Wide Area Networks

Wednesday, December 06, 2006

As the businesses are scaling at a rate never before and beyond the boundaries of cities into other countries, it has become a necessity for a truly global organization to use, maintain and manage WANs. At the same time, it is essential to keep your enterprise WAN running fast and smooth at all times. Also you need to sustain a fast response time and large window size so that user productivity is not hampered. And this is the primary reason why more and more technologies and solutions are emerging in this area. Let us explore some of them in a little detail.

WAN acceleration
WAN acceleration gives quick data availability between offices spread across distant geographical areas. Devices for this speed up data transfer by utilizing techniques like compression, data reduction, error correction and data caching. They are deployed on both ends of the link where acceleration is required. All incoming/outgoing data passes through them and suitable acceleration techniques are applied. Compression algorithms can shrink data but this will only work for compressible data such as spreadsheets and Word documents. The device dynamically selects the compression algorithm to use based on the data. This improves bandwidth utilization during data transfer. 

Another aim of acceleration is to reduce data flow over the network. This is done by replacing redundant data packets by codes and transmitting them. Either whole packets or streams of packets could be scanned for redundant data. Caching is a popular technique primarily used in proxy servers so that instead of going to the Internet to hunt for a website, the proxy caches it locally to save bandwidth. A similar thing can be done here as well. The WAN accelerators on either end inspect data being transmitted and store all duplicate data locally on their own cache. This way, every time the WAN accelerator at the other end asks for this data, only its code can be sent and the other device will deliver it locally. This will actually deliver LAN like speed for WAN traffic. This can significantly reduce traffic.

Web acceleration techniques
Compression: Uses a common compression algorithm to remove extraneous/predictable information from the traffic before it is transmitted. The information is reconstituted at the destination using that same algorithm and there's no synchronization between two ends. Data transmitted over WAN is reduced, but has limitations on how much bandwidth reduction it can achieve by itself - and has minimal impact on latency.

Caching: Data is cached by accelerator devices at both ends and each device will deliver it locally when requested for. This will deliver LAN like speeds over WAN and significantly reduce traffic. Two commonly used techniques are Byte Caching and Object Caching.

Protocol Optimization: Inefficient protocols over WAN such as HTTP, CIFS, MAPI and HTTP are made more efficient by converting a time-consuming serial communication process into parallel processes where various communication tasks are handled simultaneously. Protocol optimization does not reduce amount of bandwidth used by an application, it can accelerate delivery of applications and reduce latency in the process.

Error correction: Besides heavy traffic, re-transmission due to errors also slows down the network. Bandwidth is wasted if the appliance has to retransmit data every time there's an error. So FEC (Forward Error Correction) is used to enable data correction at the physical layer by adding an additional data corrective packet. The process of adding a FEC packet is done dynamically, depending upon channel congestion. Normal protocols usually have the ability to correct at most one or two data packets if they're lost, but not beyond that. If more packets are lost, and have to be re-fetched, then the latency and traffic on the WAN links increases. FEC prevents data to be retransmitted as it will automatically generate the correct packet and give it locally.

NComputing OfficeStation L110

A multi-user network computing terminal that uses WoIP (Windows over IP) protocol to let you share resources of a single Host PC system by connecting OfficeStation terminals to it. It provides all benefits of a thin client. You can connect it directly to Host PC or connect one or more OfficeStation terminals to one Host PC directly using a network switch. According to NStation with this terminal you can expand a PC to up to 10 L110 terminals and a Windows 2000/2003 Server to up to 30 terminals. It has one port each for mouse, keyboard, monitor, Ethernet and speakers. There are no USB ports. To connect 10 OfficeStation terminals to a single Host PC, you need at least a P4 machine with HyperThreading technology and 2048 MB RAM or higher. To connect only one Office-Station, 256 MB RAM will do. The device ships with a software called N-Control that allows remote control, access denial, remote log-off and restart/shutdown of any of the terminals connected to the Host PC or Server. It also lets you view the screens of the terminals connected. It's a plug and play terminal. Once configured, it supports auto logon. We tested it with a Win XP host machine (P4 with 256 MB RAM) and Win 2003 Server. Work on this device and you feel as if you are working on a standalone system with no noticeable decrease in the performance of the Host PC either. There is no delay in speed while using routine applications such as MS Office. Price: Rs 9900 (1 yr warranty); Contact: Digital Waves, Bangalore; Tel: 41132444; Email: ranga@digitalwaves.in; SMS BUY 131299 to 6677

