next-generation network (NGN)

The next-generation network (NGN) is body of key architectural changes in telecommunication core and access networks. The general idea behind the NGN is that one network transports all information and services (voice, data, and all sorts of media such as video) by encapsulating these into IP packets, similar to those used on the Internet. NGNs are commonly built around the Internet Protocol, and therefore the term all IP is also sometimes used to describe the transformation of formerly telephone-centric networks toward NGN.

NGN is a different concept from Future Internet, which is more focused on the evolution of Internet in terms of the variety and interactions of services offered.

Description

NGN Seminar in Fusion Technology Center by NICT(Japan) researcher

According to ITU-T, the definition is:

A next-generation network (NGN) is a packet-based network which can provide services including Telecommunication Services and is able to make use of multiple broadband, quality of Service-enabled transport technologies and in which service-related functions are independent from underlying transport-related technologies. It offers unrestricted access by users to different service providers. It supports generalized mobility which will allow consistent and ubiquitous provision of services to users.^[1]

From a practical perspective, NGN involves three main architectural changes that need to be looked at separately:

• In the core network, NGN implies a consolidation of several (dedicated or overlay) transport networks each historically built for a different service into one core transport network (often based on IP and Ethernet). It implies amongst others the migration of voice from a circuit-switched architecture (PSTN) to VoIP, and also migration of legacy services such as X.25, frame relay (either commercial migration of the customer to a new service like IP VPN, or technical emigration by emulation of the "legacy service" on the NGN).
• In the wired access network, NGN implies the migration from the dual system of legacy voice next to xDSL setup in local exchanges to a converged setup in which the DSLAMs integrate voice ports or VoIP, making it possible to remove the voice switching infrastructure from the exchange.
• In the cable access network, NGN convergence implies migration of constant bit rate voice to CableLabs PacketCable standards that provide VoIP and SIP services. Both services ride over DOCSIS as the cable data layer standard.

In an NGN, there is a more defined separation between the transport (connectivity) portion of the network and the services that run on top of that transport. This means that whenever a provider wants to enable a new service, they can do so by defining it directly at the service layer without considering the transport layer – i.e. services are independent of transport details. Increasingly applications, including voice, tend to be independent of the access network (de-layering of network and applications) and will reside more on end-user devices (phone, PC, set-top box).

Underlying technology components

Next-generation networks are based on Internet technologies including Internet Protocol (IP) and multiprotocol label switching (MPLS). At the application level, Session Initiation Protocol (SIP) seems to be taking over from ITU-T H.323.

Initially H.323 was the most popular protocol, though its popularity decreased in the "local loop" due to its original poor traversal of network address translation (NAT) and firewalls. For this reason as domestic VoIP services have been developed, SIP has been more widely adopted. However, in voice networks where everything is under the control of the network operator or telco, many of the largest carriers use H.323 as the protocol of choice in their core backbones.^{[citation needed]} With the most recent changes introduced for H.323, it is now possible for H.323 devices to easily and consistently traverse NAT and firewall devices, opening up the possibility that H.323 may again be looked upon more favorably in cases where such devices encumbered its use previously. Nonetheless, most of the telcos are extensively researching and supporting IP Multimedia Subsystem (IMS), which gives SIP a major chance of being the most widely adopted protocol.

For voice applications one of the most important devices in NGN is a Softswitch – a programmable device that controls Voice over IP (VoIP) calls. It enables correct integration of different protocols within NGN. The most important function of the Softswitch is creating the interface to the existing telephone network, PSTN, through Signalling Gateways and Media Gateways. However, the Softswitch as a term may be defined differently by the different equipment manufacturers and have somewhat different functions.

One may quite often find the term Gatekeeper in NGN literature. This was originally a VoIP device, which converted (using gateways) voice and data from their analog or digital switched-circuit form (PSTN, SS7) to the packet-based one (IP). It controlled one or more gateways. As soon as this kind of device started using the Media Gateway Control Protocol, the name was changed to Media Gateway Controller (MGC).

A Call Agent is a general name for devices/systems controlling calls.

The IP Multimedia Subsystem (IMS) is a standardised NGN architecture for an Internet media-services capability defined by the European Telecommunications Standards Institute (ETSI) and the 3rd Generation Partnership Project (3GPP).

