The contention of passive optical network standards

Sichuan Dorset-Smart Electronics Co., Ltd. Hong Honglin

In recent years, there has been controversy over the two technical standards of broadband Passive network (--apon) and Epon, and the controversy between them is essentially the continuation of ATM and IP contention in the core network in the access network.

The formation of Apon standard

As early as the "Internet Age" in 1995, when people did not know that IP would eventually rule the third tier of the network, several of the world's largest telecoms operators, the Nippon Telegraph and Telephone Company (NTT), BT and France Telecom, began to discuss the development of a voice, data, video access network-wide business solutions.

There were two logical choices: the protocol layer was ATM and the physical layer used pon.

Through the tireless efforts of the Fsan (full Business access Network) Group of 21 major telecom operators in the world, in October 1998 the standard ITU-T was approved by the Atm-pon format Standard--itu-t g.983.1;2000 year April, which was adopted by the full service access network. G.983.2;2001 also issued a standard for wavelength allocation: ITU-T g.983.3, a broadband optical access system that uses wavelength assignment to increase business capabilities.

The basic features of the current Apon standard g.983 are:

* Based on ATM signaling

* Symmetric (bidirectional 155.52mb/s) and asymmetric working mode (downlink 622.08mb/s, uplink 155.52mb/s)

* Up to 32 users can support the optical branch, the maximum transmission distance of 20km

* Single fiber or double fiber operation

* Increase business capacity with wavelength allocation

This standard is a good beginning, it provides a kind of realistic performance requirement for examining the supplier of fiber access equipment. Many manufacturers in the world have been in accordance with this standard production or development based on ATM broadband PON products, such as: Terawave, Quantum Bridge, Alcatel, Lucent/oki and other companies.

Freshman Epon started arguing

Although the APON standards have been adopted, with the development of technology and network, EPON has recently been researched and developed to form two competing groups: Ethernet Pon (EPON) and ATM based PON (APON). One side of Epon claims that ATM is obsolete and dead in the access network, while the Apon side contends that only ATM can better guarantee quality of service (QoS) and Support Service level agreements (SLAs).

The main points of the Epon side are as follows:

* With the standard is not necessarily acceptable for the market, and the g.983 standard is not perfect, but also need to improve. For example, it does not yet specify the standard of the video business, and it does not interoperate with the network adapters of different manufacturers as Ethernet standards do.

* The future of the network must be based on IP or Ethernet, through Epon transmission of IP is the best solution (IP over EPON). Their rationale is that PON is simply an access technology not a network technology, and ATM as an access technology is clearly outdated, dead. Only the Ethernet network technology combined with the technology of PON to make Epon is the best scheme of optical access network.

* The vast majority of the world's data are generated by ip/Ethernet, the transfer of data with Apon also need to switch between IP and ATM and SONET/SDH format, low efficiency, technical complexity, high cost, not suitable for all users to promote. * Contrary to Apon, Epon is based on Ethernet, while Ethernet is the most widely used network technology in the world today and in the future, with the lowest prices for related devices and devices. Epon for access network, low cost, good versatility, eliminates the IP data transmission protocol and format conversion, high efficiency, simple management.

Their conclusion, of course, is "epon to win", and in fact it has been supported by a number of new telecom operators and manufacturers.

In this respect, the apon side retorted that:

* ATM technology is a test and mature technology, only it can better support a variety of multimedia services, especially real-time business. ATM is the only option that telecom operators require that their devices provide a clear assurance of business quality and service levels.

* Only ATM can use a single network to provide the desired broadband and narrowband services, and ATM technology has a sound operation and maintenance management system, can use a single management system to complete end-to-end business monitoring and bandwidth management.

* Apon has formed recognized international standards, but also with the Fsan group of the world's more than 20 major telecommunications operators support the strong, as long as mass production, the cost will be significantly reduced.

* On the contrary, Epon is more suitable for the access and transfer of IP services, technology is not mature; IP is not able to deliver high quality guaranteed real-time business, can not achieve a single network of full service access, at the same time, Ethernet also lacks the telecommunications level of network monitoring and business management.

The technical differences between Epon and Apon

The main differences between Epon and Apon are shown in frame structure (EPON and apon frame format, frame cycle length and packaging method are all different), and their main technical difference is: Epon data transmission is in a variable length of the packet, the longest 1,518 bytes While the apon data is mainly transmitted in 53-byte fixed-length ATM signaling (48-byte net load and 5-byte overhead).

Apon proponents claim that their system has a fixed-length frame structure that enables faster and more efficient synchronization, while an ip-based epon scheme never knows how long a packet is, must be cut hard, and is ungrouped at a smaller length. This is because, according to the internet, the maximum length of IP packets is 65,535 bytes, while the Epon protocol has the longest packet size of 1,518 bytes.

In response, epon advocates argue that it is difficult and inefficient to carry IP services with Apon. Apon packet packets must be cut at a small segment per 48 byte, with 5-byte headers per paragraph, so this approach is time-consuming, complex, wasteful of bandwidth, and adds additional costs.

Who loses and who wins

The view accepted by the majority abroad is that it is too early to say who wins, who loses and who wins depending on the requirements of the application and the test of time. From a fair standpoint, both solutions are needed. For traditional telecoms companies and integrated telecoms operators, it is likely to be apon, while in the area of CATV, and for data-centric new telecoms companies and operators, it may be inclined to adopt epon. This is because it is generally believed that apon is better able to guarantee quality and deliver real-time services, while epon is less expensive and more suitable for IP data service delivery.

It seems that most people agree with the development of IP and the improvement of technology, the final optical Ethernet will occupy the dominant position in the "last kilometer". So in the long run, Epon will eventually have a better edge.

The new standard of epon and the future development of broadband PON

Apon and Epon all belong to the broadband Passive Optical Network (bpon), they actually have a lot of passive optical network common advantages. It can be said that the contention between Apon and Epon is essentially the continuation of ATM and IP contention in the core network in the access network. Just as ATM and IP technologies can seamlessly integrate with MPLS in the core network, it is believed that Epon and Apon will find their point of integration. In fact, this "standard war" has led us to see some signs of cooperation.

At the meeting of the IEEE Lan/man Standards Committee (LMSC) in July 2001, the 802.3 working Group approved the working draft of the "First mile Ethernet (Ethernet in the MILE-EFM) research group", The plan supports three kinds of user network topology and physical layer: point-to-point copper wire, lowest speed 10mb/s, at least 750m, point-to-point fiber, single fiber, speed 1,000mb/s, distance at least 10km, optical fiber with DOT to multi point, minimum 1,000mb/s speed, at least 10km. There are indications that the IEEE EFM research team will coordinate fsan efforts in this area when it comes to developing epon standards for point-to-point optical networks. Because the g.983 fsan standard file does not exclude the non-ATM protocol, and leave a lot of room. In this way, the existing content of most g.983 can be effectively referenced, while the IEEE 802.3 EFM team can focus on the research and development of Epon MAC protocol, which is the quickest way to produce epon standards. Several well-known large companies support Epon over APON, including Cisco and Nortel. The main manufacturers of epon, such as Alloptic, also believe that Epon is based on the g.983 standard set for apon. Similarly, the major apon manufacturers, such as Terawave Inc., also claim to be compatible with EPON transmissions and will soon launch Gigabit Ethernet and Gigabit PON interfaces.

To sum up, competition results, will soon appear apon and epon two kinds of broadband pon standard. We believe that the corresponding development of different standards of apon and Epon two products, will learn from each other, common development, play their respective advantages, realize the dream of full business access.