v introduction
Computers and their attachments (like networks and disks) are getting faster everyday. The current CPU speeds of processor like DEC Alpha and Pentium are well over 100MHz allowing them to perform billion instructions per second (BIPS). This speed is comparable to supercomputer's speed five years ago. With the growing speed of computers the applications which run on them are now ranging from interactive graphics, voice recognition, video conferencing, real time animations etc. All these new applications will use networks to carry more data.
Network bandwidth is also increasing concurrently with the CPU speeds.
When in 1980s 10Mbs Ethernet was considered fast, we now have 100 Mbs Ethernet. The bandwidth is approaching the speed on 1 billion bits per second
(1 Gbs), much due to the research in the field of fiber optic signalling.
The three main fields data communications, telecommunication and computing are undergoing a period of transition. The field of computing is rapidly advancing with processor speed doubling ever year. The latest RAID (Redundant Arrays of Inexpensive Disks) has given rise to file-systems with gigabit-bandwidth.
The field of data communications which facilitates the exchange of data between computing systems has to keep up with the pace of the growing computing technologies. In the past the data communications provided services like the e-mail. Now applications like virtual reality, video conferencing, video on demand services are present.
For a century the telecommunication industry has been carrying voice traffic. This scenario is changing with telephone networks carrying more data each year. The data being carried by telephone network is growing at 20% per year compared to voice traffic which is growing only at 3% per year. Soon the data traffic will overtake the voice traffic. All this, has made the telecommunication industry more interested in carrying data in their networks.
So the three communities are now converging with common interests of carrying more data at higher speeds. This has led to some joint activities. The most notable of these activities is that which has led to the setting up of gigabit testbeds in
When the gigabit networking was in its horizon, many researchers felt that the current knowledge about networking would not apply to gigabit networks which are considerably faster than existing networks. Now, after several years of research it has been found that many of the strategies and techniques (like layering the protocol) still work in gigabit networks also.
There are many working Gigabit testbeds .In five to ten years Gigabit networks will become a reality. It is now unclear whether there will be a single gigabit technology with a specific standard protocol. But it looks like that there will be many competing gigabit networking technologies (like many LAN technology) and many protocols but eventually one of them will become most popular (like IP).
The next section deals with the key concepts and technologies in the Gigabit networking. The third section deals with more specific issues in gigabit networking. The fourth sections discusses the various potential gigabit applications. The last section overviews the current state of gigabit networking. The appendix A gives a list of gigabit testbeds. The appendix B is an annotated bibiliography of the http sites, articles, papers and books refered in this paper.
| | |||
| Application | Data Types/Size | Network Traffic Implication | Network Need |
| Scientific Modeling,
| Data files; 100’s of Megabytes to Gigabytes | Large files increase bandwidth required | Higher bandwidth for desktops, servers, and backbone |
| Publications,
| Data files; 100’s of Megabytes to Gigabytes | Large files increase bandwidth required | Higher bandwidth for desktops, servers, and backbone |
| Internet/Intranet | Data files now; Audio now; Video will emerge; High Transaction Rate; Large Files, 1 MB to 100 MB | Large files increase bandwidth required; Low transmission latency; Class of service reservation; High volume of data streams | Higher bandwidth for servers and backbone; Low latency |
| Data Warehouse | Data files; Gigabytes to terabytes | Large files increase bandwidth required; Search and access require low latency | Higher bandwidth for servers and backbone; Low latency |
| Network Backup | Data files; Gigabytes to terabytes | Large number of large files; Transmitted during fixed time period | Higher bandwidth for servers and backbone; Low latency |
| Desktop
| Constant Data Stream; 1.5 to 3.5 Mbps at the desktop | Class of service reservation; High volume of data streams | Higher bandwidth for servers and backbone; Low latency; Predictable Latency |
v Basic Concepts of Gigabit Networking
What is the speed for true gigabit networks? From the ATM (Asynchronous Transfer Mode) world, it could be 622,000,000 bps (OC-12), 1,244,000,000 bps (OC-24), or/and 2,488,000,000 bps (OC-48). With 100 MBps Fiber Channel, it would be 800,000,000 bps. In Ethernet, it is 1,000,000,000 bps. It also could be 1,073,741,800 bps (which is equal to 2 30 bps, where 2 10 equals 1,024 or 1 k). Standardized by IEEE 802.3z, a true gigabit network will provide connections between two nodes at a rate of at least 1,000 Mbps. By comparison, it is approximately ten times that of both FDDI and Fast Ethernet.
