Nothing small about the Small Cells in 5G

William Clement Stone, a famous businessman once said "Small hinges swing BIG doors". That statement is very true with respect to 5G. With a promise of ubiquitous coverage, absolutely low latency and higher speeds, 5G's success is heavily dependent on the so called "Small Cells". Small Cells are almost like the building blocks for the 5G network. 

Small Cells are mini base stations that handle the radio signals, like the mobile towers.  Small Cells require very minimal power and space, unlike the large mobile towers in the neighbourhood. Small Cells can be installed on the top of a light pole or a building. Small Cells are not new to the wireless world. They were deployed in 4G networks too. However, in 4G networks, Small Cells were predominantly used to improve the indoor wireless coverage. In fact, a few years back, Service Providers thought that customers would pay for the deployment of Small Cells at their home or office, to increase coverage. However, that dream didn't become a reality. But, with 5G, small cells are again getting a lot of focus. 

There are three types of small cells that exist today - Femtocells, Picocells and Microcells.

Femtocells – Femtocells help the operators in quickly solving the network coverage problem. It takes a very long time for a service provider to install a mobile tower. However, it takes only a few days to power up a femtocell in the network. So, if there is a residential or an enterprise customer that requires extended wireless coverage, the operator can quickly deploy a Femtocell. Femtocell provides multiple benefits such as helping the service provider to offload the network congestion, provide better coverage and increase the data transfer rates. A Femtocell typically caters to 16 users and can provide coverage for a distance between 10 and 50 meters. 

Picocells – Picocells are similar to Femtocells in terms of functionality. However, their coverage area is 100 – 500 meters. Also, they can support 32 – 64 users at a time. Picocells are well suited for small enterprise applications.  

Microcells – Microcells are designed for providing wireless coverage to a large geographic area and suited for providing network coverage to outdoor applications such as smart communities. Microcells provide coverage for a distance between 500 meters and 2.5 kilometers. Microcells can support nearly 200 users at a time.  

A 5G network deployment would include a combination of these different types of Small Cells. Small Cells will help the 5G service providers in densifying the network. Some skeptics are worried about the impact of deploying hundreds and thousands of small cells in the city. People are concerned that the 5G radiations may impact human life and the environment. However, studies done so far, on the impacts of mobile tower radiation on humans are not conclusive. In the mean time, Service Providers are aggressively building their network and launching 5G services globally, by deploying Small Cells in almost every street corner. 

Control and User Plane Separation (CUPS) in 5G

What is CUPS?

CUPS stands for Control and User Plane Separation. It was introduced by 3GPP, for Evolved Packet Core (EPC) as part of their Release 14 specifications. 

Why do we need CUPS?

Service providers across the globe are seeing a jump in the mobile data growth, year-after-year, due to the growth in the consumption of video, online gaming and social media services. 5G is not only facing the challenge of supporting higher data speeds, but also has to reduce the network latency for customers. Network latency has a direct impact on the customer experience and almost a non-negotiable thing for the new 5G use-cases.

The architects of 5G are looking at multiple ways of bringing down the network latency for customers, to meet the requirements of emerging 5G use cases such as Smart Cars, AR/VR and Holograms. 5G architecture tries to reduce the network latency through multiple mechanisms such as Network Slicing, Massive MIMO, Small Cells and Multi-access Edge Computing (MEC). MEC infrastructure, being closer to the user, plays a critical role in bringing down the network latency by providing a compute infrastructure for Over-The-Top (OTT) and Internet of Things (IOT) services. CUPS is another ammunition in 5G kitty, which helps in bringing down the network latency.

When was CUPS introduced in the wireless network architecture?

CUPS was originally introduced in the 4G Evolved Packet Core (EPC) architecture. EPC with CUPS support separates the control plane function from the user plane function in the network. Network functions within 4G EPC such as Packet Gateway (PGW), Serving Gateway (SGW) and Traffic Detection Function (TDF), were split into control plane and user plane functions. EPC with CUPS support had PGW-U/PGW-C, SGW-U/SGW-C and TDF-U/TDF-C. 

When EPC supports CUPS, service providers would have the option of 

• deploying the control plane functions co-located with the user plane functions (i.e., in the same data center)
• deploying the control plane functions and user-plane functions in a distributed fashion, across multiple locations
• deploying the control plane function in a centralized location and deploy the user-plane functions in multiple locations

How does CUPS helps in reducing network latency?

The multiple deployment options supported by CUPS, provide great flexibility to the service providers, to deploy user-plane functions in one or more locations to meet the bandwidth and latency requirements of customer services. For example, a service provider may have to deploy more instances of the user plane function near a college, where several 100s of students are watching video and playing online games. However, in a shopping district, there will be several 1000s of mobile users who would be browsing Internet for checking information about stores and shopping deals. In such locations, the control plane has to scale to support several 1000s of customer sessions. So, the service provider may have to deploy more control plane functions in such geographies to support the 1000s of mobile users. 

How does 5G support CUPS?

