Integrating SDH and ATM in UMTS (3G) Access Networks

Integrating SDH and ATM in UMTS (3G)
Access Networks
Horsebridge Network Systems Ltd, 1 Pate Court, North Place, Cheltenham, GL50 4DY England.
Tel:+44 (0)1242 530630 Fax: +44 (0) 1242 530660 E-Mail www.horsebridge.net


Integrating SDH and ATM in UMTS (3G) Access Networks
White Paper
December, 2008

© Copyright by ECI Telecom, 2008. All rights reserved worldwide.
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CONTENTS
ECI Telecom Ltd. Proprietary iii
Contents
Introduction 7

Role of ATM in 3G Access Networks 8
Introduction of ATM Switching into the Access Network 8
STM-1 Interfaces in the RNC 8
Savings in Bandwidth 8
Lower Bandwidth Consumption 8
Granularity of Bandwidth Allocation 9
Statistical Multiplexing Based on Peak vs. Sustained Rate 9
Multiplexing Based on Usage Statistics 10
Higher Savings 10
Deploying a 3G Access Network 11
Deployment over Pure TDM Transmission 11
Co-location of ATM Switches and RNCs 12
ATM Concentration Devices in the Access Network 12
The Cost of Using ATM Switches in the Access 13
The Extra Costs of Maintaining IMA Groups 14
The Dilemma 14
ECI Telecom’s Solution for 3G Access Networks 15
The XDM Architecture 15
The ATS (ATM Traffic Switch) Concept 16
Traffic Concentration from Several Node Bs into One
Unchannelized VC-4
17
Advantages of the ATS vs. a Standalone ATM Switch 18
Savings in Equipment 18
Operational Savings 19
IMA Flexibility 19
Cost Flexibility 20
The XDM ATS Card as a Node B Concentrator 22
Canonical Concentration of Node B Traffic into VC-4s 22
Application Scalability 23

Sparse Deployment of Node Bs 23
Increased Bandwidth Demand 24
Savings on Intermediate Bandwidth 24
Combined VC-4 and IMA Aggregation 25
CONTENTS
iv ECI Telecom Ltd. Proprietary
Integration of 2G and 3G Traffic 26
TDM Multiplexing of 2G and 3G Traffic 26
Conclusion 27
About ECI Telecom 28


CONTENTS
ECI Telecom Ltd. Proprietary v
List of Figures
Figure 1: TDM-based access network 11
Figure 2: ATM switch co-located with the RNCs 12
Figure 3: ATM switches in the access network 12
Figure 4: ATM concentration with an external ATM switch 13
Figure 5: Schematic view of the XDM architecture 15
Figure 6: ATS card architecture 16
Figure 7: Concentration of 72 E1s into a single VC-4 17
Figure 8: Concentration of E1s into VC-4s 22
Figure 9: Configuration for a low number of Node Bs 23
Figure 10: Configuration for increased bandwidth demand 24
Figure 11: Concentration of Node B traffic into IMA groups 24
Figure 12: Combination of VC-4 and IMA concentration 25
Figure 13: TDM multiplexing of 2G and 3G data 26

List of Tables

Table 1: Two-layer implementation versus integrated implementation 18


CONTENTS
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INTRODUCTION
ECI Telecom Ltd. Proprietary 7
Introduction
The deployment of cellular UMTS (Universal Mobile Telecommunications
Systems, better known as 3G) is one of the most difficult challenges facing service
providers’ network planning experts today. They must juggle immature
technologies, limited financial resources and uncertain future market demand.
Furthermore, they must reduce capital and operational expenses and keep network
costs to a minimum in order to make 3G services economical while still providing
for network upgrades on demand. Since the actual demand for 3G services is still
unknown and network design must provide a cost-effective solution for both
optimistic and pessimistic scenarios, cost structures must be flexible.
Given the uncertainties of the services to be offered, bandwidth demand,
applications, and so on, networks must be as cost-effective as possible in their
initial, low-level usage phase. Equipment costs, as well as expenditure on leased
bandwidth and radio frequencies, must be kept to a minimum, yet allowing these
networks to provide for fast growth and cost-effective bandwidth increase.
3G access networks are based on two distinct technologies: transmission and ATM.
Conventional 3G access infrastructures implement these technologies over two
separate network layers. Although network design is simple, it is expensive and
inflexible.
In line with its tradition of responding to customer needs, ECI Telecom’s Optical

