NETWORKING
CHAPTER 2
MIDTERM
Know The OSI MODEL LAYERS
PHYSICAL: the lowest, or first layer of the OSI model. The Physical layer contains the physical networking media, such as cabling and connectors.
DATA: the second layer in the OSI model. The Data Link layer bridges the networking media with the network layer. Its primary function is to divide data it recieves from the network layer into frames that can then be transmitted by the physical layer. The Data Link layer is divided into two sublayers. The LOGICAL LINK LAYER (LLC) is the upper sublayer of the data link layer. The LLC provides a common interface and supplies reliablity and flow control services. The MEDIA ACCESS CONTROL (MAC) is the lower of the two sublayers in the data link layer. The MAC appends the physical address of the destination computer onto the frame.
NETWORK: the third layer of the OSI model. The network layer translates network addresses into their physicla counter parts and decides how to route data from the sender to the reciever.
TRANSPORT the fourth layer in the OSI model. The transport layer is primarily responsible for ensuring that data are transferred from point A to point B reliably and without errors.:
SESSION:: the fifth layer of the OSI model. This layer establishes and maintains communication between two nodes on the network. It can be considered the “traffic cop” for network communications. The term session refers to a connection for data exchange between two parties; it is most often used in context of terminal and mainframe communications.
PRESENTATION: the 6th layer of the OSI model. The presentation layer serves as a translator between the application and the network. Here data are formatted in a schema that the network can understand, with the format varying according to the type of network used. The presentation layer also manages data encryption and decryption, such as the scrambling of system passwords.
APPLICATION: The 7th layer of the OSI model. The Application layer provides interfaces to the software that enables programs to use network services. Some of the services provided by the Application layer include file tranfer, file management, and message handling for e-mail.
Data frames, simply known as “Frames” are small blocks of data with control, addressing, and handling information attached to them. Frames are composed of several smaller components. The characteristics of these components depend on the type of network on which the frames run and the standards they mus follow. The 2 major categories of frames are ethernet and Token Ring.
Each node on a network can be identified by two types of addresses: network layer addresses and Data link layer addresses. Data link layer addresses are hardwired into the networking device, and are also called physical, MAC, or hardware addresses.
Mac address is a number that uniquely identifies a network node. The manufacturer hard-codes the MAC address on the NIC. This address is composed of the Block-ID and the device-ID. The block ID is the first set of six characters that make up the MAC address and that are unique to a particular vendor. The device-ID is the second set of six characters that make up a devices MAC address. The device-ID, which is added at the factory, is based on the device’s model and manufacture date.
Network layer addresses, also called logical or virtual addresses, are assigned to devices through operating software. These logical addresses are composed of hierarchial information, so they can be easily interpreted by routers and used to direct data to their destinations.
IEEE standards in addition to applying to frame types apply also to connectivity, networking media, error checking algorithms, encryption, emerging technologies, and more. All of these specifications fall under the IEEE’s Project 802, an effort to standardize the elements of networking.
802.3 the IEEE statndard for Ethernet networking devices and data handling.
802.5 is the IEEE standard for Token Ring networking devices and data handling.