Understanding UNI (User Network Interface)

Dear Friends, 

The year 2018 is coming to a close and this is the right time to write something on request of somebody. I had provided an article explaining Provider Bridge and Provider Edge concept where I touch-based upon the aspects of bridging and tunneling. Well I believe the article needed a prequel and that was to understand the different interface types that we have in the data networking. 

The networking that we do for data services are very dynamic and there can be several combinations of port-types and service types with domains realizing one important aspect and that is to carry the traffic from one point to another with reliability, security and prioritization. 

There are two kinds of interfaces that we have

UNI ----- User Network Interface

NNI ------ Network Network Interface. 

Today my post will concentrate only on the UNI aspect as I do not want to make this a very lengthy post. People may get grossly bored to read a lengthy post as for one I have noticed, the new generation lacks some kind of patience. 

What is UNI? 

In a very short and crisp definition we can say that UNI is the interface that connects a customer to the network. UNI port is an entity of the provider, however it interacts with a customer port or an interface. Please note that I have mentioned the terms port and interface separately. The reason being that a particular physical port may carry several logical interfaces that may be of UNI nature. 

Figure-1 Representation of a UNI

The figure above visualizes the definition of UNI. 

However, the concept of UNI is deep and needs more elaboration. For this we need to understand the concept of VLANs. A VLAN is a concept where we can break the broadcast domains to different smaller domains without involving the routing. You must be knowing that a switch breaks collision domains and the router breaks broadcast domains. However, what can be done in order to break a broadcast domain within a switching network without involving routers is to use VLAN. 

The VLAN gives a kind of identification to the packet or frame that is coming to the switching device as to which service that is should follow. VLANs are of 4 bytes and that are appended to a standard 802.3 frame. 

We see the structure of VLAN below. Disected. 

Figure-2 Dissection of the structure of VLAN

The VLAN is appended in the frame and it is providing the identification of the frame to follow a service. Here the main important thing is to see how the VLAN is appended in the frame. The frame can be untagged (without a Vlan) or it can be tagged (with a VLAN ID). Basis on this we have the two different types of interfaces of UNI. 

Figure-3: Types of UNI port

The types of UNI are the the basis of how the VLAN is treated in the service and the traffic is mapped. This is the thing that we will see in detail below. 

1. Access UNI port:

Imagine a situation where there are three customers who are all sending untagged frames. However the WAN which is carrying the traffic is a common WAN. How are we going to segregate this traffic. There is one way to do it by leaving it on the Mac Learning and bridging concept. The concept over here is that every device will have a different MAC and based on the MAC filter there will be communication and we will have one common LAN. However, this aspect has some disadvantages. 

Figure-4: Situation where three customers carry different traffic

> What happens in the unlearned state? 

> How will the traffic be treated? 

> What happens if one customer is sending a broadcast? This will affect the performance of all other customers. 

However, we cannot impose the condition on the customer to tag these frames. If we do that we are putting conditions on the customer and this way we will have to put similar conditions on all other customers, which is not a good idea. 

Here the thing is to have an access UNI port. 

The access UNI port accepts an untagged port on the LAN and then appends the VLAN on the frame of customer and then forwards it to the WAN. 

The flow is explained in the figure below. 

Figure 5: How the access VLAN UNI works

Here you see that the customer 1 sends the untagged frame and then it reaches the access port. Here the access port adds a VLAN ID to the frame and this travels through the WAN. On the other side when the frame is coming out the VLAN is matched and stripped and the original frame is received by the end. 

Points to note: 

1. Access VLAN ports in the UNI append VLAN in the ingress and match and strip the VLAN in teh egress. 

2. This action is like attaching a unique envelope to the untagged frame and taking it out on the other end without distorting any information. 

In our case we can have the following scenario for our three customers. 

Figure-6: How the three customers will be segregated

Here we see that every customer is connected to a different access port and so we put the access VLAN accordingly to identify the customer. Also note that the customer 2 may have a different drop point than customer 1 so this has to be organized in that way. 

2. Trunk Port: 

Once we understand the Access VLAN port functioning understanding trunk port is very easy. The trunk port in this case is our WAN. The WAN port is not adding or stripping any VLAN however it does a validation of VLAN that it has to pass. In our case we will put a validation that the trunk link should only pass VLAN 100, 200 and 300. 

The algorithm is the trunk port accepts frames that are already tagged and then matches them with the validation. Based on that it forwards. 

So friends, this is about the UNI port. We shall see the functioning of the NNI port in a later post. Understanding the UNI interface is very important in order to do selection of interfaces in data traffic planning. Therefore, be careful in deciding the same. 

Till then have a fantastic New Years' Eve.... 

Cheers and a Happy New Year, 

Kalyan 

RSTP/MSTP Part –V How does switching take Place in RSTP and MSTP?

