Chapter 8: PHYSICAL LAYER

                       The purpose of the OSI Physical Layer  is to provide the means to transport across the network media the bits that make up a Data Link Layer transmitted onto the local media.

                                    In Physical Layer there are some following elements:

1.) The physical media and associated connectors.

2.) A representation of bits on the media

3.) Encoding of data and control information

4.) Transmitter and receiver circuitry on the network devices.

                         The job of this Layer is to retrieve these individual signals from the media, restore them to their bit representations, and pass the bits up to the Data Link Layer as a complete frame. Also, this Layer is responsible to create the electrical optical or microwave signal that represents the bits in each frame. These signals are then sent on the media at a time.

                        Physical Layer specifications are applied to areas that include: data to radio signal encoding, frequency and power of transmission, signal reception and decoding requirements, and antenna design and construction.

                        Different physical media transfer of bits at different speeds. data transfer can be measured in three ways such as bandwith, throughput, and goodput.

                       Physical Layer technologies are defined by Organizations such as:

                   ISO - the International Organization for Standardization

                 IEEE - the Institute of Electrical and electronics Engineers

                 ANSI- the American National Standards Institute

                 ITU-  the International Telecommunications Union

            EIA/ TIA- The Electronics Industry Alliance or Telecommunications Industry Association

                  There are four commons data communications standards that apply to wireless media:

1. Standard IEEE 802.15 - Wireless Personal Area Network commonly known as  "bluetooth ".
2. Standard IEEE 802.16 -  WIMAX (Worldwide Interoperability for Microwave Access)
3. Standard IEEE 802.11 - commonly referred to as WI-FI .
4. GSM - (Global System for Mobile Communications).

On the Operation of this Layer, the network media has three basic forms on which the data is represented:

1. Copper cable - the signals are patterns of electrical pulses
2. Fiber- the signals are patterns of light 
3. Wireless Media - the signals are patterns of radio transmission.

In Physical layer there are three fundamentals functions:

1. The physical components
2. Data encoding
3. Signaling

IPV6

                 Due to recent concerns over the impending depletion of the current pool of Internet addresses and the desire to provide additional functionality for modern devices, an upgrade of the current version of the Internet Protocol (IP), called IPv4, has been defined. This new version, called IP version 6 (IPv6), resolves unanticipated IPv4 design issues and takes the Internet into the 21st Century. To address these and other concerns, the Internet Engineering Task Force (IETF) has developed a suite of protocols and standards known as IP version 6 (IPv6). This new version, previously called IP-The Next Generation (IPng), incorporates the concepts of many proposed methods for updating the IPv4 protocol. The design of IPv6 is intentionally targeted for minimal impact on upper and lower layer protocols by avoiding the random addition of new features.


IPv6 (Internet Protocol version 6) is a set of specifications from the Internet Engineering Task Force (IETF) that's essentially an upgrade of IP version 4 (IPv4).

 

IPv6 is the next generation protocol for Internet networking. IPv6 expands on the current Internet Protocol standard known as IPv4. Compared to IPv4, IPv6 offers better addressing, security and other features to support large worldwide networks.


In IPv6, IP addresses change from the current 32-bit standard and dotted decimal notation to a new 128-bit address system. IPv6 addresses remain backward compatible with IPv4 addresses. For example, the IPv4 address "192.168.100.32" may appear in IPv6 notation as "0000:0000:0000:0000:0000:0000:C0A8:6420" or "::C0A8:6420".


The most obvious benefit of IPv6 is the exponentially greater number of IP addresses it can support compared to IPv4. Many countries outside the U.S. suffer from a shortage of IP addresses today. Because IPv6 and IPv4 protocols coexist, those locales with an address shortage can easily deploy new IPv6 networks that work with the rest of the Internet. Experts believe it will take many more years before all networks fully change over to IPv6.


Other benefits of IPv6 are less obvious but equally important. The internals of the IPv6 protocol have been designed with scalability and extensibility in mind. This will allow many different kinds of devices besides PCs, like cell phones and home appliances, to more easily join the Internet in future.


 IPv6 uses 128-bit addresses, so the new address space supports 2128undecillion or (approximately 340 3.4×1038) addresses. This expansion allows for many more devices and users on the internet as well as extra flexibility in allocating addresses and efficiency for routing traffic. It also eliminates the primary need for network address translation (NAT), which gained widespread deployment as an effort to alleviate IPv4 address exhaustion. IPv6 also implements additional features not present in IPv4. It simplifies aspects of address assignment (stateless address autoconfiguration), network renumbering and router announcements when changing Internet connectivity providers. The IPv6 subnet size has been standardized by fixing the size of the host identifier portion of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from link layer media addressing information (MAC address). Network security is also integrated into the design of the IPv6 architecture, and the IPv6 specification mandates support for IPsec as a fundamental interoperability requirement.

Chapter 9: ETHERNET

                       The foundation of Ethernet topology was first established in 1970, with a program called Alohanet. 

                       Alohanet required all stations to follow a protocol in which an unacknowledged transmission required re-transmitting after a short period of waiting. The techniques for using a shared medium in this way were later applied to wired technology in the form of Ethernet.

                      Ethernet was designed to accommodate multiple computers tha were interconnected on a shared bus topology.

                      The first version of this was incorporated a media access method known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD) that managed the problems that result when multiple devices attempt to communicate over a shared physical medium.

                      Ethernet operates across two layer of the OSI model. The model provides a reference to which the Ethernet can be related but it is actually implemented in the lower half of the Data Link Layer, which is known as the Media Access Control (MAC) sublayer, and the Physical Layer only.

                     Ethernet at Layer 1 involves signals, bit streams that travel on the media, physical components that put signals on the media, and various topologies. It performs a key role in the communication that take place between devices, but each of it's functions has a limitations.Ethernet stations communicate by sending each other data packets: blocks of data individually sent and delivered. As with other IEEE 802 LANs, each Ethernet station is given a 48-bit Mac Address. The MAC addresses are used to specify both the destination and the source of each data packet. Ethernet establishes link level connections, which can be defined using both the destination and sources addresses. 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. Network interfaces normally do not accept packets addressed to other Ethernet stations

          The success of Ethernet is due to the following:

1. Simplicity and ease of maintenance
2. Ability to incorporate new technologies 
3. Reliability
4. Low cost of installation and upgrade

In an overview Of Ethernet Physical Layer; "Ethernet is covered by the IEEE 802.3 standards in which four data rates are currently defined for operation over optical fiber and twisted-pair cables: 

• 10 Mbps - 10 Base- T Ethernet
• 100 Mbps - Fast Ethernet
• 1000 Mbps - Gigabit Ethernet 
• 10 Gbps - 10 Gigabit Ethernet   

                                  The principal 10 Mbps implementation of Ethernet include:

• 10 Base5 -using a thicknet coaxial cable
• 10 Base2 -using a thinnet coaxial cable
• 10 Base-T - using Cat3 / Cat5 unshielded twisted-pair cable