Technology Update /
CoS offers prioritization on private nets
By Janel Crabtree
As corporations migrate to IP-based products and services, IP-enabled frame relay and ATM provide an easy migration path to Internet-based VPNs. These solutions provide users with the benefits of IP while using the same equipment and connections they already have in place, maximizing their existing infrastructure investment and reducing their total cost of ownership.
For IP-enabled frame or ATM networks, IP traffic runs over existing infrastructure, combining the security and quality of service (QoS) of frame relay and ATM with the flexibility of IP. Other benefits of private IP-enabled networks include inherent security, significant cost savings, capital expenditure reduction, assurance of business continuity, ease of implementation and access to enhanced services.
IP-enabled frame relay or ATM with class of service (CoS) capabilities - which let a company prioritize its data based on a set of criteria - is ideal for corporations that run high-performance, high-availability applications such as video and multimedia.
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CoS enables more predictable traffic delivery of priority data by assigning different delivery status for each application.
A "first class" priority label is assigned to data applications - such as mission-critical data transactions, or video or voice transmissions - which require faster turnaround, while a lower-priority label is assigned to less time-sensitive traffic, such as e-mail and Web surfing.
Traffic is delivered around the world based on a company's designated priority, and is usually backed by stringent service-level guarantees from the service provider.
CoS differs from QoS in that QoS refers to a level of service in terms of bandwidth or delivery time, such as bandwidth prioritization or traffic shaping, while CoS refers to traffic delivery priorities. IP-enabled frame relay and ATM let users take advantage of the benefits of QoS and CoS technologies.
With CoS, priorities can be assigned and transported across a network from end to end. The network reach is unique to private networks, because one provider owns the network end to end and can therefore dictate priorities across it. With a public IP network, CoS designations can be stated at the network edge, but will be limited, and do not extend across a public network infrastructure that is unprepared to accept the priorities, because data can travel across several networks.
Here's how CoS works: Based on application requirements, traffic is prioritized at the connection endpoint by setting the Differentiated Services (Diff-Serv) code in the header of an IP data packet. Letting users manage network traffic, Diff-Serv is the protocol used to prioritize data traffic.
Then IP packets are sent as frame relay or ATM cells, in accordance with the type of network a customer has. Next, these packets are transported to an ingress switch, where the frame or ATM cells are "decapsulated" and incoming IP packets are processed. There, the ingress switch measures the incoming traffic rate against the customer's traffic requirements and, based on the priorities that were assigned to the various traffic types, reassembles the packets in the proper sequence.
Insulated into Multi-protocol Label Switching packets and transported over a network running MPLS at the core, where each switch within the core prioritizes traffic and is sent to the egress switch. At the egress switch, MPLS packets are "decapsulated" into IP packets. On the egress customer interface, IP packets are placed in the correct order and encapsulated as frame or ATM cells and transmitted over a circuit to the customer premises equipment. This equipment reconverts the packets to IP and sends them according to their assigned priority.
CoS is a technology that enables network and business efficiency for any company needing to prioritize data, voice or video on its network for more reliable and greater assurance of higher-quality traffic delivery.
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Crabtree is director of global VPN services at WorldCom. She can be reached at janel.crabtree@wcom.com.
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