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Title: MSc WLAN, IP/TCP and COMM NETWORK Topics


1
MSc WLAN, IP/TCP and COMM NETWORKTopics
By Prof R A Carrasco School of Electrical
,Electronic and Computer Engineering University
of Newcastle Upon Tyne

r.carrasco_at_ncl.ac.uk Ext 7332
2
MSc WLAN, IP/TCP and COMM NETWORK
  • References
  • 1 Tanenbaum, Andrew S., Computer Networks,
    Fourth Edition ed Pearson Education
    International, 2003, ISBN 0-13-038488-7.
  • 2 Comer, Douglas E, Computer Networks and
    Internets with Internet Applications, Third
    Edition ed Prentice Hall, 2001, ISBN
    0-13-091449-5.
  • 3 Peterson, Larry L. Davie, Bruce S.,
    Computer Networks, A Systems Approach Morgan
    Kaufman Publishers, 2000, ISBN 1-55860-577-0.
  • 4 Halsall, Fred, Data Communications, Computer
    Networks and Open Systems Adison-Wesley
    Publishing, 1995, ISBN 0-201-42293-X

3
Internet and Protocols
  • Advanced Research Projects Agency Network
    (ARPAnet), 1969.
  • The protocols in the TCP/IP suite either use
    transport control protocols (TCP) or
  • user datagram protocol (UDP) as the transport
    protocol.
  • Low level functions such as File Transfer
    Protocol (FTP), the Internet Terminal
  • Protocol (TELNET) and Electronic Mail (E-Mail),
    remote logon.
  • IP is responsible for moving packets of data
    from node to node. IP forwards each
  • packet based on a four byte destination address
    (the IP number), different
  • organisation, IP operates on a gateway machine.
  • TCP is responsible for verifying the correct
    delivery of data from client to server.
  • TCP adds support to detect errors or lost data
    to trigger retransmission until the
  • data is correctly and completely received.
  • Sockets is a name given to the package of
    subroutines that provide access to
  • TCP/IP on most systems

4
  • The Internet Protocol was developed to create a
    Network of Networks (the
  • Internet). Individual machines are first
    connected to a LAN (Ethernet or Token
  • Ring). TCP/IP shares the LAN with other users.
    One device provides the TCP/IP
  • connection between the LAN and the rest of the
    World.
  • A Network consisting of two or more far-apart
    LANs is a Wide Area Network (WAN)
  • Typical Network consisting of Switches, Hubs and
    Routers are intermediary
  • devices between clients and servers

5
The Network Layer in the Internet
  • The Internet can be viewed as a collection of
    sub-networks or autonomous systems (AS) that are
    connected together
  • There is not real structure, but several major
    backbones exist
  • These are constructed from high-bandwidth lines
    and fast routers
  • Attached to the backbones are regional networks,
    and attached to these regional networks are LANs
    (Universities, companies etc.)
  • The glue that holds the Internet together is the
    network layer protocol, IP

6
The Network Layer in the Internet
  • The Internet transmits data by packet switching
    using a standardised Internet Protocol (IP)
  • IP Datagram
  • The header has a 20-byte fixed part and a
    variable length optional part
  • It is transmitted in big edian order from left to
    right with higher-order bit of the version field
    going first

7
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8
Ethernet hub is a device for connecting multiple
twisted pair or fibre Ethernet devices together.
9
Ethernet bridge connects multiple network
segments at the data link layer ( layer 2 ) of
the OSI model.
http//netbook.cs.purdue.edu/anmtions/anim09_2.htm
10
A router is a computer networking device that
forwards data across networks towards their
destination, through a process known as routing.
http//netbook.cs.purdue.edu/anmtions/anim09_3.htm
11
Modem is a device that modulates an analogue
carrier signal to encode digital information and
also demodulate such a carrier signal to decode
the transmitted information.
12
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13
Popular Wired LAN Standards
  • High-Level Data Link Control (HDLC)
  • Ethernet (IEEE 802.3)
  • Token Bus (IEEE 802.4)
  • Token Ring (IEEE 802.5)

14
HIGH LEVEL DATA LINK CONTROL
15
HIGH LEVEL DATA LINK CONTROL(2)
  • Control Field of
  • An information frame
  • A supervisory frame
  • An unnumbered frame

16
PPP- Point to Point Protocol
Bytes
17
Ethernet (IEEE 802.3)
  • Bus Topology
  • Carrier Sense Multiple Access with Collision
    Detection (CSMA/CD)
  • 10 Bases denoting 10 Mbit/s

http//netbook.cs.purdue.edu/anmtions/anim06_1.htm
18
Ethernet (IEEE 802.3)
19
Ethernet (IEEE 802.3)
  • PR Preamble
  • SFD Start Frame Data
  • DA Destination Address
  • SA Source Address
  • TYPE Type of data
  • FCS Frame Checksum

20
CSMA/CD MAC Protocol
  • Station checks if there is data being currently
    transmitted (carrier sense)
  • If no data is present, station begins to transmit
    data
  • If two or more stations begin this process
    simultaneously, there will be a collision of
    frames
  • Station monitors its own receiver output and
    compares with transmitted signal to detect when
    this occurs (collision detection)

http//netbook.cs.purdue.edu/anmtions/anim06_2.htm
http//netbook.cs.purdue.edu/anmtions/anim06_5.htm
21
CSMA/CD MAC Protocol
  • If a collision is detected, the station aborts
    the transmission and sends a jamming signal to
    inform all other stations that a collision has
    occurred
  • Transmitting stations that have caused the
    collision wait a randomly generated time interval
    before reattempting to transmit
  • This avoids step-lock in terms of retransmission
    causing repeated collisions

22
Capacity Calculations
A
B
?
delay
23
Capacity Calculations
The maximum propagation delay to frame length
ratio
a ? / T
The figure above allows a new frame to be
transmitted immediately following the previous
one, giving a frame rate of 1/T frames/sec
24
Capacity Calculations
  • If, on average K retries are necessary before the
    next frame can be transmitted (in a lightly
    loaded network k0), then the average time for
    transmitting one frame, tv, is given by
  • tv T ? 2?K
  • T ?(1 2K)
  • T 1 ?/T(1 2K) T1 a(12K)

Where a?/T
25
Capacity Calculations
  • The utilisation factor, U, of the transmission
    medium is given by
  • U T/tv 1/(1a(12k))
  • Let Pt be the probability constant for all
    stations over all time that any particular
    station wishes to transmit at the end of a
    specific 2? collision detection interval
  • Pt 2 ?? ,(where ? is the rate of packets/s)

