IPv6 is the abbreviation of "Internet Protocol Version 6", which is the next generation IP protocol designed by IETF to replace the current version of IP protocol-IPv4-.

At present, the core technology of the second generation Internet IPV4 technology we use belongs to the United States. Its biggest problem is the limited network address resources. Theoretically, there are 4.3 billion IP addresses that can be used by IPV4 technology, of which North America accounts for 3/4, about 3 billion, while Asia with the largest population is less than 400 million, and China only has more than 30 million, which is only equivalent to the number of Massachusetts Institute of Technology. The lack of address has seriously restricted the application and development of Internet in China and other countries.

Compared with IPV4, IPV6 has the following advantages: First, the network address is almost infinite. According to this technology, its network address can reach 2128th power. If the total address of IPV4 is a bucket of sand, then the total address of IPV6 is like a bucket of sand, as big as the earth. Secondly, because everyone can have more than one IP address, the security of the network will be greatly improved. Third, the data transmission speed will be greatly improved. The main advantages of IPv6 are: improving the overall throughput of the network, improving the quality of service (QoS), supporting plug and play and mobility, and better realizing the multicast function. According to this technology, if IPV4 only realizes man-machine dialogue, and IPV6 extends to the dialogue between anything, it can not only serve human beings, but also serve many hardware devices, such as household appliances, sensors, remote cameras, cars and so on. And it will be a real broadband network that permeates every corner of society all the time. The economic benefits it will bring will be enormous. Of course, IPv6 is not perfect once and for all, and it is impossible to solve all the problems. IPv6 can only be continuously improved in the process of development, and cannot be achieved overnight. Transition takes time and cost, but in the long run, IPv6 is beneficial to the sustained and long-term development of the Internet. At present, Internet organizations have decided to set up two special working groups to formulate corresponding international standards.

IPv6 frequently asked questions

1. What is IP? What is IPv4? What is IPv6?

At present, the protocol family adopted by the global Internet is TCP/IP protocol family. IP is the protocol of the network layer in the TCP/IP protocol family and the core protocol of the TCP/IP protocol family. At present, the version number of IP protocol is 4 (abbreviated as IPv4), and its next version is IPv6. IPv6 is in the process of continuous development and perfection, and it will replace the currently widely used IPv4 in the near future.

2. What are the characteristics and advantages of 2.IPv6 compared with IPv4?

1) larger address space. IPv4 stipulates that the IP address length is 32, that is, there are two 32- 1 addresses; The length of IP address in IPv6 is 128, that is, there are two 128- 1 addresses.

2) Smaller routing table. IPv6 address aggregation follows the principle of clustering from the beginning, which makes the router use an entry in the routing table to represent a subnet, greatly reducing the length of the routing table in the router and improving the speed of forwarding packets.

3) Enhanced multicast support and flow control. This makes the multimedia application on the network have great development opportunities, and provides a good network platform for quality of service (QoS) control.

4) Support for automatic configuration is added, which is an improvement and extension of DHCP protocol and makes the management of network (especially LAN) more convenient and fast.

5) Higher security. In the IPv6 network, users can encrypt data and check IP packets at the network layer, which greatly enhances the security of the network.

3. Do we need two 128- 1 IP addresses?

Yes With the development of electronic technology and network technology, computer networks will enter people's daily lives, and everything around them may need to be connected to the global Internet. And accurately, in the network using IPv6, no two 128- 1 addresses can be fully utilized. First of all, in order to realize the automatic configuration of IP address, the subnet prefix used by LAN must be equal to 64, but there is rarely one. Secondly, because IPv6 address allocation must follow the principle of clustering, address waste is inevitable.

I want to know about IPv6. What should I do?