Networks Division offers an innovative concept: integration of SDH and ATM in
the same hardware fully optimized for 3G access networks. ECI Telecom’s
solution is not only far more economical than any other solution on the market
today; it is also flexible and scalable, providing for future expansions in network
coverage and capacity.
ROLE OF ATM IN 3G ACCESS NETWORKS
8 ECI Telecom Ltd. Proprietary
Role of ATM in 3G Access Networks
A cellular access network connects Node Bs to RNCs (Radio Network Controllers)
via the I
ub
interface. The I
ub
interface is a complex set of protocols handling all
aspects of Node B-to-RNC communications, including media, signaling, and OAM
(Operation, Administration, and Maintenance) over ATM. ATM in turn can be
transported over various TDM links.
In practice, most Node B connections range from a fractional E1 to several E1s
bundled as an ATM IMA (Inverse Multiplexing over ATM) group. RNC
connections are usually either E1s or STM-1s.
Early releases of the 3G standard defined the Node B-to-RNC connection as purely
a TDM connection. In the ATM layer, Node Bs and RNCs were connected via a
direct ATM link, without intermediate ATM switching. The definition provides the
following functions:
 Independence of the underlying transmission layer
 Definition of groups of several TDM links as one logical link using the ATM
IMA mechanism
 Ability to carry voice and data over the same link
 Implementation of statistical multiplexing between different applications on
the same Node B while maintaining QoS (Quality of Service)

Introduction of ATM Switching into the Access Network
Release 4 of the 3G standards formally stipulated how to perform ATM switching
in the access network, and how to provide the QoS guarantees required for the
successful operation of 3G applications.
ATM switching in the access network provides two major advantages:
 The ability to configure RNCs with STM-1 interfaces instead of E1s, thus
drastically reducing the cost of the RNC
 Savings in bandwidth consumption
STM-1 Interfaces in the RNC
Current deployments demonstrate that it is not economical to deploy E1 links in the
RNC. STM-1, on the other hand, has proved to be a far less expensive solution,
even with the cost of intermediate ATM switching.
Savings in Bandwidth
ATM switching in the access supports ATM concentration, providing finer
granularity and statistical multiplexing benefits. This results in savings in the
network bandwidth requirements.
Lower Bandwidth Consumption
ATM switching reduces bandwidth consumption, thus saving operating costs. The
following sections describe how to attain these savings.
ROLE OF ATM IN 3G ACCESS NETWORKS
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Granularity of Bandwidth Allocation
In a TDM-based network, the link between the Node B and the RNC has a
granularity of E1. Although fractional E1 connections are feasible, these are
usually reserved for sub-E1 rates.
This bandwidth allocation is part of the basic design of the Node B. However,
ATM concentration in the access network can improve bandwidth utilization. For
example, if the peak traffic to/from a Node B is estimated to be 3 Mbps, then two
E1 interfaces (4 Mbps) must be allocated to the Node B at the TDM level. On the
other hand, an ATM switch concentrating traffic from 10 such Node Bs can