The networks with at least 1 Gbps are feasible today basically due to the technology advancement in fiber optics, and cell networking (cell switching, or cell relay).
Ø Fiber Optics
Light has the properties of reflection and refraction. When light passes from one medium to another, some part of it gets reflected and the rest get refracted (Figure1). Fiber optics use the properties of light refraction to send signals over long distances across a thin strand glass (core), which is surrounded by a thier outer layer (cladding). The structure of a fiber is shown in Figure 2 In fiber optics, bits are sent by transmitting pulses of light through the core of fiber.
Figure 1:- fiber optics
Figure 2: Fiber structure [Partridge's Gigabit Networking].
Since the transmission speed of fiber is 0.69 the speed of light in vacuum, or about 2.1x108 m/s, it is not significantly different from the transmission speed of copper. This means a transmission through fiber is not faster than that through copper. The difference between fiber and copper then is information density (bandwidth). Fiber has more bandwidth because it can carry more bits per unit of cable than copper. According to Partridge , fiber has a bandwidth of 25 terahertz (THz) using a spectrum band of 200 nanometer centered on the wavelengths of 0.85, 1.3, and 1.5 microns. With standard equipment signaling capable of transmitting between 1 and 1.4 bits per Hz, a single fiber has a bandwidth between 50 and 75 terabits per second [Partridge's Gigabit Networking].
There are two types of fiber: single-mode fiber and multimode fiber. Single-mode fiber is superior in its transmission quality and properties, while multimode fiber is more error tolerant in fitting to transmitter or receiver. For further information on fiber optics, please refer to [Partridge's Gigabit Networking].
Ø Cell Networking
Another important concept of gigabit networking is cell networking. The basic idea of cell networking is to transmit all data in small, fixed-size packets (cells). Figure 2.3 shows the concept of cell and packets. By choosing small, fixed-size cells, it is possible to reduce waste and to minimize delays. When one sends data with any size cells, on average, half of the last cell will be unused.
Secondly, if packets vary in size, the delay will also vary. As a result, it is very difficult to guarantee delays required for interactive voice and video traffics. Other advantages of cells are as follows:
1) Reducing the number of transmission networks
2) Providing easier support for multicasting
3) Offering a better multiplexing scheme than ISDN (Integrated Services Digital Network ) for high speed.
For more explanation, please refer to [Partridge's Gigabit Networking].
Therefore, the basic concepts of cell networking introduce faster transmission and lower delays, which both are requirements for gigabit-speed networks.
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Ø Routing and Switching Issues in Developing Gigabit Networking
Today's data communications and networks would not exist without routers. Routers are essential to links LANs and remote sites. Since routing is considered to be one of the major bottlenecks in networks, within the past few years, routers have become less central of building network and being replaced by switches. The current trend is "switch when you can, route when you must " or " switch many, route once". In the LAN environment, multiport bridges (segment switches) are used instead of routers to link LANs. In WANs, frame switches have replaced the need of routers
Switching and routing issues are very crucial in designing gigabit networking. Increasing bandwidth in the magnitude of gigabit will not be very useful if the gain of bandwidth is only offset by the slowness of routers. On the other hand, routing is required more than ever, especially with the current and future network traffic moving away from the traditional 80/20 rules to the new 20/80 rule.
