Introduction to Networking

Nachos provides the abstraction of communication using mailboxes. The Nachos networking abstraction reaches to closely connected computers. The messaging is unreliable and messages can be dropped, but they are never corrupted in any way. The networking provides ordered and fixed-sized messages. There are several classes that builds the Nachos networking facility. They are described below.

PostOfficeInput & PostOfficeOutput

These classes defines a "Post Office", as a set of mailboxes. The post office handles the transfer of messages, by two main operations:

• Send : Which sends a message to a remote mailbox.
• Receive : Which waits until a message is in the mailbox. Removes and returns it.

Incoming messages are delivered into the correct mailbox and threads waiting on Receive is awakened. The post office is also used for transfer synchronization.

MailBox

The MailBox class defines a single mailbox, spoken of above. A mail box keeps the messages until they are transferred to the thread(s). The post office puts the incoming messages into the correct mailbox, so that the messages can be read by threads on the computer where the mail box resides. A mail box may contain several messages.

Mail & MailHeader

The Mail and MailHeader objects works together rather tightly. The Mail object mainly contains the data that is to be sent. The Mail object defines the format of a message. The MailHeader class defines the different parts of the message header, including, for example, the destination mail box address. When a Mail is created the MailHeader is appended.

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