Network Working Group F. Teraoka
Request for Comments: 5184 K. Gogo
Category: Experimental K. Mitsuya
R. Shibui
K. Mitani
KEIO University
May 2008
Network Working Group F. Teraoka
Request for Comments: 5184 K. Gogo
Category: Experimental K. Mitsuya
R. Shibui
K. Mitani
KEIO University
May 2008
Unified Layer 2 (L2) Abstractions for Layer 3 (L3)-Driven Fast Handover
用于第3层（L3）驱动的快速切换的统一第2层（L2）抽象
Status of This Memo
关于下段备忘
This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
这份备忘录为互联网社区定义了一个实验性协议。它没有规定任何类型的互联网标准。要求进行讨论并提出改进建议。本备忘录的分发不受限制。
IESG Note
IESG注释
This document is not an IETF Internet Standard. It represents the consensus of the MOBOPTS Research Group of the Internet Research Task Force. It may be considered for standardization by the IETF in the future.
本文件不是IETF互联网标准。它代表了互联网研究特别工作组的MOBOPTS研究小组的共识。未来IETF可能会考虑将其标准化。
Abstract
摘要
This document proposes unified Layer 2 (L2) abstractions for Layer 3 (L3)-driven fast handovers. For efficient network communication, it is vital for a protocol layer to know or utilize other layers' information, such as the form of L2 triggers. However, each protocol layer is basically designed independently. Since each protocol layer is also implemented independently in current operating systems, it is very hard to exchange control information between protocol layers. This document defines nine kinds of L2 abstractions in the form of "primitives" to achieve fast handovers in the network layer as a means of solving the problem. This mechanism is called "L3-driven fast handovers" because the network layer initiates L2 and L3 handovers by using the primitives. This document is a product of the IP Mobility Optimizations (MobOpts) Research Group.
本文档为第3层（L3）驱动的快速切换提出了统一的第2层（L2）抽象。对于高效的网络通信，协议层了解或利用其他层的信息（如L2触发器的形式）至关重要。然而，每个协议层基本上是独立设计的。由于每个协议层在当前的操作系统中也是独立实现的，因此很难在协议层之间交换控制信息。本文档以“原语”的形式定义了九种二语抽象，以实现网络层的快速切换，作为解决问题的手段。这种机制被称为“L3驱动的快速切换”，因为网络层使用原语启动L2和L3切换。本文档是IP移动性优化（MobOpts）研究组的产品。
Table of Contents
目录
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Primitives for L2 Abstractions ..................................4
4. Definitions of Primitives .......................................6
4.1. L2-LinkStatus (Type 1) .....................................6
4.2. L2-PoAList (Type 1) ........................................6
4.3. L2-PoAFound (Type 2) .......................................6
4.4. L2-PoALost (Type 2) ........................................6
4.5. L2-LinkUp (Type 2) .........................................7
4.6. L2-LinkDown (Type 2) .......................................7
4.7. L2-LinkStatusChanged (Type 2) ..............................7
4.8. L2-LinkConnect (Type 3) ....................................7
4.9. L2-LinkDisconnect (Type 3) .................................8
5. Definitions of Static Parameters ................................8
5.1. Network Interface ID .......................................8
6. Definitions of Dynamic Parameters ...............................8
6.1. PoA (Point of Attachment) ..................................8
6.2. Condition ..................................................8
6.3. PoA List ...................................................9
6.4. Enable/Disable .............................................9
6.5. Ack/Error ..................................................9
7. Architectural Considerations ....................................9
8. Security Considerations ........................................13
9. Acknowledgements ...............................................14
10. References ....................................................14
10.1. Normative References .....................................14
10.2. Informative References ...................................14
Appendix A. Example Scenario ....................................16
Appendix B. Example Operation for FMIPv6 ........................17
B.1. Example Operation-1 for FMIPv6 ............................18
B.2. Example Operation-2 for FMIPv6 ............................20
B.3. Experiment ................................................21
Appendix C. Example Mapping between L2 Primitives and
Primitives in IEEE 802.11 and IEEE 802.16e ..........22
Appendix D. Example Mapping of Primitives and IEEE 802.11 .......24
D.1. L2-LinkStatus ............................................24
D.2. L2-PoAList ................................................24
D.3. L2-PoAFound ..............................................24
D.4. L2-PoALost ................................................25
D.5. L2-LinkUp ................................................25
D.6. L2-LinkDown ..............................................25
D.7. L2-LinkStatusChanged ......................................25
D.8. L2-LinkConnect ............................................26
D.9. L2-LinkDisconnect ........................................26
Appendix E. Implementation and Evaluation of the Proposed
Model ................................................26
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Primitives for L2 Abstractions ..................................4
4. Definitions of Primitives .......................................6
4.1. L2-LinkStatus (Type 1) .....................................6
4.2. L2-PoAList (Type 1) ........................................6
4.3. L2-PoAFound (Type 2) .......................................6
4.4. L2-PoALost (Type 2) ........................................6
4.5. L2-LinkUp (Type 2) .........................................7
4.6. L2-LinkDown (Type 2) .......................................7
4.7. L2-LinkStatusChanged (Type 2) ..............................7
4.8. L2-LinkConnect (Type 3) ....................................7
4.9. L2-LinkDisconnect (Type 3) .................................8
5. Definitions of Static Parameters ................................8
5.1. Network Interface ID .......................................8
6. Definitions of Dynamic Parameters ...............................8
6.1. PoA (Point of Attachment) ..................................8
6.2. Condition ..................................................8
6.3. PoA List ...................................................9
6.4. Enable/Disable .............................................9
6.5. Ack/Error ..................................................9
7. Architectural Considerations ....................................9
8. Security Considerations ........................................13
9. Acknowledgements ...............................................14
10. References ....................................................14
10.1. Normative References .....................................14
10.2. Informative References ...................................14
Appendix A. Example Scenario ....................................16
Appendix B. Example Operation for FMIPv6 ........................17
B.1. Example Operation-1 for FMIPv6 ............................18
B.2. Example Operation-2 for FMIPv6 ............................20
B.3. Experiment ................................................21
Appendix C. Example Mapping between L2 Primitives and
Primitives in IEEE 802.11 and IEEE 802.16e ..........22
Appendix D. Example Mapping of Primitives and IEEE 802.11 .......24
D.1. L2-LinkStatus ............................................24
D.2. L2-PoAList ................................................24
D.3. L2-PoAFound ..............................................24
D.4. L2-PoALost ................................................25
D.5. L2-LinkUp ................................................25
D.6. L2-LinkDown ..............................................25
D.7. L2-LinkStatusChanged ......................................25
D.8. L2-LinkConnect ............................................26
D.9. L2-LinkDisconnect ........................................26
Appendix E. Implementation and Evaluation of the Proposed
Model ................................................26
Recent years have witnessed the rapid proliferation of wireless networks as well as mobile devices accessing them. Unlike wired network environments, wireless networks are characterized by dynamically changing radio conditions, connectivity, and available bandwidth. For efficient network communication, it is vital for a protocol layer to know or utilize other layers' control information. Mobile IPv4 [2] and Mobile IPv6 [3] have been standardized to support communication with mobile nodes. There are several proposals for seamless handovers in IPv6 networks, such as Fast Handovers for Mobile IPv6 (FMIPv6) [4] and Hierarchical Mobile IPv6 (HMIPv6) [5]. In FMIPv6, the network layer must know in advance the indication of a handover from the link layer to achieve seamless handovers. However, control information exchange between protocol layers is typically not available because each protocol layer is designed independently.
近年来，无线网络以及接入无线网络的移动设备迅速发展。与有线网络环境不同，无线网络的特点是无线条件、连接性和可用带宽动态变化。为了实现高效的网络通信，协议层了解或利用其他层的控制信息至关重要。移动IPv4[2]和移动IPv6[3]已经标准化，以支持与移动节点的通信。对于IPv6网络中的无缝切换，有几种建议，例如移动IPv6的快速切换（FMIPv6）[4]和分层移动IPv6（HMIPv6）[5]。在FMIPv6中，网络层必须提前知道来自链路层的切换指示，以实现无缝切换。但是，协议层之间的控制信息交换通常不可用，因为每个协议层都是独立设计的。
To solve the problem, this document defines nine kinds of L2 abstractions in the form of "primitives" to achieve fast handovers in the network layer. This mechanism is called "L3-driven fast handovers" because the network layer initiates L2 and L3 handovers by using the primitives.
为了解决这个问题，本文以“原语”的形式定义了九种二语抽象，以实现网络层的快速切换。这种机制被称为“L3驱动的快速切换”，因为网络层使用原语启动L2和L3切换。
IEEE 802.21 [6] also defines several services that make use of L2 information. For the sake of ease of implementation and deployment, the primitives defined in this document make use of only the information available in the mobile node, while IEEE 802.21 [6] introduces the information server in the network to provide the mobile node with network-related information, such as a global network map.
IEEE 802.21[6]还定义了几种利用二级信息的服务。为了便于实现和部署，本文档中定义的原语仅使用移动节点中可用的信息，而IEEE 802.21[6]在网络中引入了信息服务器，以向移动节点提供网络相关信息，如全球网络地图。
This document represents the consensus of the MobOpts Research Group. It has been reviewed by Research Group members active in the specific area of work.
本文件代表了MobOpts研究小组的共识。它已由活跃于特定工作领域的研究小组成员审查。
This document uses the following terms:
本文件使用以下术语：
L3-Driven Fast Handover
L3驱动的快速切换
The handover mechanism that is initiated by the network layer on a mobile node. Since this mechanism allows handover preparation in L3 before the start of an L2 handover on the mobile node, it can reduce packet loss during a handover. The L3-driven fast handover mechanism requires L2 information as a trigger for a handover procedure.
