Category: Fiber Transceivers

Fiber optic communication networks are becoming increasingly popular day by day. All of the corporate networks as well as service provider networks make use of the fiber optic communication technology to efficiently serve their end users. Fiber optic communications are also making inroads into the houses of the end users. With the advent of FTT-X networks, the usage of fiber optic cables has increased exponentially. It is not possible to have a dedicated fiber cable pair for each link as it would take a lot of space and the links would still be under-utilized.

To make fiber optic communications more effective and efficient, engineers developed a technique called multiplexing which allowed different signals to travel on a single fiber optic cable without interference. Multiplexing is widely used in its various forms across all the communication methods that are currently in use today.

OADM

An optical add-drop multiplexer (OADM) is a critical device that is used in the wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a singlemode fiber (SMF). It is one of the fundamental constructional blocks of the modern day telecommunications networks.

Components of OADM

Traditionally, an OADM has three major components which are responsible to carry out the task assigned to an OADM. These three components are given below:

Optical Demultiplexer

An Optical Demultiplexer separates the multiple of wavelengths in a fiber and directs them to many fibers

Optical Multiplexer

The optical multiplexer is used to couple two or more wavelengths into the same fiber

A set of ports for adding and dropping signals

Types of OADM

There are two main types of OADM that are widely used in communication networks, namely, Fixed OADM (FOADM) and Reconfigurable OADM (ROADM). An OADM with remotely reconfigurable optical switches in the middle stage is called a reconfigurable OADM (ROADM). Ones without this feature are known as fixed OADMs. Fixed OAMDs are used to drop or add data singles on dedicated channels, and reconfigurable OADMs have the ability to electronically alter the selected channel routing through the optical network. While the term OADM applies to both types, it is often used interchangeably with ROADM.

Fixed Optical Add-Drop Multiplexer (FOADM)

FOADMs use fixed filters that add/drop a selected wavelength and pass the rest of the wavelengths through the node. Static wavelength-filtering technology eliminates the cost and attenuation to demultiplex all DWDM signals in a signal path. The solution is called FOADM because the wavelengths added and dropped are fixed at the time of add/drop filter installation on the optical path through a node.

Reconfigurable Optical Add-Drop Multiplexers (ROADM)

Reconfigurable Optical Add Drop Multiplexers (ROADMs) are used to provide flexibility in rerouting optical streams, bypassing faulty connections, allowing minimal service disruption and the ability to adapt or upgrade the optical network to different WDM technologies my electronically configuring the OADM to achieve the required functionality.

During the past few years, there is a dramatic increase in the demand for bandwidth requirement for our communications.  Whether be in a communication service provider or in a public or private data centers, a development in connectivity that can cater higher speed, bandwidth is needed. That is why last July 2014, an industry consortium was formed to create a new Ethernet connectivity standard in data centers. This standard was called 25 Gigabit Ethernet or 25Bade-T, developed by IEEE 802-3 task force P802.3by. This standard was derived from the 100Gbe, however, its operation works as a four 25Gbps that are running on four fibers or coppers. Last June 2016, this technology was commercially released using new interfaces called SFP28 and QSFP28. This article will discuss about the SFP28.

The SFP28 was constructed in a four parallel 25Gpbs data lanes allowing a maximum rate of 100Gbps. This physical structure of the SPF28 is the same with the popular SFP and SFP+. This characteristic provides flexibility due to the fact that the 100Gbps can also be divided individually in to four 25Gbps connections. SFP28 uses a 28Gbps lane (25Gbps + error correction) specifically used for top-or-rack (TOR) switch to server connectivity. Moreover, SFP28 is available in both copper and fiber optic cables.

The copper cable version is manufactured in a single fixed-configuration module which means the copper cables are directly attached to an SFP+ module. This version is ideal to be used for short distances ranging from 1m to 5m. On the other hand, the optical fiber version functions in either an 850nm that utilizes a pair of multimode fiber and works to a maximum distance of 100m or in a 1320nm that is made with a pair of single mode fibers works up to 20km.

The development of 25G SFP28 has provided a wide range benefits especially in a web-scale data center environment where the trend is to toward a single port server due to cost.

