Packet Headers Format and Trace

蕭博鴻698430007

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Outline

IntroductionPacket ModulePacket HeaderPacket Header Mapping to OtclPacket Header Manager in NS2Defining a New Packet Header to NS2 [Step by Step]

Trace

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Introduction

Packet consists of packet header and data payload.

In most cases, NS2 extracts information from data payload and stores the information into packet header.

By default, NS2 includes All packet headers of All protocols in every packet.

In NS2, Class Packet is derived from class Event.

s.schedule(target_, p, txt + delay_)

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Packet Module

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C++ Variables of class Packet

unsigned char* bits_ AppData* data_ int hdr_len_ bool fflag_

- Set to true if the packet is currently referred to by other objects and false otherwise

Packet* free_ - Pointer to the head of the packet free list

int ref_count_ - Number of objects which currently refer to the packet

Packet* next_ - Pointer to the next packet in the linked list of packets

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C++ Functions of class Packet

void init(Packet* )- Clears the packet header bits_ of the input packet p.

Packet* copy() - Returns a pointer to a duplicated packet.

Packet* refcopy() - Increases the number of objects, which refer to the packet

Packet* alloc() - Creates a new packet and returns a pointer to the created packet.

Packet* alloc(n) - Creates a new packet with “n” bytes of data payload and returns a pointer to

the created packet.

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Cont’

void allocdata(int)- Allocates “n” bytes of data payload to the variable data_.

void free(Packet*) - Deallocates packet.

char* access(int) - Retrieves a reference to a certain point (specified by the offset “off”) of the

variable bits_ (i.e., packet header).

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Link List of Packet

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Packet Queue

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Packet Allocation

Packet* alloc() Packet* alloc(n)

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Packet Deallocation

void free(Packet*)

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Packet Header

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Packet Header Module

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Common Header

Structure

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Packet Type

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Packet Header Mapping

to OTcl

Class/Object Name

C++ Structure hdr_cmn

OTcl Class PacketHeader/Common

Mapping Class CommonHeaderClass

Mapping Variable class_cmnhdr

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Packet Header Manager in NS2

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Packet Header Manager

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Packet Header Manager add Packet Header

Add all Packet Header to Ns2Add all Packet Header to Ns2

Init SimulatorAnd Create Packet Format

Init SimulatorAnd Create Packet Format

Allocate Packet Header OffsetIn Packet And increase header length

Allocate Packet Header OffsetIn Packet And increase header length

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The Other Command

add-packet-header args- This global proc will tell simulator to include the specified packet header(s) in

your simulation.

remove-packet-header args- operates in the same syntax, but it removes the specified headers from your

simulation; notice that it does not remove the common header even it is instructed to do so.

remove-all-packet-headers- It takes no argument and removes all packet headers, except the common

header, from your simulation.

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1. Define a protocol specific header C++ struct hdr_echo_back

− Declare variable offset_

− Define function access(p)

− Include all member variables require to hold new packet attributes

2. Include new packet type into packet_t and class p_info

− Declare variable PT_ECHOBACK

− Protocol header ‘s name is “EchoBack”

3. Define a protocol specific header OTcl class PacketHeader/EchoBack

4. Derive a mapping class EchoBackHeaderClass from PacketHeaderClass

− At the construction, feed PacketHeader/EchoBack and sizeof(struct hdr_echo_back) of class PacketHeaderClass

− From within the constructor, Use bind_offset function to bind hdr_echo_back::offset_

5. Active Header into the PacketHeaderManager protocol list.

− Added EchoBack into the foreach loop

6. Edit Makefile to Compile your header, then clean the ns2 and recompile ns2.

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Defining a New Packet Header to NS2Step by Step

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抽考題目

在 NS2的封包內新增一個表頭 (EchoBack)。

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根據下面步驟來完成新增動作。1. Define a protocol specific header C++ struct hdr_echo_back

− Declare variable offset_

− Define function access(p)

− Include all member variables require to hold new packet attributes

2. Include new packet type into packet_t and class p_info

− Declare variable PT_ECHOBACK

− Protocol header ‘s name is “EchoBack”

3. Define a protocol specific header OTcl class PacketHeader/EchoBack

4. Derive a mapping class EchoBackHeaderClass from PacketHeaderClass

− At the construction, feed PacketHeader/EchoBack and sizeof(struct hdr_echo_back) of class PacketHeaderClass

− From within the constructor, Use bind_offset function to bind hdr_echo_back::offset_

5. Active Header into the PacketHeaderManager protocol list.

− Added EchoBack into the foreach loop

6. Edit Makefile to Compile your header, then clean the ns2 and recompile ns2.

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程式碼的部分已經完成，將 echo_back.cc 跟 echo_back.h 放到 NS2 的資料夾內，根據上面的步驟完成 2 、 5 、 6 的步驟

抽考題目 ( 提示 )

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THANK YOU