由移动节点上的网络层发起的切换机制。由于该机制允许在移动节点上的L2切换开始之前在L3中进行切换准备，因此它可以减少切换期间的分组丢失。L3驱动的快速切换机制需要L2信息作为切换过程的触发器。
PoA
PoA
The point of attachment of a mobile node (e.g., an access point in IEEE 802.11 networks [7]).
移动节点的连接点（例如，IEEE 802.11网络中的接入点[7]）。
Primitive
原始的
A unit of information that is sent from one layer to another. There are four classes of primitives: Request, Confirm, Indication, and Response. One or more classes of a primitive are exchanged, depending on the type of primitive.
从一层发送到另一层的信息单位。有四类原语：请求、确认、指示和响应。根据基元的类型，交换基元的一个或多个类。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [1].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[1]中所述进行解释。
Each layer offers its services in the form of primitives. Four classes of primitives are defined, as shown in Figure 1. Request is issued by the layer that wants to get the services or information from another layer, and Confirm is the acknowledgment of the request. Indication is the notification of the information to the layer that requested the service, and Response is the acknowledgment of the indication. In this architecture, communication between layers is symmetrical.
每一层都以原语的形式提供其服务。定义了四类原语，如图1所示。请求由希望从另一层获取服务或信息的层发出，确认是对请求的确认。指示是向请求服务的层通知信息，响应是对指示的确认。在这种体系结构中，层之间的通信是对称的。
------------------------- -----------------------------
Request Response
|| /\ /\ ||
Layer N || || || ||
------------||------||--- -------||------||------------
|| || || ||
\/ || || \/
Layer N-m Confirm Indication
------------------------- -----------------------------
------------------------- -----------------------------
Request Response
|| /\ /\ ||
Layer N || || || ||
------------||------||--- -------||------||------------
|| || || ||
\/ || || \/
Layer N-m Confirm Indication
------------------------- -----------------------------
Figure 1: Interaction Model between Layers
图1：层之间的交互模型
The primitive consists of five fields: protocol layer ID, protocol ID, primitive class (Request, Response, Indication, or Confirm), primitive name, and parameters. The protocol layer ID specifies to which layer this primitive should be sent, e.g., Layer 2 or Layer 3. The protocol ID specifies to which protocol entity this primitive should be sent, e.g., IEEE 802.11 [7] or IEEE 802.3 [8].
原语由五个字段组成：协议层ID、协议ID、原语类（请求、响应、指示或确认）、原语名称和参数。协议层ID指定此原语应发送到哪个层，例如，第2层或第3层。协议ID指定此原语应发送到哪个协议实体，例如IEEE 802.11[7]或IEEE 802.3[8]。
For unified L2 abstractions for L3-driven fast handovers, three different usages of primitives are defined, as described below:
对于L3驱动的快速切换的统一L2抽象，定义了原语的三种不同用法，如下所述：
Type 1. To provide L2 information to upper layers immediately
类型1。立即向上层提供L2信息
This type of primitive is used to provide the L2 information to upper layers immediately. The Request and Confirm classes of primitives MUST be exchanged for the interaction. The Request primitive is for an acquisition request for the L2 information. The Confirm primitive is for the answer.
这种类型的原语用于立即向上层提供L2信息。必须为交互交换基本体的请求和确认类。请求原语用于L2信息的获取请求。确认原语用于回答。
Type 2. To notify upper layers of L2 events asynchronously
类型2。异步通知上层L2事件
This type of primitive is used to notify upper layers of L2 events asynchronously. The Request, Confirm, and Indication classes of primitive MUST be exchanged, and the Response class MAY be exchanged for the interaction. The Request and Confirm primitives are used just for registration. When an event occurs, the Indication primitive is asynchronously delivered to the upper layer.
这种类型的原语用于异步通知上层L2事件。原语的Request、Confirm和Indication类必须交换，而Response类可以交换用于交互。请求和确认原语仅用于注册。当事件发生时，指示原语将异步传递到上层。
Type 3. To control L2 actions from upper layers
类型3。从上层控制L2动作
This type of primitive is used to control L2 actions from upper layers. The Request and Confirm classes of primitives MUST be exchanged for the interaction. The Request primitive is a request for operation. Ack or Nack returns immediately as the Confirm primitive.
这种类型的基元用于控制上层的L2操作。必须为交互交换基本体的请求和确认类。请求原语是操作请求。Ack或Nack立即作为确认原语返回。
A protocol entity can register primitives anytime by exchanging the Request and Confirm messages that include the fields defined above. When the registered event occurs, the Indication and Response messages are exchanged as well.
协议实体可以随时通过交换包含上述定义字段的请求和确认消息来注册原语。当注册事件发生时，指示和响应消息也会交换。
The way to exchange a message between protocol entities is beyond the scope of this document. Any information-exchange method between layers, such as the work in [10], can be used.
在协议实体之间交换消息的方式超出了本文档的范围。可以使用层之间的任何信息交换方法，如[10]中的工作。
The timing for sending an Indication primitive is also beyond the scope of this document. For example, a layer 2 event is generated when layer 2 status has been changed, and this depends upon how scanning algorithms, for example, are implemented.
发送指示原语的时间也超出了本文档的范围。例如，当第2层状态已更改时，将生成第2层事件，这取决于扫描算法的实现方式。
To obtain and exchange L2 information, the following primitives are defined. Appendix C shows example mapping between the L2 primitives and the primitives in IEEE 802.11 [7] and IEEE 802.16e [9].
为了获取和交换L2信息，定义了以下原语。附录C显示了L2原语与IEEE 802.11[7]和IEEE 802.16e[9]中的原语之间的映射示例。
The L2-LinkStatus.request primitive is sent to the link layer when an upper layer requires the current information of a link. The L2-LinkStatus.request primitive contains the "Network Interface ID" parameter (see Section 5.1). In response, the L2-LinkStatus.confirm primitive returns. The L2-LinkStatus.confirm primitive contains three parameters: "Network Interface ID", "PoA", and "Condition". "PoA" and "Condition" indicate the current status of the link between the mobile node and a PoA.
当上层需要链接的当前信息时，L2-LinkStatus.request原语被发送到链接层。L2-LinkStatus.request原语包含“网络接口ID”参数（见第5.1节）。作为响应，L2-LinkStatus.confirm原语返回。L2-LinkStatus.confirm原语包含三个参数：“网络接口ID”、“PoA”和“条件”。“PoA”和“条件”表示移动节点和PoA之间链路的当前状态。
The L2-PoAList.request primitive is sent to the link layer when an upper layer requires a list of the candidate PoAs. The L2-PoAList.request primitive contains the "Network Interface ID" parameter. In response, the L2-PoAList.confirm primitive returns the "Network Interface ID" parameter and the "PoA List" parameter. The "PoA List" parameter is a list of the candidate PoAs.
当上层需要候选POA列表时，L2-PoAList.request原语被发送到链路层。L2-PoAList.request原语包含“网络接口ID”参数。作为响应，L2-PoAList.confirm原语返回“网络接口ID”参数和“PoA列表”参数。“PoA列表”参数是候选PoA的列表。
The L2-PoAFound.indication primitive is asynchronously provided to an upper layer when new PoAs are detected. This primitive carries the "Network Interface ID" parameter and the "PoA List" parameter. The "PoA List" parameter contains information on new PoAs detected by the mobile node. In order to use this notification, the registration process using the L2-PoAFound.request primitive and the L2-PoAFound.confirm primitive is needed in advance. The L2-PoAFound.request primitive has two parameters: "Network Interface ID" and "Enable/Disable". The "Enable/Disable" parameter shows whether this notification function is turned on. When this registration succeeds, the L2-PoAFound.confirm primitive returns with the "Network Interface ID" parameter and the "Ack" parameter in response.
检测到新POA时，L2-PoAFound.indication原语将异步提供给上层。此原语携带“网络接口ID”参数和“PoA列表”参数。“PoA列表”参数包含移动节点检测到的新PoA的信息。为了使用此通知，需要提前使用L2-PoAFound.request原语和L2-PoAFound.confirm原语的注册过程。L2-PoAFound.request原语有两个参数：“网络接口ID”和“启用/禁用”。“启用/禁用”参数显示此通知功能是否已打开。注册成功后，L2-PoAFound.confirm原语返回“网络接口ID”参数和“Ack”参数作为响应。
The L2-PoALost.indication primitive is asynchronously provided to an upper layer when a PoA included in the list of candidate PoAs disappears. This primitive carries the "Network Interface ID" parameter and the "PoA List" parameter. The "PoA List" parameter
当候选PoA列表中包含的PoA消失时，L2-PoALost.indication原语异步提供给上层。此原语携带“网络接口ID”参数和“PoA列表”参数。“PoA列表”参数
contains information on the PoAs that disappeared from the list of candidates. The registration process using the L2-PoALost.request primitive and the L2-PoALost.confirm primitive is similar to the L2-PoAFound primitive described above.
包含从候选列表中消失的POA的信息。使用L2-PoALost.request原语和L2-PoALost.confirm原语的注册过程与上述L2-PoAFound原语类似。
The L2-LinkUp.indication primitive is asynchronously provided to an upper layer when a new link is connected and IP packets can be transmitted through the new link. As described in RFC 4957 [12], what "link is connected" means depends on link types. For example, in case of the infrastructure mode in IEEE 802.11 [7] (WiFi), this primitive is provided when an association to an access point is established. This primitive carries the "Network Interface ID" parameter and the "PoA" parameter. The L2-LinkUp.request primitive contains the "Network Interface ID" parameter and the "Enable/Disable" parameter for registration. When the registration succeeds, the L2-LinkUp.confirm primitive with the "Network Interface ID" parameter and the "Ack" parameter returns.