26
Capacity Calculations
  • For a successful event, one station transmits,
    but n-1 stations do not
  • The probability of n successful transmissions p
    is therefore given by
  • p nPt(1 - Pt)n-1
  • It can be shown by differentiating p with respect
    to Pt that the maximum value of the probability
    Pt is
  • Pt 1/n

Where n is the number of stations
27
Capacity Calculations
  • Consequently the maximum value of p is given by
  • pmax n ? 1/n(1 1/n)n-1 (1 1/n) n-1
  • If n?8 then pmax ? 1/e where e 2.718
  • At the end of a 2? collision detection interval,
    a further collision occurs with probability 1-p,
    while a successful transmission occurs with
    probability P
  • Thus, a sequence of K collision intervals
    occupying a time 2?K sec, occurs with
    probability
  • P (k) p(1-p)K-1 at least one collision
    occurring

28
Capacity Calculations
  • The average number of collisions is therefore
    given by
  • k S?k1 kp(k) S?k1 kp(1-p) k-1
  • From this it can be proven that k1/p, and we
    obtain the limiting utilisation
  • U T/tv 1/(1a(12k))
  • Umax 1 / (1a(12?2.718)) 1/(16.44a)

29
Utilisation with different values for the a
parameter
a
a
30
Ethernet OPNET Simulation
  • Ethernet with 30 nodes is connected via coaxial
    link in a bus topology
  • The bus is operating at 10Mbps
  • collision detection interval 2?51.2µsec, data
    frame length 1024 bytes

31
Network Snapshot
32
Utilization vs. Traffic Load
33
Ethernet Exercises
  • Problem A certain Ethernet system has a maximum
    bus delay of 16 µsec, and operates with a bit
    rate of 10 Mbit/sec. Each frame is 576 bits in
    length. Determine the maximum utilisation factor
    of the medium under collision conditions
  • For the system above, calculate the actual
    capacity if there are 15 active stations, each
    with an equal amount of data to transmit

34
Token Ring (IEEE 802.5)
http//netbook.cs.purdue.edu/anmtions/anim06_4.htm
35
Token Ring Frame Structures
  • SD Start Delimited (1 octet)
  • AC Access Control (1 octet)
  • FC Frame Control (1 octet)
  • DA Destination Address (2/6)
  • FCS Frame Check (4)
  • ED End Delimiter (1)
  • FS Frame Status (1)

36
Token Ring
37
Token Ring
A removes the data frame
A generates data frame for station A
Busy Token
Free Token
38
Capacity Calculations
  • Empty Ring
  • C Capacity (bits/sec)
  • ? Propagation time around ring
  • N Number of stations
  • L Delay of L bits in each station on the ring
    (station latency)

39
Capacity Calculations
  • The ring latency is given by
  • TL ? (NL)/C
  • The free token is 24 bits (3 bytes) in length,
    thus the maximum waiting time, if no other
    station is transmitting, is given by
  • Tmax,empty (24/C TL)

40
Capacity Calculations
  • Full Ring
  • Consider a full ring, where all stations have
    data to transmit
  • Each station can only transmit when it has the
    token
  • If each frame is limited to M bytes, the
    transmission time is
  • T 8M/C
  • The maximum waiting time is
  • Tmax, Full (N-1)(TTL)

41
Capacity Calculations
  • Exercise
  • A 4Mbit/s ring has 50 stations, each with a
    latency of 2 bits, the total length of the ring
    is 2km, and the propagation delay of the cable is
    5µs/km
  • Determine the maximum waiting time when the ring
    is empty, and when all stations are transmitting.
    A full frame is 64 bytes in length

42
Capacity Calculations
  • Loaded Ring
  • Traffic load of ?i frame/sec
  • T Time when transmitted on the ring for each
    frame
  • Tc time interval elapsed before the free token
    arrives
  • ti ?iTcT

43
Capacity Calculations
  • The maximum waiting time experienced by every
    station on the ring Tc is given by
  • Tc TL SNi1 ti TL tc ?T
  • Where ? SNi1 ?i
  • Here the parameter ? represents the gross input
    to the ring in frame/sec
  • Tc/TL 1 / (1-U) and U ?T

44
Token Ring OPNET Simulation
45
Token Ring Parameters
46
Single Station
  • Only one station has data to transmit
  • MSDU size 1024 bytes
  • Test under different Token Holding Timer (THT)
    values, which specifies the maximum amount of
    time a token ring MAC may use the token before
    releasing it.

47
Utilization vs. THT Duration
48
Full Ring
  • All stations have data to transmit
  • Each station can only transmit when it has the
    token
  • MSDU size 1024 bytes

49
Utilization vs. THT Duration
50
Tutorial Network Systems and Technologies by
Professor R. A. Carrasco
  • 1)      Describe the basic differences between a
    wide area network and a local area network in
    terms of
  • a)      Structure
  • b)      Operation
  •  
  • 2)      The techniques of passing information
    from node to node across a broadcast network
    differ according to the type of configuration
    employed.
  • Compare the methods used for bus and ring
    networks.
  •  
  • 3)      a) What is a baseband LAN?
  •     What is a broadband LAN?
  • b) What are the advantages of using a star ring
    architecture in a computer network? What are its
    disadvantages?
  •  
  • 4)      Describe the effects of a complete
    failure of a node in the operation of the
    following network configurations
  • a bus
  • a ring
  • a star
  •  
  • 5)      List the seven layers of the CCITT ISO
    architecture for network communications.
  • a)      Describe their function and justify the
    existence of each one.
  • b)      Which layers are essential to LAN
    communications and why?

51
  • 6)      Assuming HDLC protocol
  • a)      Distinguish between the normal response
    mode and the asynchronous mode of working. How
    are they defined in the HDLC frame structure?
  • b)      How is flow control achieved through this
    frame structure?
  •  
  • 7)      Describe the function of the logical link
    control and medium access control layers as
    defined in the IEEE 802 standards and indicate
    their relationship with the lower protocol layers
    in the ISO seven-layer reference model.
  •  
  • 8)      a) Describe the basic differences
    between circuit switching, message switching and
    packet switching.
  • b) Give examples of each switching technique.
    Advantages and disadvantages of switching 
    techniques.
  • c) For packet switching technique give an
    example. How will the network handle stream of
    packets?
  •  
  • 9)      i) Discuss IEEE 802 standards and frame
    format for CSMA/CD, token bus, token ring, 802.2
    (logical link control), 802.3, 802.4 and 802.5
    standards.
  • ii) Briefly discuss the comparison of 802.3,
    802.4 and 802.5 standards.
  •  
  • 10)  Imagine two LAN bridges, both connecting a
    pair of 802.4 networks. The first bridge is faced
    with 1000 512-byte frames per second that must
    be forwarded. The second is faced with 200
    4096-byte frames per second. Which bridge do you
    think will need the faster CPU? Discuss.
  •  
  • 11)  Suppose that the two bridges of the previous
    problem each connected an 802.4 LAN to an 802.5
    LAN. Would that change have any influence on the
    previous answer?
  •  

52
  • 12)  A bridge between an 802.3 LAN and an 802.4
    LAN has a problem with intermittent memory
    errors. Can this problem cause undetected errors
    with transmitted frames, or will these all be
    caught by the frame checksums?
  •  
  • 13)  A large FDDI ring has 100 stations and a
    token rotation time of 40 msec. The token holding
    time is 10 msec. What is the maximum achievable
    efficiency of the ring?

