一般常用的交換器 Switch 是屬於第二層交換器 Layer 2 Switch，這種交換器是利用 OSI 第二層 MAC 位址的資訊來進行資料交換，它可以記憶學習第一個 Port 連接的 MAC 位址，透過 MAC 位址及封包目的的位址的辨別，L2 Switch 會將該封包直接傳送至連接目的地的 Port，而不會將該封包傳送到其他的 Port。若並無此目的地 IP 的資訊時，則 L2 Switch 會廣播至所有的連接埠上，待目的 IP 回應時，將新的連接埠對應學習起來，那麼下次就不用廣播而直接傳送。
如果再把路由表的功能加入 L2 Switch，那麼它就會變成 L3 Switch，可以為 VLAN 建立適當的路由表，讓效能更加提昇。L3 的交換器又稱為 IP Switch 或 Switch Router，透過專屬的 ASIC 晶片來解析第三層表頭（如 IP Header）以達到傳送目的，因此通常可以提高到每秒百萬封包的效能以及數十個高速乙太網路連接埠之容量。L3 Switch 的路由表可以對 VLAN 做更有效的管制，讓廣播封包不會無限制的傳送。
2007年12月19日 星期三
2007年12月7日 星期五
啥是L3 Switch
Layer 3 Switch 又稱為IP Switch 或Switch Router, 意即其工作於第三層網路層的通信協定(如IP)，並藉由解析第三層表頭(Header)將封包傳至目的地，有別於傳統的路由器以軟體的方式來執行路由運算與傳送，Layer 3 Switch是以硬體的方式(通常由專屬ASIC構成)來加速路由運算與封包傳送率並結合Layer 2 的彈性設定，因此其效能通常可達每秒數百萬封包(Million packet per second)的傳送率，並具備數十個至上百個以上的高速乙太網路(Fast Ethernet)連接埠，或數個至數十個超高速乙太網路(Gigabit Ethernet)連接埠之容量。
傳統路由器通常可處理Multiprotocal 多重協定路由運算(如IP，IPX AppleTalk，DEC Net...etc)但Layer 3 Switch 通常只處理IP 及IPX，此乃為簡化設計，降低路由運算與軟體的複雜性以提昇效能，並配合網路協定發展的單純化(多重協定慢慢簡化至IP一種協定)趨勢所致。
由於Layer 2 的Switch 並無法有效的阻絕廣播域(Broadcast Domain)如ARP (Address Resolution Protocol)及Win95/98 中大量使用的NetBEUI協定均大量使用廣播封包，因此就算Layer 2 Switch 以VLAN (Virtual LAN)的方式(虛擬網路)將經常要通訊的群組構成一廣播域(Broadcast Domain)來試圖降低broadcast封包對網路層的影響，但仍無法完全避免廣播風暴問題(同一個VLAN間仍會產生廣播風暴)，再加上現今網路(尤其是Campus內部間流量及對外的Internet/Intranet流量)已不是80/20規則(80%流量在本地，20%是外地)，而是漸漸成為20/80規則，且加上Client/Server 及Distributor Server之運用，因此單靠Layer 2 Switch或傳統Router路由器便無法符合對效能(傳統路由器變成瓶頸)及Intranet上對安全顧忌(Layer 2 Broadcast Domain，對因廣播而使資訊傳送被盜取的安全疑慮)之要求，因此Layer 3 Switch便大量興起，初期只運用Core端(骨幹)，現在的趨勢已漸漸走向桌面(Layer 3 down to desktop)。
如同傳統路由器(Router)，Layer 3 Switch的每一個連接埠(port)都是一個子網路(Subnet)，而一個子網路就單獨是一個Broadcast Domain廣播域，因此每一個port的廣播封包並不會流竄到另一個port，其僅負責傳送要跨越子網路的封包(Routing Forward)，並以目的地的IP位址(目的地子網路的網路號碼)來決定封包要轉送至哪一個port，並以Routing Protocol(如RIP或OSPF)來交換Routing Table並學習網路拓蹼，其通常存放於Layer 3 Switch的Routing Forward Data-Base(FDB)，並以硬體及Route Cache的方式來加速IP table lookup並予以定址與更新(目前大多以ASICIC來執行)，因此才得以提昇運算效能達成Wiring Speed Forward之目的。
Layer 3 Switch通常提供較大頻寬的交換核心(Switch Fabric)以提供較大的容量(Port Capacity)與較高的交換效能，近來各廠家並不斷附以Layer 3 Switch更強大的支援能力，如Class of Service(服務等級優先權)，Quality of Service(服務品質保證)，Policy Management(策略分級品質與頻寬管制與管理)，Multicast Routing(群組廣播路由傳送)等功能，以符合網路環境的快速變化與應用。
傳統路由器通常可處理Multiprotocal 多重協定路由運算(如IP，IPX AppleTalk，DEC Net...etc)但Layer 3 Switch 通常只處理IP 及IPX，此乃為簡化設計，降低路由運算與軟體的複雜性以提昇效能，並配合網路協定發展的單純化(多重協定慢慢簡化至IP一種協定)趨勢所致。
