Arhitectura Passive Optical LAN este dezbătută într-un scurt articol publicat în Applications of Information Systems in Engineering and Bioscience, de către Nikos E Mastorakis de la Technical University of Sofia.
Ca un rezumat, articolul face referire la Rețelele optice pasive (PON), denumite generic rețele LAN pasive pe fibră optică (POL), rețele ce câștigă avans în mediul companiilor mici, medii si mari, ca mijloc de aducerea fibrei optice mai aproape de utilizatorul final, crescând astfel securitatea rețelei, economisirea spațiului util și asigurarea unei infrastructuri mai ecologice, mai sustenabile, dar și mai ieftine de realizat. Această lucrare prezintă arhitectura POL-urilor în mediul întreprinderilor, folosind tehnologia Gigabit Passive Optical Network (GPON).
Cuvinte cheie: - Single Mode Fibre (SMF), GPON, POL, Cloud Computing, WLAN, IP/RF Video, VoIP, Security, QoS
Articolul integral...
Architecting Passive Optical LANs for the Corporate-Wide Enterprise STANISLAV MILANOVIC*, NIKOS E. MASTORAKIS *o *WSEAS Agiou I. Theologou 17 15773, Zographou, Athens GREECE stanislav.milanovic@ieee.org http://www.wseas.org/ o Military Institutions of University Education Hellenic Naval Academy Terma Hatzikyriakou, 18539, Piraeus GREECE mastor@tu-sofia.bg http://www.hna.gr/snd/eng/welcome.html Abstract: - Passive optical networks (PONs), sometimes referred to as Passive Optical Local Area Networks (POLs), are gaining traction in the premise environment as a means to move optical fiber closer to the end user while increasing network security, saving space and providing a greener, more sustainable infrastructure. This paper is showcasing the architecture of the POLs in the enterprise environment, leveraging the Gigabit Passive Optical Network technology (GPON). Key-Words: - Single Mode Fibre, GPON, POL, Cloud Computing, WLAN, IP/RF Video, VoIP, Security, QoS
1 Introduction
Enterprise networks are facing disruptive change caused by the use of Internet versus enterprise based applications, increasing video content, integration of voice services onto the Local Area Network (LAN), and the transition from wired to wireless LANs. Accommodating increased bandwidth, though it is the primary agent causing disruptive change, is not the only one. Other change agents include the need to:
accommodate wired and wireless connectivity
support voice, video, and data services
migrate from perimeter to role-based security
reduce labor- intensive network operations tasks
deploy environmentally friendly solutions
While facing disruptive change to either an existing enterprise site or a new enterprise site, a global organization had the opportunity to dramatically reduce Total Cost of Ownership (TCO) by moving to a Passive Optical Network based on GPON technology, rather than continuing with use of traditional two- or three-tier switched Ethernet solution. GPON technology is used to establish a passive infrastructure that does not require any electrical power at the intermediate nodes between the aggregation and the user nodes [1].
Passive Optical LAN is being adopted at a fast pace by large government and enterprise LAN customers attracted to the benefits of significant cost savings. Migrating to a high-performance local area network does not have to mean paying more in equipment costs or energy consumption. A new generation of Passive Optical LAN technology actually reduces long-term costs, while delivering all the performance benefits expected of optical networks [2].
2 Objectives When deploying LANs, a global enterprise juggled three, often conflicting, requirements. Budgetary constraints dictated the need to control both initial and long-term networking costs. Yet enterprise business also wanted to install the latest technology — in terms of network speed, functionality and security — in a way that enables the cost-effective evolution of networks in step with inevitable advances in technology. Finally, as an environmentally conscientious enterprise, a global organization seeked the greenest-possible route to achieving the other two objectives, namely by deploying LANs that would reduce the organizations’ energy consumption.
Fortunately it now has been possible to achieve all Gigabit-speed Passive Optical Networks use single- three objectives at the same time by deploying mode fiber, connecting the headend-optical line advanced optical LANs solution, based on GPON terminal (OLT) through one or more passive optical technology.
3 Passive Optical LAN Overview Passive Optical LAN is alternative to the traditional layer-2 copper based LAN infrastructure [3]. It is covered by ITU-T G984.x industry standard (Full Service Access Network), which is based upon the GPON technology, using a Generic Encapsulation Method (GEM) that supports Ethernet, ATM, and TDM data transport. POL enables the delivery of highly-secure unified networks providing IP voice, data, and any type of video over a single fiber splitters, to multiple endpoints called optical network terminals (ONTs). GPON delivers 2.5 Gbps of bandwidth to each ONT [4]. ONT converts optical signals to the signals used in building wiring, such as Ethernet and wired analogue plain old telephone service. Each PON can incorporate from 1:1 up to 1:128 splits and is dependent upon the committed and peak information rates. In practice most PONs are deployed with a split ratio of 1:32 or 1:64 (Figure 1).
Distances of up to 20 km with a 32-way split can be supported. The technology is considered “passive” because transmission is powered directly from the OLT to the ONT and there is no switching or routing in between.
