Cisco Cisco Expressway Maintenance Manual
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its publicly-accessible address on the NAT device
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a relay address on the TURN server
The endpoints then decide, by performing connectivity checks through ICE, how they are going to communicate.
Depending upon how the NAT devices are configured, the endpoints may be able to communicate between their
public-facing addresses on the NAT devices or they may have to relay the media via the TURN server. If both
endpoints are behind the same NAT device they can send media directly between themselves using their internal host
addresses.
Depending upon how the NAT devices are configured, the endpoints may be able to communicate between their
public-facing addresses on the NAT devices or they may have to relay the media via the TURN server. If both
endpoints are behind the same NAT device they can send media directly between themselves using their internal host
addresses.
After the media route has been selected, the TURN relay allocations are released if the chosen connection paths do
not involve routing via the TURN server. Note that the signaling always goes via the Expressway, regardless of the
final media communication path chosen by the endpoints.
not involve routing via the TURN server. Note that the signaling always goes via the Expressway, regardless of the
final media communication path chosen by the endpoints.
Capabilities and limitations
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systems support up to 1800 relay allocations. This is typically enough to support 100 calls but
does depend on the network topology and the number of media stream components used for the call (for
example, some calls may use Duo Video, or other calls might be audio only).
example, some calls may use Duo Video, or other calls might be audio only).
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system supports up to 6000 relays, spread evenly across 6 ports where each port is limited to handling
1000 relays. This limit is not strictly enforced, so we recommend adding an SRV record for each port to enable
round robin.
round robin.
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Clustered Expressways: if the requested TURN server's relays are fully allocated the server will respond to the
requesting client with the details of an alternative server in the cluster (the TURN server currently with the
most available resources).
requesting client with the details of an alternative server in the cluster (the TURN server currently with the
most available resources).
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The Expressway's TURN services are supported over single and dual network interfaces (via the Advanced
Networking option). For dual network interfaces, the TURN server listens on both interfaces but relays are
allocated only on the Expressway's externally facing LAN interface.
Networking option). For dual network interfaces, the TURN server listens on both interfaces but relays are
allocated only on the Expressway's externally facing LAN interface.
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Microsoft ICE (which is not standards-based) is not supported by the Expressway-E's TURN server; to enable
communications between the Expressway and Microsoft Lync clients that are registered through a Microsoft
Edge Server you need to use the
communications between the Expressway and Microsoft Lync clients that are registered through a Microsoft
Edge Server you need to use the
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The TURN server does not support bandwidth requests. Traversal zone bandwidth limits do not apply.
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The Expressway-E TURN server supports TURN media over TCP and UDP. Configuration of the supported
protocols is available only through the CLI command
protocols is available only through the CLI command
xConfiguration Traversal Server TURN ProtocolMode
.
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The Expressway-E TURN server supports UDP relays over TCP; it does not currently support TCP relays.
Configuring TURN Services
you need the TURN Relay option
key (this controls the number of TURN relays that can be simultaneously allocated by the TURN server).
The TURN page (Configuration > Traversal > TURN) is used to configure the Expressway-E's TURN settings.
The configurable options are:
Field
Description
Usage tips
TURN
services
services
Determines whether the Expressway offers TURN
services to traversal clients.
services to traversal clients.
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Cisco Expressway Administrator Guide