Look at RFC. It's the cheapest and safest way, but it's boring. At present, there is at least one book about IPv6 in China: IPv6- New Internet Protocol (2nd Edition)/New Internet Protocol IPv6 (2nd Edition), Tsinghua University Publishing House. There is also at least one book introducing IPv6 network programming (Unix platform) in 1999: UNIX network programming volume I (2nd edition) /UNIX network programming volume I (2nd edition), Tsinghua University Publishing House, 1998.

I want to try IPv6, what should I do?

You need three things: an operating system that supports IPv6; Software supporting IPv6; Internet connection.

1) At present, the operating systems supporting IPv6 are: Windows Vista, Linux (the kernel version is at least 2.2. 1, preferably above 2.2. 12) and FreeBSD (that is, 4. X series already supports IPv6, and earlier versions need kernel patch), and WindowsNT/2000 (required). NetBSD, OpenBSD, Solaris (these are unfamiliar), and so on. At present, the operating system that definitely does not support IPv6 is Windows98 in the Windows series and its previous versions (as far as I know).

2) Operating systems that support IPv6 usually have some network programs that support IPv6 (Linux is a special case, and some software may support IPv6 itself, but the corresponding options are not turned on at compile time, because different publishers have different views on the importance and usability of IPv6). But the programs that come with these operating systems are often not the best, so you may need to go online to find some useful software that supports IPv6.

3) If you really want to try IPv6, you must connect to the Internet, at least have a local area network environment.

IPv6 packet header

The IPv6 header part improves the IPv4 header, deletes some unnecessary or rarely used fields, and adds some fields that can better provide real-time support.

IPv6 packet structure

IPv6 message consists of IPv6 header, extended header and upper layer protocol data unit, as shown in figure 1.

Figure 1, IPv6 packet structure

IPv6 packet header

40 bytes fixed length, which will be discussed in detail later in this article.

Extended packet head

An important improvement of the original IPv4 header in the design of IPv6 header is to move all optional fields out of the IPv6 header and put them into the extended header. Since most IPv6 extension headers are not checked by transit routers, the improved IPv6 headers can improve the forwarding efficiency of routers.

The IPv6 extension header may not exist, or there may be one or more. Another improvement of IPv6 is that, unlike the IPv4 option, the length of IPv6 extension header is not fixed, which is convenient for expanding new options in the future. This feature, coupled with the way options are handled, enables IPv6 options to be truly utilized.

Upper layer protocol data unit

PDU consists of a transport header and its payload (such as ICMPv6 message or UDP message). ). The payload of IPv6 packet includes IPv6 extension header and PDU. Generally, the maximum number of bytes allowed is 65,535 bytes, and loads larger than this number can be sent by using the jumbo payload option in the extension header.

IPv6 packet header

Figure 2. IPv6 header format

The length of IPv6 header is fixed at 40 bytes, which removes all optional items in IPv4 and only contains 8 required fields. Therefore, although the length of IPv6 address is 4 times that of IPv4, the length of IPv6 header is only 2 times that of IPv4.

Version: 4 digits, IP protocol version number, value = 6.

Traffic Category: 8 digits, indicating the traffic category or priority of IPv6 data flow. This function is similar to the service type (TOS) field of IPv4.

Flow label: 20 bits, a new field in IPv6, marking the data flow that needs special handling by IPv6 router. This field is used for some communications that have special requirements on the quality of service of the connection, such as real-time data transmission such as audio or video. In IPv6, there can be many different data streams between the same source and receiver, which are distinguished by non-"0" stream markers. If the router does not need to do special treatment, the value of this field is set to "0".

Payload length: 16 bit load length. The payload length includes the extension header and the upper layer PDU, and 16 bits can represent the payload length of 65535 bytes at most. For loads exceeding this number of bytes, the value of this field is set to "0" and the Jumbo Payload option in the hop-by-hop option of the extension header is used.

Next header: 8 bits, which identifies the header type immediately following the IPv6 header, such as extended header (if any) or transport layer protocol header (such as TCP, UDP or ICMPv6).

