TTM 1: Access and core networks, advanced

TTM 1: Access and core networks, advanced Based on paper:“Optical networks: From point-to-point transmission to full networking capabilities” Presented by: ZekariasTeshome

Contents • Introduction • Transmission aspects • Opaque versus transparent • Re-configurable optical networks • OADM • Optical cross connects • MPLS/GMPLS • Network architectures • The overlay model • The peer model • Reference network • Future IP solutions • Summery

Introduction • It was early realized that optical fiber has a tremendous bandwidth and • Also the low electromagnetic interference of the medium makes it ideal for secure communication • The main issue would be to find technically feasible and economical ways to capitalize on this potential.

Transmission aspects Transmission systems use WDM(method used to increase the capacity of a single strand of fiber) • From the transmitter side: many different colored lights combined by the WDM multiplexing device and put in to the single strand of fiber. • On the receiver side: each color is separated into its own color by WDM Demultiplexingdevice

Cont. • Due to the characteristic attenuation curve of fiber, there are two regions typically used for communications.

Cont. • Dense Wavelength Division Multiplexing(DWDM) and • Coarse Wavelength Division Multiplexing (CWDM) • The difference is the channel spacing. • And the range of the optical spectrum they typically cover.

DWDM Vs. CWDM DWDM • all frequencies spaced at multiples of 50 GHz • with wavelengths in the 1530 – 1565 nm range, • The tight spacing between these channels requires temperature control of the lasers and increases cost. CWDM • Here the channel spacing is increased to 200 GHz, • both the fabrication and the temperature control requirements of these lasers are lower, and • the overall cost dramatically reduced.

Opaque versus transparent • A core optical network architecture can be opaque or transparent. • An opaque architecture implies that the optical signal carrying traffic undergoes an optical to electronic to optical (OEO) conversion at different places in the network. • A transparent architecture implies that the optical signal carrying traffic stays in the optical domain.

Re-configurable optical networks • The key NEs in order to realize re-configurable optical networks are • Reconfigurable optical add-drop multiplexer (R-OADM) and • optical cross connects (OXC).

OADM • Typically close to 70 % of the traffic that arrives at a node is through-passing traffic, i.e. • traffic with destination another node. • Instead of processing and switching/routing all traffic an optical add-drop multiplexer (OADM) can allow • some of the through-passing traffic to be forwarded optically, directly through the node. • The wavelengths that have been dropped may be added back in the link.

Cont. • There are two main types of OADM that can be used in WDM optical networks; • Fixed OADMs: that are used to drop or add data signals on dedicated WDM channels, and • Reconfigurable OADMs: re-configurability refers to the ability to select the desired wavelengths to be dropped and added on the fly, as opposed to having to plan ahead and deploy appropriate equipment.

Cont.

Optical cross connects • Optical networks consist of a multiple of sub-networks. • These will need to be interconnected by optical links in an arbitrary topology, i.e. in a mesh topology • In order to be able to realize mesh networks, optical cross connects are required.

Cont. • An OXC performs in essence the same function as an R-OADM but for a larger number of line ports and directions. Schematic of an optical cross-connect; optoelectronic , all-optical

Cont. • An OXC provides several key functions in a large network: • Service provisioning • An OXC can be used to provide end-to-end light paths in a large network in an automated manner. • Protection and restoration • The OXC combined with monitoring equipment can provide swift restoration of huge amounts of traffic by redirecting wavelengths from the failed paths to alternative paths.

Cont. • Wavelength conversion • Light paths need not use one single wavelength through the whole network since this complicates wavelength management in the network. • Multiplexing and grooming • in its purest form the OXC is all-optical. However, the OXC comprises also an add-drop part where multiplexing and grooming of ingress and egress signals can take place.

Cont. • OXCs can be an opaque and employ an electrical core. • A large number of alternative all-optical solutions have been explored, • One of the most prominent OXC solutions is based on: a two-dimensional or three-dimensional array of miniature mirrors (MEMS based)

Cont. a) A picture of a miniature MEMS mirror, b) schematic of an OXC using miniature MEMS mirrors

Cont. • A new OXC architecture that uses tunable lasers and Array Waveguide Gratings (AWG) as shown in Figure below. A schematic of an OXC based on an Arrayed Waveguide Grating and tunable wavelength converters

Cont. • The port a signal will exit the OXC from, is explicitly determined by its wavelength and the AWG input it arrives at. • Hence the OXC is re-configured by tuning the wavelength of the signal in a wavelength converter using tunable lasers

MPLS/GMPLS • MPLS involves setting up a specific path for a given sequence of packets by • labeling every packet in order to figure out which outward path a packet should be switched toward its destination. • multiprotocolbecause it works with the Internet Protocol (IP), Asynchronous Transport Mode (ATM), and frame relay network protocols. • GMPLS (Generalized Multiprotocol Label Switching), • is a technology that provides enhancements to Multiprotocol Label Switching (MPLS) to support network switching for time, wavelength, and space switching as well as for packet switching.

Network architectures • Traditional transport networks can be modeled as the interaction of two operating planes: • a transport plane and • a management plane. • In this model, the transport plane carries the user data and comprises network equipment, such as line • interface cards, switch fabrics, backplanes and fiber plant. • Network OAM&P (operations, administration, maintenance and provisioning) is fully handled by the management plane.

Cont. • Now, we are beginning to see the deployment of optical control planes • sit between the management and transport planes. The control plane moves some of the network intelligence down to the NEs.

Cont. • In the optical transport field, the control plane has been called by the IETF as, • Generalized Multi-Protocol Label Switching, or GMPLS. • The IP and optical control planes can be loosely or tightly coupled in terms of, • firstly, the details of the optical network topology, resources, and routing information that is revealed to the IP layer, and • secondly, the degree of control IP routers have on optical network elements and thus the degree to which they can determine the exact paths through this optical network.

Cont. • Based on this: • The overlay model • The peer model

The overlay model • In this architecture option the optical network has full control over its network resources • by means of a fully independent optical control plane. A schematic of the Automatically Switched Optical Network, according to the overlay model

The peer model • In this architecture the control planes of the optical network and IP are fully integrated. • the optical part unintelligent and • rely on IP intelligence to run the network.

Reference network • The network can be seen as comprising three parts: • The core and long-haul part, • The metropolitan area network, and • The access part.

Cont. • The core part • is a national network connecting major cities. • The metro network • extends over a large city or a province, comprises less aggregated traffic than the core as it is closer to customers and end users, and involves lower capacities than the core. • Access part • is the part that provides a connection between an end user (e.g. a home) or a business to the metro and core networks.

Future IP solutions • IP routers do not appear to be able to scale gracefully to meet the needs of multi-Terabit networks. • Alternatively, better scalable large switching matrices may be created using both electrical and optical switches. A schematic of a hybrid optical-electrical router, using both optical switching matrices and electrical switches

Cont. • A next step is optical packet or burst switching (OPS/ OBS) – or so-called optical routers.

Summery • Optical networks may well be the key to high capacity intelligent networks that utilize • their resources in an efficient way and can provide a range of differentiated services. • Optical switching provides an economical way to handle large amounts of traffic and to build reliable networks. • Optical functionality can be introduced at a separate layer and complement higher network layers, and/or it can be directly integrated and controlled by IP routers. • Optical technology can also be employed to realize larger/higher throughput and more robust IP routers.

TTM 1: Access and core networks, advanced