A presentation I created a while ago on basics of ASON GMPLS (more…)

OSNR ( Optical Signal to Noise Ratio)  is a critical and important parameter in high speed DWDM links. If OSNR is not good it will seriously affect the distance reachability in DWDM systems before regeneration is required. OSNR testing is typically done with OSA (Optical Spectrum Analyzer).  There are standard test sets available to test OSNR of 10G lambdas; However when it comes to testing on high speed links at 40G and 100G based on Pol Mux-QPSK modulation techniques, OSNR testing in field leaves a lot to be desired. In fact there is no automated tool available today that can do OSNR testing for Pol Mux modulation.

A POLMUX-QPSK transmitter consists of two quadrature (e.g. QPSK) modulators and a polarization beam splitter (PBS) to multiplex the two outputs on orthogonal projections. This is significantly different than conventional modulation schemes based on single polarized signal. An OSA is simply not designed to test OSNR on such dual polarized signals. There have been ways around methods suggested by leading T&M ( Test and Measurement)  vendors using manual methods of testing on existing OSA. But these methods are less accurate, complex and not repeatable. They are simply not aimed for field engineers and are very prone to human mistakes.

The T&M vendors have plans to bring out OSA to test OSNR on Pol Mux signals; they are working on developing those solutions. However the progress has been very slow. It’s been a while now that we have been hearing of these plans. It is need of the hour to expedite these solutions since the industry need them badly today and without them accurate testing of OSNR would not be possible.

As data rates increase beyond 10G, the requirements for OSNR become stringent. This is because the advanced modulation techniques used at higher bit rates require higher OSNR performance. Low OSNR is directly related to poor BER performance in DWDM networks. FEC or Forward error connection is a method used to achieve coding gain for higher bit rates. It is a method of encoding optical signal with extra error detection and correction overhead bytes enabling optical receivers to detect errors and correct them. Thus FEC can reduce BER and effectively increases distances reachable by high speed signals without regeneration.

Standard FEC and Enhanced FEC ( EFEC) are methods correctly used on 10G and 40G . Both call for adding extra 7% overhead information in traffic rate for the purpose of BER monitoring and correction. The standard FEC can result is 6 db coding gain ( which is infact quadrupling the distance) while Enhanced FEC can give an additional 2 to 3 % coding gain thus increasing distances further. Both Standard FEC and EFEC are called Hard Decision FECs-the decision rules for receiver are based  on two levels ( 1 or 0);  receiver decides between 1 or 0 depending on whether signal level is above or below a certain threshold level.  A new and more effective FEC is used by some vendors at  100G which is called Soft Decision FEC ( SD FEC).  SD FEC can additionally give a confidence factor in the decision used by receiver to decide between 1 and 0 meaning how far is the signal level from 1 or 0 this results in an additional coding gain of 1 to 2 db and hence resulting in overall improvement of 20% to 40% for distance reachability on 100G. Most vendors use SD FEC these days on transponders used for long haul applications while the metro transponders are still implemented with hard decision FEC to keep the price levels low. However  it should be kept in mind that SD FEC comes at the cost of adding 20% overhead information ( FEC bytes) resulting in slightly higher optical rates.

Without  FEC these days, the distance on high speed links would be severly limited. While Hard Decision FEC is very effective in increasing distances on 10G and 40G; Soft Decision FEC can addtionally provide longer distances and few regenerators on 100G.

The debate still lingers on. When it comes to protection and re-routing  on High speed links, what is the benefit of using Optical ASON versus Electrical ASON.

The Optical ASON relates to lambda switching ( Also called WSON-Wavelength Switched Optical Network). This necessitates the need of using at  minimum Multi degree and directionless functionality. Using colorless functionality gives more degree of freedom and flexibility since in case of non-availability of a particular wavelength, ROADM has the functionality to change the color of wavelength also. When it comes to Electrical ASON, it is referred to as “ODU switching” at electrical layer of OTN switch. This necessitates the use of OTN switch along with ROADM. While Optical ASON gives one an advantage of lambda switching; the Eletcrial ASON gives advantage of control over more granular traffic at ODU level going as low as 1G traffic. In contrast, lambda switching can help to save on transponder resources because the same transponder can change direction or color thus there is no need to have multiple transponders for multiple restoration paths-a  benefit not available on electrical ASON which would need multiple lambda paths to be created from Day one. Electrical ASON on the other hand gives much faster restoration times compared to Optical ASON. So what is the verdict ?

The rule of thumb is following: If traffic granularity is less and the lambda is not filled completely, Electrical ASON is much more optimized and cost efficient, on the other hand if lambda is filled with traffic ( multiple ODUs occupying complete lambda)  that needs same SLA of restoration ( Meaning complete Lamda needs to be switched) then Opitcal ASON is much more optimized and cost efficient and ends up saving on the number of transponders.

ACG Research has done an interesting TCO of MPLS-TP versus IP/MPLS showing there is a huge reduction of  Total Cost of Ownership (TCO) in MPLS-TP versus IP/MPLS.  The analysis was done in two environments: Native Packet transport  on MPLS-TP versus IP/MPLS  and second one using TDM/Packet mix on MPLS-TP versus Circuit emulation on IP/MPLS.  The platform used for  MPLS-TP was from ECI Telecom.  Further and most importantly Mobile backhaul was chosen as the network for analysis purpose.

https://www.acgresearch.net/tcos/eci-telecom’s-mpls-tp-npt-solution.aspx

The analysis proved a couple of  things:

1. The TCO ( CAPEX and OPEX) over 5 years  for pure packet transport using MPLS-TP is 55% lower compared to IP/MPLS.

2. When TDM services were added to the network. CAPEX on ECI NPT solution increased by 5% while the Circuit emulation addition on IP/MPLS increased its CAPEX by 37%. The 55%  OPEX saving in the first study increased to 64% when TDM traffic was added.