53
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54
  • The Internet uses almost exclusively TCP for
    layer 4 and IP for layer 3
  • Clients and servers typically implement all of
    the seven OSI layers whilst
  • hubs and switches are only aware of MAC
    addresses
  • Routers are aware of network address (IP
    addresses), a layer 3 switch is really
  • a fast router
  • Routing protocols differ from routed protocols
    since they dynamically determine
  • routing and the route taken by one packet can
    be different to that of another
  • packet taking place in the same transaction.
  • Transmission Control Protocol (TCP) is a
    transport layer protocol layered on top
  • of IP and below the application layer SMTP,
    Telnet, FTP, HTTP(web) etc.

55
  • Transmission Control Protocol (TCP)
  • (RFC 793)
  • Van Jacobsons algorithm
  • Karns algorithm
  • Nagles Algorithm

56
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57
IEEE 802.x, TCP/IP and ISO/OSIArchitecture
Comparison
IEEE 802.x
58
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59
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60
IP
  • The IP is the internetworking protocol that
    offers a service with the following
    characteristics
  • It is connectionless, so units of network layer
    data protocol ,denominated datagram in the IP
    context, are dealt with in an individual way from
    the source host up to the destination host
  • It is not reliable. The data-grams can be lost,
    duplicated, or disordered, and the network does
    not detect or report this problem

http//netbook.cs.purdue.edu/anmtions/anim17_1.htm
61
IP OPNET Simulation
IP Cloud Model Packet Discard Ratio
1.0 Packet Latency (secs) Exponential (0.5)
62
Results
63
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64
IP Header format
  • The version field keeps track of which version of
    the protocol the datagram belongs to.
  • Hlen is provided to tell how long the header is
    in 32-bit words
  • The type of service field allows the host to tell
    the subnet what kind of service it wants. Various
    combinations of reliability and speed are
    possible. The three flag bits allow the host to
    specify what it cares most about from the net
    delay, throughput, reliability
  • The total length includes everything in the
    datagram both header and data

65
IP Header Format
  • The identification field is needed to allow the
    destination host to determine which datagram a
    newly arrived fragment belongs to. All the
    fragments of a datagram contain the same
    identification value
  • DF Dont Fragment
  • MF More Fragment
  • The fragment offset tells where in the current
    datagram this fragment belongs
  • The time to live field is a counter used to limit
    packet lifetimes
  • The protocol field tells it which transport
    process to give it to, TCP, UDP and some others

66
IP Header Format
  • The header checksum verifies the header only.
    Checksum is useful to detecting errors generated
    by bad memory words inside a router
  • The source address and destination address
    indicate the network number and host numbers
  • The option field was designed to provide an
    escape to allow subsequent version of the
    protocol to include information not present in
    the original design

Option
Description
Security
Specifies how secret the datagram is
Strict source routing
Gives the complete path to be followed
Loose source routing Record route Timestamp
Gives a list of routers not to be missed Makes
each router append its IP address Makes each
router append its address and timestamp
67
Fragmentation
  • The IP-level datagram must be encapsulated in a
    lower network level packet to travel in the
    network
  • The rules for the fragmentation are as follows
  • The size of the resulting fragments must be a
    multiple of an octet so that the data
    displacement records, offset, within the datagram
    are done correctly
  • The size of the fragments are freely chosen
  • The gateway must accept datagram with a greater
    size than that of the network they are connected
    to. This is so larger datagram can be admitted to
    the network
  • The host and gateways must handle datagram larger
    than 576 octets

68
http//netbook.cs.purdue.edu/anmtions/anim16_1.htm
69
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73
ARP Address Resolution Protocol
  • The IP packet are sent encapsulated in LAN or WAN
    frame such as Ethernet, token ring or ATM
  • Q. How does the host needs to know the correct
    Ethernet destination address to put in the frame?
  • EtherDes EtherSour length IP header Payload
  • A. It uses ARP to map from the IP destination
    address to the Ethernet destination address

http//netbook.cs.purdue.edu/anmtions/anim15_1.htm
74
ARP cont
  • The host broadcasts an APR request packet which
    contains the IP address of the required station
  • The station which has that IP address replies
    directly (unicast) returning the correct IP
    address
  • Now the IP packet can be sent directly to the
    correct Ethernet address

75
Reverse Address Resolution Protocol (RARP)
  • Allows a station to determine its IP address from
    its hardware address
  • A server can be configured to respond to RARP
    request automatically allocating IP address
    across the network
  • Not used much nowadays, replaced instead by more
    powerful auto configuration protocols such as
    DHCP (Dynamic Host Configuration Protocol)

76
Dynamic Host Configuration Protocol DHCP
  • Allows a client to be configured automatically
    over the network.
  • Means that machines do not have to have
    configured by hand
  • New machines can be added to the IP network more
    easily
  • Less chance of error (for example duplicate IP
    addresses being configured)

77
Domain Name Service DNS
  • IP addresses are very difficult to remember
  • DNS translates easier to remember text names
    www.soc.ncl.ac.uk
  • into IP address 128.10.20.30
  • When a host requires a domain name translation it
    makes the request to its local Domain Name Server

78
Domain Naming
  • Each name in DNS can be split up a series of
    domains
  • E.g. www.soc.ncl.ac.uk
  • ukdomain of the UK
  • ac.uk academic domain within the UK
  • ncl.ac.ukNewcastle University domain within UK
    academic
  • soc.ncl.ac.uk School of computing domain within
    Newcastle University within UK academic

79
Domain Name Servers
  • Each domain name server is responsible domain
  • The first request will go to the server which is
    the local machine domain
  • DNS server can react in 3 different way
  • -DIRECT just send back the correct IP
    address
  • -RECURSIVE if it doesnt know the IP address make
    a request to another DNS server for the IP
    address then send back the IP address
  • -INDIRECT send back the IP address of another DNS
    server

