A Metro Ethernet is a computer network based on the Ethernet standard and which covers a metropolitan area. It is commonly used as a metropolitan access network to connect subscribers and businesses to a Wide Area Network, such as the Internet. Large businesses can also use Metro Ethernet to connect branch offices to their Intranets. A computer network is a useless group of computers. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... This article does not cite any references or sources. ... An access network is that part of a communications network which connects subscribers to their immediate service provider. ... Wide Area Network (WAN) is a computer network that covers a broad area (i. ... An intranet is a private computer network that uses Internet protocols, network connectivity to securely share part of an organizations information or operations with its employees. ...

Ethernet has been a well known technology for decades. An Ethernet interface is much less expensive than a SDH or PDH interface of the same bandwidth. Ethernet also supports high bandwidths with fine granularity, which is not available with traditional SDH connections. Another distinct advantage of an Ethernet-based access network is that it can be easily connected to the customer network, due to the prevalent use of Ethernet in corporate and, more recently, residential networks. Therefore, bringing Ethernet in to the Metropolitan Area Network (MAN) introduces a lot of advantages to both the service provider and the customer (corporate and residential). It has been suggested that this article be split into articles entitled Synchronous optical networking, SONET and Synchronous digital hierarchy. ... The Plesiochronous Digital Hierarchy (PDH) is a technology used in telecommunications networks to transport large quantities of data over digital transport equipment such as fibre optic and microwave radio systems. ... Metropolitan area networks, or MANs, are large computer networks usually spanning a city. ...

Metro Ethernet system

A typical service provider Metro Ethernet network is a collection of Layer 2 or 3 switches or routers connected through optical fiber. The topology could be a ring, hub-and-spoke (star), full mesh or partial mesh. The network will also have a hierarchy; core, distribution and access. The core in most cases is an existing IP/MPLS backbone, but may migrate to newer forms of Ethernet Transport in the form of 10G or 100G Road to 100G speeds. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A network switch is a computer networking device that connects network segments. ... This article is about a computer networking device. ... Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... For other uses of topology, see topology (disambiguation). ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... In computer networking and telecommunications, Multi Protocol Label Switching (MPLS) is a data-carrying mechanism that belongs to the family of packet-switched networks. ... According to the Road to 100G Alliance website , it is a nonprofit corporation formed by its Members for the purpose of providing seamless interoperability among the disparate, standards-based components required in building high capacity network elements. ...

Ethernet on the MAN can be used as pure Ethernet, Ethernet over SDH, Ethernet over MPLS or Ethernet over DWDM. Pure Ethernet-based deployments are cheap but less reliable and scalable, and thus are usually limited to small scale or experimental deployments. SDH-based deployments are useful when there is an existing SDH infrastructure already in place, its main shortcoming being the loss of flexibility in bandwidth management due to the rigid hierarchy imposed by the SDH network. MPLS based deployments are costly but highly reliable and scalable, and are typically used by large service providers. This article or section does not cite its references or sources. ...

Pure Ethernet MANs

A pure Ethernet MAN uses only layer 2 switches for all its internal structure. This allows for a very simple and cheap design, and also for a relatively simple initial configuration. The original Ethernet technology wasn't well suited for service provider applications; as a shared-media network, it was impossible to keep traffic isolated, which made implementation of private circuits impossible. Ethernet MANs became feasible in the late 90's due to the development of new techniques to allow transparent tunneling of traffic through the use of Virtual LANs as "point to point" or "multipoint to multipoint" circuits. Combined with new features such as VLAN Stacking (also known as VLAN Tunneling), and VLAN Translation, it became possible to isolate the customer's traffic from each other and from the core network internal signaling traffic. In telecommunications a link is the communications channel that connects two or more communicating devices. ... In telecommunications a link is the communications channel that connects two or more communicating devices. ...

There are three main shortcomings with a pure Ethernet MAN approach:

• By design, layer 2 switches use fixed tables to direct traffic based on the MAC address of the endpoints. As the network gets larger, the number of MAC address transiting through the network may grow beyond the capacity of the core switches. If the core table gets full, the result is a catastrophic loss of performance due to the flooding of packets over the entire network structure.
• Network stability is relatively fragile, especially if compared to the more advanced SDH and MPLS approaches. The recovery time for the standard spanning tree protocol is in the range of tens of seconds, much higher than what can be obtained in the alternative networks (usually a fraction of second). There are a number of optimizations, some standardized through the IEEE, and others vendor-specific, that seek to alleviate this problem. The clever use of such features allow the network to achieve good stability and resilience, at the cost of a more complex configuration and possible use of non-standard, vendor-specific, mechanisms.
• Traffic engineering is very limited. There are few tools to manage the topology of the network; also, the fact that forwarding is done hop-by-hop, added to the possibility of broadcasts even for unicast packets (for instance, while learning new addresses), makes predicting the real traffic pattern very difficult. There are techniques that allow for some control of the preferential traffic paths; these techniques rely on the use of multiple spanning trees, or "per VLAN spanning trees", and are closely connected to the solutions used to achieve better stability and resiliency in the network.

