Network Fundamentals – Chapter 9 Ethernet

A set of network protocols which serves the physical and data link layers. Ethernet utilizes a linear bus or star topology. The Ethernet served as the basis for the IEEE 802.3 standard.

A topology is configuration of communication networks and is of two types, Physical and Logical. Physical topology refers to configuration of computers, cables, devices and mostly depends on various factors. A logical topology is a method of transmitting or passing data between workstations.

Computers in a star topology are connected by cables to a hub. In this topology management of the network is made much easier (such as adding and removing devices), because of the central point. However because it is centralized more cable is required.

Because most star topologies use twisted-pair cables, the initial installation of star networks is also easier.

If one computer fails the network will continue to function, but if a hub fails all computers connected to it will also be affected.

Star topologies are, or are becoming the topology of choice for networks.

In bus topologies, all computers are connected to a single cable or "trunk or backbone", by a transceiver either directly or by using a short drop cable. All ends of the cable must be terminated, that is plugged into a device such as a computer or terminator. Most bus topologies use coax cables.

The number of computers on a bus network will affect network performance, since only one computer at a time can send data, the more computers you have on the network the more computers there will be waiting send data. A line break at any point along the trunk cable will result in total network failure.

Computers on a bus only listen for data being sent they do not move data from one computer to the next, this is called passive topology.

Gigabit Ethernet is based on the same Ethernet standard that IT managers already know and use. Ethernet is now widespread throughout the world. From the first implementation of the Ethernet specification this networking technology has proven itself in terms of performance, reliability and an ever-growing number of established network installations. The principal benefits of Gigabit Ethernet Increased bandwidth for higher performance and elimination of bottlenecks. Gigabit Ethernet is fully compatible with the large installed base of Ethernet and Fast Ethernet nodes. It employs all of the same specifications defined by the original Ethernet standard.

Data Link Layer is divided into two sublayers:

1. Logical Link Control (LLC). This sublayer is responsible for the data transmission between computers or devices on a network.

2. Media Access Control (MAC). On a network, the network interface card (NIC) has an unique hardware address which identifies   a computer or device. The physical address is utilized for the MAC sublayer addressing.

The function of the Logical Link Control (LLC) is to manage and ensure the integrity of data transmissions.

The MAC sub-layer acts as an interface between the Logical Link Control (LLC) sublayer and the network's physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service. 

To display your MAC address on a Windows NT/2000/2003/XP/Visa computer:

• Click START
• Go to ACCESSORIES
• Select Command Prompt
• Type: (no quotes) "ipconfig /all"

In the "ipconfig /all" results look for the adapter you want to find the MAC address of. The MAC address is the number located next to "Physical Address" in the list. 

Address Resolution Protocol (ARP)  Sending IP packets on a multiaccess network requires mapping from an IP address to a MAC address. In an Ethernet environment, ARP is used to map a MAC address to an IP address. ARP dynamically binds the IP address (the logical address) to the correct MAC address. Before IP unicast packets can be sent, ARP discovers the MAC address used by the Ethernet interface where the IP address is configured.

Network Fundamentals – Chapter 8 OSI Physical layer

The Physical layer is responsible for the ultimate transmission of data over network communications media. Hubs and other repeaters are standard network devices that function at the Physical layer. Cables and connectors also are a part of the Physical layer. At the Physical layer, data are transmitted using the type of signaling supported by the physical medium.

Data transfer can be measured in three ways:
1. Bandwidth
2. Throughput
3. Goodput

The practical bandwidth of a network is determined by a combination of factors: the properties of the physical media and the technologies chosen for signaling and detecting network signals. Due to a number of factors, throughput usually does not match the specified bandwidth in physical layer implementations such as ethernet. Goodput measures the effective transfer of user data between application layer entities, such as between a source web server process and a destination web browser device.

Basic characteristic of copper, fiber and wireless network media.

When it comes to costs, Fibre optics is always assumed to be much more expensive than copper cabling. UTP is the most widely used cable in telephone and computer networks because it is relatively cheaper than other cables and performs well in normal electrical environment such as inside an office or a house. The electrical properties of copper cabling create resistance and interference problems with transmissions. Signals sent over copper wire are direct current electrical signals. Another medium being discussed for in-building local area networks (LAN) is wireless communication. Wireless has advantages in the mobility it provides. Wireless LAN connections are less messy - it enables computers to move and office space to be reconfigured without LAN administrators having to physically move cabling.