Figure 1. GPON Connectivity
4 ARCHITECTURE COMPARISON Throughout enterprises, Category 3/5/6 copper cables typically connect 3 layers of routers and switches in a traditional active Ethernet LAN. A router in the top- most layer(CoreLayer) links to the campus or building aggregation switches (Distribution Layer) below [5]. These switches, in turn, connect down to the access layer switches in the communications closets. Copper cables extend from the communications closets to the users (Figure 2).
Figure 2. Traditional Active Ethernet LAN
An optical LAN, on the other hand, simplifies the network and eliminates aggregation levels [6]. This solution retains the router at the top-most layer and the Optical Line Terminal (OLT) serves the same purpose as the campus aggregation switches, which effectively eliminates the campus- and building-aggregation switches, as well as the communications closets. Instead, a single-mode fiber, typically equipped with a 1x32 optical splitter, runs between the router and OLT to the Optical Network Terminals (ONTs) serving end- users [7]. An optical splitter is a passive device so there are no power requirements. (Figure 3).
Figure 3. Passive Optical LAN
Both solutions provide data access via 1000Base-T Ethernet connections to the user. Therefore, no client or PC reconfiguration is required when upgrading from active Ethernet to a GPON infrastructure.
5 GPON OVERVIEW GPON is a Layer 2 non-fragmented multiservice network architecture that complements the Layer 3 services offered by a core switch through native or tagged VLANs, native SIP support and bit, port, and segment visibility, control and management. It takes advantage of wavelength division multiplexing (WDM), using one wavelength (1490nm) for 2.5G downstream traffic and another (1310nm) for 1.2G upstream traffic on a single fiber. The 1550 nm wavelength is reserved for optional overlay services, typically RF (analog) video [8]. GPON is a point to multi-point aggregation core network architecture that offers port and bit segmentation for guaranteed Quality of Service (QoS). GPON does not broadcast and instead, it distributes all downstream signals through secure, virtual point-to- point connections, which utilize AES-128 encryption between the OLT and ONT. Upstream signals are combined using a multiple access protocol, usually time division multiple access (TDMA) or a dynamic bandwidth-allocation scheme, which prevents different users’ data frames from interfering with each other [9].
A GPON Ethernet port that connects to a VoIP phone operates in the same fashion as a traditional switched network. If the ONT is configured in support of QoS for the VoIP connection, it will support that bit rate. If additional port capacity is needed, it is a simple matter of configuring the port capacity for the required services [10]. GPON traffic flows in symmetric fashion within assigned segments and VLANs. Up to 4000 VLANs are supported per OLT. ONTs configured for one VLAN can not be swapped for another VLAN or segment at any time. This improves security, manageability and network performance. When the GPON is properly designed for Peak and Committed Information Rate (PIR/CIR), segmented by VLAN and service for QoS, and established according to the input capacity to include the core switch, performance will be exceptional largely from the elimination of switch fragmentation [11].
GPON bit rates are configured according to QoS requirements for given services. A fully integrated GPON network actually reduces the number of disjointed network management systems and bandwidth requirements within a data center or wiring closet. GPON provides convergence of voice, data, IP and RF Video, POTS, security, surveillance, alarms, environmental systems and access control systems over a single network utilizing the advanced security features of QoS, class of service and VLAN mechanisms [12].
GPON chassis (OLT) is accompanied by a management workstation (Element Management System) that presents a Graphical User Interface (GUI) and Command Line Interface (CLI) for configuration purposes. The ability to manage bit, port, and power levels across the system, in VLANs and groups, and down to individual ports provides performance assurance that is just not available in legacy switched network configurations [13].
GPON ONTs are available with Power over Ethernet (PoE), both in low power IEEE 802.3af and high power IEEE 802.3at standard configurations. The GPON configuration can also provide guaranteed power management or elimination of PoE. Broadcast storms from loopback cables are also eliminated via a 5ms default port shutdown and non-conductive fiber [14]. 6 PASSIVE OPTICAL LAN VS. TRADITIONAL LAN Figure 4 depicts differences between the POL and traditional active Ethernet LAN infrastructure.
Figure 4. Differences between Active Ethernet LAN and Passive Optical LAN
7 SHIFT TO CLOUD COMPUTING Although virtualization and consolidation are driving very high capacity needs in the corporate data center, the trend for applications and data to be increasingly located at a different physical site from most users changes some of the fundamental design requirements for enterprise premises LANs [15]. The emergence of cloud computing models compounds this effect (Figure 5). In "traditional" premises LAN designs supporting local servers, LAN (especially backbone) capacity was more important than WAN capacity. But with remote servers and resources in centralized data centers or "in the cloud“, WAN and premises LAN/backbone capacity requirements converge.
Figure 5. Trend towards the Cloud Computing Model
In addition, the enterprise networks are increasingly using wireless for user access, and Wi-Fi is becoming the default wireless choice. Because the floor area supported by a typical Wi-Fi access point is less than that supported by a typical wired Ethernet switch, the physical reach of the backbone needs to increase. Fiber-optic cabling meets these needs, and the fiber backbone/wireless access model has already been dubbed "Fi-Wi“. GPON is a good match for these needs and also enables lower-cost campus networks, as it is more cost-effective at long distances than switched Ethernet [16].