The high reason for the OPEX on IP/MPLS was attributed to the need for highly skilled technical staff needed to maintain IP/MPLS network compared to MPLS-TP.

Among OPEX, things like Network care, training, Network patches and upgrade, Cooling cost, Power cost, Service contract were compared. In all cases the OPEX cost for MPLS-TP were lower compared to IP/MPLS.

The results thus proved that MPLS-TP being a simpler technolgy contribute to much lower OPEX and CAPEX when used in metro networks and as such should be favored by the Operators if deployment is needed in Access or Metro areas.

Cloud is driving the Carrier Ethernet evolution. The MEF is serious about the evolution of Carrier Ethernet to meet the new demands of Cloud. The first and foremost would be to understand the elastic and dynamic demands of  Cloud which are pretty new to Carrier Ethernet scheme of things. MEF is trying to see how best the CE can evolve to meet these elastic demands. CE 2.0 has already set the pace. CE 2.0 addressed the major requirement for mobile backhaul in terms of managing Multiple CoS; Secondly, with CE 2.0, the number of services increased from 6 to 8. Two new services were introduced under E-Access. E-Access is needed when there is UNI that needs to be connected to ENNI-something that would be of interest to Cloud service providers e.g if a service provider owns UNI ; it can backhaul multiple cloud services to ENNI. As per MEF, it is targeting two key applications for cloud industry. One to enable private cloud connectivity of business customers through Service Provider’s cloud  and secondly to interconnect data centers of service providers. The first one is of important since business customers would need certain SLA for the connectivity of their mission critical applications. This is where Carrier Ethernet can really help in ensuring the SLA.

What is SDN?

Software-defined networking (SDN) is an approach to networking in which control is separated from hardware ( control decoupled from forwarding plane) and given to a software application called a controller.

What are the issues with today’s networks?

1. Networks are static: Today’s networks are static; e.g introducing new switches or moving any network element or routers need a lot of involvement of IT in terms touching a lot of  switches, routers, firewall and update ACLs, VLANs, QoS using device level management tools. The software version, hardware version etc need to be taken into account. Therefore today’s network are mainly static. On the hand the network needs are dynamic and growing. Applications today reside on multiple virtual machines ( VMs). VMs migrate to balance the server workloads causing the traffic pattern to change dynamically.
2. Inability to Scale: Data centers are growing in big numbers and so does their connectivity requirements. Companies such as google and Yahoo are depending on the efficiency of their data centers’ connectivity to provide fast speed processing to the users. As the network grows, the network elements grow tremendously rendering it very difficult for the IT to manage the network manually.
3. Vendor dependence: Service Providers have to depend on the vendors , their product life cycles and roadmaps to deploy new services.

How can SDN Help?

SDN makes the network control decoupled from forwarding and makes it programmable. By this decoupling, IT managers will have full control on the configuration, optimization, management via dynamic SDN programs. This programs are written by service providers themselves and they don’t have to depend on the vendors to develop the products as per their roadmaps. This enables the organization to quickly roll out the services, efficiently control network resources from a central place and cope dynamically with the dynamic demands of the network which otherwise is not possible with the static networking.

What is Open Flow ?

Open Flow is a protocol through which SDN will be standardized; It is the protocol through which the forwarding plane will be controlled by the Control layer.

Given  the attention MPLS-TP has received in the industry, it is worthwhile to discuss how this technology is different from MPLS. So here is a listing of the differences between the two.

1. MANAGEMENT PLANE SETUP :

LSPs in MPLS-TP can be setup without the use of control plane purely through the management plane. Quite opposite than MPLS which would need routing protocols or RSVP in case of MPLS-TE to set up LSPs. It is as if someone is sitting in the NOC and provisioning the LSPs from NMS centrally.

2. BIDIRECTIONAL LSPs:

Quite common in transport world is to have bidirectional Paths for circuits. In IP world, a traffic setup between two nodes can actually take any path if there is mesh available; not true about MPLS-TP. Though MPLS-TP does support unidirectional LSPs it is the bidirectional LSPs mode for which the transport world will adopt it.

3. CONTROL PLANE IS NOT MANDATORY:

MPLS-TP can be run without the assistance of control plane  which is absolutely a MUST HAVE for the MPLS environments. With MPLS-TP paths are setup by the NMS and downloaded into network elements.

4. IN BAND OAM:

All the necessary OAM information is carried inside the MPLS-TP frame; this is called in-band and also termed as ” fate sharing”. Again it is different from the MPLS where this OAM info is carried Out of Band.

5. NO IP FORWARDING:

MPLS-TP can run in an IP free environment; what does it exactly mean ? In traditional routers the IP is run on the interfaces since there is a need for the exchange of the out-of-band control messages. MPLS-TP can be run without IP in the forwarding plane.

5. SEPERATION OF MANAGEMENT/CONTROL  AND DATA PLANE

The failure of control plane in MPLS can affect traffic while this is not true for MPLS-TP. Failure of management plane in MPLS-TP will not affect the data forwarding.