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An Examination of Gigabit Ethernet Physical Layer Devices

Thursday, November 20, 2014

If you took a look at a PC you would find a series of USB ports, an Ethernet RJ45 wired port, sometimes an HDMI port, and some specified card reader port. What you do not see is a serial port, the old RS232 port: why not? 

Today the old RS232 port on a PC has been replaced. External keyboards and mice are either wireless (Bluetooth) or wired via USB. The latter being outdated as we speak. The communications port has been replaced with Ethernet. Not just 10/100; it’s now 10/100/1000, and has been for some time. 

Years of deploying products using Ethernet as a main networking application has forged many changes in the design and use of products including computers, routers, and switches in both consumer and industrial products.

The History of Ethernet Standards

Ethernet standards have evolved, but the standards committees formalized the OSI (Open System Interconnect), the official method of data flow between Ethernet enabled products. Here is a breakdown the OSI layer and their functions. 

The official OSI from the International Standards Organization was introduced as part of the IEEE 802.xx in the early 1980s. Let’s look at a description of the individual layers, then focus on layer 1: the physical layer.

Layer 1: Physical

Layer 2: Data Link

Layer 3: Network

Layer 4: Transport

Layer 5: Session

Layer 6: Presentation

Layer 7: Application

Physical Layer: Layer 1
The physical layer is the electrical interface between two devices. The data link layer and the physical layer describe the data transfers which will vary in speed. There are two parts to the physical layer: the physical media and data bandwidth. The physical media can be twisted pair copper, coax, or fiber. The bandwidth is made up of coded signal and rates that are from 10, 100, and 1000 Mb/s. 

Data Link Layer: Layer 2
The data link layer is comprised of the basic Ethernet frame and respective coding which makes up the Ethernet protocol. It moves data in and out of the physical layer.

Network Layer: Layer 3
The network layer is the routing area where Ethernet packets are sent and received. A common network layer protocol is IP (Internet Protocol). 

Transport Layer: Layer 4
This layer allows for sending messages between hosts. It lets the network layer provide errorless data back and forth and orders that data based on the protocol being used. It allows and breaks down the connections as determined by individual protocols. The most common protocol used is TCP (transmission control protocol). 

Session, Presentation, and Application Layers: Layers 5, 6, and 7
Today most embedded designs use the 5 Layer model, with layer 5 handling the applications centered on functions, such as Telnet, FTP (File Transfer Protocol), e-mail, domain name, and network management. The 5, 6, 7 layers are software enabled and currently not supported in hardware. 

A Closer Look at the Physical Layer.  

Layer 1: The Physical Layer – 10 Mbps, 100 Mbps, and 1 Gbps Ethernet

  • 10BASE-T Ethernet has a speed of up to 10 Mbps over twisted pair copper cable connected to a RJ-45 connector. 
  • Fast Ethernet has a speed of 10 times the 10BASE-T Ethernet specification (100 Mbps) while retaining many of Ethernet’s technical specifications. The same 10BASE-T applications can easily adapt to 100BASE-T without changes in network administration and management.
  • Gigabit Ethernet again increases Ethernet speed. Ten times the speed of FAST ETHERNET to 1000 Mbps, or 1 Gbps. Because it is still based upon Ethernet and is compatible with the current Ethernet and Fast Ethernet products, network administrators can handle Gigabit Ethernet without designing new platforms.
  • 10 Gigabit Ethernet, although still relatively new in the embedded world, has now developed into a transport standard in a variety of high speed data applications. It is the fastest version of Ethernet, as 10 Gigabit Ethernet an can apply itself with existing platforms, allow for easier learning curves, and offer high data rates of 10 Gbps. This makes for higher speeds and the edge of many networks which require larger data pipes into main frame computers.

The physical layer for Ethernet is defined by certain electrical and bit rate specifications. The electrical specifications are based on the IEEE 802.3 Ethernet standard. 

There are more than 300 million switched and dedicated Ethernet ports. Switched Ethernet found in routers and switches are of course the major markets for those type of products. What has been growing is the use of Ethernet in the embedded world. Ethernet is the high speed choice of many end to end applications. It offers a secure connection with end user applications to include video and audio with large files of data for in house storage.

Clearly the benefits of Gigabit Ethernet have outweighed the standard communication interfaces for many years. Increased speed, data integrity, distance, power, and overall performance are the key benefits to this technology.  Differences in technology, proven reliability, and standardization have allowed for manufacturers to deliver this world class product. Reducing the pin count allowed for miniaturization of products, giving smaller footprints in hardware design.

There are a vast selection of Gigabit Ethernet PHYs, for a variety of applications and interfaces. Many of the features are standard interfaces, however manufacturers’ analog DSP technology may differ.


If you’d like to implement Gigabit Ethernet in your application, please call Symmetry at (310) 536-6190, or contact us online. 



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