China's fiber optic network was first applied to the backbone transmission network of telecommunication system and cable TV backbone network. With the development of the economy, the wave of information is surging, and the demand for communication infrastructure is unprecedentedly high worldwide. New data services, business users, residential users, Internet applications and the popularization of home computers and internet, the urgent need for the development of broadband network. And on its integration and voice, data and video services, including VOD, interactive distance learning, telemedicine, online shopping, E-mail, Internet browsing and other functions.
The following technologies are mainly used in the backbone layer of telecommunication and broadcasting networks: The basic principle and working mode of IP over ATM is that IP packets are encapsulated into ATM credits at the ATM layer,
and transmitted in the channel in the form of ATM credits. When a switch in the network receives an IP packet, it first processes the routing address through some mechanism according to the IP address of the IP packet and forwards it according to the route. Subsequently, a virtual circuit (VC) is established on the ATM network according to the calculated route. Subsequent TP packets will be transmitted on this virtual circuit VC in a straight-through (Cut a Through) manner and then down through the router, thus effectively solving the bottleneck problem of IP's router and increasing the forwarding speed of IP packets to switching speed.
IP Over ATM has the following characteristics:
Advantages: (1) Since ATM technology itself can provide QoS guarantees, this feature can be used to improve the quality of service of IP services.
(2) It has good traffic control and equalization ability as well as fault recovery ability, and the network reliability is high.
(3) Adapt to multi-service, good network scalability.
(4) Provides support for several other network protocols such as IPX.
Disadvantages: (1) At present, IP over ATM cannot provide complete QoS guarantee. Because there is not yet a standard method to achieve: P priority (Cos) classification mapped to ATM 06.
(2) general support for IP routing, IP packet segmentation to join a large number of header information, resulting in a large waste of bandwidth (20% to 30%).
(3) Lack of high efficiency in replicating multicasts.
(4) Complicated management due to the complexity of ATM technology itself. IP Over SDH uses the SDH network as the physical transport network for the IP data network. It uses link and PPP protocols to encapsulate IP packets by simply inserting IP packets into information segments in PPP frames according to the RFC1662 specification. Then the service adapter at the SDH channel layer maps the encapsulated IP packet into the synchronous netload of the SDH, and then down, through the SDH transport layer and the segment layer, plus the appropriate overhead, to load the netload into an SDH frame, and finally reaches the optical layer for transmission in the fiber.
IP over SDH has the following characteristics:
Advantages: (1) Strong support for IP routing and high IP transmission efficiency.
(2) Conforms to the characteristics of Internet services, such as facilitating the implementation of the multi-way broadcast method.
(3) can use the SDH technology itself loop, so you can use self-healing (Self-healing Ring) ability to achieve link error correction; at the same time, the use of OSPF protocols to prevent the preparation and link failures caused by network downtime, improve the stability of the network.
(4) Omit the unnecessary ATM layer, simplify the network structure, reduce operating costs.
Disadvantages: (1) Only provides good support for IP services, not suitable for multi-service platform.
(2) Cannot provide better quality of service guarantee (QoS) as IP crver ATM technology.
(3) Limited technical support for other major network technologies such as IPX.
IP over WDM IP over WDM, Optical Internet
The basic principle and the way it works is that at the sending end, optical signals of different wavelengths are combined (multiplexed) and fed into a single optical fiber
for transmission, and at the receiving end, the combined optical signals are separated (demultiplexed) and fed to different terminals.
IP over WDM is a true link-layer data network. In it, high-performance routers are directly connected to the WDM fiber through optical ADM or WDM couplers, which control wavelength access, switching, routing, and protection.
The frame structure of IP over WDM comes in two forms: SDH frame format and Gigabit Ethernet frame format. The protocols, standards, technologies, and drafts that support IP over
WDM technology are:
DWDM (Dense Wavelength Division Multiplexing) The WDM system with a general peak wavelength in the order of 1 to 10 nm is known as DWDM.
This system, each wavelength of optical signals is called a transmission channel (channel). Each channel can be a 155Mb/s, 622Mb/s, 2.5G/b or even 10Gb/s ATM or SDH or Gigabit Ethernet signals, etc. DWDM provides the interface protocol and rate independence, in a fiber, can support ATM, SDH and Gigabit Ethernet at the same time, to protect the existing investment, and provides great flexibility.
Advantages: (1) full use of the bandwidth resources of the fiber, greatly improving the bandwidth and relative transmission rate
(2) transparent to the transmission bit rate, data format and modulation. ATM, SDH/Sonet and Gigabit Ethernet format services with different bit rates can be transmitted.
(3) It is not only compatible with existing communication networks, but also can support future broadband service networks and network upgrades, and is characterized by generalizability and high survivability.
Disadvantages: (1) At present, for wavelength standardization has not been achieved. Generally, 193.1 THz is taken as the reference frequency, and the interval is taken as 1OOGHz.
(2) The network management of WDM system should be separated from the network management of its transmitted signals. However, in the optical domain coupled with the overhead and the processing technology of optical signals is still not perfect, which leads to the network management of WDM systems is not yet mature.
(3) At present, the network topology of WDM system is only based on the point-to-point method, and has not formed the "optical network".
Through the above analysis and comparison, we can find that in the high-performance, broadband IP services, IP over SDH technology
Technology due to the removal of ATM equipment, less investment, quick results and high line utilization. Therefore, for the development of high-performance IP services, IP over SDH is a better choice. IP over ATM technology, on the other hand, makes full use of the already existing ATM network and technology, and plays the technical advantages of ATM network, which is suitable for providing high-performance integrated communication services, because it can avoid unnecessary duplication of investment, and provide Vcrice, Video, Data multiple services. For IP over WDM technology, it can greatly expand the existing network bandwidth, maximize the line utilization rate, and in the case of peripheral networks with Gigabit Ethernet becoming the mainstream, this technology can truly achieve seamless access. It should be said that IP over WDM will represent the broadband IP backbone network of tomorrow.