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Understanding EoMPLS WAN Technology

Understanding EoMPLS WAN Technology Article covers the following CCNA/ICND1 Exam Topics:

Under Operation of IP Data Networks:

1. Recognize the purpose and functions of various network devices such as Routers, Switches, Bridges, and Hubs.

2. Select the components required to meet a given network specification.

3. Predict the data flow between two hosts across a network.

Recommended Study Plan:

1. Download the ICND1v2 Exam Topics Sheet from Cisco Website.

2. Follow the Steps and the Articles under “ IP Networks Fundamentals” by order.

3. Or start with Data Link Layer Encapsulation Article.

Average Time Required Studying this Article: 1 Hour

Ethernet as a WAN Technology

As time passed, Ethernet became appropriate for LAN networks, but IEEE improved Ethernet standards in ways thatmade Ethernet a reasonable WAN technology. E.g. Ethernet Fiber 1000BASE-LX standard uses single-mode 9ufiber-cable, with support for 5-km cable length; the 1000BASE-ZX supports even longer 70-km cable length. So, astime went by, and as IEEE improved cabling distance for fiber-ethernet links, ethernet became a reasonable WANtechnology.

Note: from the Telco perspective point of view, WAN is the network where it connects the customer site to the TelcoPSTN or Frame Relay Central Office CO. The phone infrastructure was already there for serial lease lines, but fiberoptic gave the Telco companies (ISP) more bandwidth with more options such video and audio streaming through thefiber-optic cables. And Ethernet frame doesn’t really change regardless of the cable type, but of course Ethernetscale much better with some other types of cables.

Now days, many WAN services providers (SP) offer WAN services that take advantage of Ethernet protocols. SPsoffer a wide variety of these ethernet WAN services, with many different names. But all of them use a similar model,with ethernet used between the customer site and the SP’s network, as shown in the figure below.

The model shows the same ideas of how a Telco creates a leased line, but now with ethernet links and devices.Instead of using serial cables with CSU box, or a Built-in SCU/DSU T1 card, the customer simply use of the routerethernet port similar to our routers connection at home. Point of presence (POP) is the new term used instead ofCentral office (CO), so the fiber-optic Ethernet link leaves the customer building and connects to some nearby SPPOP. Instead of using Telco switch (PSTN infrastructure) SP in this case uses new Ethernet switch where it iscompatible with Fiber cables. Remember, that Ethernet is just a Language, and as long as the physical standardsunderstand it, Ethernet simply works.

Ethernet WANs that Create a Layer 2 Services

There is broad number of services, with a lot of complex networking concepts needed to understand the ServiceProvider network infrastructure. But for sake of this article, Ethernet Emulation and Ethernet over Multi-Protocol LabelSwitching (MPLS) are 2 of the technology used by SP to carry the Ethernet. Ethernet emulations is a general term,meaning that the service (EoMPLS) acts like as if one long fiber Ethernet cable or link connected between R1 and R2as shown above, but the reality that the ethernet signal is going through the MPLS infrastructure, you can say – Kindof Ethernet Pipe.

The EoMPLS service provides:

A point-to-point connection between two customer devices

Behavior as if a fiber Ethernet link existed between the two devices

So, if you imagine two routers, with single Ethernet link between two routers, you understand what this particularEoMPLS service does. The following figure shows how R1 and R2 connected through EoMPLS similar to theprevious figure, but Fiber-Optic is used instead of serial cable, and hiding the SP infrastructure. I have included aserial link connection for comparison.

How Routers Route IP Packets using EoMPLS

As you might guessed, Ethernet MAC Address System with Ethernet Header and Trailer are used in eachencapsulation and discarded in each de-encapsulation process, EoMPLS WAN is no difference than Ethernet LAN inthat regard.

Each Router discards the MAC address with its Ethernet Data-Link Header and Trailer and adds a new set, asdescribed in the following steps where Ubuntu talks to WinXP PC based on the upper figure:

Step 1: To send the IP packet to R1, Ubuntu encapsulate the IP packet in an Ethernet frame that has the destinationMAC address of R1.

