IP over DWDM as a kind of new developing network technique, though receive much concern, is come from suspicion and challenge of various fields too. Among them the most important, most essential question is whether IP over DWDM network can meet demands of telecommunications service. This usually means the requirement for two respects, first, the network must be stable and reliable; Second, service quality guarantee. Require the strong trouble restorability that the network has roots while the local fault appears.
1,Self-healing ability of the network
Because DWDM is still the transmission technology Point to point at present, network management and protective measure are incomplete. So, the traditional telecommunication trader thinks, SDH remains vital layer in the network. But, technology is always changing and developing in the gradual progress constantly, DWDM is and merging and corroding and shaking SDH and supporting the position of the network with IP technical gradual progress as telecommunications progressively. SDH Self-Healing Ring is a function worthy to be most proud in SDH technology, can guarantee from the convalescent technology in the trouble in 50 milliseconds too. Though use SDH Self-Healing Ring to mean loss half the network resources, ask oneself that was praised highly by the telecommunication expert since generation.
IP over DWDM network relies on two protocol layers to finish self-healing to protect: Transport layer and IP layer.
Realize in the DWDM layer self-healing is protected, not only can guarantee to regain speed for less than 10-2 second, and will make the route of IP network remain stable, prevents the route from shaking. However, expecting relatively much to network resource of protection of DWDM at present. Such as the multiterm optic fibre, even multiterm optical cable, that is to say. Realize the protective cost great of self-healing in the DWDM layer.
It is a basic function in IP network that the self-healing of IP layer protects the function. Have already considered the dynamic variation of the state of network in the most original IP network design, and designed the intact dynamic routing rule. However, totally rely on the protocol implementation IP network self-healing of route to resume required time by minute, so low a switch speed will cause network datas to lose in the ultra high speed network in a large amount, can’t meet telecommunications service to the requirement for the service quality at the same time.
It leaves an organic whole on equipment integration to be to solve the intersection of IP layer and thorough fare, find the speed a slow route the intersection of IP and network equipment, but this kind of method seems to contradict with principle of the open interconnected system. If it is open to adopt and transmit the network platform, the IP layer must be capable of measuring the thorough fare. And measure the periodic line detection mechanism usually using the route agreement in the thorough fare of the IP layer, it is about 60 seconds to measure the speed. Modern route technology will usually combine the detection mechanism of the lower, realize the fast alternate circuit route.
1 Fig. show network topology, when the periodic line between Router 3 and Router 5 is cut off, Router 3 measure, cut off behind the message through transport layer, know and send UPDATE information to the whole network immediately, notify all changes of state about this periodic line of node. So, Router1 will obtain break information of Router 3 - Router 5 very rapidly, but because Router1 needs resynchronization with calculating the route, then just confirm that chooses Router 4 as the new transmission path, so the speed of alternate circuit route that this way realizes is usually by second.
With the view of the telecommunication service, the self-healing of grade is unsatisfactory in speed second. In order to make IP network reach the service standard of grade of telecommunications, the suppliers of IP apparatus have made untiring efforts. Put out the intersection of MPLS and the intersection of flowrate and project, put out called Fast Rerouting technology even more, within can make the intersection of IP and self-healing of network regain speed and drop to 50 milliseconds.
MPLS flowrate project sets up two tunnels at the same time between source and router of destination place. Disposition. When the periodic line between Router2-Router 3 is cut off, Router 2 will utilize the circuitous periodic line between Router 2 - Router 4 to send the business to Router 3 to Router 4 directly. Router 3 will utilize the circuitous periodic line between Router 1 - Router 3 to send the business to Router 2 to Router 1 directly too. Because this kind of structure can guarantee all break of the periodic line can finish the recovery procedure here, do not need to notify the far-end, and switch over and only happen on the physical layer, have nothing to do with the business of upper strata, needn’t remember any state or filter any business, so this kind of guard mode can well reach with the uniform result of SDH Self-Healing Ring! But its defect is obvious, it is more complicated than SDH cyclic(al) structure, the router resource expenses are large.
2,Assured service quality of the network
Another severe challenge of IP network is how to guarantee the service quality. The traditional IP network only offers the Best Effort -type business support. IP network is as supporting unified network platform of all telecommunications service, how to meet various telecommunications service to different requirements of service qualities, it is a key issue that IP networking products need solving.