80
  • The change from IPv4 to IPv6 falls primarily
    into the following categories
  • Expanded Addressing Capabilities
  • IP address size from 32 bits to 128
  • Header format simplification
  • Improved support for extensions and options
  • Flow labelling capability
  • Authentication and privacy capabilities

81
IPv6 extension headers
82
Order of extension headers for IPv6
83
Option header formats
Hop-by-hop extension IPv6 options header
Routing Extension IPv6 header
84
Routing type 0 header
85
Fragment extension IPv6 header
TCP and UDP pseudo-header for IPv6
86
TCP Transmission Control Protocol
  • Services
  • -Guarantees end to end delivering of packets
  • -Control the flow of data from host to host and
    host into the network
  • -Multiplexing, the TCP header has a port number
    which is used to determine which application
    should receive the packet

http//netbook.cs.purdue.edu/anmtions/anim20_1.htm
87
TCP Datagram Format, RFC 793
88
TCP Client Ports
  • Q. If you have a computer running an e-mail
    package, 2 web browsers (e.g. Netscape and IE)
    how does the compute know when a TCP/IP packet
    arrives which application should receive the
    packet?
  • A. Each application sets up its connection using
    a different port number, when the replies come
    back from the server the port number is used to
    send the packet to the current connection.

89
TCP SERVER PORTS
  • The server must respond to client requests
  • Q. How does the client know which port to send
    its request to?
  • A. Well known port numbers are assigned to
    particular services

90
TCP Error control
  • The acknowledgment (ack) and sequence number
    fields are used to guarantee delivery of packets
    to the destination
  • For each packet sent out an ack must be sent
    back.
  • If no ack is sent back within a certain time the
    packet is sent again.
  • Each new packet to be transmitted is allocated a
    new sequence no. the returning ack no. informs
    the sender of the next expected sequence no.
  • The sequence no. is used to keep the packets in
    order

http//netbook.cs.purdue.edu/anmtions/anim20_5.htm
91
TCP flow control
  • The window size field is used by the receiver to
    control the flow of packets from the sender.
  • If the receiver sets the window size to 400 the
    sender is only allowed to send 400 bytes before
    stopping.
  • The receiver can stop the sender by setting the
    window size to 0

http//netbook.cs.purdue.edu/anmtions/anim20_3.htm
http//netbook.cs.purdue.edu/anmtions/anim20_3.htm
92
TCP congestion control
  • TCP uses a slow start algorithm to initially
    limit a new connections bandwidth.
  • This is so that the connection does not overload
    the network infrastructure
  • TCP increases the flow of data into the network
    until an ack timeout occurs it will then cut back

93
TCP OPNET Simulation
A packet loss
A packet loss
TCP Reno (Fast recovery)
TCP Tahoe
94
UDP User Datagram Protocol
  • Services
  • -provides port allocations the same as TCP
  • -does NOT guarantee delivery
  • -does not guarantee sequencing
  • -useful when speed is more important than
    reliability e.g. Internet telephony

95
User Datagram Protocol (UDP), RFC 768
  • Source Port
  • Destination Port
  • Length Field
  • The Checksum
  • Internet Protocol IP
  • RFC 791, RFC 792, RFC 826
  • IPv4, IPv6

96
Applications of UDP
  • Appropriate when
  • - transport layer overhead must be minimized
    or
  • - data reliability is not crucial
  • - Services such as NFS, DNS, SNMP and Voice
    over IP (VoIP) use UDP

97
Sockets
Applications
Socket references
UDP sockets
TCP sockets
Sockets bound to ports
1
2
1
2
TCP ports
UDP ports
65535
65535
TCP
UDP
IP
  • A socket allows applications to send and receive
    data.
  • It allows an application to connect to a network
    and communicate with other
  • applications on that network
  • Stream sockets use TCP as the end-to-end
    protocol with IP underneath
  • Datagram sockets use UDP end-to-end with IP
    underneath
  • A TCP/IP socket is uniquely identified by an
    Internet address, type of protocol and
  • a port number

98
Relationship of Socket Classes
UdpClient Class
TcpClient Class
TcpListener
.NET Framework Classes
Socket Class
Underlying Implementation
WinSock 2.0 Implementation
  • WinSock was developed by Microsoft and provides
    standard socket functions.
  • The .NET framework provides higher level classes
    to simplify programming tasks.
  • The .NET socket class allows access to the
    underlying sockets interface.
  • TcpListener, TcpClient and UdpClient are higher
    level .NET socket classes that are implemented
  • using the .NET Socket wrapper class.

99
TCP Sockets
  • The .NET framework provides two classes for TCP
    TcpClient and TcpListener
  • .NET uses the EndPoint class and IPEndPoint
    subclass to represent the TCP channel.
  • Communication with a TCP client is initiated in
    three steps
  • Construct an instance of TcpClient
  • Communicate using the sockets stream
  • Close the connection

100
TCP Client and Echo server in C
  • 0. using System //For string, Int32, Console,
    ArgumentException
  • 1. using System.text //For Encoding
  • 2. using System.IO //For IOException
  • 3. using System.Net.Sockets //For TcpClient,
    NetworkStream, SocketException
  • 4.
  • 5. class TcpEchoClient
  • 6.
  • 7. static void Main(string args)
  • 8.
  • 9. if ((args.Length lt 2) (args.Length gt 3))
    // Test for correct no of args
  • 10. throw new ArgumentException(Parameters
    ltServergt ltWordgt ltPortgt)
  • 11.
  • 12.
  • 13. String server args0 // Server name or IP
    address
  • 14.
  • 15.// Convert input String to bytes
  • 16. byte byteBuffer Encoding.ASCII.Getbytes(ar
    gs1)
  • 17.
  • 18. //Use port argument if supplied, otherwise
    default to 7

101
TCP Client and Echo server in C
  • 21. TcpClient client null
  • 22. NetworkStream netStream null
  • 23.
  • 24. try
  • 25. // Create socket that is connected to server
    on specified port
  • 26. client new TcpClient(server, servPort)
  • 27.
  • 28. Console.WriteLine(Connected to server
    sending echo string)
  • 29.
  • 30. netStream client.GetStream()
  • 31.
  • 32. // Send the encoded string to the server
  • 33. netStream.Write(byteBuffer, 0,
    byteBuffer.Length)
  • 34.
  • 35. Console.WriteLine(Sent 0 bytes to
    server, byteBuffer.Length)
  • 36.
  • 37. int totalBytesRcvd 0 // Total bytes
    received so far
  • 38. int bytesRcvd 0 // Bytes received in last
    read
  • 39.