Despite these shortcomings, pure Ethernet-based MANs are used for two primary purposes: Based on an algorithm invented by Radia Perlman while working for Digital Equipment Corporation[1][2], Spanning Tree Protocol Is an OSI layer-2 protocol which ensures a loop free topology for any bridged LAN. The Spanning Tree Protocol (STP), is defined in the IEEE Standard 802. ... Based on an algorithm invented by Radia Perlman while working for Digital Equipment Corporation[1][2], Spanning Tree Protocol Is an OSI layer-2 protocol which ensures a loop free topology for any bridged LAN. The Spanning Tree Protocol (STP), is defined in the IEEE Standard 802. ...

• For small scale deployments (under a few hundred customers), a pure Ethernet MAN can be highly cost-effective. It also has the advantage of not requiring advanced knowledge of IP and related protocols, such as BGP and MPLS, that are necessary for a MPLS-based deployment.
• In large scale Metro Ethernets, it's common for the access part of the network to use a pure layer 2 design. At this level, the pure layer 2 design is deemed to be cheaper while still operating under its design limitations. From the distribution layer and above, traffic is aggregated and routed using a MPLS-based Metro Ethernet design.

SDH-based Ethernet MANs

An SDH based Ethernet MAN is usually used as an intermediate step in the transition from a traditional, time-division based network, to a modern statistical network (such as Ethernet). In this model, the existing SDH infrastructure is used to transport high-speed Ethernet connections. The main advantage of this approach is the high level of reliability, achieved through the use of the native SDH protection mechanisms, which present a typical recovery time of 50 ms for severe failures. On the other hand, an SDH-based Ethernet MAN is usually more expensive, due to costs associated with the SDH/DWDM equipment that is necessary for its implementation. Traffic engineering also tends to be very limited. Hybrid designs use conventional Ethernet switches at the edge of the core SDH ring to alleviate some of these issues, allowing for more control over the traffic pattern and also for a slight reduction in cost. It has been suggested that this article be split into articles entitled Synchronous optical networking, SONET and Synchronous digital hierarchy. ...

MPLS-based Ethernet MANs

A MPLS based Metro Ethernet network uses a MPLS in the Service Provider Network. The subscriber will get an Ethernet interface on Copper (100BASE-TX) or fiber (100BASE-FX). The customer's Ethernet packet is transported over MPLS and the service provider network uses Ethernet again as the underlying technology to transport MPLS. So, it is Ethernet over MPLS over Ethernet. The following figure explains this; MPLS is a common abbreviation for Multiprotocol Label Switching. ... 100BASE-TX is the predominant form of Fast Ethernet, providing 100 Mbit/s Ethernet. ... 100BASE-FX is a version of fast ethernet over optical fiber. ...

Fig.1 Ethernet over MPLS and MPLS signaling

Here, Label Distribution Protocol (LDP) signaling is used as site to site signaling for the inner label (VC label) and Resource reSerVation Protocol-Traffic Engineering (RSVP-TE) is used as Network signaling for the outer label. Label Distribution Protocol (LDP) is a protocol using which two label-switched routers (LSR) exchange label mapping information. ... Resource Reservation Protocol Protocol that supports the reservation of resources across an IP network. ...

One of the restoration mechanisms used in a MPLS based Metro Ethernet Networks is Fast ReRoute-FRR (MPLS local protection) In MPLS local protection (also called MPLS local restoration or MPLS Fast Reroute) is a local restoration network resiliency mechanism. ...

