Optical Ethernet

Optical Ethernet

- Prepared by Tan Teow Ang, Feb 11, 2002

Content:

Introduction
Topology
Transmission Medium
Transmission Speed
Connection
Medium Access Control
Network Layer
Frame Format
Error Control Mechanism
Standards
Future
Advantages & Disadvantages
FAQ

1.0 Introduction

Ethernet is most popular since 1980s. Ethernet is a local area network (LAN) technology that transmits information between the computers. Basically the Optical Ethernet is a combination of the high-speed Ethernet with optical networking system. These Optical Ethernet exists because of taking place now is the maturing of Ethernet transmission and switching. Beside that it also reason for increased investment in metropolitan optical network [Tony Rybczynski, 2001].

2.0 Topology

Topology of the Optical Ethernet is exactly same with the normal existing Ethernet. Optical Ethernet is support any physical topology such as Star Topology, Ring Topology, and so on. Besides that Optical Ethernet also support logical topology “point-to-point links, dual-homed point-to-point links, 1gbps access ring, 10gbps access rings and dual-homed access rings” [Nan Chen, 2003].

3.0 Transmission Medium Used

Normally Optical Ethernet is running over single-mode fiber. And then for the network range of 1310-nm wavelength technology is 3 to more than 6 miles, and for 1550-nm wavelength technology is up to 43.4 miles [Ian Yates, 2001].

Other transmission medium used in the Optical Ethernet is show as below:

Table 1.0: IEEE 802.3 PHY Specifications for fiber optic [XILINE]

4.0 Transmission Speed (Mbps)

Optical Ethernet transmission speed minimum is 10 mbps and the maximum transmission speed can up to Gigabit 10-Gigabit per second [Bob Woods, 2001].

5.0 Connection Oriented or Connectionless

Optical Ethernet is using the concept of connectionless [San Jose, 2002]. Because in currently is “no any technologies enable packet switching at the optical layer” [International Engineering Consortium-recent trends].

6.0 Medium Access Control Techniques

Optical Ethernet is “shared medium for LANs using a distributed media access control (MAC) mechanism called carrier sense multiple accesses with collision detection (CSMA/CD)” [International Engineering Consortium-technology].

7.0 Network Layer

Optical Ethernet will have some changes in OSI model. The layer will be affected are:

Layer 1 – Must be using the repeaters.
Layer 2 – Two feature will occurs in Media Access Control (MAC). One is not all traffic on either end is transported. And another one is collisions is not transported. [International Engineering Consortium-history]

8.0 Frame Format

The Optical Ethernet frame format is following the standard of Ethernet frame format. Figure below is shown the Ethernet frame format.

9.0 Error Control Mechanism

Error control mechanism for Optical Ethernet system is separate dual token-bucket policing mechanisms. This mechanism is using to checks SLA, CIR and EIR values each connection. Based on the process, traffic is allowed or discarded, depending on established parameters. SLA as packets exit the ingress node they are held in queues corresponding to the traffic priority established. CIR below connection, packets will always be forwarded and will not be impacted during periods of peak network congestion. For the CIR above connection, the excess traffic will be marked for discard eligibility (DE), signifying that they will be dropped during times of congestion. If CIR is 0, then customer’s traffic will always be in excess and therefore be handled on a best-effort basis. In most cases traffic will be allowed to continue since burst rates usually exceed the CIR. EIR is the same as the CIR, it is no excess or burst traffic will be permitted. Also, if the amount of traffic exceeds the EIR, then traffic will not be permitted to go through. [San Jose, 2002]

10.0 Standards

IEEE 802.1pQ virtual LAN (VLAN) standard is used by Optical Ethernet for traffic segregation. Thus, Optical Ethernet networks can mark each user's traffic enters in VLAN and keep each user's traffic separate as it crosses the network. “Of course, 802.1pQ was designed for enterprise networks and the number of possible VLAN tags is too low. Work is under way in IEEE to extend this number from 4,096 to approximately 16 million” [Ian Yates, 2001].

11.0 Future Technology

According to the Steve Schilling, recently named president of Nortel's Optical Ethernet Group “A year from now, Optical Ethernet will be the talk; it will be a new type of circuit that acts as a virtual private Ethernet" [Jim Duffy, 2001]. Besides that Optical Ethernet will upgrade to 25 terabit per second for future enhancement.

