Next Generation BTS Architecture

1. Next Generation BTS Architecture Lucent Technologies

2. Guiding Principles for Architecture Evolution What do we want? Why do we want them? How do we get there? • Easy evolution to future access technologies with no disruption to core IP network infrastructure • Addition of new applications and services • Full support of mobility without compromising performance • Interoperability with other wireless and wireline access technologies • Ease of operations and management • Cost effective deployment and operation Maximize use of standard access agnostic (IP) protocols and technologies Flexibility Inter-operability Performance + Simplicity without compromising any of the others! • Simplicity of look and feel, operations and management • Improved fault tolerance and network reliability • Expand easily, yet gracefully and incrementally to satisfy demand • Maximal performance efficiency • Easy evolution to future access technologies with no disruption to infrastructure Minimize different types of access technology specific network elements and interfaces Scalability Efficiency

3. What Can We Do To Get There? How do we get there? What can we do to get there? Maximize use of access agnostic (IP) protocols and technologies Use IP for routing and Mobile IP for mobility Already done Minimize different types of access technology-specific network elements and interfaces Compact the protocol stack down to IP at the edge node – creates a single access specific node which terminates all wireless specific signaling and traffic functionality Building block of Flat IP network

4. RLP Anchor Slow Rate Control RLP Reassembly RLP Anchor RLP Anchor L2 QoS marking RLP Fragmentation Reassembly RLP Fragmentation Reassembly QoS Enforcement L3 PoA RLP Fragmentation Comp Header Fast Rate Control Fast Rate Control L2+L3 CAC, QoS Policy Enforcement RLP Anchor Hybrid ARQ Hybrid ARQ RLP Fragmentation Reassembly Fast Rate Control Hybrid ARQ Recap: Radio Resource Management Evolution Home Agent Home Agent Home Agent Home Agent PDSN Foreign Agent Foreign Agent Foreign Agent Header Comp Header Comp Comp Header PPP PPP PPP L3 QoS marking MIP Tunnel Signaling Interface Traffic Interface These functions move down to the BTS in LBC air interface standards RNC Signaling Interface Traffic Interface Fast Power Control BTS I-BTS CDMA2000 RTT HRPD Rev 0 HRPD Rev A LBC Flat IP is a natural progression of the existing air interface evolution Note: The HA can either be a Visited HA or a Home HA, or a combination thereof

5. Mapping Functions to Network Elements • Most functionality has now moved to the BTS anyway, so consider a single access node: Integrated BTS (I-BTS) • Replaces key elements (both user and control planes) of the RAN and Core Network with a single network element located at the network edge Layer 3: Mobility Anchor functions and access agnostic L3 functions HA Mobile IP tunnel Access agnostic tunnel; not A10/A11 Layer 3: Point of Attachment functions Layer 2.5: Anchor and interface functions Layer 2: Radio Resource Control anchor functions Layer 2: Radio Bearer functions Layer 1: PHY functions Integrated BTS (I-BTS) Layers mentioned above, and the functions within, were described in contribution X30-20060911-011 LU_arch_comparison

6. Flat IP Network Key Points - 1 • All access technology specific portions are contained in the BTS • No centralized components that are access technology specific • Thus no “hidden” bottlenecks in the system (as in alternate architectures), which makes system scaling significantly easier • Access technology specific signaling remains at the edge • Signaling is dealt with as soon as it arrives: no transmission and queuing delay to transmit to a central node • The system is more predictable because signaling operations are less dependent on a backhaul infrastructure and other (central) elements • The backhaul is fully IP and its operation can be kept separate from maintaining the access technologies • Enables route optimization from the edge • Reduces the complexity of maintaining a cellular network • Integrating various access technologies can be realized via IP, rather than a concoction of glue systems • Enables operator sharing of infrastructures

7. Flat IP Network Key Points - 2 • Fault tolerance and Reliability • Low failure rate: Fewer central components to disrupt the system as a whole • In alternative architectures, specialized centralized components must provide their own specialized recovery mechanisms • In flat architectures, failures in specialized components are localized; the IP backhaul/core can use established, redundant routing techniques for fault tolerance • Failures are local: no complex failure recovery mechanisms are required: • if a BTS in a flat system fails, it can quickly re-establish itself without intervention of central nodes; • Since there are no complex failure recovery systems required (as there is hardly any shared state information between nodes) recovery of service is much faster. • Easier deployment of various coverage options (macro/micro/pico) • IP interconnect allows seamless integration of different coverage options • Easy integration of residential/office service • High bit rate + coverage  many smaller cells compared to current macro cells • Only simple IP interconnect without central components is scalable.

