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Wireless data services are expected to encourage the adoption of Internet Protocol Version 6 (IPv6) because of the quickly expanding number of IP-addressable devices. These services are expected to increase with the move to the Third-Generation Partnership Program Universal Mobile Telephony System Technical Specifications (3GPP UMTS), including the adoption of Internet Multimedia Services (IMS). Smooth transition to IPv6 in IP backbones, and possibly later in the Radio Access Network (RAN), is the goal stated in 3GPP specifications. Multiprotocol Label Switching (MPLS) is widely deployed by mobile service providers that need IP and ATM transport. The IPv6 provider edge router (6PE) approach is best suited for the integration of IPv6 in such an infrastructure.
This paper clarifies the use of IPv6 in the 3GPP UMTS architecture. It addresses questions about how UMTS will encourage the adoption of IPv6. UMTS is first described at a high level, with background on Cisco® IP network modeling; three deployment scenarios and the rationale behind the recommendation of the MPLS 6PE solution, with IPv6 in 3G networks, are also presented.
SUMMARY
CISCO IN THE MOBILE MARKET
Multiservice IP networking products and solutions from Cisco Systems® are helping to transform the design, profitability, and cost-effectiveness of mobile networks around the world. Worldwide, mobile operators are at different stages of migrating to 3G mobile network services and architectures and new IP services and applications. Collaborative standards bodies, such as the 3GPP and 3GPP2, are recommending IP for mobile network traffic. Beyond 3G or 4G standards, development is just beginning, and this development is using IP-addressable mobile phones and other devices to advantage.
Mobile operators have been deploying mobile services for voice, data, and multimedia using disparate traditional networks. Many are now actively engaged in developing or deploying both existing and new mobile services based on an IP/MPLS backbone. As the leading global IP expert, and with broad networking experience and products, Cisco is working with mobile operators to help them take advantage of the many compelling benefits of migrating to a converged wireless network backbone based on IP/MPLS.
The Cisco IP/MPLS-based architecture and products-tried and trusted with successful deployments by most wireline service providers worldwide-provide the end-to-end quality of service (QoS), security, scalability, resiliency, and management enhancements for deploying data, voice, and video services. These carrier-class, industry-leading features run on the broad Cisco family of powerful hardware, ranging from the Cisco CRS-1 Carrier Routing System, the world's most powerful router; to Cisco 7600 Series routers, the popular provider edge and enterprise metropolitan-area network (MAN) and WAN routers; to an array of customer edge and access routers.
Mobile operators can generate new revenue streams from emerging IP services. They also can reduce complexity and lower operating expenses (OpEx) and capital expenditures (CapEx) through the consolidation and migration of their existing ATM, time-division multiplexing (TDM), and Frame Relay networks and business processes to a converged IP/MPLS backbone with VPN technologies at Layer 2 and Layer 3. Cisco IP/MPLS also can run over MPLS-enabled ATM switches, helping protect investments as mobile operators transition from ATM to IP.
CISCO MOBILE WIRELESS IPV6 BACKBONE SOLUTION
Support of IPv6 has been a fundamental requirement of proposed future UMTS releases, especially because of the increased address space that becomes essential to support always-on clients and expanding peer-to-peer traffic. Despite ongoing discussions about what IPv6 can really offer and questions about how to transition to IPv6 and how to internetwork with IPv4-based IMS, there are short-term obstacles to the full adoption of IPv6.
What could spur decisions to adopt IPv6?
Compelling reasons for IPv6 include the expansion of the address space, enabling the growth of mobile Internet applications. It allows large-scale peer-to-peer and any-to-any communications and always-on connectivity as well as easy, ready-to-use functions. Because these are the objectives of 3GPP IMS, IPv6 has been adopted as a primary technology enabler for wide-scale adoption of IMS. With true commercial deployment of IMS expected in the coming years, mobile operators want to be ready to launch IMS and, if required, IPv6 services, but they will not risk making changes if those changes impact their current IP business and associated revenue.
