Information Technology Reference
In-Depth Information
each proxy will have to serve multiple clients simultaneously. The servers are connected locally
by an interconnection network. The proxies combine data retrieved from the local storage and
data received from other servers into a single video data stream for transmission to the clients.
In this architecture, the details of the system configuration can be completely hidden from
the clients. One drawback of this approach is processing and communications overhead. For
example, to deliver
B
bytes of video data from the video servers to a client,
B
bytes of data
must first be read from one or more servers' local storage, and then transmitted via network
to the client's proxy (unless the proxy happens to share the same host as the video server,
which then requires no transmission). Finally, the proxy processes the data and transmits to the
client. If we assume requests are serviced evenly by all
N
S
servers, then on the average we need
B
(2
N
S
−
1)/
N
S
bytes of data reception (proxy and client) for every
B
bytes of data delivered from the storage
servers to a client.
1)/
N
S
bytes of data transmission (server-to-proxy, proxy-to-client) and
B
(2
N
S
−
9.2.2 Independent Proxy
Alternatively, separate computers can be used to run the proxies. Figure 9.2 shows the inde-
pendent proxy architecture using this approach. The back-end storage servers and the proxy
computers are connected locally by an interconnection network. Each proxy connects to mul-
tiple clients via another external network. Similar to the proxy-at-server architecture, this
independent proxy architecture also hides the server complexity from the clients. Moreover,
separating the proxy from the server eliminates interference between the two processes and
hence may simplify the server and proxy implementations.
Under the independent proxy architecture, data are first retrieved from the back-end server's
local storage and then transmitted to the proxy. The receiving proxy then processes and
C
C
C
...
Server S
0
Proxy P
1
C
C
C
...
Server S
1
Proxy P
2
C
C
C
...
Server S
2
Proxy P
3
C
C
C
...
Server S
3
Proxy P
4
.
.
.
C
C
C
...
Server S
N
S
--1
Proxy P
N
P
--1
Independent
Proxies
Back-end
Storage Servers
Front-end
Clients
Figure 9.2
The independent proxy architecture
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