Cisco Cisco Expressway Maintenance Manual
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Off: the Expressway always handles the call signaling.
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On: the Expressway handles the call signaling when the call is one of:
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a traversal call
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an H.323 call that has been modified by Call Policy such that the call resolves to more than one alias
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a SIP call where the incoming transport protocol (UDP, TCP, TLS) is different from the outgoing protocol
In all other cases the Expressway removes itself from the call signaling path after the call has been set up.
The Expressway does not consume a call license for any such calls, and the call signaling path is simplified.
The Expressway does not consume a call license for any such calls, and the call signaling path is simplified.
Call Loop Detection Mode
Your dial plan or that of networks to which you are neighbored may be configured in such a way that there are
potential signaling loops. An example of this is a structured dial plan, where all systems are neighbored together in a
mesh. In such a configuration, if the
potential signaling loops. An example of this is a structured dial plan, where all systems are neighbored together in a
mesh. In such a configuration, if the
are set too high, a single search request may be sent repeatedly
around the network until the hop count reaches 0, consuming resources unnecessarily.
The Expressway can be configured to detect search loops within your network and terminate such searches through
the Call loop detection mode setting, thus saving network resources. The options for this setting are:
the Call loop detection mode setting, thus saving network resources. The options for this setting are:
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On: the Expressway will fail any branch of a search that contains a loop, recording it as a level 2 "loop
detected" event. Two searches are considered to be a loop if they meet all of the following criteria:
detected" event. Two searches are considered to be a loop if they meet all of the following criteria:
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have same call tag
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are for the same destination alias
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use the same protocol
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originate from the same zone
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Off: the Expressway will not detect and fail search loops. You are recommended to use this setting only in
advanced deployments.
advanced deployments.
Identifying Calls
Each call that passes through the Expressway is assigned a Call ID and a Call Serial Number. Calls also have a Call
Tag assigned if one does not already exist.
Tag assigned if one does not already exist.
Call ID
The Expressway assigns each call currently in progress a different Call ID. The Call ID numbers start at 1 and go up to
the maximum number of calls allowed on that system.
the maximum number of calls allowed on that system.
Each time a call is made, the Expressway will assign that call the lowest available Call ID number. For example, if
there is already a call in progress with a Call ID of 1, the next call will be assigned a Call ID of 2. If Call 1 is then
disconnected, the third call to be made will be assigned a Call ID of 1.
there is already a call in progress with a Call ID of 1, the next call will be assigned a Call ID of 2. If Call 1 is then
disconnected, the third call to be made will be assigned a Call ID of 1.
The Call ID is not therefore a unique identifier: while no two calls in progress at the same time will have the same Call
ID, the same Call ID will be assigned to more than one call over time.
ID, the same Call ID will be assigned to more than one call over time.
Note that the Expressway web interface does not show the Call ID.
Call Serial Number
The Expressway assigns a unique Call Serial Number to every call passing through it. No two calls on an Expressway
will ever have the same Call Serial Number. A single call passing between two or more Expressways will be identified
by a different Call Serial Number on each system.
will ever have the same Call Serial Number. A single call passing between two or more Expressways will be identified
by a different Call Serial Number on each system.
Call Tag
Call Tags are used to track calls passing through a number of Expressways. When the Expressway receives a call, it
checks to see if there is a Call Tag already assigned to it. If so, the Expressway will use the existing Call Tag; if not, it
will assign a new Call Tag to the call. This Call Tag is then included in the call’s details when the call is forwarded on.
A single call passing between two or more Expressways will be assigned a different Call Serial Number each time it
arrives at an Expressway (including one it has already passed through) but can be identified as the same call by use of
checks to see if there is a Call Tag already assigned to it. If so, the Expressway will use the existing Call Tag; if not, it
will assign a new Call Tag to the call. This Call Tag is then included in the call’s details when the call is forwarded on.
A single call passing between two or more Expressways will be assigned a different Call Serial Number each time it
arrives at an Expressway (including one it has already passed through) but can be identified as the same call by use of
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Cisco Expressway Administrator Guide