concentrate from 40 Mbps (10 x 2 x E1) to 30 Mbps (10 x 3 Mbps, or only 15 E1s)
without violating the basic bandwidth allocation rule of 3 Mbps per Node B.
Statistical Multiplexing Based on Peak vs. Sustained Rate
An ATM link can contain many ATM virtual circuits, each with its own
parameters. The main parameters are peak cell rate and sustained cell rate.
The peak rate controls the maximum permissible cell rate, whereas the sustained
rate is the average connection rate. A Node B may transmit at the peak rate for a
short period of time only (controlled by the maximum burst size), which is
typically lower than 50 milliseconds. Over longer intervals, traffic must be
controlled by the sustained cell rate, typically much lower. In the real world, only a
few Node Bs transmit at the peak rate, whereas the majority transmits at the
sustained rate.
ATM concentration in the access layer enables maintaining the peak rate of the
connection at a high level, thus ensuring short delays. As the number of Node Bs
transmitting concurrently at the peak rate can be statistically bounded, bandwidth
must be allocated for the sustained rate for all Node Bs, with the peak rate allocated
to only some. As a result, bandwidth consumption is significantly lower.
Obviously, the possibility exists (though chances are extremely low) that all Node
Bs send a burst of traffic simultaneously with the resulting loss of ATM cells. This
can easily be computed based on the ATM policing and shaping mechanisms, thus
guaranteeing cell rate in compliance with 3G standards.
ROLE OF ATM IN 3G ACCESS NETWORKS
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Multiplexing Based on Usage Statistics
Bandwidth allocation per Node B is based on the maximum concurrent bandwidth
demanded by users served by the specific Node B. While it is desirable to provide
full service to all users in any scenario, this is economically impossible.
As with any mass service, statistical assumptions about overall usage can safely be
made. For example, in GSM (Global System for Mobile Communication, also
known as 2G) voice-based deployments, network design assumes that not all

subscribers will make a call at the same time. If they do, some will be rejected, as
network capacity planning takes into consideration the distribution of user
demands.
3G services are subject to the same design considerations. In effect, due to the
bursty nature of data, network planning must rely on the statistical nature of usage
patterns. Unlike ATM statistical multiplexing (which allows users to send high rate
traffic over short periods of time and then forces them to reduce the rate), usage
statistical multiplexing is based on the assumption that not all subscribers use the
network concurrently. Consequently, this multiplexing method may vary with
changes in usage patterns. As it is the nature of data to adapt the application to the
available bandwidth, usage-based multiplexing can be implemented even if the
service level is sometimes degraded.
Higher Savings
Reducing bandwidth consumption is always a recommended approach. However,
depending on network structure and design, the rationale behind this reduction
varies from service provider to service provider.
When using leased-lines or licensing radio frequencies to build a network, lower
bandwidth consumption obviously translates into direct savings in operational
expenses. This reduction involves more than only the monthly costs of leasing the
lines and radio frequencies. When bandwidth consumption is reduced, the entire
access network becomes smaller. Service providers can then manage a smaller
transmission network with less expensive interfaces, less equipment cards, and less
manpower.
DEPLOYING A 3G ACCESS NETWORK
ECI Telecom Ltd. Proprietary 11
Deploying a 3G Access Network
A 3G cellular access network can be deployed in one of the following
configurations:
 RNCs with E1 ports connected to the Node Bs via a pure-TDM transmission
network.

 RNCs with STM-1 ports and Node Bs with E1 ports. In this configuration,
ATM switches deployed along the connection convert E1s originating in the
Node Bs to STM-1s, by:
 Co-locating ATM concentration devices with the RNC
 Placing ATM concentration devices inside the access network
The following sections describe the advantages and disadvantages of each
approach.
Deployment over Pure TDM Transmission
ATM switching in the access network is recommended, but it is not technically
mandatory. It is possible to build a network connecting an E1 port from a Node B
directly to an E1 port from the RNC. This approach, however, lacks the advantage
of using STM-1 ports in the RNC and ATM concentration in the network that
results in savings in bandwidth and network costs.

Figure 1: TDM-based access network
DEPLOYING A 3G ACCESS NETWORK
12 ECI Telecom Ltd. Proprietary
Co-location of ATM Switches and RNCs
A second alternative is to deploy an ATM switch co-located with the RNC. In this
scenario, the access network carries TDM connections from the Node Bs to the
ATM switch; the switch concentrates E1s into a single STM-1, which in turn is
connected to the RNC.
RNCs can thus be configured with STM-1 ports, resulting in a more economical
network structure. However, bandwidth consumption in the access network is still
based on the peak demand of every Node B, without ATM concentration.

