Filter
Top Products
25-49
Cisco Prime Network 4.0 User Guide
OL-29343-01
Chapter 25 Monitoring Mobile Technologies
LTE Networks
Viewing Layer 2 Tunnel Access Concentrator Configurations (LAC)
In computer networking, Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to support
virtual private networks (VPNs) or as part of the delivery of services by ISPs. It does not provide any
encryption or confidentiality by itself; it relies on an encryption protocol that it passes within the tunnel
to provide privacy. The entire L2TP packet, including payload and L2TP header, is sent within a User
Datagram Protocol (UDP) datagram. It is common to carry Point-to-Point Protocol (PPP) sessions within
an L2TP tunnel.
The two endpoints of an L2TP tunnel are called the LAC (L2TP Access Concentrator) and the LNS
(L2TP Network Server). The LAC is the initiator of the tunnel while the LNS is the server, which waits
for new tunnels. Once a tunnel is established, the network traffic between the peers is bidirectional.
LAC allows users and telecommuters to connect to their corporate intranets or extranets using L2TP. In
other words, it forwards packets to and from the LNS and a remote system. It connects to the LNS using
a local area network or wide area network and directs subscriber sessions into L2TP tunnels based on
the domain of each session. Figure 25-4 denotes the LAC architecture.
Figure 25-4 LAC Architecture
Uplink DSCP marking to be used for encapsulation and UDP for uplink traffic
Downlink DSCP marking to be used for encapsulation and UDP for downlink traffic
Max Packet Delay Maximum packet delay, in milliseconds, that can be applied to the data.
Max Error Rate Maximum error loss rate of non congestion related packet loss.
Delay Class Packet delay.
Precedence Class Indicates packet precedence.
Reliability Class Indicates packet reliability.
Traffic Policing Interval Traffic policing interval.
Table 25-29 QCI-QoS Mapping (continued)
Field Description
CPE
PPP in L2TP
sessions
Retail LNS
provider
Provider 1
Provider 2
Provider n
320487
L2TP sessions
are terminated
and placed in a VRF
Wholesale LNS
provider
Cisco 10000 ESR
VRF 1
VRF n
VRF 2
LAC
IP
transport
network
Access network
(ATM or Ethernet)