Access Service Network Gateway In WiMAX

Transcription

1 Access Service Network Gateway In WiMAX This paper discusses the Access Service Network Gateway (ASN-GW) Architecture and its profiles. ASN-GW profiles are designed with a vision of keeping the ASN-GW interoperable, scalable, and fault tolerable.

2 About the Domain TCS is involved in many trendsetter technology developments in the Telecom field. It works on fourth generation WiMAX and LTE telecommunication protocol. 1

3 About the Author Shrawan N. Jha Shrawan has over 4 years of experience in the development of different protocol stacks for networking technologies spread across Bluetooth, WiMAX and LTE. Suresh Babu Angadi Suresh has over 8 years of experience in the development of different protocol stacks for networking technologies spread across GSM, GPRS, UMTS, WiMAX and LTE. Keywords : ASN GW, Wimax, e, Access service network, Interface,ASN Gateway, Gateways 2

4 Table of Contents 1. Abbreviations 4 2. Introduction 5 3. ASN-GW: A Network Entity 6 4. ASN-GW Architecture 7 5. ASN Profiles 10 Profile A 10 Profile B 12 Profile C Conclusion References 15 Figures Figure 1: ASN-GW In WIMAX Network 5 Figure 2: ASN-GW Functionality Segregation 7 Figure 3: Typical Components of an ASN-GW 8 Figure 4: Data Plane of ASN-GW in WIMAX Network 10 Figure 5: ASN Architecture for Profile A 11 Figure 6: ASN Architecture for Profile B 12 Figure 7: Interoperability of Profile B ASN With ASN of Profiles B and C Over R4 Interface, 12 Figure 8: ASN Architecture for Profile C 13 Tables Table 1: Challenges of ASN-GW Development 7 Table 2: Comparison of Three Profiles of ASN-GW 12 3

5 Abbreviations AS AR ASN ASN-GW BS CSN DCD DP EP FA GRE MAC MIP NAS NWG OFDMA QoS PDU PHY RRC RRM SFA SFM UCD WiMAX Access Stratum Access Router Area Service Network Area Service Network Gateway Base Station Connectivity Service Network Downlink Channel Descriptor Decision Point Enforcement Point Foreign Agent Generic Routing Encapsulation Medium Access Control Mobile Station Mobile IP Non Access Stratum Network Working Group Orthogonal Frequency Division Multiple Access Quality of service Protocol Data Unit Physical Layer Radio Resource Control Radio Resource Management Service Flow Authenticator Service Flow Management Uplink Channel Descriptor Worldwide Interoperability for Microwave Access 4

6 Introduction The high data rate demand for applications such as real-time audio, video, online gaming, service on demand, and live conference has always kept challenges way ahead of available technical dexterity. WiMAX with very high data rate [4] and huge spectral radius along with OFDMA based IP technology is well equipped to overcome the above challenges. Efficient back-end support for different sizes of base stations and handling data hungry applications are possible because of all the IP technology used. Mobile WiMAX is based on the IEEE e-2005 standard and WiMAX Forum Network Working Group (NWG) specification. The IEEE e-2005 standard specifies the PHY and MAC requirements and provisions for the mobile WiMAX. WiMAX network comprises of mobile station (), Access Service Network Gateway [that is, ASN comprises of base station (BS), Access Service Network Gateway (ASN-GW)] and Connectivity Service Network (CSN). Fixed SS Fixed SS CSN Fixed SS R8 BS R4 ASN GW R5 BS CSN Other Network ASN GW R1 interface Figure 1: ASN-GW in Wimax Network The Mobile Station is the end-user equipment for forwarding and receiving network data according to the user s subscription. It connects with the Base Station over air and with ASN-GW or CSN using a logical interface. The Base Station is the next hop in the network, which mainly deals with the air interface between and itself for better service quality. It takes care of registration and connectivity of in the network. The ASN-GW can be seen as a network entity, in the WiMAX network, between Base Station (BS) and Connectivity Service Network (CSN), and broadly helps in service flow management, mobility, authentications, accounting, and MIP management in home and visiting networks. Its interfaces with BS, other ASN-GWs and CSN have been shown in the Figure 1: ASN-GW in Wimax Network. Interaction between ASN-GW and BS can be one to many or many to one. The same kind of interfaces between ASN-GW and CSN is also possible. 5