由於Layer 2 的Switch 並無法有效的阻絕廣播域(Broadcast Domain)如ARP (Address Resolution Protocol)及Win95/98 中大量使用的NetBEUI協定均大量使用廣播封包，因此就算Layer 2 Switch 以VLAN (Virtual LAN)的方式(虛擬網路)將經常要通訊的群組構成一廣播域(Broadcast Domain)來試圖降低broadcast封包對網路層的影響，但仍無法完全避免廣播風暴問題(同一個VLAN間仍會產生廣播風暴)，再加上現今網路(尤其是Campus內部間流量及對外的Internet/Intranet流量)已不是80/20規則(80%流量在本地，20%是外地)，而是漸漸成為20/80規則，且加上Client/Server 及Distributor Server之運用，因此單靠Layer 2 Switch或傳統Router路由器便無法符合對效能(傳統路由器變成瓶頸)及Intranet上對安全顧忌(Layer 2 Broadcast Domain，對因廣播而使資訊傳送被盜取的安全疑慮)之要求，因此Layer 3 Switch便大量興起，初期只運用Core端(骨幹)，現在的趨勢已漸漸走向桌面(Layer 3 down to desktop)。
如同傳統路由器(Router)，Layer 3 Switch的每一個連接埠(port)都是一個子網路(Subnet)，而一個子網路就單獨是一個Broadcast Domain廣播域，因此每一個port的廣播封包並不會流竄到另一個port，其僅負責傳送要跨越子網路的封包(Routing Forward)，並以目的地的IP位址(目的地子網路的網路號碼)來決定封包要轉送至哪一個port，並以Routing Protocol(如RIP或OSPF)來交換Routing Table並學習網路拓蹼，其通常存放於Layer 3 Switch的Routing Forward Data-Base(FDB)，並以硬體及Route Cache的方式來加速IP table lookup並予以定址與更新(目前大多以ASICIC來執行)，因此才得以提昇運算效能達成Wiring Speed Forward之目的。
Layer 3 Switch通常提供較大頻寬的交換核心(Switch Fabric)以提供較大的容量(Port Capacity)與較高的交換效能，近來各廠家並不斷附以Layer 3 Switch更強大的支援能力，如Class of Service(服務等級優先權)，Quality of Service(服務品質保證)，Policy Management(策略分級品質與頻寬管制與管理)，Multicast Routing(群組廣播路由傳送)等功能，以符合網路環境的快速變化與應用。
2007年11月8日 星期四
Cisco Catalyst 2950 switch password recovery procedure
Cisco Catalyst 2950 Series Switches
Cisco Catalyst Fixed Configuration Layer 2 and Layer 3 Switches
Downloads
Cisco Catalyst Fixed Configuration Layer 2 and Layer 3 Switches
Document ID: 12040
--------------------------------------------------------------------------------
Contents
Introduction
Before You Begin
Conventions
Prerequisites
Step-by-Step Procedure
Related Information
--------------------------------------------------------------------------------
Introduction
This document describes the password recovery procedure for the Cisco Catalyst Layer 2 fixed configuration switches 2900XL/3500XL, 2940, 2950/2955, 2960, and 2970 Series, as well as the Cisco Catalyst Layer 3 fixed configuration switches 3550, 3560, and 3750 Series.
Before You Begin
Conventions
For more information on document conventions, see the Cisco Technical Tips Conventions.
Prerequisites
There are no specific prerequisites for this document.
Step-by-Step Procedure
Follow the password recovery procedure below.
Attach a terminal or PC with terminal emulation (for example, Hyper Terminal) to the console port of the switch.
