COMMUNICATION NETWORK PROTOCOLS

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COMMUNICATION NETWORK PROTOCOLS

• Simply the rules and standards set up to govern
  communications over a network architecture
• More specifically, communication protocols are
  sets of rules that regulate the exchange of
  messages to provide a reliable and orderly flow
  of information among communicating processes

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CATEGORIES OF COMMUNICATION SERVICES

• Connection-Oriented require explicit set up of
  connection before communication commences
• Messages are delivered reliably and in sequence
• Connectionless no initial connection set up
  required
• Messages are delivered on a best-effort basis in
  timing and route, and may arrive in arbitrary
  order useful analogy is the postal service

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OSI PROTOCOL SUITE

• A protocol suite consists of the layers of a
  standardized network architecture
• The first of the two most popular of these is the
  the Open Systems Interconnection (OSI) from the
  International Standards Organization
• Consists of 7 layers
• Serves to abstract away the details of the
  network communication from the communicating
  processes
• The above is achieved through the process of
  encapsulation
• Specifically, each layer in the protocol receives
  a Protocol Data Unit (PDU) from its upper layer
  and encapsulates it with a header of information
  for its peer layer in the communicating process,
  which peels these encapsulations off in reverse
  order

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OSI MODEL
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THE PHYSICAL LAYER

• The physical layer specifies the electrical and
  mechanical characteristics of the physical
  communication link between two nodes
• This is where electrical or optical signals are
  converted to bits, or vice versa
• Bit synchronization is the process of detecting
  the beginning of a bit, or sequence of bits

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BIT SYNCHRONOUS VERSUS CHARACTER ASYNCHRONOUS

• Bit sequences may be bit synchronous or character
  asynchronous
• Bit synchronous sequences are large blocks of
  bits transmitted at a regular rate
• Results in higher data transfer rate and more
  efficient utilization of the link
• Character asynchronous data are small fixed-size
  bit sequences transmitted asynchronously
• Low-speed character-oriented terminals generally
  use this method

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STANDARDIZATION OF PHYSICAL LINKS

• Standardization required to allow peers to
  communicate extends all the way down to the
  physical level, for things like coding method,
  modulation technique, and wire and connector
  specifications
• RS232C and X.21 are two typical such
  standardizations

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THE DATALINK LAYER

• Ensures reliable data transfer for groups of
  bits, called frames
• Protocols here handle configuration setup, error
  controls, sequencing and flow control of frames
• Configuration concerns the establishment and
  termination of a connection, and whether it
  should be full or half duplex, and synchronous or
  asynchronous
• Errors include transmission errors and loss or
  replication of data frames
• Sequencing uses sequence numbers to maintain
  orderly delivery of frames
• Flow control is necessary when receiver cannot
  keep pace with sender, perhaps because of limited
  buffer space

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THE DATALINK LAYER

• All of these control functions contribute
  overhead bits which are added to frames as
  headers or trailers
• Consequentially, each control protocol at this
  layer has a particular format so that bits can
  be interpreted correctly

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THE NETWORK LAYER

• The Network Layer is concerned with sending
  packets over multiple links, as opposed to the
  previous two layers which are each concerned with
  only one physical link
• Packets, the fundamental data unit of the network
  layer, are not analogous to frames, as they are
  not bounded by the size of the physical link
• The routing function of the network layer
  consists of determining, given the destination
  address of a packet, what link to forward that
  packet to
• Congestion control is the alleviation of node
  bottlenecks in the network through routing changes

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THE NETWORK LAYER

• When routing decisions are made when a connection
  is established it is called a virtual circuit
• These deliver packets, called datagrams, in order
• Datagrams require reassembly in proper sequence
• Not all packets are data packets
• Control packets are also used for network address
  resolution and status broadcasting
• Such protocols generally use datagram services
  since packets are small and short-lived

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THE TRANSPORT LAYER

• Serves as the interface between the communication
  subnetwork (physical, data link and network
  layers), and network independent layers (session,
  presentation and application)
• Primary responsibility is to provide reliable
  end-to-end communication between processes
• All network-dependent issues are abstracted away
  before we reach this level
• At the Transport layer is where messages are
  broken into packets, or, at the receiving
  process, packets are assembled into messages
• Several sessions may be multiplexed into a single
  transport connection, or alternatively a single
  session could occupy multiple transport
  connections

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SESSIONS

• Sessions are categorized according to their
  requirements for error handling and multiplexing
• OSI defines 5 classes of transport services to
  support sessions, TP0-TP4
• TP4 is the most common transport service, and
  allows multiplexing, sessions, error detection,
  and retransmission
• It is a reliable connection-oriented service for
  unreliable networks