In this section, the basic routing functions, and the significance and shortcomings of routers are discussed. Several approaches to improve the performance of routing and routers are also observed.
v Technologies Supporting Gigabit Networking
Some technologies and products have been introduced recently to support the development of gigabit networking. In this paper , Routing Switch, IBM's HPR, Gigabit Routers , Multigigabit Routers , and I/O Switching are presented. These technologies described here might become obsolete pretty soon in favor of new upcoming techniques and technologies. (As a side note, there might be other new technologies introduced as this paper was written.)
Ø Switching Technology
Switching has become the key element in most networks in segmenting traffic, reducing latency, and improving performance. It is simple, cost-effective to implement, and requires only a minimum amount of hardware implementation. Switching allows specific computers, workgroups, or servers to have their own dedicated access to the full bandwidth available on the network. As a result, switching provides more bandwidth for users than a shared network . One switching technology to produce quicker network throughput is crossbar switching . It uses a non-blockingswitching matrix to allow multiple simultaneous connections with very low latency and fast throughput. This technology has been implemented today in the design of high-speed routers like the NetStar GigaRouter and Multigigabit Router.
Ø IBM's HPR (High Performance Routing)
IBM's High Performance Routing (HPR) is the advanced System Network Architecture (SNA) technology, based on the latest standards from the ATM Forum and the APPN (Advanced Peer-to-Peer Network) Implementers' Workshop. The key features of HPR are high performance, dynamic rerouting, priority and class of service, congestion avoidance, scalability, and economy.
Ø Gigabit Routers
Gigabit Routers , such as Multigigabit Router , are on their way to the market. Some companies have recently introduced their gigabit routers, such as Cisco ( Cisco 12000 series), NetStar (GigaRouter), and FORE. Basically, all the designs of high-speed routing adopt the same functional component as shown in Figure 5 [ Newman et al's Paper ]. The functions of each component in a general high-speed router are shown in Table 2.
| Table 2: The functions of each component of a general high-speed router. | |
| Component | Functions |
| Line Card | Contains physical layer components to interface the external data link to the switch fabric |
| Switch Fabric | Interconnects the various components of the gigabit router; Offers higher aggregate capacity than that of the more conventional backplane bus |
| Forwarding Engine | Inspects packet headers; Determines outgoing line card of a packet; Rewrites the header |
| Network Processor | Runs the routing protocol; Computes the routing tables that are copied into each of the forwarding engines; Handles network management; Processes special handling for unusual packets |
There are two types of approaches used in designing a fabric switch: crossbar switchand ATM switch. The NetStar GigaRouter uses a 16 port crossbar switch with each port operating at 1 Gbps. Cisco 12000 series use multigigabit crossbar switch fabric.Multigigabit Routers will use a crossbar switch with 15 port each operating at 3.3 Gbps. On the other hand, IP/ATM, Cell Switch Router, and IP switching use ATM switch.
The forwarding engine may be designed physically as a separate component or an integrated component with either the line card or the network processor. The packet-forwarding rate of a separate forwarding engine can be changed independently from the aggregate capacity based on the ratio of forwarding engines to line cards. However, this approach creates additional overhead across the switch fabric.
Multigigabit Router implements separate forwarding engines in its architecture. The NetStar GigaRouter integrates its forwarding engine with each line card. The architecture of IP Switch allows integration of its forwarding engine with the network processor,although it is not prohibited to have combination with the line card or a separate implementation.
Since the average packet size now is about 2000 bits, the packet-forwarding rate required is about 500 kilo packets per second (kpps) for each 1 Gbps traffic. To achieve this magnitude of rate, two approaches have been proposed: the silicon forwarding engine and a high-speed general-purpose processor with destination address on an internal (on-chip) cache.The features of both approaches are shown in Table 3.