Implementations

In the UK another popular acronym was introduced by BT (British Telecom) as 21CN (21st Century Networks, sometimes mistakenly quoted as C21N) — this is another loose term for NGN and denotes BT's initiative to deploy and operate NGN switches and networks in the period 2006–2008 (the aim being by 2008 BT to have only all-IP switches in their network). The concept was abandoned, however, in favor of maintaining current-generation equipment.

The first company in the UK to roll out a NGN  which started deployment back in 1999. THUS' NGN contains 10,600 km of fibre optic cable with more than 190 points of presence throughout the UK. The core optical network uses dense wavelength-division multiplexing (DWDM) technology to provide scalability to many hundreds of gigabits per second of bandwidth, in line with growth demand. On top of this, the THUS backbone network uses MPLS technology to deliver the highest possible performance. IP/MPLS-based services carry voice, video and data traffic across a converged infrastructure, potentially allowing organisations to enjoy lower infrastructure costs, as well as added flexibility and functionality. Traffic can be prioritised with Classes of Service, coupled with Service Level Agreements (SLAs) that underpin quality of service performance guarantees. The THUS NGN accommodates seven Classes of Service, four of which are currently offered on MPLS IP VPN.

In the Netherlands, KPN is developing an NGN in a network transformation program called all-IP. Next Generation Networks also extends into the messaging domain and in Ireland, Openmind Networks has designed, built and deployed Traffic Control to handle the demands and requirements of all IP networks.

In Bulgaria, BTC (Bulgarian Telecommunications Company) has implemented the NGN as underlying network of its telco services on a large scale project in 2004. The inherent flexibility and scalability of the new core network approach resulted in an unprecedented rise of classical services deployment as POTS/ISDN, Centrex, ADSL, VPN, as well as implementation of higher bandwidths for the Metro and Long-distance Ethernet / VPN services, cross-national transits and WebTV/IPTV application.

In Canada, startup Wind Mobile owned by Globalive is deploying an all-ip wireless backbone for its mobile phone service.

In mid 2005, China Telecom announced its commercial roll-out of China Telecom's Next Generation Carrying Network, or CN2, using Internet Protocol Next-Generation Network (IP NGN) architecture. It's IPv6-capable backbone network leverages softswitches (the control layer) and protocols like DiffServ and MPLS, which boosts performance of its bearer layer. The MPLS-optimized architecture also enables Frame Relay and ATM traffic to be transported over a Layer 2 VPN, which supports both legacy traffic and new IP services over a single IP/MPLS network.^[3]

Reliance Jio is the only network in India that is all-IP and supports RCS and VoLTE.^[4] India has set up NGN lab at Odisha which is capable of subjecting Internet Protocol based equipment for Conformance and Interoperability testing. The government has planned to launch NGN in major cities of Maharashtra and Goa in financial year 2016-17, aimed at better quality broadband connectivity.^[5]

1. Jump up

OTDR - Optical Time Domain Reflectometer

An Optical Time Domain Reflectometer (OTDR) is an important instrument used by organizations to certify the performance of new fiber optics links and detect problems with existing fiber links.

Certifying New Links

The health of your network depends on the quality of your network infrastructure. This quality begins with complete certificationby contractors or systems integrators that the fiber cabling infrastructure was properly installed. Maintaining a reliable fiber plant is also essential in protecting your business-critical applications. As a network administrator, it is important to understand how to get the best performance from your cabling investment and how to solve problems quickly when they occur.

Most customers are familiar with Basic Certification - sometimes known as Tier 1 fiber certification – which measures attenuation (insertion loss), length and polarity. This test ensures that the fiber link exhibits less loss than the maximum allowable loss budget for the immediate application. Simple Light Source/ Power Meters or more automated Optical Loss Test Sets can perform this function.

Extended or Tier 2 fiber certification supplements Tier 1 testing with the addition of an Optical Time Domain Reflectometer (OTDR) from end to end. An OTDR trace is a graphical signature of a fiber's attenuation along its length which provides insight into the performance of the link components (cable, connectors and splices) and the quality of the installation by examining non-uniformities in the OTDR trace. More advanced units can provide easy to understand Event Maps and loss values for individual components as well as the link.

An OTDR trace helps characterize individual events that can often be invisible when conducting only loss/length (tier 1) testing. Only with a complete fiber certification can installers have a complete picture of the fiber installation and network owners have proof of a quality installation.. This fiber test certifies that the workmanship and quality of the installation meets the design and warrantee specifications for current and future applications.

