A: OSI reference model and the corresponding local area network technology --------------------------
LAN technology designed primarily physical layer and the data link layer, which covers the cable standards, protocols, standards, etc., the following relationship:
Two: LAN and IEEE802 standard: -------------------------
the IEEE: Institute of Electrical and Electronics Engineers, developed a series of local area networks and metropolitan area standard network, relates to a variable packet transport networks, protocols, services corresponding to the OSI physical layer and the data link layer.
As these specified criteria :( too, several commonly used sentence)
the IEEE 802.2: Logical Link Control sublayer defined (LLC) is.
IEEE 802.3: Ethernet medium access control protocol (CSMA / CD) and physical layer specification [. 1]
the IEEE 802.11: Wireless LAN (WLAN) medium access control protocol and physical layer specification.
LAN: mainly explained in the IEEE standard specified, local area networks in a physical layer and a data link layer and defines how the distribution
LLC sublayer:
One of the main functions of the data link layer is an upper package and the identification data, this function is performed by the LLC sublayer. The LLC sublayer is defined IEEE802.2 standard
LLC sublayer IEEE802.2LLC added to the network layer encapsulation header data. In order to distinguish the type of network, multiple protocol multiplexing link, LLC with SAP logo upper-layer protocols .
LLC standards include two service access points: the SSAP (Source Service Access Point), and the DSAP (destination service access point) of
the MAC sublayer:
main functions: accommodate a varied media medium, and up processing channel at any particular medium indicating the site and addressing issues. Relates IEE Standard: Ethernet 802.3, 802.4 token bus network, 802.5 token ring network, etc.
mac sublayer using mac address identify each node. Mac sublayer typically sender adds mac address of the destination computer to the data frame, when transmitted to a receiver mac sublayer, which the frame is checked whether the destination address with their match, If not discarded, the matching is sent to the on the one LLC sublayer.
Three: LAN development -------------------
common Ethernet technologies including Ethernet, Token Ring, FDDI
Ethernet: the Xerox (real music) developed Ethernet standard, originally directed to communicate via a shared coaxial multiple computers, using CSMA / CD mechanism to detect conflicts.
The main difference between the standard and the 802.3 Ethernet standard is: only describes the use of a standard Ethernet coaxial cable 50gou, transmission speed of 10Mbps LAN bus. The entire contents of ISO standard 802.3 data link layer and physical layer.
(I understand: 802.X standard is an international standard, which is mainly given to develop a variety of standard data link layer protocols, such as 802.2,802.3 etc; and Ethernet physical layer aspects of the definition, such as an electrical, physical media, etc., such as CSMA / CD )
original Ethernet star topology using coaxial cable with bus topology ---- --- then composed hub hUB to the current through the bridge's Ethernet switches
today has formed a series of standard Ethernet , from the early standard 10Mbps Ethernet, 100Mps fast Ethernet, 1Gbps to 10Gbps Gigabit Ethernet Gigabit Ethernet. Ethernet has become the mainstream LAN technology.
Here addition: Listed below are some of the IEEE802.3 Ethernet standard, these standards in front of a digital representation of the transmission speed, the unit is "Mbps", the last segment of a digital representation of a single length of cable (reference units 100m), Base represents a "baseband" means, Broad stands for "the bandwidth."
· 10Base-5 thick coaxial cable used, the maximum segment length of 500m, a baseband transmission method;
· 10Base-2 thin coaxial cable used, the maximum segment length of 185m, a baseband transmission method;
· 10Base-T twisted-pair cable, the maximum segment length of 100m;
·-1Base. 5 twisted pair cable is a maximum segment length of 500m, the transmission rate of 1Mbps;
· 10Broad-36 using a coaxial cable (RG-59 / U CATV) , the maximum net length is 3600m, a broadband transmission mode;
· 10Base-F. using optical fiber transmission medium, the transmission rate is 10Mbps;
benefits: standard open, simple technology, coupled with constant speed and improve the reliability, costs continue to decrease to obtain increasingly the more widely used.
(The original bus Ethernet)
Token: physical star topology logical ring, all operating points by connecting IBM data connector, two equivalent token is a special mac null pointer, a node wants to send data, the token must be obtained.
Token of "free / busy" flag, as data can be transmitted in a state where "relax";
advantages: Theoretically stronger than Ethernet, for example, to avoid competition for the disorder, conflict reducing medium;
disadvantages: Token the need to maintain separate and complex technical conservatism and expensive equipment, and only supports cable.
FDDI: Fiber Distributed Date Interface, FDDI, ring topology for LAN technology, LAN technology is the development of the mid-1980s.
Transmission FDDI token ring access method and the like, using the "timed token", a node needs to transmit at the assigned, it will set the "target token rotation time", which can be transmitted according to user needs as much as possible frame.
FDDI (100Mbps) was beyond Ethernet (10mbps) and Token Ring (4 or 16mbps) LAN technology, get up early reused.
Advantages: token-protocol feature that supports the optical fiber, to prevent jamming and eavesdropping
disadvantages: the high price of the device only supports 5 cable and fiber optics, face significant upgrade from the Ethernet over Transplantation
