Data Comm Concepts

1
Introduction


Necessary to connect LAN to LAN or WAN LAN to LAN
connections are often performed with bridge-like
device. LAN to WAN connections are usually
performed with router. Third device, switch, can
be used to interconnect segments of LAN.
2
Local Area Network Hardware

• Focus on hardware technology
• Transition from shared media network
  architectures to hardware based switched network
  architectures

3
Why Interconnect


To connect one division with another. To connect
two LANs with different protocols. To connect LAN
to Internet. To break LAN into segments to
relieve traffic congestion. To provide security
between different users.
4
LAN Requirements

• LAN requires following components 
• Central wiring concentrator (Hub)
• Media - cable or wireless
• NIC - internal or external
• Other switch, repeater, etc.
• NIC drivers - programs that interface between NIC
  and NOS.

5
LAN Architecture
6
Implications of LAN Technology Choices

• Choosing particular technology in one LAN
  technology category has significant
  implications/limitations on available technology
  choices in other LAN technology categories

7
Implications of LAN Technology Choices
8
Media Sharing vs. Switched

• Client/server systems and distributed computing
  has put increasing demands on LAN infrastructure
  with demands for amount of data traffic to be
  transferred
• One solution to bandwidth problem is to offer
  higher speed shared media network architectures

9
Media Sharing vs. Switched contd

• LAN switches resolve one at time limitation of
  shared-media LAN architectures by offering
  attached workstations access to switching matrix
  that provided point-to-point connections between
  any two ports.
• Each port on LAN switch is dedicated LAN segment
  with dedicated bandwidth

10
Media Sharing vs. Switched contd

• Limiting factor in switch-based LAN architecture
  is number of simultaneous point-to-point
  connections that switch can support.
• Coming slide contrasts differences in wiring
  center functionality between media sharing and
  switch based LAN architecture.

11
Switched LAN Architectures vs. Media-Sharing LAN
Architectures Wiring Center Functionality
12
Building Bandwidth Hierarchy with Switched LAN
Architecture
13
Workstation Connected to LAN


14


15
ADVANTAGES of SWITCHED LAN ARCHITECTURES

• Switched LAN architecture only change wiring
  center technology and manner in which
  workstations set up point to point communication
  to each other.
• Installing LAN switch is often easiest
  alternative chosen when network bandwidth demands
  exceed current supply.

16
Implementation Scenarios for Switched LAN
Architectures

• Stand-alone workgroup/departmental LAN switches
• Backbone attached workgroup/departmental LAN
  switches
• Backbone/data center switches
• Switches offer switched connectivity to other
  workgroup switches, media sharing hubs, and
  corporate servers that must be accessed by
  multiple departments/groups

17
Implementation Scenarios for Switched LAN
Architectures
18
Network Interface Card

• NIC - Physical link between client and server PC
  and media of network
• NIC have ability to adhere to access methodology
  (CSMA/CD or token passing) of network
  architecture
• Software rules, implemented by NIC, control
  access to shared network media and are known as
  media access control (MAC) protocols

19
Network Interface Card, contd

• NIC cards determine network architecture and
  constituent protocols more than any other
  component
• NIC act like mediator or translator
• Has demands of client/server PC
• Has network architecture with rules for accessing
  network media or LAN switch.

20
Technology Analysis

• Bus into which network adapter card allows
  different types of cards to be attached in
  pathway leading to CPU and RAM memory.
• PCI bus offers clocking signaling and low CPU
  utilization and seems to be bus of choice for
  high performance NICs.

21
Technology Analysis, contd

• Important choice related to bus architecture is
  that network adapter card chosen is compatible
  with installed bus and takes advantage of data
  transfer capability bus may offer.
• Key job of NIC is to transfer data between local
  PC and shared network media.

