Network Communications 28th Edition (Fall 2010)

Fall 2010 Network Communications 28th Edition

Network communications provide the required connectivity to support distributed  computer processing. Network products support a stable and dependable communication protocol for distributed data transport. A variety of communication protocols supports distributed applications and data  resources located at sites throughout an organization.

For several years, network technology was a relatively static environment  while computer performance was increasing at an accelerating rate. Today communication technology supports a dramatic shift in network  solutions, providing worldwide communications over the Internet and  bringing information from millions of sources directly to the desktop in  real time. Cell phone technology provides real time public access to wireless communications connecting us to global Internet information  resources no matter where we might be.

GIS Communications
GIS applications rate among the heavy users of network traffic along with  document management and video conferencing as portrayed in figure 6-1. GIS technology provides a visual display environment to the user supporting very quick analysis of large amounts of graphic data. Access to distributed data sources for real-time display and analysis puts  large demands on network communications. Data must be transported across the network to where the program is executed to display the  information.



Data is a collection of digital computer information stored in media that  have the capability to record and retain the data structure. This data is represented by little pieces of information called bits. Each bit takes up the same space on storage or transmission media. For convenience, these little bits can be grouped into bytes of information  with each byte containing eight bits. Data can be transported from one location to another within packets that protect the integrity of this  data.

Data is typically transported from one storage location to another over copper wire or glass fiber physical networks. Other types of transport media include microwave, radio wave, and satellite digital transmissions. Each network protocol has limits to its supported rate of data transport based on the technology used to  support the transmission.

Communication Network Technology
Network transport solutions can be grouped into two general technology classes. These classes include LANs and WANs. The volume of data (measured in bits) that can be transported per second represents the transport rate  (capacity) of a specific network segment. This capacity is called network bandwidth and is typically measured in millions of bits  (megabits [Mb]) or billions of bits (gigabits [Gb]) per second.

Figure 6-2 illustrates the different types of networks and following are their descriptions.





Local Area Networks
Local area networks support high-bandwidth communication for short distances. This environment supports local operating environments (usually within a building or local campus environment). Data transport over a single technology is single threaded, which means only one data transmission  can be supported on a single LAN segment at any time. The cost for LAN environments is inexpensive relative to other hardware costs supporting  the system environment.

Wide Area Networks
Wide area networks support communication between remote locations. Technology supports much lower bandwidth than LAN environments, but transmission is possible over long distances. This is a data transport environment, which means data is packaged in a series of additional  packets and transported as a stream of data along the transmission  medium. The cost for WAN connections is relatively high compared to LAN environments.

Wireless Communications
Wireless communications use radio frequency bands as a data transport media. Radio frequencies used for wireless transmissions connect user devices to area communication transceivers, and the transceivers connect the  communications to the local or wide area communication networks. Wireless communications broadcast over shared public frequencies and tend to experience higher latency than hard wire connections.

Network Bandwidth
Network traffic capacity is measured in terms of connection bandwidth. Figure 6-3 provides an overview of currently popular network protocols and  available traffic capacity.



The capacity of a network segment is established by the connection  (communication port) bandwidth specifications. Computers are connected to the network through a network interface card (NIC) or a wireless  transmitter. Network segments are connected by routers and switches, boxes that provide communication ports for connecting network segments. Wireless communications transmit over radio frequencies to antennas that are connected to the communication network infrastructure (routers and  switches). All of these routers, switches, and transmitters are connected by wires that represent the network communication  infrastructure.

Local area (LAN) wired networks have standardized on Ethernet protocols - they are simple to manage and  provide the capacity we need for local network communications. Wide area networks still use a variety of protocols, including a collection of  telephone wire and fiber transmissions (modem, T-carrier and E-carrier  fiber communications, Cable TV lines, digital subscriber lines-DSL, etc)  as well as wireless communications (radio frequencies, infrared  transmitters, satellite communications, etc).

Data Units
Data capacity is measured in terms of megabytes or gigabytes when stored on  computer disk. Megabyte is abbreviated using a large "B," while megabit is abbreviated using a small "b." One must remember 1 MB = 8 Mb when converting data volume from disk storage to network traffic. Network traffic also includes some protocol overhead, so a simple rule-of-thumb  is to translate 1MB of data to about 10 Mb of traffic.