Limit of hops: 8 bits, similar to TTL field of IPv4. Unlike IPv4, which uses time to define the life cycle of packets, IPv6 uses the number of times packets are forwarded between routers to define the life cycle of packets. Every time a packet is forwarded, this field is reduced by 1, and when it is reduced to 0, the packet is discarded.

Source address: 128 bits, the host address of the sender.

Destination address: 128 digits. In most cases, the destination address is the destination address. However, if there is a routing extension header, the destination address may be the next router interface in the sender's routing table.

IPv6 extended packet header

IPv6 moves all options out of the IPv6 header and puts them in the extended header. Because the transit router does not check or process the extension header except the hop-by-hop option extension header, the performance of the router in processing IPv6 packets containing options can be improved.

Typically, a typical IPv6 packet has no extended header. Only when the router or destination node needs to do some special processing can the sender add one or more extension headers. Different from IPv4, the length of IPv6 extension header is arbitrary and is not limited by 40 bytes, but in order to improve the performance of dealing with option header and transport layer protocol, the extension header is always an integer multiple of 8 bytes.

At present, RFC 2460 defines the following six IPv6 extension headers: hop-by-hop option header, destination option header, routing header, segment header, authentication header and ESP protocol header.

1) hop-by-hop option header

Contains special parameter options that each router must check and handle during packet transmission.

The options in the hop-by-hop option header describe some characteristics of the packet or are used to provide padding. These options are:

Pad 1 option (option type is 0), which fills a single byte.

PadN option (option type is 1), which is filled with more than 2 bytes.

Jumbo payload option (option type is 194), which is used to transmit very large packets. With the jumbo payload option, the packet payload length can reach 4,294,967,295 bytes. IPv6 packets with a payload length exceeding 65,535 bytes are called "jumbo packets".

The router warning option (option type 5) reminds the router that the packet content needs special handling. The router warning option is used for multicast listener discovery and RSVP (resource reservation) protocol.

2) Destination Option Title

Information that needs to be checked by an intermediate destination or a final destination. There are two purposes:

If there is a routing extension header, each transit router must handle these options.

If there is no routing extension header, only the final destination node needs to handle these options.

3) Routing packet header

Loose source routing similar to IPv4. The source node of IPv6 can use the route extension header to specify the loose source route, that is, the list of transit routers that a packet needs to pass from the source to the destination.

4) segmented packet header

Provide segmentation and reorganization services. When the data packet is larger than the maximum transmission unit (MTU) of the link, the source node is responsible for segmenting the data packet and providing reassembly information in the segment extension header.

The inseparable parts of IPv6 packet include: IPv6 header, hop-by-hop option header, destination option header (applicable to transit routers) and routing header. The segmentable part of IPv6 data packet includes authentication header, ESP protocol header, destination option header (suitable for final destination) and upper layer protocol data unit PDU.

Note: A: In IPv6, only the source node can segment the load. B This service cannot be used for IPv6 oversized packages.

5) Certification of Baotou

Provide data source authentication, data integrity check and replay protection. Authentication packet header does not provide data encryption service, and packets that need encryption service can be combined with ESP protocol.

6)ESP protocol header

Provide encryption service.

Ultra-wideband (UWB) pulse wireless transmission technology is a revolutionary wireless communication technology that has emerged in the world in recent two or three years. Compared with other wireless communication technologies, it is very different: it does not need to use carriers, but relies on continuous and extremely short-time baseband pulse signals (usually) to transmit data, so it occupies a wide frequency band, usually in the order of several GHz.

UWB technology is synonymous with the following terms: extremely short pulse, carrier-free, time domain, non-sinusoidal, orthogonal function and large relative bandwidth wireless/radar signal. Because of its excellent and unique technical characteristics, ultra-wideband pulse communication has attracted more and more attention from communication academia and industry, and has also attracted the attention of all walks of life. It will be widely used in small and indoor high-capacity high-speed wireless multimedia communication, radar, accurate positioning, wall detection, imaging and measurement.

