• executes all application logic on hte server;
  minimizes network traffic;
• uses standard LAN and WAN protocols;
• enables applications to perform at LAN-like speed even over low bandwith connections;
• permits the lastest 16 and 32 bit applications to run on legacy clients that normally would not be able to run them;

ICA Packet Overview

Consists of a required one byte command followed by optional data.

Components :

• frame head
• reliable
• encryption
• compression
• command (required)
• command data
• frame trail

Only Command is always present in the packet.

ICA Packet Encapsulation

The ICA packet encapsulates data by passing it through a series of drivers such as encryption ,compression and framing.
After the data is encapsulated within the necessary drivers ,the ICA packet is placed on the transport layer and sent to ICA client.
At the ICA client ,the ICA packet passes through the same layers in the opposite order.

Virtual Channels

ICA protocol uses the virtual channels to extend its capabilities to include data types ,such as audio and video ,and client devices such as badge readers ,wands and scanners.

Can support up to 32 virtual channels

ICA protocols bundles the channels within an ICA packet rather than sending one packet per virtual channel.
Examples of virtual channels : audio ,clipboard ,drive mapping ,font and keyboard layout ,parallel port mapping,printer spooling ,serial port mapping ,speedscreen control channel ,ICA display.

ICA display support : vector graphics ,anti aliasing routines ,screen theorical resolution 64.000x64.000 ,high color depth (65.535) ,multiple monitos at the client ,command and object intelligent compression with state persistence ,intellignet caching of bitmanps ,cross.session persisten caching.

An administrator can configure ICA connection settings that determine graphics performance over the CIA display virtual channel using the TWOCONFIG command.

SPEEDSCREEN TECNOLOGY

Is the ICA protocol agent that reduces the latency by reducing the amounts of bandwith consumed.
Consists of several components :

• Reducer 1 and Reducer 2
• Persistent Bitmap Cache
• Alternate Caching Method
• Queing and Discarding
• Speedscreen Latency Reduction :
  • Mouse Click Feedback changes the mouse pointer temporarily to iundicate that an action is pending.
    Does not accelerate the requested action.
  • Local Text Echo provides instant feedback to the user in response to typed data by simulating the response that the XPO server will likely make.
    The actual result from the server is applied as soon as it is available.

  Reduces latency on connections whee the round trip latency is between 150ms and 500 ms.
  Connections with a round trip latency between 250ms and 500ms will notice the most improvement in latency reduction.
  On connections with less that 150ms latency ,there will be no perceived benefit from using this feature.
  Speedscreen Latency Reduction consists of two components :

  • Client uses the info gathered from the server components to determine which level of support can be provided for the particular input field in the application.
    ICA client can enable or disable Speedscreen Latency Reduction with the CTRL+F4 keys.
  • Server provides info about the application's input fileds ,font type ,font size ,font color and input field background color.
    S.L.R. categorizes applications into one of four behavioral types :
    • Edit Control applications can use only one font per control.
    • Rich Edit Control applications can use more than one font per control.
    • Generic#1 Control applications are similar to Rich Edit Control applications.
    • Generic@2 Control applications cannot reduce the info necessary dor S.L.R

S.L.R. is disabled by default for ICA conneciton over a LAN.

INDEPENDENT MANAGEMENT ARCHITECTURE

It provides the framework for server to server comunication and allows XP to perform in both small and large enterprises.
IMA is a centralyzed management facility constructed on a collection of core subsystems that define and control the execution of products in XP server enterprise.
IMA runs on all XP servers and operate in a peer to peer model.

Citrix Management Console
Replaces the Citrx Server Administration ,Published Application Manager ,Citrix Licensing and Load Balancing Administration utilities found in Metaframe 1.8.
It can be run on any system with a Java Runtime Environment (JRE) version 1.3 or higher ,TCP/IP and one of the following os : W2k (Pro,server,advanced server,data center) ,NT 4.0 (server or workstation),NT server 4.0 TSE.

IMA Subsystems

Subsystem is a data link library (DLL)file.
Make IMA modular and extensible.
Subsystems interact via a messaging layer ,which routes data among the subsystems on XP servers in the farm.
IMA includes :

• Application Management : manages all published applications in the farm and a central location for all info pertaining to published applications.
• Citrix License : enforces the Citrix license policies.
• Distribution : is responsible for the transferring of files to other subsystems.
• Ica Browser : is active only in mixed mode oe when servers are confiured to respond to UDP broadcast from ICA clients.
• Load Management : work in conjunction with the application management to perform load balancing support.
• Persistent Storage : interfaces eith the data store on behalf of other subsystems.
• Printer Management : allows printers to be configured ,updated ,controlled ,removed and monitored.
• Program Neighborhood : handles the PN communications with the ICA clients.
• Remote Procedure Call : allows external processes to communicate with IMA.
• Runtime : provides services such as the data collector ,zone management and subscription events.
• Server Management : manages user sessions and provides support for hierarchical tree structure of XP servers in the CMC.
• User Management : uses and enhances existing security and authentication facilities provided by the operating system environment.

