Determine the technology and media access control method for Ethernet networks

chapter 2:Switching technology LAN

    Determine the technology and media access control method for Ethernet networks

  • LAN switching technology

    LAN switching is a form of packet switching in which the data packets are transferred from one computer to another over a network. Switching technologies are vital to network design, as these technologies permit the traffic to be sent only where it is required. LAN switching technology helps to improve the overall efficiency of local area networks and address the existing bandwidth issues.

    Ethernet switches receive Ethernet frames in one port and then forward (switch) the frames out one (or more) other port. This first major section focuses on how switches make these switching decisions.

    How LAN switching technology works?

    LAN switching includes mainly 4 types of switching. They are as follows: 

    Layer 2 Switching

    Layer 2 switching is hardware-based switching. It makes use of the (media access control (MAC) addresses on the network interface cards (NICs) of the host to determine the location to forward the frames. Advantages of layer 2 switching are its high data transmission speed with low latency and cost.

    Layer 3 switching

    Layer 3 switching provides similar functionality as router. Some fundamental functions are as follows: Uses TL (time to live) Identify paths on the basis of logical addressing Offers security Enables hardware-based packet forwarding Offers highly efficient packet switching High speed data transmission with low latency 

    Layer 4 switching

    An enhanced version of layer 3 switching, layer 4 switching uses hardware-based switching with the addition of applications like Telnet and FTP. Layer 4 switching uses routing on the basis of port numbers. Access list filtering completely functions on layer 4 switching. The most significant advantage of layer 4 switching is that the network admin is able to configure a layer 4 switch for prioritizing data traffic by application, which implies that a quality of service (QoS) may be defined for every user.

    Multi-Layer Switching

    Multi-layer switching (MLS) provides low latency and high performance. All three layer switching (2, 3 and 4) are combined in MLS. MLS makes use of the following while making switching decisions: Source and destination address (MAC and IP) Protocols details (fields) Source port number and destination port number


    Ethernet has been a relatively inexpensive, reasonably fast and very popular LAN technology for several decades and standardized as IEEE 802.3 in the early 1980s.

    A network access method (or media access method) originated by the University of Hawaii, later adopted by Xerox Corporation.

    Most pervasive network access method in use

    Most commonly implemented media access method in new LANs.

    Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. 

    Ethernet uses the CSMA/CD access method to handle simultaneous demands.

    The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps.

    Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards.

    Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second). 10-Gigabit Ethernet provides up to 10 billion bits per second.

    MAC for Ethernet networks

    In the seven-layer OSI model of computer networking, media access control (MAC) data communication protocol is a sublayer of the data link layer, which itself is layer 2. The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium, e.g. Ethernet. The hardware that implements the MAC is referred to as a medium access controller. 

    Ethernet is used for linking cables to each other. It is the dominant cabling and data delivery used in the local area network. Some of its features is transmission of data that is up to ten million bits in a second.

    MAC - Getting Data to the Media

    Media Access Control (MAC) is the lower Ethernet sublayer of the Data Link layer. Media Access Control is implemented by hardware, typically in the computer Network Interface Card (NIC).

    The Ethernet MAC sublayer has two primary responsibilities: (i) Data Encapsulation, (ii) Media Access Control

    Data Encapsulation

    Data encapsulation provides three primary functions:
    Frame delimiting 
    Error detection
    The data encapsulation process includes frame assembly before transmission and frame parsing upon reception of a frame. In forming the frame, the MAC layer adds a header and trailer to the Layer 3 PDU. The use of frames aids in the transmission of bits as they are placed on the media and in the grouping of bits at the receiving node. 
    The framing process provides important delimiters that are used to identify a group of bits that make up a frame. This process provides synchronization between the transmitting and receiving nodes. 
    The encapsulation process also provides for Data Link layer addressing. Each Ethernet header added in the frame contains the physical address (MAC address) that enables a frame to be delivered to a destination node.
    An additional function of data encapsulation is error detection. Each Ethernet frame contains a trailer with a cyclic redundancy check (CRC) of the frame contents. After reception of a frame, the receiving node creates a CRC to compare to the one in the frame. If these two CRC calculations match, the frame can be trusted to have been received without error.

    Media Access Control

    The MAC sublayer controls the placement of frames on the media and the removal of frames from the media. As its name implies, it manages the media access control. This includes the initiation of frame transmission and recovery from transmission failure due to collisions. 

    Logical Topology

    The underlying logical topology of Ethernet is a multi-access bus. This means that all the nodes (devices) in that network segment share the medium. This further means that all the nodes in that segment receive all the frames transmitted by any node on that segment.

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