2. Overview of UWB

At present, UWB is essentially a carrier-free spread spectrum technology with low duty cycle (as low as 0.5%) as the information carrier. It directly modulates shock pulses with steep rise and fall times. The typical UWB directly transmits the pulse train, which no longer has the traditional concepts of intermediate frequency and radio frequency. At this time, the transmitted signal can be regarded as a baseband signal (according to conventional radio) or a radio frequency signal (considering the spectral components of the transmitted signal). Impulse pulse usually adopts single-period Gaussian pulse, and one information bit can be mapped into hundreds of such pulses. The width of monocycle signal is ns, which has a wide frequency spectrum. UWB has developed a new wireless channel with GHz capacity and the highest spatial capacity.

The basic composition of UWB pulse wireless transceiver based on CDMA is shown in figure 1. The clock generator at the transmitter generates a pulse sequence with a certain repetition period. The information to be sent by the user and the pseudo-random code representing the user address are modulated in some way or synthesized respectively. The modulated pulse sequence drives the pulse generating circuit to form a pulse sequence with certain pulse shape and regularity, which is then amplified to the required power and then coupled to the UWB antenna for transmission.

At the receiving end, the signal received by UWB antenna is amplified by low noise amplifier and sent to one input end of correlator and the other input end of correlator, where the locally generated pulse sequence modulated by user's pseudo-random code is added. The signal of the receiver and the pulse sequence modulated by the local synchronous pseudo-random code are multiplied, integrated and sample-and-hold in the correlator to generate a signal with separated user address information, which only contains user transmission information and other interference. Then the signal is demodulated, that is, each pulse is judged according to the modulation mode of the originator, and the transmitted information is recovered. Synchronization circuit includes capture and tracking circuit, whose function is to accurately extract the position and repetition period information of clock pulse and apply it to local timing circuit to generate various clock and timing signals needed by receiver.

2. 1 Main indicators of UWB

Frequency range: 3.1-10.6 GHz;

System power consumption:1-4mw;

Pulse width: 0.2- 1.5 ns, repetition period: 25 ns-1ms;

Transmit power:

Data rate: tens to hundreds of Mbit/s;

Decomposition multipath delay: ≤1ns;

Multipath fading: ≤ 5dB;

System capacity: much higher than 3G system;

Space capacity: 1000kB/m? .

3. Key technologies of UWB.

3. 1 pulse signal generation

Essentially, generating a signal source with a pulse width of nanosecond (10-9 s) is a prerequisite for UWB technology. A single carrier-free narrow pulse signal has two characteristics: first, the waveform of the excitation signal is a single short pulse with steep leading edge and trailing edge; Second, the excitation signal includes a wide spectrum from DC to microwave. At present, there are two methods to generate pulse source: (1) photoelectric method, and the basic principle is to obtain pulse signal by using the steep rising/falling edge of photoconductive switch. The pulse width excited by laser pulse signal can reach the order of picosecond (10- 12 s), which is the most promising method. (2) Electronic method, whose basic principle is to use the reverse power of transistor PN junction to obtain a steep rising edge at the turn-on moment of avalanche state, and obtain a very short pulse after shaping, is the most widely used scheme at present. Limited by the withstand voltage characteristics of transistors, this method can only generate pulses from tens of volts to hundreds of volts, and the pulse width can reach below 1ns. A long series of ultrashort pulses are used in practical communication.

3.2 UWB modulation and multiple access mode

3.2. 1 modulation mode

The transmission power of UWB is limited by the power spectral density of the transmitted signal, which affects the selection of modulation methods in two aspects: one is to provide the best error performance for energy modulation per bit; Secondly, the choice of modulation scheme affects the structure of signal power spectral density, so some additional restrictions can be imposed on transmission power.

In UWB, information is transmitted by modulating pulses. It can transmit different information with a single pulse or transmit the same information with multiple pulses.

