Mobile network operators (MNOs) have long relied on services in the mobile SGi-LAN to optimize network traffic and manage network bandwidth. While the tools of the SGi-LAN have historically helped MNOs understand the traffic traversing their network, apply the right set of optimizations for that traffic, deliver an improved subscriber experience and alleviate congestion on the radio access network, the historical deployment model of network appliances in the SGi-LAN carried with it expensive CAPEX and OPEX.
Currently the Third Generation Partnership Project (3GPP) defines the SG Interface (SGi) between the PDN Gateway (P-GW) and packet data network. Although there are no specifications for networks services deployed in the SGi-LAN (or its 3G counterpart, the Gi-LAN), the functions in the SGi-LAN are critical to MNO operations.
Today, software-defined networking (SDN) and network functions virtualization (NFV) provide a new set of tools for to reconsider the architecture of the SGi-LAN. By leveraging SDN service chaining capabilities and virtualized network functions, MNOs can eliminate the complexity associated with manually provisioned routing paths through a series of proprietary appliances and instead deploy an easier-to-manage service mesh.
The SGi-LAN today
Within the SGi-LAN today, network appliances, such as firewalls, NAT, deep packet inspection (DPI) nodes, video and TCP optimizers, performance enhancing or header enriching application-aware proxies (i.e., session border controllers [SBCs], web proxies, etc.) and content caches all provide unique value in delivering mobile services.
The SGi-LAN is logically and topologically organized into a number of parallel service paths, each providing value to either a particular subscribers subset (i.e., enterprise customers) or a particular traffic type (i.e., video, web). In order to ensure that traffic is mapped through the appropriate service sequence, a set of static tools, including static and policy routing, virtual routing and forwarding (VRF) assignment and DHCP pooling (Source IP Match) are used.
The SGi-LAN today
An example of the mobile SGi-LAN today with four service chains and ten appliances.
As MNOs deploy new services, the current SGi-LAN architecture encounters a number of scaling challenges:
Increased time and cost to insert a new appliance
Increased number of unique service chains
Increased number of static rules
Decreased size of IP pools allocated to individual service chains
Different individual scaling properties of appliances within a service chain
Less visible interdependencies between functions within a service chain
In short, introducing new appliances into the SGi-LAN has a multiplier effect on complexity, resulting in increased operational expenses and decreased flexibility. As MNOs seek to introduce agility into their culture to effectively compete for new revenue streams, such as machine-to-machine or build cooperative relationships with cloud and media companies, the increasing complexity in the SGi-LAN is an inhibitor to success.
SDN and NFV in the SGi-LAN
Today, SDN and NFV allow MNOs to simplify their SGi-LAN architecture and operations, eliminating or mitigating the service chain scaling challenges discussed previously. SDN solves the challenges of creating and modifying service chains while NFV provides a solution for the individual scaling limitations and interdependencies of service chain functions.
Specifically, SDN provides MNOs with the ability to decouple the rules and topologies associated with the SGi-LAN service functions and chains from the forwarding functions. With this capability, the static provisioning, assignment and sequencing of service functions within a service chain is eliminated in favor of dynamic decision-making. Such capabilities can be realized whether the service function is a physical appliance or a virtual network function, without any expectation that the service function is aware of the service chain itself.
By incorporating metadata about subscribers, services, or network conditions, real-time service chain and forwarding decisions can be made. This decision-making may even be an extension to the existing policy and charging rules function (PCRF), interacting with the northbound APIs of the SDN controller, allowing a MNO to centralize flow-handling decisions across both the SGi-LAN and mobile network.
SGi-LAN service functions are currently transitioning from physical appliances to virtual functions. Much like the forwarding plane can be dynamically provisioned with SDN, NFV provides tools for orchestrating and automating the virtual network functions themselves. As the SDN controller forwards packets through the individual virtual network functions, the NFV orchestrator (NFV-O) is able to respond by scaling the resources, such as compute, memory or bandwidth, assigned to each function.
SDN in the SGi-LAN
Integrating SDN into the SGi-LAN for dynamic service chaining.
Integrating SDN and NFV into the SGi-LAN delivers both economic and operational benefits, such as capex and opex savings, simplified management and improved time-to-market. Together, SDN and NFV create a powerful combination that transforms the SGi-LAN from its current static, inflexible state to one that allows MNOs to rapidly respond to changes in subscriber sentiment, service preference and network utilization while maintaining a high quality of service.
SDN and NFV into the SGi-LAN
Integrating SDN and NFV into the SGi-LAN for dynamic service chaining and virtual network function orchestration.
— Kevin Shatzkamer, CTO, Mobile Networking, Brocade, special to The New IP