Clarify network throttling and bandwidth limits in docs

Updated the explanation of network throttling in CloudStack, clarifying how network rate settings are applied and providing details on bandwidth limits for different offerings.

Author: daviftorres

source/adminguide/service_offerings.rst

@@ -674,36 +674,41 @@ You can modify any of the settings as needed before clicking Add to create the n
 Network Throttling
 ------------------
 
-Network throttling is the process of controlling the network bandwidth. CloudStack controls this
-behaviour of the guest networks in the cloud by using the network rate
-parameter. This parameter is defined as the default data transfer rate
-in Mbps (Megabits Per Second) allowed in a guest network. It defines the
-upper limits for network bandwidth.
+In CloudStack, this is done using network rate settings. These settings 
+define the maximum data transfer speed (in Mbps) that guest instance's 
+network interface can use.
 
-You can throttle the network bandwidth either to control the usage above
-a certain limit for some accounts, or to control network congestion in a
-large cloud environment. The network rate for your cloud can be
-configured on the following:
+There are 3 places where network rate (bandwidth limit) can be defined:
+
+-  Global Parameter
 
 -  Network Offering
 
 -  Service Offering
 
--  Global parameter
+If the network rate is **NULL** at:
+
+* The **Compute Offering**, it uses the ``vm.network.throttling.rate`` global setting.
+* The **Network Offering**, it uses the ``network.throttling.rate`` global setting.
+
+For system's networks (Public, Storage, and Management), the rate
+is set to 0. This implies unlimited bandwidth by default.
+
+For guest networks, the default rate is set to ``NULL``. In this case, the rate is
+defaulted to the mentioned global parameter values.
+
+Changing defaults cannot be done via the UI. But you can either create new offerings,
+or directly update existing ones in the database:
 
-If network rate is set to NULL in service offering, the value provided
-in the vm.network.throttling.rate global parameter is applied. If the
-value is set to NULL for network offering, the value provided in the
-network.throttling.rate global parameter is considered.
+* ``cloud.network_offerings`` for Network Offerings.
+* ``cloud.service_offering`` for System VMs.
 
-For the default public, storage, and management networks, network rate
-is set to 0. This implies that the public, storage, and management
-networks will have unlimited bandwidth by default. For default guest
-networks, network rate is set to NULL. In this case, network rate is
-defaulted to the global parameter value.
+.. Note:: ``nw_rate`` stands for Network Rate,
+          ``mc_rate`` stand for Multi Cast Rate,
+          and `0`, mean unlimited bandwidth.
 
-The following table gives you an overview of how network rate is applied
-on different types of networks in CloudStack.
+The following table gives an overview of how network rate is applied on
+different types of networks in CloudStack.
 
 .. cssclass:: table-striped table-bordered table-hover
 
@@ -759,12 +764,12 @@ the instance if any, similar to shared networks.
 
 For example:
 
-Network rate of network offering = 10 Mbps
-Network rate of compute offering = 200 Mbps
+Network rate of network offering = 200 Mbps
+Network rate of compute offering = 1000 Mbps
 
 In shared networks, ingress traffic will not be limited for CloudStack,
-while egress traffic will be limited to 200 Mbps. In an isolated
-network, ingress traffic will be limited to 10 Mbps and egress to 200
+while egress traffic will be limited to 1000 Mbps. In an isolated
+network, ingress traffic will be limited to 200 Mbps and egress to 1000
 Mbps.