Clark Woodworth

A wireless broadband ad-hoc ATM local-area network

We describe the theory, design and ongoing prototyping of a wireless ATM LAN/PBX capable of supporting mobile users with multi-Mb/s access rates and multi-Gb/s aggregate capacities. Our proposed LAN Consists of network nodes called Portable Base Stations (PBS) providing microcell coverage. The PBSs are designed to be low-cost, compact and high-speed and can be relocated conveniently. We employ a concept ofad-hoc networking in the layout of the PBS-to-PBS interconnection. That is, the PBSs can be distributed in an arbitrary topology to form a backbone network and can be reconfigured with relative ease. The PBS-to-PBS backbone links are high-speed (Gb/s) for supporting high system capacity. Although they can either be wired or wireless, our emphasis is on wireless implementations. The user-to-PBS links, on the other hand, are primarily for mobile access (e.g., 2–20 Mb/s) and therefore are wireless. Wired connections from stationary users to PBSs are also possible. Typical mobile users are assumed to be laptops or notebook computers. Services supported include conventional data applications (e.g., over TCP/IP or SPX/IPX) as well as multimedia (video, voice and data) applications with QoS (Quality-of-Service) guarantees. A “wireless ATM” concept is proposed so as to provide seamless internetworking with other wired ATM local and wide-area net-works. Algorithms and control in our network are highly distributed for simple implementations and ease of mobility management. A new wireless VP/VC concept and a Homing Algorithm are described to provide ATM cell routing and connections in the network. PBS hardware and software architectures are discussed. Call management, network management and signaling are designed for simplicity, high performance and modular implementations. A fast network restoration scheme is proposed to cope with the potential link or node failures in the ad-hoc network. Error control is addressed taking the unreliable wireless links into consideration. Finally, a prototyping project called BAHAMA (Broadband Ad Hoc ATM Anywhere) for demonstrating this network concept is briefly outlined.

Real-time processing for virtual circuits in ATM switching

We propose adding real-time hardware primitives to packet switches, ATM in particular, to provide efficient support for inward multicasting similar to some of todays switches that support real-time multicast in the switch hardware. To implement this, we propose extending the lookup table used for routing by adding additional opcode and operand fields (or pointers to those fields) into the routing table and by including ALU circuitry to process these fields and corresponding fields in the arriving cells. With the rapid capacity growth of todays RAM and the modest gate count required for ALUs, memory word widths can be extended with minimal additional chip count and the ALU can be a small addition in a header processing VLSI, thereby giving only a modest increase in complexity. The benefit of including real-time processing in the switch is that it is now possible to solve the ACK implosion problem associated with high-speed reliable multicasting transport protocols. By keeping the primitives as general as possible, other applications can benefit from these real-time primitives.

Congestion control in ATM networks

A multifaceted congestion control technique is proposed for asynchronous transfer mode (ATM) broadband integrated services digital networks (B-ISDN). This technique is consistent with the framework outlined in the US contribution to the CCITT standards organization and is based on separating traffic into classes. For continuous-rate services, controls based on bandwidth allocation are specified. The authors also present input policing techniques as a means of preventing a malevolent user from adversely affecting the other users. Previous hardware experience is discussed, and some of the questions that need to be addressed by simulation or hardware experience are considered.<<ETX>>

Multiplexing and DQPSK Precoding of 10.7-Gb/s Client Signals to 107 Gb/s Using an FPGA

We implemented a real-time DQPSK precoder for 107-Gb/s data, together with a highspeed channel alignment scheme and the required rate adaptation from 10.7 Gb/s to 13.375 Gb/s, on a Xilinx Virtex II Pro X FPGA.

Spectrally efficient universal time slots using time-frequency-code slicing

We propose a time-frequency-code-slicing technique that allows multiple users with different speed requirements access to a communications resource in a manner that is cost effective over a wide range of access speeds. Conventional systems require low-speed users to either pay a cost premium (e.g., high-speed burst modems for TDMA) or end up wasting some of the spectrum (e.g., universal time slots). The advantages of our proposed scheme can be demonstrated with any two combinations (or all three) of time slicing, frequency slicing, and code slicing. For instance, with a time-frequency-slicing approach, users can be assigned different portions of the spectrum (e.g., on a slot-by-slot basis), allowing them access to only the needed fraction of the shared resource. With time-code slicing, users are dynamically granted portions of the code space, during specified time periods. Finally, in frequency-code slicing, a user may be assigned a number of codes in different frequency bands. These codes can be of constant or variable chip rates.

Connection request protocol (CRP) for IP over ATM

All current protocol models for transporting IP packets over ATM require two operations across the UNI (user network interface): address resolution and connection setup. We propose combining the address resolution and setup operations into a single operation across the UNI interface thereby simplifying the end-host signaling software and improving performance. The protocol defined to support this combined scheme is called CRP (connection request protocol). The three IP over ATM models:, classical IP over ATM, LAN emulation; and routing over large clouds, are supported in the CRP scheme.