当连接新链路时，L2-LinkUp.indication原语异步提供给上层，IP数据包可以通过新链路传输。如RFC 4957[12]所述，“链路已连接”的含义取决于链路类型。例如，在IEEE 802.11[7]（WiFi）中的基础设施模式的情况下，当建立到接入点的关联时提供该原语。此原语携带“网络接口ID”参数和“PoA”参数。L2-LinkUp.request原语包含用于注册的“网络接口ID”参数和“启用/禁用”参数。注册成功后，带有“Network Interface ID”参数和“Ack”参数的L2-LinkUp.confirm原语返回。
The L2-LinkDown.indication primitive is asynchronously provided to an upper layer when an existing link is disconnected and IP packets cannot be transmitted through the link. The registration processing is the same as the L2-LinkUp primitive described above.
当现有链路断开且IP数据包无法通过链路传输时，L2-LinkDown.indication原语将异步提供给上层。注册处理与上述L2链接原语相同。
The L2-LinkStatusChanged.indication primitive is asynchronously provided to an upper layer when the status of a link has changed. This notification contains three parameters: "Network Interface ID", "PoA", and "Condition". The "PoA" parameter indicates the attachment point at which the link quality changed. In the registration processing, the L2-LinkStatusChanged.request primitive carries the "Network Interface ID" parameter, the "Enable/Disable" parameter, and the "Condition" parameter. "Condition" indicates the event type and the threshold for the Indication.
当链路状态发生变化时，L2-LinkStatusChanged.indication原语将异步提供给上层。此通知包含三个参数：“网络接口ID”、“PoA”和“条件”。“PoA”参数表示链路质量发生变化的连接点。在注册处理中，L2-LinkStatusChanged.request原语携带“网络接口ID”参数、“启用/禁用”参数和“条件”参数。“条件”表示事件类型和指示阈值。
The L2-LinkConnect.request primitive is sent to the link layer when an upper layer has to establish a new link to the specific "PoA". This primitive carries the "Network Interface ID" parameter and the "PoA" parameter. This operation begins after the link layer returns the L2-LinkConnect.confirm primitive with "Ack".
当上层必须建立到特定“PoA”的新链接时，L2-LinkConnect.request原语被发送到链接层。此原语携带“网络接口ID”参数和“PoA”参数。此操作在链接层返回带有“Ack”的L2-LinkConnect.confirm原语后开始。
The L2-LinkDisconnect.request primitive is sent to the link layer when an upper layer has to tear down an existing link to the specific "PoA". This primitive carries the "Network Interface ID" parameter and the "PoA" parameter. This operation begins after the link layer returns the L2-LinkDisconnect.confirm primitive with "Ack".
当上层必须拆除到特定“PoA”的现有链接时，L2-LinkDisconnect.request原语被发送到链接层。此原语携带“网络接口ID”参数和“PoA”参数。此操作在链路层返回L2-LinkDisconnect.confirm原语（带有“Ack”）后开始。
This section lists static parameters. Once the values of static parameters are configured, they basically remain unchanged during communication. The following parameters are transferred as a part of primitives.
本节列出了静态参数。一旦配置了静态参数的值，它们在通信过程中基本保持不变。以下参数作为基本体的一部分传输。
The "Network Interface ID" parameter uniquely identifies the network interface in the node. The syntax of the identifier is implementation-specific (e.g., name, index, or unique address assigned to each interface). This parameter also contains the network interface type that indicates the kind of technology of the network interface (e.g., IEEE 802.11a/b/g [7], Third Generation Partnership Project (3GPP), etc.). This parameter is required in all primitives.
“Network Interface ID”参数唯一标识节点中的网络接口。标识符的语法是特定于实现的（例如，名称、索引或分配给每个接口的唯一地址）。此参数还包含指示网络接口技术类型的网络接口类型（例如，IEEE 802.11a/b/g[7]、第三代合作伙伴关系项目（3GPP）等）。此参数在所有基本体中都是必需的。
This section lists dynamic parameters. The values of dynamic parameters change frequently during communication. The following parameters are transferred as a part of primitives.
本节列出了动态参数。在通信过程中，动态参数的值经常变化。以下参数作为基本体的一部分传输。
The "PoA" parameter uniquely identifies the PoA.
“PoA”参数唯一标识PoA。
The "Condition" parameter consists of the following sub-parameters: available bandwidth and link quality level. These sub-parameters are the abstracted information that indicates the current quality of service. The abstraction algorithms of sub-parameters depend on hardware devices and software implementation. The useful range of link quality is divided into five levels: EXCELLENT, GOOD, FAIR, BAD, and NONE, in descending order. The quality levels of an L2 device
“条件”参数包括以下子参数：可用带宽和链路质量级别。这些子参数是表示当前服务质量的抽象信息。子参数的提取算法依赖于硬件设备和软件实现。链接质量的有用范围按降序分为五个级别：优秀、良好、一般、差和无。二语设备的质量级别
are independent of those of other devices. However, making decisions based on these metrics is error prone and not guaranteed to result in an optimal choice of links. An example of the thresholds among the five levels in IEEE 802.11 [7] is described in Appendix E.
与其他设备的设备无关。然而，基于这些指标进行决策容易出错，并且不能保证能够获得最佳的链接选择。附录E中描述了IEEE 802.11[7]中五个级别之间的阈值示例。
The "PoA List" parameter consists of arbitrary couples of two sub-parameters: "PoA" and "Condition". This parameter shows a list of PoAs and their conditions.
“PoA列表”参数由两个子参数“PoA”和“条件”的任意组合组成。此参数显示POA及其条件的列表。
The "Enable/Disable" flag is used for turning event notification on/ off. When an upper layer needs notifications, the Request primitive with "Enable" is sent to the link layer as registration. When an upper layer needs no more notifications, the Request primitive with "Disable" is sent.
“启用/禁用”标志用于打开/关闭事件通知。当上层需要通知时，带有“Enable”的请求原语作为注册发送到链接层。当上层不再需要通知时，发送带有“Disable”的请求原语。
When an upper layer requests some notifications, the link layer receives and confirms this Request. If the Request is valid, the Confirm primitive with "Ack" is sent to the upper layer. If it is invalid, the Confirm with "Error" is sent to the upper layer.
当上层请求一些通知时，链路层接收并确认该请求。如果请求有效，则向上层发送带有“Ack”的确认原语。如果无效，则向上层发送带有“错误”的确认。
RFC 4907 [11] discusses the role and the issues of link indications within the Internet Architecture. This section discusses the architectural considerations mentioned in Section 2 of RFC 4907.
RFC 4907[11]讨论了互联网体系结构中链路指示的作用和问题。本节讨论RFC 4907第2节中提到的架构注意事项。
1. Proposals should avoid use of simplified link models in circumstances where they do not apply.
1. 提案应避免在不适用的情况下使用简化链接模型。
The information in each layer should be abstracted before it is sent to another layer. For example, in IEEE 802.11 [7], the Received Signal Strength Indicator (RSSI), the number of retransmissions, and the existence of association between the mobile node and the access point are used so that the link layer indications can adjust themselves to various environments or situations. The thresholds needed for some link indications are defined from empirical study.
每一层中的信息在发送到另一层之前都应该进行抽象。例如，在IEEE 802.11[7]中，使用接收信号强度指示符（RSSI）、重传次数以及移动节点和接入点之间存在的关联，以便链路层指示可以根据各种环境或情况进行自我调整。一些链路指示所需的阈值是通过实证研究确定的。
In the conventional protocol-layering model, the Protocol Entity (PE) is defined as the entity that processes a specific protocol. Our proposal introduced the Abstract Entity (AE) to
在传统的协议分层模型中，协议实体（PE）被定义为处理特定协议的实体。我们的提案将抽象实体（AE）引入
achieve link independency of the link indications. An AE and a PE make a pair. An AE abstracts the PE-dependent information to the PE-independent information.
实现链路指示的链路独立性。AE和PE是一对。AE将PE相关信息抽象为PE独立信息。
Figure 2 shows AEs and PEs using primitives.
图2显示了使用原语的AEs和PEs。
2. Link indications should be clearly defined, so that it is understood when they are generated on different link layers.
2. 链路指示应明确定义，以便在不同链路层上生成时理解。
To make the link information/indications clear, our proposal defines the 4 types of primitives: Request/Confirm and Indication/Response, as described in Section 3. The Request is used to obtain the information of another layer. The Confirm is the reply to the request and it includes the requested information. The Indication is generated when a particular event occurs. The Response is the reply to the indication.
为了明确链接信息/指示，我们的提案定义了4种基本类型：请求/确认和指示/响应，如第3节所述。该请求用于获取另一层的信息。确认是对请求的回复，包括请求的信息。该指示在特定事件发生时生成。响应是对指示的响应。
In our proposal on IEEE 802.11b [7], L2-LinkUp is defined as the status in which an association to the Access Point (AP) is established, and L2-LinkDown is defined as the status in which an association to the AP is not established. L2-LinkStatusChanged is generated when the link quality goes below the predefined threshold. Since the Received Signal Strength Indicator (RSSI) and the number of retransmissions are used to abstract and evaluate the link quality, L2- LinkStatusChanged represents the link quality in both directions. It should use an average of the RSSI or the number of retransmissions damped for one second or more to cope with transient link conditions.