Viewing trace results is simplified with advanced features such as pinch and zoom

Bi-Directional Testing

Bi-directional testing of fiber links for Tier 2 (OTDR) testing is not only required by industry standards and most manufacturers for warranty, it's also the only way to know the actual overall loss for a link. That's because measuring the loss of fiber connectors and splices, as well as overall link loss, depends on the test direction. Testing a fiber link in one direction can give you different results than testing the same fiber link in the opposite direction.

Because of the significant time and cost involved in testing from both ends, technicians often try to save as much time as possible by testing all links from one end before moving to the other end. Unfortunately this method does not work. To accurately test a fiber link in both directions, the launch and tail cords must remain in their initial measurement positions (even the standards say so) during both tests. But that is simply not possible if you test all the links from one end before moving to the other.

To solve this dilemma, you can test two fibers at the same time and use a loop to connect the two fibers together. This allows the two fibers of a duplex link to be tested in one shot without moving the OTDR to the far end. OTDRs like Fluke Networks’ OptiFiber® Pro feature “SmartLoop” Technology that checks for the presence of the launch, loop and tail fiber when testing a duplex fiber link.

The OptiFiber Pro Event Map displays Pass/Fail results and the loss for the overall fiber as well as for each event.

With SmartLoop, technicians can deploy multiple loops at the far end and perform a set of bidirectional tests without ever having to leave the near end--cutting test time by at least 50%.

Detecting Problems

When selecting the right OTDR, network engineers should make sure the tool has certain functionality, such as loss-length certification, channel/event map view, power meter capabilities, an easy-to-use interface, and smart-remote options. In addition, the OTDR needs to provide a reliable means to document the results. Features that make the OTDR easy to operate such as automated setup and Event Map are essential for users who aren’t OTDR experts but need to locate problems fast.OTDRs are also used for maintaining fiber plant performance. An OTDR maps the cabling and can illustrate termination quality and location of faults that may hinder network performance. An OTDR allows discovery of issues along the length of a channel that may affect long term reliability. OTDRs characterize features such as attenuation uniformity and attenuation rate, segment length, location and insertion loss of connectors and splices, and other events such as sharp bends that may have been incurred during cable installation or afterwards.

Tools such as the award winning OptiFiber® Pro OTDR provide the ultimate testing and troubleshooting solution to ensure the health of your most critical network cabling. With the OptiFiber Pro OTDR, network engineers have the in-house capability to perform inspection, verification, certification, troubleshooting, and documentation of fiber cabling in a single, easy-to-use OTDR tool.

virtual private network(vpn)

A virtual private network (VPN) extends a private network across a public network, such as the Internet. It enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. Applications running across the VPN may therefore benefit from the functionality, security, and management of the private network.^[1]

VPNs may allow employees to securely access a corporate intranet while located outside the office. They are used to securely connect geographically separated offices of an organization, creating one cohesive network. Individual Internet users may secure their wirelesstransactions with a VPN, to circumvent geo-restrictions and censorship, or to connect to proxy servers for the purpose of protecting personal identity and location. However, some Internet sites block access to known VPN technology to prevent the circumvention of their geo-restrictions.

A VPN is created by establishing a virtual point-to-point connection through the use of dedicated connections, virtual tunneling protocols, or traffic encryption. A VPN available from the public Internet can provide some of the benefits of a wide area network (WAN). From a user perspective, the resources available within the private network can be accessed remotely.

Traditional VPNs are characterized by a point-to-point topology, and they do not tend to support or connect broadcast domains, so services such as Microsoft Windows NetBIOS may not be fully supported or work as they would on a local area network (LAN). Designers have developed VPN variants, such as Virtual Private LAN Service (VPLS), and layer-2 tunneling protocols, to overcome this limitation.

Types

Early data networks allowed VPN-style remote connectivity through dial-up modem or through leased line connections utilizing Frame Relay and Asynchronous Transfer Mode (ATM) virtual circuits, provisioned through a network owned and operated by telecommunication carriers. These networks are not considered true VPNs because they passively secure the data being transmitted by the creation of logical data streams. They have been replaced by VPNs based on IP and IP/Multi-protocol Label Switching (MPLS) Networks, due to significant cost-reductions and increased bandwidth provided by new technologies such as Digital Subscriber Line (DSL)  and fiber-optic networks.

VPNs can be either remote-access (connecting a computer to a network) or site-to-site (connecting two networks). In a corporate setting, remote-access VPNs allow employees to access their company's intranet from home or while travelling outside the office, and site-to-site VPNs allow employees in geographically disparate offices to share one cohesive virtual network. A VPN can also be used to interconnect two similar networks over a dissimilar middle network; for example, two IPv6 networks over an IPv4 network.

