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Introduction to Software Defined
Networking (SDN)

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Overview
• Evolution of routers
• The Clean Slate project
• OpenFlow
• Emergence and evolution of SDN
• SDN architecture today
• Use cases
• Standards development

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Routers
• Two key roles:
Packet forwarding
Determining Network Paths

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Planes
Control plane
• Developed by
various SDOs
• Needs to be
interoperable
• Strives to maintain
backwards
compatibility
• Sometimes takes
years to achieve
stability
Data plane
• Hardware-
dependent and
closed
• Used by vendors
to provide
differentiation
• Can be fairly
complicated,
incorporating a
number of inline
functions e.g.
ACLs, QoS, NAT
Management
plane
• Uses a
combination of
standard (e.g.
SNMP) and non-
standard tools
such as CLI
• Generally requires
low-level operator
input
Forwarding
Device
Data Plane
Element/Network
Management System
Control Plane
Mgmt
Plane
Management Plane
Determines how
packets should be
switched/forwarded
Responsible for
actual forwarding of
packets
FCAPS (Fault,
Configuration,
Accounting,
Performance &
Security)

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Clean Slate Project (1)
With what we know today, if we
were to start again with a clean
slate, how would we design a
global communications
infrastructure
Mission: Re-invent the Internet
Two research questions:
How should the Internet look in 15
years?

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Clean Slate Project (2)
• One of the flagship projects was ‘Internet Infrastructure:
OpenFlow and Software Defined Networking’
• Seminal paper on OpenFlow…
...kicked off the SDN movement and the data
communications world would never be the same again

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OpenFlow: The Solution (1)
FROM TO
Routing/Bridging
Protocols, RIBs,
routing policy and
logic
Forwarding Tables
Secure Channel
Abstracted Flow
Table
OpenFlow
Controller
OpenFlow
Protocol
Control
Plane
Data
Plane
Data
Plane
Control
Plane
Control
Plane
Data
Plane
Protocols and algorithms to calculate
forwarding paths
Forwarding frames/packets based on paths
calculated by control plane

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OpenFlow: How it works (1)
Secure Channel
Abstracted Flow
Table
OpenFlow
Controller
OpenFlow
Protocol
Control
Plane
* Ingress Port, Ethernet SA, Ethernet DA, VLAN ID, VLAN PCP, IP SA, IP DA, IP Proto, IP ToS, Source L4 Port, Dest L2 Port etc….
Adds, deletes and
modifies flow table
entries
Header Fields* Actions Counters
Flow 1 Forward to port
1/1
Flow 2 Drop
Flow n Send to controller
Switch forwards traffic by matching
against header fields and taking
corresponding actions

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Defining SDN ONF: The physical separation of the network
control plane from the forwarding plane, and
where a control plane controls several devices.
This definition is too narrow…
As much a marketing term as a technical one
Automation through enhanced
programmability and open
interfaces
Dis-aggregation and abstraction
Centralisation of network control
with real-time network visibility
SDN is …
A new approach
to networking that
provides greater
network agility
and flexibility by:

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SDN Standards Developing Organisations
(SDOs)
https://sdn.ieee.org/outreach/resources

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SDN architectural framework (1)
ITU-T
Y.3300
SDN
Controllers
SDN
Applications
Network
Resources

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SDN architectural framework (2)
Application Plane
Application Service
Network Services Abstraction Layer
Control Plane
Service App
Control Abstraction Layer (CAL)
Management Plane
App
Mgmt Abstraction Layer (MAL)
Service Interface
Device & Resource Abstraction Layer (DAL)
Forwarding Plane App Operational Plane
Network Device
CP Southbound Interface MP Southbound Interface
RFC
7426

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SDN architectural framework (3)
Application
Plane
Application Service
Topology
Discovery &
Management
Network Devices – IP/MPLS/Transport
Southbound Interfaces
REST/RESTCONF/NETCONF/XMPP
Control
Plane
(controller)
Traffic Engineering
Route selection &
failover
Resource
Management
BGP-LS PCE-P
i2RS
SNMP
MIBs OpenFlow YANG
Configuration
Open
Flow
SNMP Netconf
Data
Plane
(with some
distributed
control plane
elements)
BGP PCC
RIBs
Segment
Routing
RSVP-
TE
East/West-
bound
interfaces –
BGP
IPFIX
ForCES
Northbound Interfaces
Note: designations of north-bound and south-bound are relative to the control plane (“controller”)
Device & Resource
Abstraction Layer (DAL)
Network Services Abstraction Layer

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Comparing and contrasting with NFV
FROM TO
Tightly
coupled
Software
Purpose-built
hardware
COTS
hardware
Virtualised
Software
SDN: decouples elements of the control plane
from the data plane
NFV: decouples network software from closed,
proprietary hardware systems

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SDN Standards Developing Organisations
(SDOs)
https://sdn.ieee.org/outreach/resources

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ONF projects
https://opennetworking.org/

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SEBA - SDN Enabled Broadband Access
• Virtualised Access technologies at the edge of the carrier
network.
https://gonorthforge.com/seba-sdn-enabled-broadband-access-the-next-generation-of-broadband-access/

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Traditional FTTH Residential Access
RG - Residential Gateway
ONU - Optical Network Unit
OLT - Optical Line Termination
BNG - Broadband Network Gateway https://youtu.be/jBeRYVVM7u8?t=231
VOLTHA

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VOLTHA
• Virtual Optical Line Terminal
(OLT) Hardware Abstraction
• Provides a common, vendor
agnostic, GPON control and
management system, for a set of
white-box and vendor-specific
PON hardware devices.
https://opennetworking.org/voltha/

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VOLTHA
• Network as a Switch:
– It makes a set of connected access network devices to look like a SDN
programmable switch.
• Evolution to virtualisation:
– it can work with a variety of access network technologies and devices
• Unified OAM abstraction:
– it provides unified, vendor- and technology agnostic handling of device
management tasks, such as service lifecycle, device lifecycle (including
discovery, upgrade), system monitoring, alarms, troubleshooting, security, etc.
• Cloud/DevOps bridge to modernisation:
– it does all above while using a microservices architecture running on top of
Docker and/or Kubernetes.
https://docs.voltha.org/master/index.html

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Open Network Operating System (ONOS)
• Build carrier-grade solutions using white-box hardware.
• Create and deploy network services with simplified
programmatic interfaces.
https://opennetworking.org/onos/

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ONF projects
https://opennetworking.org/

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SD-RAN
• Mobile RAN networks historically used vendor proprietary
base stations.
• Operators would like to see interoperable RAN
components.
• Operators, through the O-RAN consortium, are advocating
for a disaggregation of RAN networks into interoperable
Radio Unit (RU), distributed unit (DU), centralised unit (CU)
components.
• RAN Intelligent Controller (RIC) is integral to the O-RAN
architecture.
https://opennetworking.org/open-ran/

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SD-RAN
https://opennetworking.org/open-ran/

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ONF projects
https://opennetworking.org/

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Programming Protocol-independent
Packet Processors (P4)
• Open source, programming language for network devices.
• Specifying how data plane devices process packets.
https://p4.org

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P4 Integrated Network Stack (PINS)
• Enables the use of SDN (and an external controller) to
dynamically add new advanced functions to a traditional
routed network.
https://opennetworking.org/pins/