Packet Ring with High Resilience, For the carriers’ metropolitan and national SONET and Ethernet networks, a packet-based protocol that enables fault tolerance and statistical multiplexing. The RPR architecture is frequently used to enable SONET networks to carry packets. RPR is a fault-tolerant data link layer protocol (layer 2) that employs two counter-rotating rings.

In a packet environment (Ethernet), RPR nodes are often routers and switches, while in a TDM environment, they are add/drop multiplexers (ADMs) (SONET). With its 802.17 specification, the IEEE has standardised RPR.

RPR is a protocol for data transfer across fiber-optic ring networks that is standardised by IEEE 802.17. It operates at the OSI model’s MAC layer. It is packet-based and focuses on increasing the efficiency of IP and Ethernet services.

The implementation of robust packet rings improves the network’s bandwidth utilisation, throughput, deployment speed, and operational cost and equipment optimization. Because standard ethernet cannot handle or provide business-class reliability, RPR was created. It also struggles to deal with latency and the quality of voice packet services.

Resilient Packet Ring Fundamentals (RPR)

Where fibre installation is done in a ringway, a robust packet ring station is constructed. It evolved from previously installed Ethernet and SONET networks. It’s a type of media access control packet that facilitates numerical multiplexing over a spatial reuse infrastructure. The spatial reuse infrastructure provides for the continuing use of freed space in order to increase the amount of traffic transported over. It satisfies the requirements of a packet-based metropolitan area network.

Wrapping and steering are employed by nodes to ensure effective bandwidth transmission. If a node is damaged during steering, traffic is forwarded to the previous node before the injured one. If any of the lines break, the ring is altered to make one of the rings a return node. As a result, the architecture recovers faster, resulting in less downtime.

Rings that rotate in opposite directions

Two fibres join RPR nodes in a ring topology, each transmitting in the opposite direction. At the same moment, both the inner and outer ringlets are active. If there is a fault, traffic capacity is reduced.

Packets travel across the ring, passing via each node until they reach the destination node, where they are stripped. Multiple nodes’ traffic travels on the ring at the same time in an RPR.

A “fairness” algorithm is included in RPR. Because packets flow via all intermediary nodes, if a node cannot receive its fair portion of bandwidth on the ring to transmit, it can inform the others to slow the transmission. This traffic modification improves statistical multiplexing and assures equal access during peak periods.

Principle of Operation

Dual counter rotating fibre optic rings called ringlets connect the stations in an RPR. Transmission happens on both rings. When opposed to systems where a secondary ring is preserved solely for backup purposes, this allows for better utilisation of the total available bandwidth.

Both the ringlets are used for data transfer and control signal transmission. The control signal travels in the opposite direction of the data transmission that contains the information. For example, if the outer ring transmits data, the inner ring carries control information.

An RPR node can negotiate bandwidth concerns with other nodes in real time. It’s a Quality of Service (QoS)-aware facility that can prioritise traffic and schedule it accordingly. This reduces transmission failures and avoids congestion. If a link in any ringlet is broken, data transfer continues using steering and wrapping techniques. All nodes are notified of the broken link in steering, and they divert their traffic accordingly. Wrapping involves looping data traffic back to the last node before the link breaks and routing it to the destination station via the other ringlet.

In the event of a fibre break or other loss, SONET has built-in resiliency that provides very rapid restoral times (less 50 milliseconds). Because end-to-end circuit-switched data is not processed at intermediary nodes, it also provides very low latency and jitter. However, it is costly: bandwidth is fixed on a circuit-by-circuit basis (reliable, but capacity-inefficient).

For voice traffic, Ethernet has lacked the ability to deliver business-class dependability and manage latency and jitter QoS criteria.

As a result, the Ethernet community created IEEE 802.17, often known as RPR, to combine the features of the two technologies. “SONET performance at Ethernet economics!” is the RPR rallying cry.

It’s worth noting that different vendors’ prestandard RPR implementations – Cisco, Nortel, and others – have different brand names. RPR specifies a new media-access control (MAC) packet format for statistical multiplexing over SONET networks (also called “spatial reuse”). According to Martin Green, Cisco’s product manager of high-end routing, the client side of the CPE could “speak” Ethernet, while the MAN/WAN side could “speak” RPR.

RPR enables for two types of service to handle latency and jitter, according to Green: high priority and low priority. “It’s a more straightforward method of implementing QoS since, like SONET, it’s end-to-end, with no processing in intermediate nodes.”

However, while restoral times are comparable to SONET’s sub-50-millisecond failover, there is momentarily less bandwidth available if a fibre is cut. This is in contrast to SONET, which reserves 50% of its bandwidth for such such occasions.

Resilience Packet Ring traffic queues and service classes

When data packets are aligned in a sequence or in order in computer networking, this is referred to as a queue. Queues are made up of numerous packets that are sent out according to a predetermined network mechanism. First In First Out and Last In First Out are two examples of such algorithms.

The traffic in this RPR technology is assigned to a service class, which is divided into three categories: A, B, and C. They concurrently denote heavy, medium, and low traffic.

Class A is a virtual circuit bandwidth that supports applications with low latency, such as video. Class B is defined as a combination of the virtual circuit’s bandwidth and a burst intensity that is greater than the CIR. Class C is the most effective effort traffic, and it is extremely adaptable because it incorporates any available bandwidth to provide internet access traffic.

