RPR ups efficiency of metro

Ethernet(!)

Companies traditionally have gained basic resiliency for their metropolitan Ethernet networks through a Layer 2 mechanism such as Spanning Tree or Layer 3 routing protocols. But these mechanisms, with their few-second network restoration times, are inadequate for delay- and jitter-sensitive data applications that are proliferating rapidly on enterprise networks. To gain greater resiliency, corporations have had to install fixed-bandwidth point-to-point circuits, or fiber pairs, between campus nodes along with back-up paths for protection - a costly endeavor.

What companies need is a metropolitan Ethernet architecture with the resiliency of SONET but with significant network efficiencies for packet-based services. Resilient Packet Ring (RPR) is an emerging Layer 2 media access control (MAC) technology that meets those needs. The IEEE created a draft specification for RPR and is expected to ratify the standard this year.

RPR uses Ethernet switching and a dual counter-rotating ring topology to provide SONET-like network resiliency and optimized bandwidth usage, while delivering multipoint Ethernet/IP services. RPR maintains its own protection scheme and uses physical-layer alarm information and Layer 2 protocol communications to detect node and/or link failures. When a failure is detected, the RPR switching mechanism restores networks in less than 50 millisec.

Because RPR is a Layer 2 MAC-based technology, it can operate over multiple physical layers, including SONET. Therefore, corporations can reap the benefits of RPR by having it ride over the SONET network to deliver the resilient, efficient, multipoint functionality and scalability of data applications such as VoIP, packet video, business continuance and distance learning.

Or they can install multiservice provisioning platforms, which are optimized for TDM services but also can support advanced data applications via RPR over SONET. The advantage is that existing TDM services are maintained, while a smooth migration to packet-based services is enabled. (To Be Contiued)

時(shí)文選讀

彈性分組環(huán)( RPR)技術(shù)提升城域以太網(wǎng)的效率(1)

傳統(tǒng)上，各個(gè)公司是通過第二層機(jī)制(如生成樹)或第三層路由協(xié)議，獲得城域以太網(wǎng)的基本彈性。但這些機(jī)制具有幾秒鐘的網(wǎng)絡(luò)復(fù)原時(shí)間，對延遲和抖動(dòng)敏感的數(shù)據(jù)應(yīng)用是不適合的，而這樣的應(yīng)用卻在企業(yè)網(wǎng)上迅速增多。為了獲得更大的彈性，各公司不得不在有保護(hù)用備份通道的園區(qū)節(jié)點(diǎn)之間安裝固定帶寬的點(diǎn)對點(diǎn)電路，即光纖對，而這是很費(fèi)錢的事。

公司所需要的是城域以太網(wǎng)的架構(gòu)加上 SONET的彈性，但要具有適合基于分組服務(wù)的網(wǎng)絡(luò)高效率。RPR是新興的第二層媒體訪問控制(MAC)技術(shù)，能滿足這些要求。IEEE為RPR制定了一個(gè)規(guī)范草案，可望今年內(nèi)獲得批準(zhǔn)成為標(biāo)準(zhǔn)。

RPR利用以太網(wǎng)的交換和雙逆向旋轉(zhuǎn)環(huán)的拓?fù)浣Y(jié)構(gòu)，提供像SONET那樣的網(wǎng)絡(luò)彈性和優(yōu)化的帶寬應(yīng)用，同時(shí)提供多點(diǎn)的以太網(wǎng)/IP服務(wù)。RPR保留了它自己的保護(hù)方案，并使用物理層的報(bào)警信息和第二層協(xié)議通信來檢測節(jié)點(diǎn)和(或)鏈路的故障。當(dāng)檢測到故障時(shí)，RPR交換的機(jī)制能在不足50毫秒的時(shí)間內(nèi)恢復(fù)網(wǎng)絡(luò)。

由于 RPR是第二層基于MAC的技術(shù)，所以它能在多個(gè)物理層上工作，包括SONET。因此，企業(yè)能通過運(yùn)行在SONET網(wǎng)上提供彈性、高效、多點(diǎn)的功能性和數(shù)據(jù)應(yīng)用(如VoIP、分組視頻、業(yè)務(wù)連續(xù)和遠(yuǎn)程學(xué)習(xí)等)的可擴(kuò)性，從而獲得RPR的好處。

或者他們可以安裝多服務(wù)提供平臺(tái)，這些平臺(tái)為提供時(shí)分復(fù)用( TDM )服務(wù)進(jìn)行了優(yōu)化，同時(shí)也能通過 SONET 上的 RPR 支持高級的數(shù)據(jù)應(yīng)用。其優(yōu)點(diǎn)是在實(shí)現(xiàn)向基于分組服務(wù)平穩(wěn)過渡的同時(shí)保留了已有的 TDM 服務(wù)。