What is layered architecture of computer network?

Answer 1

1.The process of establishing a link between two devices to communicate and share information is complex.

2. The communication functions are grouped into manageable sets called as layer.

3. The design process of layer architecture is very simple as the function of each layer and their interaction are well defined.

4. It provides flexibility to modify network services.

5. Addition of new services and management of network architecture is easy.

6. Due to segmentation it is easy to solve complex problems.

Answer 2

Structure of an Operating System

An operating system is composed of a

kernel, possibly some servers, and

posssibly some user-level libraries. The

kernel provides operating system services

through a set of procedures, which may be

invoked by user processes through

system calls. System calls look like

procedure calls when they appear in a

program, but transfer control to the kernel

when they are invoked at run time. ( read is

an example of a system call in Unix.)

In some operating systems, the kernel and

user-processes run in a single (physical or

virtual) address space. In these systems, a

system call is simply a procedure call. In

more robust systems, the kernel runs in its

own address space and in a special

privileged mode in which it can execute

instructions not available to ordinary user

processes. In such systems, a system call

invokes a trap as discussed below.

A trap is a hardware event that invokes a

trap handler in the kernel. The trap

indicates, in appropriate hardware status

fields, the kind of trap. Traps may be

generated implicitly by the hardware to

signal events such as division by zero and

address faults (which we will discuss later),

or explicitly by a process when it executes a

special instruction. Explicit or user-initiated

traps are used to handle system calls. A

system call stores the name of the call and

its arguments on the stack and generates a

user-initiated trap. The trap handler in the

kernel knows, from the type of the trap, that

it is a user-initiated trap asking for a system

call, finds the name of the systems call, and

calls the appropriate kernel procedure to

handle the call passing it the arguments

stored on the stack.

We will later consider the various techniques

for structuring the kernel. As we shall see,

kernels may be layered, object-oriented, or

decomposed into kernel processes.

Not all operating services have to be

provided by the kernel. Modern operating

systems also define servers, which are

user processes that offer operating system

services to other processes. These services

are invoked by clients through interprocess

communication (IPC) primitives. We shall

see later the rationale for transferring

functionality from the kernel to servers. We

shall also see the minimum functionality that

needs to be supported in the kernel. In

micorkernel-based systems, the kernel

provides this minimum functionality.

The cost of invoking system calls and IPC

primitives is more than the cost of invoking

a simple procedure call when multiple

address spaces are supported by the

system. Therefore, as we shall see later,

some of the traditional OS functionality is

sometimes also provided by user-level

libraries.

Answer 3

1. A set of layers and protocols is called as network architecture.

2. Protocol stach is defined as a list of protocols used for a certain system, one protocol per layer.

Answer 4

The OSI Model

Answer 5

what is a protocol architecture?