12.0 Advantages and Disadvantages

Below is shown the advantages and disadvantages for the optical Ethernet:

Advantages
- Is Simpler, Faster, More reliable networking
- Opportunities for rethinking server
- The storage distribution
- Increased knowledge-worker productivity
- Best technology for carrying IP traffic, advanced traffic management capabilities
- Provide benefits of scalability, performance and interoperability
- Using end-to-end service level agreements
- Provide virtual circuits over Optical Ethernet
- Integrated optical switching
- Carrier-class solutions can bandwidth relief support cable modem connections.
- “Optical Ethernet switches are up to 1/10th the cost of traditional ATM or SONET/SDH gear. Additionally, true Optical Ethernet solutions can support Ethernet-based transport and traditional TDM traffic”.
Disadvantages
- Is very expensive but cheaper then SONET Technology.
- Is very difficult to implement [Tony Rybczynski, 2001], [Nan Chen, 2003]

13.0 Frequently Ask Question

1. What is Optical Ethernet?
Ethernet is a local area network (LAN) technology that transmits information between the computers. However Optical Ethernet is a combination of the high-speed Ethernet with optical networking system.

2. What is topology of Optical Ethernet?
Topology is considered physical topology and logical topology. Optical Ethernet can support any Physical topology such as Star Topology, Ring Topology, and so on. For the logical topology is including point-to-point links, dual-homed point-to-point links, 1gbps access ring, 10gbps access rings and dual-homed access rings.

3. What is the transmission medium for the Optical Ethernet?
Normally Optical Ethernet is running over single-mode fiber. And then for the network range of 1310-nm wavelength technology is 3 to more than 6 miles, and for 1550-nm wavelength technology is up to 43.4 miles.

4. What is the error control mechanism of Optical Ethernet?
Separate dual token-bucket policing mechanisms are error control mechanism used by Optical Ethernet. This mechanism is used to checks SLA, CIR and EIR values each connection. Based on the process, traffic is allowed or discarded, depending on established parameters.

5. What are the advantages for the Optical Ethernet?
The Optical Ethernet provides many advantages. Some of the advantages are including:

Is Simpler, Faster, More reliable networking
Opportunities for rethinking server
The storage distribution
Increased knowledge-worker productivity
Best technology for carrying IP traffic, advanced traffic management capabilities
Provide benefits of scalability, performance and interoperability
Using end-to-end service level agreements
Provide virtual circuits over Optical Ethernet
Integrated optical switching
Carrier-class solutions can bandwidth relief support cable modem connections.
“Optical Ethernet switches are up to 1/10th the cost of traditional ATM or SONET/SDH gear. Additionally, true Optical Ethernet solutions can support Ethernet-based transport and traditional TDM traffic”.

6. What is the strandard of Optical Ethernet?
The standard os the Optical Ethernet is IEEE 802.1pQ virtual LAN (VLAN) Thus, Optical Ethernet networks can mark each user's traffic enters in VLAN and keep each user's traffic separate as it crosses the network. Of course, 802.1pQ was designed for enterprise networks and the number of possible VLAN tags is too low. Work is under way in IEEE to extend this number from 4,096 to approximately 16 million.

7. What is the transmission Speed of the Optical Ethernet?
Optical Ethernet transmission speed minimum is 10 mbps and the maximum transmission speed can up to Gigabit 10-Gigabit per second.

8. Which layer of ISO model is affected for Optical Ethernet?
The layer will be affected is Layer 1 and Layer 2, because the Optical Ethernet is using repeaters. However Layer 2 is provide feature in Media Access Control (MAC). One is not all traffic on either end is transported. And another one is collisions is not transported.

9. Optical Ethernet only can implement in Local Area Network (LAN)?
No, Optical Ethernet also can implement in Campus Area Network (CAN), Metropolitan Area Network (MAN), and also Wide Area Network (WAN). Figure below will show the LAN, CAN, MAN, and WAN.

10 Which connection concept used by Optical Ethernet?
Optical Ethernet is using the concept of connectionless. Because in currently is no any technologies enable packet switching at the optical layer.

Reference:

Web Site:
[Tony Rybczynski, 2001] “Optical Ethernet—Preparing For the Transition” 23/1/2002 http://www.bcr.com/bcrmag/2001/10/p51.asp

[Bob Woods, 2001] “End-to-End Optical Ethernet a "Dream"” 23/1/2002 http://www.opticallynetworked.com/features/article/0,,10516_913791,00.html

[Jim Duffy, 2001] “Nortel launches into optical Ethernet” 23/1/2002 http://www.itworld.com/Net/3099/NWW010509nortel/

[Ian Yates, 2001] “Optical Ethernet for metropolitan nets” 23/1/2002 23/1/2002 http://www.itworld.com/Net/2570/NWW010402tech/

[Nan Chen, 2003] ”The Benefit” 23/1/2002 http://www.xchangemag.com/webextra/281webx1.html