Use the following terminal settings:
Bits per second (baud): 9600
Data bits: 8
Parity: None
Stop bits: 1
Flow Control: Xon/Xoff
Note: For additional information on cabling and connecting a terminal to the console port, refer to Connecting a Terminal to the Console Port on Catalyst Switches.
Unplug the power cable.
Power the switch and bring it to the switch: prompt:
For 2900XL, 3500XL, 2940, 2950, 2960, 2970, 3550, 3560, and 3750 series switches, do this:
Hold down the mode button located on the left side of the front panel, while you reconnect the power cable to the switch.
Catalyst Switch Series
LED Behavior and Mode Button Release Action
2900XL, 3500XL, 3550
Release the Mode button when the LED above Port1x goes out.
2940, 2950
Release the Mode button after approximately 5 seconds when the Status (STAT) LED goes out. When you release the Mode button, the SYST LED blinks amber.
2960, 2970
Release the Mode button when the SYST LED blinks amber and then turns solid green. When you release the Mode button, the SYST LED blinks green.
3560, 3750
Release the Mode button after approximately 15 seconds when the SYST LED turns solid green. When you release the Mode button, the SYST LED blinks green.
Note: LED position may vary slightly depending on the model.
Catalyst 3524XL
Catalyst 2950-24
For 2955 series switches only:
The Catalyst 2955 series switches do not use an external mode button for password recovery. Instead the switch boot loader uses the break-key detection to stop the automatic boot sequence for the password recovery purposes. The break sequence is determined by the terminal application and operating system used. Hyperterm running on Windows 2000 uses Ctrl + Break. On a workstation running UNIX, Ctrl-C is the break key. For more information, refer to Standard Break Key Sequence Combinations During Password Recovery.
The example below uses Hyperterm to break into switch: mode on a 2955.
C2955 Boot Loader (C2955-HBOOT-M) Version 12.1(0.0.514), CISCO DEVELOPMENT TEST
VERSION
Compiled Fri 13-Dec-02 17:38 by madison
WS-C2955T-12 starting...
Base ethernet MAC Address: 00:0b:be:b6:ee:00
Xmodem file system is available.
Initializing Flash...
flashfs[0]: 19 files, 2 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 7741440
flashfs[0]: Bytes used: 4510720
flashfs[0]: Bytes available: 3230720
flashfs[0]: flashfs fsck took 7 seconds.
...done initializing flash.
Boot Sector Filesystem (bs:) installed, fsid: 3
Parameter Block Filesystem (pb:) installed, fsid: 4
*** The system will autoboot in 15 seconds ***
Send break character to prevent autobooting.
!--- Wait until you see this message before
!--- you issue the break sequence.
!--- Ctrl+Break is entered using Hyperterm.
The system has been interrupted prior to initializing the flash file system to finish
loading the operating system software:
flash_init
load_helper
boot
switch:Issue the flash_init command.
switch: flash_init
Initializing Flash...
flashfs[0]: 143 files, 4 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 3612672
flashfs[0]: Bytes used: 2729472
flashfs[0]: Bytes available: 883200
flashfs[0]: flashfs fsck took 86 seconds
....done Initializing Flash.
Boot Sector Filesystem (bs:) installed, fsid: 3
Parameter Block Filesystem (pb:) installed, fsid: 4
switch:
!--- This output is from a 2900XL switch. Output from
!--- other switches will vary slightly.
Issue the load_helper command.
switch: load_helper
switch:Issue the dir flash: command.
Note: Make sure to type a colon ":" after the dir flash.
The switch file system is displayed:
switch: dir flash:
Directory of flash:/
2 -rwx 1803357 c3500xl-c3h2s-mz.120-5.WC7.bin
!--- This is the current version of software.
4 -rwx 1131 config.text
!--- This is the configuration file.
5 -rwx 109 info
6 -rwx 389 env_vars
7 drwx 640 html
18 -rwx 109 info.ver
403968 bytes available (3208704 bytes used)
switch:
!--- This output is from a 3500XL switch. Output from
!--- other switches will vary slightly.
Type rename flash:config.text flash:config.old to rename the configuration file.
switch: rename flash:config.text flash:config.old
switch:
!--- The config.text file contains the password
!--- definition.
Issue the boot command to boot the system.
switch: boot
Loading "flash:c3500xl-c3h2s-mz.120-5.WC7.bin"...###############################
################################################################################
######################################################################
File "flash:c3500xl-c3h2s-mz.120-5.WC7.bin" uncompressed and installed, entry po
int: 0x3000
executing...
