3 facts about PON (Passive Optical Network) technology

 

PON (Passive Optical Network) is the main technology to realize fiber to the home(FTTH), providing point-to-multipoint fiber access. It consists of OLT (Optical Line Terminal) on the bureau side, ONU (Optical Network Unit) and ODN (Optical Distribution Network) on the user side. The biggest highlight of PON technology is “passive”, which means the ODN does not contain any active electronic components and electronic power supply; it is all composed of passive components such as optical splitter, with low management, maintenance and operation cost.

1. 10G PON vs. 25G PON vs. 50G PON

 

In 1987, British Telecom researchers first put forward the concept of PON. 10G PON is divided into 10G Ethernet PON (EPON) and 10G Gigabit PON (GPON). In 2006, the Institute of Electrical and Electronics Engineers (IEEE) 802.3av began to study and formulate the 10G EPON standard. In September 2009, IEEE 802.3av officially released the 10G EPON standard. Since 2008, the International Telecommunication Union Telecommunication Standards (ITU-T) started to develop standards for next-generation GPON technologies, namely NG-PON1 and NG-PON2. NG-PON1 usually refers to XG-PON1 (ITU-T G.987), with downlink and uplink rates of 10Gb/s and 2.5Gb/s, respectively.

Perhaps, its most important feature is the fact that 10G is the first technology that provides operators the ability to deploy a converged architecture – a unified network for both business and residential services – which offers a number of advantages. This includes the ability to simplify network technology and deliver unified domains between Access, Transport, Edge and Core. Furthermore, it enables an operator to converge all services — such as residential, mobile, business and more — onto one network. This converged network ultimately spreads network infrastructure costs across all customers, from cost-sensitive home and SOHO subscribers to SLA-driven corporations and enterprises.

Although 10G PON is a widely used technology these days, the pursuit of 25G/50G PON has made the future speedy and internet-driven. The downstream speeds of 25G and 50G PON are 25Gbps and 50Gbps transmission rates over a single wavelength, respectively. 1) 25G PON Viewpoint: 50G will require a number of new technologies, and the industry is at least 10 years away from 50G PON maturity. That is just too long a wait for broadband operators. 2) 50G PON Viewpoint: A 25 Gbps upgrade step would be considered too close to 10 Gbps and so not sufficiently future proof and, hence, wasteful of the huge investment by network operators in FTTH deployment. 100 Gbps would be nice to have, but this is currently considered too challenging when considered from the whole PON industry perspective. Weigh the pros and cons of technology and requirements, it should select 50G PON.

It is acknowledged that the 50G PON may have more applications with its higher downstream speeds and transmission rate. The 50G PON technology will be a big win for enterprises, which are in pursuit of rigorous connectivity among all their branches and cloud services through private lines. In the data revolution and the emerging Artificial Intelligence technology, the need for continuous high-speed bandwidth can only be fulfilled with 50G PON services. While 25G PON, on the other hand, applies to mobile transport services and business sectors that need technology beyond 10 G PON urgently.

 

2. What is PON transceiver?

 

The wide application of PON Ethernet passive optical network cannot be achieved without PON transceiver, because It is an important component of the PON system. There are mainly three types of PON transceivers:

• SFF vs. SFP vs. SFP+ vs. XFP transceiver

 According to different package types, PON transceiver can be divided into SFF (small form factor), SFP (small form pluggable, 4G), SFP+ (enhanced small form pluggable, Ethernet 10G) or XFP (standard small form pluggable, serial 10G). Among them, SFP + with its advantages of miniaturization and low cost meets the demand for equipment for high-density optical modules and has gradually replaced XFP as the mainstream of 10G market.

• OLT vs. ONU transceiver

According to different plug-in devices, PON transceivers include OLT optical modules and ONU optical modules, and they are all in the SFP form factor. OLT optical modules are more complex than ONU optical modules because each OLT optical module must transmit signals with 64 pieces of GPON ONU optical modules.

• APON vs. BPON vs. GPON vs. EPON

 According to different technical standards (i.e. transmission protocols), PON optical modules can be divided into APON (ATM PON), BPON (broadband passive optical network), EPON (Ethernet passive optical network) and GPON (gigabit passive optical network).

At present, the GPON and EPON transceivers are most widely used.

 

3. GPON vs. EPON: what’s the difference?

 

GPON (Gigabit Capable PON) was proposed by FSAN in September 2002, and then ITU passed G.984.1 and G.984.2 protocols in March 2003. The G.984.1 protocol specifies the overall characteristics of GPON access system; The G.984.2 protocol specifies the physical medium-related sub-layer of ODN (Optical Distribution Network) of GPON. In June 2004, ITU passed the G.984.3 protocol, which stipulates the relevant requirements of GPON transmission convergence layer (TC).

For many years, the industry has always believed that PON is the future development direction of access networks. On the one hand, the bandwidth it provides can meet the needs of various broadband services now and in the future, so PON is ideal in solving the problem of broadband access; On the other hand, the overall cost is relatively low in terms of equipment cost and operation&maintenance cost.

GPON and EPON have their own advantages as two ways of optical network access. Next, this paper will comprehensively analyze and compare the two from four aspects: technical specification, cost, level of development, application and security.

EPON vs GPON: Technical Specification

Overall, the technical differences between GPON and EPON are very small. The difference between the two is mainly on the interface, while the switching, network element management, user management are similar, or even the same. In comparison, GPON has more advantages in multi-service bearing and full-service operation, which is mainly due to the GPON standard is developed by FSAN, which is an operator-led organization.

Regarding the cost, GPON is more expensive than EPON when measured in terms of individual optical ports. However, operators mainly focus on the network construction cost, not the equipment cost. This is because in terms of bandwidth and service support capability, each GPON port can access 64 or even 128 users, while each EPON port can only access 32 users. In addition, in the actual network construction, the cost of office-end equipment accounts for less than 10%, while OLT accounts for 50%. Therefore, GPON is cheaper in terms of overall network construction cost.

All in all, when we are talking about GPON and EPON, the first thing is that GPON has a larger bandwidth than EPON. Its service carrying capacity is more efficient and its optical splitting ability is stronger. However, the implementation of GPON is more complex, which leads to its higher cost compared with EPON. Luckily, with the large-scale deployment of GPON technology, the cost difference between GPON and EPON is gradually narrowing.