Linux Kernel Architecture

Chapter 12: Networks Contents

Network Layer

Transport Layer

Application Layer

Transport layer

Network Access Layer

Data link layer

Physical layer

Host-to-host

Internet (IP)

Transport (TCP, UDP)

Application

(HTTP, FTP etc.)

ISO/OSI and TCP/IP Reference Model

models.

The various layers perform the following tasks:

❑ The host-to-network layer is responsible for transferring information from one computer to a

distant computer. It deals with the physical properties of the transmission medium^1 and with

dividing the data stream intoframesof a certain size to permit retransmission of data chunks

if transmission errors occur. If several computers are sharing a transmission line, the network

adapters must have a unique ID number known as aMAC addressthat is usually burned into the

hardware. An agreement between manufacturers ensures that this number is globally unique.

An example of a MAC address is08:00:46:2B:FE:E8.

In the view of the kernel, this layer is implemented by device drivers for network cards.

❑ The network layer of the OSI model is called theInternet layerin the TCP/IP model, but both

refer basically to the same task of exchanging data between any computers in a network, not

necessarily computers that are directly connected, as shown in Figure 12-2.

A direct transmission link between computers A and B is not possible because they are not phys-

ically connected to each other. The task of the network layer is therefore to find a route via which

the computers can talk to each other; for example, A–E–B or A–E–C–B.

A

C B

D E

Figure 12-2:

Network-linked

computers.

(^1) Predominantly coaxial cable, twisted-pair cable, and fiber opticlinks are used, but there is an increasing trend toward wireless
transmission.