Resilient Packet Ring (RPR), as defined by

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...

standard 802.17, is a protocol designed for the transport of data traffic over

optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...

ring networks. The standard began development in November 2000 and has undergone several amendments since its initial standard was completed in June 2004. The amended standards are 802.17a through 802.17d, the last of which was adopted in May 2011. It is designed to provide the resilience found in SONET and

Synchronous Digital Hierarchy Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diode ...

networks (50 ms protection) but, instead of setting up circuit oriented connections, provides a packet based transmission, in order to increase the efficiency of

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

and IP services.

Technical details

RPR works on a concept of dual counter rotating rings called ringlets. These ringlets are set up by creating RPR stations at nodes where traffic is supposed to drop, per flow (a flow is the ingress and egress of data traffic). RPR uses Media Access Control protocol (MAC) messages to direct the traffic, which can use either ringlet of the ring. The nodes also negotiate for bandwidth among themselves using fairness algorithms, avoiding congestion and failed spans. The avoidance of failed spans is accomplished by using one of two techniques known as ''steering'' and ''wrapping''. Under steering, if a node or span is broken, all nodes are notified of a topology change and they reroute their traffic. In wrapping, the traffic is looped back at the last node prior to the break and routed to the destination station.

Class of service and traffic queues

All traffic on the ring is assigned a Class of Service (CoS) and the standard specifies three classes. Class A (or High) traffic is a pure

committed information rate In a Frame Relay network, committed information rate (CIR) is the bandwidth for a virtual circuit guaranteed by an internet service provider to work under normal conditions. Committed data rate (CDR) is the payload portion of the CIR. At any giv ...

(CIR) and is designed to support applications requiring low latency and

jitter In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a significa ...

, such as voice and video. Class B (or Medium) traffic is a mix of both a CIR and an

excess information rate Peak information rate (PIR) is a burstable billing, burstable rate set on routers and/or switches that allows throughput overhead. Related to committed information rate (CIR) which is a committed rate speed guaranteed/capped. For example, a CIR of ...

(EIR; which is subject to fairness queuing). Class C (or Low) is best effort traffic, utilizing whatever bandwidth is available. This is primarily used to support

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

access traffic.

Spatial reuse

Another concept within RPR is what is known as ''spatial reuse''. Because RPR strips the signal once it reaches the destination (unlike a SONET UPSR/SDH SNCP ring, in which the bandwidth is consumed around the entire ring) it can reuse the freed space to carry additional traffic. The RPR standard also supports the use of learning bridges ( IEEE 802.1D) to further enhance efficiency in point to multipoint applications and VLAN tagging (

IEEE 802.1Q IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual local area networking (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying proc ...

). One drawback of the first version of RPR was that it did not provide spatial reuse for frame transmission to/from

MAC address A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking techno ...

es not present in the

ring topology A ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node – a ring. Data travels from node to node, with each node along the way handling ever ...

. This was addressed by

802.17b, which defines an optional ''spatially aware sublayer'' (''SAS''). This allows spatial reuse for frame transmission to/from MAC address not present in the ring topology.

References

External links

IEEE 802.17 Resilient Packet Ring Working Group
{{IEEE standards IEEE 802 Network architecture IEEE standards

Technical details

Class of service and traffic queues

Spatial reuse

See also

References

External links