The preferred strategy for service providers is often to begin inserting IPv6 support at the edge of their current IP networks when feasible. Most assume that IPv6 traffic will grow slowly and that the previous 3GPP definition of IMS as exclusively using IPv6 from its introduction is now questionable. MPLS 6PE is the best solution to propose as soon as mobile network operators (MNOs) consider IPv6 support. 6PE has the following advantages that fit MNO concerns:
• Low cost-Start with a current platform, use existing routers as an IPv6 edge when needed, and conduct trial integration. No large OpEx plan is necessary.
• Risk protection-No backbone upgrade is necessary. Business is secured by a proven IPv4 backbone.
• Performance-IPv6 is independent in the backbone because IPv6 paths use MPLS forwarding.
• Hardware support-IPv6 and 6PE at line rate are available when and where they are needed.
With MPLS 6PE, any IPv6 traffic introduction has no impact on the other traffic that uses the same backbone network. Business applications are, therefore, not impacted by IPv6 adoption. As in the example in Figure 1, an IPv6 IMS trial network can be built and then deployed over a common MPLS network involving only the IMS network and a 6PE device. For the IP Universal Terrestrial Radio Access Network (UTRAN), the IP UTRAN nodes can use IPv6 and the MPLS network through the 6PE device without any other transition mechanism such as tunneling.
Figure 1
Insertion of IPv6 Networks in a Mobile Wireless MPLS Backbone
If separate IPv6 domains (for example, along with IMS and GPRS Tunnel Protocol [GTP] domains) are needed, the use of MPLS 6PE with the carrier supporting carrier (CsC) feature is fast and well-known. It can avoid a long evaluation code phase by mobile operator teams without preventing the evolution to an MPLS IPv6 VPN provider edge router (6VPE).
IP IN THE UMTS ARCHITECTURE: AN OVERVIEW
From its creation, 3GPP has used IP as a convergence layer in its architecture as a long-term strategy. This use of IP in the network is often referred to as the "all-IP" architecture. It means that IP is used everywhere for both services to mobile subscribers and for transport. 3GPP is delivering sets of new capabilities and enhancements in specific releases. IPv6 is appearing in multiple places and at different stages of the release process in the 3GPP specifications.
Figure 2 shows the different parts of the UMTS mobile wireless architecture that are discussed later. This is not intended as a detailed description of how wireless networks work.
Figure 2
Mobile Wireless Network Components
The mobile station can be a handset, a laptop with a Personal Computer Memory Card International Association (PCMCIA), a personal digital assistant (PDA), or a mobile router (such as the Cisco 3200 Mobile Access Router). In 3GPP, the access network (AN) also is known as the UTRAN, excluding here the radio interface. Node B is the 3G UMTS base transmission station (BTS); it is part of the RAN and provides the radio air interface to the mobile station. The radio network controller (RNC) controls multiple node Bs (in 2G networks or 3GPP2 Code Division Multiple Access [CDMA] networks, the base station controller [BSC] is performing an equivalent role) and is part of the RAN. The circuit-switched (CS) domain is rooted in Global System for Mobile Communications (GSM) networks providing voice services. The General Packet Radio Service (GPRS) architecture was defined as the packet-switched (PS) domain.
The core network (CN) is composed of the media gateway (MGW) and the modular-services-card server to handle circuit-switched traffic. The MGW and MSC-S can be interconnected through an IP backbone. The core network also is composed of the Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN) for the packet-switched domain. The packet-switched domain includes the packet or public data network (PDN) and the IP Multimedia Subsystem. A 3GPP core network is an architectural term relating to the part of a 3GPP system that is independent of the connection technology of the terminal (for example, radio or wired). Sometimes the term "core network" is used in a broader context and may lead to confusion. In this document, a backbone network encompasses part of or the entire "core network" as in the next-generation network vision. The mobile operator backbone network also encompasses a part of the PDN. The PDN provides a set of services to subscribers either by the mobile operator or by an external network such as a subscriber's corporate network or the Internet.
The Public Land Mobile Network (PLMN) comprises the access network and the core network. In a circuit-switched domain, the last PLMN equipment is the GGSN, which is the gateway between the PLMN and the PDN. The SGSNs are in charge of maintaining the relationship between the mobile station and the GGSN when the mobile station is moving. The PDN represents the rest of the packet-switched domain. The PDN provides the data services to the mobile station.
