Dynamic packet transport (DPT) is a Cisco

Cisco

Cisco may refer to:Companies:*Cisco Systems, a computer networking company* Certis CISCO, corporatised entity of the former Commercial and Industrial Security Corporation in Singapore...

 transport protocol designed for use in optical fiber

Optical fiber

An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

 ring network

Ring network

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...

s. In overview, it is quite similar to POS

Packet over SONET/SDH

Packet over SONET/SDH, abbreviated POS, is a communications protocol for transmitting packets in the form of the Point to Point Protocol over SDH or SONET, which are both standard protocols for communicating digital information using lasers or light emitting diodes over optical fibre at high...

 and DTM

Dynamic synchronous Transfer Mode

Dynamic synchronous transfer mode is an optical networking technology standardized by the European Telecommunications Standards Institute in 2001 with specification ETSI ES 201 803-1. DTM is a time division multiplexing and a circuit-switching network technology that combines switching and...

. It was one of the major influences on the Resilient Packet Ring

Resilient Packet Ring

Resilient Packet Ring , also known as IEEE 802.17, is a standard designed for the optimized transport of data traffic over optical fiber ring networks...

/802.17 standard.

Protocol Design

DPT is implemented as two counter-rotating rings. This means the network is composed of two completely separate rings of fiber that are both able to transmit data concurrently. This design provides for redundancy in case of a fiber cut or link failure, and increased throughput in common situations. DPT as opposed to POS or normal SONET/SDH is able to use both rings at the same time whereas POS only uses one ring under normal circumstances but switches to the second upon failure of the first. Cisco claims that DPT can run with double the bit-rate of POS due to this characteristic. DPT is not a PPP

Point-to-Point Protocol

In networking, the Point-to-Point Protocol is a data link protocol commonly used in establishing a direct connection between two networking nodes...

 whereas POS is, this means that traffic between two nodes of a DPT ring does not affect intermediate nodes. With the introduction of DPT came the introduction of another Cisco developed MAC layer protocol, Spatial Reuse Protocol

Spatial Reuse Protocol

Spatial Reuse Protocol is a networking protocol developed by Cisco. It is a MAC-layer protocol for ring-based packet internetworking that is commonly used in optical fiber ring networks...

 or SRP. The use of SRP in conjunction with DPT makes it possible for DPT to communicate with the physical layer.

Types of Data in DPT Networks

As with most other lower layer protocols, there are methods for communicating not only application data between the nodes of a DPT network. It is necessary for the nodes to be able to communicate control data between each other in case of a fiber cut or link failure so the nodes can forward traffic on the appropriate interfaces and maintain network connectivity. Both control packets, and data packets are transmitted on both rings in order to maintain connectivity and full bandwidth utilization in normal situations; but once a failure occurs, the control data will notify the applicable routers of the failure and all the routers will switch to using only their active interfaces for data and control packets.

DPT Packet Structure

The structure of a DPT Packet is quite similar to that of Ethernet

Ethernet

Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....

. It contains a source and destination MAC address (both 48-bits long), a protocol type identifier (used for identifying the upper layer protocol contained in the payload), and an FCS

Frame Check Sequence

A frame check sequence refers to the extra checksum characters added to a frame in a communication protocol for error detection and correction. Frames are used to send upper-layer data and ultimately the user application data from a source to a destination. The data package includes the message...

 used to validate the data.

DPT Topologies

Both DPT and SRP are independent of their physical layers. This means that the DPT protocol can operate above several physical mediums such as SONET/SDH, Gigabit Ethernet

Gigabit Ethernet

Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second , as defined by the IEEE 802.3-2008 standard. It came into use beginning in 1999, gradually supplanting Fast Ethernet in wired local networks where it performed...

, and others. As aforementioned, DPT is composed of two rings for fault tolerance and increased throughput. The method for switching between these two rings in the event of a failure is called Intelligent Protection Switching, or IPS. This ensures that a fiber cut or link failure (layer 1 error) will be rectified and IP traffic will be resumed within 50 ms. DPT also contains a "plug and play" feature which dynamically fetches the MAC addresses of neighboring devices which provides for very simple configuration with little to no setup prior to functional data transfer.