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

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 info@horsebridge.net 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. The information contained in the documentation and/or disk is proprietary and is subject to all relevant copyright, patent, and other laws protecting intellectual property, as well as any specific agreement protecting ECI Telecom's rights in the aforesaid information. Neither this document nor the information contained in the documentation and/or disk may be published, reproduced, copied, modified or disclosed to third parties, in whole or in part, without the express prior written permission of ECI Telecom. 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Information contained in the documentation and in the disk is periodically updated, and changes will be incorporated in subsequent editions. If you have encountered an error, please notify ECI Telecom. All specifications are subject to change without prior notice. 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 vi ECI Telecom Ltd. Proprietary 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 ECI Telecom Ltd. Proprietary 9 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 10 ECI Telecom Ltd. Proprietary 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. [...]... 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. .. Telecom Ltd Proprietary 13 DEPLOYING A 3G ACCESS NETWORK 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... 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 ECI Telecom Ltd Proprietary 11 DEPLOYING A 3G ACCESS NETWORK 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... 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... Two-layer implementation versus integrated implementation Separate SDH and ATM layers 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 Integrated SDH/ ATM solution One XDM MSPP with ATM capabilities, including: 20 x E1 tributary ports 2 x... 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 12 ECI Telecom Ltd Proprietary DEPLOYING A 3G ACCESS NETWORK The Cost of Using ATM Switches... 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,... 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... 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... E1 ports into one VC4 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