What is Data (i.e. Why so many Protocols?)
I remember a trip I made to the Chicago Science and Industry Museum when I  was a young boy. They had a simple light bulb display that demonstrated how computers think. This was in the early 1960's back when computers were not common household appliances. The display showed how a series of on and off light bulbs could be used to add and subtract numbers - the  scientific breakthrough that gave us computers. Who ever thought we could share our thoughts and ideas with a mechanical device that could  be trained to do our brain work? Figure 6-4 answers a fundamental question that changed our world.



We call these patterns of 1's and 0's data. Patterns that represent our thoughts and ideas, and can be manipulated to produce information  products we can use in our work. Data is not a physical thing that has mass and takes up space - the content is a pattern representing our  ideas. Understanding this concept is important, since it explains why we have so many different ways to store and move data. It is also important since it suggests the physical laws of space and travel do not  apply directly to data itself, only to the medium we use to store and  move data. This opens a world of possibilities to communicate and store data in ways we may not even imagine today - we are limited only by our  imagination. Satellites collecting high resolution images of our world that we can display on our cell phones - changes beyond our imagination  less than 10 years ago. Will science soon overcome the communication infrastructure limitations we experience today? I expect so.



Client/Server Communications
Data is passed over the network using a variety of client/server  communication protocols. Communication processes located on client and server platforms define the communication format and address  information. Data is packaged in communication packets as shown in Figure 6-5; packets which contain communication control information  required to transport the data from its source client process to the  destination server process.



Network Transport Protocol
The communication packet is constructed at different layers during the  transmission process. In figure 6-6, a data stream from the host A application is sent through the protocol layers to establish a data  frame for network transmission. The Transmission Control Protocol (TCP) header packages the data at the transport layer, the Internet Protocol  (IP) header is added at the Internet layer, and the Media Access Control  (MAC) address information is included at the physical network layer. The data frame is then transmitted across the network to host B where the reverse process moves the data to the host application. A single data transfer can include several communications back and forth between  the host applications.





GIS Client/Server Communication Protocols
Figure 6-7 provides an overview of the primary communication protocols used  for GIS operations. Each protocol implementation includes client and server components to support data delivery. The client process prepares the data for transmission, and the server process delivers the data to  the application environment.



Network file services (NFS) (UNIX) and Common Internet File System (CIFS) (Windows) Protocols
Support remote disk mounting enabling a client application to access data from a  distributed server platform (network file share). All query intelligence resides in the client application, providing query  instructions to access data located on the server platform. Data must be transferred to the client application to support query execution.

Database Access Protocols
ArcSDE includes client and server communication components. The database management system (DBMS) includes intelligence to support query  processing. Compressed data is provided for network transfer and database storage. Data is uncompressed by the client application (ArcObjects). Data must be transferred to the client application to support analysis and display.

An alternative ArcSDE client direct connect option is available that connects with a DBMS  client application program interface (API) executed on the client  desktop. The ArcSDE middleware functions are supported on the client platform, and the DBMS network client supports data transmission to the  server. Query processing remains on the DBMS server.

ICA and RDP Protocols
The protocols support remote terminal display and control of applications  hosted on a shared Windows Terminal Server. Both protocols transmit display and control information to the terminal client. Both the Independent Computing Architecture (ICA) protocol and Remote Desktop  Protocol (RDP) compress data for transmission.

HTTP Protocols
The Hypertext Transfer Protocol (HTTP) is a standard Web transmission  protocol. In this transaction-based environment, service selection and display are controlled by the browser client. Data is compressed for transmission. There are a variety of Internet Protocols that can be implemented within the HTTP framework.

HTTP display traffic resolution is established by the published map service for Web  browser clients, and by the desktop resolution for ArcGIS Desktop  clients. Traffic for the ArcGIS Desktop is normally higher because of the larger image transfers. Image size is directly proportional to the physical screen display resolution; thus, larger image displays result  in higher traffic.



Client/Server Network Performance
The data transfer traffic and the network bandwidth can be used to estimate  minimum network transport times for a single map display transaction. A typical GIS application requires up to 1 MB of data to generate a new  map display. Typical terminal/browser display traffic is about 100 KB of data for the same map display.