The all-IP nature of UMTS, beyond Release 5, is designed to expand the packet-switched domain without ignoring the circuit-switched domain for backward compatibility. With Release 5 as the initial baseline, the 3G all-IP architecture should provide:
• An alignment between IP solutions being adopted by fixed networks and mobile networks
• Cost reductions based on the use of off-the-shelf IP technology and economies of scale for both the backbone and the edge
• The ability to add additional access networks transparently to the upper layers of the architecture
• Transparent use with the 3GPP2 IP architecture, both for economies of scale for operators and for more benefits to subscribers
Because IP is a clear direction in mobile networks, Cisco Systems is interested in working both on the control plane and on user specifications for mobile wireless networks. Cisco is working in different standardization groups such as 3GPP and 3GPP2 to understand and contribute to the creation of a global infrastructure.
IP FOR THE MOBILE OPERATOR NETWORKS
Multiple networks exist within the IP domain in a current mobile operator environment (Figures 3 and 4). UMTS networks are thus a subset of a mobile service provider network.
Figure 3
Mobile Wireless Service Provider's Multiple Networks
The different networks support some types of services for user applications (or "external services"), services that are the foundation of the mobile service provider (MSP) backbone (or "internal services"), or are the aggregation of access networks.
A main goal of building IP/MPLS backbones is to support both external and internal services as well as aggregation networks using Layer 3 VPNs (L3 VPNs) for IP or pseudowire service (using Layer 2 transport using Any Transport over MPLS [AToM] for GPRS Frame Relay and UMTS ATM traffic), as Figure 4 depicts. Such next-generation multiservice backbones are providing the necessary network convergence to decrease CapEx and OpEx.
Figure 4
Multiservice MPLS Backbone for Network Convergence
As the different wireless and wireline access technologies migrate to IP, the aggregation points will likely provide IP services. All these services require the same IP backbone infrastructure and management structure. Different characteristics of these services include packet size; QoS, including delay, jitter, loss, and bandwidth; and reliability. Aggregation must support multiple Layer 2 protocols that may require different and rich sets of features in oversubscribed environments.
The more restrictive characteristics will come from the UTRAN either when UMTS radio equipment uses IP or if IP is used for carrying current traditional transport protocols such as TDM and ATM. For at least the next few years, 2G GPRS and 3G UMTS will use a common set of services because the IP backbone should be independent of the radio access technology. An aggregation layer should enable this wireless technology agnosticism to the IP backbone.
As Figure 5 shows, IP appears at two different layers. It is a data bearer in the path for user and application traffic flowing between the mobile station and the PDN. This traffic can go beyond the PLMN of the mobile operator.
IP also is a transport bearer (that is, IP used to transport bearer traffic for IP UTRAN as specified as optionally defined in 3GPP Release 5 or GTP traffic in GPRS). Note that GPRS traffic can be exchanged between PLMNs when the user is roaming. Then, an inter-PLMN IP network is specifically involved: the GPRS Roaming Exchange (GRX).
Figure 5
IP in the 3GPP Mobile Wireless Architecture
ABOUT GTP ENCAPSULATION
Core-network transport uses the GTP to support the mobility of the mobile station in relation to the GGSN. These are the blue arrows in Figure 5. In GPRS 2.5G, GTP is only between SGSN and GGSN (dotted arrow). With UMTS, GTP-U (user traffic) is extended to the RAN because tunnels are terminated in the RNC (solid arrow).
GTP is an important protocol for mobile wireless networking because it maintains the connection with the GGSN, which is the anchor point for all mobile data connections. When moving, the mobile station can change between BTS/node B, BSC/RNC, and SGSN. Thus, GTP helps maintain the relationship between the Packet Data Protocol (PDP) context of the user and the GGSN that is in charge of the user's connection.
ROAMING SCENARIOS IN BRIEF
Roaming happens when the mobile station is not registered to its home PLMN (that is, the mobile operator to which the mobile-station user is subscribed). When roaming, the mobile station is registered within a "visited PLMN."