Figure 2: ATM switch co-located with the RNCs
ATM Concentration Devices in the Access Network
The deployment of ATM switches in the access network is therefore the most
efficient and cost-effective implementation of 3G in these networks. The switches

concentrate traffic from Node Bs into VC-4 containers, enabling an economical
RNC configuration.

Figure 3: ATM switches in the access network
DEPLOYING A 3G ACCESS NETWORK
ECI Telecom Ltd. Proprietary 13
The Cost of Using ATM Switches in the Access
ATM access networks are necessary, but expensive, as ATM is an expensive
technology. Moreover, the installation of a simple ATM switch for traffic
concentration includes the addition of ATM hardware, as well as support of a
significant number of PDH and SDH interfaces.
Figure 4 depicts a typical scenario in which STM-1 links concentrate traffic from
Node Bs. In this example, the site concentrates traffic from a channelized STM-1
with 52 active channels, with 20 E1s from local Node Bs.

Figure 4: ATM concentration with an external ATM switch
The total number of E1s is 72 and therefore a channelized STM-1 is no longer
sufficient. Concentration must be performed at the ATM level, as TDM
concentration results in the need for additional STM-1s – clearly a waste of
bandwidth for only the 9 E1s in the second STM-1.
As already described, an ATM switch can easily compress traffic originally carried
on 72 E1s into one VC-4. However, as shown in
Figure 4, the ATM switch must
connect to 72 E1 ports and one STM-1 port. Therefore, to enable ATM
concentration, the following components must also be added:
 An ATM switch with 72 E1 interfaces and one STM-1 interface
 An additional STM-1 interface in the transmission network
 Additional 72 E1 interfaces in the transmission network

NOTE: In theory it is possible to add only 52 new
E1 interfaces and connect the 20 local interfaces
directly to the ATM switch. From the management
viewpoint, however, this is not recommended, as
these 20 links cannot be controlled by the
transmission network’s management system.

The above configuration is extremely expensive and casts a shadow on the cost-
effectiveness of ATM concentration in the access network. Clearly, a far more
economical solution is required.
DEPLOYING A 3G ACCESS NETWORK
14 ECI Telecom Ltd. Proprietary
The Extra Costs of Maintaining IMA Groups
IMA is a low level protocol transporting ATM over multiple E1 links. It configures
multiple physical links as a single ATM link, and adds and drops physical links
without affecting traffic.
The capability to add and drop TDM capacity from the IMA link without affecting
ATM traffic is extremely powerful but costly. IMA is implemented at the hardware
level, and therefore all links in the same IMA group must reside on the same
interface card. In many cases, the assignment of IMA groups to a single interface
card is restricted, as all E1s belonging to the same IMA group must be processed
by the same ASIC.
These limitations make the network-planning scenario virtually impossible.
Continuing with the example in
Figure 4, let us assume that the 72 E1 ports
originate in 36 Node Bs, where each Node B is connected via an IMA group of two
E1s. Let us also assume there are plans to upgrade the Node B links to an IMA
group of four E1s. In this case, the operator has two choices:
 Deploy an ATM switch with 72 E1 interfaces and upgrade them when traffic
volume increases, or

 Deploy an ATM switch with 144 interfaces, leaving room for future IMA
expansion
The first option is extremely complicated. When upgrading the network connection
of the Node Bs from two to four E1 links, the new links must all be allocated to the
same interface card. At some point in time, a new ATM interface card will be
needed, requiring a rewiring of the physical cables. The resulting upgrade is a
complicated traffic-affecting cable management procedure.
The second option of reserving ports for future use is simpler, but requires
investing in equipment that will not be used until needed, if at all. The deployment
of ATM interfaces based on future upgrade plans is not economically justifiable
due to uncertain changes in the traffic volume.
In conclusion, assigning E1 links to IMA groups when planning future upgrades
places the cellular operator in an impossible situation. In addition, upgrade
procedures are extremely complex and demand traffic-affecting cable changes. The
alternatives are expensive and require initial rollouts for unpredictable future
scenarios.
The Dilemma
When deciding on the deployment of ATM in the access network, operators are
faced with a dilemma: they cannot afford not to do it, but they cannot afford to do
it either.
ATM concentration in the access in essential for maintaining affordable operational
costs, thus facilitating a reasonable cost structure for 3G services. On the other
hand, the cost of deploying a future-proof ATM network is high, and hence capital
expenses may rule this option out.
ECI TELECOM’S SOLUTION FOR 3G ACCESS NETWORKS
ECI Telecom Ltd. Proprietary 15
ECI Telecom’s Solution for 3G Access Networks
The cellular communications industry is and has always been an important ECI
Telecom target market. With this in mind, the company developed an innovative
and unrivaled solution for deploying 3G access networks. It is tailored specifically

