sion detection
•Binary exponential backoff
The combination of techniques described above is known by the name Carrier Sense Multi-Access with Collision Detection.(CSMA/CD) Algorithm 3.1 summarizes CSMA/CD.3.4.2 CSMA/CA
To ensure that all stations share the transminssion media correctly, wireless LANs use a modified access protocol known as Carrier Sense Multiple Access With CollisionAvoidance (CSMA/CA). Instead of depending on all other computers to receive all transmissions, the CSMA/CA used with wireless LANs triggers a brief transmission from the intended receiver before transmitting a packet. The idea is that if both the sender and receiver transmit a message, all computers within range of either will know a packet transmission is beginning. Figure 3.1 illustrates the sequence.
Figure 3.1
In the figure, computer 3 sends a short message to announce that it is ready to transmit a packet to computer 2,and computer 2 responds by sending a short message announcing that it is ready to receive the packet. All compters in the range of computer 3 receive the initial announcement, and all computers in the range of computer 2 receive the response. As a result,even though it cannot receive the signal or sense a carrier, computer 1 knows that a packet transmission is taking palces
3.5 Distributed Route Computation
All packet switches must participate in distributed route computation. There are two general forms:
•Link-State Routing (LSR), which uses Dijkstra's algorithm
•Distance-Vector Routing (DVR), which uses another approach
3.5.1 Link-State Routing (LSR)
An LSR algorithm can adapt to hardware failures. If a link between packet switches fails, the attached packet switches will detect the failure and broadcast a status message that specifies the link is down. All packet seitches receive the broadcast, change their copy of the graph to reflect the change in the link's status, and recomputed shortest paths. Similarly, when a link becomes available again the packet switches connected to the link detect that it is working and start sending status messages that report its availability.
Algorithm 3.2
3.5.1 Distance Vector Routing (DVR)
Chapter 4 Internetworking with TCP/IP summary
The router is the basic building block of an internet. hardware component used to connect heterogeneous networks. Physically, routers resemble bridges ---- each router is a special-purpose computer dedicated to the task of interconnecting networks. The network treats a connection to a router the same as a connection to any other computer. A router can connect two LANs, a LAN and a WAN, or two WANs. Furthermore, when a router connects two networks in the same general category, the networks do not need to use the same technology. For example, a router can connect an Ethernet LAN to an FDDI LAN. Thus, each cloud represents an arbitrary network technology.
An organization seldom uses a single router to connect all of is networks. There are two reasons:
Because the CPU and memory in a router are used to process each packet, the processor in one router is insufficient to handle the traffic passing among an arbitrary number of networks.
Redundancy improve internet reliability. Protocol software continuously monitors internet connections, and instructs the routers to send traffic along alternative paths whe
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