The likely cause of slow network

Bandwidth throttling is the intentional slowing
of Internet service by an Internet service
provider . It is a reactive measure employed in
communication networks in an apparent
attempt to regulate network traffic and
minimize bandwidth congestion. Bandwidth
throttling can occur at different locations on
the network. On a local area network ( LAN), a
sysadmin may employ bandwidth throttling to
help limit network congestion and server
crashes. On a broader level, the Internet
service provider may use bandwidth throttling
to help reduce a user's usage of bandwidth
that is supplied to the local network.
Throttling can be used to actively limit a
user's upload and download rates on
programs such as video streaming, BitTorrent
protocols and other file sharing applications,
as well as even out the usage of the total
bandwidth supplied across all users on the
network. Bandwidth throttling is also often
used in Internet applications, in order to
spread a load over a wider network to reduce
local network congestion, or over a number of
servers to avoid overloading individual ones,
and so reduce their risk of crashing, and gain
additional revenue by compelling users to use
more expensive pricing schemes where
bandwidth is not throttled.
Operation
A computer network typically consists of a
number of servers, which host data and
provide services to clients . The Internet is a
good example, in which web servers are used
to host websites, providing information to a
potentially very large number of client
computers.
Clients will make requests to servers, which
will respond by sending the required data. As
there will typically be many clients per server,
the data processing demand on a server will
generally be considerably greater than on any
individual client. And so servers are typically
implemented using computers with high data
capacity and processing power.
The traffic on such a network will vary over
time, and there will be periods when client
requests will peak, sometimes exceeding the
capacity of parts of network and causing
congestion, especially in parts of the network
that form bottlenecks . This can cause data
request failures, or in worst cases, server
crashes.
In order to prevent such occurrences, a server
administrator may implement bandwidth
throttling to control the number of requests a
server responds to within a specified period of
time.
Source: Wikipedia