Table 3: Silicon approach vs. General-purpose processor with caching approach | ||
| | Silicon Design | Processor with Caching Design |
| Design | Silicon hardware | A 415 MHz general purpose processor with internal cache |
| Memory | 4 MB | Additional 8 MB (for a complete routing table of several hundred thousand routes) |
| Forwarding Capability | 5 Mpps on average 10 Gbps of traffic | 11 Mpps if all the requested destinations in the cache |
| Advantage | Maintains its maximum forwarding rate regardless past history of destination addresses | Maintains its full forwarding rate if at least 60% chance the required destination address has been seen in the past and is still in the cache |
| Disadvantage | Fixed Solution | Flexible to the traffic profile and traffic change |
Further, there is an ongoing discussion about the best way to include additional functions, such as multicasting , Quality of Service , firewall filtering, and complex policy-based routing in Gigabit Routers. To offer such functionality, more fields in the packet header, besides the destination address, should be used.
Ø Routing Switch
Routing Switch is designed to improve the performance of routers to achieve the identical performance of switching. The concept is to apply switching techniques to those protocols that require optimized routing performance and fully integrate high performance routing into switch fabric.
v Current Gigabit Technologies Available for High-speed LAN
There are four technologies competing eachother in production or development today to provide gigabit networks. They are ATM, Fiber Channel, Gigabit Ethernet, and Serial HIPPI.
Ø Asynchronous Transfer Mode (ATM)
Originally , the goal of ATM design was to simplify and standardize international telecommunications. Today, it has become standard for WANs.ATM provides a high-speed transmission for all types of communications, from voice to video to data , over one network with small , fixed-size cells. It also provides unparalleled scalability and Quality of Service.Currently,ATM technology is used in network backbones or specific workgroup applications with heavy traffic load with the mix traffics of voice , video, and data into a single network. To achieve gigabit speeds, ATM is being developed to operate on 622 Mbps (OC-12) and 1.244 Gbps (OC-24).
The future of ATM is still unknown. It depends heavily on its ability to integrate with existing LAN and WAN network technologies. Most observers feel ATM technology will not become a major force in future networks since the other networking technologies can easily achieve the advantages of ATM. Other obser-vers believe that ATM seems to meet the future needs of WAN and a few highly specialized LAN environments.
Ø Fiber Channel
The standards and architectures of Fiber Channel are still under development although some vendors have settled on a standard known as Arbitrated Loop,which is basically a ring topology. It is very sensitive to adding new users, which can cause increased congestion and reduced bandwidth to each user. At present, Fiber Channel is used to attach storage devices to computers.
Arbitrated Loop Fiber Channel runs at a gigabit per second and supports the SCSI protocol. This design seems to be a good choice for peripheral-attachment operations. However, many experts agree that Fiber Channel is not a good choice to replace IP technology and to provide future gigabit networks.
Ø Gigabit Ethernet
Many network experts agree that Gigabit Ethernet will become the gigabit technology for the LAN environments. It is a good choice for providing a higher capacity enterprise backbone throughout an organization and high-performance workstations with a cost-effective gigabit networking connection. Nevertheless, Gigabit Ethernet is not a good solution for moving applications with huge data rapi-dly due to the issues of the Ethernet-based CSMA/CD support, host-bust connection issues, and relatively small packet size.
Ø Serial HIPPI (High Performance Parallel Interface)
Serial HIPPI is the fiber-optic version of the HIPPI, which was originally developed in the late 1980s to serve the connectivity and high-bandwidth needs of super computers and high-end workstations. It provides a simple, fast point-to-point unidirectional connection. Recently, this technology shows its establishment as the gigabit technology for big data applications, clustering and a broad of server-connectivity environments, providing a speed of 1.2 Gbps over distances up to 10 kilometers. Serial HIPPI implements non-blocking switching technology and packet sizing up to 64 KB in size. It also provides reliable ANSI and ISO-standardized Gbps connectivity with the packet loss rate approaching zero percent.
Serial HIPPI operates within the physical- and data-link layers in the ISO seven-layer model. At higher layers, Serial HIPPI supports IPI-3 for storage connection and TCP/IP for networking which makes it compatible with Ethernet, Token Ring, FDDI, and the wide-area protocols used on the Internet. It also supports ARP (Address Resolution Protocol) to automatically specify how to find IP addresses on its network. At physical layer, Serial HIPPI provides flow control to eliminate errors and data loss due to congestion, guaranteed end-to-end, in-order packet delivery, and error reporting. Other protocols have to rely on TCP/IP for data lost detection, which is not efficient.
