In his written statement to the Senate Committee on Commerce, Science and Transportation on Tuesday of this week, FCC Chairman Kevin Martin referred to a particular method of traffic management as a “blunt means to reduce peer-to-peer traffic by blocking certain traffic completely.”
The blunt means was referring to how some Deep Packet Inspection (DPI) platforms manage traffic when placed out of line. If a device is out of line, then one of the ways to control traffic is to directly or indirectly signal the sender to slow down or terminate the communication session. Terminating a session is the low hanging fruit because:
1) It’s easy to send a TCP reset message to the sender;
2) How harmful can it be to reset a peer to peer connection, most peer to peer file sharing clients have hundreds of sessions open!
For DPI, out of line versus in line has been an ongoing debate. Overall, out of line DPI is easier to deploy in a network, and easier to engineer as a product. Because out of line placements “tap” into the optical links or receive a mirrored copy of the packet from another network device, there is less risk in inserting into the network. The DPI processing is not in the critical service delivery path of subscriber traffic. If the DPI element fails, it is not service-effecting. “Hey the out of line DPI element crashed! No worries! The subscriber’s real packets are somewhere else!” By being out of line, there are significantly less performance constraints to engineer into the product because the packet seen by the DPI is only a copy. “One half second of latency? No worries! Dropped packets? No worries!”
Out of line is not the only traffic management option, as FCC Chairman Martin, in his written statement, alludes “… more modern equipment can be finely tuned to slow traffic to certain speeds based on various levels of congestion.” This type of finely tuned traffic management requires DPI to be placed in line. In line DPI can gently slow aggressive peer to peer applications during periods of congestion, while simultaneously ensuring that every active subscriber has an equal share of the bandwidth. In line DPI can promote fairness, while still providing the freedom of subscribers to access content and services of their choice.
Traffic management made possible by in line DPI should resonate with the Chairman. Why? In 2005 the FCC established four principles to promote the open and interconnected nature of the public Internet:
• Consumers are entitled to access the lawful Internet content of their choice;
• Consumers are entitled to run applications and use services of their choice, subject to the needs of law enforcement;
• Consumers are entitled to connect their choice of legal devices that do not harm the network;
• Consumers are entitled to competition among network providers, application and service providers, and content providers.
The Commission also noted that these principles were subject to reasonable network management, so it seems to support in line traffic management, under periods of congestion, which ensures fair access to available bandwidth, content, and services without blocking or denying service.
But, deploying DPI in line is a whole different ball game. Every “live” packet of every subscriber is directly processed by the DPI platform. In line placement has to be certified for being in the service delivery path of subscribers; it has to have failover and redundancy so there is no service loss in case of failure, and it has to have low latency and no dropped packets in order to preserve the service quality of real time applications like voice and video. However, engineering this type of traffic management, say at 10G Full Duplex bandwidth rates, with low latency, no packet loss, and full failover capability is both costly and difficult. But more importantly, it takes a certain mindset and discipline for in line DPI, as evidenced by the European Advanced Networking Test Center AG (EANTC) P2P test report.
The benefits of DPI for traffic management, while well known to service providers, are not well understood by consumers, and the entire debate about Network Neutrality has been misshaped by the lack of transparency. I’ll talk about transparency in a future blog.