This module manages Cisco's WiMAX ASN Gateway (ASN-GW).
A WiMAX network supports wireless data communication through
WiMAX radio (802.16) technology. 
        
The high level architecture of a first generation WiMAX network
with the respective protocols for each interface is shown below:
        
   +--------------------------------------------------------+
   |                                                     R2 |
+------+        +------+         +--------+                 |
|      |    R1  |      |   R6    |        |                 |
|  MS  |--------|  BS  |---------| ASN-GW |                 |
|      |        |      |         |        |---+             |
+------+        +------+         +--------+   |             | 
                   |                  |       |  R3      |-----|
               R8  |               R4 |       |----------| CSN |
                   |                  |       |          |-----|
+------+        +------+         +--------+   |             |
|      |   R1   |      |   R6    |        |---+             |
|  MS  |--------|  BS  |---------| ASN-GW |                 |
|      |        |      |         |        |                 |
+------+        +------+         +--------+              R2 | 
   |                                                        |
   +--------------------------------------------------------+
        
The diagram below depicts the relation of the subscriber to the
session and flows:
        
+--------+                       -Flow (connected via data path)
| ASN-GW | - Subscriber -Session -Flow (connected via data path)
+--------+                  |    -Flow (connected via data path)
                            |    -Flow (connected via data path)
                            |
                            +--- (connected via signaling path)
        
A subscriber initiates a call from a MS. A session is created
between the BS and the ASN-GW for that call. Multiple flows can
be created for the session with different QOS parameters. For
example one flow can created for a voice stream and another
for data. Data paths are created between the BS and ASN-GW to
forward the data packets of the created flows.
When the first subscriber from any MS connected to a BS
initiates a call via the BS to the ASN-GW, a signaling path is
created between the BS and the ASN-GW. There is only one 
signaling path between each BS and ASN-GW. Signaling paths 
and base stations can be used interchangeably.
        
The signaling and data paths remains active as long as there are
subscribers connected to the ASN-GW from any MS connected to the
BS. If a path has no session/flow connected, it will be purged
after a certain period of time. This situation can occur when
all subscribers on a certain path are disconnected. A subscriber
disconnecting from a certain path does not indicate that the
subscriber has left the network, it could simply be handing off
to a different path. 
        
The IP addresses of the signaling and data paths can be the same
or different both in the BS side and in the ASN-GW side.
        
+--------+              +--------+
| Base   |              | ASN-GW |
| Station|              |        |
|        |    SigPath   |        |
|  IP(B1)|<............>|IP(A1)  |
|        |              |        |
|        |              |        |
|        |  DataPath 1  |        |
|  IP(B2)|<............>|IP(A2)  |
|        |              |        |
|        |  DataPath 2  |        |
|  IP(B3)|<............>|IP(A3)  |
+--------+              +--------+
        
        
Relationships:
        
Base Station        1 to many         Mobile Stations
ASN-GW              1 to many         Base Stations
Subscriber          1 to 1            Sessions   
Session             1 to many         Flows
Datapath            1 to many         Flows
Signaling Path      1 to 1            Base Station
        
Acronyms and terms:
        
 AAA                AAA refers to a framework that specifies the
                    protocols procedures for authentications, 
                    authorizatitin and accounting associated 
                    with the user, MS and subscribed serviced.
        
 AGW                ASN-GW
        
 ASN                ASN (Access Service network) is defined as  
                    a complete set of network functions needed
                    to provide radio access to a WiMAX 
                    subscriber.
        
 ASN-GW             ASN-Gateway is a logical entity that 
                    represents an aggregation of Control Plane 
                    functional entities that are either paired 
                    with a corresponding function in the ASN 
                    (for e.g BS instance) a resident function is
                    the CSN or another functions in the ASN.
                    For every MS, a BS is associated with 
                    exactly one default ASN-GW. However,
                    ASN-GW functions for every MS may be 
                    distributes amongst multiple
                    ASN-GWs located in one or more ASNs. The
                    ASN-GW utilizes Session Redudancy to ensure
                    a backup ASN-GW is available in case the
                    primary ASN-GW goes down.
        
 BS                 Base Station is a logical entity that 
                    represents an aggregation of Control Plane 
                    functional entities that are either paired 
                    with a corresponding function in the ASN
                    (e.g. BS instance), a resident function
                    in the CSN or a function in another ASN. The
                    ASN-GW may also perform Bearer Plane routing
                    or bridging function.
        
 BSID               The Base Station Identifier is a global
                    unique identifier for a WiMAX base station.
        
 CPE                Customer Premise Equipment.
        
 CSN                CSN (Connectivity Service Network) is 
                    defined as a set of network functions that 
                    provide IP connectivity services to the 
                    WiMAX subscribers. 
        
