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DPNSS Versus QSIG - Can They Coexist?

很多人聽過PBX之間交換的標準-QSIG,但是可能比較少人聽過DPNSS,事實上DPNSS也是另外一種跟QSIG類似的PBX交換標準,但是它們之間到底有那些不相同的地方及歷史上演進的結果為何?

請參閱下文Q&A:

http://www.pqmconsultants.com/coexist.htm

Q. What are DPNSS and QSIG?
DPNSS and QSIG are inter-exchange signalling protocols, primarily intended for the interconnection of nodes in a Corporate telecommunication Network (CN). The interconnection of PABXs using leased circuits is a typical application. Both DPNSS and QSIG are common channel signalling systems based on ISDN technology. They are open standards; that is, they permit signalling between equipment from different vendors.

Q. How did DPNSS come about?
The development of DPNSS commenced in 1981 with the decision by the UK telecomms industry (British Telecom, as was, and a number of PABX manufacturers) to develop a vendor independent private network signalling system. This work resulted in the protocol that is today widely used throughout the UK and elsewhere. The drivers behind DPNSS development are well known. They were the…

Silence Insertion Descriptor(SID)

A method of compression used in speech encoding that transmits a data packet in place of silence at a compressed rate.

SID mathematically describes the background noise during a session so that the receiving end can artificially reproduce that noise during silence periods.

Transmitting the SID requires almost no bandwidth as transmitting the actual background noise does.

SIP的關鍵元件

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SIP通過類似E-mail形式的資源識別標誌(URI)來標名用戶地址,它通過諸如用戶電話號碼、帳號、主機名等元素來構成SIP URI,其格式為user@domain的表示方式。其中user也可以是傳統電信網路中的e.164電信交換碼。 

SIP關鍵元件及其呼叫模式。
SIP的關鍵元件有下列幾項: 
用戶代理User Agent:
通常簡稱為UA,是SIP網路環境中的用戶終端設備,其角色相當於H.323 Terminal。在邏輯上包含有User Agent Client (UAC) 以及 User Agent Server(UAS)兩種,UAC負責產生請求,而UAS負責產生依照請求產生應答。每一個UA都同時扮演者UAC和UAS的角色,當它是呼叫別人的主叫端時,就是UAC;當它是被別人呼叫的被叫端時,就是UAS。 

目前我們所能看到的各種話機,本質上都是一種SIP UA裝置。有一種USB Phone是配合Soft Phone使用的,它的本質是一種音效裝置,雖然很多人也叫它做網路話機,但是它並不屬於SIP UA的角色。 

代理伺服器Proxy Server:
為SIP協議運作的中心,同時具有伺服器端和客戶端雙重角色的中介元件,負責代表SIP UA或者其他的Proxy Server產生請求或將收到的請求代為轉送到另外一個目標SIP元件去。由Proxy Server提供對用戶定位的服務,以轉送到正確的UA位置去,且UA回覆結果也是一樣會經由相反的路由將結果回覆給請求端的UA,這就是Proxy Server的路由功能。 

Proxy Server其實就是扮演傳統電信領域中,交換總機的角色。由於它的存在,可大幅簡化UA的設計複雜度(否則UA要能記得所有通訊對象的IP網址),也是VoIP業者營運的中樞。 

重定向伺服器Redirect Server:
SIP的其中一個主要特性就是,它將用戶的邏輯位址和實際位址分開,這使得用戶可以定義一個不變的邏輯位置,然後將它映射成別名至一個或多個變化的實際位置。重定向伺服器接受任何SIP元件的請求,並將被呼叫方的SIP位址映射成一個或多個位址並將回應給客戶端。和代理伺服器不同的是,重定向伺服器不會轉遞任何請求到其他伺服器。 

註冊伺服器Register Server:
接受註冊請求的伺服器,其目的是記錄用戶在請求中的聯繫資訊,或更新位置伺服器中的位址資料庫。註冊伺服器…

如何辨識PSP主機是否可以改機?

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我想這個問題是每一位想要買PSP新手的最大問號,沒有一個人希望買到的PSP只能發揮一小部份的功能,網路上大部份文章只提到「PSP 1000一定可以改,PSP 2000要看情況(舊款可以,新款不行),PSP 3000目前尚未有正式破解的解決方案。」雖然看來答案很明確,但是問題是PSP 2000要如何選購才能買到可以打開小宇宙的PSP呢?  另一種最簡單的方式是直接到店面去問老闆,或是直接參考售價(物以稀為貴,能改機的PSP售價至少比不能改機的PSP高出 NT$1000~NT$1500以上)。為了避免自己成為冤大頭,請各位在敗家之前先看看以下文章:
Is This PSP Hackable?! Allow me to Answer That!!
2009/02/01 (YYYY/MM/DD)

First thing's first, know your PSP.

There are three types of PSPs:
1- 1000 Series (Also known as Phat/Fat)
2- 2000 Series (Also known as Slim or Lite & Slim)
3- 3000 Series (Also known as Brite)

Now, what do I mean by "Hackable"?
That means you can install a Custom Firmware (CFW) on it. The most popular (& sometimes only) way to do it is by using a Pandora Battery & Magic Memory Stick (MMS).

Why Hack a PSP?
A Hacked PSP could run Homebrew, which are programs that have been developed by people that don’t have a contract with Sony. A PSP with Custom Firmware could also back up your games from the UMD to your computer; …