Exchange methods between nbma and BMA

NbmaIs a network term, translated as" Non-broadcast Multi-Channel Access", Then BMAYes "Broadcast Multi-Channel Access. These two concepts describe Data Link LayerAnd one n or less can affect the design of the link layer switch. In general, nbma is used by the switch to determine how to forward data frames, while BMA is used by the host to determine whether to accept a certain data frame. The switch only plays a secondary optimization role, for example, filter unnecessary broadcasts. The nbma switch must be manually configured (even if there is a so-called dynamic configuration protocol, the protocol operation policy is also set). On the contrary, the BMA switch, such as the Ethernet switch, is passively learned. 1. nbma Switching Although everyone is connected to a link, this does not mean that data frames can be anywhere at will.. In the nbma network, the control is on the switch, and the terminal host can only reach the target host through the switch. That is to say, only when the "data frame from this port has passed some test" is configured on the switch, the data frame can pass only when the policy can be issued from that port. For the nbma network, the implementation of the switch is more complex, because it has a lot of built-in protocol layer logic, rather than a passive learning. It may be better if we use several nbma instances. For nbma, Frame Relay and ATM are the most typical ones.The widely used technology is ATM. We know that ATM is much more complicated than Ethernet, and I think it is more complicated than IP. An important concept of ATM is Virtual circuit and virtual channelThe virtual circuit must be established before communication. The operation of the ATM switch is to exchange virtual paths so that data frames are transmitted in the configured virtual channel. A specific data frame can only forward along one virtual channel, no other virtual channels will be reached. The virtual channel configuration of the ATM is performed on the switch, that is, the switch controls how data frames are forwarded, and the terminal host can only passively accept this arrangement. The advantage of nbma is its controllability, unlike BMA. For the WAN, BMA is rarely used, and most of them use nbma. Because the WAN forwarding policy is quite complex, the link layer is generally forwarded by a specific target under the guidance of BGP, there must be no arbitrary broadcast, which is related to the mandatory policies of various as. If any broadcast occurs, the WAN will not be secure. The security here may be highly related to politics and national security.   2. BMA Switching In fact, the BMA network is not an exchange network.And does not need to be exchanged, The logical topology of the BMA network is always a bus topology.The concept of switching is introduced in the BMA network to optimize the network. Taking Ethernet as an example, the original Ethernet is bus-type. Later, in order to facilitate expansion, the hub was introduced. Bridge is used to connect heterogeneous EthernetLater, powered by the fact that Ethernet switches were widely used in high-performance and low-cost twisted pair wires, the bus-based axis gradually exited. The biggest advantage of an Ethernet switch is its learning function, which is a kind of passive learning, Although there is no secret in the BMA network, due to the existence of a Learning switch, the secret is limited to mutually recognized communication parties.. Throughout the history, we can find that the Ethernet switch is a latecomer, although it really subverts the Ethernet architecture, so that the later Gigabit Ethernet is only compatible with the traditional 802.3 for the sake of compatibility, what is the essence of Ethernet? This is the ARP Protocol. ARP requests are a broadcast. This broadcast confirms that Ethernet is the original broadcast network. Any communication has to use the ARP protocol for address resolution (without considering static ARP ing configuration). This address resolution and subsequent unicast communication give the switch a learning opportunity, knowing the port on which a MAC address is accessible to the vswitch, The vswitch can filter out unnecessary broadcasts.
This kind of learning is passive boosting.Even if there is no such learning mechanism, data packets can still reach the target, because the BMA network is implemented on the end host rather than the switch. For Ethernet, the default data frame will reach any host on the same link, the host filters out data frames on the target Mac instead of the local host. Nature of BMA--- That is, on the host, the switch only helps, When a vswitch is unable to judge (such as aging MAC/port ing entries), it will return to the essence of BMA, that is, broadcast data frames on each port. IPv6 removes ARP broadcast, which in turn completely destroys the foundation of Ethernet broadcast. However, even so, a data frame can still change the target MAC address to a broadcast address. Before the standard changes, when the vswitch is still in the blind state for multicast, the switch still forwards the data frame on all ports.