22
Technology Analysis, contd

• Hardware related network adapter characteristics
  that bare on data transfer efficiency are
• Amount of on board memory
• Processing power of onboard CPU contained on
  network adapter card

23
Technology Analysis, contd

• Coming figure summarizes NIC to PC memory data
  transfer techniques.
• Techniques are
• Programmed I/O
• Direct Memory Access (DMA)
• Shared memory
• Bus mastering DMA

24
Network Interface Cards Data Transfer Methods
25
Technology Analysis, contd

• Only bus mastering DMA data transfer technique
  leaves system CPU alone to process other
  applications
• In bus mastering DMA, CPU on network adapter card
  manages movement of data directly into PCs RAM
  without interrupting system CPU by taking control
  of PCs expansion bus

26
Technology Analysis, contd

• Bus mastering DMA on adapter cards requires
  expansion bus in PC to support being mastered
  by CPU on network adapter card.
• CPU and operating system must have capability to
  relinquish control of expansion bus for bus
  mastering network adapter cards to function
  correctly

27
Technology Analysis, contd

• NIC must be properly configured to interact
  successfully with that computer
• NIC configuration issues
• IRQ (Interrupt request) IRQ must not be used by
  other device and must be supported by NIC
• Base I/O port address defines memory location
  through which data will flow between NIC and CPU

28
Technology Analysis, contd

• Base Memory Address Some NICs require base
  memory address to indicate starting location in
  computers memory to be used by NIC as buffer
  memory

29
Technology Analysis, contd

• NIC must worry about hardware compatibility in
  two directions
• NIC must be compatible with expansion bus into
  which it will be inserted
• NIC must be compatible with media of network
  architecture
• Some NICs come with interfaces for more than one
  media type.
• Jumpers on NIC enable one media type or another

30
Ethernet Media Interfaces
31
Technology Analysis, contd

• Possible for NIC to be connected externally to PC
  via PCs parallel port
• USB NICs communicate with PC at speeds greater
  than 12 Mbps
• Actual USB performance depends on number of
  devices sharing bus

32
Network Interface Card Trends

• Dual speed cards 10/100 Ethernet cards feature
  auto sensing, automatically determine whether
  traffic is being transmitted and received at 10
  or 100 Mbps through single media interface card.
• Integrated or on board NICs Build Ethernet NIC
  onto motherboard
• Multiport NICS Ability of PCI bus allows
  multiport NICs to be manufactured on single card.

33
Network Interface Card Trends, contd

• On-NIC virus protection and security Some NICS
  now offer encryption, virus protection, or both
•  Integrated repeater modules allow up to seven
  additional devices to be cascaded from NIC and
  attached to network via single 10BaseT hub port.
•  Full duplex mode Some Ethernet NICs have full
  duplex capability that can be enabled.

34
Network Interface Card Trends, contd

•  Performance improvements Mfg of Ethernet NICs
  implemented fast packet forwarding technology
• Next packet of information is forwarded as soon
  as start of frame is detected rather than waiting
  for previous frame to be totally on network media
  before beginning transmission of next packet.

35
NIC Drivers

• Interoperability depends on compatibility between
  NIC and NOS installed in given computer, and is
  delivered by network interface card drivers
• It was to an adapter card vendor s advantage to
  ship drivers for as many operating systems as
  possible.

36
Approaches for NIC Drivers

• Supply drivers that could interact successfully
  with either NetBIOS or TCP/IP.
• Emulate adapter interface specifications of
  market leading network interface cards for which
  drivers are most commonly available.

37
Multiprotocol NIC Drivers

• By allowing adapter card vendors to develop one
  file called IPX.COM which was linked with Novell
  file called IPX.OBJ through process known as
  WSGEN, unique drivers could be more easily
  created and updated.

38
Network Driver Interface Specification (NDIS)

• NDIS - driver specification offering standard
  commands for communication between NDIS compliant
  NOS protocol stacks (NDIS protected driver) and
  NDIS compliant network adapter card drivers (NDIS
  MAC drivers).
• NDIS specifies binding operation managed by
  protocol manager
• NDIS specifies standard commands for
  communication between protocol manager program
  and protocol or MAC drivers.

39
Open Datalink Interface (ODI)

• ODI allows users to load several protocol stacks
  simultaneously for operation with single network
  adapter card and supports independent development
  with subsequent linking of protocol drivers and
  adapter drivers.

40
PCMCIA Drivers

• When NICs are PCMCIA based, two levels of driver
  software are required
• Drivers to interface to OS and NOS.
• Drivers to interface PCMCIA controller to PCMCIA
  card and on client software drivers.