在我们关于IEEE 802.11b[7]的提案中，L2链接被定义为与接入点（AP）建立关联的状态，L2链接被定义为与AP未建立关联的状态。链路质量低于预定义阈值时，会生成L2 LinkStatusChanged。由于接收信号强度指示器（RSSI）和重传次数用于提取和评估链路质量，因此L2-LinkStatusChanged表示两个方向上的链路质量。它应该使用RSSI的平均值或延迟一秒或更长时间的重传次数来应对瞬态链路条件。
3. Proposals must demonstrate robustness against misleading indications.
3. 提案必须证明其针对误导性指示的稳健性。
Since RSSI changes significantly even when the mobile node stands still according to the measurements in our experiments, our proposal uses the RSSI, the number of retransmissions, and the existence of an association to calculate the link status, as described above. In our experiments, there were some "ping-pong" handovers between two APs. Such ping-pong handovers could be reduced by detecting the most suitable AP by L2-LinkStatus when L2-LinkStatusChanged is notified. The use of L2 indications is related to parameter thresholds that trigger handover. These thresholds vary based on the deployment scenario and, if not configured properly, could lead to misleading indications.
由于根据我们实验中的测量，即使移动节点静止，RSSI也会发生显著变化，因此我们的方案使用RSSI、重传次数和关联的存在来计算链路状态，如上所述。在我们的实验中，两个AP之间有一些“乒乓”切换。当通知L2 LinkStatus更改时，通过L2 LinkStatus检测最合适的AP，可以减少此类乒乓切换。L2指示的使用与触发切换的参数阈值有关。这些阈值因部署场景而异，如果配置不当，可能会导致误导性指示。
4. Upper layers should utilize a timely recovery step so as to limit the potential damage from link indications determined to be invalid after they have been acted on.
4. 上层应采用及时的恢复步骤，以限制链路指示在作用后被确定为无效的潜在损害。
The proposed L3-driven handover described in Appendix E uses the L2-LinkStatusChanged indication as the trigger for starting handover. L2-LinkStatusChanged is indicated when the link quality goes below a specific threshold. This indication is not canceled even if the link quality goes up soon. As described above, L2-LinkStatus can be used to detect the most suitable AP. The IP layer can cancel a handover if it finds that the current AP is the most suitable one by using L2-LinkStatus when L2-LinkStatusChanged is notified.
附录E中描述的拟议三级驱动切换使用二级链路状态更改指示作为启动切换的触发器。链路质量低于特定阈值时，会指示L2 LinkStatusChanged。即使链路质量很快提高，也不会取消此指示。如上所述，L2链路状态可用于检测最合适的AP。当L2 LinkStatusChanged收到通知时，如果IP层发现当前AP是最合适的AP，则可以使用L2 LinkStatus取消切换。
5. Proposals must demonstrate that effective congestion control is maintained.
5. 提案必须证明维持了有效的拥塞控制。
Since this mechanism is coupled to the IP layer, and not directly to the transport layer, the proposed mechanism does not directly affect congestion control.
由于该机制耦合到IP层，而不是直接耦合到传输层，因此所提出的机制不会直接影响拥塞控制。
6. Proposals must demonstrate the effectiveness of proposed optimizations.
6. 提案必须证明拟议优化的有效性。
In IPv6 mobility, the L3-driven handover mechanism using link indications can dramatically reduce gap time due to handover. The L3-driven handover mechanism needs the L2-LinkStatusChanged indication to predict disconnection. But L2-LinkStatusChanged is not trusted sometimes because it is difficult to abstract the link quality. Invalid L2-LinkStatusChanged may cause redundant handover. A handover mechanism using only L2-LinkUp/ L2-LinkDown can also reduce gap time modestly. An example of an implementation and evaluation of the L3-driven handover mechanism is described in Appendix E.
在IPv6移动性中，使用链路指示的L3驱动的切换机制可以显著减少切换造成的间隔时间。L3驱动的切换机制需要L2 LinkStatusChanged指示来预测断开。但L2 LinkStatusChanged有时不可信，因为很难提取链接质量。无效的L2链路状态更改可能会导致冗余切换。仅使用二级链路上行/二级链路下行的切换机制也可以适度减少间隔时间。附录E中描述了L3驱动切换机制的实施和评估示例。
7. Link indications should not be required by upper layers in order to maintain link independence.
7. 为了保持链路独立性，上层不需要链路指示。
Our proposal does not require any modifications to the transport and upper layers.
我们的建议不需要对传输层和上层进行任何修改。
8. Proposals should avoid race conditions, which can occur where link indications are utilized directly by multiple layers of the stack.
8. 建议应避免竞争条件，这可能发生在多个堆栈层直接使用链接指示的情况下。
Since our proposal defines the link indications only to the IP layer, race conditions between multiple layers never occur.
由于我们的方案仅定义了IP层的链路指示，因此不会出现多个层之间的竞争条件。
9. Proposals should avoid inconsistencies between link and routing layer metrics.
9. 建议应避免链路和路由层指标之间的不一致。
Our proposal does not deal with routing metrics.
我们的建议不涉及路由度量。
10. Overhead reduction schemes must avoid compromising interoperability and introducing link-layer dependencies into the Internet and transport layers.
10. 开销减少方案必须避免损害互操作性，并将链路层依赖性引入Internet和传输层。
As described above, the link indications in our proposal are abstracted to the information independent of link types to reduce the gap time due to a handover, and the ordinary host can execute handover without using the link indications defined in our proposal.
如上所述，我们方案中的链路指示被抽象为独立于链路类型的信息，以减少由于切换而产生的间隔时间，并且普通主机可以执行切换，而不使用我们方案中定义的链路指示。
11. Proposals advocating the transport of link indications beyond the local host need to carefully consider the layering, security, and transport implications. In general, implicit signals are preferred to explicit transport of link indications since they add no new packets in times of network distress, operate more reliably in the presence of middle boxes, such as NA(P)Ts (Network Address (Port) Translations), are more likely to be backward compatible, and are less likely to result in security vulnerabilities.
11. 主张运输指示超出当地主机的建议需要仔细考虑分层、安全和运输的影响。一般而言，隐式信号优先于链路指示的显式传输，因为它们在网络故障时不添加新分组，在存在中间盒的情况下运行更可靠，例如NA（P）Ts（网络地址（端口）翻译），更可能向后兼容，并且不太可能导致安全漏洞。
Our proposal does not define the exchange of link indications between nodes.
我们的建议没有定义节点之间链路指示的交换。
---------------------------------------------------------
----------=========== ----------===========
| |[ ] | |[ ]
| PE |[ AE ] | PE |[ AE ]
| |[ ] | |[ ]
----------=========== ----------===========
Layer N || /\ || /\
------------||---||-------------------||---||------------
Request|| || Response|| ||
|| || || ||
|| || || ||
|| ||Confirm || ||Indication
------------||---||-------------------||---||------------
\/ || \/ ||
----------=========== ----------===========
| |[ ] | |[ ]
| PE |[ AE ] | PE |[ AE ]
| |[ ] | |[ ]
----------=========== ----------===========
Layer N-m
---------------------------------------------------------
---------------------------------------------------------
----------=========== ----------===========
| |[ ] | |[ ]
| PE |[ AE ] | PE |[ AE ]
| |[ ] | |[ ]
----------=========== ----------===========
Layer N || /\ || /\
------------||---||-------------------||---||------------
Request|| || Response|| ||
|| || || ||
|| || || ||
|| ||Confirm || ||Indication
------------||---||-------------------||---||------------
\/ || \/ ||
----------=========== ----------===========
| |[ ] | |[ ]
| PE |[ AE ] | PE |[ AE ]
| |[ ] | |[ ]
----------=========== ----------===========
Layer N-m
---------------------------------------------------------
Figure 2: AE and PE with Primitives
图2：带有原语的AE和PE
RFC 4907 [11] discusses the role and issues of link indications within the Internet Architecture. This section discusses the security considerations mentioned in Section 4 of RFC 4907.
RFC 4907[11]讨论了互联网体系结构中链路指示的作用和问题。本节讨论RFC 4907第4节中提到的安全注意事项。
1. Spoofing
1. 欺骗
The proposed primitives suffer from spoofed link-layer control frames. For example, if a malicious access point is set up and spoofed beacon frames are transmitted, L2-PoAFound.indication is generated in the mobile node. As a result, the mobile node may establish an association with the malicious access point by an L2-LinkConnect.request.
所提出的原语受到欺骗链路层控制帧的影响。例如，如果设置恶意接入点并发送伪造的信标帧，则在移动节点中生成L2-PoAFound.indication。结果，移动节点可通过L2-LinkConnect.request与恶意接入点建立关联。
2. Indication validation
2. 适应症验证
Transportation of the link indications between nodes is not assumed; hence, this consideration is beyond the scope of our proposal.
不假设在节点之间传输链路指示；因此，这一考虑超出了我们提案的范围。
3. Denial of service
3. 拒绝服务
Since this proposal does not change link-layer protocols, no more insecurity is added to a particular link-layer protocol. However, the proposed primitives suffer from denial-of-service attacks by spoofed link-layer frames. For example, L2- PoAFound.indication and L2-PoALost.indication may frequently be generated alternately if a malicious access point frequently transmits control frames that indicate strong RSSI and weak RSSI alternately.
由于此建议不会更改链路层协议，因此不会向特定链路层协议添加更多的不安全性。然而，所提出的原语受到伪造链路层帧的拒绝服务攻击。例如，如果恶意接入点频繁传输交替指示强RSSI和弱RSSI的控制帧，则L2-PoAFound.indication和L2-PoALost.indication可能频繁交替生成。
The authors gratefully acknowledge the contributions of Jukka Manner, Christian Vogt, and John Levine for their review.