for the needs of the cellular industry and has a reasonable cost structure.
The solution is based on the integration of SDH and ATM into a single platform –
the XDM
®
. This integration provides outstanding cost-effective flexibility and
future-readiness. This unique ATM solution is configured for the needs of 3G
access networks, and optimized both in terms of cost and features.
The XDM Architecture
To better understand the ECI Telecom ATM solution, it is necessary to first
understand the XDM, the company’s flagship MSPP (MultiService Provisioning
Platform), designed for cellular and metro networks.
The XDM supports a myriad of TDM and optical capabilities. The key feature
enabling ATM implementation is the full VC-12 granularity of the XDM matrix
that supports a full range of PDH and SDH interfaces from E1 to STM-64. The
XDM can cross connect any E1 to any other E1 over these interfaces, without
limitations.

Figure 5: Schematic view of the XDM architecture
ECI TELECOM’S SOLUTION FOR 3G ACCESS NETWORKS
16 ECI Telecom Ltd. Proprietary
The ATS (ATM Traffic Switch) Concept
In the ECI Telecom ATM solution, the ATS is an interface card that connects to
the system’s matrix rather than to the physical interface ports.
The ATS is in fact an ATM switch. However, rather than being equipped with
physical ports, it features SDH/PDH connections that are transported by the matrix
from any physical interface.

Figure 6: ATS card architecture
The ATS supports three types of ATM ports:
 VC-4 ports from STM-1 interfaces or VC-4s on any higher order virtual

container
 E1 ports from any physical E1 interface or any E1 channel from any other
interface
 IMA groups of multiple E1s
ATM switching has no limitations, and traffic can be switched at the ATM level
from/to any other port.
ECI TELECOM’S SOLUTION FOR 3G ACCESS NETWORKS
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Traffic Concentration from Several Node Bs into One Unchannelized VC-4
Let us continue with the example of concentration of ATM traffic over 52 E1s that
are part of an aggregate STM-1 port, together with 20 E1s connected as tributaries.
In the non-integrated ATM solution, an ATM switch is required as well as 72 E1
and one STM-1 interfaces. In addition, 72 new E1 and one STM-1 interfaces must
be added to the SDH equipment.
With the integrated XDM ATS solution (Figure 7), the matrix routes 52 E1
interfaces to the incoming STM-1, and the 20 PDH E1 interfaces to the ATS card.
The ATS card serves as an ATM switch, aggregating the 72 E1 ports into one VC-
4. The matrix then routes the resulting VC-4 to the STM-1 port.

Figure 7: Concentration of 72 E1s into a single VC-4
A single device therefore accomplishes two tasks: managing the SDH transport
layer and concentrating ATM traffic. Technically, this is equivalent to an SDH
node connected to an ATM switch, but the integration of the two functions in one
box is less expensive and more flexible.
ECI TELECOM’S SOLUTION FOR 3G ACCESS NETWORKS
18 ECI Telecom Ltd. Proprietary
Advantages of the ATS vs. a Standalone ATM Switch
The XDM integrated SDH/ATM solution is more compact (requires less boxes),
flexible, cost-effective and easier to manage. The following sections describe these
benefits in more detail.