Wide Area Data Services
Wide Area Data Services (WADS, also known as WDS) technologies help enable the consolidation of file servers from remote sites to the data center without compromising end user performance. WDS includes technologies like WAFS (Wide Area File Services), WAN Optimization and application acceleration. WAFS is a caching technology and a WAFS appliance has an application server, which enables local delivery of the content. It is kept between clients and applications, where it saves local copy of the files requested. If another request for the same file is made, WAFS appliance acts as a proxy and delivers that file directly without going back to the original server on the WAN. The challenge, here, for WAFS appliances is to keep remote cached copy synchronized with the original, and vice versa. Another problem with WAFS is how secure is the data lying in the cache? or What if the link goes down during a file transfer.

WDS appliances claim to provide solutions to all these problems and a better performance than WAF appliances. A WDS solution uses techniques like TCP optimization, Data reduction, QoS, Application Acceleration etc with WAFS. WDS technology can accelerate a wide range of applications used on WANs like file sharing, email, Web applications, backup and replication, and many others. Though quite a few vendors have adopted WDS, Riverbed is the key player in this area and claims to have complete WDS solutions.

Thin clients
Over the past few years we saw a lot of vendors launching thin client solutions. While there is no significant changes in thin clients as most of them are basic thin clients, Robust thin client or PXE thin client and mainly use RDP, ICA etc protocols to work. One trend that has been catching up is streaming technology to deliver software on demand to thin clients. In streaming, OS and applications are deployed from a central location to clients through streaming. Thus, you need to deploy updates and patches for OS and applications on the central server, ensuring software consistency throughout the organization. It also gives you control over a number of application licenses used and real-time license metering within the enterprise. Another trend catching up is accessing corporate applications using mobile devices. PDAs and cellphones are coming with thin client plug-ins, enabling users access corporate servers when they are on move. PDAs running Windows CE can use Window Terminal Client or VNC to access Windows Terminal services, VNC server, etc. Idokorro Mobile Desktop is a client for Windows Terminal Services, Remote Desktop and VNC (Virtual Network Computing) for Smartphone devices and BleckBerry.

FTPs over WAN
These include TCP , CIFS (Common Internet File System), and NFS. These protocols need to do a number of round trip requests and acknowledgements before sending the requested document/files. This can cause serious congestion on WAN links. TCP acceleration
requires packets resizing for optimal performance, which is done using TCP window adjustment algorithms. TCP acceleration also requires high speed TCP management and round-trip management to provide correction for more than one packet loss. Similarly for CIFS and NFS, caching techniques are used in which acceleration devices can generate read-ahead or write-behind requests to the server to reduce delays.

WAN QoS
MPLS is a widely used protocol for QoS over WANs. In MPLS, each router determines the next efficient hop (or router) for the traffic or packets by looking up a label. The first router (ingres point) calculates the route for the traffic according to the priority and adds a label to the packets, which identifies the priority. The calculated route for the traffic is stored in a table where the next hop (router) is determined by using the label as the index value.

Thus, the subsequent routers do a lookup for the next hop (or router) in the table by using the label as an index. The lookup results into a new label, which is substituted for the existing label, and the packet is routed to the next router. By using a label to determine the next hop or routing path, the routers are off burdened from the task of using complex routing algorithms and the label specifies a route for the traffic as per the decided priority.

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