OPTICAL ACCESS NETWORK’s (OAN’s)
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Microwave Course Term Paper in Fiber Optics / 20101. History & Reason of Existence
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Microwave Course Term Paper in Fiber Optics / 2010The experience with active and passive optical networks have been gained within ten years of experience with active and passive optical networks .These networks has different features that causes both of them to have advantages and disadvantages. Fiber optics network can be laid directly to households (Fiber to Home [FTTH]) by using direct networks which include the main types of network that are Passive optical networks (PON) & Active optical networks (AON).
In the mid-1990s, the first large-scale PON installations were commissioned in Japan. In many other parts of the world, FTTH concepts were a long way off. The existence of the internet and the need of better bandwidth has a great attract to customers but the technology was much too expensive in any case ,so earlier customers didn’t believe it’s necessary to have a higher bandwidth capacity until the beginning of the new millennium.
The subsequent escalation of bandwidth, fuelled by the availability of broadband DSL connections via copper wire, has turned the internet and associated services into an unparalleled success story.
Today, considering all the new services like high definition IPTV, online gaming and remote surveillance, ICT service providers are well advised to seek access network solutions with even more bandwidth for the post-DSL era. However, due to the physical properties of copper wire in the last mile, VDSL2 has reached its limits, even if technology called DSM (Dynamic Spectrum Management) is being developed to boost the transmission capacity on copper. Communication solutions like WiMAX, or LTE in mobile telephony, reach the limits of their capabilities even more quickly because of poorer physical transmission properties (in comparison with copper). To date, the only solution for seemingly infinite bandwidths has been the optical wave guide, also called Fiber optics.
2. Basic Facts
The main difference between PON & AON is that PON uses passive splitters. The splitter is basically a kind of multi-mirror that distributes the optical signal for the subscriber line to fiber optic routes without any electrical current (which is why it is called passive).
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Microwave Course Term Paper in Fiber Optics / 20106 | Page
Microwave Course Term Paper in Fiber Optics / 2010The first active optical access networks used TDM technology. The first passive optical networks on the other hand used ATM for voice and data traffic. (Because early PON systems could already transmit a TV broadcast signal on a separate wavelength in the optical spectrum, simultaneously to the voice-data signal, they were popular in cable TV networks. The topologies of PON and CATV networks are also very similar to one another, so existing cable lines, or ducts can be used and costs saved in the network rollout. The objective of both PON and AON is to get the fiber optics as close as possible, ideally right into the subscribers’ houses and apartments. This FTTH- solution is technically the best option with respect to the transmission quality and the bandwidth.
2.1. Passive Optical Networks (PONs)
The first network element in Passive Optical Network is the Line Termination Unit), that provides n x 1 Gbps and n x 10 Gbps Ethernet interfaces to the core network and the PON interfaces to the subscriber . The PON types used here today are usually Ethernet-PON or its called (EPON), Gigabit-PON (GPON) or Gigabit-Ethernet-PON (GEPON). Ethernet technology is the common denominator in all these technologies.
In FTTH network architecture, subscriber t access is implemented using optical network termination (ONT) that terminates the optical signal and converts it into one or more electrical interfaces, such as for example 100BaseTx, POTS, ISDN or Coax.
If copper wire is used for the last mile, an optical network unit (ONU) can
be used instead of the optical network termination in the PON, which then provides interfaces such as POTS, ISDN or DSL.
In this case, the network architecture is a Fiber-to-the-Curb (FTTC) connection.
All PON subscribers receive the same optical signal at the end of the fiber optics. The personal allocation of data is carried out via a time multiplex procedure, i.e. each subscriber receives their own time slot to transmit and receive. Synchronization of the right user time slot is carried out in the ONT.
2.2 Active Optical Networks (AONs)
AON is a point-to-point network structure (PTP), i.e. each subscriber has their own fiber optic line that is terminated on an optical concentrator (Access Node [AN]).
This type of AN can be designed differently, depending on specific locations. Usually Metro Ethernet-Switches, IP-Edge routers or Multi-Service Access Nodes (MSANs) with optical Ethernet interfaces are used in this case. The Fiber optics can be terminated by an ONT here too, but also by any Ethernet switch or IP router with an optical uplink interface. If the last mile to the subscriber is to be bridged using copper wire, DSLAMs or other MSANs are used. When MSANs are used, both copper and optical lines can be used for the last mile from the same access node.