Primarily, it gives way to efficiently utilize data and switch port density. The reason for this is that, existing 100G port can be used as a 4x25G with as QSFP to SFP28 break out cable instead of using for different ports. For example, a 25Gbe strand can provide 2.5 times more data than the popular 10G solution and can provide greater port density.

Moreover, it provided an extremely efficient increase in speed to server to top-of-rack(TOR) especially when using the Direct Attached Copper assembly. It also simplifies development of interoperability specification and system due to the fact that its backward compatibility and gives an easier upgrade path from an existing 10G ToR server configuration.

Furthermore, using 25G SFP28 for ToR servers are more economical. This is because it can provide higher port densities, fewer ToR switches and cables are needed. It allows a more cost-effective alternative top-of-rack server connection that uses point-to-point patch cords. It enables End of Row(EoR) or Middle of Row (MoR) by using the 30-meter structured cabling. As a result, it reduces the capital expense in the construction cost compared to other configurations like the 40GbE.

Ultimately, the 25G SFP28 assemble features a reduced power and smaller footprint requirements for data centers because it limits the power per port to under 3W.

Due to this benefits that the 25G SFP28 assembly provides, it is forecasted that it will be popular in the years to come. It is believed that the dominant next generation server connection is toward the 25Gbps speed in server and in the near future, there will be more equipment that will use the 25G SFP28 cable assembly.

Computer network topologies have evolved from a bunch of hosts and servers that share resources in a clear defined space of a office building called Local Area Network – LAN,  to  the largest topology of networks called WAN’s – Wide Area Networks connecting dispersed geographically networks. The middle size networks are called MAN’s – Metropolitan Area Networks. The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines.

The diameter of such a network can range from 5 to 50 kilometers. As a rule, MAN does not belong to any particular organization, in most cases, a group of users or a provider who takes charge for the service own its connecting elements and other equipment. The transmission support for the MAN is represented by the links of fibre optic cable laid in a ring formation in a metropolitan area.

ATM (Asynchronous Transfer Mode) combines the characteristics of circuit switching and packet switching, which allows it to transfer even the real time data.

The MAN can be used to provide services including telecoms, Internet access, television and CCTV to businesses and citizens in these metropolitan areas.

Nowadays, MAN networks are connecting a number of Campus LAN networks which  are designed in hierarchical structure such as: access , distribution and core.

Next Generation MAN : The Metro Ethernet Solutions

Service providers use Metro Ethernet to provide Layer 2 Ethernet connections between customer sites in metro area networks. Driven by its relative simplicity, high bandwidth, and low-cost switches, Ethernet has become the transport technology of choice in metro area networks. There are numerous applications that require pure Layer 2 connectivity in the metro area network (MAN) for providing simple point-to-point, point-to-multipoint, or multipoint-to-multipoint services with a relatively low number of customer sites. However, Ethernet limitations become apparent in large MANs with thousands of access nodes. In this

case, service providers are more likely to offer Layer 3 Virtual Private Network (L3 – VPN) services based on multiprotocol label switch (MPLS) transport. When interconnecting hundreds or thousands of customer sites, this approach gives more flexibility, better scale, and ease of OAM.

MPLS is best and most widely used to interconnect data centers with branch offices and branches to other branches. Ethernet is best for interconnecting data centers. MPLS can handle any-to-any connectivity, including voice and video. Ethernet offers low-latency and high-throughput, which is ideal for disaster recovery. Using MPLS for WAN connectivity requires that all network devices and management tools be compatible with both MPLS and Ethernet. Because LANs use Ethernet, using Ethernet for the WAN gives organizations an all-Ethernet infrastructure, which simplifies network management.

For the above-mentioned reasons, operators are thirst for carrying all services over one network. Several networks coexist within the existing MAN, of which the IP MAN is the best choice. Nevertheless, the IP MAN also has some problems in handling these services, which can be explained in detail as follows:

The existing IP MAN is out of order, in which the Layer 2 switching and Layer 3 routing are mixed. So it cannot meet the requirements of providing QoS guaranteed services.