41
PCMCIA Drivers, contd

• PCMCIA version 2.1 has Card and Socket Service
  (CSS) driver specifications.
• CSS is split into two logical sub layers
• 1. Card services sub layer is hardware
  independent and interfaces to NOS driver
  software.
• 2. Socket services sub layer is written
  specifically for type of PCMCIA controller
  included in laptop.

42
PCMCIA Drivers, contd

• If compatible card and socket service (CSS)
  drivers are not available for particular PC
  card/controller combination or if amount of
  memory CSS drivers requires is unacceptable, then
  lower level drivers known as direct enablers must
  be configured and installed.

43
LAN Wiring Centers

• Most common network physical topology employed
  today is star topology
• Token ring wiring centers are known as MAUs
  (Multistation Access Units)
• Wiring centers for other networks are known as
  hubs.
• Hubs and MAUs are multiport digital signal
  repeaters

44
Hubs

• Active central element of star layout.
• When single station transmits, hub repeats signal
  on outgoing line to each station.
• Physically star logically bus.
• Hubs can be cascaded in hierarchical
  configuration.

45
Types of Wiring Center Categories
46
Wiring Center Categories

• Wiring centers can be separated into three broad
  categories.
• 1. Stand-alone hubs - Offers limited number of
  ports of particular type of network architecture
  and media.
• 2. Stackable hubs - add expandability and
  manageability. Stackable hubs can be linked
  together to form one larger virtual hub of single
  type of network architecture and media.

47
Wiring Center Categories, contd

• 3. Enterprise hubs - modular by design and offer
  chassis based architecture to which variety of
  different modules can be inserted.

48
Major Categories of Hubs
49
Wiring Center Functional Comparison
50
Repeater

• Repeater - repeats each bit of digital data that
  it receives.
• Repeating action cleans up digital signal by
  retiming and regenerating signal before passing
  this repeated data from one attached device or
  LAN segment to next.

51
Hub

• Hubs - are subnet of repeaters that allow
  attachment of single devices rather than LAN
  segments to each hub port.
• Terms hub and concentrator or intelligent
  concentrator are often used interchangeably.

52
Hubs, contd

Hub interconnects two or more workstations into
local area network. When workstation transmits,
hub resends data frame out all connecting
links. Hub can be managed or unmanaged. managed
hub possesses enough processing power that it can
be managed from remote location.

53
Multistation Access Unit (MAU)

• MAU (Multistation Access Unit) is IBMs name for
  token ring hub.
• MAUs offer varying degrees of management
  capability.
• Active management MAUs send alerts to
  management consoles regarding malfunctioning
  token ring adapters and forcibly remove
  misbehaving adapters from ring.

54
Enterprise Hubs

• Hub allows concentrator to mix cards
• Cards could be added for connections with
  Ethernet modules, Token ring adapters, PCs,
  workstations with FDDI adapters, or dumb
  asynchronous terminals
• Additional modules available for some
  concentrators may allow data traffic to travel to
  other local LANs via bridge or router add-on
  modules

55
Enterprise Hubs, contd

• Local network traffic travels through single
  enterprise hub ideal location for security
  modules to be added for either encryption or
  authorization functionality

56
Hub Management

• Hub - ideal place for installation of management
  software to monitor and manage network traffic
• In stackable and enterprise hubs, two layers of
  management software may be found
• 1. Software is supplied by hub vendor. Allows
  monitoring and management of hub.
• 2. Hubs - capable of sharing MIS with enterprise
  network management systems.

57
Hub Management, contd

• Standards that govern network management
  communication is part of TCP/IP family of
  protocols, more correctly known as Internet suite
  of protocols.
• Network management information is formatted
  according to simple network management protocol
  (SNMP)

58
Standards-Based Network Management Communications
Protocols
59
LAN Switches

• LAN switch - seeks to overcome this one at time
  broadcast scheme, which can lead to data
  collisions, retransmissions, and reduced
  throughput between high bandwidth demanding
  devices
• Switched LAN Architectures vs. Media-Sharing LAN
  Architectures Wiring Center Functionality

60
LAN Switches, contd

• Many high-end LAN switches support ATM
  (Asynchronous Transfer Mode), which is type of
  switching that not only allow previously
  mentioned LAN architectures to be switched
  extremely quickly, but also allows similarly
  quick switching of voice, video, and image traffic

61
Switches, contd


Switch is combination of hub and bridge. It can
interconnect two or more workstations, but like
bridge, it observes traffic flow and learns. When
frame arrives at switch, switch examines
destination address and forwards frame out one
necessary connection.
62
Switches, contd

• Workstations that connect to hub are on shared
  segment.
• Workstations that connect to switch are on
  switched segment.