Mobile data traffic has two roaming scenarios:
• The Internet service provider's (ISP's) scenario wherein the mobile station reaches its home services through the PDN (depicted in orange in Figure 6)
• PLMN roaming, also known as the GRX scenario, which uses third-party networks to interconnect PLMNs (depicted in blue in Figure 6)
Figure 6
Roaming Scenarios Overview
In ISP roaming, the mobile station uses the visited PLMN SGSN and GGSN. To reach a subscriber's home operator network, the user traffic goes through the PDN, where one or multiple ISPs link the two mobile operator networks. In the GRX scenario, the linkage of virtual PLMN (V-PLMN) SGSN to the home PLMN (H-PLMN) GGSN avoids the use of PDN.
The ISP roaming scenario relies on the data bearer to transmit the mobile-station packets up to the H-PLMN (that is, using the mobile-station IP address for routing), whereas the GRX scenario uses the GPRS transport bearer (that is, forwarding GTP traffic does not use the mobile-station IP user address by itself). The GRX scenario is the MNO short-term preferred method for accessing home-based services.
IPV6 IN THE UMTS MOBILE WIRELESS INFRASTRUCTURE
Figure 7 summarizes the areas where IPv6 may appear in the 3GPP mobile wireless architecture.
Figure 7
IPv6 Areas in a Mobile Wireless Architecture
ARCHITECTURE
Compared to Figure 5, IPv6 obviously appears where IP can be used as a data bearer or as a transport bearer. The difference is generally defined in the 3GPP specifications. The specifications describe the use of IPv6, recommending it as mandatory or optional and also giving indications about how to introduce, migrate, or coexist with IPv4 implementation and networks.
IPV6 IN 3GPP SPECIFICATIONS: AN OVERVIEW
The wireless mobile market is perceived as one of the main factors for IPv6 adoption in Europe. In other countries within the Asia Pacific region for which there is a lack of IPv4 address space, additional factors include growing Internet adoption and adoption of Internet-connected appliances.
In 3GPP, IPv6 might appear in four different areas, two at the user level (data-bearer level) and two in the PLMN or transport-bearer level, as shown in Figure 7.
User Layer
At the user layer, IPv6 is available for optional use for GPRS data either for 2G GPRS or 3G. Adoption is left up to a mobile provider's discretion.
Also concerning user traffic, IPv6 has been originally mandated exclusively for the IMS in UMTS Release 5. Since then, IPv4-based user equipment (UE) and IMS dual-stack user equipment have been introduced in the IMS specifications. Internetworking and migration scenarios between IPv4-based IMS and IPv6-based IMS are ongoing working items that should be completed as part of 3GPP Release 6.
To support IPv6 on the user layer, all involved network elements (that is, mobile station and SGSN recognizing the IP address field for charging purposes, GGSN and also various network services used for billing, address provisioning, and name services, including Domain Name System [DNS]) have to support IPv6. As of today, the main focus area is in the delivery of commercial IPv6 services at the two endpoints-the user equipment and the applications. Internetworking and coexistence also are becoming important topics as the service goes beyond the mobile operator network. For this, the peering node is an important element.
Transport Layer
At the transport layer, IPv6 is specified as mandatory (but a full IPv4 solution is still valid) for the IP UTRAN mode, as specified as part of 3GPP Release 5. Because other protocols are included in the UTRAN architecture (for example, ATM and GTP, which is IP over ATM), it is not sufficient to have a native IPv6-only model. An IPv4-IPv6 dual-stack network is considered more appropriate, and the choice of introducing a new IP version is left to the mobile operator.
Also at the transport layer, the GTP can use IPv6, and this has been an option since GSM Release 97 for 2G GPRS. However, this option has been left open in the specifications, so real deployment will depend on implementation by the radio vendors and operator choices.
IPV6 FOR USER TRAFFIC
As mentioned earlier, IMS will be the most important factor for the adoption of IPv6 within mobile operator networks.
