Fiber Optic Wiki

30 Metro Ethernet

December 16, 2011

Protocols and configurationsMany DSL technologies implement an Asynchronous Transfer Mode (ATM) layer over the low-level bitstream layer to enable the adaptation of a number of different technologies over the same link.

A typical service provider Metro Ethernet network

December 16, 2011

A typical service provider Metro Ethernet network is a collection of Layer 2 or/and Layer 3 switches or/and routers connected through optical fiber. The topology could be a ring, hub-and-spoke (star), or full or partial mesh.

Metro Area Network topology

December 16, 2011

Familiar network domains are likely to exist regardless of the transport technology chosen to implement Metro Area Networks: Access, Aggregation/Distribution, Metro, and Core.Access devices normally exist at a customer's premises, unit, or wireless base station. This is the network that connects customer equipment, and may include ONT and/or Residential gateway, or office router.

Pure Ethernet MANs

December 16, 2011

A pure Ethernet MAN uses only layer 2 switches for all of its internal structure. This allows for a very simple and cheap design, and also for a relatively simple initial configuration. The original Ethernet technology was not 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.

Traffic engineering is very limited

December 16, 2011

There are three main shortcomings with a pure non PBT/PBB enabled 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.

The local loop connecting the telephone exchange

December 15, 2011

The local loop connecting the telephone exchange to most subscribers has the capability of carrying frequencies well beyond the 3.4 kHz upper limit of POTS. Depending on the length and quality of the loop, the upper limit can be tens of megahertz. DSL takes advantage of this unused bandwidth of the local loop by creating 4312.5 Hz wide channels starting between 10 and 100 kHz, depending on how the system is configured. Allocation of channels continues at higher and higher frequencies (up to 1.1 MHz for ADSL) until new channels are deemed unusable.

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