Name Resolution Techniques and Functional Elements of A Name Resolution System
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As we discussed earlier in this section, using a name system creates two parallel identification systems for computers: the numbers used by machines and the names used by people. The job of the name system is to integrate these two schemes. Name registration allows humans to specify which machines use which names. This is only half the process, however; we also need a way for machines to take a name given to them by a human and translate it into the real address it can actually use for communication. This is called name resolution.
Name resolution, also sometimes called name translation, mapping or binding, is the most well-known aspect of name systems, because it is where most of the heavy lifting of a name system occurs. The name space is generally set up once, and name registration occurs infrequently: only when names must be created or changed. In contrast, every user of a name system instructs the machines he or she uses to perform name resolution, hundreds or even thousands of times a day.
There are several different techniques that can be use for name resolution. How this function is implemented depends a great deal on the other two name system functions, name space and name registration. As you might imagine, a simple name system with a simple name registration method will most often use a simple resolution method as well. Complex hierarchical systems with distributed databases require more sophistication in how names are resolved.
There are three common name resolution methods.
The table used for table-based name registration is consulted by a device when resolution needs to be performed. The table tells the device how to transform the name of the machine it needs to contact into an address.
This technique obviously corresponds to table name registration; it is the simplest and least capable of the three methods. Table name resolution is suitable for standalone use only in very small name systems, but can be a supplement to other methods as well.
When a device needs to resolve a name, it broadcasts a query that says something to this effect: I need to send to the device named 'X', who is that? The device whose name is 'X' responds back saying I'm 'X' and my numeric address is 'N'.
This is the complement of broadcast name registration, of course. It too can only be used in simple systems where every device can hear a broadcast. The use of broadcasts also makes it wasteful of network bandwidth.
Servers are programmed with software that allows them to respond to name resolution requests sent by clients. These servers take the name in the request, look up the associated numeric identifier in a database, and send it back in a response.
This technique is, of course, generally used in conjunction with database name registration. It is the most complex of name resolution methods, but is also the most efficient, and the only one that can really work properly on a large, distributed hierarchical name system.
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