VPN systems may be classified by:

• The protocols used to tunnel the traffic
• The tunnel's termination point location, e.g., on the customer edge or network-provider edge
• The type of topology of connections, such as site-to-site or network-to-network
• The levels of security provided
• The OSI layer they present to the connecting network, such as Layer 2 circuits or Layer 3 network connectivity.

optical add-drop multiplexer (OADM)

An optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing systems for multiplexing and routingdifferent channels of light into or out of a single mode fiber (SMF). This is a type of optical node, which is generally used for the formation and the construction of optical telecommunications networks. "Add" and "drop" here refer to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal, and/or to drop (remove) one or more channels, passing those signals to another network path. An OADM may be considered to be a specific type of optical cross-connect.

A traditional OADM consists of three stages: an optical demultiplexer, an optical multiplexer, and between them a method of reconfiguring the paths between the demultiplexer, the multiplexer and a set of ports for adding and dropping signals. The demultiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the multiplexer or to drop ports. The multiplexer multiplexes the wavelength channels that are to continue on from demultiplexer ports with those from the add ports, onto a single output fiber.

OADM module for CDWM transmission

All the light paths that directly pass an OADM are termed cut-through lightpaths, while those that are added or dropped at the OADM node are termed added/dropped lightpaths. An OADM with remotely reconfigurable optical switches (for example 1×2) in the middle stage is called a reconfigurable OADM(ROADM). Ones without this feature are known as fixed OADMs. While the term OADM applies to both types, it is often used interchangeably with ROADM.

Physically, there are several ways to make an OADM. There are a variety of demultiplexer and multiplexer technologies including thin film filters, fiber Bragg gratings with optical circulators, free space grating devices and integrated planar arrayed waveguide gratings. The switching or reconfiguration functions range from the manual fiber patch panel to a variety of switching technologies including microelectromechanical systems (MEMS), liquid crystal and thermo-optic switchesin planar waveguide circuits.

Although both have add/drop functionality, OADMs are distinct from add-drop multiplexers. The former function in the photonic domain under wavelength-division multiplexing, while the latter are implicitly considered to function in the traditional SONET/SDH networks.

FTTH IN INDIA BY BSNL

Fibre to the Home (FTTH) is a unique technology being deployed by BSNL for the first time in India. The fibre connectivity having unlimited bandwidth and state of the art technology provides fix access platform to deliver the high speed broadband from 256 Kbps to 100 Mbps, IPTV having different type of contents like HDTV and future coming 3D TV and range of voice telephony services. It provides a comprehensive solution for the IP leased line, internet, Closed User Group (CUG), MPLS-VPN, VoIP, video conferencing, video calls etc whatever the services available on the internet platform, bandwidth on demand can be delivered by this connectivity to the without changing the access fibre and home device. Customer will get a CPE called Home Optical Network Termination (HONT) consist of 4X100 Mpbs Ethernet ports and 2 normal telephone ports. Each 100 Mbps ports will provide broadband, IPTVs, IP Video call and leased line etc as required by the customers. Customer will get power back unit having full load backup of four hours and normal backup of three days. This power backup will be AC input and connecting to the HONT on 12V DC. 

Connectivity via FTTH:

BSNL will extend fibre from its nearest Central Office (CO) location directly or through franchisee and install HONT and battery backup at the customers identified locations. The services such as Voice, Broadband, IPTV etc. will be enabled as per the customer”s request plans for the same. 

The services over FTTH:

Basic internet Access Service controlled and uncontrolled from 256Kbps to 1000Mbps. 

• TV over IP Service (MPEG2).
• Video on Demand (VoD)(MPEG4) play like VCR
• Audio on Demand Service
• Bandwidth on Demand (User and or service configurable)
• Remote Education
• Point to Point and Point to Multi Point Video Conferencing, virtual classroom
• Voice and Video Telephony over IP: Connection under control of centrally located soft switches
• Interactive Gaming
• VPN on broadband
• Dial up VPN Service
• Virtual Private LAN Service (VPLS)

Types of Network Topology

Types of Network Topology

Network Topology is the schematic description of a network arrangement, connecting various nodes(sender and receiver) through lines of connection.

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BUS Topology

Bus topology is a network type in which every computer and network device is connected to single cable. When it has exactly two endpoints, then it is called Linear Bus topology.