Savings in Equipment
Table 1 shows the BOM (Bill of Materials) required to concentrate 52 aggregated
E1s and 20 tributary E1s into one unchannelized VC-4 over two layers, vis a vis
the equipment required with the XDM ATS solution.
Table 1: Two-layer implementation versus integrated implementation
Separate SDH and ATM layers Integrated SDH/ATM solution
One SDH ADM, including:
| 20 x E1 tributary ports
| 72 x E1 ports connected to the ATM switch
| 2 x STM-1 aggregate ports
| 1 x STM-1 port connected to the ATM switch
One ATM switch, including
| 72 x E1 ports
| 1 x STM-1 port
One XDM MSPP with ATM
capabilities, including:
| 20 x E1 tributary ports
| 2 x STM-1 aggregate ports
| 1 x ATS card

The integrated approach offers the same solution with only a fraction of the
equipment: A single card in the integrated SDH/ATM solution replaces an ATM
switch containing an enclosure, power supplies, a backplane, a matrix, and
interface cards. In addition, the SDH system is smaller as it does not require
additional interfaces for connection to the ATM switch.


NOTE: It is sometimes technically possible to
connect the ATM switch directly to the network
and not through SDH equipment. In this particular

example, 20 tributaries from the Node Bs can be
connected directly to the ATM switch. However,
this constitutes a huge burden on management and
administration, as not all Layer 1 connections are
managed via the transmission system.

This drastic reduction in equipment is due to the integration of ATM and SDH into
the same hardware. When implementing each technology with a different box, the
standard telecom connection between them requires its own hardware, connectors,
and cables. When the two technologies are integrated in the same box, the interface
between the SDH and ATM components is via internal hardware buses. This
results in higher port density and lower costs. Since the ATS does not have
physical ports, it can support 126 E1 interfaces (configured in up to 84 IMA
groups) in a single card. No other ATM system on the market reaches this density.
ECI TELECOM’S SOLUTION FOR 3G ACCESS NETWORKS
ECI Telecom Ltd. Proprietary 19
Operational Savings
The operational costs of the integrated solution are obviously much lower than that
of maintaining two separate layers. The following factors play a major role in this
cost reduction:
 A single management system manages both network layers, thus reducing
overhead costs
 Only one type of equipment is deployed; different layers are supported by
different interface cards in the same equipment
 Smaller footprint
 Reduced power consumption
 Less physical cabling, as management-based provisioning replaces physical
connections
IMA Flexibility
As described in the section entitled

The Extra Costs of Maintaining IMA Groups,
planning access network IMA groups can be a discouraging task. A minimalist
design that deploys the number of ATM E1 ports presently needed means that
future expansions will require cabling changes. This is inconceivable as far as the
network planner is concerned. On the other hand, future-proof designs must allow
for the provisioning of empty ports for future IMA expansion. Since predicting
future expansion is always risky, present financial expenses based on assumptions
of future demands are usually ruled out, and justifiable so.
The ATS card integrated in the XDM is the ideal solution. Unlike conventional
ATM switches, the ATS can combine any set of E1 ports, including ports residing
in different PDH interface cards, into one IMA group. This is due to the VC-12
granularity of the XDM matrix. In our example, the 20 tributary E1 ports can be
arranged into 10 IMA groups (each containing traffic from one Node B), with two
E1s each. In the future, the existing IMA groups may be upgraded to three or four
E1s, or even more.
With the conventional approach, it is necessary to reserve empty ATM E1 ports for
future use. With the integrated XDM ATS solution, new E1s arriving from each
Node B can be connected to a new PDH interface card. The XDM matrix then
routes all E1s from the same Node B to the same destination, even if they are
connected to different PDH interfaces.
ECI TELECOM’S SOLUTION FOR 3G ACCESS NETWORKS
20 ECI Telecom Ltd. Proprietary
Cost Flexibility
When designing a network, cost is a primary factor. Network planning, however,
should not be seen as an expenditure, but rather as a means to generate revenues.
Ideally, network design should accommodate the demands of all users, while
generating maximum revenue. In other words, the optimum design should be
attained at minimum cost.
But unlike other network planning scenarios where demand may be known in
advance, it has as yet been impossible to foresee the increase in the demand for 3G

