Aug 092012
 

Zone Bandwidth Strategy

One of the things I run into regularly with deployments is an issue where the installer improperly configures the Zone Bandwidth Strategy. This information can be checked by printing the interzone and intrazone configurations in LD 117.

=> prt zone
Use the PRT INTERZONE or PRT INTRAZONE

=> prt interzone
 ______________________________________________________________________________________________________________________
 |Near end  |Far end   |State| Type  |Stra|MO/ |QoS| Bandwidth | Sliding |  Usage  |  Quota  |Peak|  Calls  |  Alarm  |
 |          |          |     |       |tegy|BMG/|Fac|Configured |   max   |         |         |    |         |         |
 |          |          |     |       |    |VTRK|tor|           |         |         |         |    |         |         |
 |----------|----------|-----|-------|----|----|---|-----------|---------|---------|---------|----|---------|---------|
 |Zone|VPNI |Zone|VPNI |     |       |    |    | % |    kbps   |   kbps  |   kbps  |   kbps  | %  |   Cph   |   Aph   |
 |----|-----|----|-----|-----|-------|----|----|---|-----------|---------|---------|---------|----|---------|---------|
 |   1|     |    |     | ENL |SHARED |  BB|  MO|   |    1000000|         |      380|        0|   0|         |         |
 |--------------------------------------------------------------------------------------------------------------------|
 |   5|     |    |     | ENL |SHARED |  BB|VTRK|   |    1000000|         |      380|        0|   0|         |         |
 |--------------------------------------------------------------------------------------------------------------------|
 |  42|     |    |     | ENL |SHARED |  BB|  MO|   |    1000000|         |        0|        0|   0|         |         |
 |--------------------------------------------------------------------------------------------------------------------|

=> prt intrazone
 _________________________________________________________________________
 |Zone|State| Type  |Strategy|MO/ | Bandwidth |  Usage  |  Quota  | Peak |
 |    |     |       |        |BMG/|    kbps   |   kbps  |   kbps  |   %  |
 |    |     |       |        |VTRK|           |         |         |      |
 |----|-----|-------|--------|----|-----------|---------|---------|------|
 |   1| ENL |SHARED |   BQ   |  MO|    1000000|      380|        0|    0 |
 |-----------------------------------------------------------------------|
 |   5| ENL |SHARED |   BQ   |VTRK|    1000000|      380|        0|    0 |
 |-----------------------------------------------------------------------|
 |  42| ENL |SHARED |   BQ   |  MO|    1000000|        0|        0|    0 |
 |-----------------------------------------------------------------------|
  Number of Zones configured = 3

=>

The Strategy column for intrazone and interzone can be configured as either:

  • BQ aka Best Quality aka G.711 codec selection
  • BB aka Best Bandwidth aka G.729 codec selection

BB should be used when a WAN interface is handling VoIP with the following limitations/restrictions:

  • Bandwidth shaping or rate limiting restrictions
  • Bandwidth availability limitations (either the pipe is too small, or other usage + VoIP traffic exceeds available bandwidth)
  • No QoS policies configured

Even if you believe your WAN can support the bandwidth demands of VoIP + other usage, if you are experiencing any quality issues with VoIP, it’s worth changing your bandwidth strategy to BB (i.e., Best Bandwidth, G.729) as part of your troubleshooting efforts. I also recommend that you configure the available bandwidth to match the actual available bandwidth.

Interzone

As the word root suggests, the Interzone Strategy is used for all VoIP calls that leave the zone wherein the caller is configured. This strategy is also used for calls that are inter-site.

Intrazone

As the word root suggests, the Intrazone Strategy is used for all VoIP calls within the zone.

Purpose of Zones

Zones provide a way of controlling the behavior of VoIP and QoS within a site (and between sites). Zones work best when used to represent physical locations.

Example

Zone 1 is set up for all phones within a site (on the LAN). BQ strategy is used for intrazone and BB is used for interzone.

Zone 2 is set up for all phones at a branch office. BQ strategy is used for intrazone and BB is used for interzone.

Zone 3 is set up for all softphones connected via VPN (remote employees). BB strategy is used for both intrazone and interzone.

If a caller in Zone 1 calls anyone in Zone 1, they use G.711 (BQ). If they call anyone outside of Zone 1 (a VPN user softphone, or the branch office) they use the G.729 (BB strategy) codec.

If a caller in Zone 2 calls anyone in Zone 2, they use G.711 (BQ), but calls out of Zone 2 use G.729 (BB). Just like Zone 1.

If a caller in Zone 3 calls anyone they use G.729 (BB).

Mixed VoIP/TDM environments

TDM resources are sometimes configured to be in a separate zone by installers. I’ve never understood this, because following the logic above, if all the TDM equipment (Media Gateways, MGCs, MC32s, IP Trunks, etc.) are put in Zone 4 and everyone uses BB for interzone, then all calls between Zone 1 and TDM resources in Zone 4 will use the G.729 codec (BB) (even if those Zone 4 resources are physically located in the same site as Zone 1).

From my way of thinking, all physical TDM equipment should be configured in the zone appropriate to its physical location in the network. Zone 1 VoIP users should share the zone with Zone 1 TDM equipment/users. But, if there is TDM resources at the branch office, they would go into Zone 2 (using the above example).

Virtual Trunking would be a special case, in that Virtual Trunks are not used by IP Phones, so putting them in a separate zone has no negative impact (and the fact that they show up as a zone type in the Intrazone/Interzone print out tells us it was Nortel’s Design Intent that they be put in their own zone.)