17-07-2013, 01:17 PM
ATM Transport in Mobile Networks with Tellabs 8600 Managed Edge System
ATM Transport in Mobile.pdf (Size: 499.44 KB / Downloads: 26)
Executive Summary
ATM is used as a transport protocol in 3G WCMDA Radio Access
Networks (RAN). ATM transport can be implemented with native
ATM switches or alternatively with MPLS switch/routers. MPLS is
the latest technology for telecommunication networks which
enables the transport of existing Layer 2 protocols like ATM and
Frame Relay as well as new services carried on Ethernet or IP. This
document shows 3G RAN deployment alternatives for MPLS
switches, introduces ATM pseudo wires which carry ATM on MPLS
traffic and shows some delay calculation examples. These examples
demonstrate that MPLS packet switches can be used for carrying
real-time services like voice and video in 3G mobile RAN.
Additionally, the statistical multiplexing feature enables cost-efficient
data services in the same infrastructure.
Introduction
This document illustrates how the Tellabs 8600 managed edge
system can be used for ATM transport. There is an increasing
demand for cost-effective ATM transport solutions in 3G WCDMA
Radio Access Networks, so it is shown as a specific application
example. However, the same principles in terms of queuing delays
and transport effectiveness apply to any ATM transport.
ATM and MPLS in 3G RAN
ATM switching in 3G RAN R99 can be implemented with ATM or
MPLS based equipment. This chapter discusses implementation
alternatives. Figure 2 shows the minimum functionality that has to
be implemented in every network: there has to be an element that
switches ATM cells from E1 to STM-1 ATM interface. This can be
located at the same site with RNC or it can be in a remote location
as illustrated in Figure 5. If ATM switching takes place in a remote
location, VC-4 has to be used between the ATM switch and RNC.
This resembles Case 3 in Figure 3. However, if an ATM switch is
missing from the BSC/RNC site, the network can carry 3G traffic
only and 2G traffic needs a separate VC-12 granularity SDH
network. If the ATM switching takes place at the RNC site, common
VC-12 SDH transport can be used for 2G and 3G. There needs to
be a 4/1 SDH cross connect at the RNC site that separates 2G
traffic from 3G, as illustrated in Case 1 in Figure 3. The most
optimal physical interface between the ATM switch and the SDH
cross connect is in a STM-1/VC-12 because it gives the greatest
2 Mbps (E1) density and lowest cost. The other alternative is to use
physical E1 interfaces in case the ATM switch does not support
STM-1/VC-12 interface.
Conclusions
MPLS switching with ATM pseudowires provides an effective
alternative to native ATM switching. The overhead caused by ATM
pseudowire encapsulation can be compensated with ATM cell
concatenation. The increased serialization delay caused by the
larger packet size can be compensated by bundling links with
ML-PPP or by using higher speed links like STM-1 or Gigabit
Ethernet. The CBR service category carrying real-time traffic always
has minimal delay and the traffic load on UBR service category
does not affect the delay in the CBR service category. Therefore,
the UBR (or VBR) traffic can be overbooked and that enables
savings in the transport costs and network equipment. Overbooking
and statistical multiplexing is essential for data services to ensure
cost-effective networks.