!--- Output suppressed.
!--- This output is from a 3500XL switch. Output from other switches
!--- will vary slightly.
Enter "n" at the prompt to abort the initial configuration dialog.
--- System Configuration Dialog ---
At any point you may enter a question mark '?' for help.
Use ctrl-c to abort configuration dialog at any prompt.
Default settings are in square brackets '[]'.
Continue with configuration dialog? [yes/no]: n
!--- Type "n" for no.
Press RETURN to get started.
!--- Press Return or Enter.
Switch>
!--- The Switch> prompt is displayed.
At the switch prompt, type en to enter enable mode.
Switch>en
Switch#Type rename flash:config.old flash:config.text to rename the configuration file with its original name.
Switch#rename flash:config.old flash:config.text
Destination filename [config.text]
!--- Press Return or Enter.
Switch#Copy the configuration file into memory.
Switch#copy flash:config.text system:running-config
Destination filename [running-config]?
!--- Press Return or Enter.
1131 bytes copied in 0.760 secs
Sw1#The configuration file is now reloaded.
Overwrite the current passwords that you do not know. Choose a strong password with at least one capital letter, one number, and one special character.
Note: Overwrite the passwords which are necessary. You need not overwrite all of the mentioned passwords.
Sw1# conf t
!--- To overwrite existing secret password
Sw1(config)#enable secret
!--- To overwrite existing enable password
Sw1(config)#enable password
!--- To overwrite existing vty password
Sw1(config)#line vty 0 15
Sw1(config-line)#password
Sw1(config-line)#login
!--- To overwrite existing console password
Sw1(config-line)#line con 0
Sw1(config-line)#password
Write the running configuration to the configuration file with the write memory command.
Sw1#write memory
Building configuration...
[OK]
Sw1#
--------------------------------------------------------------------------------
Related Information
Password Recovery Procedures
Switches Product Support
LAN Switching Technology Support
Technical Support - Cisco Systems
Cisco Catalyst Fixed Configuration Layer 2 and Layer 3 Switches
Downloads
Cisco Catalyst Fixed Configuration Layer 2 and Layer 3 Switches
Document ID: 12040
--------------------------------------------------------------------------------
Contents
Introduction
Before You Begin
Conventions
Prerequisites
Step-by-Step Procedure
Related Information
--------------------------------------------------------------------------------
Introduction
This document describes the password recovery procedure for the Cisco Catalyst Layer 2 fixed configuration switches 2900XL/3500XL, 2940, 2950/2955, 2960, and 2970 Series, as well as the Cisco Catalyst Layer 3 fixed configuration switches 3550, 3560, and 3750 Series.
Before You Begin
Conventions
For more information on document conventions, see the Cisco Technical Tips Conventions.
Prerequisites
There are no specific prerequisites for this document.
Step-by-Step Procedure
Follow the password recovery procedure below.
Attach a terminal or PC with terminal emulation (for example, Hyper Terminal) to the console port of the switch.
Use the following terminal settings:
Bits per second (baud): 9600
Data bits: 8
Parity: None
Stop bits: 1
Flow Control: Xon/Xoff
Note: For additional information on cabling and connecting a terminal to the console port, refer to Connecting a Terminal to the Console Port on Catalyst Switches.
Unplug the power cable.
Power the switch and bring it to the switch: prompt:
For 2900XL, 3500XL, 2940, 2950, 2960, 2970, 3550, 3560, and 3750 series switches, do this:
Hold down the mode button located on the left side of the front panel, while you reconnect the power cable to the switch.
Catalyst Switch Series
LED Behavior and Mode Button Release Action
2900XL, 3500XL, 3550
Release the Mode button when the LED above Port1x goes out.
2940, 2950
Release the Mode button after approximately 5 seconds when the Status (STAT) LED goes out. When you release the Mode button, the SYST LED blinks amber.
2960, 2970
Release the Mode button when the SYST LED blinks amber and then turns solid green. When you release the Mode button, the SYST LED blinks green.
3560, 3750
Release the Mode button after approximately 15 seconds when the SYST LED turns solid green. When you release the Mode button, the SYST LED blinks green.
Note: LED position may vary slightly depending on the model.