IMS is not an application but rather a framework to offer Session Initiation Protocol (SIP)-based applications on a GPRS bearer. It is based on three primary technologies:
• SIP as the control plane for the establishment of IMS sessions
• IPv6
• Diameter for authentication, authorization, accounting (AAA) and billing
Examples of IMS-based applications include Push-To-Talk over cellular or rich voice applications based on voice over IP (VoIP). Other aspects of IMS are QoS enforcement at Layer 2 (radio bearer) and Layer 3 (IP), authentication and security, and charging and support of multiple types of devices. Many IMS network elements (marked green in Figure 8) have been placed within the PDN, and all require an IPv6 address.
Figure 8
IMS in the UMTS Architecture
Splitting the control plane from the data plane when looking at multimedia, peer-to-peer, always-on applications naturally affected the consideration of IPv6 for the user plane. However, because mobile operators are keen to develop and offer new applications to take advantage of SIP, the original forced adoption of IPv6 by IMS has been debated among MNOs. Despite its limited scalability, IPv4 could be used within the IMS model for initial IMS deployments. Moreover, considering that all SIP-enabled peer devices will not immediately adopt IPv6, 3GPP modified the exclusive statement of IPv6 to allow IPv4. The following extract from 3GPP TS23.221 confirms this:
"3GPP specifications design the IM CN subsystem elements and interfaces to exclusively support IPv6. However, early IMS implementations and deployments may use IPv4."
This statement reinforced the discussions and the work on SIP, IPv6, and IPv4 and IPv6 internetworking.
Note that 3GPP2 also adopted IMS, called MultiMedia Domain (MMD), which will eventually allow for the convergence of mobile architectures. However, in 3GPP2 MMD IPv6 is optional. The IMS architecture is currently being considered for adoption by other standards bodies worldwide, including the European Telecommunications Standards Institute, for their next-generation networking projects.
Currently, most IP traffic from the mobile station is IPv4. Adoption of IPv6 will probably take a few more years because of multiple factors, including availability of IPv6 mass-market handsets, applications for IMS based on a SIP framework supported by both 3GPP and IETF, and also the IMS and GPRS support-node infrastructure. However, mainly because of the growth of IMSs and expected numbers of data users, the support of IPv6 by MNOs should be considered now.
The speed of IPv6 adoption in the mobile wireless world also depends upon several other factors, including:
• Government standards
• Mobile data service strategies
• Market situations and rates of mobile data subscriber adoption
• CapEx and OpEx reductions
• Agreement of implementation of IPv6 SGSN support by roaming partners
The prudent approach for commercial services is to build a reliable IP backbone based on well-known technologies to serve current needs and technologies (for example, GPRS), and then to transport IPv6 on top of it. This is the approach enabled by some of the transition and coexistence tools. One of these tools is 6PE, one of the IPv6-over-MPLS solutions. 6PE does not preclude the use of any other coexistence tools such as 6-to-4 tunneling, Intra-Site Automatic Tunnel Access Protocol (ISATAP), dual stack, Network Address Translation-Protocol Translation (NAT-PT), Stateless IP/ICMP Translation Algorithm (SIIT), or bump-in-the-stack. Those mechanisms will surely be complementary to MPLS 6PE. For example, a dual-stack server would be necessary to provide the same application over IPv4 and IPv6, or ISATAP, which is a recent addition to the 3GPP IETF Dependencies list for encapsulating IPv6 over IPv4 from the handset.
6PE provides the same capabilities, flexibility, and scalability of an IP/MPLS backbone to IPv4 and IPv6. It includes fast forwarding and traffic engineering (including Cisco MPLS Fast Reroute [FRR], VPN, and Cisco MPLS-Aware Differentiated Services [DiffServ] in Cisco IOS® Software) without destabilizing the construction of the backbone. All IPv6 functions are processed at the edge, helping enable a smooth insertion of IPv6 traffic. 6PE avoids the business risk of not being IPv6-ready and also avoids the risk of modifying the backbone right away.
IPV6 FOR THE TRANSPORT BEARER
As mentioned earlier, on the transport side two parts of the infrastructure must be considered. Referring to the 3GPP terminology, the core network and RAN can make use of IPv6.