8. Example Advantage: QoS • Air interface scheduler has visibility into the IP packets  cross-layer optimization can be leveraged to enhance performance • ACK and Window regulation • Application-aware scheduling • E.g. in the case of Video-on-Demand, prioritize I-frames and drop B-frames if necessary • Such advances not possible in the hierarchical architecture since the BTS has no visibility into (possibly encrypted) IP packets

9. Example Advantage: Enhanced Availability • Resilience to attacks • Any IP-based network element can be attacked • Centralized Architecture: If RNC or IP gateway is attacked then a large set of cell sites affected • Flat IP: If I-BTS is attacked, only one cell site affected! • Attack effects naturally localized • Enhanced availability compared to centralized architecture • If a cell-site is attacked, that cell-site can be disabled • The neighboring cell-site can offer coverage temporarily • Enhanced reliability due to distributed architecture • Fewer software-based failures • Functions implemented in I-BTS code base are inherently simpler to implement compared to IP-Gateway due to limited scaling

10. Seamless Integration of Flat IP Flat IP coexists with legacy architecture as well as other access technologies

11. Re-use IETF Interfaces • The interface between HA and I-BTS • IETF-based • Same interface can be used for legacy network, 3GPP network, WLAN interworking • Protocols • AAA protocol (Diameter) for fast EAP re-authentication • Mobile IP • The interface between I-BTS and AAA • AAA protocol (Diameter) for EAP Authentication and authorization

12. Mobility Management • L1/L2 issues addressed by RAN standards • Pilot measurements • Active set update messages • FL and RL serving sector selection indicators • FLSS and RLSS can be separate in LBC • L3 issues addressed by Mobile IP standards • Support for both IPv4 and IPv6 • Allows for seamless inter-technology handoff

13. Layer 3 Mobility Management • L3 Point of Attachment (PoA) is typically co-located with the Forward Link Serving Sector • MN performs Simple IP (clientless) or Client MIP • For Client MIP, the MN performs re-registration if it detects a change in the CoA or C-CoA • Fast Handoff between I-BTS’s addressed by • L3 tunneling • Network based mobility management (e.g.,Proxy MIP) • Context Transfer • Proxy Mobility Agent will be co-located with L3 PoA

14. Flat IP Security Architecture Key Features • Security does not rely on physical security of the network • Link layer security functions already down at cell sites • A cell site only holds a few session keys compared to RNC/PDSN • Session keys can be refreshed during handoff • Means to satisfy cell site security features • Tamper-resistant processing inside the cell site • Secure booting techniques of secure hypervisors, hardened operating systems • Secure tunnel to the AAA, HA, inter-cell site, and MN • Protection against • Physical intrusion • Network eavesdropping • Radio resource related DoS • Hijacking of sessions

15. Flat IP Security Architecture Secure Computing Environment at cell sites: Provides secure storage of all session keys - ciphering (CK) and integrity (IK) Performs ciphering and integrity protection for user and signaling plane Establishes and maintains secure tunnels to home agent and AAA HA To public/private IP network Shared secret key Secure computing environment at cell site inter-cell site AAA RLP, Mobile IP Session Keys UIM CK + IK Protocol stack Protocol stack CK + IK Bearer + Signaling over the air Secure/trusted environment Non-trusted environment Flat system’s cell site Secure tunnel User equipment

16. Paging in a Flat Network • Paging in today’s hierarchical network • AT’s paging controller (PC) is the RNC at which it is anchored • HA  FA/PDSN  PC  BTS  AT • Paging in a flat network • AT’s PC is the pre-dormant anchor I-BTS • L3 PoA is typically co-located with pre-dormant anchor I-BTS • MIPv4: HA  FA  PC  BTS  AT • MIPv6: HA  PC  BTS  AT • Key difference • AT’s PC is distributed and dynamically determined in a flat network • AT’s PC is centralized and statically located at the RNC in a hierarchical network

