Bandwidth areas

This is where you create the bandwidth model. Bandwidth control determines, with the help of the bandwidth model, the optimum transmission parameters for call connection on the IP network and prevents connections from being set up if too little bandwidth is available

The available bandwidth on the IP network for a call connection can be very different as the connection may pass through different LAN areas and WAN links. Bandwidth control determines for each connection the optimum transmission parameters and monitors the number of simultaneous connections and their bandwidth requirement. If there is not enough bandwidth for another connection, said connection is not set up.

Bandwidth control depends on bandwidth model. This should actually reflect the bandwidth situation as much as possible.

Bandwidth  model

In each case it calculates before a connection is set up whether or not the bandwidth available is sufficient. If not, the connection is not set up and the user obtains the congestion tone. The better the model simulates reality, the more reliably the bandwidth resources can be managed.

The model consists of bandwidth areas and WAN links. A bandwidth area is a network section with the same bandwidth properties. In most cases it is a LAN but the internet as a whole is also mapped as a bandwidth area.

A WAN link connects two bandwidth areas. Usually they consist of connections to an internet provider or leased lines. Frequently they have a limited bandwidth.

The WAN links are assigned to the bandwidth areas on the VoIP routing table. In the process the necessary WAN links are selected from a bandwidth area in order to set up a connection to each desired destination.

Available codecs

On a WAN link with limited bandwidth it is advisable to use a compressing codec such as G.729. It considerably reduces the bandwidth requirement and the loss of voice quality remains tolerable. In the LAN area there is usually sufficient bandwidth available and better results are achieved with the uncompressed codec. Available codecs:

  • G.711a: Uncompressed codec with high audio quality.  Suitable for LAN and WAN links with large bandwidths. The bit rate is 64 kbit/s. Uses the German tone signalling process.

  • G.711u: Uncompressed codec with higher audio quality. Suitable for LAN and WAN links with large bandwidths. The bit rate is 64 kbit/s. Uses the American tone signalling process.

  • G.729: Compressed codec with medium audio quality. Suitable for WAN links with limited bandwidth. The bit rate is 8 kbit/s.

  • G.722: Uncompressed codec with very high audio quality. Condition for Hi-Q deployment of Mitel SIP phones. The bit rate is 48, 56 or 64 kbit/s.

The bandwidth control checks, before connection set up and for all partial areas of a connection (bandwidth areas and WAN links), the set codec (Preferred codec setting) and chooses the smallest of them.

DSP resources are required for real-time encoding and decoding processes in the communication server and IP terminals. G.711  required to process less DSP resources than G.729. DSP resources are provided in the form of VoIP channels.

Available frame lengths

The smaller the frame length of voice packets, the smaller the delay values generated but the greater the bandwidth requirement. For this reason we recommend that the frame length of voice packets be kept relatively small within the LAN area and relatively large for WAN connections with limited bandwidth.

The bandwidth control checks, before connection set up and for all partial areas of a connection (bandwidth areas and WAN links), the set frame length (Preferred frame length setting) and chooses the smallest of them.

Note:

You wish to keep the delay values low in case of very low bandwidth resources and, thus, choose the shortest frame length. This may prove counter-productive as the amount of frame packet is then increased, which may lead to data congestion.

Configuration

Table 1. Bandwidth areas

Parameter

Explanation

Area name

Bandwidth area name (max. 20 characters)

Preferred codec

The ideal codec for this area.

Preferred frame length

The ideal frame length for this area.
Table 2. WAN links

Parameter

Explanation

Name

WAN link name (max. 20 characters)

Bandwidth area A

The first WAN link endpoint

Bandwidth area B

The second WAN link endpoint

Bandwidth (kbit/s)

Enter here the bandwidth available for VoIP on this WAN link.

Bandwidth reserved for audio (kbit/s)

Enter here the lowest bandwidth which in case of video connections must be made available for voice transmission.

VoIP channels

Displays the maximum possible number of VoIP channels that can be set up simultaneously over this WAN link

RTP compression

Compresses the IP header on this link.