63


64
Switches, contd


Backplane of switch is fast enough to support
multiple data transfers at one time. Switch that
employs cut-through architecture is passing on
frame before entire frame has arrived at switch.
65
Switches, contd

• Multiple workstations connected to switch use
  dedicated segments. Very efficient way to
  isolate heavy users from network.
• Switch can allow simultaneous access to multiple
  servers, or multiple simultaneous connections to
  single server.

66


67


68


69


70
Full Duplex Switches


Full duplex switch allows for simultaneous
transmission and reception of data to and from
workstation. Full duplex connection helps to
eliminate collisions. To support full duplex
connection to switch, two sets of wires are
necessary - one for receive operation and one for
transmit operation.
71


72
Types of Switches Cut Through Switch

• Cut through switches - read only address
  information in MAC layer head before beginning
  processing.
• After reading destination address, switch
  consults an address look up table to determine
  which port on switch this frame should be
  forwarded to.
• Once address look up is completed, point-to-point
  connection is created and frame is immediately
  forwarded.

73
Types of Switches- Store and Forward

• Store and Forward switches read entire frame
  into shared memory area in switch.
• Contents of transmitted Frame Check Sequence
  (FCS) field is read and compared to locally
  recalculated frame check sequence.
• If results match, switch consults address look up
  table, builds appropriate point-to-point
  connection, and forwards frame.

74
Types of Switches- Error free cut through
switches

• Error free cut through switches read both
  addresses and frame check sequences for every
  frame.
• Frames are forwarded immediately to destination
  nodes in an identical fashion to cut through
  switches.

75
Types of Switches - Error free cut through
switches, contd

• Should bad frames be forwarded, error free cut
  through switch is able to reconfigure those
  individual ports producing bad frames to use
  store and forward switching.
• As errors diminish to preset thresholds, port is
  set back to cut through switching for higher
  performance throughput.

76
Ethernet Hubs and Switches

• Shared medium hubs
• Switched LAN hubs

x
77
Advantages of Switched Hubs

• No modifications needed to workstations when
  replacing shared-medium hub
• Each device has dedicated capacity equivalent to
  entire LAN
• Easy to attach additional devices to network

78
Types of Switched Hubs

• Store and forward switch
• Accepts frame on input line
• Buffers it briefly
• Routes it to appropriate output line
• Cut-through switch
• Begins repeating frame as soon as it recognizes
  destination MAC address
• Higher throughput, increased chance of error

79
Layer 3 Switches

• Problems With Layer 2 Switches
• Broadcast overload
• Lack of multiple links
• Can be solved with subnetworks connected by
  routers
• Layer 3 switches implement packet-forwarding
  logic of router in hardware.

80
More on Switches

• Circuit-switched
• Packet-switched

81
Circuit-Switching

• Definition Communication in which dedicated
  communications path is established between two
  devices through one or more intermediate
  switching nodes
• Dominant in both voice and data communications
  today
• e.g. PSTN is circuit-switched network
• Relatively inefficient (100 dedication even
  without 100 utilization)

82
Circuit-Switching Stages

• Circuit establishment
• Transfer of information
• point-to-point from endpoints to node
• internal switching/multiplexing among nodes
• Circuit disconnect

83
Circuit Establishment

• Station requests connection from node
• Node determines best route, sends message to next
  link
• Each subsequent node continues establishment of
  path
• Once nodes have established connection, test
  message is sent to determine if receiver is
  ready/able to accept message

84
Information Transfer

• Point-to-point transfer from source to node
• Internal switching and multiplexed transfer from
  node to node
• Point-to-point transfer from node to receiver
• Usually full-duplex connection throughout