Features of Bus Topology

1. It transmits data only in one direction.
2. Every device is connected to a single cable

Advantages of Bus Topology

1. It is cost effective.
2. Cable required is least compared to other network topology.
3. Used in small networks.
4. It is easy to understand.
5. Easy to expand joining two cables together.

Disadvantages of Bus Topology

1. Cables fails then whole network fails.
2. If network traffic is heavy or nodes are more the performance of the network decreases.
3. Cable has a limited length.
4. It is slower than the ring topology.

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RING Topology

It is called ring topology because it forms a ring as each computer is connected to another computer, with the last one connected to the first. Exactly two neighbours for each device.

Features of Ring Topology

1. A number of repeaters are used for Ring topology with large number of nodes, because if someone wants to send some data to the last node in the ring topology with 100 nodes, then the data will have to pass through 99 nodes to reach the 100th node. Hence to prevent data loss repeaters are used in the network.
2. The transmission is unidirectional, but it can be made bidirectional by having 2 connections between each Network Node, it is called Dual Ring Topology.
3. In Dual Ring Topology, two ring networks are formed, and data flow is in opposite direction in them. Also, if one ring fails, the second ring can act as a backup, to keep the network up.
4. Data is transferred in a sequential manner that is bit by bit. Data transmitted, has to pass through each node of the network, till the destination node.

Advantages of Ring Topology

1. Transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data.
2. Cheap to install and expand

Disadvantages of Ring Topology

1. Troubleshooting is difficult in ring topology.
2. Adding or deleting the computers disturbs the network activity.
3. Failure of one computer disturbs the whole network.

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STAR Topology

In this type of topology all the computers are connected to a single hub through a cable. This hub is the central node and all others nodes are connected to the central node.

Features of Star Topology

1. Every node has its own dedicated connection to the hub.
2. Hub acts as a repeater for data flow.
3. Can be used with twisted pair, Optical Fibre or coaxial cable.

Advantages of Star Topology

1. Fast performance with few nodes and low network traffic.
2. Hub can be upgraded easily.
3. Easy to troubleshoot.
4. Easy to setup and modify.
5. Only that node is affected which has failed, rest of the nodes can work smoothly.

Disadvantages of Star Topology

1. Cost of installation is high.
2. Expensive to use.
3. If the hub fails then the whole network is stopped because all the nodes depend on the hub.
4. Performance is based on the hub that is it depends on its capacity

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MESH Topology

It is a point-to-point connection to other nodes or devices. All the network nodes are connected to each other. Mesh has n(n-2)/2 physical channels to link n devices.

There are two techniques to transmit data over the Mesh topology, they are :

1. Routing
2. Flooding

Routing

In routing, the nodes have a routing logic, as per the network requirements. Like routing logic to direct the data to reach the destination using the shortest distance. Or, routing logic which has information about the broken links, and it avoids those node etc. We can even have routing logic, to re-configure the failed nodes.

Flooding

In flooding, the same data is transmitted to all the network nodes, hence no routing logic is required. The network is robust, and the its very unlikely to lose the data. But it leads to unwanted load over the network.

Types of Mesh Topology

1. Partial Mesh Topology : In this topology some of the systems are connected in the same fashion as mesh topology but some devices are only connected to two or three devices.
2. Full Mesh Topology : Each and every nodes or devices are connected to each other.

Features of Mesh Topology

1. Fully connected.
2. Robust.
3. Not flexible.

Advantages of Mesh Topology

1. Each connection can carry its own data load.
2. It is robust.
3. Fault is diagnosed easily.
4. Provides security and privacy.

Disadvantages of Mesh Topology

1. Installation and configuration is difficult.
2. Cabling cost is more.
3. Bulk wiring is required.

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TREE Topology

It has a root node and all other nodes are connected to it forming a hierarchy. It is also called hierarchical topology. It should at least have three levels to the hierarchy.

Features of Tree Topology

1. Ideal if workstations are located in groups.
2. Used in Wide Area Network.

Advantages of Tree Topology

1. Extension of bus and star topologies.
2. Expansion of nodes is possible and easy.
3. Easily managed and maintained.
4. Error detection is easily done.

Disadvantages of Tree Topology

1. Heavily cabled.
2. Costly.
3. If more nodes are added maintenance is difficult.
4. Central hub fails, network fails.

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HYBRID Topology

It is two different types of topologies which is a mixture of two or more topologies. For example if in an office in one department ring topology is used and in another star topology is used, connecting these topologies will result in Hybrid Topology (ring topology and star topology).