[XILINE] “IEEE 802.3 PHY Specifications” 23/1/2002 http://www.espteam@xilinx.com

[San Jose, 2002] “Atrica Optical Ethernet Alert - November 2002” 23/1/2002 http://www.atrica.com/news/newsletter/november2002.html

[International Engineering Consortium-technology] “Technology” 23/1/2002 http://www.iec.org/online/tutorials/opt_ethernet/topic01.html

[International Engineering Consortium-history] “History” 23/1/2002 http://www.iec.org/online/tutorials/opt_ethernet/topic02.html

[International Engineering Consortium-recent trends] “Recent Trends” 23/1/2002 http://www.iec.org/online/tutorials/opt_ethernet/topic04.html

Glossary:

Campus Area Network (CAN) - High-speed, low-error data network covering a relatively medium geographic area, larger then LAN, and smaller then MAN.

CIR - committed information rate. The rate at which a Frame Relay network agrees to transfer information under normal conditions, averaged over a minimum increment of time. CIR, measured in bits per second, is one of the key negotiated tariff metrics

CSMA/CD - carrier sense multiple access collision detect. Media-access mechanisms wherein devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time. CSMA/CD access is used by Ethernet and IEEE 802.3.

Discard eligibility (DE) - ATM cells that have their CLP bit set to 1. If the network is congested, tagged traffic can be dropped to ensure delivery of higher-priority traffic. Sometimes called DE (discard eligible) traffic

Dual-homed - Network topology in which a device connected to the network by way of two independent access points (points of attachment). One access point is the primary connection, and the other is a standby connection that is activated in the event of a failure of the primary connection.

Frame - Logical grouping of information sent as a data link layer unit over a transmission medium. Often refers to the header and trailer, used for synchronization and error control that surround the user data contained in the unit. The terms datagram, message, packet, and segment are also used to describe logical information groupings at various layers of the OSI reference model and in various technology circles.

Half Duplex - Capability for data transmission in only one direction at a time between a sending station and a receiving station.

Full Duplex - Capability for simultaneous data transmission between a sending station and a receiving station.

IEEE - Institute of Electrical and Electronics Engineers. Professional organization whose activities include the development of communications and network standards. IEEE LAN standards are the predominant LAN standards today.

IEEE 802.1pQ - IEEE specification that describes an algorithm that prevents bridging loops by creating a spanning tree. The algorithm was invented by Digital Equipment Corporation. The Digital algorithm and the IEEE 802.1 algorithm are not not exactly the same, nor are they compatible.

Local Area Network (LAN) - High-speed, low-error data network covering a relatively small geographic area (up to a few thousand meters). LANs connect workstations, peripherals, terminals, and other devices in a single building or other geographically limited area. LAN standards specify cabling and signaling at the physical and data link layers of the OSI model. Ethernet, FDDI, and Token Ring are widely used LAN technologies.

Metropolitan optical network (MAN) - Network that spans a Metropolitan area. Generally, a MAN spans a larger geographic area than a LAN, but a smaller geographic area than a WAN.

Ring Topology - Network topology that consists of a series of repeaters connected to one another by unidirectional transmission links to form a single closed loop. Each station on the network connects to the network at a repeater. While logically a ring, ring topologies are most often organized in a closed-loop star.

Synchronous Optical Network (SONET) -High-speed (up to 2.5 Gbps) synchronous network specification developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET. Approved as an international standard in 1988.

Synchronous Digital Hierarchy (SDH) - European standard that defines a set of rate and format standards that are transmitted using optical signals over fiber. SDH is similar to SONET, with a basic SDH rate of 155.52 Mbps, designated at STM-1.

Star Topology- LAN topology in which end points on a network are connected to a common central switch by point-to-point links. A ring topology that is organized as star implements a unidirectional closed-loop star, instead of point-to-point links.

Topology - Physical arrangement of network nodes and media within an enterprise networking structure.

Virtual circuits- Logical circuit created to ensure reliable communication between two network devices. A virtual circuit is defined by a VPI/VCI pair, and can be either permanent (a PVC) or switched (an SVC). Virtual circuits are used in Frame Relay and X.25. In ATM, a virtual circuit is called a virtual channel.

Virtual LAN (VLAN) - virtual LAN. Group of devices on a LAN that are configured (using management software) so that they can communicate as if they were attached to the same wire, when in fact they are located on a number of different LAN segments. Because VLANs are based on logical instead of physical connections, they are extremely flexible.

Wide Area Network (WAN) - Data communications network that serves users across a broad geographic area and often uses transmission devices provided by common carriers. Frame Relay, SMDS, and X.25 are examples of WANs.