Remote Access, and Wireless

1
Remote Access, and Wireless

• First category of remote LAN access is often
  referred to as telecommuting with information
  resources of office LAN available
• Important to understand remote access is
  relatively limited bandwidth of wide area network
  links that individuals will use to connect to
  corporate information resources

2
Mobile Telephony

• First Generation
• analog voice using frequency modulation.
• Second Generation
• digital techniques and time-division multiple
  access (TDMA) or code-division multiple access
  (CDMA)
• Third Generation
• evolving from second-generation wireless systems
• will integrate services into one set of standards.

3
Remote Access and Wireless Networking, contd

• Focus of mobile worker is evident in following
  benefits
• Faster responses to customer inquiries.
• Improved communications with co-workers and
  support staff at corporate offices.
• Better, more efficient customer support.
• Increased ability to be on road in front of
  customers.
• More efficient service from service personnel.

4
Remote Access and Wireless Networking, contd

• Use of remote commuting is for technical support
  organizations that must be able to dial-in client
  systems to diagnose and correct problems remotely
• Telecommuting employees generally fall into one
  of following categories
• Full-time, day shift, at-home workers.
• After hours workers who work overtime by
  extending workday by working remotely from home

5
Remote Access and Wireless Networking, contd

• Hidden costs to be considered when evaluating
  cost/benefits of telecommuting
• Workers may not be within local calling area of
  corporate resources, thereby incurring
  long-distance charges
• Additional phone lines
• Some applications run slowly on dial up lines

6
Architectural Issues of Remote Access

• Determine what is to be accomplished in terms of
  LAN based applications and use of other LAN
  attached resources
• Purpose is to validate need for remote PC user to
  establish connection to local LAN that offers
  all of capabilities of locally attached PCs

7
Architectural Issues of Remote Access

• Two major remote PC operation mode possibilities
  are
• Remote node (client) 
• Remote control
• Next slide shows difference between remote node
  and remote control installations

8
Remote Node vs. Remote Control Installations
9
Remote Node vs. Remote Control Installations,
contd

• Remote node (client) - computing implies that
  remote client PC should be able to operate as if
  locally attached to network resources.
  Transparent geographic separation between client
  and LAN resources.
• Client/server applications requiring large
  transfers of data will not run well in remote
  node mode.

10
Remote Node vs. Remote Control Installations,
contd

• Remote node mode requires full client NOS
  protocol stack to be installed on remote client.
• Remote control remote PC is supplying input
  and output devices for local client which
  interacts as normal with local server and locally
  attached resources

11
Remote Node vs. Remote Control Installations,
contd

• Remote control mode requires remote control
  software installed at remote PC rather than full
  NOS client protocol stack that is compatible with
  NOS installed at local LAN.
• Purpose of remote control software is only to
  extend input/output capabilities of local client
  out to keyboard and monitor attached to remote PC.

12
Remote Access Protocols and Compatibility

• Shortcomings of both remote node and remote
  control nodes caused by transport protocols
  responsible for delivering data across WAN link.
• Proprietary protocols used between guest and host
  remote control software is reason remote control
  software from various vendors is not
  interoperable.

13
Security

• Security issues specifically related to remote
  access corporate information resources are
  introduced here.
• Security related procedures can be logically
  grouped into following categories
• Password assignment and management
• Intrusion responses User accounts locked after
  preset number of unsuccessful logins

14
Security

• Separate public, private, and confidential data
  onto separate physical servers to avoid users
  gaining unauthorized access.
• Encryption
• Dial-back systems systems terminate call and
  dial back unauthorized user at preprogrammed
  phone number.
• Remote client software authentication protocol
  often include software based authentication
  protocols.

15
Security, contd

• Coming slide illustrates physical topology of
  typical hardware based token authentication
  remote access security arrangement.

16
Security, contd

• Basic ways in which remote PC user can gain
  access to local LAN resources.
• Serial port of LAN attached PC Simplest
  physical topology or remote access arrangement is
  to establish communications link to user PC
  located in corporate office.

17
Security, contd

• Communications server - remote users could attach
  to dedicated multi-user server known as an access
  or communications server through one or more
  modems.
• LAN modem Another alternative is to install
  specialized device known as LAN modem, also known
  as dial-in server, to offer shared remote access
  to LAN resources.

18
Physical Topology Alternative Access Points
19
Network Topology Alternative Network Access
Services

• Among alternatives are following
• PSTN
• ISDN
• XDSL
• VPN (Virtual Private Network)
• Coming slide shows alternative network access
  services might be used to construct remote access
  network topology.

