Chapter 2. Background

Mobility includes all the mobile network types - Macro, Micro and Wi-Fi. Macro network is the 3th Generation (3G), 4th Generation Long Term Evolution (4G/LTE) networks that we connect to from our cell phones. Micro networks are small-cell networks which are overlay networks that provide 3G/4G access over an IP infrastructure (public or private). Increasingly the trend has been to provide seamless service to the end-user (subscriber) regardless of the access-type.

The motivation for NFV in mobility can be be captured through Table 1:

Criteria

Past

Present

Network usage

People

People & Machines (Internet of Things)

Network Access

Macro

Macro/Micro/Wi-Fi

Network Service

Voice/Text

Voice/Text/Data/Social Networking, Apps, Gaming

Network Usage

Predictable

Dynamic based on events (e.g. Super Bowl, Super Tuesday)

Network Architecture

Fixed

Elastic

Table 1: Evolution of Mobile Networks

We have seen that the adoption rate and interest for NFV is huge amongst mobile operators around the world. While there are few VNFs available for Wi-Fi, major use cases for NFV in mobility are:

  • Virtual Packet Core (sometimes referred to as Virtual EPC - Virtual Evolved Packet Core abbreviated as vEPC)
  • GiLAN
  • Voice over LTE (VoLTE)/Virtual IP Multimedia System (vIMS)
Note

It should be noted that even though this document covers the above three use cases in general, more emphasis is placed on vEPC as is more widely deployed by mobile operators around the globe. Adoption of GiLAN is in pockets. vIMS will pick up as VoLTE deployments grow.

2.1. Virtual Packet Core

Packet Core is the term used to refer to the part of the mobile network where the 3GPP gateway functions such as Service Gateway (SGW)/Packet Data Switch Network Gateway (PGW)/Mobile Management Entity (MME) (4G/LTE) and Service GPRS Support Node (SGSN)/Gateway GPRS Support Node (GGSN)/Packet Data Serving Node (PDSN) (3G) reside. A virtualized instance of packet core is referred to as Virtual Packet Core(VPC). Mobile Gateways get deployed differently based on requirement/function:

  • Virtual Evolved Packet Core is when a mobile operator who may have a 3G core has decided to start offering 4G/LTE service and is building an evolved packet core. In this case typically most of the functions listed above may be virtualized - PGW, SGW, MME, PCRF, FW, Router, DPI, Switches, LB. This use case is typically for operators who are building a brand new mobile packet core or upgrading and want to take the virtualization route rather than to invest in purpose built hardware. This also covers Trusted Wireless Local Area Network (WLAN) Access Gateway (TWAG)/Trusted WLAN AAA Proxy (TWAP) for Wi-Fi termination from trusted networks and Evolved Packet Data Gateway (EPDG) case which is responsible for terminating WiFi connections from untrusted networks. It should be noted that the untrusted (EPDG) case typically uses IPSec and encryption which could have a higher compute demand of the NFV Infrastructure (NFVi) (This is typically performed in hardware).
  • Enterprise Overlay Services/Enterprise Access Point Name (APN - A private instance for an enterprise customer). Mobile Network Operators (MNOs) offer dedicated APN services to large enterprises. The services offered for these enterprise APNs vary from simply having dedicated gateways to having additional security, custom QoS, VPN services to connect end-points to enterprise hub locations, Enterprise Billing and other value added services. Typically, creating enterprise APNs means having a dedicated GGSN/PGW while other nodes that constitute the mobile packet core may be shared or dedicated based on the design and deployment. An example of enterprise APN may be a packaging and logistics company like FedEx who may choose to have their own APN where their mobile devices connect. By connecting to FedEx APN these devices will automatically inherit certain connectivity (e.g. to FedEx Corp Cloud), have certain services enabled (firewall, NAT) etc.
  • D-Core/Mobile Virtual Network Operators (MVNO) offer mobile services using parts of the actual network that is owned and operated by MNOs. D-Core stands for Dedicated Core where a MNO offers a mobile packet core per network instance per customer. For example, if a large logistics company needs to have their own mobile network, they can buy radio (air-time) from one or more MNOs and use a dedicated core which usually is a virtual packet core (VPC) instance created for the logistic company.
  • Public Safety - During major events such as Republican National Convention (RNC) it is common to create a local channel for communication amongst all public safety factions - police, fire, medics etc. Nowadays this could be standing up a specialized 4G network for the duration of the event. This could be done in one of many ways - 4G in a box on a truck, temporary datacenter setup at the venue or in the cloud. Regardless of the choice the main point to be noted is that this network is temporary and lives for the period of the event. Although purpose built hardware can also be used they have a huge footprint in terms of real estate, power, cooling and simply difficult to manage and operate. Virtual Packet Core (VPC) lends itself perfectly for such an application
  • Machine to Machine/Internet of Things (IoT) - Machine to Machine(M2M) is another application that requires dedicated gateways to be setup per M2M instance. M2M traffic tends to be sparse and have lower throughput while having a higher session count requirement. Adding these gateways based on consumption and keeping it elastic makes M2M a classic use-case for VPC. A more successful and visible M2M/IoT use-case is “Connected Cars” which has been deployed successfully by major mobile operators in North America

2.2. GiLAN

Mobile Packet Core networks can be viewed as having two connections - Radio network or wireless side where the subscribers connect from and the Internet facing side. The Internet facing side of the network in a 3G network is labelled as “Gi” interface (referred to as “SGi” in a 4G/LTE/EPC network). IP services such as Firewall (FW), Network Address Translation (NAT), Deep Packet Inspection (DPI), Parental Control, Video and Web optimization reside on the Gi or SGi interfaces after leaving the gateway towards the Internet.

Depending on the APN and the services being offered, mobile operators are looking to create dynamic chains of these services. For e.g. when a subscriber roams from a 4G/LTE coverage area to a 3G coverage area, if they are watching video, their viewing experience may become degraded due to network congestion. In such situations, the mobile operator would like to dynamically apply video optimization (transsizing and transcoding) to keep the user experience consistent. This ability to dynamically apply different functions to the subscriber traffic is referred to as “Service Chaining” (https://datatracker.ietf.org/wg/sfc/documents/). Software Defined Networking (SDN) capabilities of programmable APIs and actual use of SDN controllers (policy aware) in conjunction with NFV (ability to create capacity on the fly) makes it possible to deploy such features/functions in production. The operational nightmare of creating the permutations and combinations of all these functions when overlaid with subscriber policy and intelligence (Location Based Services) made it impossible to deploy prior to NFV/SDN.

2.3. VoLTE

LTE is an “All-IP” network. This allows applications such as voice that was traditionally analog to be offered as Voice over IP (VoIP). VoIP in an LTE network is referred to as Voice over LTE or VoLTE for short. VoLTE has service function chains that offer different functions such as Session Border Controller (SBC), Call Session Control Function (CSCF) etc., which are being virtualized to fit into the NFV model.