7 The ASN-GW is a combination of Control Plane and Bearer Plane routing or bridging functionality. The ASN-GW operational functionalities are present as corresponding functionalities in Base Station and the CSN. At any particular moment of time a subscriber in the network has to associate with exactly one default ASN-GW while several ASN-GWs along with the serving ASN-GW can collectively provide services. This paper has four main sections, which throw light on ASN-GW s role in the network, architecture and its different profiles. ASN-GW A Network Entity ASN-GW Architecture ASN-GW Profiles Conclusion Discusses different roles for ASN-GW Explains the functional relationship among the different components of the ASN-GW Highlights different options available for a vendor to manufacture an ASN-GW and their impact on interoperability Author s comparison of different profiles of ASN ASN-GW: A Network Entity Functionality This section deals with requirements of the ASN-GW in the WiMAX network. ASN-GW handles the following aspects of the network: Effective traffic load sharing among Base Stations: A serving BS can have home and visiting subscribers with limited bandwidth spectrum which may not be sufficient for providing services with guaranteed Quality of Service (QoS) for any further incoming subscribers. Here ASN-GW can help in load sharing of this serving BS with other attached BSs and ensure new subscribers with guaranteed QoS. Handling mobility at ASN and CSN level for efficient use of radio spectrum and network resources: Handover can happen at different spectral spans of ASN or CSN. In both the cases, the role of ASN-GW s control and the bearer plane is crucial for effective and smooth network connectivity. Accounting and billing in the WiMAX network: ASN-GW can effectively participate in Accounting and Billing at ASN as well as CSN level. Challenges Stakes are high for a network entity which exists at the core of the network and manages load balancing, traffic routing, mobility, accounting, and monitoring QoS for numerous subscribers. Though the following points are not crucial from the development angle, they are critical for better business. 6

8 Table 1: Challenges of ASN-GW development Reliability Reliability or fault tolerance is no doubt the first priorities of the customer as well as any other stakeholder. Reliability can be achieved by two methods: (1) Redundancy in the network (2) Adopting a design such that even if one node fails, it still acts as a relay and forwards the subscribers request of service to a nearby similar node, thereby providing another node (and network) an opportunity to serve the subscriber. Scalability Being in the most competitive and evolving time of the telecom industry, each product should have the capability to handle any possible increase in traffic and also the ability to work with any other corresponding network entity of an existing or a proposed network. Manageability Providing runtime configuration, control over different attributes, monitoring, and policy definitions will together help in better manageability. ASN-GW Architecture ASN-GW functionality can be grouped in two different sets of functions, namely, the Decision Point (DP) and the Enforcement Point (EP). The EP includes bearer plane functions and DP contains control plane functions. DP functions in any ASN-GW may interact with multiple ASN-GWs as shown in the Figure 2. R7 BS Decision Point Enforcement Point CSN R4 ASN-GW 1 ASN-GW 2 ASN-GW 3 Figure 2: ASN-GW functionality segregation 7

9 A typical ASN-GW contains components, which can be segregated in bearer plane and the control plane. Control and the bearer plane are shown in the Figure 3 Authenticator MIP AR Key Distributor MIP FA Tunneling Paging Controller Policy Function Hand Over Relay Service Flow Data Forwarding Data Path Function RRC Relay Control Plane Data Plane ASN-GW Figure 3: Typical components of an ASN-GW 8

10 Authenticator Enforce authentication before allowing access to services that are accessible to the subscriber () attached to the other end of the network. Data Path function Handles the bearer plane functionality of data transfer between BS and CSN in the uplink and from CSN to BS in the downlink. Handover Relay Helps in mobility at ASN-GW and CSN level. Key distributor Enabling authentication key distribution MIP FA Stores information about the subscriber visiting another network and advertises care-of addresses. MIP AR Performs registration of in the visiting CSN in CSN level mobility scenario. Paging Controller Controls the procedure used by the network to seek an in an idle mode in the coverage area of a predefined set of BS identified by a Paging Group at ASN-GW level. Policy Functions Manages the policy and rules applicable to QoS, billing, and authentication. RRC relay RRC functions in BS, controls its local RRA functions, and also communicates to its neighboring RRCs in other BSs. Release 1.00 does not support RRC-RRC communication directly from BS to BS, so it is relayed through ASN_GW (or ASN-GWs). RRC relay in ASN- GW helps in RRM signaling communication between ASNs of all profiles A, B, and C. SFA Controls and authenticates service flow creation, modification and deletion at ASN-GW level. The Bearer Plane consists of Tunneling and Data Forwarding functions. Tunneling function makes use of the GRE protocol to encapsulate user payload and send it over IP protocol as shown in Figure 4: Data Plane of ASN-GW in WiMAX network. 9

11 R1 Payload IP Forwarding IP Routing MAC MAC GRE IP GRE IP IP IP PHY PHY BS ASN - GW CSN Figure 4: Data Plane of ASN-GW in WiMAX network In Figure 4, MAC PDU in BS will be encapsulated using the GRE protocol and then using IP protocol it will be sent over interface. When some data is to be forwarded from ASN-GW to BS, ASN-GW will first encapsulate its data using GRE protocol and then send it over IP. Once BS will receive the ASN-GW packet, it will remove the GRE header and forward it to concerned subscriber. Between ASN-GW and CSN, the IP protocol is used for data transfer. ASN Profiles WiMAX Forum Network Architecture came up with three ASN profiles (A, B, and C) with three different possible implementations. Inter ASN interoperability is maintained in all the three profiles and ASN-GW of any ASN Profile (A, B, or C) should be capable of interoperating with other ASNs of any profile type. In Profile A, ASN-GW controls the overall handover procedure. Profile B has a design of closed system ASN where there is no exposure of interface and all of ASN-GW functionalities are implemented inside BS, which leaves very little scope for functional optimization. In Profile C ASN functions are distributed across the ASN-GW and the Base Station. Profile A ASN functions in profile A are distributed between ASN-GW and BS. The main characteristics of profile A are: HO Control is in the ASN GW RRC is in ASN GW that allows RRM among multiple BSs ASN centered mobility among BSs should utilize and R4 physical connections. 10