Figure 6-8 shares typical data transfer requirements in megabytes, shows the conversion to  megabits of traffic for transmission, includes any adjustments of this  data performed by the communication protocol, and identifies the total  volume of traffic in megabits that must be transmitted (protocol  overhead may be greater than what was used in this sample conversion).

The minimum data transport times are calculated for five standard bandwidth  solutions (56 kilobits per second [Kbps] for standard dial-up  communications; 1.54 megabits per second [Mbps] for typical WAN  communications; and 10 Mbps, 100 Mbps, and 1 gigabit per second [Gbps])  for LAN communications. Any existing data traffic on shared network segments would increase these network transfer times.



During peak work periods, operational workflow performance can slow to a crawl  similar to what is experienced in larger cities when driving on major  highway arteries during rush hour. This simple illustration identifies the primary cause for many remote client performance problems. Sufficient bandwidth is critical to support productive user workflow performance requirements.

File server configurations support query from the client applications. When selecting data from a file (coverage or shape file), the total file (file index for large  spatial data file formats) must be delivered to the client for query  processing. Data not required by the application is rejected at the client location. This accounts for the considerable amount of traffic overhead experienced by these communications.

ArcSDE client/server configurations support DBMS query processing on the server  platform. The query processing includes locating the requested data and filtering that data so only the specific data extent requested by the  client is returned over the network. If the client application requests a small volume of data (e.g., point data or a single parcel in a parcel  layer), the resulting data transfer can be small and network transport  time would improve accordingly.

Best practices are established for network configuration alternatives. Desktop applications accessing file or DBMS data sources perform best in a local area  network environment. Transaction-based services, or persistent Windows Terminal Server connections, provide reliable environments for  processing over less stable wide area network connections.



Network Latency Considerations
The maximum bandwidth capacity used by a single user is limited by the  total system transaction time. With standard client/server database display transactions, hundreds of data requests are sent to the server  spread throughout the display transaction time (ArcGIS Desktop provides  sequential requests for each layer in the display, completing each layer  transaction before sending requests for the next display layer). A typical map display may have 10–20 data layers supporting the display  analysis, which can translate to hundreds of sequential database  transactions. Figure 6-9 shows a typical map display profile, showing the client desktop processing time, network transport time, and database  processing time required to support a typical map display.



Bandwidth capacity is typically measured in megabits per second. During a typical local map display transaction, the total display response time can be  1.32 seconds. A total of 5 Mb of data must be transferred from the server to the client application to support a typical map display (see  figure 6-8). The average bandwidth utilized by a single user on the LAN is 3.78 Mbps. Increasing the desktop network interface to 1 GB bandwidth would have limited user performance impact when accessing an ArcSDE  data source.

 Normal database access protocols are "chatty," which means a typical database  query requires a large number of trips to and from the server to  complete the client display transaction. There are many trips to and from the server (query transactions) for each layer in the map display. Figure 6-10 shows 200 query transactions are required to support a single map display.



Network latency can impact bandwidth utilization over long WAN distances. Latency is easy to measure, using a simple Windows command prompt (tracert "server host name"). Results provide the number of network hops and the associated network latency time for a single trip.

For LAN environments, network latency is very low (typically < 0.001  milliseconds per trip to the server). Many trips between the server and client have limited performance impact. The primary system latency contribution is client and server processing service times.

For longer WAN distances that involve several router hops, there can be a  measurable network latency delay, and for chatty database protocols,  network latency can have a measurable performance impact. In the example above, total transaction time over the WAN (including cumulative  network latency) is 7.12 seconds. The maximum bandwidth utilized by a single user on this WAN connection is 0.71 Mbps. A single user would not experience performance improvements with increased WAN bandwidth. These days, many global WAN connections include satellite communication  links. The fastest communication transfer is limited by the speed of light, which for very long distances will require a minimum bandwidth  latency that technology will not overcome. Good performance over WAN environments results from protocols that minimize trips (communication  chatter) between the client and server platforms.