 Dear friends of the Telecom Fraternity,

I was writing a series of RSTP in 2013 and possibly, there are many things to catch up. I would like to divert your attention to this blog that was the fourth part of my RSTP series.

RSTP-MSTP part IV

It is from this blog we continue our journey ahead to this vast topic called RSTP. Generally, people believe that RSTP is for switching, but I had clarified before that this is a Loop avoidance Mechanism. RSTP makes the switching of services in case of Failure more salient because there is a transition of paths.

In this section, we will concentrate on a simple architecture and that is RSTP Ring. As explained before we optimize the ring with a selection of optimal blocking port in the service.

Figure-1: RSTP ring topology example

Now in this ring let us understand that there is a service from the root Bridge to N-2 with SVLAN 200 and another service from Root Bridge to N-3 with SVLAN 300. This can be shown in the figure below.

Figure-2 Service configuration in the RSTP domain

To understand the concept of service switching let us understand a failure scenario. So in our case we imagine that the link between N-1 and N-2 has failed. Definitely, the service will be routed from another direction. However, in our case we will see this in a step-by-step basis.  Please remember that a service switching in RSTP is not as simple as it looks. Because there are no predefined main and protection paths like you have in TDM or MPLS. Here the entire switching of the service from one direction to another is working broadly on two principles.

1. RSTP Re-convergence
2. Mac Learning renewal at all switching points. 

We will see all these happening but you have to remember that all these happen very instantly. Typically the re-routing time of the services in the event of failure in RSTP is 200ms. Note this is not 50ms and that is why it is not recommended to run voice services or any real time services involving voice in the RSTP network. This is the reason why RSTP is regarded to be a Non-Carrier grade method. However, for a normal http service or a https service it does not matter as there is a TCP retransmission always happening and so RSTP works very well.

So we see the figure below to understand the failure scenario. 

Figure -3 Failure Occurrence in the link

 After this failure has occurred the first thing that happens is that N-2 does not get the BPDU packets from the N-1 (its designated bridge). So a Root port transition takes place and the link that is between N-2 and N-3 becomes a forwarding link. One special thing to remember over here is that in the N-2 to N-3 link, which is the blocking one of the ports between N-2 and N-3 will be the discarding port. RSTP in this case will not have two discarding port. So we have two cases over here. 

1. In case the discarding port is N-2 and there is a Root port failure on the N-2 then the Topology Change request of RSTP will immediately come into action and N-2 discarding port will turn to forwarding. 

2. In case the discarding port is N-3 then the TC message is communicated from N-2 to N-3  and N-3 changes the port from discarding to forwarding. 

Here the critical part is the topology change notification message that is carried by the BPDU and this always happen after a minimum hold-off time which is 200ms. The difference between STP and RSTP is over here. In STP there is a wait of three hello intervals which makes the initiation of TCN happens delayed. This results to a switching time that is more than 3 seconds. However, when we talk about RSTP (Rapid Spanning Tree Protocol) the TCN notification are subject to port transitions in any switch. Therefore N-2 and N-1 will both have transition changes and will initiate TCN immediately after the expiry of the hold-off timer. 

Now after the TCN is communicated the new state of RSTP will be as the figure below. Please note we have not yet considered how the service is being rerouted, we are still seeing the first part of the switching and that is RSTP re-convergence. 

Figure-4: RSTP topology change

Now the topology change has occurred. But what is remaining still is the re-routing of the service. I told this earlier that RSTP does not have a pre-defined protection and main path so the service re-routing is happening plainly on the basis of Mac Learning. RSTP is a scheme that is used in the case of Provider Bridge networks. To understand what is a provider Bridge network please refer to my earlier blog post in the permalink given below. 

Provider Bridge and Provider Edge Networks

In this blog post you will find clearly how the traffic moves in the provider bridge networks. So as this is a provider bridge we see that for the service affected, which is the service with SVLAN = 200, the mac learning has been done in the following manner of (Root Bridge - N1-N2). Now the path between N1-N2 has failed and there has to be a sort of notification to the root bridge to send the traffic via the other path. 

The self healing way of such a scenario is that the traffic stops and we wait for the expiry of the aging time of the mac table. The aging time of the mac table is a user configurable parameter, however the minimum value is 10 seconds. So technically if such a failure has occurred the service rerouting should take place after 10 seconds (aging time). 

Phew!!!!!! This is long. So the developers of RSTP thought of another approach and this was to flush the mac-table of every bridge that is involved in the RSTP domain. Therefore, the TCN also sends a command to flush the mac-table of all the bridges involved in a particular RSTP domain. 

Something like the figure below. 

Figure-5 Mac-Flush happening n all the nodes involved in RSTP

Here we see that all the points of the RSTP domain are flushed. 