17. QoS and Policy Mgt – Overall Architecture App Infrastructure A significant part of QoS and Policy Mgt consists of the interaction between Application Functions and a Policy Manager (PM). This part is independent of the network architecture and not further considered in this presentation 1. Session setup 2. Resource Request PM 3 Policy Rules 4. Policy enforcement Once PM (based on the execution of policy rules) determines the required QoS, it triggers one or more policy enforcement points. I-BTS HA Context transfer at handoff I-BTS

18. Criterion Flat Hierarchical Multi-vendor interoperability at BTS (plug-n-play) Just one access-specific node type; integrated BTS is fully IP capable, and can be plugged in with minimal effort. Multiple acess-specific node types (PDSN, RNC, BTS) need special configuration and testing. Fault tolerance, reliability Failures remain strictly local; example: integrated BTS failure implies only local outage. 99.9 % reliability at the integrated BTS is sufficient to achieve 99.999 % network reliability. This translates to significant cost savings since every "nine" entails exponential increase in cost. Failure at high density equipment such as PDSNs and RNCs leads to widespread outage. High density nature of such nodes requires them to be individually 99.999 % reliable, which results in high costs. Scalability Designed to scale gracefully and incrementally; add one I-BTS at a time! May not scale gracefully; may require upgrades or additions of multiple network elements Upgradability to newer wireless access technologies and standards Need for upgrades limited to the cell site; can be done one cell site at a time. Hardware upgrades may only require replacing a channel card. Upgrades will affect multiple network elements, and have to performed system-wide. Hardware upgrades may apply to centralized network elements such as RNC and PDSN. Backhaul efficiency Integrated BTS offers key advantages. Local traffic can be kept local, which reduces backhaul usage. Local caching is possible due to IP visibility; this not only enables a high quality user experience, but also prevents unnecessary backhaul usage. Moreover, IP visibility at the I-BTS provides the opportunity for route optimization from the edge, leading to further savings in backhaul utilization. Local traffic does not remain local - it has to travel all the way to the PDSN and back. Local caching is not possible due to IP invisibility. The earliest point at which route optimization is possible is the PDSN, which is often deep in the network. Comparisons - 1

19. Security Advances in tamper-resistant hardware technology as well as secure computing techniques enable cost effective security at the I-BTS. No additional CAPEX due to any centralized security processing. Furthermore, distributed architecture offers greater resilience to denial of service attacks, thereby significantly enhancing availability. Given the migration of all air-interface layers, including security, to the cell site, tamper-resistant hardware at the cell site is necessary even for the hierarchical architecture. Even so, centralized architecture renders it more vulnerable since DoS attacks directed at the RNC and the PDSN can create outages over large geographical areas. Handoff Performance Due to migration of all air interface layers down to the cell site in LBC, handoff from one cell site to another requires migration of layer 2 functionality during handoff. This is independent of whether the layer 3 point of attachment is at the cell site. Due to migration of all air interface layers down to the cell site in LBC, handoff from one cell site to another requires migration of layer 2 functionality during handoff. This is independent of whether the layer 3 point of attachment is at the cell site. QoS (Application and subscriber) Full IP packet visibility at the I-BTS allows for uniform IP QoS throughout the network, including the air interface. Application level information can be extracted at the I-BTS to enable cross-layer optimization via application-aware scheduling and resource management. No necessity to translate into technology specific QoS parameters, and hence no loss of granularity from IP QoS. IP QoS has to be translated per flow into technology specific QoS parameters and propagated through the network. This is in addition to other packet processing that the PDSN does. Therefore, the PDSN needs heavy computing resources to address the large volume of flows. Further, IP QoS granularity is likely lost in translation. Moreover, corss-layer optimization cannot be performed in hierarchical architectures. Infrastructure Cost There is only one access technology-specific network element. The rest of the network consists of standard off-the-shelf router components, which affords economy of scale. Moreover, given the distributed architecture, auxiliary functionality such as firewalls will become software components in the I-BTS; no special hardware is required. Further, the core network (home agent) is common across all access technologies. There are multiple access technology-specific network elements. More over, the core network elements such as the PDSN are technology specific and require special development, resulting in higher costs. Given the centralized nature of the hierarchical architecture, auxiliary functionality such as firewalls will have to be offloaded onto special hardware at centralized network elements such as the PDSN. Reliability requirements are higher for such high density equipment, leading to further cost increases. Comparisons - 2

