Cluster over the WAN and ICCS bandwidth requirements

[darcop]

The Call Manager SRND says the following regarding bandwidth for cluster over the WAN deployments

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Every 10,000 busy hour call attempts (BHCA) in the cluster requires 900 kbps of bandwidth for

Intra-Cluster Communication Signaling (ICCS). This is a minimum bandwidth requirement, and

bandwidth is allocated in multiples of 900 kbps.

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Since ICCS runs between all cluster members and not just Publisher to Subscriber do I need to architect for:

- 900 kbps per circuit in a full mesh between sites with cluster members?

- 900 kbps for each server at a site in a full mesh between sites with cluster members?

- 900 kbps for each remote cluster member that a server at a particular site will need to talk to?

I realize there is additional overhead that needs to be added in but I am not clear on when to multiply for ICCS. I have asked a number of people, including several Cisco SE's, but nobody can find a definitive answer.

Has anyone ever gotten a more complete explanation?

Thanks,

Pete

[mdybka]

The ICCS traffic referred to in the design guide occurs between each pair of devices that run the CCM.exe process in the cluster.

If you do not require a server to process calls/handle phone registrations it is valid to disable the CCM process on that server. This is frequently done on a publisher, or a dedicated tftp, moh, conferencing, etc server. In this case these servers do not need to be included in the calculation of bandwidth.

The bandwidth number of 900Kbps must be accounted once between each pair of sites that have cluster members. For example if three sites exist, each site must have 900Kbps to each other site.

No distinction is made for how calls flow.

BTW, the next revision of the design guide will clarify all this.

[darcop]

cool, thats better than I had been previously told. If I could just pose an example to make sure I've got this straight?

If I had 2 servers at one site and 3 other servers at the other all running CCM.exe would I need the following on the WAN (excluding other overhead)?

2700kbps = (900kbps * 3 remote servers)

x 2 = (servers at this site)

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5400kbps? or just 900kbps between the 2 sites?

[mdybka]

That is correct, 900kbps between the two sites.

Shared lines will cause additional WAN overhead for ICCS traffic between the two Subscribers that control the phones/shared lines.

If you will not share lines over the WAN, then it has no further WAN bandwidth requirements.

With shared lines the requirement for bandwidth is currently modeled by a full mesh between subscribers and require the 5400kbps in your example. The worst case is all lines are shared across the WAN. Hardly anyone gets remotely close to worst case ( although we have seen it).

The next design guide will distinguish a design without shared lines across the WAN from one that has shared lines.

[Wes Sisk]

Pete,

This is 900kbps per instance of CCM.exe. Intracluster communication is full mesh so every server sets up SDL connections to every other server in the cluster.

site1-----site2

site1 has 1 CCM

site2 has 2 CCM

You need 1800 kbps WAN absolute minimum.

Note the 900kbps was measured on CCM 3.2 before many of the new features of 3.3 and 4.0 so consider 900 a bare bones base minimum with NO additional features (extension mobility, IPMA, attendant console.....)

Please also consider that all of CCM change management is TCP based but has no delivery confirmation scheme above the Microsoft Windows TCP stack. This makes it necessitates almost 100% uptime for your WAN. In a CoW environment CallManager servers should be rebooted after any WAN outage.

/Wes