102
TCP Client and Echo server in C
  • 40. //Receive the same string back from the
    server
  • 41. while(totalBytesRcvd lt byteBuffer.Length)
  • 42. if((bytesRcvd netStream.Read(byteBuffer,
    totalBytesRcvd, byteBuffer.Length
    totalBytesRcvd)) 0)
  • 43. Console.WriteLine(Connection closed
    prematurely.)
  • 45. break
  • 46.
  • 47. totalBytesRcvd bytesRcvd
  • 48.
  • 49.
  • 50. Console.WriteLine(Received 0 bytes from
    server 1, totalBytesRcvd,
  • 51. Encoding.ASCII.Getstring(byteBuffer, 0,
    totalBytesRcvd))
  • 52.
  • 53. catch (Exception e)
  • 54. Console.WriteLine(e.Message)
  • 55. finally
  • 56. netStream.Close()
  • 57. client.Close()
  • 58.
  • 59.

103
TCP Client and Echo server in C
  • Lines 15-16 convert the echo string to bytes
  • Line 19 finds the echo server port
  • Lines 25-26 create the TCP socket
  • Line 30 gets the socket stream
  • Lines 32-33 send the string to the echo server
  • Line 40-48 receive the reply from the echo server
  • Lines 50-51 print the echoed string
  • Lines 53-54 handle errors
  • Lines 55-58 close the stream and socket

104
UDP Sockets
  • The .NET framework provides UDP sockets
    functionality using the class UdpClient. This
    allows for both sending and receiving UDP
    packets, and can be used to construct a UDP
    client and server.
  • The UDP client works in the following way
  • Construct an instance of UdpClient
  • Communicate using the Send() and Receive()
    methods of UdpClient
  • Use the Close() method of UdpClient to deallocate
    the socket.

105
UDP Client and Echo Server in C
  • 0. using System //For String, Int32, Console
  • 1. using System.Text //For Encoding
  • 2. using System.Net //For IPEndPoint
  • 3. using System.Net.Sockets //For UdpClient,
    SocketException
  • 4.
  • 5. class UdpEchoClient
  • 6.
  • 7. static void Main(string args)
  • 8.
  • 9. if((args.Length lt 2) (args.Length gt 3))
    // Test for correct no of args
  • 10. throw new System.ArgumentException(Parameter
    s ltServergt ltWordgt ltPortgt)
  • 11.
  • 12.
  • 13. String server args0 // Server name or
    IP address
  • 14.
  • 15. // Use port argument if supplied, otherwise
    default to 7
  • 16. int servPort (args.Length 3) ?
    Int32.Parse(args2) 7
  • 17.
  • 18. // Convert input String to an array of bytes

106
UDP Client and Echo Server in C
  • 23 try
  • 24. // Send the echo string to the specified
    host and port
  • 25. client.Send(sendPacket,
    sendPacket.Length, server, servPort)
  • 26.
  • 27. Console.WriteLine(Sent 0 bytes to
    the server, sendPacket.Length)
  • 28.
  • 29. // This IPEndPoint instance will be
    populated with the remote senders endpoint
    information after the Receive() call
  • 30. IPEndPoint remoteIPEndPoint new
    IPEndPoint(IPAddress.Any, 0)
  • 31.
  • 32. // Attempt echo reply receive
  • 33. byte rcvPacket client.Receive(ref
    remoteIPEndPoint)
  • 34.
  • 35. Console.Writeline(Received 0 bytes
    from 1 2, rcvPacket.Length,
    remoteIPEndPoint,
  • 36. Encoding.ASCII.Getstring(rcvPacket, 0,
    rcvPacket.Length))
  • 37.
  • 38. catch (SocketException se)
  • 39. Console.WriteLine(se.ErrorCode
    se.Message)
  • 40.
  • 41.

107
UDP Client and Echo Server in C
  • Lines 21-22 create the UDP socket
  • Lines 24-25 send the datagram
  • Lines 29-30 create a remote IP end point for
    receiving
  • Lines 32-33 handle datagram reception
  • Lines 35-36 print reception results
  • Line 42 closes the socket

108
Voice over IP (VoIP)
  • VoIP is the routing of voice signals over an
    IP-based network.
  • The analogue voice signal is converted to a
    digital signal.
  • The digital signal is compressed using a codec
    (G.7xxx for voice, H.26xx for video)
  • The digital signal is then split into packets by
    a process called Packetization

109
Voice over IP (VoIP)
  • Advantages
  • Incoming calls can be routed to a VoIP phone
    anywhere on the network
  • Lower cost especially for international calls
  • Disadvantages
  • Received IP packets can arrive in any order or
    even be missing resulting in poor QoS.
  • Susceptible to power cuts

110
Voice over IP Protocols
Audio/Video Applications
RTSP
ENUM
Codecs G.xxx, H.26x
SDP
RSVP
MEGACO/ H.248
DNS
SAP
RTCP
MGCP
SIP
RTP
H.323
TCP
UDP
IP
Network Interface Layer Protocols
111
Protocols supporting VoIP
  • Multicast IP
  • Real-Time Transport Protocol (RTP)
  • Real-Time Control Protocol (RTCP)
  • Resource Reservation Protocol (RSVP)
  • Real-Time Streaming Protocol (RTSP)
  • Session Description Protocol (SDP)
  • Session Initiation Protocol (SIP)
  • Electronic Numbers (ENUM)

112
Protocols supporting VoIP
  • Multicast IP efficiently sends data to multiple
    receivers at the same time on TCP/IP networks.
  • RTP provides end-to-end delivery services for
    data that requires real-time support.
  • RTCP monitors the QoS and conveys information
    about each user in the communication session.
  • RSVP requests an appropriate level of service
    from the network.
  • RTSP controls the delivery of data that has
    real-time properties.
  • SDP describes a multimedia session for the
    purposes of session announcement and invitation.

113
Protocols supporting VoIP
  • SIP establishes a communication session between
    two end-points. It creates, modifies and
    terminates sessions between participants.
  • ENUM bridges the gap between telephone numbers
    and IP addresses.

114
Real-Time Transport Protocol (RTP)
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
Bits
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
5 6 7 8 9 0 1
P
X
CC
M
PT
Sequence Number
V2
Timestamp
Synchronisation Source (SSRC) Identifier
Contributing Source (CSRC) Identifier (0 to 15
items)
20 ms Voice Sample
  • V Version (currently 2)
  • CC CSRC Count. Counts the number of CSRC
    identifiers in the RTP header
  • CSRC Identifies contributing sources
    (conferencing) in the payload. There can only be
    a
  • maximum of 15 contributing sources. These are
    inserted by a mixer.
  • SSRC Identifies synchronisation sources. It is
    chosen randomly so that two or more
  • synchronisation sources in the same RTP
    session have the same SSRC identifier.

