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1.In describing messages used in most message passing systems, it was observed that header information was usually fixed-length but the data in the
1. In describing messages used in most message passing systems, it was observed that header information was usually fixed-length but the data in the message (often called the payload) was usually variable length.
a. What makes this a very efficient way to handle messages, i.e., why is it efficient for headers to be fixed length and payloads to be variable length?
b. How do you know where the payload ends if it is variable length? Is it inefficient if the payload is fixed length and most messages are much shorter than that fixed size?
c. There are two ways to know where the end of a variable length item, like a message payload, is. What are they? Which one does the Internet Protocol v4 use?
2. We saw that a mailbox tied to a particular process on a system is called a port; each port is identified by a number. So, for example, the port to which to direct a request for a web page is number 80. What port numbers are used for:
a. ssh (secure shell logins)?
b. smtp (simple mail transfer protocol)?
c. ntp (network time protocol)?
Are these port numbers the same across standard Internet-connected systems?