Types of transmission media that have been adopted

What is the definition of transmission media?

A transmission media in networking is any channel that is used to send data or packets from point A (source) to point B (destination) (destination). The primary purpose of communication media is to transport data in the form of bits across a network. In data communication, transmission media are also known as pathways that connect the sender and recipient. In the Open System Interconnection (OSI) paradigm, transmission media are considered layer one components.

In RPR, what kind of transmission media is used?

Access to the media Control panels are the pieces of hardware that allow you to communicate with a wireless or wired transmission channel. It has a logical link control layer linked to the data link layer that allows for flow control and multiplexing of the transmission medium.

MAC captures frames during data transfers and adds synchronisation for efficient transmission. The frame is then given an error-detection code. After detecting a jam signal, the MAC remedies for collisions by re-originating transmission. Through the inspection of the sequence for the sender’s frame check, it assures data integrity.

Packet Ring Technology’s Applications

  • Resilient packet ring is a relatively new technique that is quickly and widely implemented. The following are some examples of how network architecture is used:
  • Carrier networks for national SONET, metropolitan, and ethernet
  • This architecture is usually implemented in SONET networks in order for them to be able to transfer packets. This is because the RPR technique provides fault-tolerant network statistical multiplexing.
  • Enhancement of Efficiency

RPR is a network architecture that is designed to meet the requirements of a packet-based Metropolitan Area Network based on packets. This network is made up of packet-switching nodes that are connected by a pair of fibres to adjacent nodes. It also features two rings that rotate in opposite directions. This design ensures that the architecture is as efficient as possible for the users.

  • RPR Fault Tolerance

A robust packet ring employs two counter-rotating rings to achieve fault tolerance. Fiber connects both of these rings, providing a ring topology. On the other hand, the nodes that make up the RPR send packets in opposite directions. The inner and outer rings, or nodes, operate simultaneously, and if one fails, the capacity of traffic conveyed is reduced but there is no unavailability.

Resilient Packet Ring Limitations

The following are RPR’s primary drawbacks:

  • Reuse of Space

The inability to provide spatial reuse for frame transmission from or to media access control addresses, which is not possible in ring topologies, was one of RPR’s primary flaws. This was remedied, however, by introducing a spatially aware sublayer known as SAS. This method allows frame broadcasts from or to media access control addresses that aren’t available in ring topologies to be reused.

  • Algorithm RPR

An algorithm defines how traffic will be routed across the nodes in a resilient packet ring design. Despite its fairness and simplicity, this algorithm still has certain important flaws that should be addressed. In cases with unbalanced traffic, for example, there is a significant oscillation of allocated bandwidth.

When it comes to obtaining high bandwidth utilisation and spatial reuse, such oscillations are a hurdle. Furthermore, the sensitivity of this algorithm’s parameters is really high.

RPR Advantages


Multicast – A single RPR multicast packet is sent around the ring and can be received by any number of nodes. Multicast packets must be replicated over all feasible pathways in mesh topologies, wasting bandwidth.

Spatial Reuse — At their destination, RPR unicast packets are stripped. Unlike SONET/SDH networks, which require circuits to consume bandwidth across the entire ring, RPR permits capacity to be shared across numerous idle spans.


Topology Discovery– Nodes are added and removed from the topology map automatically.

Protection – Within 50 milliseconds, RPR shields failed spans.

High-Priority Service — High-priority packets are sent with the least amount of jitter and latency possible.

Reliable – RPR provides lossless transmission, which means no packets are dropped between nodes on the ring.

RPR Market Expansion

  • Networks of Internet Service Providers

RPR solutions help ISPs deliver reliable Internet services (such as IP and video) and address the growing bandwidth service requirements for next-generation intra-point of presence (POP), exchange point, and server farm/storage applications without the barriers of traditional SONET/SDH infrastructures.

  • Networks of Regional Metros

RPR enables regional metro networks to bring Internet services to the metro (such as IP, VoIP, and video). For transport through dark fibre, wavelength division multiplexing (WDM), SONET/SDH, cable MSO, and enterprise/campus MANs, RPR regional metro solutions are offered.

  • Networks of Metro Access

For service providers wishing to supply Internet services (such as IP, VoIP, and VPN) via metro access networks with direct Ethernet connectivity for multi-tenant/multidwelling clients and edge programmability, RPR provides metro access solutions.


The IEEE 802.17 working group is developing an RPR MAC industry standard. This group was founded in January 2001 and plans to finish the standard by the middle of 2003.

RPR in the Future

For both enterprise and service-provider networks, RPRs provide a dependable, efficient, and service-aware transport. RPR maximises economics while offering carrier-class service by combining the finest characteristics of legacy SONET/SDH and Ethernet into one layer. RPR will allow for the carriage of voice, video, and data services to be combined.


RPR technology promises to provide smart metro technology with classical time-division multiplexing to users. Furthermore, it provides a novel packet-data service. Both of these aspects are quite efficient. It can be characterised as a layer two protocol (data-link) that provides media access control for packets delivered via ring topology.

Various Layer 1 systems, such as SONET, benefit from resilient packet ring technology. It is a Layer 2 device that can communicate over Ethernet or SONET. It enables service providers to use physical layers such as Ethernet to ensure scalability and efficient metro networks. This technology is simple to integrate with other existing technologies. As a result, it is able to provide a significant-based approach to the construction of efficient metro networks.

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