115
Voice over IP Packet Format
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
Bits
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
5 6 7 8 9 0 1
VER
IHL
Type of service
Total Length
IPv4 Header 20 octets Options Padding
Identifier
Fragment Offset
Flags
Time to live
Protocol
Header Checksum
Source Address
Destination Address
Options Padding
Source Port
Destination Port
UDP Header 8 Octets
Length
Checksum
V2
P
X
CC
M
PT
Sequence Number
Timestamp
Synchronisation Source (SSRC) Identifier
RTP Header 12 octets Identifiers
Contributing Source (CSRC) Identifier (0 15
items)
20 ms Voice Sample
Data 20 octets
116
References
  • TCP/IP Illustrated, Volume 1, The Protocols, W.
    Richard Stevens, Addison-Wesley Professional
    Computing Series, 1994
  • TCP/IP Sockets in C, Practical Guide for
    Programmers, David B. Makofske, Michael J.
    Donahoo, Kenneth L. Calvert, The Practical Guide
    Series, Elsevier, 2004
  • Voice over IP Technologies, Building the
    Converged Network, Mark A. Miller, MT Books,
    2002

117
Tutorial Sheet  Network Systems and
Technologies by Prof R. A. Carrasco
  • 1)      What is the principal difference between
    connectionless communication and
    connection-oriented communication?
  •  
  • 2)      Two networks each provide reliable
    connection-oriented service. One of them offers a
    reliable byte stream and the other offers a
    reliable message stream. Are these identical? If
    so, why is the distinction mode? If not, give an
    example of how they differ.
  •  
  • 3)      What are two reasons for using layered
    protocols?
  •  
  • 4)      Give two example applications for which
    connection-oriented service is appropriate. Now
    give two examples for which connectionless
    service is best.
  •  
  • 5)      Are there any circumstances when a
    virtual circuit service will (or at least should)
    deliver packets out of order? Explain.
  •  
  • 6)      Datagram subnets route each packet as a
    separate unit, independent of all others. Virtual
    circuit subnets do not have to do this, since
    each data packet follows a predetermined route.
    Does this observation mean that virtual circuit
    subnets do not need the capability to route
    isolated packets from an arbitrary source to an
    arbitrary destination? Explain your answer.
  •  
  • 7)      What does negotiation mean when
    discussing network protocols? Give an example of
    it.
  •  

118
  • 8)      Give three examples of protocol
    parameters that might be negotiated when a
    connection is set up.
  •  
  • 9)      Discuss the advantages and disadvantages
    of message switching over circuit switching and
    performance comparison.
  •  
  • 10)  Discuss the advantages/disadvantages of
    packet switching over circuit switching (and
    performance comparison)
  •  
  • 11)  Discuss the characteristics and medium
    access control techniques of Broadcast Networks.
  •  
  • 12)  Describe the routing functions attributes
    and their elements.
  •  
  • 13)  Describe the following routing strategies
  • Fixed Routing
  • Flooding
  • Random Routing
  • Adaptive Routing

119
Wireless LANs
  • Advantages
  • Increased mobility of users
  • Increased flexibility and fluidity, including
    ad-hoc networks
  • Instant networking
  • Availability of LAN technology

120
Wireless LANs
  • Disadvantages
  • Higher Cost
  • Lower Performance
  • Lower Reliability (Variable Channel
    Characteristics)
  • Multiple Standards
  • Poor Inherent Security

121
LAN Design
122
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123
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124
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125
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126
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127
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128
IEEE 802.11 Wireless LAN Draft Standard
  • Professor R. A. Carrasco

129
Introduction
  • IEEE 802.11 Draft 5.0 is a draft standard for
    Wireless Local Area Network (WLAN) communication.
  • This tutorial is intended to describe the
    relationship between 802.11 and other LANs, and
    to describe some of the details of its operation.
  • It is assumed that the audience is familiar with
    serial data communications, the use of LANs and
    has some knowledge of radios.

130
802.11 Data Frame
Bytes
2
2
6
6
4
6
2
6
0-2312
Address 1
Frame Control
Check- sum
Seq
Duration
Address 2
Address 3
Address 4
Data
Bits
2
2
4
1
1
1
1
1
1
1
1
To DS
From DS
Re- try
Version
Type
Subtype
Pwr
More
Frame Control
MF
W
O
131
Contents
  • Glossary of 802.11 Wireless Terms
  • Overview
  • 802.11 Media Access Control (MAC)
  • Frequency Hopping and Direct Sequence Spread
    Spectrum Techniques
  • 802.11 Physical Layer (PHY)
  • Security
  • Performance
  • Inter Access Point Protocol
  • Implementation Support
  • Raytheon Implementation

132
Glossary of 802.11 Wireless Terms
  • Station (STA) A computer or device with a
    wireless network interface.
  • Access Point (AP) Device used to bridge the
    wireless-wired boundary, or to increase distance
    as a wireless packet repeater.
  • Ad Hoc Network A temporary one made up of
    stations in mutual range.
  • Infrastructure Network One with one or more
    Access Points.
  • Channel A radio frequency band, or Infrared,
    used for shared communication.
  • Basic Service Set (BSS) A set of stations
    communicating wirelessly on the same channel in
    the same area, Ad Hoc or Infrastructure.
  • Extended Service Set (ESS) A set BSSs and wired
    LANs with Access Points that appear as a single
    logical BSS.

133
Glossary of 802.11 Wireless Terms, cont.
  • BSSID ESSID Data fields identifying a
    stations BSS ESS.
  • Clear Channel Assessment (CCA) A station
    function used to determine when it is OK to
    transmit.
  • Association A function that maps a station to
    an Access Point.
  • MAC Service Data Unit (MSDU) Data Frame passed
    between user MAC.
  • MAC Protocol Data Unit (MPDU) Data Frame passed
    between MAC PHY.
  • PLCP Packet (PLCP_PDU) Data Packet passed from
    PHY to PHY over the Wireless Medium.