12 RRC R1 RRA RRM HO control BS 1 ASN-GW 1 R4 RRC R1 RRA RRM HO control BS 2 ASN-GW 2 Figure 5: ASN architecture for profile A In the Figure 5, in the left is attached with the ASN-GW 1 and BS 1. As this ASN is of profile A, the handover control functionality is in ASN-GW. The broken line on the left shows movement towards BS 2. The mobility of is managed using and R4 interface as BS 2 is connected with only ASN-GW 2 and not with ASN-GW 1. RRC in ASN-GW enquires spare capability of BSs which report to it and it may become possible to target BS. RRC in ASN-GW can also query physical layer parameters from BS for QoS adjustment or triggering handover and critical resource configuration from RRA in BS such as DCD and UCD burst profile changes. RRC in ASN-GW may inform BS about the current load situation of its neighbor BSs which can be passed to for better handover decision making. 11

13 Profile B ASNs falling under Profile B category are characterized by undivided ASN-GW and BS functions as shown in the Figure 6 BS Functionality ASN-GW Functionality Profile B Figure 6: ASN architecture for profile B However this peculiarity does not deter its interoperability with other ASNs of any profile type through an R4 interfaces. Inter-ASN centered mobility should be possible through R4. Undivided functions between ASN-GW and BS in profile B provide less flexibility to vendors and manufacturers to deal with scalability. Profile A ASN Profile C ASN R4 R4 R1 Profile B ASN CSN Figure 7: Interoperability of profile B ASN with ASN of profiles B and C over R4 interface In the Figure 7, ASN of profile B and its interaction with the other ASNs of different profiles have been shown. Profile B ASN has a closed system design and there is less scope of functional optimization for manufacturers and vendors. Monotonous design does not hinder its capability of interaction with other ASN of different profiles through R4 interface. 12

14 Profile C ASN of profile C has its functions mapped into ASN-GW and BS. Functional distribution in this ASN is as follows: Handover control in BS RRC and RRM exist in BS. There is an RRC Relay in ASN-GW for relaying RRM messages from one BS to other BS through interface. ASN centered mobility among BSs should utilize and R4 physical connections similar to profile A. R1 RRC HO control RRM relay BS 1 ASN-GW 1 R4 R1 RRC RRM relay HO control BS 2 ASN-GW 2 Figure 8: ASN architecture for profile C In Figure 8, in the left is attached with the ASN-GW 1 and BS 1. In profile C ASN handover control functionality lies in BS. Broken line on the left is showing movement towards BS 2. Mobility of is managed using and R4 interface because BS 2 is connected only with ASN-GW 2 and not with ASN-GW 1. RRC in the serving BS may retrieve the current load situation of any neighboring BS for a handover decision by forwarding the request through RRM relay in the ASN-GW as it cannot communicate with the other BSs directly. RRC in the serving BS can enquire critical radio resource configuration such as DCD and UCD burst profile from other BSs through the RRM relay. 13

15 Table 2: Comparison of three profiles of ASN-GW compares all three variants of ASN-GW on the various design issues. Table 2: Comparison of three profiles of ASN-GW Differentiators Profile A Profile B Profile C Scope for functional optimization Limited Scope Scope is absent More scope Interoperability Supported Supported Supported Bulkiness Less bulky than B Bulky Least Bulky More control Less control Less control More control Handover control Present in ASN-GW Present in ASN-GW Absent in ASN-GW Complexity Less complex Complex Simplest Proprietary solution Not Suitable Suitable Not Suitable 14

16 Conclusion Profile B has the design of the closed system ASN, and is recommended for a manufacturer who is providing a complete end-to-end ASN solution. It is less flexible, complex, and monotonous but these design issues do not hinder its interoperability with other types of ASN profiles. ASN-GW of Profile A is very similar to the profile C in the approach but still lacks the simplicity of profile C ASN-GW. Profile C is ideal to ensure the multi vendor network component s interoperability because of its modular approach and scope for functional optimization. ASN-GW of profile C is less bulky in functionality and comparatively more powerful because of the presence of different relays. References 1. WiMAX Network Architecture Stage 2-3 Release documents. 2. WiMAX forum (URL as on Tuesday, November 04, 2008). 3. WIMAX.COM (URL as on Tuesday, November 04, 2008). 4. WIMAX.COM (URL as on Wednesday, June 17, 2009) Or 2.2 section of book Fundamentals of WiMAX: Understanding Broadband Wireless Networking Or WiMAX forum (URL as on Wednesday, June 17, 2009). 15

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