This opens up opportunity for GPON's simpler and less expensive, but shared bandwidth model for enterprise premises LAN (Figure 6).
Figure 6. Opportunity to rethink the enterprise LAN
8 Implemented PON Architecture Applied architecture for optical LANs leveraging GPON technology was applied for several corporate use cases to provide connectivity between the OLT and the ONT:
large branch office (campus) and a global data center, encompassing between 1000 and 5000 locally connected users
medium branch office and a local data room, encompassing between 250 and 1000 locally connected users
small branch office encompassing between 50 and 250 locally connected users
very small branch office encompassing up to 50 locally connected users
The transmission is powered directly from the OLT to the ONT and there is no switching or routing in between. The Figure 7 describes the high-level architecture of deployed optical LAN solution. It depicts Passive Optical LANs deployment for a global organization, based on GPON technology, including the LAN use cases for a large office, medium office, small office, and a very small office, as well as a global data center operating in a hybrid cloud model.
Figure 7. Applied architecture for the GPON based POLs in the enterprise environment
ONT converts fiber optic “light signals” to copper’s “electric signals” for delivery of advanced services like IPTV, VoD (Video on Demand), VoIP and other packet-based video and voice services directly to the end user equipment. At the end user desktop, an ONT provides a managed demarcation point for network services. The ONT itself has no user controls and is managed via the OLT’s Element Management System. A key security feature provided by optical LAN solution ensures that the ONT cannot function unless provisioned by the OLT. OLT enables symmetrical broadband service delivery to the end-user device, which is the ONT, and end user equipment like IPTV box, surveillance camera, VoIP phone and laptop computers. It also supports quality of service (QoS) and flexible dynamic bandwidth allocation. OLT sends a single stream of downstream traffic that is seen by all ONTs.
Each ONT only reads the content of those packets that are addressed to it. Encryption is used to prevent eavesdropping on downstream traffic. The data stream between the OLT and the ONT is encrypted using AES encryption standard with AES-128 block cipher. Applied GPON based POLs in the enterprise environment enabled the convergence of voice, data and video onto a single strand of single mode fiber, which reduced the network infrastructure hardware to a fraction of what is required in terms of cabling and electronics in the conventional Ethernet approach. The solution not only enabled easier maintenance, but also improved efficiency with regard to end user-related, adds, moves and changes. Since there are no active electronic components between the data center and the end user, particularly in the riser closets, there are significant power savings as cooling is not required in the riser closets. Implemented fiber optical LANs are more energy- efficient and environmentally friendly and they take up less floor, rack and closet space than traditional active Ethernet LANs. Applied solution also requires no signal regeneration for up to 20 kilometers between the data center and the end user. Those features and capabilities enable a faster return on investment and significantly reduce total cost of ownership, both in terms of capital and operating expenditures during the life of the infrastructure (Figure 8).
Figure 8. POL savings compared to active Ethernet LAN
Single-mode fiber is expected to support advances in GPON technology for years to come. Passive Optical LANs can be upgraded without new cable infrastructure deployment. Expanding a GPON based POL is simply a matter of adding new OLT connectivity. As 10GPON (or XGPON) emerges, a global enterprise can upgrade its Optical LANs simply by upgrading the terminal electronics. Unlike traditional Ethernet LANs where the cabling infrastructure must be replaced each time the Ethernet switches increase link speed, Optical LANs will not require fiber infrastructure upgrades or any work environment changes. Thus by replacing its legacy LANs with optical solution based on GPON technology, a global organization could readily achieve its overriding LAN objectives. Applied GPON based POLs delivered the necessary speeds, capacity and functionalities in the enterprise environment. The Enterprise controls now both near- and long-term CapEx and OpEx. Equally important, by deploying GPON based POLs, a global organization has got a network that’s designed to satisfy its unique requirements for years to come.
9 Conclusion The centralization of data centers and emergence of cloud computing, combined with the increasing shift from wired to wireless at the edge of the enterprise network, are subtly changing the requirements for enterprise LANs [17]. These trends are shifting the needs for high-performance and advanced features into data center networks, with a resulting opportunity for simpler premises LANs. Deployed GPON based POLs in the enterprise environment extended service to any stationary Ethernet end point. It enabled the delivery of reliable and highly-secure unified network providing IP voice, data, and any type of video over a single fiber. It also increased the size of the network building block which greatly simplified enterprise network deployment, operation, and management. The solution supported energy conservation, since the optical LAN infrastructure utilized passive components like optical distribution hubs and fiber plant that required no power or cooling, resulting in significant energy savings. Implemented POLs provided immediate return on investment and a low total cost of ownership compared to copper-based LANs. Communications Service Providers (CSPs) that are already operating GPON as part of their FTTH services will be in an interesting position to operate passive optical LAN infrastructure for enterprises that are interested in outsourcing their LANs. As such, passive optical LAN could become an integral part of CSPs' cloud strategies. References:
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