Metro Ethernet Fundamentals for WAN Connectivity
By Shaun Hummel
Overview
The increasing popularity of Metro Ethernet is the result of the cost effectiveness,
availability and seamless protocol transition it offers from the campus network to the WAN.
Ethernet is already optimized for use with the TCP/IP protocol. There is no WAN protocol transition
(handoff) to another WAN protocol such as SONET or Serial T3 links for example.
With Metro Ethernet, there is no need to buy and manage a WAN router. Most enterprise
companies have already deployed high speed Cisco routers and network switches with GE and 10
GE interfaces. Those same interface can be used for Metro Ethernet services. In addition there
is the Cisco 3750M and 3400ME switches optimized and designed for Metro Ethernet services.
The comparative cost per Mbps for a Metro Ethernet circuit is astoundingly cost effective
compared with T1, T3 circuits and SONET. The disadvantage of Metro Ethernet is with long haul
WAN connectivity.
Most service providers offer services for state and multi-state connectivity. The service
providers have deployed SONET for years and use that with Metro Ethernet for network connectivity
on a national scale. Metro Ethernet and DWDM technology make it a viable alternative to SONET
for long haul circuits as service providers continuing to increase fiber network infrastructure
across the country.
Metro Ethernet Components
The Metro Ethernet network include customer edge (CE) devices, a user network interface
(UNI), service provider edge equipment (PE) and the provider core (PC) network devices.
Customer Edge (CE)
The Customer Edge (CE) is a router or switch with an Ethernet interface preferably optimized
for Metro Ethernet services. Some companies now deploy Metro Ethernet from a Cisco 6500 switch
Gigabit interface. The Gigabit port bandwidth is then configured with QoS traffic shaping to
limit bandwidth according to the service provider CIR selected by the company as part of the
service level agreement.
User Network Interface (UNI)
This is the demarcation point between what the customer manages and what the service
provider manages. The management of various network services is defined by the UNI interface
to the Metro Ethernet service provider. Those services include QoS, security, encryption, etc.
Provider Edge (PE)
The provider edge equipment is typically a carrier class device that aggregates hundreds
of Metro Ethernet connections from customers onto a DWDM or SONET network for long haul connectivity
Provider Core (PC)
The provider core network is a high speed DWDM or SONET switched network that aggregates
and forwards packets from thousands of customers using a carrier class DWDM switched core.
There is typically no quality of service added to customer packets. The customer network stream
is tunneled across the core using a private VLAN where packets are forwarded to the provider
edge router. The provider edge router then forwards packets to the customer edge router or switch.
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