NS-2中实现多信道支持的详细指南

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"这篇文档详细介绍了如何在NS-2（网络模拟器2）中实现多信道支持。作者Ramón Agüero Calvo和Jesús Pérez Campo来自西班牙卡坦布里亚大学，该文档发布于2007年1月。主要内容包括多信道模型的需求与假设、节点模型的构建、Tcl代码的修改、C++代码的改动以及路由协议代码的调整。此外，还提供了一个AODV路由协议的示例，以及一个场景脚本作为应用展示。" **多信道模型** 在NS-2中添加多信道支持涉及多个层面的修改。首先，多信道模型需要满足一些基本需求和工作假设，例如支持多个接口同时通信、独立的信道分配和管理等。**多信道节点模型**是实现这一功能的基础，它允许每个节点拥有多个无线接口，每个接口可以独立地连接到不同的信道。 **Tcl代码的修改** 在Tcl层面上，主要的变化集中在`ns-lib.tcl`和`ns-mobilenode.tcl`两个文件。`ns-lib.tcl`的修改可能涉及到对新模型的注册和初始化，而`ns-mobilenode.tcl`的改动可能包括对多接口节点的创建和配置。 **C++代码的改动** 在C++代码部分，主要更新了`mobilenode.cc`、`channel.cc`和`mac-80211.cc`。`mobilenode.cc`的修改可能涉及到节点类的扩展，以容纳多个接口；`channel.cc`的更新可能涉及信道对象的管理和交互；`mac-80211.cc`的改动则可能与802.11MAC层的多信道支持有关。 **路由协议代码的调整** 在路由协议层面，文档详细阐述了如何适应多信道环境。这包括对`routingagent`实现的修改，以处理多个接口的路由信息；对`RouteTable`结构的更新，以支持多个接口的路由条目；以及对AODV路由协议的具体示例，展示了在AODV协议的`aodv.h`和`aodv.cc`文件中的改动，以及`aodvrtable.[cc,h]`中路由表实现的修改。 **场景脚本** 最后，文档提供了一个场景脚本，用以演示如何在实际模拟环境中应用这些更改，以展示多信道通信的运行效果。这篇文档为在NS-2中添加多信道支持提供了全面的指南，涵盖了从模型设计到代码实现再到实际应用的全过程。对于想要研究和实现多信道网络模拟的学者和开发者来说，具有很高的参考价值。

Chapter 2. Multiple Interface Model

Iface 0

Application

Routing Agent

255

Channel 0

Channel 1

Channel 2

Propagation

Model

Iface 1 Iface 2

Figure 2.2: Modiﬁed MobileNode architec ture, with multiple interface support

Chapter 3

Changes on Tcl Code

3.1 Introduction

As has been discussed within Chapter 2, we decided to base the multi-interface extension

mostly on th e Tcl implementation of the simulator, since we believed that this would probably

better ﬁt the intrinsic operation of the ns architecture. Most of the used Tcl procedures are

either within the tcl/lib/ns-lib.tcl or tcl/lib/ns-mobilenode.tcl ﬁles. In this chapter

we detail the changes that are required within each of them so as to extend the simulator to

be able to add multiple interfaces per node.

3.2 Changes on ns-lib.tcl

One aspect that is worth mentioning is that the developments described herewith d o require

creating the channel before calling the node-config procedu re (providing it as an argument),

instead of specifying the type of channel within the node-config call. Ch apter 6 extensively

discusses the script that needs to be used so as to simulate multiple interfaces.

We need to create four new procedures. The ﬁrst one change-numifs (see Listing 3.1) is

called before creating the wireless node, and allows the user to specify a diﬀerent number of

interfaces per node. Obviously, if called only once, it will aﬀect all nodes. This procedure,

as will be seen later, is called from the scenario script, and needs one argument, being the

number of interfaces that a particular node has.

Listing 3.1: (ns-lib.tcl) Procedure to change the number of interfaces

Si mu la to r i n s t p r o c change−numifs { newnumifs } {

$ s e l f i n s t v a r numi f s

s e t numi f s $newnumifs

}

The second one allows to add an interface (channel) to a node; it must be called, also

from the scenario script, before the node is created, and requires two argum ents: the ﬁrst one

is the index of such interface within the node, while the second one is the channel itself (Tcl

object previously created).

The third procedure we have added within the ns-lib.tcl does not need to be called

from the scenario script, but is required so that we can gather the number of interfaces from

Chapter 3. Changes on Tcl Code

Listing 3.2: (ns-lib.tcl) Pr ocedure to add an interface on a node

Si mu la to r i n s t p r o c add−channel { indexc h ch} {

$ s e l f i n s t v a r chan

s e t chan ( $indexc h ) $ch

}

other parts of the Tcl architecture, as will be seen later. It is called get-numifs and it is

shown in Listing 3.3.

Listing 3.3: (ns-lib.tcl) Pr ocedure to get the number of interfaces

Si mu la to r i n s t p r o c get−numifs { } {

$ s e l f i n s t v a r numi f s

i f [ i n f o e x i s t s nu mif s ] {

r etu r n $ numifs

} e l s e {

r etu r n ””

}

Last, we need to create another procedure, so that we can add the number of interfaces

as an argument to the node-config command of the Tcl script, as will be seen in Ch apter 6.

Listing 3.4: (ns-lib.tcl) Pr ocedure to add multiple interfaces as an argument to

node-conﬁg label

Si mu la to r i n s t p r o c ifNum { v a l } { $ s e l f s e t n u mif s $ val }

In addition to the new ones shown above, two of the already existing procedures need to

be modiﬁed. The ﬁrst one is node-config, in which we have to initialize the chan variable,

either as a single variable, if normal operation is being used, or as an array, when the multi-

interface is enabled. Furthermore, we add the numifs variable to the list of arguments passed

to the method. The changes are shown on Listing 3.5.

Listing 3.5: (ns-lib.tcl) Changes on node-conﬁg procedure

Si mu la to r i n s t p r o c node−config args {

# O b j e c t : : i n i t − v a r s {} i s de f i n e d in ˜ t c l c l / t c l − o b j e c t . t c l .

# I t i n i t i a l i z e s a l l d e f a u l t v a r i a b l e s i n the f o l l o w i n g

way:

# 1 . Look f o r p a i r s of {−cmd v a l } i n a r g s

# 2 . I f ” $ s e l f $cmd $ val ” i s not v a l i d then put i t i n a

l i s t o f

# arguments to be r e t urne d to the c a l l e r .

# Sin c e we do not handle unde f ined {−cmd val } p a i r s , we

i g n o r e

# r e tur n v a l ue from i n i t − v ar s {} .

s e t a r g s [ e va l $ s e l f i n i t− v a r s $args ]

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