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Computer Networking : A Top-Down Approach

Computer Networking : A Top-down Approach

James F. Kurose, Keith W. Ross
Transport Layer



Consider a planet where everyone belongs to a family of six, every family lives in its own house, each house has a unique address, and each person in a given house has a unique name. Suppose this planet has a mail service that delivers letters from source house to destination house. The mail service requires that (1) the letter be in an envelope, and that (2) the address of the destination house (and nothing more) be clearly written on the envelope. Suppose each family has a delegate family member who collects and distributes letters for the other family members. The letters do not necessarily provide any indication of the recipients of the letters.

a. Using the solution to Problem R1 above as inspiration, describe a protocol that the delegates can use to deliver letters from a sending family member to a receiving family member.

b. In your protocol, does the mail service ever have to open the envelope and examine the letter in order to provide its service?



  • Sender has to provide the address of the destination name. It is written by the delegate to the planet’s mail service..
  • After receive the destination address, the envelop the written on the top details.


No. The mail service ever have not to open the envelope and examine the letter in order to provide its service.

1 0


Ankur Singh

1. For sending a letter, the family member is required to give the delegate the letter itself, the address of the destination house, and the name of the recipient. The delegate clearly writes the recipient's name on the top of the letter. The delegate then puts the letter in an envelope and writes the address of the destination house on the envelope. The delegate then gives the letter to the planet's mail service. At the receiving side, the delegate receives the letter from the mail service, takes the letter out of the envelope, and takes note of the recipient name written at the top of the letter. The delegate then gives the letter to the family member with this name. 

2. No, the mail service does not have to open the envelope; it only examines the address on the envelope.

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