Catalyst 3524XL
Catalyst 2950-24
For 2955 series switches only:
The Catalyst 2955 series switches do not use an external mode button for password recovery. Instead the switch boot loader uses the break-key detection to stop the automatic boot sequence for the password recovery purposes. The break sequence is determined by the terminal application and operating system used. Hyperterm running on Windows 2000 uses Ctrl + Break. On a workstation running UNIX, Ctrl-C is the break key. For more information, refer to Standard Break Key Sequence Combinations During Password Recovery.
The example below uses Hyperterm to break into switch: mode on a 2955.
C2955 Boot Loader (C2955-HBOOT-M) Version 12.1(0.0.514), CISCO DEVELOPMENT TEST
VERSION
Compiled Fri 13-Dec-02 17:38 by madison
WS-C2955T-12 starting...
Base ethernet MAC Address: 00:0b:be:b6:ee:00
Xmodem file system is available.
Initializing Flash...
flashfs[0]: 19 files, 2 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 7741440
flashfs[0]: Bytes used: 4510720
flashfs[0]: Bytes available: 3230720
flashfs[0]: flashfs fsck took 7 seconds.
...done initializing flash.
Boot Sector Filesystem (bs:) installed, fsid: 3
Parameter Block Filesystem (pb:) installed, fsid: 4
*** The system will autoboot in 15 seconds ***
Send break character to prevent autobooting.
!--- Wait until you see this message before
!--- you issue the break sequence.
!--- Ctrl+Break is entered using Hyperterm.
The system has been interrupted prior to initializing the flash file system to finish
loading the operating system software:
flash_init
load_helper
boot
switch:Issue the flash_init command.
switch: flash_init
Initializing Flash...
flashfs[0]: 143 files, 4 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 3612672
flashfs[0]: Bytes used: 2729472
flashfs[0]: Bytes available: 883200
flashfs[0]: flashfs fsck took 86 seconds
....done Initializing Flash.
Boot Sector Filesystem (bs:) installed, fsid: 3
Parameter Block Filesystem (pb:) installed, fsid: 4
switch:
!--- This output is from a 2900XL switch. Output from
!--- other switches will vary slightly.
Issue the load_helper command.
switch: load_helper
switch:Issue the dir flash: command.
Note: Make sure to type a colon ":" after the dir flash.
The switch file system is displayed:
switch: dir flash:
Directory of flash:/
2 -rwx 1803357
!--- This is the current version of software.
4 -rwx 1131
!--- This is the configuration file.
5 -rwx 109
6 -rwx 389
7 drwx 640
18 -rwx 109
403968 bytes available (3208704 bytes used)
switch:
!--- This output is from a 3500XL switch. Output from
!--- other switches will vary slightly.
Type rename flash:config.text flash:config.old to rename the configuration file.
switch: rename flash:config.text flash:config.old
switch:
!--- The config.text file contains the password
!--- definition.
Issue the boot command to boot the system.
switch: boot
Loading "flash:c3500xl-c3h2s-mz.120-5.WC7.bin"...###############################
################################################################################
######################################################################
File "flash:c3500xl-c3h2s-mz.120-5.WC7.bin" uncompressed and installed, entry po
int: 0x3000
executing...
!--- Output suppressed.
!--- This output is from a 3500XL switch. Output from other switches
!--- will vary slightly.
Enter "n" at the prompt to abort the initial configuration dialog.
--- System Configuration Dialog ---
At any point you may enter a question mark '?' for help.
Use ctrl-c to abort configuration dialog at any prompt.
Default settings are in square brackets '[]'.
Continue with configuration dialog? [yes/no]: n
!--- Type "n" for no.
Press RETURN to get started.
!--- Press Return or Enter.
Switch>
!--- The Switch> prompt is displayed.
At the switch prompt, type en to enter enable mode.
Switch>en
Switch#Type rename flash:config.old flash:config.text to rename the configuration file with its original name.
Switch#rename flash:config.old flash:config.text
Destination filename [config.text]
!--- Press Return or Enter.
Switch#Copy the configuration file into memory.
Switch#copy flash:config.text system:running-config
Destination filename [running-config]?
!--- Press Return or Enter.
1131 bytes copied in 0.760 secs
Sw1#The configuration file is now reloaded.
Overwrite the current passwords that you do not know. Choose a strong password with at least one capital letter, one number, and one special character.
Note: Overwrite the passwords which are necessary. You need not overwrite all of the mentioned passwords.
