A transport layer protocol usually has several responsibilities．One is to create a process-to-process communication；UDP uses (1) numbers to accomplish this．Another responsibility is to provide control mechanisms at the transport level．UDP does this task at a very minimal level．There is no flow control mechanism and there is no(2) for received packet．UDP, however, does provide error control to some extent．If UDP detects an error in the received packet，it will silently drop it． The transport layer also provides a connection mechanism for the processes．The (3) must be able to send streams of data to the transport layer．It is the responsibility of the transport layer at (4) station to make the connection with the receiver, chop the stream into transportable units，number them，and send them one by one．It is the responsibility of the transport layer at the receiving end to wait until all the different units belonging to the same process have arrived，check and pass those that are (5) fre
A. hop
B. port
C. route
D. packet
Passage Three
An employer has several choices he can consider when he wants to hire a new employee. First, he may look within his own company. But if none of the present employees are suitable for the position, he will have to look outside the company. If his company has a personnel office, he can ask them to help find qualified applicants.
There are other valuable sources the employer can use, such as employment agencies, professional societies and so on. He can also advertise in the newspapers and magazines and ask prospective candidates to send in resumes.
The employer has two kinds of qualifications to consider when he wants to choose from among applicants. He must consider both professional qualifications and personal characteristics. A candidate’s professional qualifications include his education, experience and skills. These can be listed on a resume. Personal characteristics must be evaluated through interviews.
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