The main advantages of a MPLS-based Metro Ethernet against a pure Ethernet are:

• Scalability: pure Ethernet MAN are limited to a maximum of 4,096 VLANs for the whole network, when using MPLS, Ethernet VLANs have local meaning only (like Frame Relay PVC). Same scalability considerations applies to the MAC addresses where in a pure Ethernet MAN all MAC addresses are being shared among the network while only having local meaning in the MPLS context.
• Resiliency: pure Ethernet network resiliency relies on STP or RSTP (30 to 1 sec convergence) while MPLS-based MANs use MPLS-based mechanism (i.e. MPLS Fast Reroute) to achieve SDH-like (50 msecs) convergence times.
• Multiprotocol convergence: with the maturity on pseudowires standards (ATM VLL, FR VLL, etc.) an MPLS-based Metro Ethernet can backhaul not only IP/Ethernet traffic but virtually any type of traffic coming from customers networks or other access networks (i.e. ATM aggregation for UMTS).
• End to End OAM: MPLS-based MAN offers a wider set of troubleshooting and OAM MPLS-based tools which enrich Service Providers ability to effectively troubleshoot and diagnose network problems.

The Metro Ethernet Forum (MEF) has defined two types of services that can be delivered through Metro Ethernet: The Metro Ethernet Forum (MEF) was founded in 2002. ...

• E-Line also known as Virtual Leased Line and Point-to-Point.
• E-LAN also known as Virtual Private LAN Services, Transparent LAN Services and MultiPoint-to-MultiPoint.

Additionally, various access services can be provided with Metro Ethernet including; High Speed Internet access and IP/VPN access. Virtual Leased Line (VLL) is a way to provide Ethernet based point to point communication over IP/MPLS networks. ... This article or section does not cite its references or sources. ... Virtual private LAN service (VPLS) is a way to provide Ethernet based multipoint to multipoint communication over IP/MPLS networks. ...

There are lot of vendors supplying equipment for Metro Ethernet deployments. They include Alcatel-Lucent, Ericsson, C-COR, Cisco Systems, Ethos Networks, Extreme Networks, Foundry Networks, Huawei, Nortel Networks, Tellabs, ZTE, Alcatel and many more. Software solutions for vendors are provided by [IP Infusion]. Alcatel Lucent (or Alcatel-Lucent according to some sources) is the name of the new company formed after the merge agreement signed by Alcatel and Lucent Technologies. ... Ericsson () NASDAQ: ERIC. Founded in 1876, Ericsson is a leading provider of communications networks, related services and handset technology platforms. ... C-COR (NASDAQ: CCBL) is a communication services company incorporated in 1953 and based in State College, Pennsylvania. ... “Cisco” redirects here. ... Extreme Networks, is a creator of enterprise level switching routers. ... Foundry Networks is a network system vendor selling high-end managed ethernet switches. ... Huawei Technologies Co. ... Nortel Networks Corporation TSX: NT NYSE: NT, formerly known as Northern Telecom Limited and now known simply as Nortel, is a multinational telecommunications equipment manufacturer headquartered in Toronto, Canada. ... Tellabs, Inc. ... ZTE Corporation (Chinese： 中兴通讯）(Zhong Xing Telecommunication Equipment Company Limited) SEHK: 0763, a state-owned corporation launched in 1985, is one of the largest telecommunications (GSM, 3G, WCDMA, CDMA, SDH, ADSL, IPTV, PSTN) manufacturers and wireless solutions providers in the Peoples Republic of China. ... Alcatel SA is a global company, headquartered in France that provides hardware, software and services to telecommunications service providers and enterprises. ...

In June 2002, HKBN built the largest Metro Ethernet IP network in the world, covering 1.2 million homes. Hong Kong Broadband Network Limited (HKBN, 香港寬頻) is a wholly-owned subsidiary of City Telecom (H.K.) Limited and a broadband telecommunication enterprise in Hong Kong. ...

In late September 2007 Verizon Business announced that it is implementing a Metro Ethernet solution across Asia-Pacific including Australia, Singapore, Japan and Hong Kong using Nortel equipment.[[1]]

Africa's largest and most developed privately owned MPLS Based Metro Ethernet Network is in Kenya. Reaching more than 5000 corporate entities, Kenya Data Networks is providing High End Services using Alcatel Core and Siemens Access equipment. KDN is now moving into FTTH projects and intends to cover more than 100 000 buildings in East Africa within the next 3 years. Kenya Data Networks (KDN), is Kenyas largest private data carrier and infrastructure provider. ... Kenya Data Networks (KDN), is Kenyas largest private data carrier and infrastructure provider. ...

Further reading

• Halabi, Sam (2003). Metro Ethernet. Cisco Press. ISBN 1-58705-096-X. 

External links

• VPLS.ORG
• MEF