Appe n dix : Glossa r y
1 . ARP ( Addr e ss Re solu t ion Pr ot ocol)
Consider two machines A and B that share a physical network. Each has an assigned IP
address IP
A
and IP
B
, and a MAC address, MAC
A
and MAC
B
. The goal is to devise low-level
software that hides MAC addresses and allows higher-level programs to work only with the
IP addresses. Ultimately, however, communication must be carried out by the physical
networks using whatever MAC address scheme the hardware supplies.
Suppose machine A wants to send a packet to machine B across a physical network to
which they are both attached, but A only has the Internet address for B, IP
B
. The question
arises: how does A map that address to the MAC address for B, MAC
B
?
ARP provides a method of dynamically mapping 32-bit IP address to the corresponding 48-
bit MAC address. The term dynamic is used since it happens automatically and is normally
not a concern for either the application user or the system administrator.
2 . Clie n t s a n d Se r v e r s
The client-server paradigm uses the direction of initiation to categorize whether a program
is a client or server. In general, an application program that initiates peer-to-peer
communication is called a client. End users usually invoke client programs when they use
network services.
Most client programs consist of conventional application program
development tools. Each
time a client program is executed, it contacts a server, sends a request and waits for a
response. When the response arrives, the client program continues processing. Client
programs are often easier to develop than servers, and usually require no special system
privileges to operate.
By comparison, a server is any program that waits for incoming requests from a client
program. The server receives a request from a client, performs the necessary computation
and returns the result to the client.
t GW - 7 0 0 Se r ie s Use r M a n u a l, V e r sion 1 .6 , Ju l. 2 0 1 1
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