Computer network and Internet

What is Internet

Traditional and non-traditional Internet terminals, all of which are called host or end systems. The end system is connected by a communication link and a packet switch.

When data is transmitted from one end system to another, the sender system segments the data and adds the first byte to each segment. The resulting information package is called packet ).

A group switch receives a packet from an inbound communication link and forwards the packet from an outbound communication link. The most famous type is a router and a link layer switch.

PATH (route and Path): From the sending system to the receiving system, a group experiences a series of communication links and group switches called the path through this network (route and Path ).

ISP: the end system accesses the Internet through an Internet Service Provider (ISP. ISP also provides Internet access services for content providers to directly connect websites to the Internet.

Protocol: a protocol defines the format and order of messages exchanged between two or more communication entities, as well as the actions taken in terms of message transmission and/or receipt or other events.

Network edge

End System: a computer or other device connected to the Internet. Because they are on the edge of the Internet. Terminal Systems are also called hosts, which run applications such as Web browsers and web server programs.

A host is divided into a client and a server ).

Client Program: A program running on one end system. It sends a request and receives a service from the server program running on another end system.

Access Network: link the end system to the physical link of the edge router. An edge router is the first vro in the path from the end system to any remote end system.

• Residential access: connects the home terminal system to the network.
• Company access: connects end systems in commercial or educational institutions to the network.
• Wireless Access: connect the mobile terminal system to the network.

Network core

There are two basic methods for moving data through network links and switches: Circuit Switching (Circuit Switching) and packet switching (Packet Switching ).

Circuit Switching:

In a circuit switching network, resources provided for inter-system communication along the terminal system communication path are reserved during communication sessions. These resources are not reserved in the group exchange network.

The circuit in the link is implemented through frequency division multiplexing (OFDM) or time division multiplexing (TDM.

For OFDM, the spectrum of the link is shared by all connections created across the link.

For a TDM link, the time is divided into frames in a fixed interval, and each frame is divided into a fixed number of time slots. When a Network creates a connection across a link, the network specifies a time slot for the connection in each frame. These time slots are exclusively used by the connection. A time slot can be used to transmit data of the connection within each frame.

The circuit switching efficiency is low because the dedicated circuit is idle during the silent period.

Group exchange:

Various applications need to exchange messages when completing tasks ). The source host divides long packets into smaller data blocks and is called packet ). Between the source and destination, each of these groups is transmitted through a communication link and a group switch.

The storage and forwarding mechanisms are used at the end of the link. Before a vswitch can output the first bit of the group, it must accept the entire group.

How long does it take for a host to send an L-bit group to another host through the group switch network? Set the Q-segment link between two hosts. The frequency of each link is r bps. This is the only group in the network. The total latency is QL/R.

Group switching provides better bandwidth sharing than circuit switching. It is simpler and more effective than circuit switching, with lower implementation cost.

On-demand, instead of pre-allocated shared resources are sometimes referred to as statistical multiplexing of resources.

The ISP at the first layer is also called the Internet backbone network. ISP on the second layer has regional or national coverage, and it is very important to connect only with a few ISP on the first layer. The second ISP is called the customer of the first ISP connected to it, and the first ISP is the provider relative to the customer.

Latency, packet loss, and throughput in A group exchange network

The most important latency is the node processing latency, queuing latency, transmission experiment, and propagation latency. The total latency is accumulated.

Processing latency: checks the group header and determines the time required to direct the group to any location.

Queuing latency: in a queue, when a group is waiting for transmission on the link, it is subject to queuing latency.

Transmission latency: l/R.

Propagation latency: the time required for transmission from the starting point of the link to the router is the propagation latency, depending on the physical media of the link, close to the speed of light.

Instantaneous throughput: the speed at which the host receives the file is measured in bps. If the file is composed of F bits and host B receives all f bits in T seconds, the average throughput of file transfer is F/T bps.

The transfer rate of the bottleneck link: min {RC, RS }. RS indicates the link rate between the server and the router. RC indicates the link rate between the router and the customer.

Protocol layers and their service models

The layered architecture only provides the same service to the layer above it, and uses the same service from the following layers. When the implementation of a layer changes, the rest of the system will remain unchanged.

Network designers organize protocols and network hardware and software that implement these protocols in a hierarchical manner. All protocols at each layer are called protocol stacks.

Five-layer Internet Protocol Stack: application layer, transport layer, network layer, link layer, and physical layer.

Layer-7 iso osi reference model: application layer, presentation layer, Session Layer, transport layer, network layer, link layer, and physical layer.

 

Computer network and Internet