20
Alternative Network Access Services
21
Communications Services and Remote Access Servers

• Communications server offers both management
  advantages and financial payback when larger
  numbers of uses wish to gain remote access
  to/from LAN.
• Perhaps more important are gains in control over
  remote access to LAN and attached resources.

22
Communications Services and Remote Access Servers

• Key hardware components of communication serve
  are
• Serial ports
• CPU(s)
• Network Interface Card(s)
• Next slide shows key components of communications
  server

23
Communications Server Components
24
Communications Server Components, contd

• Differentiation between communications servers
  and remote node servers is generally considered
  following
• Comm servers include several CPU boards inside
  single enclosure.
• Comm servers are often used for remote control
  functionality as an alternative to have several
  separate desktop PCs available for remote
  control.

25
Communications Server Components, contd

• Consolidating CPUs into single enclosure provides
  additional fault tolerance and management
  capabilities over separate PCs model.
• Remote node serves are strictly concerned with
  controlling remote access to LAN attached
  resources and acting as gateway to those
  resources.

26
Communications Server Components, contd

• Functional differences between communications
  server and remote node servers are illustrated in
  coming slide.

27
Communications Server Components, contd

• Remote node server solutions fall into four major
  categories
• Software only solutions in which user supplies
  sufficiently powerful server and adds remote node
  server software package.
• Turnkey or hardware/software solutions - fully
  configured remote node servers are compatible
  with existing network architectures and operating
  systems.

28
Communications Server Components, contd

• - LAN modems, also occasionally known as dial up
  servers, could be thought of as remote node
  server with one or more integrated modems.
• - Large-scale remote access servers (RAS) also
  known as Monster RAS are differentiated from
  previously mentioned RAS hardware by their
  scalability (number of modem ports),
  manageability, and security.

29
Communications Servers vs. Remote Node Servers
30
Dialing Out from LAN
31
Wireless LANs

• Wireless LANs do play role in overall objective
  of increasing worker productivity and customer
  satisfaction.
• Portable PCs equipped with wireless LAN adapters
  can create an instant LAN connection by getting
  within range server based wireless LAN adapter or
  wireless hub.

32
Wireless LANs, contd

• Meeting rooms equipped with wireless hubs to
  allow spontaneous workgroups to log into network
  resources without running cables all over meeting
  room.
• Wireless LAN technology allows LANs to be
  pre-configured at central site and shipped ready
  to run to remote sites.

33
Wireless LANs, contd

• Wireless LANs do offer significant flexibility
  and spontaneity not possible with traditional
  wire bound LANs. It is important to note that
  wireless LANs cannot match speed of their wired
  equivalent network architectures.

34
Reasons for Wireless Networks

• Mobile communication is needed.
• Communication must take place in terrain that
  makes wired communication difficult.
• Communication system must be deployed quickly.
• Communication facilities must be installed at low
  initial cost.
• Same information broadcast to many locations.

35
Reasons for Wireless Networks

• Mobile communication is needed.
• Communication must take place in a terrain that
  makes wired communication difficult or
  impossible.
• A communication system must be deployed quickly.
• Communication facilities must be installed at low
  initial cost.
• The same information must be broadcast to many
  locations.

36
Wireless LAN Standards - Software

• Remote control software, especially designed to
  allow remote PCs to take over control of local
  PCs, should not be confused with asynchronous
  communication software used for dial up
  connections to asynchronous host via modems.

37
Remote Control Software

• Taking over remote control of local PC is
  generally only available via remote control
  software.
• Remote control software allows keyboard of remote
  PC to control actions of local PC, with screen
  output being reflected on remote PCs screen.
• Guest (remote) Host (local).

38
Remote Node Software

• Windows NT RAS and NetWare Connect - examples of
  NOS specific remote node server software.
• Remote node server software packages include
  compatibility remote node client software.
• Problem - single remote node client needs to log
  into variety of different servers running variety
  of different network operating systems.

39
Remote Node Software, contd

• What is required is some sort of universal remote
  access client. Such remote clients are
  available. Those that support IPX are generally
  installable as either NetWare VLMs or NLMs.

40
Mobile-Aware Operating Systems

• Mobile computer user requires flexible computing
  functionality to support at least three possible
  distinct computing scenarios
• Stand alone computing on laptops
• Remote node or remote control computing to
  corporate headquarters.
• Synchronization of files and directories with
  desktop workstations at home or in corporate
  office.

41
Mobile-Aware OS, contd

• OS that are able to adapt to different computing
  modes with variety of included supporting
  accessory programs and utilities are referred to
  as mobile aware OS.

