\(11.2.\)Networks

1.The Physical Interface

• The adapter provides the physical interface to the network.

• Data received from the network are copied from the adapter typically by a DMA transfer.

2.Ethernet Segment

• One end is attached to an adapter on a host, and the other end is attached to a port on the hub.

• A host can send a chunk of bits called a frame to any other host on the segment.

• Every host adapter sees the frame, but only the destination host actually reads it.

3.LAN

• Multiple Ethernet segments can be connected into larger LANs(Local Area Network), called bridged Ethernets, using a set of wires and small boxes called bridges.

• Bridges automatically learn over time which hosts are reachable from which ports and only copy frames from one port to another when necessary.

4.Internet

• Multiple incompatible LANs can be connected by specialized computers called routers to form an internet.

• Each router has an adapter(port) for each network it connected to.

5.Protocol Software Layer

  A layer of protocol software smoothes out the differences between the different networks. This software implements a protocol that governs how hosts and routers cooperate in order to transfer data.

  The following figure shows an example of using protocol software layer for data transferring:

1. The client on host A invokes a system call that copies the data from the client's virtual address space into a kernel buffer.