Thursday, December 23, 2010

【 Weak current College 】 broadband router principle techniques】


Preface
If now someone needs to be a small range of a few computers to connect to the Internet, and internal LAN, believe that the first consideration will be given to the broadband router to implement such functionality. In the broadband router is not universal, common users to implement such a feature, usually a computer after you install the gateway software as a server that has two network adapters, one for connecting to the external network or modem, one used to connect to intranet and intranet to put you through to a hub or a simple switch. This way not only the cost of early input into the larger, and regardless of the client or the server side is set to be cumbersome, and more trouble; in addition, as the gateway server generally need protection for a long time to open, to let the rest of the computers on the Internet, not only in the later use of costly (Server tariff), but also for the users of this server also brought a lot of trouble.

For Soho, small offices a broadband router
While the broadband router is also equipped with a router functionality, but also have a simple switch function. This entire network's core equipment by traditional server + switch, converted to a broadband router, it can at the same time and the Internet (or modem) and the computer within the network. Only 100 years the value of money and not to 30W power consumption, making both frontloaded or later-use costs are very low, its stability and function also no weaker than previously.
No wonder it is based on the above advantages, for personal users of broadband router can in a few short years, rapid development, has become the formed small multi-functional network at present is one of the indispensable part.
Tracing, the predecessor of the router
Broadband router still belongs to the router family is a branch, it is believed that our readers can understand. But the router is how developed? here is necessary to explain. In the early stages of development ofcomputer networks, although it does not appear on the Internet, but has the certain scale of local area networks have emerged. Because these networks are too large, the original segment (a segment of 255 IP addresses) has been insufficient to meet its scale, thus causing the necessary use of multiple network segments to meet each other to form a complete network. But the problem is a result of the switch or hub, although you can put the entire network of computers connected together, but unable to break through the different network segment between the restrictions cannot be connected, and therefore are not able to meet the demand. This requires a device able to complete a variety of multiple network segments between packet forwarding to each other, bridges (Bridges) it is for this needs to be developed.

Bridge products
Bridge work to network model in the second layer, i.e. the link layer, it can take two LANs connected together, and then under network adapter physical address to a forwards packets from one network to another network, so as to achieve the purpose of mutual connection. The way forward is is based on the data source in the frame to a physical address and physical address to determine whether a frame should be forwarded, and forwarded to which port.

Bridge typical effect chart
But bridge is a very powerful device, although some bridges products can be used for different LAN (e.g., FDDI LAN and Ethernet) connection, but generally speaking, it is connected to the network are homogeneous (e.g. Ethernet), so if you have problems with the agreement of the network type (e.g., Ethernet and token ring, Ethernet and X.25), the bridge will not be able to play its role. And the network bridge to remember all the independent on the network computer. If you use the network bridge to connect to a very large network, issues regarding the crime. At this time because the device is outside the scope of management of the bridge, the result can not understand the network number, anywhere on the network generated broadcast will be sent to the Internet everywhere, creating a network of turmoil, the entire network is broadcast information is full, until completely, therefore greatly reducing the stability. In addition when the internal network and external network interconnection, network bridge will put the internal and external networks combined, forming a whole network, both automatically to the other side completely open their network resources, security issues are not apparent.
So as your network further expanded and further increasing the network type, there is an urgent need for a more advanced way to address the above challenges.
The birth of the router
In 1984, comes from Stanford University's Leonard Bosack and Sandy Lerner couples in the United States in Silicon Valley in San Jose set up a home for Cisco (Cisco) e company, they designed a name of "multi-protocol router (Access Gateway Server)" networked device, you can enable Stanford in non-compliant computers networked together. This is now being hailed as the network traffic of the router (Router).
Router is used to connect to multiple networks or segment of the network devices. These networks can be several different protocols and architectures of networks (such as Internet and local area network) that can be several different segments of the network (such as large Internet in different departments of the network), when the data information from such disparate one network to another network, their work is done by the router.
And unlike the router bridge no longer works in the network model in the link layer, which is the layer of work at the network layer, the layer 3. The resulting benefit is that a variety of different network protocols, most of them can run on a network layer protocol, so the router IP to easily connect to different types of networks. But this time the router can also take advantage of the network defined IP addressto complete for each computer's location, not the physical address of the bridge. In this way the benefit is that, since each network IP addresses are within a certain range that do not conflict, unique, the router can accordingly to various networkTo group for distinction, judge, thereby achieving network interconnects while also maintaining the independence of their network. This is used to set up by the many small network to interconnect to form a network of large or very large network became possible. Furthermore routers do not forward broadcasts news, and broadcast message restrictions in their network. Need to send to the other network's data is to be sent to the router, and judgment, and then forwarded by the router to the destination computer to the network, this network storm case to avoid.

