What if Access Network is Redesigned as a Data Center?

Professors Mohamed Cheriet and Kim Khoa Nguyen, of the Synchromedia laboratory, organised a mini-conference, as part of IEEE’s 12th International Conference on Network and Service Management (CNSM), hosted from October 31 to November 4, 2016, at the École de technologie supérieure (ÉTS).

This article is an overview of CORD: Central Office Re-architected as a Datacenter, presented by Larry Peterson, Chief Architect at the Open Networking Laboratory, Director of the PlanetLab Consortium, and the Robert E. Kahn Emeritus, and a Professor of Computer Science at Princeton University. It was written by Rim ElFahem, a student researcher of the Synchromedia laboratory who attended the conference.

Introduction

Nowadays, with the exponential increase of video and streaming traffic, network operators are facing significant difficulties in meeting bandwidth requirements. In addition, providing new and improved services is a challenging task since adding a new feature takes too long.

To face these challenges, a collaborative work between AT&T and the Open Networking Lab focused on redesigning the access network particularly the central office (CO) as a datacenter to benefit from the agility and economics of scale that cloud computing, Software Defined Networking (SDN) and Network Function Virtualization (NFV) offer.

• SDN is a new architecture of network in which the control and data plane are separated. This can lead to an open and programmable control plane and a simplified network infrastructure with inexpensive switches.
• NFV virtualizes the data plane from hardware devices to virtual machines (VMs) running on commodity servers.
• Cloud is the use of storage, processing and networking capabilities. This will provide agility and elastic scaling enabling to add new services efficiently and rapidly.
• A central office is a building block containing telephone switches. Subscribers connect to it to provide them services such as switching their calls.

CORD architecture

The CORD high level architecture is composed of a minimal home router inside the subscriber’s home, which is connected to the CORD hardware composed of a set of commodity servers and switches. On top of this hardware architecture, we find the software architecture composed of ONOS, Openstack and XOS running services of the virtual version of Optical Line Terminal (OLT), Customer Premises Equipment (CPE) and Broadband Network Gateway (BNG) (figure 2).

a. CORD hardware

CORD hardware is composed of a set of commodity servers and leaf-spine switches (figure 2).

Leaf-spine switches are white-box switches that are particularly adjusted for an east-to-west traffic, representing the connection from the customers to the backbone of the operator passing by the CO.

b. CORD software

CORD software consists of three main components. XOS is a framework responsible of service management. ONOS hosts the control applications and Openstack is an Infrastructure as a Service that manages compute instances (figure 3).

c. How the traditional CO is transformed to CORD?

Re-architecting a traditional CO to CORD is performed in two main stages:

• Virtualize the existing hardware devices to a software running on a commodity hardware.
• Unify these virtualized components to produce a coherent system.

First step

CORD work focuses on virtualizing three particular components, the OLT, CPE, and BNG as shown in figure 4.

• The virtualization of CPE can be split into a simplified device at home and a virtual subscriber gateway (vSG) that runs on a set of subscriber-selected functions (e.g. NAT, DHCP, VoIP Firewall Parental Control, etc) and located at the CO.
• vOLT, the virtual version of the OLT, is responsible of the authentication of the subscriber, the connection of the subscriber to the CO by establishing VLANs.
• vRouter, the virtual version of the BNG is responsible for features such as the Quality of Service (QoS), Virtual Private Network (VPN), etc.

Second step

In this step, a framework is done unifying these virtualized commodity hardware and outputting a coherent system where these three virtualized components are considered as multi-tenant services. First, we have the Access-as-a-Service (ACCaaS), ensured by vOLT where each user corresponds to a Subscriber VLAN, the Subscriber-as-a-Service (SUBaaS) ensured by vCPE where each user corresponds to a Subscriber Bundle and the Internet-as-a-Service (INTaaS) where each user corresponds to a Routable Subnet (figure 5).

Conclusion

CORD is an innovative project that converts the traditional CO to data centers with commodity infrastructure canceling the high CAPEX and OPEX costs and enabling rapid creation of new services.

For more information

For more information, we invite you to read the following research paper:
Larry Peterson, Ali Al-Shabibi, Tom Anshutz, Scott Baker, Andy Bavier, Saurav Das, Jonathan Hart, Guru Palukar, and William Snow. Central Office Re-Architected as a Data Center. IEEE Communications Magazine, October 2016.