Cisco ASR 5000 Series, Обзор продукта

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ASN Gateway Overview
▀ Supported Features
▄ Cisco ASR 5000 Series Product Overview
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addresses from subscriber profiles during authentication from a AAA server. Alternatively, the ASN-GW uses a DHCP
relay process to forward the DHCP request to an external DHCP server.
In a Proxy Mobile IP use case, the ASN-GW uses a DHCP proxy to trigger a local foreign agent function to initiate a
Mobile IP Request via the R3 interface to a home agent. The home agent returns the address via the Mobile IP
Response. The DHCP Proxy component on the ASN Gateway conveys the address in a DHCP Response message to the
DHCP client running on the user‘s access device.
This solution enables mobility on intra-ASN handovers between neighboring base stations. It also permits inter-ASN
mobility via an R4 interface between ASN Gateways.
ASN Gateway Micro-Mobility
ASN Gateway micro-mobility provides ASN Gateway-anchored L2 handovers. This low-latency procedure assures the
seamless mobility of mobile access devices within a WiMAX network. The ASN Gateway supports both uncontrolled
and controlled handovers for micro-mobility.
Uncontrolled Handovers
In an uncontrolled handover scenario, a mobile subscriber attempts to re-enter the WiMAX network at a target base
station without the handover preparation procedures with the serving base station. In order to authenticate the roaming
user, the target base station obtains the subscriber and security context information from the serving ASN. The anchor
authenticator ASN Gateway conveys the context response message and assists in the establishment of a new R6 GRE
bearer connection to the target base station. It is referred to as an L2 operation because the previously assigned IP
address for the binding remains the same on the anchor authenticator/data path ASN Gateway while the L2 BSID
(Ethernet MAC address) is updated for the target base station. Uncontrolled handovers are supported for both Simple IP
or Mobile IP use cases.
With uncontrolled L2 handover procedures, interactive and non-real-time applications incur minimal performance
degradation and packet loss during subscriber movement between cell sites.
Controlled Handovers
A controlled handover occurs when a subscriber access device explicitly requests handover assistance from the serving
base station to a new target base station. This process minimizes packet loss to the WiMAX access device. During the
handover request, the serving base station provides the subscriber‘s context information to the anchor authenticator
ASN Gateway and a list of target base stations that are preferred by the mobile device. Upon a successful response from
potential target base stations, the anchor authenticator ASN Gateway initiates a data path for the mobile subscriber to
the target base station. It also transfers all contextual information for the session to the target base station. The downlink
traffic for the mobile subscriber is simultaneously broadcast and subsequently buffered by each of the target base
stations.
Controlled handovers may be triggered by the mobile access device or the serving base station as a congestion overload
control mechanism.
Controlled handovers and associated data path pre-registrations minimize the impact on performance to a greater extent
than uncontrolled handovers and significantly reduce datapath outages.