作者非常感谢Jukka、Christian Vogt和John Levine对他们的评论所做的贡献。
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[1] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[2] Perkins, C., Ed., "IP Mobility Support for IPv4", RFC 3344, August 2002.
[2] Perkins，C.，编辑，“IPv4的IP移动支持”，RFC 3344，2002年8月。
[3] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004.
[3] Johnson，D.，Perkins，C.，和J.Arkko，“IPv6中的移动支持”，RFC 37752004年6月。
[4] Koodli, R., Ed., "Fast Handovers for Mobile IPv6", RFC 4068, July 2005.
[4] Koodli，R.，Ed.，“移动IPv6的快速切换”，RFC 4068，2005年7月。
[5] Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier, "Hierarchical Mobile IPv6 Mobility Management (HMIPv6)", RFC 4140, August 2005.
[5] Soliman，H.，Castelluccia，C.，El Malki，K.，和L.Bellier，“分层移动IPv6移动性管理（HMIPv6）”，RFC 41402005年8月。
[6] "Draft IEEE Standard for Local and Metropolitan Area Networks: Media Independent Handover Services", IEEE P802.21/D02.00, September 2006.
[6] “局域网和城域网IEEE标准草案：媒体独立切换服务”，IEEE P802.21/D02.00，2006年9月。
[7] IEEE, "802.11-2007 IEEE Standard for LAN/MAN - Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", 2007.
[7] IEEE，“802.11-2007 IEEE LAN/MAN标准-特定要求第11部分：无线LAN介质访问控制（MAC）和物理层（PHY）规范”，2007年。
[8] IEEE, "802.3, 2000 EDITION ISO/IEC 8802-3:2000 (E) Information Technology - LAN/MAN - Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications", 2000.
[8] IEEE，“802.3，2000版ISO/IEC 8802-3:2000（E）信息技术-局域网/城域网-第3部分：带冲突检测的载波侦听多址接入（CSMA/CD）接入方法和物理层规范”，2000年。
[9] IEEE, "802.16e-2005 & 802.16/COR1 Part 16: Amendment for Physical & Medium Access Control Layers for Combined Fixed & Mobile Operation", 2006.
[9] IEEE，“802.16e-2005和802.16/COR1第16部分：固定和移动组合操作的物理和介质访问控制层修正案”，2006年。
[10] Gogo, K., Shibu, R., and F. Teraoka, "An L3-Driven Fast Handover Mechanism in IPv6 Mobility", In Proc. of International Symposium on Applications and the Internet (SAINT2006) Workshop in IPv6, February 2006.
[10] Gogo，K.，Shibu，R.，和F.Teraoka，“IPv6移动性中的L3驱动的快速切换机制”，在Proc。2006年2月，国际应用和互联网研讨会（SAINT2006）在IPv6上的研讨会。
[11] Aboba, B., Ed., "Architectural Implications of Link Indications", RFC 4907, June 2007.
[11] Aboba，B.，编辑，“连接指示的建筑含义”，RFC 49072007年6月。
[12] Krishnan, S., Ed., Montavont, N., Njedjou, E., Veerepalli, S., and A. Yegin, Ed., "Link-Layer Event Notifications for Detecting Network Attachments", RFC 4957, August 2007.
[12] Krishnan，S.，Ed.，Montavont，N.，Njedjou，E.，Veerepalli，S.，和A.Yegin，Ed.，“检测网络附件的链路层事件通知”，RFC 4957，2007年8月。
[13] Ishiyama, M., Kunishi, M., Uehara, K., Esaki, H., and F. Teraoka, "LINA: A New Approach to Mobility Support in Wide Area Networks", IEICE Transactions on Communication vol. E84-B, no. 8, pp. 2076-2086, August 2001.
[13] Ishiyama，M.，Kunishi，M.，Uehara，K.，Esaki，H.，和F.Teraoka，“LINA：广域网中移动支持的新方法”，IEICE通信交易卷E84-B，第8期，第2076-2086页，2001年8月。
For example, the picture below shows L3-driven fast handover mechanism using the L2 triggers on a mobile node (MN).
例如，下图显示了在移动节点（MN）上使用L2触发器的L3驱动的快速切换机制。
L2 L3
| |
|<----------LinkUP.req-----------|
|-----------LinkUP.cnf---------->|
|<-----LinkStatusChanged.req-----|
|------LinkStatusChanged.cnf---->|
= =
| |
Low |
Signal---LinkStatusChanged.ind---->|
| |
|<----------PoAList.req----------|
|-----------PoAList.cnf------>Handover
| Preparation
|<-------LinkConnect.req---------|
L2 Handover--LinkConnect.cnf-------->:
: :
: :
finish---------LinkUp.ind----->L3 Handover
| finish
| |
L2 L3
| |
|<----------LinkUP.req-----------|
|-----------LinkUP.cnf---------->|
|<-----LinkStatusChanged.req-----|
|------LinkStatusChanged.cnf---->|
= =
| |
Low |
Signal---LinkStatusChanged.ind---->|
| |
|<----------PoAList.req----------|
|-----------PoAList.cnf------>Handover
| Preparation
|<-------LinkConnect.req---------|
L2 Handover--LinkConnect.cnf-------->:
: :
: :
finish---------LinkUp.ind----->L3 Handover
| finish
| |
L2: Link Layer on MN L3: Network Layer on MN req: Request cnf: Confirm ind: Indication
L2：MN上的链路层L3：MN上的网络层req:请求cnf:确认ind:指示
Figure 3: L3-Driven Fast Handover Mechanism
图3:L3驱动的快速切换机制
First, L3 issues LinkUp.request to receive LinkUp.indication when the link becomes available. L3 also issues LinkStatusChanged.request to receive LinkStatusChanged.indication when the link quality goes below the threshold.
首先，L3发出LinkUp.request以在链接可用时接收LinkUp.indication。L3还发出LinkStatusChanged.request以在链路质量低于阈值时接收LinkStatusChanged.indication。
In the beginning of the L3-driven handover procedure, L2 detects that the radio signal strength is going down. Then, L2 sends L2-LinkStatusChanged.indication to L3. L3 prepares for handover (e.g., Care-of Address (CoA) generation, Duplicate Address Detection (DAD), Neighbor Discovery (ND) cache creation, and routing table setting) and sends L2-PoAList.request to L2 if the list of access points is needed.
在L3驱动的移交程序开始时，L2检测到无线电信号强度下降。然后，L2向L3发送L2-LinkStatusChanged.indication。L3准备切换（例如，转交地址（CoA）生成、重复地址检测（DAD）、邻居发现（ND）缓存创建和路由表设置），并在需要访问点列表时向L2发送L2-PoAList.request。
If L3 decides to perform handover according to some rules, L3 sends L2-LinkConnect.request with some parameters about candidate access points to request L2 handover. L2 handover begins after L2 sends L2-LinkConnect.confirm to L3. When the L2 handover finishes, L2 sends L2-LinkUp.indication to notify L3. Finally, L3 performs handover (e.g., sending a Binding Update (BU)).
如果L3决定根据某些规则执行切换，L3将发送L2-LinkConnect.request，其中包含关于候选接入点的一些参数，以请求L2切换。L2发送L2-LinkConnect后，L2切换开始。确认到L3。当L2切换完成时，L2发送L2-LinkUp.indication通知L3。最后，L3执行切换（例如，发送绑定更新（BU））。
One of the important features of L3-driven fast handover using primitives is that L3 handover preparation can be done during communication. So, it can reduce disruption time during handover.
使用原语的三级驱动快速切换的一个重要特征是，三级切换准备可以在通信过程中完成。因此，它可以减少切换期间的中断时间。
There are two scenarios of L3-driven fast handover for FMIPv6. Scenario 2 is different from scenario 1 for the timing of sending some messages.
FMIPv6有两种L3驱动的快速切换方案。场景2在发送某些消息的时间上与场景1不同。
Figure 4 shows the predictive mode of FMIPv6 operation with an L3-driven link-switching mechanism.
