Logical Topologies
Logical topology -the way in which data are transmitted between nodes, rather than the layout of the paths that the data take. Also known as a network transport system.
Switching - a component of a networks logical topology that determines how connections are created between nodes.
Circuit switching - a connection established between two network nodes before they begin transmitting data.
Message switching - a connection established between two devices, transfers the information to the second device, then breaks the connection.
Packet switching - breaks data into packets before they are transported, packets can travel any path on the network to their destinations, because each packet contains the destination address and sequencing information.
Ethernet - a logical topology originally developed by Xerox in the 1970's and later improved by Xerox, Digital Equipment Corporation (DEC), and Intel.
Carrier Sense Multiple Access with Collision Detection (CSMA/CD) - access method used in Ethernet.
Demand Priority - each device on a star or hierarchical network sends a request to transmit to the central hub. The hub then grants the requests one at a time. It examines incoming data packets, determines the location of the destination node, and forwards the packets to that destination. Demand priority requires an intelligent hub- a hub that can manage transmissions.
Switched Ethernet - enables multiple nodes to simultaneously transmit and receive data over different logical network segments.
Shared Ethernet - supply a fixed amount of bandwidth that must be shared by all devices on a segment.
Gigabit Ethernet
1 Gigabit Ethernet - runs at 1000 MBPS, can technically run over UTP cable.
Ethernet Frame Types
IEEE 802.3 (LLC) - default frame type for versions 4.x and higher of the Novell NetWare network operating system.
Novell Propriety 802.3 - original NetWare frame type and the default frame type for networks running NetWare versions lower than 3.12
Ethernet II - original Ethernet frame type developed by DEC, Intel, and Xerox, before IEEE began to standardize Ethernet.
IEEE 802.3 SNAP (Sub - Network Access Protocol) - adaptation of IEEE 802.3 and Ethernet II.
Design Considerations for Ethernet Networks
Cabling - Ethernet networks can use coaxial cable or unshielded twisted - pair cabling.
Connectivity devices - Ethernet NIC's, switches, hubs, routers, and bridges are generally less expensive than comparable Token Ring or LocalTalk equipment.
Number of stations - The number of allowable stations on a 10BaseT or 100BaseTX Ethernet network is limited to 1024.
Speed - Ethernet networks may have a throughput of 10 Mbps, 100 Mbps, 1 Gbps, and soon, 10 Gbps.
Scalability - You can easily expand Ethernet networks by adding connectivity devices on the bus. However, bear in mind each type of network's size limitations.
Topology - 10BaseT and 100BaseTX Ethernet networks use a star - wired bus hybrid topology, which is highly fault tolerant.
LocalTalk - logical topology designed by Apple Computer, Inc. specifically for networking Macintosh computers. uses CSMA/CD as its transmission method.