Figure 6-11 shows how network latency is addressed in the CPT Calculator tool. Rows 12, 13, and 14 address network communication traffic. Row 12 is the LAN traffic, while rows 13 and 14 represent remote site communications. Network bandwidth connections are identified in column G. Total number  of remote users sharing the remote site connections is identified in  column D.  Latency is identified for remote connections in column E.   Communication chatter is identified in column I (default of 10 for Web  and WTS workflows; 200 for medium workstation workflows adjusted by  display complexity). Latency delay is shown as pink in the Workflow Performance Summary.

Figure 6-12 shows how network latency is addressed in the CPT Design tool. The GREY rows represent the data center LAN, WAN, and Internet connections. Network bandwidth for each network row is set in column H. The  Network latency setting (milliseconds) is set in column AE (network  chatter for each workflow is also identified in column AE). Latency delay is shown as pink in the Workflow Performance Summary.



Shared Network Capacity
The total number of clients on a single network segment is a function of  network traffic transport time (size of data transfer and network  bandwidth) and the total number of concurrent clients. Only one client data frame can be transmitted over a shared network segment at any time.

With older switch technology, multiple transmissions on the same Ethernet  network segment would result in collisions, which require another  transmission to complete data frame delivery. Ethernet segments fail rapidly during saturation because of the rapidly increasing number of  transmissions. Ethernet switches today include provide options for configuring shared segments in a full duplex mode, which when configured  properly take advantage of switch buffer cache and improve transmission  efficiency.

Figure 6-13 shows multiple client sessions sharing the same network segment where each data exchange is  represented by the small boxes. Only one data exchange can be supported at one time on the same network segment.

Shared networks must adjust traffic flow to accommodate random transmission  arrival times. Concurrent transactions must wait for network connection, resulting in transmission delays. Delays will increase during heavy traffic loads as the network reaches saturation. Wait time is a function of network transport time (figure 6-8) and bandwidth utilization. Higher traffic per display and busier shared network segments contribute to longer wait times.

 A GIS application may require 1 MB of spatial data, or up to 10 Mb of  network traffic, to support a single map display as illustrated in  figure 6-14. Applications can be tuned to prevent display of specific layers when the map extent  exceeds defined thresholds. Only the appropriate data should be displayed for each map extent (e.g., it may not be appropriate to  display individual parcel layers in a map showing the full extent of San  Diego, California). Proper tuning of the application can reduce network traffic and improve display performance.



Network Design Guidelines
For many years,  standard  published guidelines were used for configuring network communication  environments. Figure 6-15 identifies the importance of designing to network communication standards and also monitoring network utilization. These standards were application specific and based on typical user  environment needs. Communication environments are statistical in nature, since only a percentage of user processing time requires transmission  over the network. Network data transfer time is a small fraction of the GIS users' total response time (on properly configured high capacity  networks). Network data transfer time can dominate response time when bandwidth is too small or when too many clients are on the same shared  network segment.

The network must be designed to support peak traffic demands. The amount of traffic varies based on the different types of applications and user work patterns. Standard guidelines provide a place to start configuring a network environment. Once the network is operational, network traffic demands should be monitored and necessary adjustments made to support peak user  requirements.



Enterprise System Architecture
GIS user workflows access applications, services, and/or data sources maintained within the enterprise data center. Users may be located on the LAN, at remote locations over the WAN, or operate  from mobile clients over wireless WAN or Internet connections. Remote and local users may also access a variety of Web services over the  public Internet. Figure 6-16 provides a sample Enterprise GIS network communication diagrams showing GIS users located at three remote sites,  one connected over an Internet connection and the other two connected  over a WAN connection. Additional GIS users are located within the central LAN environment.

Network connections within the local LAN infrastructure can normally be adjusted to accommodate peak  traffic loads. Remote WAN and Internet connections often present constraints that must be addressed in the system design, and may limit  software technology deployment options.



CPT Calculator Network Analysis
Figure 6-17 provides an overview of the CPT Calculator highlighting the  network performance analysis components. Data Center and Remote site service connections identify bandwidth constraints that must be  evaluated during the system design. Standard ESRI workflow display traffic loads are used to evaluate network  suitability across all WAN and Internet site connections. The Capacity Planning Calculator can be used to estimate workflow client display  traffic (megabits per display). Client traffic (Mbpd) is included with the workflow service times on the CPT Workflow tab and used by the  Design tab to complete the network suitability analysis.



