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
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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

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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

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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

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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

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Ethernet hub is a device for connecting multiple
twisted pair or fibre Ethernet devices together.
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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
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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
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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.
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Popular Wired LAN Standards

• High-Level Data Link Control (HDLC)
• Ethernet (IEEE 802.3)
• Token Bus (IEEE 802.4)
• Token Ring (IEEE 802.5)

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HIGH LEVEL DATA LINK CONTROL
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HIGH LEVEL DATA LINK CONTROL(2)

• Control Field of
• An information frame
• A supervisory frame
• An unnumbered frame

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PPP- Point to Point Protocol
Bytes
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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
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Ethernet (IEEE 802.3)
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Ethernet (IEEE 802.3)

• PR Preamble
• SFD Start Frame Data
• DA Destination Address
• SA Source Address
• TYPE Type of data
• FCS Frame Checksum

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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
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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

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Capacity Calculations
A
B
?
delay
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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
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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
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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)

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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
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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

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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)

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Utilisation with different values for the a
parameter
a
a
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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

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Network Snapshot
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Utilization vs. Traffic Load
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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

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Token Ring (IEEE 802.5)
http//netbook.cs.purdue.edu/anmtions/anim06_4.htm
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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)

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Token Ring
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Token Ring
A removes the data frame
A generates data frame for station A
Busy Token
Free Token
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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)

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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)

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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)

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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

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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

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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

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Token Ring OPNET Simulation
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Token Ring Parameters
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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.

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Utilization vs. THT Duration
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Full Ring

• All stations have data to transmit
• Each station can only transmit when it has the
  token
• MSDU size 1024 bytes

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Utilization vs. THT Duration
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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?

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• 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?
•  

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• 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?

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• 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.

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

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IEEE 802.x, TCP/IP and ISO/OSIArchitecture
Comparison
IEEE 802.x
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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
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IP OPNET Simulation
IP Cloud Model Packet Discard Ratio
1.0 Packet Latency (secs) Exponential (0.5)
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Results
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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

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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

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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
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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

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http//netbook.cs.purdue.edu/anmtions/anim16_1.htm
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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
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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

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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)

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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)

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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

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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

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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

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• 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

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IPv6 extension headers
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Order of extension headers for IPv6
83
Option header formats
Hop-by-hop extension IPv6 options header
Routing Extension IPv6 header
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Routing type 0 header
85
Fragment extension IPv6 header
TCP and UDP pseudo-header for IPv6
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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
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TCP Datagram Format, RFC 793
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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.

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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

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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
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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
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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

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TCP OPNET Simulation
A packet loss
A packet loss
TCP Reno (Fast recovery)
TCP Tahoe
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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

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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

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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

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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

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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.

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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

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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

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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.

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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