services. A network design should therefore account for a variety of scenarios.
Ideally, it should follow these guidelines, usually referred to as “cost flexibility”:
 The initial design to be a small low-cost network that facilitates rollout and
handles sparse usage.
 With increasing demand to upgrade the network so that revenues are never
jeopardized by insufficient capacity.
Unfortunately, trying to cater for both needs – small initial investment and easy
cost-effective upgrade with increasing demand is not always feasible.
When measuring the cost of a specific network solution, cost flexibility – that is,
the ability to adjust the cost of the network to actual demand – is an extremely
important factor. At the outset assumptions are made about network current usage,
as well as possible scenarios for network upgrades.
The major consideration, therefore, is not the correlation between capacity and
demand, but that between the cost of the network and the revenues it produces. To
maintain a feasible economical model, the cost of the network must be offset by the
revenues obtained from the services it provides.
Even after making the correct assumptions, service demand may lag behind or
exceed initial expectations. But, there should never be loss of revenue due to
insufficient capacity. It therefore emerges that network capacity should be
calculated so that it guarantees no loss of revenue.
When opting for a particular network design, a capacity upgrade strategy must be
predicted. Unfortunately, upgrades for a future-ready network always come at a
price and includes:
 Buying bigger enclosures that provide for the future addition of more cards
 Installing high capacity interfaces even if not required in the first phase
 Leaving empty ports for future IMA expansion
 Using high-instead of low-density interface cards that would need to be
replaced
This results in the all-familiar dilemma: deploy a network today with the minimum
configuration required and pay a high price for future upgrades, or build a future-

ready network today, incurring costs that may prove to be a waste of money in the
future.
ECI TELECOM’S SOLUTION FOR 3G ACCESS NETWORKS
ECI Telecom Ltd. Proprietary 21
The XDM is a build-as-you-grow™ and pay-as-you-grow platform, and the ATS
card was designed with these premises in mind. Since the ATS is an interface card
(not a standalone box), the cost of adding more ATM capacity to the network is
substantially lower. Specific network design is consequently more economical, and
future upgrades are simpler, easier, and more cost-effective. There are no concerns
as to what size of ATM switch should be installed, but rather how many ATS
switching cards are required if and when demands change.
THE XDM ATS CARD AS A NODE B CONCENTRATOR
22 ECI Telecom Ltd. Proprietary
The XDM ATS Card as a Node B Concentrator
This section reviews several network scenarios in which the XDM platform is used
to implement 3G access networks. In each application the compactness and
flexibility of the ATS solution enables an optimal network solution.
Canonical Concentration of Node B Traffic into VC-4s
A typical ATS application consists of the concentration of E1s from Node Bs into
VC-4s carried to the RNC.
Figure 8 shows a schematic view of this
implementation.

Figure 8: Concentration of E1s into VC-4s
In this application, Node Bs send traffic via E1s, either as E1 ATM or as groups of
IMA E1s. The ATS cards terminate these E1s at the ATM level and concentrate
them into a single unchannelized VC-4 carrying ATM traffic from all Node Bs.
Each ATS card then functions as a concentrator ATM switch, carrying all VCs
from the incoming VC-4 to the outgoing VC-4, and adding local traffic from Node
Bs.