L2 overhead

Enter the IP header size here. The numerical value corresponds to the header size in bytes. You can use the value based on the value table below.

Preferred codec

The ideal codec for this area.

Preferred frame length

The ideal frame length for this area.

VoIP channels

Displays the maximum possible number of VoIP channels that can be set up simultaneously over this WAN link.
Table 3. Table of values for L2 overheads

Protocol

VPN (IPsec Header = 56 Byte)

Resultant L2 overhead

Ethernet (ETH)

no

18

yes

74

PPP / PPPoA / FrameRelay

no

6

yes

62

PPPoE

no

26

yes

82
Table 4. VoIP routing

Parameter

Explanation

Own bandwidth area

Bandwidth area from which the connections are set up.

Destination bandwidth area

Nearest bandwidth area on the control path to the connection destination.

WAN link

VPN peer bandwidth area

You need to identify links with VPN by entering the VPN end (VPN peer). The bandwidth model then automatically takes the 56 byte larger L2 overhead into account when calculating the bandwidth requirements.
Table 5. Standard media switch / EIP modules

Parameter

Explanation

Node

Node number in an AIN. The master has number 0.

Card/module

Card slot on which the module is fitted (no entry for the standard media switch).

Slot on card

Module slot on the card (no entry for the standard media switch).

Module

Short description of the module (no entry for the standard media switch).

State

When the card is in operation, In service is displayed here.

IP address

Module IP address (the standard switch has the same IP address as the nodes)

Bandwidth area

Bandwidth area in which the node is located.
Figure 1. Example of a bandwidth topology. Bandwidth area 4 represents the internet.


First steps.: Determining the bandwidth topology

In the following you map out the bandwidth areas and the WAN links.

  1. Draw up a diagram of the bandwidth topology. To do so map out one bandwidth area for each IP section with its own LAN.

  2. Map out another bandwidth area to represent the internet.

  3. Map out the WAN links that connect the individual bandwidth areas.

  4. For all the WAN links determine the bandwidth available for voice traffic. To do so measure the level of data traffic on the WAN link and subtract that value from the available bandwidth.

Note:

The model’s accuracy depends on this calculation.

Second step: Set up bandwidth areas

The instructions below explain the procedure for configuring the bandwidth areas:

  1. First create the bandwidth area in which the communication server or Master is located. The easiest way to do this is to use the standard bandwidth area. Besides the name enter the values for the preferred frame length and codec. The bandwidth control uses these values to find the optimum setting for a call connection. As we are dealing with a LAN, a good choice is G.711 and a frame length of 20 ms.

  2. Open the remaining bandwidth areas.

Third step: Set up WAN links

The instructions below explain the procedure for configuring the WAN links:

  1. First open one or more WAN links to the bandwidth area of the communication server/Master. Enter as available bandwidth the values fixed in the bandwidth topology.

  2. Define the WAN link parameters. Fix the codec and frame length based on the available bandwidth.

  3. Open and configure the remaining WAN links.

Fourth step: Configure VoIP table

When the WAN links are created, the VoIP routing table is filled out automatically as much as possible. Configure the entries in accordance with the information given in AIN.

  1. Define all the routing paths starting from the first bandwidth area and enter them. If routing paths pass through the same WAN links to destinations in various bandwidth areas, select for the destination bandwidth area the option Undetermined.

  2. Repeat this procedure for each bandwidth area.

Table 6. Automatically configured VoIP routing table for the example on the figure

Own bandwidth area

Destination bandwidth area

WAN link

B1

Undetermined

L12

B2

Undetermined

L12

B4

Undetermined

L14

B3

Undetermined

L34

B5

Undetermined

L45
Table 7. Fully configured VoIP routing table for the example on the figure

Own bandwidth area

Destination bandwidth area

WAN link

B1

Undetermined

L14

B2

Undetermined

L12

B4

Undetermined

L14

B3

Undetermined

L34

B5

Undetermined

L45

B1

B2

L12

B4

B3

L34

B4

B5

L45

See also...

"Using VPN in AIN"

"Bandwidth control of video links"

Parent topic: Multi site
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