The IP MAN mainly implements L3 switching architecture. With a single access mode, poor access capability and without overall planning of service access points, this kind of access mode is hardly possible to support

“full-coverage full-service network”.

Highly positioned Provider Edge Router (PE) is a networking that cannot take the advantages of MPLS VPN technology. Layer 2 network too large, which is confined by the Virtual LAN (VLAN) ID resources and makes network troubleshooting difficult.

It causes serious waste of optical fibers and transmission resources. In order to attract more group users, IP MAN mainly employs the direct optical-fiber connection mode. Users are directly connected to PE. In some cases nearly half of the fibers in MAN are used only to connect group users, really being a great burden of carriers.

The IP MAN equipment has differentiated capabilities. Most IP MAN is unable to deploy either the QoS guaranteed services or the multicast services over the entire network.

The construction problem of multi-layer network design for a high-speed telecommunication network based on Synchronous Digital Hierarchy (SDH) and Wavelength Division Multiplex (WDM) technology, has to carry a certain set of demands with the objective of minimizing the investment in the equipment.

It all start with the design phase – where the effective costs of either optical SDH or DWDM networks has to be competitive.

Design processA network design method proceeds by generating cycles, evaluating the economics of building rings on those cycle, and building any economic rings. Generating a cycle involves picking two endpoints between which two disjoint link and node paths are desired — the two nodes selected are thus nodes on the candidate rings.

In a telecommunications network, a “ring” is a sequence of nodes arranged in a “cycle” so that no node is repeated. The “links” between nodes are places where fiber can be placed. Nodes are generally physical locations such as buildings where fiber bundles can be connected to each other and where equipment such as multiplexers, amplifiers, regenerators, transponders, etc., can be placed. Ring design entails in part the making of decisions as to ring placement, i.e., which nodes and which links are to be included. Ring design also concerns the selection of equipment, i.e., what types and rates of multiplexers, amplifiers, regenerators, transponders, etc., and where to place the equipment. Finally, ring design necessarily entails decisions as to what demand to place on the rings.

The models used for SONET/SDH provide for the following costs and parameters:

frame and installation,

regeneration loss thresholds,

maximum number of SONET ADMs on a ring, and

fiber material, sheath installation, and structure expansion cost.

Currently, Dense Wavelength Division Multiplexing (DWDM) is being installed largely on long-distance routes. The DWDM vintage normally used is point-to-point DWDM, or in other words, DWDM systems are utilized as fiber concentrators. The reason for this equipment being so prevalent for long-distance carriers is simple economics: DWDM can substantially reduce capital investment because of the ability to multiply the number of signals being carried by each fiber and thus avoid expensive cable or route upgrade and also save the cost of multiple regenerators.

DWDM is multiple signal transmit over a single fiber called DWDM or Different frequencies (colors/wavelengths/lambdas) for different connections over the single fiber. Full featured DWDM equipment can comprise the same range of cards as SDH. They can support fully configurable cross connect features. DWDM technology provides very high bandwidth long haul inter-connect links. DWDM is considered as one of the best technologies to increase bandwidth over an existing fiber plant. It enables one to create multiple “virtual fibers” over one physical fiber.

The DWDM layer is protocol and bit rate independent, which means that it can carry ATM (Asynchronous Transfer Mode), SONET, and/or IP packets simultaneously. WDM technology may also be used in Passive Optical Networks (PONs) which are access networks in which the entire transport, switching and routing happens in optical mode.

The differences between demand types mostly are caused by the design efficiency of these two technologies’ interface cards in terms of density and price.

Cost from IP – Internet Protocol – traffic approach

IP traffic is growing exponentially as customers migrate to IP-based applications. As these networks evolve to include bandwidth-intensive IP based voice, video, and data services, carriers must boost capacity in response to demand, knowing that the collected revenue will not scale at the same rate. Therefore, carriers must find ways to optimize the operating and cost efficiency of service networks and drastically reduce costs per bit.

Traditionally this was implemented using (IP) Internet Protocol over SDH approach which has the inconvenient of the optical to electrical to optical (OEO) conversion at the aggregate interfaces. The IP over DWDM is practically implemented as connection between DWDM router interfaces with an optically switched DWDM layer.