Now it is anybody's guess what will happen after the flush of the FDB occurs. There will be relearning of mac address for the services. In this case the service with SVLAN 300 will have the same path of mac learning but the service with SVLAN-200 will not have the same path of mac learning. Now N-2 which is the destination point will learn the mac via N-3 and not N-1 and this will make N-3 the Designated Bridge for N-2 and the service will now be re-routed. 

Figure-6 Final Re-routing of the service

So here we see a complete step-by-step process of re-routing of the services. Tough but not so tough to understand. 

In this case please note, now the bandwidth distribution in the ring is not optimized and there can be a scene of congestion between the link of RB to N-4 and N-4 to N-3. Under such scenario the QoS will come to play and the RSTP domain has to be properly traffic engineered. 

What happens when the link restores?

Now we saw about the failure the restoration of the link is also treated like a seperate failure in this case. RSTP recognizes only topology changes and now with the link repaired there is another topology change. A similar TCN will pass through the ring and there will be re-convergence and the block port will now be as per before. The TCN will flush the Mac tables of all the bridges and this will lead to service re-routing again. 

So friends, pretty long blog post, but cannot help. In order to understand the switching part there has to be more description, which I have tried to bring in. But, we have just touched the tip of the ice-berg. There are lot many things happening beneath the skin of the water and to dissect it threadbare it would need another 50 blog posts. We will see the operational aspect of RSTP in multiple topology scenarios as well and dual homing cases. 

Till then 

See you.

Regards, 

Kalyan 

Keep thinking!!!! Keep Reading!!!! Keep Evolving!!!!

How to do things differently in Telecom?????

I remember the last blog-post that I had written. Telcos do not need engineers. This invited a lot of censure and on the other side showed the mirror of reality to many telco veterans and contemporaries. I had ended the blog by saying what is needed then? Well here I am to make an effort to answer these things.

Change is a continuous process and not that what will be valid today will be valid after five years. Technology changes as we speak and so does the methods to manage technology in a great deal.  So let us understand what are the new things that we should adapt to. I believe the members of the telecom fraternity should have reptilian tendencies these days in order to survive and be a positive contributor of this industry for a long time. We will classify these things as What is In and What is out?

1.    IN: “Work with me”  OUT: “Work under me”

The most critical point of management is the degree of authority. Authority is a responsibility and not just a right of seniority. However when authority becomes dogmatic then there is definitely a problem in the management style. There is an old saying “People join companies, people leave bosses.”; The saying unfortunately is true till date. Instead of this, it is required to behold a sense of "espirit-de-corps" that should prevail across the ranks. Vertical conflicts are a thing of past. Intellectual conflicts are the new things to watch out for. Ideas are nobody’s monopoly and definitely not a privilege of seniority. Therefore it is always necessary to take your juniors with you. Working with has a lot of advantages than making work under.

2.    IN: “Opinions of Juniors” OUT: “Approvals from Seniors”

Another very rebellious statement, but true! Telecom is an industry that is always shaped by fresh ideas. Fresh ideas cannot be expected from veterans of 10-20 years old, unless there is an unbelievable streak of innovation, which is rare in the Indian context. Any fresher that comes to your company is an asset. Not because you can make him/her laboriously, toil over mundane works but harvest new ideas from him/her. A fresher has a lot of imagination because he/she is undaunted by experiential difficulties and obstructions. A fresher or your junior is just scared to speak because of the weight of position that you throw to him/her knowingly or unknowingly. They are not outspoken sometimes because they feel they will be judged. An approval is a formality but an opinion can lead to a breakthrough and this can only come from the new generation. Experiences are good but they are good to guide the new generation and make them aware of the mistakes that had been made in past. Not to scare them with positional authority. Approvals are needed, only for leaves and protocols.

3.    IN: “Affinity for Automation” OUT: “Justifying the Manual Cause”

Times have changed and so have the approaches to a problem. Gone are the days were we needed a lot of manual staff to manage things that are routine. These have to be automated so that the expectations from human resources can be raised. Contrary to the feeling that automation is a killer of human opportunities, I believe it is an opportunity to raise the bar of human involvement in the field of telecom from being grossly mundane to being innovative and creative. Today’s telecom demands innovation and creativity. This has to come from every levels of the organization. For being creative the human mind needs something which is essential and that is time to think. Of course, there is a corollary which says that work keeps humans busy, but definitely mundane work makes them morose and more like zombies who after some years become of no use. Every human asset of the telecom company has to be a generator of creative and productive idea and that is why automation is required to shun the monotony that is prevalent in the industry.

