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LANCOM 1722 VoIP – LANCOM 1724 VoIP
Chapter 1: Introduction
1.5
Call switching: Call routing
All calls between internal subscribers and subscribers who can be reached
over external lines are handled as SIP calls by the LANCOM—even if the con-
nection is between two ISDN subscribers.
The call router in the LANCOM VoIP Router switches the call. The switching
relies mainly on the information in two tables:
The bandwidth reservation, QoS settings and firewall settings that are necessary for reliable
transmission of voice data are carried out automatically by the LANCOM.
When establishing a connection, the LANCOM checks (under consideration of the permitted
codecs) which maximum bandwidth will potentially be required.
This bandwidth is then automatically reserved by the QoS module upon initiation of the
connection.
If negotiation shows that the maximum bandwidth is not available, the connection will
not be made.
If negotiations between the terminal devices can agree upon a codec with lower band-
width requirements, then the reserved bandwidth will be lowered accordingly.
All packets from ISDN users are given a DiffServ marking by the LANCOM (with SIP users,
the QoS marking is usually handled by the telephones or softphones).
SIP packets for signaling are marked as CS1.
RTP packets are marked as EF.
The ports required for the transmissions are activated automatically.
LCOS 6.0 does not support QoS tags on Layer 2 (Ethernet)
22
Maximum 4 connections to upstream SIP PBXs. These lines are generally
connections to large PBXs in the network at headquarters which can be
reached via a VPN connection.
The precise number of users and lines available varies between mod-
els and software options.
For telephone numbers arriving at the call router, rules in the call-routing
table are able to alter these numbers if needed and can decide which line
to use for a call.
The table for the locally registered user provides information about which
terminal device is available at which internal telephone number.
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