Since the Internet started changing people’s lives engineers have been constantly trying to find a way to provide the highest performance possible to their customers. In addition they have been focusing on providing the best possible service to their businesses. One of the main and most important developments in the Internet Era has been the optical network technology. This technology provided a huge leap forward for every Internet user and has been the main foundation of today’s high performance demanding businesses and Internet users.

This technology is based on the optical fiber which is the main part of optical networking. The optical fiber is defined as a single, hair thin, filament drawn from molten silica glass. These optical fibers have substituted the copper wires to produce high performance and high capacity transmission. They are optimized and pure so that light transmitted by optical devices like transceivers, can pass through them carrying the network traffic across a network architecture. The transceivers are the ones converting this light in electrical input and vice-versa, so various switches, routers, firewalls etc. can understand the traffic.

The main ingredient of the optical fibers is a chemical called silicon dioxide (SiO 2). In addition there are other chemical compounds found such as germanium tetrachloride (GeCl 4) and phosphorus oxychloride (POC1 3), however these are mainly used to produce the outer layer of the fiber, also known as the cladding. In the early days of this technology researchers were trying to connect the purity of the glass used to the attenuation of the signal and because in recent years this has been proved, the main focus today is developing optical fibers made from silica glass with the highest possible purity. One of the most important part of the composition of the glass is the fluoride content. It has been confirmed that glass with high fluoride content is improving the overall performance due to its purity along the whole fiber. This makes it suitable for deployment in multi-mode solutions because of the fact that multi-mode fibers transmit hundreds of discrete light wave signals concurrently.

In optic network architectures light travels across many individual optical fibers which are bound together around a high-strength plastic carrier for support. This is also called the core of the cable. In addition the core is then covered with a couple protective layers to protect it from outside stress. The protective layers are mainly made of Aluminum, Kevlar, and polyethylene which is the main ingredient of the cladding. The cladding plays a very important part of the network. This is mainly because light will constantly bounce off of it while traveling across the optical fiber. The amount of energy lost from the bouncing is called attenuation. The attenuation is measured in terms of loss (in decibels, a unit of energy) per distance of fiber. A high quality optical fiber should not lose more than 0.3 decibels per kilometer. This attenuation causes the light to lose power eventually therefore the signal must be repeated and strengthened with the help of laser repeaters. In today’s high performance networks these laser repeaters are deployed at every 30 kilometers in average. However, the good news is that recent studies showed that the newly developed ultra-pure glass will eventually provide the optical fiber to reach the 100 kilometer mark without the need of a laser repeater.

As with every electronical device found today, the manufacturing process is one of the most interesting parts of the whole picture. When it comes to optical fibers there are two methods in manufacturing them and each of those methods has its own purpose. To produce a multi-mode fiber where multiple light waves will pass through it and bounce off the cladding, reducing in shorter reach, the so called crucible method is used. This is the easier and simpler method out of the two because simply put the silica glass is melted and shaped to produce a fatter optical fiber.

The second method is called a vapor deposition process. Researchers developed three different vapor deposition techniques:

Outer Vapor Phase Deposition

Vapor Phase Axial Deposition

Modified Chemical Vapor Deposition (MCVD)

The most common technique used at present is the MCVD technique. With this technique a solid cylinder of core is produced and cladding material is put on top of it. After that process the core is heated and drawn into a thinner, single-mode fiber for long-distance communication. The step by step process shown below is far more interesting:

By depositing layers of specially formulated silicon dioxide on the inside surface of a hollow substrate rod, a cylindrical shape is formed. The deposition happens by applying pure oxygen, in gas form, to the rod. Together with the vaporized gas a couple of important chemicals are added including silicon tetrachloride (SiCl 4), germanium tetrachloride (GeCl 4) and phosphorous oxychloride (POC1 3). With the help of underneath flames the surface of the rod is kept constantly hot and when the oxygen contacts the rod a high purity silicon dioxide is formed inside the rod itself. This high purity silicon dioxide is the basis of the fiber optic core.