图4显示了具有L3驱动的链路切换机制的FMIPv6操作的预测模式。
MN-L2 MN-L3 PAR-L3
| | |
AP<----------PoAList.req----------| |
Scan----------PoAList.cnf--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
|----------PoAFound.ind--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
| | |
~ ~ ~
| | |
Low | |
Signal---LinkStatusChanged.ind---->| | NAR-L3
| |-----FBU---->| |
| | |----HI---->|
| | |<--HAck----|
| |<----FBack---| |
|<-------LinkConnect.req---L3 Handover | |
L2 Handover--LinkConnect.cnf-------->: |
: : |
: : |
finish---------LinkUp.ind---------->: |
| :-----------FNA---------->|
| finish<======packets=========|
| | |
MN-L2 MN-L3 PAR-L3
| | |
AP<----------PoAList.req----------| |
Scan----------PoAList.cnf--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
|----------PoAFound.ind--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
| | |
~ ~ ~
| | |
Low | |
Signal---LinkStatusChanged.ind---->| | NAR-L3
| |-----FBU---->| |
| | |----HI---->|
| | |<--HAck----|
| |<----FBack---| |
|<-------LinkConnect.req---L3 Handover | |
L2 Handover--LinkConnect.cnf-------->: |
: : |
: : |
finish---------LinkUp.ind---------->: |
| :-----------FNA---------->|
| finish<======packets=========|
| | |
MN-L2 : Link Layer on Mobile Node MN-L3 : Network Layer on Mobile Node PAR-L3 : Network Layer on Previous Access Router NAR-L3 : Network Layer on New Access Router req : Request cnf : Confirm ind : Indication RtSolPr : Router Solicitation for Proxy PrRtAdv : Proxy Router Advertisement FBU : Fast Binding Update FBack : Fast Binding Acknowledgment FNA : Fast Neighbor Advertisement HI : Handover Initiate HAck : Handover Acknowledge
MN-L2:移动节点上的链路层MN-L3:移动节点上的网络层PAR-L3:先前接入路由器上的网络层NAR-L3:新接入路由器上的网络层req:请求cnf:确认ind:指示RtSolPr:路由器请求代理PrRtAdv:代理路由器广告FBU:快速绑定更新FBack:快速绑定确认FNA:快速邻居广告HI:切换发起攻击：切换确认
Figure 4: L3-Driven Fast Handover Mechanism with FMIPv6 Scenario 1
图4:FMIPv6场景1中L3驱动的快速切换机制
When MN establishes link connectivity to PAR, it performs router discovery. MN sends an RtSolPr message to PAR to resolve the access point identifiers to the subnet router information. To send RtSolPr, MN discovers one or more access points by sending L2-PoAList.request to the link layer. As a response to L2-PoAList.request, L2-PoAList.confirm returns with "PoA List" parameter that contains identifiers and conditions of nearby access points. After initial AP discovery, L2-PoAFound.indication with "PoA List" is also sent from the link layer when one or more access points are discovered.
当MN建立到PAR的链路连通性时，它执行路由器发现。MN发送一个RTSOPR消息到PAR，以解析到子网路由器信息的接入点标识符。为了发送RtSolPr，MN通过向链路层发送L2-PoAList.request来发现一个或多个接入点。作为对L2-PoAList.request的响应，L2-PoAList.confirm返回“PoA List”参数，该参数包含附近接入点的标识符和条件。在初始AP发现之后，当发现一个或多个接入点时，还从链路层发送带有“PoA列表”的L2-PoAFound.indication。
When the link layer of MN detects that radio signal strength is dropping, it sends L2-LinkStatusChanged.indication to the network layer. Then, MN sends the FBU message to PAR as the beginning of the L3 handover procedure. The NCoA required for the FBU message is determined according to the MN's policy database and the received PrRtAdv message. As a response to the FBU message, MN receives the FBack message and then immediately switches its link by L2-LinkConnect.request with the specific "PoA" parameter. The handover policy of the MN is outside the scope of this document.
当MN链路层检测到无线信号强度下降时，向网络层发送L2-LinkStatusChanged.indication。然后，MN将FBU消息发送到PAR作为L3切换过程的开始。FBU消息所需的NCoA根据MN的策略数据库和接收到的PrRtAdv消息确定。作为对FBU消息的响应，MN接收FBack消息，然后立即通过L2-LinkConnect.request使用特定的“PoA”参数切换其链路。MN的移交政策不在本文件范围内。
After L2 handover, the link layer of the MN sends L2-LinkUp.indication to the network layer. MN immediately sends the FNA message to the New Access Router (NAR). The NAR will send tunneled and buffered packets to MN.
L2切换后，MN链路层向网络层发送L2-LinkUp.indication。MN立即将FNA消息发送到新的接入路由器（NAR）。NAR将向MN发送隧道和缓冲数据包。
Figure 5 shows the predictive mode of FMIPv6 operation with an L3-driven link-switching mechanism.
图5显示了具有L3驱动的链路切换机制的FMIPv6操作的预测模式。
MN-L2 MN-L3 PAR-L3
| | |
AP<----------PoAList.req----------| |
Scan----------PoAList.cnf--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
|----------PoAFound.ind--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
| | |
~ ~ ~
| | |
Low | |
Signal---LinkStatusChanged.ind---->| | NAR-L3
| |-----FBU---->| |
|<-------LinkConnect.req---L3 Handover | |
L2 Handover--LinkConnect.cnf-------->: | |
| | |----HI---->|
| | |<--HAck----|
| | <-FBack-|---FBack-->|
| |<----FBack---------------|
: : |
finish---------LinkUp.ind---------->: |
| :-----------FNA---------->|
| finish<======packets=========|
| | |
MN-L2 MN-L3 PAR-L3
| | |
AP<----------PoAList.req----------| |
Scan----------PoAList.cnf--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
|----------PoAFound.ind--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
| | |
~ ~ ~
| | |
Low | |
Signal---LinkStatusChanged.ind---->| | NAR-L3
| |-----FBU---->| |
|<-------LinkConnect.req---L3 Handover | |
L2 Handover--LinkConnect.cnf-------->: | |
| | |----HI---->|
| | |<--HAck----|
| | <-FBack-|---FBack-->|
| |<----FBack---------------|
: : |
finish---------LinkUp.ind---------->: |
| :-----------FNA---------->|
| finish<======packets=========|
| | |
MN-L2 : Link Layer on Mobile Node MN-L3 : Network Layer on Mobile Node PAR-L3 : Network Layer on Previous Access Router NAR-L3 : Network Layer on New Access Router req : Request cnf : Confirm ind : Indication RtSolPr : Router Solicitation for Proxy PrRtAdv : Proxy Router Advertisement FBU : Fast Binding Update FBack : Fast Binding Acknowledgment FNA : Fast Neighbor Advertisement HI : Handover Initiate HAck : Handover Acknowledge
MN-L2:移动节点上的链路层MN-L3:移动节点上的网络层PAR-L3:先前接入路由器上的网络层NAR-L3:新接入路由器上的网络层req:请求cnf:确认ind:指示RtSolPr:路由器请求代理PrRtAdv:代理路由器广告FBU:快速绑定更新FBack:快速绑定确认FNA:快速邻居广告HI:切换发起攻击：切换确认
Figure 5: L3-Driven Fast Handover Mechanism with FMIPv6 Scenario 2
图5:FMIPv6场景2中L3驱动的快速切换机制
Unlike scenario 1, MN in scenario 2 sends LinkConnect.req from the network layer to the link layer after MN sends the FBU message. As PAR sends the FBack messages not only to PAR's subnet but also to NAR's subnet, MN can get the FBack message sent by PAR through NAR, and then it moves to NAR.
Unlike scenario 1, MN in scenario 2 sends LinkConnect.req from the network layer to the link layer after MN sends the FBU message. As PAR sends the FBack messages not only to PAR's subnet but also to NAR's subnet, MN can get the FBack message sent by PAR through NAR, and then it moves to NAR.translate error, please retry
We implemented FMIPv6 and the proposed L2 primitives on FreeBSD-5.4. Figure 6 shows our test network. MN is connected to access routers by using IEEE802.11a wireless LAN. MN moves from PAR to NAR.
我们在FreeBSD-5.4上实现了FMIPv6和提议的L2原语。图6显示了我们的测试网络。MN通过使用IEEE802.11a无线LAN连接到接入路由器。MN从PAR移动到NAR。
|
+--+---+
|Router|
+--+---+
| 100BaseTX
---+--------+---------+---------+---------+------------
| | | |
+--+--+ +--+--+ +--+--+ +--+--+
| PAR | | NAR | | HA | | CN |
+-----+ +-----+ +-----+ +-----+
| |
IEEE802.11a IEEE802.11a PAR, NAR: nexcom EBC
|Channel 7 |Channel7 MN: ThinkPad X31
OS: FreeBSD-5.4
| | KAME/SHISA/TARZAN
+-----+ +-----+
| MN | -------> | MN |
+-----+ +-----+
|
+--+---+
|Router|
+--+---+
| 100BaseTX
---+--------+---------+---------+---------+------------
| | | |
+--+--+ +--+--+ +--+--+ +--+--+
| PAR | | NAR | | HA | | CN |
+-----+ +-----+ +-----+ +-----+
| |
IEEE802.11a IEEE802.11a PAR, NAR: nexcom EBC
|Channel 7 |Channel7 MN: ThinkPad X31
OS: FreeBSD-5.4
| | KAME/SHISA/TARZAN
+-----+ +-----+
| MN | -------> | MN |
+-----+ +-----+
Figure 6: Test Network
图6：测试网络
Scenario 1 was used in this experiment since it was more stable than scenario 2. Upon receiving L2-LinkStatusChanged.indication, L3 of MN sent the FBU message and then received the FBack message. It took 20ms from the transmission of the FBU message to the reception of the FBack message. After receiving the FBack message, L3 of MN issued L2-LinkConnect.request to L2. When L2 handover finished, L3 received L2-LinkUp.indication from L2. It took 1ms for an L2 handover. Next, MN sent the FNA message to NAR. Upon receiving the FNA message, NAR started forwarding packets to NM. ICMP echo request packets were sent at 10ms intervals. It was observed that zero or one ICMP echo reply packet was lost during a handover.