Network Suitability Analysis
Many network administrators establish and maintain metrics on network  utilization, which help them estimate increased network demands when  planning for future user deployments. The CPT Design tab includes a network suitability analysis which uses display traffic from  the Workflow tab to compute peak site traffic workflow loads. Sum of all site traffic workflows is compared with the site bandwidth to identify  peak network utilization. Figure 6-18 identifies network suitability analysis performance by the CPT Design tab.

 The CPT Design tab computes display response times for each workflow, based  on total of all system component service times and queue times during  peak system loads. User productivity must be adjusted if workflow response time does not support  minimum think time. Figure 6-19 provides an overview of the workflow performance validation process and shows the final workflow performance  summary (available once system level performance validation and any  required workflow productivity adjustments are complete).



CPT Calculator Network Analysis Comparison
Figure 6-20 provides CPT Calculator design solution for two standard ESRI  workflows. The first analysis compares local and remote client display response time for a light ArcGIS Desktop 9.3.1  Workstation client. Local network client display was about 0.56 sec, while the same map display takes 6.09 sec for a remote workstation  client accessing over a 1.5 Mbps WAN connection. The second analysis compares local and remote display response time for a light ArcGIS  Server 9.3.1 REST map service over the same bandwidth connections (0.28  seconds for a local client and 1.78 seconds for the remote client).



Network Performance Impact
Figure 6-21 provides a workflow performance summary overview of common ArcGIS Desktop and ArcGIS Server deployment patterns. Workstation clients connect to the data source over a 100 Mbps connection, while  remote client access over a 1.5 Mbps WAN connection. Network transport times present the most significant impact on Web mapping service display  response times.



Standard Workflow Network Traffic Guidelines
Figure 6-22 provides an overview of the standard network design performance factors. Baseline display traffic design factors are validated during ESRI performance  benchmark testing. Capacity Planning Calculator workflow traffic estimates are further modified base on performance adjustment parameters  gathered from ESRI performance sensitivity benchmarks. Performance adjustments were discussed in the System Design Strategies chapter on  Software Performance.

<br style="clear: both" />

CPT Workflow tab Network Metrics
Figure 6-23 provides an overview of the Capacity Planning Workflow tab  highlighting workflow display chatter, client display traffic, and  database traffic columns used by the CPT Design tab to complete an  Enterprise level network suitability analysis.

<br style="clear: both" />

Capacity Planning Network Traffic Adjustments
Figure 6-24 provides an overview of the CPT Lookup table use for traffic adjustments based on data source selection. Traffic adjustment factors are applied to all traffic accessing the data selected source.

<br style="clear: both" />

Enterprise Design Network Suitability Analysis
Figure 6-25 shows how network suitability is addressed on the CPT Design tab. This is where all of the user workflows and network traffic comes together,  providing an opportunity to complete a comprehensive Enterprise network  suitability analysis.

Network suitability analysis is completed by the CPT Design tool. User workflows are configured within their respective GREY data center network segments (LAN, WAN, INTERNET)  and within their GREEN remote site locations. Network traffic for each workflow is calculated in column G.   Workflow traffic is calculated  from the traffic per display (Mbpd) in column R and the total display  throughput (DPM) in column F (DPM x Mbpd / 60 sec). The total traffic for each network is collected in column F (centered across columns F and  G for better display). Total network traffic for a specific network segment is the sum of all the workflow traffic located on that network  (network traffic summations must be updated manually when adding new  remote sites). Network bandwidth for each site connection is identified in column H.  Traffic bandwidth utilization for each network is  identified in column R (traffic / bandwidth).

The following video provides an overview of the CPT Calculator network  traffic functions. The video also provides an overview of the CPT Design User Requirements Module and shows how the CPT Design completes the  network suitability analysis.

<br style="clear: both" />

Previous Editions
[Spring 2010 Network Communications 27th Edition]

Page Footer Specific license terms for this content System Design Strategies 26th edition - An Esri ® Technical Reference  Document • 2009 (final PDF release)