The second process of this technique starts by measuring the thickness of the formed silicon dioxide inside the rod. When the expected thickness is reached the rod will be put under a couple heating procedures to remove excess bubbles and moisture trapped inside. After this second step the formed silicon dioxide is usually 10 to 25 mm in diameter.

The solid shape of silicon dioxide is then transferred to an automatic fiber drawing system. This system can be up to two stories high and has the ability to produce continuous fibers of up to 300km.

In the above system the fiber first passes through a furnace where will be heated up to 2000 degrees Celsius. As the fiber is being pulled through the system the material in the original substrate rod forms the outer layer called the cladding.

As the fiber is pulled and drawn out, special sensors monitor its diameter and at the same time a separate device applies a protective coating on top. The process ends when the optical fiber reaches the desired thickness and is then sent to quality control.

It is safe to say that this process is the foundation to producing ultra-pure optical fibers. Today researchers try to find another solution which will offer even lower attenuation. They focus their hope on experimental fibers which are high in zirconium fluoride (ZrF 4) in content. These fibers have been tested and their attenuation results are astonishing, providing performance loss of only 0.005 to 0.008 decibels per kilometer. When these fibers enter in production and reach the networking market, they will provide a huge window to the future and honestly, we can’t wait for that to happen!

During the past few years, there is a dramatic increase in the demand for bandwidth requirement for our communications.  Whether be in a communication service provider or in a public or private data centers, a development in connectivity that can cater higher speed, bandwidth is needed. That is why last July 2014, an industry consortium was formed to create a new Ethernet connectivity standard in data centers. This standard was called 25 Gigabit Ethernet or 25Bade-T, developed by IEEE 802-3 task force P802.3by. This standard was derived from the 100Gbe, however, its operation works as a four 25Gbps that are running on four fibers or coppers. Last June 2016, this technology was commercially released using new interfaces called SFP28 and QSFP28. This article will discuss about the SFP28.

The SFP28 was constructed in a four parallel 25Gpbs data lanes allowing a maximum rate of 100Gbps. This physical structure of the SPF28 is the same with the popular SFP and SFP+. This characteristic provides flexibility due to the fact that the 100Gbps can also be divided individually in to four 25Gbps connections. SFP28 uses a 28Gbps lane (25Gbps + error correction) specifically used for top-or-rack (TOR) switch to server connectivity. Moreover, SFP28 is available in both copper and fiber optic cables.

The copper cable version is manufactured in a single fixed-configuration module which means the copper cables are directly attached to an SFP+ module. This version is ideal to be used for short distances ranging from 1m to 5m. On the other hand, the optical fiber version functions in either an 850nm that utilizes a pair of multimode fiber and works to a maximum distance of 100m or in a 1320nm that is made with a pair of single mode fibers works up to 20km.

The development of 25G SFP28 has provided a wide range benefits especially in a web-scale data center environment where the trend is to toward a single port server due to cost.

Primarily, it gives way to efficiently utilize data and switch port density. The reason for this is that, existing 100G port can be used as a 4x25G with as QSFP to SFP28 break out cable instead of using for different ports. For example, a 25Gbe strand can provide 2.5 times more data than the popular 10G solution and can provide greater port density.

Moreover, it provided an extremely efficient increase in speed to server to top-of-rack(TOR) especially when using the Direct Attached Copper assembly. It also simplifies development of interoperability specification and system due to the fact that its backward compatibility and gives an easier upgrade path from an existing 10G ToR server configuration.

Furthermore, using 25G SFP28 for ToR servers are more economical. This is because it can provide higher port densities, fewer ToR switches and cables are needed. It allows a more cost-effective alternative top-of-rack server connection that uses point-to-point patch cords. It enables End of Row(EoR) or Middle of Row (MoR) by using the 30-meter structured cabling. As a result, it reduces the capital expense in the construction cost compared to other configurations like the 40GbE.

Ultimately, the 25G SFP28 assemble features a reduced power and smaller footprint requirements for data centers because it limits the power per port to under 3W.

Due to this benefits that the 25G SFP28 assembly provides, it is forecasted that it will be popular in the years to come. It is believed that the dominant next generation server connection is toward the 25Gbps speed in server and in the near future, there will be more equipment that will use the 25G SFP28 cable assembly.