134
Overview, IEEE 802, and 802.11 Working Group
  • IEEE Project 802 charter
  • Local Metropolitan Area Networks
  • 1Mb/s to 100Mb/s and higher
  • 2 lower layers of 7 Layer OSI Reference Model
  • IEEE 802.11 Working Group scope
  • Wireless connectivity for fixed, portable and
    moving stations within a limited area
  • Appear to higher layers (LLC) the same as
    existing 802 standards
  • Transparent support of mobility (mobility across
    router ports is being address by a higher layer
    committee)

135
Overview, IEEE 802.11 Committee
  • Committee formed in 1990
  • Wide attendance
  • Multiple Physical Layers
  • Frequency Hopping Spread Spectrum
  • Direct Sequence Spread Spectrum
  • Infrared
  • 2.4GHz Industrial, Scientific Medical shared
    unlicensed band
  • 2.4 to 2.4835GHz with FCC transmitted power
    limits
  • 2Mb/s 1Mb/s data transfer
  • 50 to 200 feet radius wireless coverage
  • Draft 5.0 Letter Ballot passed and forwarded to
    Sponsor Ballot
  • Published Standard anticipated 1997
  • Next 802.11 - November 11-14, Vancouver, BC
  • Chairman - Victor Hayes, v.hayes_at_ieee.org

136
Overview, 802.11 Architecture
ESS
Existing Wired LAN
AP
AP
STA
STA
STA
STA
BSS
BSS
Infrastructure Network
STA
STA
Ad Hoc Network
Ad Hoc Network
BSS
BSS
STA
STA
137
Overview, Wired vs. Wireless LANs
  • 802.3 (Ethernet) uses CSMA/CD, Carrier Sense
    Multiple Access with 100 Collision Detect for
    reliable data transfer
  • 802.11 has CSMA/CA (Collision Avoidance)
  • Large differences in signal strengths
  • Collisions can only be inferred afterward
  • Transmitters fail to get a response
  • Receivers see corrupted data through a CRC error

138
802.11 Media Access Control
  • Carrier Sense Listen before talking
  • Handshaking to infer collisions
  • DATA-ACK packets
  • Collision Avoidance
  • RTS-CTS-DATA-ACK to request the medium
  • Duration information in each packet
  • Random Backoff after collision is determined
  • Net Allocation Vector (NAV) to reserve bandwidth
  • Hidden Nodes use CTS duration information

139
802.11 Media Access Control, cont.
  • Fragmentation
  • Bit Error Rate (BER) goes up with distance and
    decreases the probability of successfully
    transmitting long frames
  • MSDUs given to MAC can be broken up into smaller
    MPDUs given to PHY, each with a sequence number
    for reassembly
  • Can increase range by allowing operation at
    higher BER
  • Lessens the impact of collisions
  • Trade overhead for overhead of RTS-CTS
  • Less impact from Hidden Nodes

140
802.11 Media Access Control, cont
  • Beacons used convey network parameters such as
    hop sequence
  • Probe Requests and Responses used to join a
    network
  • Power Savings Mode
  • Frames stored at Access Point or Stations for
    sleeping Stations
  • Traffic Indication Map (TIM) in Frames alerts
    awaking Stations

141
802.11 Protocol Stack
Upper Layers
Logical Link Control
Data Link Layer
MAC Sub- layer
802.11 Infrared
802.11 FHSS
802.11 DSSS
802.11a OFDM
802.11b HR-DSSS
802.11g OFDM
Physical Layer
142
Performance of IEEE802.11b
MAC Header 30 Bytes
CRC 4 Bytes
Data
MPDU
DIFS
Backoff
PLCP Preamble
PLCP Header
SIFS
PLCP Preamble
Ack 14 Bytes
Header
MPDU
143
Performance of IEEE802.11b
  • Successful transmission of a single frame
  • PLCP physical layer convergence protocol
    preamble

Header transmission time (varies according to the
bit rate used by the host
SIFS 10 ?sec (Short Inter Frame Space) is the
MAC acknowledgement transmission time (10 ?sec
if the selected rate is 11Mb/sec, as the ACK
length is 112 bits
144
Performance of IEEE802.11b
  • DIFS

is the frame transmission time, when it
transmits at 1Mb/s, the long PLCP header is used
and

If it uses 2, 5.5 or 11 Mb/s, then the short PLCP
header can be optionally used

145
Performance of IEEE802.11b
  • For bit rates greater than 1Mb/s and the frame
    size of 1500 Bytes of data (MPDU of total 1534
    Bytes), proportion p of the useful throughput
    measured above the MAC layer will be
  • So, a single host sending long frames over a
    11Mb/s radio channel will have a maximum useful
    throughput of 7.74Mb/s

146
Performance of IEEE802.11b
  • If we neglect propagation time, the overall
    transmission time is composed of the transmission
    time and a constant overhead

Where the constant overhead
147
Performance of IEEE802.11b
  • For N hosts, assuming that multiple successive
    collisions are negligible, the proportion of
    collisions experienced for each packet
    successfully acknowledged at the MAC is given by

148
Performance of IEEE802.11b
  • The overall frame transmission time experienced
    by a single host when competing with N 1 other
    hosts has to be increased by time interval tcont
    that accounts for the time spent in contention
    procedures

149
Performance of IEEE802.11b
  • N stations, mean wait interval per transmission
  • Backoff interval is doubled when a collision
    occurs

150
Performance of IEEE802.11b
  • So the overall transmission time

proportion p of the useful throughput measured
obtained by a host
151
Performance Anomaly of IEEE802.11b
  • Consider how the situation in which N hosts of
    different bit rate compete for the radio channel.
    N-1 hosts use the high transmission rate R
    11Mb/s and one host transmits at a degraded rate
    r 5.5, 2, or 1Mb/s

Where
is the data frame length in bits
152
Performance Anomaly of IEEE802.11b
  • Let Tf be the overall transmission time for a
    fast host transmitting at rate R
  • Similarly, let Ts be the corresponding time for a
    slow host transmitting at rate r

and
the associated overhead time
153
Performance Anomaly of IEEE802.11b
  • We can express the channel utilization of the
    fast host as

where
  • The throughput obtained by a fast host is given
    by

154
Performance Anomaly of IEEE802.11b
  • Similarly, we can express the channel utilization
    of the slow host as
  • The throughput obtained by a slow host is given
    by

155
Performance Anomaly of IEEE802.11b
  • Result
  • Fast hosts transmitting at a higher rate R
    obtain the same throughput as slow hosts
    transmitting at a lower rate r.

