superior performance in 1998.

â‘£IP over SDH, IP over DWDM

The technological progress in this area stems entirely from the progress of optical fiber communication technology. As the core position of IP is gradually recognized, IP over ATM and then ATM over SDH are replaced by IP directly over SDH. SDH uses time division multiplexing to carry multiple channels of data. Therefore, a large number of multiplexer cross-connectors are required in the core network. DWDM (Dense Wavelength Division Multiplexing) makes it possible to transmit multiple signals with different wavelengths on one fiber.


Better service quality

The aforementioned increase in the speed of the router is still just to adapt to the rapid increase in data traffic. The development trend of the router is more essential and more profound: IP-based packet-switched data will quickly replace the circuit-switched communication method that has been developed for nearly a hundred years in the next few years and become the mainstream of the communication business model. This means that not only should IP routers provide faster speeds to adapt to the rapidly increasing traditional computer data traffic, but also that IP routers will gradually provide various services provided by the original telecommunications network. However, traditional IP routers do not care about and do not know the service type of IP packets. Generally, they only forward data packets according to the first-in first-out principle. The data of various service types such as voice calls, real-time video, and Internet browsing are all indistinguishable. treat.

This shows that if IP routers want to provide all services including telecommunications and broadcasting, improving the quality of service (QoS) is the key. This is exactly the direction that major network equipment manufacturers (including Cisco, 3Com, Nortel, etc.) are striving to advance. The newly launched high-, medium-, and low-end routers of major manufacturers all support QoS to varying degrees. For example, Cisco's highest-end 12000 series has strong support for QoS from both hardware and software protocols. The end product 2600 series also supports new business applications such as voice telephony. In fact, QoS is not only a development trend of routers, the entire IP network with routers as its core is developing in this direction.

The concept of "three networks in one" is the product of this direction. However, the network with traditional IP routers as the core has been unable to adapt to the "three networks in one" trend. Developed countries led by the United States are advancing the research and development of network technologies that can provide better and faster service quality. The research and development of routers is the key, and the company has become the main driving force for this technology.

Support for QoS comes from both software and hardware. In terms of hardware, faster forwarding speed and wider bandwidth are the basic premise. In terms of software protocols, after years of efforts, the following results have been produced:

â‘ IPv4 packet header service type field

There is a 3-bit area in the IPv4 packet header to identify the priority of this IP packet. Based on this priority, the IP router can determine the priority of forwarding different IP packets. It can be said that since the IP protocol was formulated, it has provided a better QoS reservation mechanism in the future.

â‘¡RSVP (Resource Reservation Protocol) and corresponding series of agreements

This is a profound step forward for IP routers to provide better service quality. Traditionally, IP routers are only responsible for packet forwarding, and know the addresses of neighboring routers through routing protocols. RSVP is similar to the signaling protocol of the circuit-switched system. It notifies each node (IP router) it passes through for a data stream, and negotiates with the endpoint to provide quality assurance for the data stream.

â‘¢ DiffServ (DifferenTIated Service)

For the above two reasons, IETF has launched another new QoS strategy-DiffServ. At present, the framework of DiffServ has been basically determined, and Internet2 in the United States has also selected DiffServ as its QoS strategy. Compared with DiffServ, RSVP is an Integrated Service (centralized control strategy), while DiffServ is a decentralized control strategy, the essence of which is to control every action in the path. The terminal application equipment negotiates with the edge router through the SLA (Service Level Agreement) to obtain a guaranteed service level for its application data flow.

â‘£Multi-protocol mark exchange

MPLS is also used to solve QoS problems, but its coverage is the core network router. In order to establish a reasonable switching path between core routes, core routers need to regularly exchange traffic and other status information.


Smarter management

With the explosive growth of network traffic, the increasing scale of the network, and the increasingly high requirements for network service quality, the network management system on the router has become increasingly important, and network connection has become an indispensable part of daily work and life . Under the condition of ensuring quality, maximizing the use of bandwidth, early detection and diagnosis of equipment failures, and quick and convenient configuration changes as needed, these network management functions are increasingly becoming important factors that directly affect the interests of network users and network operators. In the seven-layer network protocol model, network management is a high-level application. At present, an important development trend of network management of various manufacturers is to develop in the direction of intelligence. The intelligence is reflected in two aspects, one is the intelligence of information interaction between network devices (routers); the second is the intelligence of information interaction between network devices and network managers. In the general trend of intelligent network management, the two technical concepts of "policy-based management" and "traffic engineering" are currently the most compelling. All router manufacturers in the newly launched products all advertise that their network management supporting system has or partially has the functions of these two aspects.

The concept of "policy-based management" will affect the information interaction behavior pattern between routers and routers and network managers at the same time, making it easier for network managers to define and constrain network behavior from the perspective of users. It will directly affect the basic behavior of the network, so that the traditional routing algorithm will be developed into a strategy-based routing algorithm, so that the information interaction between routers must include the information content covered by the strategy.

"Traffic engineering" is the most concern of core network operators. New protocols such as MPLS, while solving label switching, also provide a good solution to "traffic engineering", that is, by exchanging traffic status information between routers between routers, and using convergence algorithms to calculate labels in the network over a period of time The explicit path, constrained shortest path first algorithm is adopted to make the flow of the entire network as balanced as possible for each period of time.

The development of network technology is changing rapidly. When we are immersed in the great joy brought to us by the IP-based Internet, the router technology, especially the core router technology, is undergoing tremendous changes. The router is no longer the same as the old one. To borrow the words of Bill Gates: We have only been 18 months without a router.

Switched routing technology is a hot topic in this field. It not only solves the problem of communication traffic, but also has higher network control and management capabilities.

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