It is important to note the features making this application so flexible:
 The E1s from the Node Bs can be treated as ATM UNI E1s or be combined
into IMA groups
 The E1s may be either physical ports connected to the XDM PDH interface
cards, or a channel in the XDM SDH interfaces
 IMA groups may contain any type of E1s, even those that reside in a mixture
of PDH/SDH interfaces
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Application Scalability
Each network solution should scale from the initial phase of sparse deployment and
a low number of users, to full network coverage for mass usage. In each phase, the
network should provide the services required while maintaining a reasonable ratio
between expenses and revenues.
When translating this scalability into concrete terms, three factors define network
demands:
 Number of users and resulting capacity requirements
 Number of Node Bs in the network
 Bandwidth availability
The first factor is directly related to the bandwidth of the links carrying
concentrated traffic. Even with huge Node B deployment, if the number of users is
low, the actual bandwidth required is minimal. In our example, a single VC-4 can
concentrate traffic from a very large number of Node Bs since the number of
end-users that actually generate traffic is low.
The second factor (number of Node Bs in the network), relates directly to the
quantity of ATS cards required as each ATS card can support a certain number of
E1 ports and IMA groups from the Node Bs.
The third factor (bandwidth availability) determines the requirement for
intermediate concentration. If it calls for carrying traffic through a specific pipe,
additional ATS cards will be required to concentrate the traffic at the ATM level

and meet this demand.
The next sections describe how this canonical design can easily be adapted to
actual scenarios based on changing network needs.
Sparse Deployment of Node Bs
It is reasonable to assume that the initial network deployment consists of a few
Node Bs. Thus, installation of an extra ATS card at every intermediate point would
be an unnecessary and superfluous expense. The solution would then be to deploy
ATS cards only in some locations and carry and connect Node Bs traffic in
intermediate points via the SDH concentration links.

Figure 9: Configuration for a low number of Node Bs
In this scenario, the ATS card can use both E1s from local PDH interfaces and E1s
carried from remote E1 ports over SDH channels.
A typical network deployment can start with this scheme that is sufficient when
only a few Node Bs are connected to each site. Later, as more Node Bs are
deployed, additional ATS cards can be installed at intermediate points.
THE XDM ATS CARD AS A NODE B CONCENTRATOR
24 ECI Telecom Ltd. Proprietary
Note also that only the management-based provisioning needs to be modified when
a new ATS card is added at an intermediate port. It is not necessary to reconnect or
reroute cables or physical devices. This is another example of the future-readiness
of the ATS versus an external ATM switch, which makes the upgrade a tedious
task entailing the installation of new equipment and rerouting of physical cables.
Increased Bandwidth Demand
In
Figure 8, traffic concentration from Node Bs into a VC-4 is accomplished over a
single VC-4 trail. As the actual number of users increases, more and more
bandwidth is required. A simple reconfiguration of the network (as shown in
Figure 10) caters for the required increase in capacity.

Figure 10: Configuration for increased bandwidth demand
The same number of Node Bs with the same number of ATS cards therefore serves
additional bandwidth towards the RNC.
Note again that the increase in network capacity is achieved without adding a
single new card or interface. A simple management operation routes traffic from
the Node Bs over two VC-4s instead of one.
Savings on Intermediate Bandwidth
A capacity of one VC-4 may be excessive for the demands in the first phases of
network deployment. The ATS can accommodate actual demand using large IMA
groups.
IMA groups are usually used to carry traffic from Node Bs. In this example IMA
groups of two to eight E1s are sufficient. The ATS, however, can support larger
IMA groups of up to 32 E1s. These large IMA groups may be used for traffic
concentration, consuming only the needed bandwidth instead of occupying an
entire VC-4.
Figure 11 illustrates this concept.

Figure 11: Concentration of Node B traffic into IMA groups
In this configuration, the benefits of ATS flexibility are enormous:
 3G traffic consumption is controlled by the E1 granularity of the XDM matrix.
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 Modification of the size of the IMA groups is a simple management
provisioning operation (unlike the external ATM switch solution, which
requires new E1 ports).
 Upgrade from an IMA-based solution to a VC-4-based solution is
management-controlled. With external ATM switches, the upgrade would
involve changes to the hardware configuration of the switches.
Combined VC-4 and IMA Aggregation
VC-4s and IMA groups can also be combined into a single network design, thus

accounting for the capacity vs. cost paradigm.
Figure 12 shows how IMA group
concentration can be added when the existing VC-4 has been fully utilized.

Figure 12: Combination of VC-4 and IMA concentration
Similarly, the initial deployment can consist of a single IMA group and later, when
traffic increases, it can be concentrated into a VC-4.