In 3GPP core networks, IPv6 is optional. Core-network transport uses GTP to support the mobility of the mobile station in relation to the GGSN. Note that in 3GPP2 CDMA, this function is performed either by a generic-routing-encapsulation (GRE) tunnel or with Mobile IP.
GTP is a Layer 3 encapsulation protocol used in core networks and for PLMN roaming through a GRX operator, for instance. It appeared with the first release of GPRS Release 97. GTP can use IPv4 or IPv6. Because there is no compelling reason to use IPv6, it is optional. As previously discussed and as shown in Figure 9, the IP version of the transport bearer (here it is the GTP IP layer) is independent of the IP data bearer.
Figure 9
GTP Encapsulation
If the IPv6 option is considered, MPLS 6PE can easily enable such deployment. For the mobile operator intra-PLMN GTP traffic, the same MPLS network can support whatever IP version of GTP is required because the mechanism is the same as the GPRS IMS data bearer traffic previously described. The now IPv6 PLMN core network can quickly be supported, in that case because the IMS IPv6 traffic (user traffic) and the GTP traffic (operator traffic) might use the same MPLS provider edge devices, adding CsC to connect separate IPv6 domains. Also the MPLS 6VPE capability, the Border Gateway Protocol (BGP)-MPLS VPN extension for IPv6 VPN over IPv4 or IPv6 (including MPLS) infrastructures, could be used for traffic separation. Indeed, if a VPN has been created based on IPv4 for GTP traffic, usually the case, the 6VPE (RFC 2547bis extension for IPv6) would be enabled using the same VPN configuration for both GTP versions.
GRX OPERATION
The GRX is the preferred deployment for GPRS roaming. The GRX is a dedicated IP transport network, owned by the operator or by a trusted partner, also called the GRX operator. It is used to route GTP traffic from the visited network to the home network. Only the GTP IP header is relevant for the routing. The GRX is used to transport any GPRS traffic and may require support of IPv6 (that is, when IPv6 is required on the transport layer).
A GRX operator should provide a VPN that groups the different mobile operators that have a common roaming agreement. An IP/MPLS network is thus very flexible whether IPv4 or IPv6 is agreed upon between the two roaming operators.
Other mechanisms could be considered for a GRX network, such as dual stack or tunneling. Dual-stack GRX, like dual-stack backbones, requires more investigation into the design and knowledge of security in particular. If a mobile operator is considering tunneling methods, such as 6-to-4, it would be more efficient to remain in IPv4 for the GTP transport layer. Operators that carefully evaluate their OpEx would benefit from MPLS in deploying 6PE or 6VPE devices at the edge.
RADIO ACCESS NETWORK
The UTRAN specifications up to Release 4 mention ATM only as the transport method. However, as shown in Figures 5 and 7, as early as UMTS R99, GTP tunnels are terminated to the RNC. This means that for the interface for packet-switched data (Iu-ps), IP is transported over ATM. Note that it is feasible to terminate the ATM virtual channel connection (VCC) of GTP to transmit this IP traffic over an MPLS VPN, for example, the one used for the core network.
Within UMTS Release 5, the radio transport can be based on IP while ATM remains a valid option. When ATM is said to be required before Release 5, it is because the radio equipment that has interfaces (Iub, Iur, or Iu) in the RAN must use ATM. Thus, from Release 5, using IP enables the use of any data link layer in the RAN, including ATM.
In IP RAN (Iu, Iur, and Iub interfaces starting in Release 5), the way IPv6 should be positioned has been carefully considered. For the specification of Iub and Iur interfaces, IPv6 is mandated and IPv4 is optional, not precluding single implementation and use of IPv4. If both IPv6 and IPv4 can be used, dual-stack support is recommended. This aligns the requirements of both 3GPP working groups for core networks and RAN, considering the overlap as shown in Figure 10.