Features of Hybrid Topology

1. It is a combination of two or topologies
2. Inherits the advantages and disadvantages of the topologies included

Advantages of Hybrid Topology

1. Reliable as Error detecting and trouble shooting is easy.
2. Effective.
3. Scalable as size can be increased easily.
4. Flexible.

Disadvantages of Hybrid Topology

1. Complex in design.
2. Costly.

An Introduction to Resilient Packet Ring Technology

  Introduction
                 An important trend in networking is the migration of packet-based technologies from Local Area Networks to Metropolitan Area Networks (MANs). The rapidly increasing volume of data traffic in metro networks is challenging the capacity limits of existing transport infrastructures based on circuit-oriented technologies like SONET and ATM. Inefficiencies associated with carrying increasing quantities of data traffic over voice-optimized circuit-switched networks makes it difficult to provision new services and increases the cost of building additional capacity beyond the limits of most carriers’ capital expense budgets. Packetbased transport technology is considered by many to be the only alternative for scaling metro networks to meet the demand. 2.0 Ethernet in the Metro Defined simply, an Ethernet service is any data service offered via an Ethernet interface (10 Mbps, 100 Mbps, 1 Gbps Ethernet port). A key difference between Ethernet services and legacy data services such as leased lines, Frame Relay or ATM is the scalability of the service interface. With legacy data services, physical interface requirements vary with the speed of the service. Thus hardware required for a T1 service is completely different from that required for DS-3 or OC-3 services. With Ethernet service, on the other hand, a service provider can drop a Fast Ethernet (100 Mbps capacity) or Gigabit Ethernet (1000 Mbps capacity) port to a subscriber once and upgrade many times, without additional truck rolls beyond the initial installation. Bandwidth and other service changes can be administered remotely, simplifying and accelerating service provisioning. Ethernet services are widely viewed as an offering that holds promise for rapid acceptance in the marketplace. The question remains as to what infrastructure can cost effectively scale to meet this demand. Ethernet has evolved over the past 25 years from 10 Mbps to 100 Mbps to 1 Gbps and now to 10 Gbps. These and other changes adopted by the IEEE make Optical Gigabit Ethernet Transport Circuit: SONET/ATM Packet Mesh: Ethernet Ring: ??? Figure 1: Packet Rings: The Next Step in Packet-Based Transport RPR Alliance White Paper www.rpralliance.org Page 4 technology, capable of supporting fiber spans of more than 50 miles, now emerge as a viable alternative for data transport in public networks. As nearly all data packets begin and end their trip across the Internet as Ethernet frames, carrying data in a consistent packet format from start to finish throughout the entire transport path eliminates the need for additional layers of protocol and synchronization that result in extra costs and complexities. In addition to efficient handling of IP packets, Ethernet has the advantages of familiarity, simplicity, and low cost. Gigabit Ethernet, however, is only the first step in the evolution of packet-based transport in the MAN. Though well suited for point-to-point and mesh network topologies, it is difficult to deploy Ethernet in ring configurations and as a shared media. Rings act as a shared media and need media access control (MAC) mechanisms to manage access across multiple users. Ethernet has evolved to support full duplex switched infrastructures and lacks this MAC. Yet, most of the existing fiber plant in metro areas is in ring form, because the incumbent transport technology, SONET, is typically deployed over fiber rings. Ring topologies also enable SONET to implement a fast (sub 50ms) protection mechanism that can restore connectivity using an alternate path around the ring in case of fiber cuts or equipment failure. Unlike SONET, Ethernet does not have a built-in fast protection mechanism. There are, therefore, great benefits in a new technology that can fully exploit fiber rings (in particular, ring resiliency) while retaining all the inherent advantages of a packet-based transport mechanism like Ethernet. The emerging solution for metro data transport applications is Resilient Packet Ring (RPR) technology. It offers two key features that have heretofore been exclusive to SONET: efficient support for ring topology and fast recovery from fiber cuts and link failures. At the same time, Packet Ring technology can provide data efficiency, simplicity, and cost advantages that are typical to Ethernet. In addition, RPR solves problems such as fairness and congestion control that have not been addressed heretofore by incumbent technologies. Several vendors are already developing and introducing RPR technologies to address this emerging market. This paper introduces RPR networking, explains its advantages in the metro environment, and gives some examples that illustrate applications that can make the best use of Packet Ring technology.