85
Circuit Disconnect

• When transfer is complete, one station initiates
  termination
• Signals must be propagated to all nodes used in
  transit in order to free up resources

86
Public Switched Telephone Network (PSTN)

• Subscribers
• Local loop
• Connects subscriber to local telco exchange
• Exchanges
• Telco switching centers
• Also known as end office

• Trunks
• Connections between exchanges
• Carry multiple voice circuits using FDM or
  synchronous TDM
• Managed by IXCs (inter-exchange carriers)

87
Digital Circuit-Switching Node
88
Circuit Switching NodeDigital Switch

• Provides transparent signal path between any pair
  of attached devices
• Typically full-duplex

89
Circuit-Switching NodeNetwork Interface

• Provides hardware and functions to connect
  digital devices to switch
• Analog devices can be connected if interface
  includes CODEC functions
• Typically full-duplex

90
Circuit-Switching NodeControl Unit

• Establishes on-demand connections
• Maintains connection while needed
• Breaks down connection on completion

91
Blocking/Nonblocking Networks

• Blocking network is unable to connect two
  stations because all possible paths are already
  in use
• Nonblocking permits all possible connection
  requests because any two stations can be connected

92
Switching Techniques

• Space-Division Switching
• Developed for analog environment, but has been
  carried over into digital communication
• Requires separate physical paths for each signal
  connection

• Time-Division Switching
• Used in digital transmission
• Utilizes multiplexing to place all signals onto
  common transmission path
• Bus must have higher data rate than individual
  I/O lines

93
Routing in Circuit-Switched Networks

• Requires balancing efficiency and resiliency
• Traditional circuit-switched model is
  hierarchical, sometimes supplemented with
  peer-to-peer trunks
• Newer circuit-switched networks are dynamically
  routed all nodes are peer-to-peer, making
  routing more complex

94
Alternate Routing

• Possible routes between two end offices are
  predefined
• Originating switch selects best route for each
  call
• Routing paths can be fixed (1 route) or dynamic
  (multiple routes, selected based on current and
  historical traffic)

95
Control Signaling

• Manage establishment, maintenance, and
  termination of signal paths
• Includes signaling from subscriber to network,
  and signals within network
• In-channel signaling uses same channel for
  control signals and calls
• Common-channel signaling uses independent
  channels for controls (SS7)

96
ISDN

• 1st generation narrowband ISDN
• Basic Rate Interface (BRI)
• Two 64Kbps bearer channels 16Kbps data channel
  (2BD) 144 Kbps
• Circuit-switched
• 2nd generation broadband ISDN (B-ISDN)
• Primary Rate Interface (PRI)
• Twenty-three 64Kbps bearer channels 64 data
  channel (23BD) 1.536 Mbps
• Packet-switched network
• Development effort led to ATM/cell relay

97
Packet-Switching Networks

• Includes X.25, ISDN, ATM and frame-relay
  technologies
• Data is broken into packets, each of which can be
  routed separately
• Advantages better line efficiency, signals can
  always be routed, prioritization option
• Disadvantages transmission delay in nodes,
  variable delays can cause jitter, extra overhead
  for packet addresses

98
Packet-Switching Techniques

• Datagram
• each packet treated independently and referred to
  as datagram
• packets may take different routes, arrive out of
  sequence
• Virtual Circuit
• preplanned route established for all packets
• similar to circuit switching, but circuit is not
  dedicated

99
Packet-Switched Routing

• Adaptive routing changes based on network
  conditions
• Factors influencing routing are failure and
  congestion
• Nodes must exchange information on network status
• Tradeoff between quality and amount of overhead

100
Packet-Switched Congestion Control

• When line utilization is gt80, queue length grows
  too quickly
• Congestion control limits queue length to avoid
  throughput problems
• Status information exchanged among nodes
• Control signals regulate data flow using
  interface protocols (usually X.25)

101
X.25 Interface Standard

• ITU-T standard for interface between host and
  packet-switched network
• Physical level handles physical connection
  between host and link to node
• Technically X.21, but other standards can be
  substituted, including RS-232
• Link level provides for reliable data transfer
• Uses LAPB, which is subset of HDLC
• Packet level provides virtual circuits between
  subscribers