5G adopts CUPS based architecture for the 5G Core. 5G Core has a distinct User Plane Function (UPF) that handles all of the user-plane functions performed by SGW-U and PGW-U in 4G EPC. 5G's control plane functions are distributed across different network functions such as Authentication Server Function (AUSF), User Data Management (UDM), Policy and Charging Function (PCF) and Session Management Function (SMF). This gives a lot of flexibility for the service providers to decide the network functions which have to be deployed at the edge of the network vs. core of the network. 

Since 5G supports cloud-native network services, it becomes easy for the vendors and service providers to implement CUPS in the 5G network architecture (when compared to the 4G network). 

Also read: Is 5G radiation going to kill us?

SDN in Transport Networks - Challenges, Solutions & Benefits

According to a recent report from Market Research Future, the market size of transport networks is growing at a rate of 16% CAGR to reach $34 billion by 2023. The growth in the mobile towers, enterprise connectivity services and the rise of data centers are fueling the growth of transport networks. SDN-izing the transport network is not an easy task. This article provides some details on the challenges of managing the transport network, solutions available in the market and the benefits of SDN-izing transport networks. 

SDN had its roots in the data center - but, the technology has slowly crept into Enterprises, Campuses and even into the service provider networks. SDN is a powerful technology, if implemented right, can provide numerous operational benefits to the service providers.  SDN not only provides operational efficiencies, but also helps service providers to create newer revenue streams. SDN can potentially be deployed by the service providers at the Edge, Access and Transport segments of the network. Software Defined WAN (SD-WAN) solution is one of the popular WAN offerings from the service providers across the globe. According to IHS Markit, from just $444 million revenue in 2017, SD-WAN revenue has already surpassed $667 million as of 3Q'18. Now, service providers are exploring how SDN can be deployed in other segments of the WAN, especially to simplify the management of Transport Networks.

What is a Transport Network?

A transport network provides connectivity services for

• Mobile Towers - Connecting the mobile 3G/4G/5G towers to the core network
• Enterprises - Connecting the corporate and branch offices of an Enterprise, to provide a secure private IP network.
• Datacenters - By connecting the data centers together, using a secure link. 

A transport network includes multiple technologies such as packet, optical, microwave and satellite communications. Traditionally, the transport network had dedicated circuit switched technologies such as Synchronous Digital Hierarchy (SDH) and optical transport networks (OTNs). But, today packet/IP based technologies are deployed in the transport networks (in addition to the optical technologies), to share the same links across multiple customers. For example, Multi-Protocol Label Switching (MPLS) is a popular IP based protocol used in packet transport networks today.

Challenges faced by Service Providers in Transport Networks

Managing transport networks is always a nightmare for the service providers. Some of the challenges faced by service providers while managing transport networks are:

• The vendors who supply optical network equipment are different from the ones who supply packet network equipment. There is no standard way of managing these network equipment and hence, Service providers need to have specialists to manage these equipment. 
• Optical network equipment are managed by vendor specific proprietary Element Management Systems (EMS). This increases the number of "devices" that sit in the network, consuming additional power, cooling and space
• The packet layer and the optical layer equipment are managed separately. Hence, change management activities are complex, potentially taking several days or even weeks to implement.
• Any link failures in the optical layer doesn't immediately reflect in the packet layer (and vice versa). This negatively impacts the quality of service and the customer experience. 

How can SDN solve the Transport Network Challenges?

The need for SDN is today well understood and acknowledge by the industry. SDN can solve multiple problems faced by service providers while managing the Transport Networks.

1. SDN introduces standard APIs for managing multi-vendor network equipment. For example, the industry is looking at standardizing the management of ROADM (Reconfigurable Optical Add-Drop Multiplexer) devices. One such initiative is the Open ROADM initiative championed by AT&T. This group has recently reached a critical milestone where vendors such as Ciena and Fujitsu are able to demonstrate the interoperability of multi-vendor optical equipment, through standard APIs. Open Optical and Packet Transport group which is part of the Telecom Infra project, championed by Facebook is looking at standardizing the management of optical transponders, line systems, IP access devices, network simulation and planning tools
2. SDN supports multi-layer / multi-domain management capabilities. For example, Infinera and Sedona systems support capabilities to manage both optical layer and packet layer equipment through their SDN platforms such as Xceed and NetFusion, respectively. It is important to note that Xceed is based on open source OpenDaylight SDN controller platform. 
3. SDN allows programmatically creating and managing multiple virtual networks on top of a physical network. For example, a small cell in 5G network can automatically register with the network and establish a connectivity with the 5G core network. Or, an Enterprise customer can dynamically manage the bandwidth of their virtual pipe though a mobile application. 

What are some critical use cases of SDN in Transport Networks?

• Dynamically modify bandwidth based on the application requirements 
• Simplify operations through automation of multi-layer (packet/optical), multivendor & multi-domain orchestration 
• Improve the utilization of network resources by optimizing between the different layers and selecting an optimal network path 
• Improves the speed of rolling out new services by providing an API access to transport layer 

Benefits of SDN-izing the Transport Networks

SDN-izing transport networks provides both short-term and long-term business benefits such as the following:

• Lowers costs (CAPEX & OPEX) by standardizing the management of multi-layer, multi-vendor, multi-domain packet/optical network equipment
• Dramatically improves the speed of service provisioning and service activation, thereby improving customer experience 
• Makes transport resources dynamic and visible to applications for newer services