Sw1# conf t
!--- To overwrite existing secret password
Sw1(config)#enable secret
!--- To overwrite existing enable password
Sw1(config)#enable password
!--- To overwrite existing vty password
Sw1(config)#line vty 0 15
Sw1(config-line)#password
Sw1(config-line)#login
!--- To overwrite existing console password
Sw1(config-line)#line con 0
Sw1(config-line)#password
Write the running configuration to the configuration file with the write memory command.
Sw1#write memory
Building configuration...
[OK]
Sw1#
--------------------------------------------------------------------------------
Related Information
Password Recovery Procedures
Switches Product Support
LAN Switching Technology Support
Technical Support - Cisco Systems
2007年10月7日 星期日
What is "AGPS"
輔助全球衛星定位系統（英語：Assisted Global Positioning System，簡稱：AGPS）是一種 GPS 的運行方式。它可以利用手機基地台的資訊，配合傳統 GPS 衛星，讓定位的速度更快。一般 GPS 使用太空中的 24 個人造衛星來三角定位 GPS 接受器的位置，並提供經緯度座標，而且需要一個空曠的地點並且需要至少 4 顆 GPS 衛星訊號才能 3D 定位。AGPS 是使用協助服務的技術，可以利用手機基地台的資訊，透過連結遠端伺服器的方式下載 衛星星曆 (英語：Almanac Data)，再配合傳統 GPS 衛星接受器，讓定位的速度更快，用來減少定位所需的時間。
普通的 GPS 系統是由 GPS 衛星和 GPS 接受器組成，與普通的 GPS 不同，AGPS在系統中還有一個輔助伺服器，在 AGPS 網路中，由於受到接收器工作功率和地理位置的影響而不能獲得理想的定位效果，接受器往往與有著較高功率的輔助伺服器通信並接入網路，雖然與蜂窩系統的覆蓋範圍有關，但由於 AGPS 接收器與輔助伺服器間的任務共享，所以 AGPS 往往比普通的 GPS 系統有速度更快的定位能力、有更高的效率。
在蜂窩移動通信系統中，AGPS 系統通過手機定位伺服器作為輔助伺服器來協助 GPS 接收器完成測距和定位服務，輔助定位伺服器有比 GPS接收器強大得多的功率來接受 GPS 信號，在這種情況下，輔助定位伺服器通過網路與手機的 GPS 接收器通信，由於有了移動網路的協助，GPS接收器的效率比沒有協助定位伺服器 AGPS 的時候有了很大的提高，因為有部分原本由接收器處理的工作被輔助定位伺服器所處理，例如GPS接收器冷開機到暖開機的工作，就是由協助定位伺服器 AGPS 所處理。
通常情況下，一個標準的 GPS 接收器需要至少 4 顆 GPS 衛星訊號才能 3D 定位。另外，還需要有足夠的處理功率來把衛星的數據轉換成坐標，使用 AGPS 接收 GPS 衛星信號，計算定位的任務都由輔助定位伺服器完成。--------------------------Content from Wiki
普通的 GPS 系統是由 GPS 衛星和 GPS 接受器組成，與普通的 GPS 不同，AGPS在系統中還有一個輔助伺服器，在 AGPS 網路中，由於受到接收器工作功率和地理位置的影響而不能獲得理想的定位效果，接受器往往與有著較高功率的輔助伺服器通信並接入網路，雖然與蜂窩系統的覆蓋範圍有關，但由於 AGPS 接收器與輔助伺服器間的任務共享，所以 AGPS 往往比普通的 GPS 系統有速度更快的定位能力、有更高的效率。
在蜂窩移動通信系統中，AGPS 系統通過手機定位伺服器作為輔助伺服器來協助 GPS 接收器完成測距和定位服務，輔助定位伺服器有比 GPS接收器強大得多的功率來接受 GPS 信號，在這種情況下，輔助定位伺服器通過網路與手機的 GPS 接收器通信，由於有了移動網路的協助，GPS接收器的效率比沒有協助定位伺服器 AGPS 的時候有了很大的提高，因為有部分原本由接收器處理的工作被輔助定位伺服器所處理，例如GPS接收器冷開機到暖開機的工作，就是由協助定位伺服器 AGPS 所處理。
通常情況下，一個標準的 GPS 接收器需要至少 4 顆 GPS 衛星訊號才能 3D 定位。另外，還需要有足夠的處理功率來把衛星的數據轉換成坐標，使用 AGPS 接收 GPS 衛星信號，計算定位的任務都由輔助定位伺服器完成。--------------------------Content from Wiki
2007年6月24日 星期日
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