由于场景1比场景2更稳定，因此在本实验中使用了场景1。MN的L3在收到L2-LinkStatusChanged.indication后发送FBU消息，然后接收FBack消息。从发送FBU消息到接收FBack消息需要20毫秒。在收到FBack消息后，MN的L3向L2发出L2-LinkConnect.request。L2移交完成后，L3收到L2的L2-LinkUp.指示。L2切换需要1毫秒的时间。接下来，MN向NAR发送FNA消息。收到FNA消息后，NAR开始向NM转发数据包。ICMP回送请求数据包以10毫秒的间隔发送。据观察，在切换过程中，零个或一个ICMP回送回复数据包丢失。
MN PAR NAR
| | |
|----- RtSolPr --->| |
|<---- PrRtAdv ----| |
| | |
+--- |------ FBU ------>| |
| | |------- HI ------>|
20ms| | | |
| | |<----- HAck ------|
| | | |
+--- |<-------------- FBack -------------->|
| | |
+-- disconnect | |
| 1ms| | |
| connect | |
8-10ms| | | |
| 7ms| | |
| | | |
| +----- FNA -------------------------->|
+-- |<------------------------ deliver packets
| | |
MN PAR NAR
| | |
|----- RtSolPr --->| |
|<---- PrRtAdv ----| |
| | |
+--- |------ FBU ------>| |
| | |------- HI ------>|
20ms| | | |
| | |<----- HAck ------|
| | | |
+--- |<-------------- FBack -------------->|
| | |
+-- disconnect | |
| 1ms| | |
| connect | |
8-10ms| | | |
| 7ms| | |
| | | |
| +----- FNA -------------------------->|
+-- |<------------------------ deliver packets
| | |
Figure 7: Measured Results
图7：测量结果
Appendix C. Example Mapping between L2 Primitives and the Primitives in IEEE 802.11 and IEEE 802.16e
附录C.L2原语与IEEE 802.11和IEEE 802.16e中原语之间的映射示例
This section shows example mapping between the L2 primitives and the primitives in IEEE 802.11 [7] and IEEE 802.16e [9] in Table 1.
本节显示了L2原语与表1中IEEE 802.11[7]和IEEE 802.16e[9]中的原语之间的映射示例。
+-------------------+----------------------+------------------+
| L2 Primitive | IEEE802.11 | IEEE802.16e |
+-------------------+----------------------+------------------+
| L2-LinkStatus | PMD_RSSI | Available |
| | | |
| | PMD_RATE | |
| | | |
| L2-PoAList | MLME-SCAN | M_ScanScheduling |
| | | |
| | | M_Scanning |
| | | |
| L2-PoAFound | MLME-SCAN | M_Neighbor |
| | | |
| | | M_Scanning |
| | | |
| L2-PoALost | MLME-SCAN | M_Neighbor |
| | | |
| | | M_Scanning |
| | | |
| L2-LinkUp | MLME-ASSOCIATE | M_Registration |
| | | |
| | MLME-AUTHENTICATE | |
| | | |
| L2-LinkDown | MLME-DEASSOCIATE | M_Ranging |
| | | |
| | MLME-DISAUTHENTICATE | |
| | | |
| L2-StatusChanged | PMD_RSSI | M_Ranging |
| | | |
| | | M_ScanReport |
| | | |
| | | M_Scanning |
| | | |
| L2-LinkConnect | MLME-JOIN | M_MACHandover |
| | | |
| | MLME-ASSOCIATE | M_HOIND |
| | | |
| | MLME-REASSOCIATE | |
| | | |
| | MLME-AUTHENTICATE | |
| | | |
| L2-LinkDisconnect | MLME-DISASSOCIATE | M_Management |
| | | |
| | MLME-DEASSOCIATE | (Deregistration) |
+-------------------+----------------------+------------------+
+-------------------+----------------------+------------------+
| L2 Primitive | IEEE802.11 | IEEE802.16e |
+-------------------+----------------------+------------------+
| L2-LinkStatus | PMD_RSSI | Available |
| | | |
| | PMD_RATE | |
| | | |
| L2-PoAList | MLME-SCAN | M_ScanScheduling |
| | | |
| | | M_Scanning |
| | | |
| L2-PoAFound | MLME-SCAN | M_Neighbor |
| | | |
| | | M_Scanning |
| | | |
| L2-PoALost | MLME-SCAN | M_Neighbor |
| | | |
| | | M_Scanning |
| | | |
| L2-LinkUp | MLME-ASSOCIATE | M_Registration |
| | | |
| | MLME-AUTHENTICATE | |
| | | |
| L2-LinkDown | MLME-DEASSOCIATE | M_Ranging |
| | | |
| | MLME-DISAUTHENTICATE | |
| | | |
| L2-StatusChanged | PMD_RSSI | M_Ranging |
| | | |
| | | M_ScanReport |
| | | |
| | | M_Scanning |
| | | |
| L2-LinkConnect | MLME-JOIN | M_MACHandover |
| | | |
| | MLME-ASSOCIATE | M_HOIND |
| | | |
| | MLME-REASSOCIATE | |
| | | |
| | MLME-AUTHENTICATE | |
| | | |
| L2-LinkDisconnect | MLME-DISASSOCIATE | M_Management |
| | | |
| | MLME-DEASSOCIATE | (Deregistration) |
+-------------------+----------------------+------------------+
Table 1: Mapping between L2 Primitives and the Primitives in IEEE 802.11 and IEEE 802.16e
表1:IEEE 802.11和IEEE 802.16e中L2原语和原语之间的映射
This section shows examples of the mapping between primitives and IEEE 802.11 [7] parameters.
本节显示了原语和IEEE 802.11[7]参数之间的映射示例。
Most parameters of L2-LinkStatus are related to the configuration of network-interface hardware. The operating system and the device-driver module can easily collect such information. However, to create the "Condition" parameter, the MN should maintain statistics and parameters related to the current wireless environment.
L2链路状态的大多数参数与网络接口硬件的配置有关。操作系统和设备驱动程序模块可以轻松地收集此类信息。然而，为了创建“条件”参数，MN应该维护与当前无线环境相关的统计信息和参数。
There are two sub-parameters of the "Condition" parameter: available bandwidth and link quality level. The available bandwidth of the current PoA can be obtained by maintaining the transmission rate indication and the statistics of frame transmission every time a frame is sent. A link quality level can be updated by maintaining the following parameters and statistics every time a frame is received: Received Signal Strength Indicator (RSSI), transmission/ reception rate indication, transmit/receive latency, bit-error rate, frame-error rate, and noise level. Link quality level is divided into five levels: EXCELLENT, GOOD, FAIR, BAD, and NONE, in descending order. Some parameters can be managed by setting thresholds from software. When the parameters cross the threshold, an interrupt is generated for the software.
“条件”参数有两个子参数：可用带宽和链路质量级别。通过保持传输速率指示和每次发送帧时的帧传输统计，可以获得当前PoA的可用带宽。链路质量级别可以通过在每次接收帧时保持以下参数和统计信息来更新：接收信号强度指示器（RSSI）、发送/接收速率指示、发送/接收延迟、误码率、帧错误率和噪声级。链接质量级别按降序分为五个级别：优秀、良好、一般、不良和无。一些参数可以通过从软件设置阈值来管理。当参数超过阈值时，将为软件生成一个中断。
In IEEE 802.11 networks, L2-PoAList returns the detected APs whose quality level exceeds the specified threshold for PoA candidates (by the "PoA List" parameter). Therefore, an MN should always maintain the database of available access points according to reception of beacon frame, probe response frame, and all frames. This AP database is managed in consideration of time, number of frames, and signal strength. There are some kinds of network-interface hardware that can notify events to operating system only when the desired event occurs by setting a threshold from software. Moreover, MN can transmit the probe request frame for access point discovery, if needed.
在IEEE 802.11网络中，L2 PoAList返回检测到的AP，其质量级别超过PoA候选的指定阈值（通过“PoA列表”参数）。因此，MN应始终根据信标帧、探测响应帧和所有帧的接收来维护可用接入点的数据库。该AP数据库的管理考虑了时间、帧数和信号强度。有一些类型的网络接口硬件可以通过从软件设置阈值，仅在所需事件发生时向操作系统通知事件。此外，如果需要，MN可以发送用于接入点发现的探测请求帧。
In IEEE 802.11 networks, L2-PoAFound is notified when new PoAs whose link quality level exceeds the specified threshold are detected by listening beacons or scanning APs. If the received frame (mainly the
在IEEE 802.11网络中，当侦听信标或扫描AP检测到链路质量级别超过指定阈值的新POA时，会通知L2 POA。如果接收到的帧（主要是
beacon or the probe response) is not in the AP database described in Appendix D.2, then the link layer creates L2-PoAFound.indication.
信标或探测响应）不在附录D.2中描述的AP数据库中，则链路层创建L2-PoAFound.indication。
For example, if the threshold of link quality level specified by L2-PoAFound.request is GOOD, L2-PoAFound.indication is created and sent to the upper layer when PoA's link quality becomes better than GOOD.
例如，如果L2-PoAFound.request指定的链路质量级别阈值为良好，则当PoA的链路质量变得比良好时，会创建L2-PoAFound.indication并将其发送到上层。
In IEEE 802.11 networks, L2-PoALost is notified when an AP included in the list of candidate APs is lost by listening beacons or scanning APs. If the entry in the AP database described in Appendix D.2 expires, or link quality level goes under the threshold, then the link layer creates L2-PoALost.indication. To calculate the link quality level, the signal strength of the received frame (mainly the beacon or the probe response) can be used. For example, if the threshold of the link quality specified by L2-PoALost is BAD, L2-PoALost.indication is created and sent to the upper layer when PoA's link quality becomes worse than BAD.
在IEEE 802.11网络中，当候选AP列表中包含的AP因侦听信标或扫描AP而丢失时，会通知L2 PoALost。如果附录D.2中描述的AP数据库中的条目过期，或者链路质量级别低于阈值，则链路层创建L2-PoALost.指示。为了计算链路质量水平，可以使用接收帧的信号强度（主要是信标或探头响应）。例如，如果L2 PoALost指定的链路质量阈值不好，则当PoA的链路质量变得比不好时，会创建L2-PoALost.indication并发送到上层。
In IEEE 802.11 networks, L2-LinkUp is notified when association or reassociation event occurs. When such an event occurs, MN receives the association response frame or the reassociation response frame. Immediately after receiving it, the link layer creates L2-LinkUp.indication.