(1) monopulse modulation

For a single pulse, the amplitude, position and polarity changes of the pulse can be used to convey information. The main monopulse modulation technologies suitable for UWB include: pulse amplitude modulation (PAM), pulse position modulation (PPM), on-off keying (OOK), biphase modulation (BPM) and time-hopping /DS-BPSK modulation.

PAM is a pulse modulation technology, which transmits information by changing the amplitude of pulses. PAM can not only change the polarity of pulse amplitude, but also only change the absolute value of pulse amplitude. PAM usually only changes the absolute value of pulse amplitude. BPM and OOK are two simplified forms of PAM. BPM modulates binary information by changing the positive and negative polarities of pulses, and the absolute values of all pulse amplitudes are the same. OOK transmits information by the presence or absence of pulses. In PAM, BPM and OOK modulation, the time interval of transmitting pulse is fixed. In fact, we can also transmit information by changing the time interval of transmitting pulse or the position of transmitting pulse relative to reference time, which is the basic principle of PPM. In PPM, the polarity and amplitude of the pulse are unchanged.

The advantages of PAM, OOK and PPM*** are that information can be recovered through incoherent detection. PAM and PPM can also improve the information transmission rate by multiple amplitude modulation or multiple position modulation. However, PAM, OOK and PPM all have a common disadvantage: the pulse signals modulated by these methods will have a wired spectrum. Line spectrum will not only make the signal of UWB pulse system difficult to meet certain spectrum requirements (such as FCC's regulation of UWB signal spectrum), but also reduce the utilization rate of power.

As far as the above five modulation methods are concerned, considering the reliability, effectiveness and multiple access performance, the latter two modulation methods, TH-PPM and TH/DS-BPSK, are widely concerned at present. The difference between them is that the performance of TH/DS-BPSK is better than that of TH-PPM when using matched filter for single user detection. For TH/DS-BPSK, when the rate is high, DS-BPSK mode should be preferred. When the rate is low, TH-BPSK should be chosen because it is less affected by the near-far effect. In the application of multi-user receiver with minimum mean square error (MMSE) detection, there is little difference between them. However, at high speed, the performance of TH/DS-BPSK system is better than that of TH-PPM system. On the other hand, BPM can avoid the line spectrum phenomenon and is the most effective pulse modulation technology. BPM is an ideal pulse modulation technology for UWB pulse wireless system with limited power and power to obtain better communication quality or higher communication capacity.

(2) Multi-pulse modulation

In fact, in order to reduce the amplitude of a single pulse or improve the anti-jamming performance, multiple pulses are often used to transmit the same information in UWB pulse wireless systems, which is the basic idea of multi-pulse modulation.

When multi-pulse modulation is used, multiple pulses that transmit the same information are called a group of pulses, so the multi-pulse modulation process can be divided into two steps: the first step is the modulation of a single pulse in each group of pulses; The second step is to modulate each group of pulses as a whole. In the first step, the single pulse in each pulse group usually adopts PPM or BPM modulation; In the second step, each group of pulses as a whole can usually be modulated by PAM, PPM or BPM. Generally, the first step is called spread spectrum and the second step is called information modulation. Therefore, in the first step, PPM is called time-hopping spread spectrum (TH-SS), that is, each pulse in each group has the same amplitude and polarity, but its time position is different; BPM is called Direct Sequence Spread Spectrum (DS-SS), that is, each pulse in each pulse group has a fixed time interval and the same amplitude, but has different polarities. In the second step, PAM changes the amplitude of each group of pulses, PPM adjusts the time position of each group of pulses, and BPM changes the polarity of each group of pulses according to the information bits to be transmitted. In this way, it is not difficult to obtain the following multi-pulse modulation technologies by combining the first step and the second step: TH-SS PPM, DS-SS PPM, TH-SS PAM, DS-SS PAM, TH-SS BPM, DS-SS BPM.