Dale’s Web Log

If this keeps up, the copper industry is going to crumble.

Researchers at the University of Tokyo have demonstrated a prototype that could offer a new way to power gadgets. The prototype, which consists of plastic and flexible electronics, can wirelessly supply power to any device that touches its surface.

The power sheet, says Takao Someya, professor of engineering at the University of Tokyo, relies on the well-known physical principle of electromagnetic induction, used to charge electric toothbrushes and some RFID tags. However, he says, his system is designed in a way that overcomes the limitations of common induction schemes. Traditional induction systems can only spread small amounts of power over a relatively large area, and fairly large amounts of power can only be supplied to precise locations (such as a toothbrush mount). Someya’s power sheets, in contrast, can be large, and they can still supply a large amount of power to gadgets placed near them.

Plastic Sheet of Power

WiMAX (802.16) Service Specific Convergence Sub-layer (CS)

The Service Specific Convergence Sub-layer is at the top of the 802.16 protocol stack. It is responsible for performing the following functions:

• Accepting higher layer PDU’s from the higher layer service
• Classifying and processing the higher layer PDU’s
• Delivering the PDU’s received from the higher layer to the appropriate MAC SAP
• Receiving CS PDU’s from the peer and delivering them to the higher layer

At the present time, there are only two convergence sub-layer definitions for 802.16; the ATM CS and the Packet CS. Thus, only these types of traffic can be transported over the 802.16 network. The standard does leave open the possibility of specifying additional CS’s in the future.

WiMAX (802.16) Packet Convergence Sub-layer (CS)

The first Convergence Sub-layer (CS) I will discuss is the Packet CS. While the packet CS is generic in that it supports any number of packet protocols including IP, PPP, and Ethernet, the most common implementation will likely be for IP networks. In addition to the generic functions above, the packet CS also has the “optional” responsibility for suppressing and rebuilding the packet header information to save bandwidth over the wireless link.

So, how exactly is a protocol data unit (PDU) mapped into the wireless network? Well, essentially the entire packet contents are wrapped into a MAC “Service Delivery Unit” (SDU) – i.e. the packet is encapsulated with the MAC SDU header information (see figure below). Essentially, this is an additional field added to the packet identifying the Packet Header Suppression Identifier (PHSI) if used.

Once the packet has been encapsulated into an SDU, the SDU must be classified and associated with a connection identifier (CID) for transmission to the appropriate peer node. Each CID is known as a “service flow”. The process of classification involves matching each packet against a set of protocol specific matching criteria (e.g. ip address, priority, QoS, etc.) to determine the appropriate CID, or service flow, for that packet. If a packet fails to match any of the classifiers defined for the system, that packet is discarded.

Payload Header Suppression

As we all know, there is a lot of repetitive data in the packet headers on an IP network (Source destination addresses, port numbers, version numbers, etc.). There have even been a fair number of efforts to implement compression schemes based on that repetitiveness (Van Jacobsen compression being the most popular). The folks on the 802.16 committee decided it would be a good idea to build a header compression/suppression scheme into the specification. This way, they would ensure that all WiMAX devices that supported Header Suppression would be interoperable.

The 802.16 Header Suppression technique works by having the MAC SDU of the sending node suppress the header information while the receiving node restores it. Simple enough right? Well not so fast, the sending and receiving nodes need to have a method of sharing connection information such that the suppressed header information is known/recoverable by both nodes. That’s where the Payload header Suppression Index (PHSI) and the Payload Header Suppression Field (PHSF) come into play.

As I described above, the transmitting node uses a classification process to assign packets into specific service flows. For systems that support Payload Header Suppression (PHS), the classifiers will include a PHS rule. On the receiving side, the node uses the CID and PHSI to restore the suppressed header.

Included within the PHS function are two options known as Payload Header Suppression Valid (PHSV) and Payload Header Suppression Mask (PHSM). When the PHSV option is enabled, the transmitting node must verify the payload header before suppressing it. With PHSM, the nodes negotiate which header bytes to suppress and which to transmit. For example, the static header fields (IP address, version, etc.) can easily be suppressed, while the more dynamic fields (ACK number, length, etc.) can continue to be transmitted.

Payload Header Suppression Protocol

• A packet to be transmitted over the 802.16 network is received on the wired interface of the transmitting node and forwarded to the Convergence Sublayer (CS).
• The CS classifies the packet and provides as an output an uplink service flow, a CID, and a PHS rule. The PHS rule identifies the PHSF, PHSI, PHSM, PHSS, and PHSV to be used for this packet.
• If the PHSV value is set, or is not provided as a classification output, the subscriber terminal will compare the bytes in the packet header with the bytes in the PHSF that are slated to be suppressed. If they match, the subscriber will suppress the bytes in the PHSF with the exception of those bytes masked by the PHSM. If they do not match, the transmitting node sets the PHSI to 0 and the header is not suppressed.
• The transmitting node appends the PHSI to the packet and transmits it to the receiving node.
• At the receiving node, the packet received over the air interface is forwarded to the service flow associated with the received CID.
• The convergence sublayer on the receiving node uses the CID and the PHSI to recover the PHSF, PHSM, and PHSS.
• The packet is then reconstructed with the original packet header fields and forwarded normally.
• If PHSV was enabled on the transmitter, then the PHSF bytes recovered by the receiver are guaranteed to match what was transmitted.
• If PHSV was not enabled on the transmitter, then there is no guarantee that the PHSF bytes recovered by the receiver will match what was transmitted.

The figure below is an excerpt from the 802.16 specification and depicts the decision logic involved in PHS.



I hope this is useful. I know it’s helping me learn the protocol. Next I will start into the specific packet CS’s covered by the specification (Ethernet, PPP, and IP).

It seems as if they finally came to their senses. Quad (4-channel) Small Form-factor Pluggable (QSFP) optical module specification was released today. It seems as if feedback from the public review resulted in increased speed capabilities from 5Gbps to 10Gbps. With four channels each running at 10Gbps, it provides a practical approach to achieving 40Gbps links. However, I for one am not overly impressed with speed claims that simply tout multiple lower level rates in parallel.

That aside, I do see a benefit to this specification - primarily for I/O density on boards. By increasing the density, costs should decrease in the long run. Here is an artists rendition of a QSFP transceiver.

The complete specification can be downloaded here:

http://www.qsfpmsa.org/downloads/QSFP_Specification_Revision_1_0.pdf

This is an overview presentation that has some nice pictures and stuff:

http://www.qsfpmsa.org/downloads/QSFP_MSA-December_2006_R3.pdf