Step 2: R1 applies FCS, de-encapsulates the IP packet from the Ethernet frame, discard the old frame (Old Headerand Trailer), and encapsulates the IP packet into new Ethernet frame, with new header and trailer. R1 includes adestination MAC address of R2’s f0/0 interface, and a source MAC address of R1’s f0/0 interface. finally, R1 forwardsthe frame over the EoMPLS service to R2 as a next-hop.

Step 3: R2 applies FCS, de-encapsulates the IP packet from the Ethernet frame, discard the Old frame,encapsulates the IP packet into a new Ethernet frame that has destination MAC address of WinXP, and forwards theEthernet frame to WinXP PC.

Accessing the Internet

The most known 3 WAN technologies used to gain access to the internet:

Leased Line T1 and T3Digital Subscriber Line (DSL)And Cable TV (CATV)

Leased lines meant for Business and the other 2 WAN technologies meant to for home and small business only.

Internet considered as Large Multiple WANs

Internet is simply one huge TCP/IP network. In fact, the name “Internet” comes from the core network layer protocol:Internet Protocol. The internet includes many LANs, and because the Internet spans the globe, it of course needsWAN links to connect all these different LANs or ISP sites together.

As a network of networks, the Internet is actually owned by countless companies and people. The Internet includesmost every enterprise TCP/IP network and huge number of home-based networks, as well as a huge number ofindividuals from their phones and other wireless devices.

ISP cooperate among each other to create a mesh of links between each other on the Internet core, so that no matterthrough which ISP a particular company or person connects, some path exists to every device. ISP networks connectto both their customers, as well as each other, so that IP packets can flow from every customer of every ISP to everyother customer of every other ISP.

WAN Links as Internet Access Links

Internet uses a large number of WAN links. Some Home and Businesses connect to ISP1, others connect to ISP2,and Cell phones connect to the Wireless carrier which has internet access as well. All these devices’ links go by thesame name Internet Access Links. Businesses often use lease lines (these days as Virtual Leased Lines with VPN),connecting their Router to the ISP Router. Consumers often use technologies like DSL and Cable for Internet AccessLinks. These technologies use cabling that already installed in most homes, making these services somewhatinexpensive for home users. DSL uses the analog phone lines that already installed in homes, while cable internetuses the cable TV (CATV) cable.

Some businesses use DSL and cable connections. Some DSL services even provide Symmetric connections as wellwith equal Upstream and Downstream, only at some locations.

Digital Subscriber Line

DSL creates relatively short (miles long, not ten of miles) high-speed link WAN between a Telco customer and an ISP.It uses the single-pair phone line. DSL does not replace PPP Leased Lines or EoMPLS Ethernet Leased Lines. Mostof the time, DSL supports only asymmetric speeds.

DSL Access Multiplexer

At the Telco Central Office, DSLAM splits the single-pair cable to 2 channels: One out the data over to an InternetRouter, and another One out to the voice signal to the Voice switch called Public Switch Telephone Network (PSTN).

Cable Internet

Cable internet takes full advantage of existing cabling, using the existing cable TV (CATV) to send data. In general,Cable and DSL internet connections use asymmetric rate, sending data faster on the downstream than the upstream,which works better than symmetric speeds for most consumer locations. CATV does not replace leased Lines;instead focus on the short WAN links from a customer to an ISP. In terms of cabling, here the phone cable has beenreplaced by coaxial cable, and the DSL modem box been replaced by a cable modem.

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About Imad Daou He is the founder of CCNA HUB, a CCNA Training HUB to help CCNA students get certified. Imad has more than 10years of IT experience as Field Service and Consulting Engineer. A+, Network+, Server+, Security+, Storage+, HP,Dell, and IBM Hardware Certified. He's a Professional SMB IT Consultant.

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