Figure 10
IP UTRAN Reference Interfaces and Transport Layer Coverage
MPLS permits the transport of IP RAN traffic, whatever version is used. However, MPLS might not be deployed up to cell sites, for example, because of its additional overhead, but can be used on some preaggregation sites when close to backbone points of presence or in metropolitan areas. MPLS also can permit the transport of traditional RAN traffic. The reference here is the IETF's Pseudowire End-to-End Emulation (PWE3) workgroup. This technology that can use MPLS with Label Distribution Protocol (LDP) control plane (or IP with Layer 2 Tunneling Protocol Version 3 [L2TPv3] control plane) encapsulates Layer 2 and Layer 1 traffic like ATM, Frame Relay, or TDM over packet networks. Hence, MPLS can ease the migration to IP RAN and also provide a coexistence mechanism for traditional RAN traffic. It is well-understood that for meeting service requirements the network must provide a high degree of reliability and scalability. MPLS is a primary component of mobile operator backbones as well as an important technology for next-generation all-IP mobile networks, Figure 11.
Figure 11
MPLS in the Next-Generation RAN
MPLS FOR INTRODUCING IPV6 IN MOBILE WIRELESS NETWORKS
2G GPRS, as well as the different releases of 3G UMTS and the evolution of GSM to GSM/Enhanced Data Rates for GSM Evolution (GSM/EDGE) require different transport protocols and functions. The transport requirements differ from one mobile operator to another, and they depend on the operators' migration strategy. For example, 2G requires TDM circuits and Frame Relay for the RAN, whereas the early releases of 3G mandate ATM (on top of Plesiochronous Digital Hierarchy [PDH] or SDH links). Even if upcoming 3G releases introduce IP more intensively, this does not preclude keeping ATM in UTRAN and TDM in GSM EDGE Radio Access Network (GERAN). Also as an option, the operator can choose to deploy IPv4 or IPv6. Operators can define their own deployment scenarios based on:
• The defined strategy, including risk assessment
• The radio vendor support of this strategy
• The availability of new technologies
REQUIREMENTS FOR MOBILE WIRELESS IP NETWORKS
Considering the expected growth of IP traffic due to increasing data traffic, IP networks must be scalable, flexible, and feature-rich. The following topics must be addressed:
Security Requirements
The use of VPNs and their provisioning should be considered for both internal and external services (such as billing, management, and internal Gn versus Gp interfaces that require some external interfaces).
Addressing Design Issues
Because of IPv4 address allocation and cost, IPv4 private addressing should be considered when looking at closed internal services. Thus MPLS VPN helps manage overlap addressing.
Transport of Frame Relay (Gb) or ATM AAL5 and AAL2 (Iub, Iur, Iu)
If the service definition is well-known and -engineered, this solution should be considered specifically for ATM Adaptation Layer 2 (AAL2) and voice traffic. (Refer to the section Layer 2 over MPLS below.) The solution must be scalable and ATM services-aware (for example, it must be able to handle traffic delay and jitter, cell delivery, and order retention; track numerous virtual circuits; prioritize virtual-circuit transport between them and with other IP traffic; and support operation, administration, and maintenance [OAM] at the edges and in the backbone). Also, the different 3G UTRAN reference points must be considered separately.
QoS
QoS of all IP traffic (that is, GTP with appropriate marking, billing, management, and signaling; Short Message Service [SMS] offload; virtual trunking networks [VTNs]; and routing protocols) and any Layer 2-over-IP/MPLS traffic must be well-defined, -provisioned, and -managed. Strict guarantees should be in place for voice traffic specifically.
Reliability and Convergence
These variables must be tuned in the backbone as soon as critical traffic such as voice or Signaling System 7 (SS7) is carried over it.
Optimization of the Bandwidth in the Backbone
This should be provisioned and managed according to traffic and service-level agreement (SLA) reports.
INTRODUCTION OF IPV6
In a smooth and low-risk scenario, IPv6 has to be considered for future IMS and IP UTRAN environments. IPv6 must be considered potentially sooner in some markets or geographies for GPRS data that can optionally use and benefit from IPv6.
