Ethernet is the most popular way for a local area network (LAN) or wide area network (WAN) to connect to devices, such as computers, printers and servers that require a connection to the internet.
Introduced in 1980 and standardized in 1983 it is one of the most widely used communication channel in networking. It doesn’t just connect devices to the internet though. It’s also used to connect devices to each other – for example, computers to computers, computers to printers, to speakers for video conferencing and more. This is possible because of use of Ethernet supports electrical connection through twisted pair cables between devices.
Ethernet was developed at Xerox PARC in 1974. It initially competed with Token Ring and Token Bus but it was able to adapt to the market and shift to inexpensive twisted pair wiring and thus became popular very fast. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, and that year started selling adapters for PDP-11s and VAXes, as well as Multibus-based Intel and Sun Microsystems computers. This was followed quickly by DEC’s Unibus to Ethernet adapter, which DEC sold and used internally to build its own corporate network, which reached over 10,000 nodes by 1986, making it one of the largest computer networks in the world at that time. By the early 1990s, Ethernet became a necessary feature for computers, and Ethernet ports began to appear on some PCs and most workstations.
Ethernet has evolved since then to have better bandwidth, control and access mechanisms. Ethernet communicates by sending data packets called frames. Each Ethernet station is given a globally unique identification called the MAC address and the source and destination MAC address are mentioned in each frame of data sent. On reception of a transmission, the receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored. A network interface normally does not accept packets addressed to other Ethernet stations. An EtherType field in each frame is used by the operating system on the receiving station to select the appropriate protocol module. Ethernet frames are said to be self-identifying, because of the EtherType field, which allows to intermix multiple protocols on the same physical network and allow a single computer to use multiple protocols together. Despite the evolution of Ethernet technology, all generations of Ethernet use the same frame formats.
Original Ethernet was developed to connect computers to a shared channel in a local space to communicate between each other. Thus there was a common link (the coaxial cable) through which all the information on the network passed. Thus, irrespective of whom the data was meant to be every computer connected to the network received the message. But the network interface card interrupts the CPU only when applicable packets are received: the card ignores information not addressed to it. Use of a single cable also means that the data bandwidth is shared, such that, for example, available data bandwidth to each device is halved when two stations are simultaneously active. A collision happens when two stations attempt to transmit at the same time. They corrupt transmitted data and require stations to re-transmit. The lost data and re-transmission reduces throughput. In the worst case, where multiple active hosts connected with maximum allowed cable length attempt to transmit many short frames, excessive collisions can reduce throughput dramatically. But in present Ethernet connections the stations don’t share a single channel instead each station is connected to a switch which routes the traffic to their respective channels.
Fig 1: Ethernet Layers
Since Ethernet is completely based on electronic transmission signal degradation and timing restrict the size of the network. Repeaters are used in many cases to enlarge the network but it increases the establishment cost of the network. In a multi-channel network multiple bridges would be required for each channel and all the network traffic, be it good or bad frames are sent to the respective devices through them. Bridges, a kind of filter and repeater, are used now a days to filter bad frames or frames with errors and send only the good packets to respective devices. At initial startup, Ethernet bridges work somewhat like Ethernet repeaters, passing all traffic between segments. By observing the source addresses of incoming frames, the bridge then builds an address table associating addresses to segments. Once an address is learned, the bridge forwards network traffic destined for that address only to the associated segment, improving overall performance. Broadcast traffic is still forwarded to all network segments. Bridges also overcome the limits on total segments between two hosts and allow the mixing of speeds, both of which are critical to deployment of Fast Ethernet.
Ethernet, has gained its stature because of its ease of access, scalability and interface with various kinds of computers. We will now compare its functionality with SONET.
Ethernet and SONET were primarily developed to support two different causes. SONET was for voice whereas Ethernet was more aligned towards data.
- Application and speed
SONET/SDH is a time division multiplexing protocol, it transporting (and switching) data by dividing and marking it on time basis, synchronize the data by time stamping. It’s obviously synchronous. SONET/SDH mostly used in backhaul transport network, up to 40Gbps of bandwidth. While Ethernet basically an asynchronous packet switching network, both are L2 protocol. It means, Ethernet doesn’t care about the order of the packet/data on time basis, so it is not reliable for time sensitive data, such as, voice and video, in backhaul/long range network infrastructure.
SONET/SDH hardware elements require complexity and precision that not only affect the initial capital expenditure, but also the cost and configuration of operating and scaling the network. Even minor modifications to SONET/SDH bandwidth require major hardware reconfigurations that can sometimes take weeks to implement as opposed to hours or even real-time for similar changes using Ethernet. Because all generations of Ethernet are functionally compatible, users typically enjoy “plug-and-play” provisioning and scaling capabilities.
- Flexible Topologies
Most SONET/SDH networks are deployed in fixed ring-based designs making changes to the network cumbersome. Adding a node requires reconfiguring the entire system. Because Ethernet supports ring, mesh, tree, and string based topologies, it offers significantly more design flexibility and deployment options for industrial communication networks.
SONET/SDH networks are designed to use fixed bandwidth circuits which contribute to overall complexity and operation inefficiencies. In short, SONET/SDH bandwidth allocation is rigid; Ethernet is flexible.