At present, Serial HIPPI seems to be the only available technology that offers gigabit performance with 100% reliability. However, this does not eliminate the possibility of other technologies,such as ATM and Gigabit Ethernet to be asignificant factor in the implementation of gigabit networking.
v Challenges in Gigabit Networks
The major challenges in networking research are to take advantage of the newly developed techniques for building high-speed networks, and find ways to evolve it to meet new applications needs, to keep pace with other computing tech-
nologies, and to encourage the transistions of gigabit technologies into the wider community. To achieve these goals the Gigabit Netowrking Workshop identified important problems in the following areas :
[1]. Performance evaluation
Higher speeds and new traffic mixes are causing a much needed re-
examination of models and algorithms for networking performance.
[2]. Switching technology
Achieving higher speeds and new types of traffic are forcing the networking community to develop innovative techniques for minimizing the cost of per packet processing in switches and routers. A continuing challenge is finding a way for these techniques to scale to switch designs with more connections per switch and higher bandwidths per connection.
[3]. Network management and control
A combination of new types of traffic, larger bandwidths, and the long relative delays in gigabit networks have made the problems congestion control and finding routes for data transfers substantially more difficult. Research is needed on how to best balance congestion control between the network and end-systems and on methods to quickly find valid routes for new data transfers
[4]. Internetworking
Gigabit networking technologies will have to interoperate both with each other and with existing networking technologies. As a result, internetworking will be at least as important in the future as it is now. While the basic ideas of IP architecture apply to gigabit networks it is also true that our internetworking technology needs to evolve to take advantage of the new capabilities of gigabit networks.
[5]. Interfacing computers and application to networks
While it is now feasible to deliver data at gigabit rates to a computer's interface, we continue to have great difficulty getting the data through the interface and computer's operating system to the application quickly and at gigabit rates.Considerable work, probably in conjunction with the operating system community, is needed if applications are to use gigabit networks to their full potential.
[6]. Gigabit interfaces for PCs
Gigabit networking is no longer the domain of supercomputers and high-end workstations. PCs will soon need gigabit capabilities too and we need to encourage the development of interfaces with low costs and low heat and power consumption.
[7]. End-to-end protocols
Better ways to develop end-to-end protocols that meet the needs of applications are needed. Ideas like the ability for applications to synthesize new protocols from functional components need to be explored.
[8]. Shared media access technologies
The traditional thinking is that the high bandwidths and relatively long delays in gigabit networks limit our choices of local media access techniques but emering research suggests that there may be a wide diversity of media access tecniques that work for gigabit networks and these options should be explored.
[9].Parallel channels and striping
It is often more cost effective to send data in parallel over multiple links than send the data at a higher bandwidth over a single link, a technique known as striping. While the idea of striping is well-known, it is still inadequately understood.
[10].Design and verification of protocols
A tremendously frustrating problem in networking is our inability to design protocols of even modest sophistication and prove that they work correctly. Some new ideas are being developed in this area which combine design with formal verification, and given that current verfication technology is nearly15 years behind the rest of the field, we need to encourage new work in this area.
v Gigabit Applications
Most of today's data network applications are not very sensitive to delay and variations in bandwidth. It does not matter very much if your files take a little longer to travel across the net. But in telecommunications (telephone) industry the appli-cations are delay sensitive.
Normally , when humans speak they pause in between sentences and if the pause is longer the other speaker speaks. If due to network delay if the pause is large then both the speaker may speak at the same time leading to confusion. So delay should be bounded in telephones.
Other applications like X Windows, remote login etc will be faster if gigabit networks are used.
