SMTP is the protocol for sending email and relaying it from one mail server to another.
Sender's device
Sender's mail server
Recipient's mail server
Recipient's device
The recipient collects the message from their own mail server via POP or IMAP
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A mail server holds users' mail, delivers it onward, and stores mail that arrives. SMTP is used both on the leg from the sender's device to a mail server and on the legs where mail servers pass the message along to its destination.
AnalogyIt covers dropping a letter in the postbox and the post offices passing it along to the office in the recipient's area. It does not include the recipient going to pick up the mail held at that office.
How to rememberIt stands for Simple Mail Transfer Protocol, and "Transfer" means to carry or move. Read it as the protocol whose job is moving mail.
Exam points
ExamSMTP is the protocol for the sending side of email. It is used both when a mail client sends a message out and when mail servers (メールサーバ) relay it toward the destination.
Mix-upSending and receiving are handled by different protocols. A mail client is configured with a separate SMTP server for outgoing mail and a POP or IMAP server for incoming mail.
POP is the protocol a mail client uses to retrieve mail addressed to you from the mail server and download it to the device.
The widely used version is POP3. By default it downloads mail to the device, manages it there, and deletes the original on the server, though a setting can keep a copy.
AnalogyIt is like collecting everything in your post office box and taking it home. Once home, you sort it there.
How to rememberIt stands for Post Office Protocol, literally "post office." Think of it as going to the post office to pick up the mail held for you.
Exam points
ExamPOP is a receiving protocol, used when the mail client on a user's device pulls mail from that user's mailbox (メールボックス) on the server.
IMAP is a receiving protocol for reading and organizing mail from a device while the mail stays on the server.
The widely used version is IMAP4. The device connects to the server mailbox each time mail is read, and works with the mail without copying all of it locally.
AnalogyIt is like leaving your photos in your own online album and opening it from whichever device you have at hand to view and sort them.
How to rememberFocus on "Access" in Internet Message Access Protocol. You do not take the mail home; you go and access it where it sits on the server.
Exam points
ExamWith IMAP, the server keeps both the mail and the results of organizing it. Every device connects to the same mailbox (メールボックス), so its state looks the same from any of them.
FTP is the protocol for transferring files between computers on a network.
Operation
Direction of the file
Download
From the server to your computer
Upload
From your computer to the server
It works both for bringing a file from the server to your machine and for placing a local file on the server. The original FTP does not encrypt what it sends, so methods that support encryption are used where a secure exchange is needed.
AnalogyIt is a parcel courier rather than a letter service, moving the goods themselves. You can ship something out or collect something you left in storage.
How to rememberIt stands for File Transfer Protocol. Remember that the leading F is for File and it will not get mixed up with the mail protocols.
Exam points
ExamFTP exists to exchange files between computers such as PCs and servers.
ExamAnonymous FTP is a way of running FTP in which people without their own account log in under a shared name and download the files made public.
ExamFTP and the mail protocols belong to the application layer (アプリケーション層). Beneath them, TCP/IP provides the common basic communication functions.
NTP is the protocol for synchronizing the time of devices over a network.
Device clock that has drifted
Query the time server
Receive the accurate time
Adjust the device clock
The device corrects its own clock to match the time it received
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A device queries a time server that provides the accurate time and sets its own clock to the time returned. Once the devices on a network agree on the time, records left on different devices can be lined up on a single timeline.
AnalogyIt is like everyone setting their watch to the time signal before the morning meeting.
How to rememberIt stands for Network Time Protocol. Remember that the T in the middle is for Time.
Exam points
ExamNTP synchronizes the clocks of networked PCs, servers, and other devices to a server that has an accurate time source.
DHCP is the protocol that automatically assigns an IP address and other settings needed for communication to devices joining a network.
Connect the device to the LAN
Request settings from the DHCP server
IP address and other settings assigned
The device starts communicating
With the settings received, the device can communicate on the network right away
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The assigning is done by a DHCP server on the LAN, and the device only needs to be set to receive its settings automatically. Assigned IP addresses are lent out for a limited period, and once one is no longer in use it can go to another device.
AnalogyIt is like checking in at a hotel front desk and being handed the key to a vacant room. Once a guest checks out, the room goes to the next guest.
How to rememberIt stands for Dynamic Host Configuration Protocol. Take "Dynamic" to mean the settings are decided on the spot when you connect.
Exam points
ExamWith DHCP, a PC automatically receives an IP address (IPアドレス) from a server the moment it connects to the network.