42
Mobile-Aware Operating Systems, contd

• Key functions offered by such mobile aware
  operating systems are
• Auto detection of multiple configurations
• Built in Multiprotocol remote node client
  Remote node client should support variety of
  network protocols
• Direct Cable Connotation Link to portable PC
  via direct connection through existing serial or
  parallel ports

43
Mobile-Aware Operating Systems, contd

• File transfer and file/directory synchronizations
  - Software utilities to synchronize files
  directories between either laptop and desktop or
  LAN server
• Deferred Printing
• Power Management 
• Infrared Connection

44
Mobile Aware Applications

• Coming slide shows Oracle Mobile Agents
  architectures adhere to overall
  client-agent-server architecture, compared to
  more common LAN based client/server architecture.
• Objective of architecture is to reduce amount of
  client to server network traffic by building as
  intelligence into server-based agent so that it
  can act on behalf of client application.

45
Mobile Aware Applications, contd

• Agent portion of client/agent/server architecture
  consists of three components
• Message manager - executes on mobile client and
  acts as an interface between client applications
  requesting services and wireless link over which
  requests must be forwarded.
• Message gateway - executes on local server or on
  dedicated UNIX or Windows workstation and acts as
  an interface between clients message manager and
  intelligent agent on local server

46
Mobile Aware Applications, contd

• Agent event manager - combined with customer
  written transaction handler to form an entity
  known as intelligent agent, which resides on
  local server acts on behalf of client in
  communications with local server until original
  client request is fulfilled

47
Client/Agent/Server Architecture Support
Mobile-Aware Applications
48
Mobile Middleware

• Goal of mobile middleware is to offer mobile
  users transparent client/server access
  independent of following variables
• Client or server platforms
• Applications
• Wireless transmission services.
• Coming slide illustrates basic components and
  interactions of mobile middleware

49
Mobile Middleware
50
Mobile Middleware, contd

• Primary purpose of mobile middleware is to
  consolidate client/sever traffic from multiple
  applications for transmission over variety of
  potential wireless transmission services.
• Overall transmission time and expense can be
  reduced

51
Mobile Middleware, contd

• Mobile middleware is an emerging category of
  software characterized by proprietary APIs and
  resultant lack of interoperability.
• Standardization efforts are currently underway in
  following areas
• Winsock2 Forum - developing standardized
  Winsock2 APIs for linking mobile middleware with
  Windows-based applications.

52
Mobile Middleware, contd

• PCC (Portable Computer and Communications
  Association) - developing standardized API for
  linking mobile middleware to variety of wireless
  transmission services.

53
OPTIMIZING REMOTE NODE AND REMOTE CONTROL
PERFORMANCE

• Opportunities to improve remote access and remote
  control performance
• V.90 modems
• Use ISDN services
• Use 16550 UARTs and matching serial port drivers
  transmits and receives data to and from PCs
  serial port

54
OPTIMIZING REMOTE NODE AND REMOTE CONTROL
PERFORMANCE

• Use data compression software/hardware
• Make sure remote control or remote node software
  being used supports screen catching, which allows
  only changes to screens rather than entire
  screens to be transmitted over limited bandwidth
  WAN links
• Network caching or LAN caching software

55
Mobile MIB

• Mobile MIB - capable of feeding configuration and
  location information to enterprise network
  management systems via SNMP.
• Key to design of mobile MIB was to balance amount
  of information required to effectively manage
  remote clients while taking into account limited
  bandwidth and expense of remote links over which
  management data must be transmitted.

56
Network Services

• Wireless WAN Services
• Circuit switched analog cellular
• CDPD (Cellular Digital Packet Data)
• Private packet radio
• Enhanced paging and two way messaging
• ESMR (Enhanced specialized mobile radio)
• Micro-cellular spread spectrum
• PCS (Personal Communications Services).

57
Network Services, contdTwo-Way Messaging

• Two-way messaging allows short text messages to
  be transmitted between relatively inexpensive
  transmission devices such as PDAs (Personal
  Digital Assistants) and alphanumeric pagers.

58
Wireless Personal Digital Assistants (PDAs)

• These devices are most often web enabled and are
  capable of accessing Internet.
• To deliver transparent wireless web-based
  services to users, combination of hardware
  devices, specialized protocols, and wireless
  middleware and services must be properly
  combined.
• Palm pilots, etc

59
Network Services, contdAnalog Cellular

• Transmitting data over analog cellular networks
  requires modems that support specialized cellular
  transmission protocols on both ends of cellular
  transmission to maximize throughput.
• Coming figure shows data transmission over
  circuit switched analog cellular network

60
Data Transmission over Circuit-Switched Analog
Cellular Network
61
Network Services, contdDigital
Cellular/Personal Communications Services

• Deliver variety of telecommunications services
  transparently to users at any time regardless of
  their geographic location.
• Premise of PCS is straightforward One person
  One phone number.
• Coming slide for basic elements of PCS

62
Digital Cellular/Personal Communications Services

• Key challenge for PCS is ability to maximize
  conversations over finite amount of bandwidth
• Methods being tested
• TDMA based digital cellular may be able to
  support three times transmission capacity of
  analog cellular.