MPLS-based networks take advantage of multiple applications that MPLS technology enables, including:
• MPLS VPN for security and private addressing
• MPLS CsC to enable one MPLS VPN-based service provider to allow other service providers to use a segment of its backbone network
• MPLS QoS with strict priority and optimal congestion avoidance
• MPLS traffic engineering for bandwidth efficiency
• MPLS FRR with traffic-engineering link and node protection in multiples of 10 ms below 100 ms for fast restoration and high scalability
• MPLS DiffServ traffic engineering for building strict point-to-point guarantees
• MPLS Traffic Engineering Autobandwidth Allocator to automatically adjust the bandwidth of a traffic-engineering tunnel and easily provide traffic statistics between two endpoints
• MPLS AToM with QoS, traffic engineering, DiffServe traffic engineering, FRR, and sequencing guarantees to capably support Layer 2 protocols over MPLS
• MPLS 6PE for incremental, risk-controlled upgrades or deployment, directed by business factors and with strict cost control; this permits the use of other MPLS applications such as traffic engineering that an IP-only setup does not provide and evolution to IPv6 VPN (using 6VPE)
• Interior Gateway Protocol (IGP) and BGP or multiprotocol BGP (MPBGP) tuning for convergence optimization
• Carrier-class dependability with high-availability equipment and MPLS high availability (in the Cisco roadmap)
CONCLUSION
In the current market climate, an IP architecture has to be flexible and feature-rich to help the mobile operator increase or maintain market share. The network should facilitate the introduction of data services, one of the main factors of the UMTS technology and the main factor for revenue generation in the mobile market.
Figure 12 summarizes how IP/MPLS can serve as a feature-rich convergence infrastructure for mobile wireless service providers either directly for the mobile service provider PLMN and home PDN networks or indirectly when using ISP, shared split RAN, or GRX networks based on MPLS.
Figure 12
MPLS for Mobile Wireless Networks
The Cisco Next-Generation Mobility Framework for Mobile Operators, based on a Cisco IP/MPLS network backbone, includes six technology pillars (Figure 13):
• Cisco IP/MPLS Backbone, a common transport and integrated management platform for the convergence of packetized data, voice, and video services over existing ATM, TDM, and Frame Relay networks
• Cisco Mobile Exchange, the intelligent mobile Internet edge solution set that links the RAN to IP networks and their value-added services; and simplifies and enhances service delivery independent of underlying access technologies with functions supporting service selection and control, flexible billing models, security, Mobile IP, and load balancing
• Cisco RAN optimization and pseudowire technologies, which take IP all the way to the cellular site and interoperate with leading wireless vendors, and can dramatically lower backhaul costs, improve cell site maintenance, and enable operators to more easily add 3G radios to a cell site
• The Cisco IP Transfer Point (ITP) platform, which increases SS7 signaling efficiency and lowers circuit costs by moving signaling traffic to IP, and can help mobile operators dramatically decrease the costs of services such as SMS, mobile-number portability, custom ring-tone downloads, and other resource-intensive new applications
• Cisco Mobile Voice solutions, including high-capacity, carrier-class voice gateways that offer standards-based support for VoIP and voice-over-ATM (VoATM) services; and wireless trunking that replaces traditional TDM trunking with aggregated VoIP transport between mobile switching centers
• Cisco Public and Private Wireless LAN solutions, which offer access points, access zone routers, and Cisco Mobile Exchange for service selection, content billing, and other features for consumer, enterprise, and service provider markets
Figure 13
Six Pillars of the Cisco Next-Generation Mobility Framework for Mobile Operators
BUSINESS TRANSFORMATION FOR MOBILE OPERATORS
IP is the foundation and base technology for the next-generation communications architecture. IP/MPLS is one stepping stone in the move to 3G and 4G network services where IP is of increasing importance. To help mobile operators manage the complexity of their existing array of networks and applications while introducing next-generation services cost-effectively, the Cisco IP Factory was created. Available through the Cisco Customer Advocacy Organization, the Cisco IP Factory helps mobile operators capture and simplify existing processes and technologies, creating modular service components. Successful application of this model can yield up to 20 to 25 percent in operational cost savings per year for MNOs.
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3GPP:
IMS: 23.221; 23.228; 23.981
GPRS data bearer and GTP: 23.060; 29.061
IP RAN: 25.414; 25.426
Cisco IOS Software Release specifics for IPv6 features:
Cisco IPv6 solutions (2004 and beyond):
IPv6 provider edge router over MPLS-Cisco 6PE