156
Performance Anomaly of IEEE802.11b
  • Validated by OPNET Simulation

157
Performance of IEEE802.11b
  • Study
  • The UDP traffic
  • TCP traffic.
  • Flows in IEEE 802.11 WLANs

158
Frequency Hopping and Direct Sequence Spread
Spectrum Techniques
  • Spread Spectrum used to avoid interference from
    licensed and other non-licensed users, and from
    noise, e.g., microwave ovens
  • Frequency Hopping (FHSS)
  • Using one of 78 hop sequences, hop to a new 1MHz
    channel (out of the total of 79 channels) at
    least every 400milliseconds
  • Requires hop acquisition and synchronization
  • Hops away from interference
  • Direct Sequence (DSSS)
  • Using one of 11 overlapping channels, multiply
    the data by an 11-bit number to spread the
    1M-symbol/sec data over 11MHz
  • Requires RF linearity over 11MHz
  • Spreading yields processing gain at receiver
  • Less immune to interference

159
802.11 Physical Layer
  • Preamble Sync, 16-bit Start Frame Delimiter, PLCP
    Header including 16-bit Header CRC, MPDU, 32-bit
    CRC
  • FHSS
  • 2 4GFSK
  • Data Whitening for Bias Suppression
  • 32/33 bit stuffing and block inversion
  • 7-bit LFSR scrambler
  • 80-bit Preamble Sync pattern
  • 32-bit Header
  • DSSS
  • DBPSK DQPSK
  • Data Scrambling using 8-bit LFSR
  • 128-bit Preamble Sync pattern
  • 48-bit Header

160
802.11 Physical Layer, cont.
  • Antenna Diversity
  • Multipath fading a signal can inhibit reception
  • Multiple antennas can significantly minimize
  • Spacial Separation of Orthoganality
  • Choose Antenna during Preamble Sync pattern
  • Presence of Preamble Sync pattern
  • Presence of energy
  • RSSI - Received Signal Strength Indication
  • Combination of both
  • Clear Channel Assessment
  • Require reliable indication that channel is in
    use to defer transmission
  • Use same mechanisms as for Antenna Diversity
  • Use NAV information

161
A Fragment Burst
Fragment Burst
Frag1
RTS
Frag2
Frag3
A
ACK
CTS
ACK
ACK
B
NAV
C
NAV
D
Time
162
Security
  • Authentication A function that determines
    whether a Station is allowed to participate in
    network communication
  • Open System (null authentication) Shared Key
  • WEP - Wired Equivalent Privacy
  • Encryption of data
  • ESSID offers casual separation of traffic

163
Performance, Theoretical Maximum Throughput
  • Throughput numbers in Mbits/sec
  • Assumes 100ms beacon interval, RTS, CTS used, no
    collision
  • Slide courtesy of Matt Fischer, AMD

164
WLAN OPNET Simulation
  • Maximum throughput of a single station as a
    function of MSDU size (802.11b, 11Mb/s)

165
Background for broadband wireless technologies
  • UWB Ultra Wide Band
  • High speed wireless personal area network
  • Wi-Fi Wireless fidelity
  • Wireless technology for indoor environment
    (WLANS)
  • broader range that WPANs
  • WiMAX Worldwide Interoperability for Microwave
    Access
  • Wireless Metropolitan Area Networks (WMANs)
  • For outdoor coverage in LOS and NLOS environment
  • Fixed and Mobile standards
  • 3G Third generation
  • Wireless Wide Area Networks (WMANs) are the
    broadest range wireless networks
  • High speed data transmission and greater voice
    capacity for mobile users
  • Bluetooth -

166
What is WiMax?
  • WiMAX is an IEEE802.16/ETSI HiperMAN based
    certificate for equipments fulfilling the
    interoperability requirements set by WiMAX Forum.
  • WiMAX Forum comprises of industry leaders who are
    committed to the open interoperability of all
    products used for broadband wireless access.
  • The technique or technology behind the standards
    is often referred as WiMAX

167
What is WiMax?
  • Broadband is thus a Broadband Wireless Access
    (BWA) technique
  • WiMax offers fast broadband connections over long
    distances
  • The interpretability of different vendors
    product is the most important factor when
    comparing to the other techniques.

168
The IEEE 802.16 Standards
  • The IEEE 802.16 standards family
  • - broadband wireless wideband internet
    connection
  • - wider coverage than any wired or wireless
    connection before
  • Wireless system have the capacity to address
    broad geographic areas without the expensive
    wired infrastructure
  • For example, a study made in University of Oulu
    state that WiMax is clearly more cost effective
    solution for providing broadband internet
    connection in Kainuu than xDSL

169
The IEEE 802.16 Standards
  • The IEEE 802.16 standards family
  • - broadband wireless wideband internet
    connection
  • - wider coverage than any wired or wireless
    connection before
  • Wireless system have the capacity to address
    broad geographic areas without the expensive
    wired infrastructure
  • For example, a study made in University of Oulu
    state that WiMax is clearly more cost effective
    solution for providing broadband internet
    connection in Kainuu than xDSL

170
The IEEE 802.16 Standards
  • 802.16, published in April 2002
  • - A set od air interfaces on a common MAC
    protocol
  • - Addresses frequencies 10 to 66 GHz
  • - Single carrier (SC) and only LOS
  • 802.16a, published in January 2003
  • - A completed amendment that extends the
    physical layer to the 2 to 11 GHz both licensed
    and lincensed-exempt frequencies
  • - SC, 256 point FFT OFDM and 2048 point FFT
    OFDMA
  • - LOS and NLOS
  • 802.16-2004, published in July 2004
  • - Revises and replaces 802.16, 802.16a and
    802.16 REVd.
  • - This announcements marks a significant
    milestone in the development of future WiMax
    technology
  • - P802.16-2004/Corl published on 8.11.2005

171
IEEE 802.16 Broadband Wireless MAN Standard
(WiMAX)
  • An 802.16 wireless service provides a
    communications path between a subscriber site and
    a core network such as the public telephone
    network and the Internet. This wireless broadband
    access standard provides the missing link for the
    "last mile" connection in metropolitan area
    networks where DSL, Cable and other broadband
    access methods are not available or too
    expensive.

172
Comparison Overview of IEEE 802.16a
  • IEEE 802.16 and WiMAX are designed as a
    complimentary technology to Wi-Fi and Bluetooth.
    The following
  • table provides a quick comparison of 802.16a
    with to 802.11b

Parameters 802.16a (WiMax) 802.11 (WLAN) 802.15 (Bluetooth)
Frequency Band 2-11GHz 2.4GHz Varies
Range 31miles 100meters 10meters
Data transfer rate 70 Mbps 11 Mbps 55 Mbps 20Kbps 55 Mbps
Number of Users Thousands Dozens Dozens
173
Protocol Structure -IEEE 802.16 Standard (WiMAX)
  • IEEE 802.16 Protocol Arc
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