63
Network Services, contdDigital
Cellular/Personal Communications Services

• CDMA transmits digitized voice packets from
  numerous calls at different frequencies spread
  all over entire allocated bandwidth spectrum
• Code is appended to each packet indicating which
  voice conversation it belongs
• See next slide

64
Maximizing Minimum Bandwidth TDMA and CDMA
65
Problems with Wireless Networks

• Operates in less controlled environment, more
  susceptible to interference, signal loss, noise,
  and eavesdropping.
• Wireless facilities have lower data rates than
  guided facilities.
• Frequencies can be more easily reused with guided
  media than with wireless media.

66
Mobile Telephony

• First Generation
• analog voice communication using frequency
  modulation.
• Second Generation
• digital techniques and time-division multiple
  access (TDMA) or code-division multiple access
  (CDMA)
• Third Generation
• evolving from second-generation wireless systems
• will integrate services into one set of standards.

67
Advanced Mobile Phone Service
68
AMPS Components

• Mobile Units
• contains modem that can switch between many
  frequencies
• 3 identification numbers electronic serial
  number, system ID number, mobile ID number
• Base Transceiver
• full-duplex communication with mobile
• Mobile Switching Center

69
Global System for Mobile Communication

• Developed to provide common 2nd-generation
  technology for Europe
• 200 million customers worldwide, almost 5 million
  in North America
• GSM transmission is encrypted
• Spectral allocation 25 MHz for base transmission
  (935960 MHz), 25 MHz for mobile transmission
  (890915 MHz)

70
GSM Layout
71
Multiple Access

• Four ways to divide spectrum among active users
• frequency-division multiplexing (FDM)
• time-division multiplexing (TDM)
• code-division multiplexing (CDM)
• space-division multiplexing (SDM)

72
Choice of Access Methods

• FDM, used in 1st generation systems, wastes
  spectrum
• Debate over TDMA vs CDMA for 2nd generation
• TDMA advocates argue there is more successful
  experience with TDMA.
• CDMA proponents argue that CDMA offers additional
  features as well, such as increased range.
• TDMA systems have achieved an early lead in
  actual implementations
• CDMA seems to be access method of choice for
  third-generation systems

73
Third Generation Systems

• Intended to provide provide high speed wireless
  communications for multimedia, data, and video
• Personal communications services (PCSs) and
  personal communication networks (PCNs) are
  objectives for third-generation wireless.
• Planned technology is digital using TDMA or CDMA
  to provide efficient spectrum use and high
  capacity

74
Wireless Application Protocol (WAP)

• Programming model based on WWW Programming Model
• Wireless Markup Language, adhering to XML
• Specification of small browser suitable for
  mobile, wireless terminal
• A lightweight communications protocol stack
• A framework for wireless telephony applications
  (WTAs)

75
WAP Programming Model
76
WAP Protocol Stack
77
Wireless Telephony ApplicationsA Sample
Configuration
78
Geostationary Satellites

• Circular orbit 35,838 km above earths surface
• rotates in equatorial plane of earth at exactly
  same angular speed as earth
• will remain above same spot on equator as earth
  rotates.

79
Advantages of Geostationary Orbits

• Satellite is stationary relative to earth, so no
  frequency changes due to relative motion of
  satellite and antennas on earth (Doppler effect).
  
• Tracking of satellite by its earth stations is
  simplified.
• One satellite can communicate with roughly fourth
  of earth three satellites separated by 120
  cover most of inhabited portions of entire earth
  excluding only areas near north and south poles

80
Problems withGeostationary Orbits

• Signal can weaken after traveling gt 35,000 km
• Polar regions and far northern and southern
  hemispheres are poorly served
• Even at speed of light, about 300,000 km/sec,
  delay in sending signal from point on equator
  beneath satellite 35,838 km to satellite and
  35,838 km back is substantial.

81
LEO and MEO Orbits

• Alternatives to geostationary orbits
• LEO Low earth orbiting
• MEO Medium earth orbiting

82
Satellite Orbits
83
Types of LEOs

• Little LEOs Intended to work at communication
  frequencies below 1 GHz using no more than 5 MHz
  of bandwidth and supporting data rates up to 10
  kbps
• Big LEOs Work at frequencies above 1 GHz and
  supporting data rates up to few megabits per
  second