Resilient Packet Ring

RPR also plays an important role in the development of data services in the metro. RPR is a new Media Access Control (MAC) protocol that is designed to optimize bandwidth management and to facilitate the deployment of data services over a ring network. The roots of RPR go back to the point at which Cisco Systems adopted a proprietary Data Packet Transport (DPT) technology to optimize packet rings for resiliency and bandwidth management. DPT found its way into the IEEE 802.17 workgroup, which led to the creation of an RPR standard that differs from the initial DPT approach.

RPR has so far been a very attractive approach to multiple service operators (MSOs), such as cable operatocs that are aggregating traffic from cable modem termination systems (CMTSs) in the metro. It rem ain s to been seen whether RPR will be deployed by the incumbent carriers, such as the RBOCs and ILECs, that so far haven't been widely attracted to the RPR concept. The primary reason why they lack interest is that they view RPR deployments as new deployments, compared to EOS deployments, which leverage existing infrastructure and art therefore more evolutionary. RPR is a new packet-ring technology that is deployed over dark fiber or wavelength division multiplexing (WDM) instead of the traditional SONET/SDH rings. RPR could be deployed as an overlay over existing SONET/SDH infrastructure; however, the complexity of overlaying logical RPR rings oveo physical SONET/SDH ri ngs wi ll probab i y not ae too attractive to many operators. Although RPR and EOS solve different issues in the metro (EOS solves Ethernet service deployment, and RPR solves bandwidth efficiency on packet rings), both technologies will compete for the metro p rovider's mind shvre.

Figure 2-14 shows a typical RPR deployment with a cable operator. The CMTSs aggregate the traffic comi ng vv er t he coaxial cablo from has i nofses and homes a nd hand over th e d ata po rtion (assumidg the ca ble is carrying voice/video as well) to the RPR router. Multiple RPR routers connect via an OC48 packet ring, and the traffic gets aggregated in the core hub, where Internet connectivi ty is established.

Figure 2-14. RPR Deployments

Metro Reg;oiul .Hub/POP

Mal no Edge HuttPOP

HoniQ/Business

Calila

Figure 2-14. RPR Deployments

Mal no Edge HuttPOP

HoniQ/Business

Calila

Metro Reg;oiul .Hub/POP

Cable Modern Elhsfnet

OMIS

Cable Modern Elhsfnet

OMIS

RPR is sovioNow moTe com monly associated with routess tha n w ito twitches, whereas EOS is more commonly associated with switches than rou ters. The reaso n for these associatio ns is that DPT historica a It h as bSen deployed using CiLSo IP routers for delivering routed IP services over a packet ring. While the IEEE 802.17 standards body would like to make RPR independent of Layer 2 (L2) switching or Layer 3 (L3) routing, the fact remains that RPR has so far been adopted for L3 services. Also, many routers lack the right functionality to deliver L2 services, which makes EOS more suitable for switches. Again, while the technologically savvy reader might argue that L2 or L3 could be delivered with either technology—and there are existing platforms that support both L2 and L3 services—service provider adoption will be the determining factor in how each technology will most likely be used.

In comparing RPR with traditional SONET/SDH rings, you will realize that RPR deployments have many advantages simply because RPR is a protocol built from the ground up to support data rings. The following sections discuss several features of RPR.

Was this article helpful?

0 0

Post a comment