3. AON vs. PON
3.1. Bandwidth
The trend towards increasing bandwidth continues unabated. Due to the launch of TV-over-IP (IPTV) there is no sign of the increase in bandwidth tailing off, in fact quite the opposite. Because of the recent launch of (HDTV) and other technically complex services Such as online gaming, network operators are being encourage to outdo one another by providing more and more bandwidth. The following table compares PON and AON transmission bandwidth.
When comparing PON and AON from the bandwidth Allocation, it can be noticed that AON is better since in AON the amount allocated to the subscribe is governed by the interface type, or traffic shaping on the access node and
is therefore adjustable in kilobit increments.
While for PON, The GPON interface on the OLT nowadays is 2.5/1.25 Gbps (downlink/uplink). The bandwidth per subscriber is determined by the splitting factor (usually 1:32 or 1:64). Modern PON system show ever permits bundling of several time slots and therefore an increase in bandwidth per PON terminal point.
And so AON clearly has the edge because of its flexibility. Due to the static splitting factor and the interfaces on the OLT, PON is at a disadvantage.
Also another issue that is to be looked at, when dealing with the ability to increase the bandwidth, As the active access node has a modular structure, subscriber interfaces can be upgraded to include more Bandwidth. It is often sufficient to just switch the fiber optic lead to be able to operate it again.
While it’s very difficult when it’s done in PON, since it depend on the systems technology. It would be feasible in the future to bundle several time slots and therefore, at the cost of the maximum number of subscribers per PON branch, to increase individual bandwidth by a factor of n + 1. The bandwidth of the PON port on the OLT is the absolute limit.
3.2. Security and quality of services
An aspect in public networks that is regaining importance is Quality-of-Service (QoS), which considering today‘s financial restraints is often forced to take a back seat. At the dawn of the ADSL rollout, the majority of services offered took a best effort approach, i.e. the data channel guaranteed neither a minimum bandwidth, nor any other quality features worth mentioning. As today however, Triply Play services (telephony, data and TV down one single line) are already transmitted to the subscriber, QoS applies more than ever .
When surfing the Web, short delays of 1 – 2 seconds, e.g. when clicking on a link, do not really matter. During a phone call, this level of delay is however completely unacceptable. When watching TV, it is also no fun if the picture freezes before a goal is scored. As a result, the Triple Play services must be clearly separate and allocated priority. Although theoretically unlimited bandwidth is available in a fiber optic line, QoS not be forgotten. Not all QoS aspects can be responded to with bandwidth and neither PON nor AON can really provide unlimited bandwidth.
Nowadays, the Triple Play offerings, implemented via copper wire often consist of two television channels with standard resolution (SDTV), a high-speed Internet connection (>3 Mbps) and at least one POTS or ISDN telephone connection. The current state of the art is that network operators are planning approx. 15 Mbps downlink capacity.
In the future the end customer will be demanding high definition TV (HDTV). Two simultaneous TV channels will mean an unacceptable restriction for a family of four in the long term. Furthermore, currently ADSL 16 Mbps Internet access is already being marketed to private customers and including n telephone lines.
Online gaming – in the Far East popular for years – is also looking promising in Europe. In this case, top rates of 50 Mbps per subscriber line could easily be reached. Today, standard VDSL2 access would not be able to cope.
The scenario described above indicates what the private consumer will look like in the near future. If such a scenario appears exaggerated, we only have to recall the situation 10 years ago when modern end customers still used 56 kbps dial-up modems to read emails, for
sending faxes and for home banking. In
comparison to today’ s standard 3.5 Mbps ADSL connection, the bandwidth has increased 62-fold! Special requirements from business customers, or demands for the backhaul of sub-networks, server connections or high performance IT applications would easily exceed these quality specifications and require even greater high quality performance.
3.3. Business case aspects
Using fiber optic cable promises virtually unlimited bandwidths, however the network operator only ever has just the copper wire line in the last mile. That means that if the DSL technology is no longer adequate, new optical cables must always be laid.
But when making a comparison between POS and AOS from different Investment views it can be noticed that
PON Vs.AON in CostAON / PON
Low / High
Cost of (active components)
High / Low
Costs of (passive components and infrastructure)
High / LOW
Network rollout costs
High / Low
4. Summery
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