Any applications which needs low response time or high bandwidth is suitable to be a gigabit application. The recent advent of gigabit networks have given rise to many new applications. One of them is IVOD ( Interactive Video on Demand ). Here the consumers order which ever program they want to see and the programs are sent from a centeral server to the consumers. Since video applications use a large band-width and also different viewers may want to see different programs at the same time, this application will benefit from gigabit networking. Though compression methods like MPEGmay be used for compression, every once in a while full screen data has to be sent. This can be done using gigabit networking technology.
Highly computation intensive problems can be broken into smaller problems and given to computers with high bandwidth networks connecting them for interchanging data.
For example in UCLA, researchers are experimenting with simulation studies of atmosphere and ocean interactions. One supercomputer ( CM-2 ) simulates the ocean and another simulates the atmosphere and these interchange huge amounts of data and the interactions are studied. Typically 5 to 10 Mbs of data is exchanged per cycle, this will take a second in a 10 Mbs Ethernet while it will take only 100ms in a gigabit networking environment.
Another class of applications are those which have real-time interactions with humans. A typical example is video conferencing. Humans are capable of absorbing large amounts of visual data and are very sensitive to the quality of the visual data.
Another class is the virtual realityapplications which give the user the illusion of being somewhere else.There have been interesting experiments done in NASA. They developed a system, by which the geologists can interact with the surface of the Mars. Geologists study by interacting with the surface, touching it (virtually), seeing the 3D scene from different angles etc. All these require large amount bandwidth, and gigabit networking comes to help them out.
One of the main difference between the traditional data-communication applications and those of interactive nature is that the later need timing requirements about spacing between samples. Recently there has been some work in some innovative experiments with adaptive applications. These applications change their behaviour dynamically and require only loose performance guarantees from the network.
An example of the adaptive application is the vatvoice-conferencing system developed by Van Jacobson. vatis like a telephone but uses the computer and internet to connect two peoples. The vatavoids isochoronous samples by keeping a large buffer and timestamping all the data it receives. Traffic which arrives earlier are buffered appropriately and then played. The time of the delay is called the playbackpoint. So adaptive applications could have a major impact in network designing in future. The vat also has demonstrated that slow networks like Internet can support real-time applications with enough buffering.
v Advantage of gigabit networking
Gigabit Ethernet (gbe) is 100 times faster than regular 10 mbps Ethernet and 10 times faster mbps .faster ethernet .advantage as a networking technology include:
§ Increase bandwidth for higher performance and elimination of bottleneck.
§ Power to transfer large amount of data across a network quickly.
§ Ability to aggregate network bandwidth to multi-gigabit speed usin gbe server adapters,link aggregation,and switches
§ Quality of service features to help configure network traffic and optimize critical data.
§ Low cost of acquisition and owership.
§ Seamless integration with Ethernet and fast Ethernet-installed base.
v Conclusion
Today's advanced technology in fiber optics , computing systems and networking has made the development of gigabit networks possible. With the bandwidth more than 1 Gbps, gigabit networks can support the demand of increasing network traffic, and many sophisticated computer applications.
To achieve true gigabit networks, other aspects of networking, such as routing, switching, protocols should also be considered.
Although routers are considered the major bottleneck and being replaced by cost-effective switches, they are still the key component in building future high-speed networks. With 80% of today's network traffic crossing subnet boundaries, routers are required more than ever because they can provide network security and firewalls.
Thus, several approaches have been developed recently to improve the performance of routing and routers. Such approaches described in this paper are Routing Switch , High Performance Routing, Gigabit Routers, and I/O Switching. However,it is important to note that these technologies described here might become obsolete in favor of new upcoming techniques and technologies.
Finally, there are at least four gigabit technologies available for high-speed LAN today. They are ATM, Fiber Channel, Gigabit Ethernet, and Serial HIPPI.This listing may soon be changing with new emerging technologies.
At present, Serial HIPPI seems to be the only available technology that offers gigabit performance with 100% reliability. However, this does not eliminate the possibility of other technologies , such as ATM and Gigabit Ethernet to be a significant factor in the implementation of gigabit networking.
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