From DS3 to Switched Ethernet
Why switched Ethernet technology gives you more connectivity options at lower cost than T1, DS3 or SONET.
By: John Shepler
A major trend in telecom services is the massive migration from traditional circuit switched to packet switched networks. Right along with this has come the availability of Ethernet connections door to door and to the Internet. Even so, many organizations still embrace traditional technology and are loath to give up their trusty T1 lines and SONET fiber optic services. Why should they consider making change…. and to what?
Aren’t All Networks Ethernet?
Pretty much all Local Area Networks (LANs), including wireless networks, are based on the Ethernet protocol. There are exceptions, such as Fibre Channel that connects computers to Storage Area Networks (SANs), but the vast majority of networking equipment and software is based on supporting Ethernet.
So, What are T1, DS3 and SONET?
Traditional telecom standards were developed long before anyone thought of using packet technology to communicate. Their intended application was for bundling or trunking telephone lines between phone company offices. Their architecture is based on circuit switching instead of packet switching plus segmenting the line into many individual channels. Each channel carries a single phone conversation. The process for doing this is called TDM or Time Division Multiplexing.
Connecting TDM to Ethernet Networks
You can see there is a technology gap between TDM and Ethernet or IP networks. Fortunately, technology comes to the rescue to make this largely invisible to you, the user. All those little (64 Kbps) telephone channels can be combined on a given line to create one large bandwidth pipe. Plug in modules allow routers to connect to TDM lines going outside and LANs within the company. While this approach has allowed modern computer to computer communications to flourish, there are some good reasons to move on from this protocol conversion approach.
Ethernet vs Ethernet
The Ethernet protocol envisioned by Bob Metcalfe in the 70’s is a different animal than what we use today. The original Ethernet was based on a single wire channel with all packets from all systems vying for access in a giant “collision domain.” This technology is described by the mouthful, “Carrier Sense Multiple Access with Collision Detection” or CSMA/CD for short. It’s a self-policing system where each connection to the network is responsible for making sure that the line is clear before launching a packet and recovering if the packet gets in a collision with another.
This system works, but network gets crowded fast as devices are added and lines interconnected with simple hubs. Communication is limited to half-duplex because only one connection can talk at a time. The big improvement to the technology, and one we still use today, is called switched Ethernet.
The Switched Advantage
The Ethernet switch directs traffic from source to destination rather than having a single party line for everybody. Transmission and reception paths are physically separate on different wire pairs. This alone doubles the network rate from half-duplex to full duplex because devices and talk and listen at the same time. There is no collision domain anymore. Each device has its own network port and the switch takes care of getting the packets to the right place.
Beyond the LAN
It seems logical that the way to connect networks across town should be the same as connecting multiple small networks into one LAN in-house. It hasn’t been because you lose control of the net when you leave your property. Two business locations across town have to be connected through a no-man’s land in-between by a common carrier. This was originally the role of the local phone company but competition has opened the carrier business to many other players.
Scaling Up Ethernet
For decades, the transportation of voice, data and video between locations has been done using legacy switched circuit telecom technologies. Ethernet, by design, was limited to the LAN because of fairly short distance limitations for each network line. To get around this, Carrier Ethernet was developed. It’s pretty much the same switched Ethernet, but with additional provisions for long distance transmission and the operation and maintenance features needed by the carriers to maintain the lines. Carrier Ethernet scales up switched Ethernet so that packets can be carried across town or even around the world.
Ethernet All the Way
Now it is possible to plug your edge router into a familiar Ethernet connection (copper or fiber) at each of your business locations. In-between, the common carrier reliably transports your packets from location to location. It’s Ethernet all the way with no protocol conversions required.
Switched Ethernet Service Advantages
Think of the world as your network. Well, at least your parts of the world. With switched Ethernet, you can bridge two or more locations to put their LANs on one larger network… just like you would in-house. Ethernet Line Service (E-Line) replaces T1, DS3, and SONET OCx lines one a one to one basis. Carrier Ethernet also adds a couple of new options. Ethernet LAN Service (E-LAN) creates a fully meshed network for you. All you need is an Ethernet line connection at each location. Ethernet Tree Service (E-Tree) is a one to many connection that is popular with content providers. One location generates the traffic to be used by many, many other locations.
The Ethernet Cost Advantage
Carrier Ethernet networks are designed to be both easily scalable and lower in cost than what you are used to with traditional telecom services. It is not uncommon to get Ethernet over Copper connections at 3 Mbps for the same price or less than T1 lines at 1.5 Mbps. At higher speeds, the difference in cost is even more dramatic. The scalability technology lets you upgrade the speed of your service quickly and easily, often without needing new equipment installed.
Switched Ethernet For You
Are you thinking that you may be missing out on service improvements and more bandwidth for your money that can be offered by switched Ethernet service? No need to wait. Copper and fiber optic Carrier Ethernet services are available coast to coast and worldwide right now.
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