在IEEE 802.11网络中，当发生关联或重新关联事件时，会通知二级链接。当此类事件发生时，MN接收关联响应帧或重新关联响应帧。链路层在接收后立即创建L2-LinkUp.indication。
In IEEE 802.11 networks, L2-LinkDown is notified when a disassociation event occurs or when no beacon is received during a certain time. When such an event occurs, MN sends the disassociation frame to AP, or the entry of the specific AP is deleted from the AP database described in Appendix D.2. By detecting such events, the link layer creates an L2-LinkDown.indication.
在IEEE 802.11网络中，当发生解除关联事件或在特定时间内未接收到信标时，会通知L2链路断开。当此类事件发生时，MN向AP发送解除关联帧，或者从附录D.2中描述的AP数据库中删除特定AP的条目。通过检测此类事件，链路层创建L2-LinkDown.indication。
In IEEE 802.11 networks, L2-LinkStatusChanged is notified when the radio signal strength of the connected AP drops below the specified threshold.
在IEEE 802.11网络中，当所连接AP的无线信号强度下降到指定阈值以下时，会通知L2 LinkStatusChanged。
In IEEE 802.11 networks, each AP is identified by the BSSID and the service set of several APs is identified by the SSID. When L2-LinkConnect is used to connect a specific AP or a service set, the link layer should set the Basic Service Set Identifier (BSSID) or the Service Set Identifier (SSID). Also, the channel should be set appropriately at the same time by searching the database described in Appendix D.2. To connect to AP, MN should be authenticated by AP. MN sends the authentication message to AP, and then MN sends the association message to associate with AP.
在IEEE 802.11网络中，每个AP由BSSID标识，多个AP的服务集由SSID标识。当L2 LinkConnect用于连接特定AP或服务集时，链路层应设置基本服务集标识符（BSSID）或服务集标识符（SSID）。此外，应通过搜索附录D.2中所述的数据库，同时适当设置通道。要连接到AP，MN应该由AP进行身份验证。MN向AP发送认证消息，然后MN向AP发送关联消息以关联AP。
In IEEE 802.11 networks, MN sends the disassociation message to AP for disconnection. When L2-LinkDisconnect is used for disconnection from the current AP, the link layer should send the disassociation message to the appropriate AP, and stop data transmission.
在IEEE 802.11网络中，MN向AP发送解除关联消息以断开连接。当L2 LinkDisconnect用于断开与当前AP的连接时，链路层应向相应AP发送断开消息，并停止数据传输。
This section describes an implementation of the proposed link indication architecture and its evaluation.
本节描述拟议链路指示架构的实现及其评估。
An IEEE 802.11a wireless LAN device driver was modified to provide abstract link-layer information in the form of primitives defined in Section 4. The modified driver has two AP lists. One contains the device-dependent information such as RSSI, retransmission count, various AP parameters, and various statistics. The device-dependent information, except for the AP parameters, is updated whenever the device receives a frame. If the received frame is the management frame, the AP parameters are also updated according to the parameters in the frame.
对IEEE 802.11a无线LAN设备驱动程序进行了修改，以第4节中定义的原语形式提供抽象链路层信息。修改后的驱动程序有两个AP列表。其中一个包含设备相关信息，例如RSSI、重传计数、各种AP参数和各种统计信息。设备相关信息（AP参数除外）在设备接收到帧时更新。如果接收到的帧是管理帧，则AP参数也根据帧中的参数更新。
Another AP list contains the abstract information. The abstract information is updated periodically by using the device-dependent information. In the abstraction processing, for example, RSSI or the retransmission count is converted to the common indicator "link quality". In our outdoor testbed described below, the thresholds of the RSSI value between the link quality levels were defined as follows:
另一个AP列表包含抽象信息。通过使用设备相关信息定期更新抽象信息。例如，在抽象处理中，RSSI或重传计数被转换为公共指示符“链路质量”。在下面描述的室外试验台中，链路质量等级之间的RSSI值阈值定义如下：
o EXCELLENT -- 34 -- GOOD
o 很好，34，很好
o GOOD -- 27 -- FAIR
o 好，27，一般
o FIAR -- 22 -- BAD
o 菲亚尔-22--糟糕
o BAD -- 15 -- NONE
o 坏，15，没有
L2-PoAList and L2-LinkStatus were implemented by using only the abstract information. Thus, the upper layers can use information of the current AP and the adjacent APs without depending on the devices. L2-PoAFound or L2-PoALost is notified if the link quality rises or falls beyond the thresholds when the abstract information is updated. If the link quality of the current AP goes below the specific threshold, L2-LinkStatusChanged is notified. L2-LinkUp or L2-LinkDown is notified when an association with an AP is established or destroyed. To realize L2-LinkConnect and L2-LinkDisconnect, functions to connect or disconnect to the specified AP were implemented. In these functions, since only abstract information is needed to specify the AP, other layers need not know the device-dependent information.
L2 POLIST和L2 LinkStatus仅通过使用抽象信息实现。因此，上层可以在不依赖于设备的情况下使用当前AP和相邻AP的信息。更新抽象信息时，如果链接质量上升或下降超过阈值，则会通知L2 PoAFound或L2 PoALost。如果当前AP的链路质量低于特定阈值，则会通知L2 LinkStatusChanged。当与AP的关联建立或销毁时，会通知L2 LinkUp或L2 LinkDown。为了实现L2 LinkConnect和L2 LinkDisconnect，实现了连接或断开指定AP的功能。在这些函数中，由于只需要抽象信息来指定AP，所以其他层不需要知道设备相关信息。
In our outdoor testbed, there are eight Access Routers (ARs) located at 80-100m intervals. AP is collocated at AR. IEEE 802.11a was used as the link layer. The same wireless channel was used at all APs. Thus, there are eight wireless IPv6 subnets in the testbed. The mobile node was in a car moving at a speed of 30-40 km/h. When link quality of the current AP goes down, the mobile node executes L3-driven handover, described in Appendix A. An application called Digital Video Transport System (DVTS) was running on the mobile node and sent digital video data at a data rate of about 15Mbps through the wireless IPv6 subnet to the correspondent node, which replayed received digital video data. In this environment, the L2 handover required less than 1 msec, and the mobility protocol Location Independent Networking in IPv6 (LIN6) [13] required a few msecs for location registration. Thus, the total gap time due to the handover was 3-4 msec. In most cases, there was no effect on the replayed pictures due to handover.
在我们的室外试验台上，有八个接入路由器（AR），间隔80-100米。AP配置在AR。IEEE 802.11a用作链路层。所有AP均使用相同的无线信道。因此，试验台中有八个无线IPv6子网。移动节点位于一辆以30-40 km/h的速度行驶的汽车中。当当前AP的链路质量下降时，移动节点执行L3驱动的切换，如附录A所述。称为数字视频传输系统（DVTS）的应用程序正在移动节点上运行，并通过无线IPv6子网以约15Mbps的数据速率将数字视频数据发送到对应节点，重放接收到的数字视频数据。在这种环境中，L2切换所需的时间少于1毫秒，IPv6（LIN6）[13]中的移动协议位置独立网络需要几毫秒的时间进行位置注册。因此，由于切换而导致的总间隔时间为3-4毫秒。在大多数情况下，切换对重放的图片没有影响。
Authors' Addresses
作者地址
Fumio Teraoka Faculty of Science and Technology, KEIO University 3-14-1 Hiyoshi, Kohoku-ku Yokohama, Kanagawa 223-8522 Japan
日本神奈川市横滨市小冈区Hiyoshi 3-14-1庆应大学Teraoka科学技术学院，邮编223-8522
Phone: +81-45-566-1425
EMail: tera@ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Phone: +81-45-566-1425
EMail: tera@ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Kazutaka Gogo Graduate School of Science and Technology, KEIO University 3-14-1 Hiyoshi, Kohoku-ku Yokohama, Kanagawa 223-8522 Japan
日本神奈川市横滨市小冈区Hiyoshi 3-14-1号庆应大学和隆高科技研究生院223-8522
Phone: +81-45-566-1425
EMail: gogo@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Phone: +81-45-566-1425
EMail: gogo@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Koshiro Mitsuya Jun Murai Lab, Shonan Fujisawa Campus, KEIO University 5322 Endo Fujisawa, Kanagawa 252-8520 Japan
日本神奈川庆应大学藤泽昭南校区光谷村俊实验室5322藤泽内，神奈川252-8520
Phone: +81-466-49-1100
EMail: mitsuya@sfc.wide.ad.jp
Phone: +81-466-49-1100
EMail: mitsuya@sfc.wide.ad.jp
Rie Shibui Graduate School of Science and Technology, KEIO University 3-14-1 Hiyoshi, Kohoku-ku Yokohama, Kanagawa 223-8522 Japan
日本神奈川市横滨市小冈区Hiyoshi 3-14-1号庆应大学理建科学技术研究生院223-8522
Phone: +81-45-566-1425
EMail: shibrie@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Phone: +81-45-566-1425
EMail: shibrie@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Koki Mitani Graduate School of Science and Technology, KEIO University 3-14-1 Hiyoshi, Kohoku-ku Yokohama, Kanagawa 223-8522 Japan
日本神奈川市横滨市小冈区3-14-1 Hiyoshi庆应大学Koki Mitani科学技术研究生院223-8522
Phone: +81-45-566-1425
EMail: koki@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Phone: +81-45-566-1425
EMail: koki@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
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