20. Lower Latency (bearer and network entry) The flat architecture eliminates all inter-network element protocol translations and processing (such as the R-P and RNC-BTS interfaces). Route optimization with Mobile IP enables lower latency and better QoS. Distributed architecture provides significantly higher path diversity, thus reducing possibility of congestion. The hierarchical architecture requires inter-network element protocol translations and processing, which leads to an increase in latency. Route optimization possible only north of the PDSN, which is typically deep in the network. Thus, little or no benefit can be derived. Self healing, self optimizing, self configuring infrastructure mesh capability Distributed architecture ideally suited to fully exploit self configuring mesh backhaul design. Hierarchical architecture cannot exploit mesh backhaul design. Wireless/wireline convergence More consistent with wireline access, allowing for converged L2/L3 data network to support both wireline and wireless. Ability to provide uniform IP QoS on both wireline and wireless networks. Network has more wireless specific elements, complicating seamless wireline-wireless convergence. Not possible to provide uniform IP QoS over wireline and wireless networks. Intra-system mobility context transfer BTS's need to know policy information in order to provide over-the-air QoS and to prioritize upstream traffic, regardless of architecture. No need to re-establish security and policy rules during handoff for flat architectures. Even if policy information requires 50 bytes per flow, one single IP packet is sufficient to transfer it during handoff! Policy information and security associations can be transferred over secure inter-BTS tunnels during handoff. BTS's need to know policy information in order to provide over-the-air QoS and to prioritize upstream traffic, regardless of architecture. With hierarchical architecture, the PDSN has to translate L3 (IP) QoS policy information to L2 and then convey this to target BTS. Further, due to migration of all air interface layers to the cell site in LBC, context transfer is still necessary during handoff. Policy control The BTS is a key policy enforcement point regardless of architecture. Policy information needs to be propagated down to BTS's, as well as made available to intermediate nodes in the network for end-to-end QoS. Use of IP all the way to the BTS's allows for uniform IP QoS policy enforcement throughout the network. The BTS is a key policy enforcement point regardless of architecture. Policy information needs to be propagated down to BTS's, as well as made available to intermediate nodes in the network for end-to-end QoS. However, IP QoS is not straightforward south of the PDSN since any IP QoS markings (e.g DSCP) are not visible. Comparisons - 3

21. Deployment suitability Suitable for deployment in macro-, micro-, pico-cellular, and even home-scale environments. In fact, due to higher data rates, cell sizes are shrinking, which increases backhaul density requirements regardless of architecture. Standardized IP-based networks are best suited for such dense deployments. For micro- and pico-cellular deployments, fully integrated IP-capable base stations are closer in spirit to well-known devices such as WLAN routers. Ideally positioned to exploit high capacity mesh backhaul possible in micro and pico deployments. With high density deployments, hierarchical architecture leads to heavy backhaul utilization, and the inability to distribute load soon manifests itself unfavorably. Multiple wireless specific nodes make it less suitable for micro-, pico-, and home-scale deployments. OAM&P (Operations, administration, Management & Provisioning) Simplicity of management and provisioning due to just one type of wireless specific device. Management of the wireless network can be merged with management of the rest of the routed IP network. Different wireless specific node types (PDSN, RNC, and BTS) to manage, each with its management requirements. Software complexity at cell sites All access specific functions implemented at cell-site, leading to higher software complexity. Only a subset of access-specific functions implemented at cell-site. Billing Number of billing records is independent of architecture; billing records generated at integrated BTS and securely transferred to charging gateway. Number of billing records is independent of architecture. Billing records generated at BTS and transferred to the PDSN en route to the charging gateway. Comparisons - 4

22. Summary • Flat IP guiding principle: simplicity and limiting access-specific functions to the edge • Natural progression of air interface evolution • Seamless interoperability with legacy and hierarchical networks as well as other access technologies • Clear advantages in multiple dimensions over hierarchical architectures • Adopt Flat IP as the next generation architecture