Typical role map router
With the router, the router processing performance not only more and more powerful, you can connect a larger network, and multiple ports to connect multiple IP subnets, joined the management functionality allows for a more intelligent, and so on, these are the traditional network bridge are incomparable. So, with the rise of the Internet, the router has become the network node in the ratio of the device, connect the LAN and the Internet are various bridges, internal local area network, local area network and between the local network and local area network and Internet connectivity hub, known as "Web traffic" and then fit it.
Broadband router, a product of the multi-technology
According to the different usage type classification, routers can be divided into: access router, enterprise-class router and backbone-class routers, terabit routers these four types, which we call broadband router is a router. It will use to connect to a home or small-and medium-sized enterprises within the ISP customers. Can be connected to the Internet or Internet access device WAN port and connect to a local area network or the computer's LAN port.
r>Cisco router early 2500
Initial broadband router can in fact be seen as a feature to simplify, but on the one hand more single-minded computer host, of course, it has no hard drive, optical drive, video card, sound card, such devices, but only by common CPU (Intel x 86 or other RISC reduced instruction-set processors), memory, a dedicated Board and multiple network controller, and other network hosts the necessary context. The operating system is curable in ROM, although features a single, but has excellent complete routing this important task, and the relative computer, stability is also greatly enhanced. Mass production of the router's price compared to achieve such a computer, much cheaper, formed into a dedicated network hardware products.
But the technology is progressing, as router, it produces a single bus, single-CPU architecture, single bus master CPU structure, single bus symmetric multi-CPU architectures; multibus multiple CPU architectures, shared car structure, cross switch architecture and DSDM price, and so on many kinds of router of schema types to enable it to meet the growing needs of the network. But judging from the hardware structure or schema of the host computer and are very similar.
Broadband router on performance requirements is usually not too high, the function is also more of a single, so most of them use the inexpensive single bus, single-CPU structure can meet, the schema includes a shared central bus, CPU, memory, ROM, and hung on the shared bus on multiple network physical ports.
Shared central bus can transmit on the same bus, various data signal is of simple structure, high universality, inexpensive, simple switch also uses a shared central bus to complete data exchange tasks, and so on in the broadband router, use this type of bus provides additional requirements not high switch function is also very easy. Bus bandwidth has to a certain extent determines the router processing performance, because the bus signal through the network device back plate transfer, so the General manufacturers have also often share the bandwidth of a central bus to backplane bandwidth manner.
Broadband router CPU with embedded processors and general purpose processor two different types. A powerful general purpose processor performance, universal strong, and can implement multiple parallel processing, and other rich features, often in large scale router can see it, such as: Pentium series, Alpha, Power, PA-RISC, UltraSparc, etc, in fact, is a personal computer or server's processor, but the disadvantage is expensive and complex design, the price is high, therefore use in broadband router is obviously inappropriate. This embedded processor with Schema simple, low power consumption, low price, has become the choice of broadband routers, x86 ARM7, ARM9, and MIPS, RDC, etc are all this kind of CPU is, of course, they also have a certain versatility that can be applied to cell phones, printers, home appliances and other products.

ARM7-based embedded processor technology licensing
Memory used to store CPU arithmetic operations on the data and place the routing table, and so on, so a powerful processor capacity, connected to the network users more broadband router, the demand for memory, in object-oriented multi-user broadband router, equipped with more capacity 128MB. While the broadband router in ROM is usually from Flash, EEPROM such chips, it is mainly used to is used for storing broadband router's proprietary operating systems and applications, natural product functionality and user interface fancy drop a broadband router, its ROM capacity are large, and at the same time, the ROM is also available through the program to be upgraded, to solve the Bug and enhance the functionality and performance.
Physical ports you have decided the broadband router can apply those network types, it is oriented to the extranet of WAN port and facing the intranet's LAN port. WAN port can provide, such as SLIP and PPP, PPPoE, PPPoA, and other network protocols support to facilitate broadband access in a variety of ways, at the same time, the software can achieve, automatic dialing and other useful features. The LAN port is used to connect to the LAN, the General can also provide multiple LAN port, implements a simple switch function.
> Can see broadband router is a router for the low-end product, its features, the ability to manage relatively single network node. Its structure is the reference computer and switch products and inlaid type of software system is also derived from the computer, so it is a combination of multiple technologies, integrated hardware product, its features and performance are also quite comprehensive, and can have very high intelligent degree.

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