Links and Pipes on Cisco Expressway Demystified


Links on a Cisco Expressway are used to create routing connections between a subzone at one end and another subzone or zone at the other end. Each end of the link is known as a ‘node’. In the link configuration you will find Node 1 and Node 2 to play the role of source and destination call. Pipes are applied to links to limit the bandwidth available between the two nodes.

All links and pipes are two-way. For example, if you have a link that has been configured with Node 1 as HQ-zone and Node 2 as Branch Subzone, this will mean that traffic can flow from the HQ Subzone to the BR-zone as well as from the BRzone to the HQ-zone. Any pipes applied to this link will affect bandwidth in both directions.

To summarize, Subzones on Cisco Expressway are similar to region on Cisco Unified Communication Manager, the links are similar to location and Pipes defines the max bandwitdh for a given links, pipes are similare to the max bandwidth defined between locations.

You can configure the default call bandwitdh for all calls when the initiating endpoint does not specify bandwitdh. You can also set what happens to a call if the bandwitdh restriction on a subzone or pipe lacks the sufficient bandwitdh to place a call at the requested rate.

You can set this bandwitdh restriction in a per-call or total bandwitdh that is based on a subzone. In both options, you can configure to downspeed or to reject the call. The downspeed is a function on Expressway to use he remaining bandwitdh for a call, when the entire configured per-call bandwitdh is not available. If you disable the downspeed mode, then endpoint users will get an “Exceeds Call Capacity” or “Gatekeeper Resources Unavailable” message when initiating a new call.

Example 1

  • An endpoint makes a call request to another subzone with a bandwidth of 2048.
  • The per-call link bandwidth of 512 and the total bandwitdh 2048.
  • The default call bandwitdh set on Expressway is 1024.
  • The downspeed mode is to On for per-call and total bandwidth.
  • There are already active calls using this link, so before the endpoint made the call request, the available total bandwidth was 256.
  1. Endpoint initiates the call request.
  2. Expressway checks if the bandwidth is provided from the endpoint. In this example, the bandwidth 2048 is provided.
  3. Expressway checks for sufficient per-call bandwidth 512.
  4. Because there is insufficient per-call bandwidth.
  5. Expressway checks the downspeed per-call mode settings.
  6. The downspeed per-call mode is enabled.
  7. The bandwidth for the call is reduced to 512.
  8. Now Expressway checks if there is sufficient total available bandwidth 256.
  9. Because there is insufficient total available bandwidth.
  10. Expressway checks the downspeed total mode settings.
  11. The downspeed total mode is enabled.
  12. The bandwidth for the call is reduced to 256.
  13. The call is then admitted and the available total bandwidth is reduced to 0.

Example 2

  • An endpoint makes a call request to another subzone without bandwidth information.
  • The bandwidth limitation per-call is 1024 and the total bandwidth is 8192.
  • The default call bandwitdh set on Expressway is 1024.
  • The downspeed mode is set to OFF for per-call and total bandwidth.
  • There are already active calls using this link, so therefore the endpoint made the call request, the available total bandwidth was 768.
  1. The endpoint initiates the call request.
  2. Expressway checks if the bandwidth is provided from the endpoint.
  3. The bandwidth is not provided.
  4. Therefore, Expressway uses the default call bandwidth 1024.
  5. Expressway checks for sufficient per-call bandwidth 1024.
  6. There is sufficient per-call bandwidth.
  7. Expressway checks if there is sufficient total available bandwidth 768.
  8. There is insufficient total available bandwidth.
  9. Expressway checks the downspeed total mode settings.
  10. The downspeed total mode is disabled.
  11. The call is rejected.
  12. The total available bandwidth remains the same.
Categories: Collaboration

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