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SESSION, PRESENTATION AND APPLICATION LAYERS

• Layers above the Transport Layer are considered
  to be 'on top' of the implementation of the
  system, and thus can be considered together
• The Session Layer provides additional dialog and
  synchronization services to the Transport Layer
• The Presentation Layer provides data encryption,
  compression and code conversion for messages that
  use different coding schemes
• The standard for the Application Layer is left
  entirely up to the developer of the application
  in question

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TCP/IP

• There are two major types of system interactions
  interprocess and internode
• Stated another way, as system designers we are
  primarily concerned with 1) how is communication
  maintained between a pair of processes, and 2)
  how are messages routed through network nodes?
• Thus the Transport and Network Layers are most
  important to us

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ENTER TCP/IP

• TCP/IP is a protocol suite designed to address
  these needs
• TCP is a Transport Layer protocol equivalent to
  TP4 in the OSI
• IP is an internet protocol which encompasses a
  bit more than the network layer of the OSI
• The primary focus of TCP/IP is connecting
  networks, rather than connecting computers as in
  the OSI

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TCP/IP
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TCP/IP

• At the Transport Layer we have the option of
  connection-oriented or connectionless service
• Either can be implemented through virtual circuit
  or datagram at the network level
• Connection-oriented communication has a more
  stringent requirement for correct and orderly
  delivery of of messages
• On the other hand, a datagram is a simpler and
  more efficient implementation at the network
  level

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PHILOSOPHY OF TCP/IP

• By combining the connection-oriented transport
  layer with a datagram network layer we
  accommodate a large class of network applications
• In other words shift the burden of providing
  reliable from the network to the operating system
  level
• Here we have more control of the host than we do
  in the network

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PROCESS COMMUNICATION

• Generally uses ports, identified by a port id
• A process may have multiple ports, and different
  processes may share a common destination port
• Only unique within a local host
• A nonambiguous network-wide endpoint can thus be
  established by concatenating the port id with the
  host and network addresses

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INTERNET ADDRESSES

• Full internet address consists of a network
  address and a host address within that network
• May contain subnetwork address
• Internet IP address is 32 bits long

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SOCKETS

• A socket specifies the interface to a port
• It is an abstraction of network I/O that allows
  standard read and write operations
• The socket is configured to conform to a
  particular protocol family and communication
  service
• For TCP the socket must be bound to a destination
  transport port before read and write operations
  can take place
• The destination port number is chosen by the
  operating system

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Ef?ciency Study of TCP Protocols in
Infrastructured Wireless Networks

• Goal of research to isolate most efficient
  solution to non-congestion packet loss in TCP
  protocol over wireless network
• TCP is inherently inefficient over wireless
  networks
• TCP Tahoe and Reno, the two most common TCP
  distributions, both assume packet loss to be the
  result of congestion, since random loss occurs in
  wired networks less than 1 of the time

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Ef?ciency Study of TCP Protocols in
Infrastructured Wireless Networks

• However, in a wireless network schema two other
  kinds of packet loss become common, these being
  random packet loss, which manifests through bit
  corruption, and disconnection packet loss, which
  occurs when a mobile host disconnects from the
  network
• Both Tahoe and Reno will interpret this as
  congestion and trigger defensive action, which
  slows throughput rates

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FOUR PROPOSED SOLUTIONS

• TCP Westwood Relies on a more optimistic
  estimation of the available bandwidth after a
  loss event has occurred
• TCP Jersey Actually distinguishes between
  congestion and noncongestion loss
• TCP Veno focuses on solving the random
  non-congestion loss problem by using two
  parameters, the expected rate, and the actual
  rate, to calculate the backlog in the router
  queue that is used as an indication of congestion
• Expected rate is calculated as the ratio of the
  congestion window over the best RTT
• Actual rate is calculated as the ratio of the
  congestion window over the latest RTT
• JTCP assumes network congestion can be inferred
  from the difference in interarrival times of
  successive packet ACKs
• Interarrival jitter time difference between two
  packets on the sender side versus the time
  difference between the same two packets on the
  receiver side
• If greater than 0, then the second packet
  traveled longer through the network than the
  first
• Jitter ratio variance of the queue rate
  remember that queues form because rate of arrival
  of packets is greater than service rate at the
  router
• JTCP uses jitter ratio, or variance in queue
  length, to determine types of loss in the network

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BENCHMARK METRICS

• Throughput the ratio of the total data
  transferred to the time it took to transfer
• Average Congestion Window the sum of all
  congestion window sizes divided by the number of
  transmissions provides an idea of the protocols
  resilience to loss and ability to recover
• Time to Complete time to transfer a continuous
  block of memory (file)

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RESULTS
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RESUTS
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RESULTS
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REFERENCES

• Milan Todorovic, Noe Lopez-Benitez. Ef?ciency
  Study of TCP Protocols in Infrastructured
  Wireless NetworksNetworking and Services, 2006.
• ICNS '06. International conference on
• 103,16-18 July 2006.