4.    IN: “Leaders”    OUT: “Bosses”

Explained this before and now again explaining it. It has been long this discussion of leaders vs bosses have taken place and the toying of this idea has gained a lot of popularity. Now is the time to implement and evaluate this idea. A leader is a person who gives direction and takes the initiative to walk the talk. A boss on the other side is a generator of instructions and orders. Industry definitely needs leaders. In war-time you need leaders who can take you safe from the cross-fires and inflict minimum casualties rather than a boss who is not on the field and just instructing from a safe haven.

5.    IN: “Evaluating Technical Edge”   OUT: “Compliance”

This is especially to the people who are evaluating vendors or technology for their implementation. Most of the time they are obsessed about compliance overlooking the technical edge. This leads to a lower shelf-life of the network. There will be solutions that are unique in the market and are innovative, processes have to be bypassed for absorbing those. Regular processes make regular companies. To be a company that stands out there has to unconventionality in the processes. Because unconventional evaluation makes unconventional companies. The idea of providing internet through hot-air balloons was not evolved from a telco. Because a Telco always focuses of compliance, obliterating anything that is unique and outstanding. This definitely has to change.

6.    IN: “Process Management”  OUT: “People Management”

This is the generation of the millennials. They are focused. They know what they want and how they want it. They are coming inbuilt with a management guidance system in their personality. They are intrepid and they are also adventurous. They are passionate at times and at times they are totally detached. A traditional people management approach is futile in managing this generation of people. There is a need to accept the fact that this is the generation with most of the ideas and that too the creative ones. They are a treasure and a treasure is not people managed but protected and preserved. So the requirement is to have a process and a management of the process that lets the company and the industry at large harvest from this amazing pools of knowledge.

So there are a lot of things to change. These changes will come. Today it may seem to be a giggle factor or some philosophy in book, but they will certainly come and I am hopeful. I am betting on this change because of a simple philosophy. “If there was somebody who could stop progress and change we would be still living in the caves.”

On that note, I leave you now to decide and comment on this post of mine.

Cheers,

Kalyan

TELCOS DO NOT NEED ENGINEERS!!!!!!

Yes, you heard it right. Telcos do not need engineers anymore. Infact the engineers that the telcos have are not more than a liability. The engineers, heads, managers, technical team….. a mere cost item, precisely the Right hand side of the balance sheet.

Surprised! You ought to be. I, myself am an engineer in this industry for the last 18 odd years and I am saying that. So why such a change? Why such an iconoclastic statement?

The reason is the definition of “Engineer” that the conventional telco understands is way outdated and way under the requirement. An engineer in today’s telco industry is a person who has to tread a line of processes, forgetting creativity and unconventional thinking. There are sets of ground rules that have to be adhered, sometimes breaking those ground rules is not only a flouting of policy but like a criminal offence.

Result! The same old thing repeating again and again. So called engineers become human robots following monotonous orders and doing the same stuff. Working in this industry in the conventional way does not seem interesting anymore and this affects the overall performance and nature of the company. Every technical staff, of the 100% effort that he/she makes, 90% is devoted to saving himself/herself from something. The attitude that shouts out loud, “I AM NOT RESPONSIBLE” is written everywhere in the company and finally we have “NOBODY RESPONSIBLE” in the entire structure.

The thing that happens is that nothing new comes out of the industry and we have same old services again and again without a shade of change. Scary job environment just mandates one thing and that is to keep your job. The best thing over here is when the planning guy feels insecure he does a charade of taking out a tender as if he/she were to design a NASA space shuttle. Tender process goes on for six to eight months and this is the time the planning guy looks out for another job. The outcome is either the planning guy has moved out to a new company or the tender is postponed for another six months.

Operations is funnier. Sometimes in order to see that they have work, they pray for some fault to come, and when it really comes and they are helpless, they just pick up their phones and make calls to the managed service partner, without applying any significant brains on the problem. As if they were hired in the company to just be telephone operators, they just drain the batteries of their phones and their energy bags shouting at the managed service partner and vendor. Once the fault is fixed, a thank you note to the vendor and a gallantry award from the operations manager who is equally scared of his/her job. Finally, a breather for another three months and life goes on.

IN ALL THIS CIRCUS THE BIGGEST CASUALTY IS THE CONCEPT OF “ENGINEERING”…. RIP

It is much better that such mundane activities are now being outsourced to machines through Artificial Intelligence and automation. Automation today can replace most of the monotonous work in the telecom industry and believe me most of the work is monotonous even planning. Artificial intelligence and automation comes as a boon and not bane. At least if not everything, it shows the mirror to the engineers at all level that they have to be “engineers”, because robots can be made by synthetic things as well.

Well after all this acerbity that I have spat out, I am surely expected to be trolled. After all telling the truth comes with its occupational hazards. However, I have spoken out.

So what is needed? What do we need to do in order to come out of this vicious circle?

Will speak about this in the next article.

Cheers,

Kalyan