Chapter 5 Topologies and Ethernet Standards

Topologies and Ethernet Standards
When building a Network, whether building a small LAN or a large Global Network, you need to keep the end/finished product in mind. With both small and larger networks, you will see phases of a network completion. However, just like learning, you will really never see a Network 100% finished/complete. As time moves, the Network will continue to evolve staying abreast of technology and meeting the needs of the organizations network professionals are working in. In just the past 10 years, these network professionals have rarely been using technologies such as Bus or Ring topologies, Hubs, Modems etc… This chapter examines old and new technologies. Here are some of the current and future technologies thought to be the most important for us, network professionals, to understand and master.

The physical topologies- the Network physical layout has three main categories: Bus, Ring and Star. Star topologies are the most widely used topologies today and are also the most fault tolerant. Looking at the Star topology, everything comes to the center to communicate with other devices and resources (Switches and Servers), making the connections directly to the central resources not relying on other systems to be live to make their connection to these resources.

Hybrid Physical Topologies- There are two types: Star-Wired Ring and Star-Wired Bus. Of the two the most commonly used technologies; Star-Wired Bus is the most popular. It connects the devices using a single bus between devices (Routers, Hubs, Switches etc…).

Backbone Networks- There are four types: Serial Backbone, Distributed Backbone, Collapsed Backbone, and Parallel Backbone. None of these are the main types of backbone that would be used across enterprise. All four types may be used depending on the needs (number of users, the fault tolerance, scalability, cost etc…) of the segment you are setting up within the enterprise.

Switching- There are four types: Circuit Switching, Message Switching, Packet Switching, and MPLS (Multiprotocol Label Switching). The most popular method is Packet Switching; it breaks data into packets before they are transported. The packets contain both destination and sequence information; each packet can travel its own route to the destination. Each packet does not have to arrive at the same time because they will be reassembled with their sequencing information.

Ethernet technology was developed by Xerox in the 1970s, and later improved by DEC (Digital Equipment Corporation), Intel and XEROX make up the acronym of DIX. It is by far the most popular technology used on LANs today. All types have one thing in common: they use an access method known as CSMA/CD (Carrier Sense Multiple Access with Collision Detection). Basically CSMA/CD is listening on the network for activity and if it detects no activity it transmits data. If it detects collision, it stops transmission and goes back to listening for no activity and trying again until it is successful.

Ethernet Standards for Copper Cable- (The T stand for Twisted Pair)”:

100Base-T (Fast Ethernet)- IEEE 802.3u standard with the max length 100 meters.
1000Base-T (Gigabit Ethernet)- IEEE 802.3ab standard with the max length 200 meters.
10GBase-T- IEEE 802.3an standard with the max length 100 meters.

Ethernet Standards for Fiber-Optic Cable:

100Base-FX- (Fast Ethernet) IEEE 802.3u standard with the max length 412 meters in half duplex and 2000 meters in full duplex.
1000Base-LX- (1-Gigabit Ethernet) IEEE 802.3z standard with the max length 412 meters using multimode and 000 meters in single mode. The LX stands for Long wave length 1300 nanometers.
1000Base-SX- (1-Gigabit Ethernet) IEEE 802.3ae

10-Gigabit Fiber-Optic Standards: (IEEE 802.3ae)

10GBase-SR and 10GBase-SW (S stands for short reach max 300 meters)
10GBase-LR and 10GBase-LW (L stands for long reach max 10,000 meters)
10GBase-ER and 10GBase-EW (E stands for extended reach 40,000 meters)

SR, LR, & ER the R stands for LAN connections, where SW, LR, & ER the W specifies that it is specially encoded for SONET WAN links.

Ethernet Frames: There are four types: Ethernet_802.2 (Raw), Ethernet_802.3 (Novell proprietary), Ethernet_II (DIX), and Ethernet_SNAP. Of the four Ethernet_II (DIX) is the most commonly used today. Where the first two do not contain a 2 byte Ether net type both Ethernet_II and Ethernet_SNAP, do, however, SNAP calls for additional field controls making less room for data therefore Ethernet II is used more often. (Below is a sample of a Ethernet II Frame).