Ethernet Network Structures

Ethernet Network Structures : The way devices on a network are connected together defines its topology.  In the telecom network there are three basic topologies: Bus, Star, and Ring.  The bus topology is most often associated with Ethernet. All network devices on a segment share a common coax cable, terminated on both ends. The star topology is most often associated with Ethernet. All network devices are linked via their own dedicated cables to a hub/concentrator.

The ring topology is most often associated with Token Ring LANs.  All network devices are linked together in a ring. Networks can be physically connected together with one topology, but logically connected together by another topology.  For example, most LANs today are physically connected together using a star topology.  Cables from all workstations are brought together into a central room (the Telecom Closet).  In the telecom closet, they are connected in such a way as to form a logical Bus or Ring. Before discussing about Ethernet network structures, I shall discuss some specific points.

LAN – Local Area Network

Local Area Network ( LANs ) are mostly used to connect computers / workstations in company offices to share resources (e.g., printers, scanner or any other devices) like below image and easily exchange the information in which network are restricted in size.

Prior to the early 1980s, most networking was done in a host to dumb-terminal environment.  All processing was done on the host computer (mainframe) and communicated to dumb-terminals and printers. Following the emergence of the Personal Computer (PC), users began processing data on their individual machines.  In order to tie these machines together (to share data and resources), high speed Local Area Networks (LANs) were formed.

The idea that the processing of the data is no longer the job of a mainframe, but done locally on the individual PCs, is known as distributed processing. Common needs for distributed processing are peer-to-peer networking or client/server computing.

In a peer-to-peer network, the individual workstations have equal access to the network without having to wait for permission from a control node.  They can share files, E-Mail, and resources (such as printers or modem pools).  A client/server network consists of one or more file servers located on the network serving as an applications/resources access device for a number of workstations.

MAN – Metropolitan Area Network

MANs is widely used to add a group of corporate offices that are restricted in the region or city. This is basically a larger version of LAN. e.g., city wide regional network.

WAN – Wide Area Network

WANs are networks that connect multiple MANs and LANs over a large geographic area, such as a country-wide national network.

Network Structures of Ethernet

Four types of networks are widely used for Ethernet-

1. Ring Network 

2. Bus Network 

3. Star Network 

4. LAN Structure - Meshed Network 

1. Ring Network :  I have already mentioned above that all network devices are linked together in a ring like below image-

2. Bus Network : As mentioned above all network devices on a segment share a common coax cable, terminated on both ends called Bus Network like below image.

3. Star Network : All network devices are linked via their own dedicated cables to a hub/concentrator as shown in below image-

I must write here that the "shared" Ethernet segments have retreated from the local network and have made room for "switched" systems.  Access interfaces of 10Mbps or 100Mbps are usually used today. The subscriber connection density continuously increases. Therefore future-oriented cable networks must be built based on structural planning and then executed. One differentiates between primary, secondary and tertiary sections. Testing the connection between two connection points is called an ”End-to-End Test of a transmission channel” and provides information on the quality of the connection.

The technology which brings Ethernet to the work stations (tertiary section) is implemented using dedicated 10Mbps or 100Mbps connections. Here, mostly copper cabling is used. However, the technology in the backbone (primary and secondary sections) is implemented using Optical Fiber Cable. Where the bandwidth of 100Mbps between the floor distributor and the backbone distributor is insufficient the cabling can be upgraded to Gigabit Ethernet (1000Mbps). The reliability of the system should be checked by means of extensive tests with regard to redundancy. Existing minor defects e.g. cabling defects can be corrected in the run-up. See the image below for easy understanding.

Why Ethernet Now?

Of course, the question arises, Why Ethernet Now? We all know that Ethernet is the best transport method of choice for Data Applications. Apart from this, there are some special features of Ethernet.

➤Ethernet is more efficient than TDM for the transport of data.

➤Ethernet is widely deployment in the Enterprise, data centers, ISPs, etc.

➤Ethernet is far less expensive than similar speed TDM technologies.

Original Ethernet

Ethernet has it’s roots in the University of Hawaii’s ALOHA project.  Xerox later continued development to create the first LAN, but was not until 1980 when Ethernet was first commercialized by the “ Gang of Three ”  Digital, Intel, Xerox…as Ethernet version 1 or DIX80.

This early implementation of Ethernet was a shared bus topology over coax, ran at 10 Mbps in half duplex mode using CSMA/CD with variable frame sizes ranging from 64 bytes to 1518 bytes.

Later a UTP implementation was created which implemented a star topology with a hub at the center.  This still operated in a shared logical bus topology, in a half duplex mode, employed CSMA/CD and variable frame sizes from 64 bytes to 1518 bytes. Both are prone to collisions.

10Mbps Standard

10Base2: Used Coaxial Cable thin wire  (50ohm) with a maximum segment length of 200 meters uses BNC Connector.

10Base5: Used coaxial cable thick wire (50ohm) with a maximum segment length of 500 meters uses AUI connector.

10BaseT: Used twisted pair wire (CAT5,5e) with a maximum segment length of 100 meters uses RJ45 connector.

10BaseF: Used optical fiber cable with a maximum  segment length of 2000 meters uses SC/LC connector.

keep in your mind that 10BaseT means that it operates at 10Mbps uses baseband signaling on twisted pair.

100Mbps Standard

100BaseTx: Use type of cable CAT5,5e UTP (unshielded twisted pair) cable covers maximum segment length of 100 meters uses RJ45 connector.

100BaseFx MMF: Use Optical fiber cable covers maximum segment length of 2000 meters on Multimode Fiber (850nm) uses SC/LC connector.

100BaseFx SMF: Also use Optical fiber cable covers maximum segment length of 10,000 meters on Single mode Fiber (1310/1550)  uses SC/LC connector.

Gigabit Ethernet

1000 Mbps or Gigabit Ethernet is the natural progression of Ethernet.  It is fully backwards compatible with 10-100 Mbps Ethernet, but usually is implemented with switches in a full duplex mode.  

Most manufacturers use a color code for SM vs. MM GBICs. If the plastic at each end is Black the GBIC is Multi-Mode (SX). If the plastic parts are Blue then the GBIC is Single Mode (ZX).

Most new PC’s are being equipped with Gigabit Ethernet cards. Even though most PC’s and servers can not sustain 1000 Mbps transfers for any length of time, it is still beneficial as the transfers are sent at 1000 Mbps across the line.  This means that information is sent more quickly and more often. If it takes less time to transmit a frame then the PC or server is available more quickly to process other tasks or other frames.  

Last Word

My telecom friends I hope that with the help of this article you will have understood the network structure of Ethernet. I have tried every possible way to provide complete information to all of you, now you comment me and tell me how successful my efforts have been. Let me know how you liked this article "Ethernet Network Structures" and also share it to your friends.