 Data Path          Corresponding to each subscriber, data paths
                    are created to foward packets between the 
                    ASN-GW and the subscribers.
        
 DPID               Data Path ID is used to identify the tunnel
                    carrying MS traffic between ASN gateways or
                    between the ASN gateway and base station.
                    As of 8/28/07, only the GRE key is to be
                    used as the DPID.
        
 Flow               A service flow is a unidirectional logical
                    flow between the network and the Subscriber
                    Station. A service flow is created to handle
                    a different QoS over the connection oriented
                    MAC. A subscriber can have multiple service
                    flows associated and each service flow is
                    associcated with an uplink and downlink
                    classifier. 
        
 GRE                Generic Routing Encapsulation. Refer to
                    RFC 1701 for more details.
        
 LB                 Load Balancing
        
 Messages           Messages are packets exchanged on the
                    signaling paths.
        
 MS                 The Mobile Station is a generalized mobile 
                    equipment set providing connectivity between
                    subscriber equipment and a base station (BS)
                    The Mobile Station may be a host or a CPE 
                    type of device that can support multiple 
                    hosts.
        
 MSID               The Mobile Station Identifier is the 802.16 
                    identifier used for all subscriber stations,
                    and is used in all the messages over R6. The
                    identifier associates all requests from a 
                    mobile to the ASN-GW.
        
 Packets            Packets are datagrams fowarded over the data
                    paths.
        
 R1                 Communication protocol between mobile and BS
                    as per the air interface (PHY and MAC)
                    specifications (IEEE P802.16d/e). R1 may
                    include additional protocols related to the
                    management plane.
        
 R2                 The interface between the MS and CSN 
                    associated with Authentication, 
                    Services Authorization, IP Host 
                    Configuration management, and mobility
                    management. This is a logical interface thus
                    does not reflect a direct protocol interface
                    between MS and CSN.
        
 R3                 The interface between the ASN and the CSN to
                    support AAA, policy enforcement and mobility
                    management capabilities. It also encompasses
                    the bearer plane methods (e.g., tunneling)
                    to transfer IP data between the ASN and the
                    CSN.
        
 R4                 Communication protocol between ASN-GWs.
                    R4 consists of a set of control and bearer
                    plane protocols originating/terminating in
                    various entities within the ASN that 
                    coordinate MS mobility between ASNs. 
                    In Release 1, R4 is the only interoperable 
                    interface between
                    heterogeneous or dissimilar ASNs.
        
 R5                 Consists of a set of control plane and 
                    bearer plane protocols for internetworking 
                    between CSNs operated by either the home or
                    visited NSP.
        
 R6                 Communication protocol between ASN-GW and BS
                    R6 consists of a set of control and bearer
                    plane protocols for communication between 
                    the BS and the ASN GW.
                    The bearer plane consists of intra-ASN 
                    data path or inter-ASN tunnels between the
                    BS and ASN-GW.
                    The control plane includes protocols for
                    IP tunnel management (establish, modify, and
                    release) in accordance with the MS mobility
                    events. R6 may also serve as a conduit for
                    exchange of MAC states information between
                    neighboring BSs.
        
 R8                 Communication protocol between base 
                    stations.
                    R8 consists of a set of control plane 
                    message flows and, in some situations, 
                    bearer plane data flows between the 
                    base stations to ensure fast and seamless
                    handover.
                    Bearer plane consists of protocols that 
                    allow the data transfer between Base 
                    Stations involved in handover of a 
                    certain MS.
                    Control plane consists of the inter-BS 
                    communication protocol defined in IEEE 
                    802.16 and additional set of protocols 
                    that allow controlling the data
                    transfer between the Base Stations involved
                    in handover of a certain MS.
        
 Session            Session is a connection between one or more
                    MS and a network element in order to
                    exchange link-level frames or packets. 
        
 SFID               The service flow is identified using a SFID
                    (Service Flow Identifier). 
        
 Signaling Path     A signaling path exists between the BS and
                    ASN-GW, and is used for all signaling such 
                    as creating, dleteing, authenticating, 
                    as we as additional functions related to 
                    the subscriber. 
        
 SR                 Session Redundancy
        
 Subscriber         The 802.16 subscriber entity connects over
                    the 802.16 airlink, and eventually results
                    in the creation of the subscriber object at
                    the ASN-GW.
        
 UHO                Unpredicitive Handoff 
        
 PMIP               Proxy Mobile Internet Protocol 
        
 HA                 Home Agent 
        
REFERENCE
        
[1] WIMAX Forum Network Architecture,
    (Stage 3: Detailed Protocols and Procedures)
    Release 1.1.1 September 14, 2007.