In the protocol stack, the transport layer enables logical communication between processes on different hosts, while the network layer enables logical communication between the hosts themselves. This distinction may seem small, but it's crucial to understanding how data is managed across a network. To help clarify this, let’s use a family analogy:
Imagine you have two houses—one on the east coast and one on the west coast—each with 10 children. These children are cousins, and they enjoy writing letters to each other every week. Each child sends a letter to every cousin, so each house receives 100 letters per week (a lot of paper if they weren’t using email!). The letters are delivered through a local post office.
In this scenario, the postal service handles the delivery between the two houses, not directly between individuals. Meanwhile, two specific children—Ann from the west and Bill from the east—are responsible for collecting and distributing the letters within their respective homes. Ann gathers all the letters from her siblings and sends them to the post office, while Bill does the same on the east coast. When the letters arrive, Ann distributes them to her cousins, and Bill does the same on his side.
From the perspective of the cousins, Ann and Bill act as intermediaries in the mail process, even though they’re only part of the end-to-end delivery system. The postal service provides a logical connection between the houses, while Ann and Bill provide a logical connection between the cousins.
This example illustrates the difference between the network layer and the transport layer. In this analogy:
- **Host (or terminal system)** = House
- **Process** = Cousin
- **Application message** = Letter in an envelope
- **Network layer protocol** = Postal service (including the postman)
- **Transport layer protocol** = Ann and Bill
Ann and Bill handle all the work within their own homes. They don’t sort or route mail between postal offices; that’s handled by the postal service. Similarly, the transport layer in an end system passes messages to the network layer and vice versa, but it doesn’t manage how those messages are transmitted across the network. Routers along the way can’t see or process the information added by the transport layer.
Now, imagine Ann and Bill go on vacation, and Susan and Harvey take over their duties. However, Susan and Harvey aren’t as reliable—they collect and deliver letters less frequently and sometimes lose some. This shows that different transport protocols can offer different levels of service. Just like how a computer network can support various transport protocols, each one offers a different service model to the application.
The services Ann and Bill can provide are also limited by the postal service. If the postal service doesn’t guarantee delivery within a certain time frame, Ann and Bill can’t promise timely delivery to the cousins. Similarly, the transport layer’s capabilities are constrained by the network layer below it. If the network layer can’t ensure delay or bandwidth, the transport layer can’t offer those guarantees either.
Understanding this relationship helps explain why the transport and network layers work together to ensure reliable and efficient communication across the internet.
AC Power Supplies
AC power supply is a kind of power supply that converts the input mains or DC input into a pure sine wave output after AC-DC-AC or DC-AC conversion. The ideal AC power supply is characterized by stable frequency, stable voltage, zero internal resistance and pure sine wave output voltage wave (without distortion). Mainly used for power grid simulation tests conducted by various electrical appliance manufacturers on electrical appliances according to the voltage/frequency requirements of different countries, various AC motors, AC transformers, aircraft & mechanical equipment and other electronic devices that require pure, regulated and frequency-stabilized output.
Our AC power supply mainly includes three types
1. AC Power Supplies converting the input mains AC by AC-DC-AC, output voltage and frequency are stable and adjustable with pure sine wave output waveform, so called: Variable Frequency AC Power Supplies.
2. AC Power Supplies converting the DC output of the battery and other DC equipment by DC-AC, giving an AC sinusoidal output with stable output voltage and frequency. so called: Inversion AC Power Supplies.
3. AC Power Supplies converting the input mains AC by AC-DC-AC, giving a variable voltage AC output at constant 400Hz output frequency ultra-high output frequency stability. so called: Intermediate Frequency AC Power Supplies.
4. According to the difference in the number of output phases, the AC Power Supplies can be divided into single-phase output AC power supplies and three-phase output AC power supplies.
Different from Variac and AC voltage regulators, our AC power supplies support the setting of output voltage and frequency and has superior high precision, high stability, and high efficiency stable frequency AC output, not only for AC power conversion but also for AC high precision test purpose.
Through the friendly operation panel, you can read the output data such as output voltage, output current, output power, power factor, etc., providing accurate data records for your test, and can add RS485 interfaces as standard, following the MODBUS-RTU international communication protocol, which can realize remote control and operating status monitoring of the power supplies.
Our AC Power Supplies have comprehensive protection functions, such as: over voltage, over current, over temperature and short circuit protections, which can protect the AC power supplies and DUT from damages.
AC Power Sources, AC Sources, AC - AC Power Supplies, DC - AC Power Supplies, AC Switching Power Supplies
Yangzhou IdealTek Electronics Co., Ltd. , https://www.idealtekpower.com