Data Store

Keeps configuration and tracks XP server farm info that does nnot change frequently.
Is a database that uses : MS Access ,SQL server ,Oracle.In previuos versions of Metaframe ,data was stored in the registry of each servers ;each servers shared the info with every server in the farm.
Data store contains the following info :

• Published application info ,the application name ,users that can connect to the application ,the window size ,the color depth ,the encryptionlevel and the audio setting.
• Pooled license number and license counts for the server farm ,and license assignements to specific servers in the server farm.
• Server configuration info for the server farm.
• User configuration info for the server farm.
• Prnter and print driver info.

When a change to static info occurs ,XP server sends the info to the data store ,at the same time ,the server sends out a broadcast (not UDP) containing all of the data that has changed.
If all XP servers in the farm receive the data .they can update their local host cache.
If XP servers did not receive the broadcast they must wait until their local host cache receives its next update from the data store.
Changes are sent to the local host cache every 15 minutes.

• If the changes to the static info exceed 10KB ,a notification to read the data store are sent to all XP servers instead of the changed data.
• CMC does not comunicate directly to the data store.
  if the data store is down ,CMC does not manage XP servers ,but the server farm continue to operate using the local host cache.
• If the data store goes down ,connection licenses wll be availble for 48 hours.
• The data store database should be a separate database and shoul not be piggybacked on to another database.

Local Host Cache

Exist on every XP server in the farm.
Contains a subset of the configuration data that is kept in the data store.
When a server joins a server farm ,it receives a copy of the info in the data store and saves it to a local host cahce.
If a server is rebooted ,it reads its local host cahce to get info it needs to partecipate in the server farm.
LHC is checked for coherency every 15 minutes.
A refresh can be forced by stopping and starting the server's IMA service.
Stopping and starting IMA service does not affect the connected user sessions ,but users attempt to log on ,will be refused.
The LHC is stored in the Program Files7Citrix/Independent Management Architecture\IMALHC.MBD.
LHC is stored in MS access format ,the data is encrypted ,is not a subsystem.

Zones

Contains a subset of servers within the farm.
Each zone has a data collector that gathers and disseminates info to servers in the zone and to data collectors in other zones.
By default the zone is the equivalent of the TCP/IP subnet and all serers are added to the default zone.
A zone is designed to enhance the performance of XP serer farm by allowing geographycally related servers to be grouped together ,whether they are connected to the same network subnet or not.
The data collctor's assignments in the zone are :

• does not store license num,ber info ,but it does store info about the number of licenses in use;
• can span multiple subnets and a single subnet can have multiple zones;
• zones should not span low speed network segments;

Data Collectors

Is an in-memory databse that maintains zone specific data.
Store dynamic non configuration info ,such as server loads ,active sessions and disconnected sessions ,and users and liceses in use.
Is the ICA master browser for the zone (in mixed mode).
By default the first server in the zone is the data collector.
If the server designated to data collector goes down ,another server in the zone is elected based on its priority.
The priority determines which servers will be the data collector.
The administrator can settign the priority in the CMC.
The following are the levelsof priority :

• most preferred
• preferred
• default preference
• not preferred

The election process use the TCP not UDP as was the case of Metaframe 1.8.
XP does not use backup data collectors ,if goes down a new data collector is elected.
256 are the maximum number of servers in the zone.
It possbile to use a dedicated data collector for the zone.
Servers shuold be demoted to use the Not Preferred priority prior to moving them to another zone.This reduces the possibility of causing data collector elections in the server's new zone.

LISTENER PORTS ,IDLE SESSIONS AND ICA SESSIONS

XP uses a listener ports and idle sessions to make the connections to a server.
When XP is setup :

• two idle sessions are created ;each sessions use 1.7 MB of memory
• at least one listener port is created for each transport protocol that is configured on the server.

The listener prots deliver incoming connectionss to idle sessions ,which are preinitialized and ready to accept the incoming connection.
When an initialized session combines with an incoming connection ,the idle session becomes an ICA session and a new idle session is created to await another connection.
Adding ICA listener ports does not consume substantial resources beyond the initial 3.4 MB used by the two idle sessions.
If multiple network cards are installed ,the number of listener ports could be multiplied by the number of network cards.
HKEY_LOCAL_MACHINE\CurrentControSet\Control\Terminal Server\IdleWinstationPoolCount.
For performance reasons the number of idle sessions should not exceed ten.
The valid states of an ICA connection include : Listen ,ConnQ ,Conn ,Active ,Idle ,Disc ,Shadow ,Down ,Init.

CITRIX DEVICE LICENSING

Reduces the number of licenses require dby ICA clients to access XP servers.
It allows ICA clients to run multiple ICA sessions on multiple XP servers while using only one connction license.
When an ICA client esteblish an ica session ,it is given an identifier that identifies the physical device used to connect to the server.
Data collector uses the identifier to track connected sessions and to direct physical devices back to the correct disconnected sessions.
If another ICA sessions are started from the same physical device ,no additional licenses are consumed even if a connection goes to another different server.