102
Virtual-Circuit Service

• External virtual circuit logical connection
  between two stations on network
• Internal virtual circuit specific preplanned
  route through network
• X.25 usually has 11 relationship between
  external and internal circuits
• In some cases, X.25 can be implemented as
  packet-switched network

103
Bridges

• Allow connections between LANs and WANs
• Operates at Layer 2 (Data Link Layer) of OSI
• Used between networks using identical physical
  and link layer protocols
• Provide number of advantages
• Reliability Creates self-contained units
• Performance Less contention
• Security Not all data broadcast to all users
• Geography Allows long-distance links

104
Bridge Functions

• Read all frames from each network
• Accept frames from sender on one network that are
  addressed to receiver on other network
• Retransmit frames from sender using MAC protocol
  for receiver
• Must have some routing information stored in
  order to know which frames to pass

105
Bridges


Bridge (or bridge-like device) can be used to
connect two similar LANs, such as two CSMA/CD
LANs. Bridge can connect two closely similar
LANs, such as CSMA/CD LAN and token ring LAN.
106
Bridges, contd

• Bridge examines destination address in frame and
  either forwards this frame onto next LAN or does
  not.
• Bridge examines source address in frame and
  places this address in routing table, to be used
  for future routing decisions.

107
Bridge Interconnecting


108
Bridge Similar LANs


109
Bridge Operation
110
Transparent Bridges


Transparent bridge does not need programming but
observes all traffic and builds routing tables
from this observation. This observation is called
backward learning. Each bridge has two
connections (ports) and there is routing table
associated with each port.
111
Transparent Bridges, contd

• Bridge observes each frame that arrives at port,
  extracts source address from frame, and places
  that address in ports routing table.
• Transparent bridge is CSMA/CD LANs.

112
Bridge CSMA/CD LANs


113
Transparent Bridge


Transparent bridge can also convert one frame
format to another. Note that some
people/manufacturers call bridge such as this
gateway or sometimes router. Bridge removes
headers and trailers from one frame format and
inserts (encapsulates) headers and trailers for
second frame format.
114
Data Frame CSMA/CD to Token


115
Source-Routing Bridge

Source-routing bridge used with token ring
networks. Source-routing bridges do not learn
from watching tables. When workstation wants to
send frame, it must know exact path of network /
bridge

116
Source-Routing Bridge, contd

• If workstation does not know exact path, it sends
  out discovery frame.
• Discovery frame makes its way to final
  destination, as it returns, it records path.

117


118
Remote Bridge

Remote bridge is capable of passing data frame
from LAN to LAN when LANs are separated by long
distance and there is WAN connecting two
LANs. Remote bridge takes frame before it leaves
first LAN and encapsulates WAN headers and
trailers. When packet arrives at destination
remote bridge, bridge removes WAN headers and
trailers leaving original frame.

119
LAN with Frame Relay Network


120
Routers


Device that connects LAN to WAN or WAN to
WAN. Router accepts an outgoing packet, removes
any LAN headers and trailers, and encapsulates
necessary WAN headers and trailers.
121
Routers, contd


Because router has to make WAN routing decisions,
router has to dig down into network layer of
packet to retrieve network destination
address. Routers operate at third layer, or OSI
network layer, of packet. Routers often
incorporate firewall functions.
122
Asynchronous Transfer Mode

• Connection oriented switched transmission
  methodology
• ATM characteristics is capability of delivering
  variety of traffic over both local and wide area
  networks
• ATM has fixed length 53-byte cell
• Uniform length allows timed, dependable delivery
  for streaming traffic (voice, video), and
  simplifies troubleshooting, administration,
  setup, and design

123
Migration Strategies to ATM

• IP over ATM Known as classical IP, adapts CP/IP
  protocol stack to employ ATM services as native
  transport protocol directly
• LAN emulation - allows all current upper layer
  LAN protocols to be transported by ATM services
  in an unmodified fashion. Provides translation
  between ATM addressing scheme and scheme native
  to particular emulated LAN.

124
Migration Strategies to ATM, contd

• Multi-Protocol Over ATM (MPOA), provides support
  for multiple local area network protocols running
  on top of ATM cell switched network

125
ATM Implementation