Review on Transport Layer

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Review on Transport Layer

• Process-to-process communication
• UDP, TCP
• Mutiplexing, demultiplexing
• Building a reliable data transfer protocol
• Finite State Machine protocol error free
• Automatic Repeat reQuest Protocol stop and wait
• Sequence , ACK, duplicate ACKs

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Review

• Alternating bit-protocol
• Pipelining Techniques
• Go-Back-N Sliding Window Protocol
• Selective Repeat
• Use Timeout
• TCP Connection
• TCP Segment FIN, SYN , RECEIVE WINDOW
• Detect packet loss through Duplicate ACKs

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Review

• Flow Control
• Congestion Control

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Network Layer

• PART I

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Network Layer

• Network layer (NL) provides a host-to-host
  communication service
• NL is one of the most complex layers in the
  protocol stack
• The role of the NL is to move packets from a
  sending host to a receiving host

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Network Layer

• Two important NL functions
• Forwarding
• Routing
• Forwarding determine an appropriate output link
  at a router
• Routing determine a route/path to let a packet
  flow from a sending host to a receiving host
• End-to-end

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Forwarding

• Every router has a forwarding table
• A router forwards a packet by examining the value
  of a field in the arriving packets header, then
  uses the value to index into the routers
  forwarding table

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Forwarding

• How to configure forwarding tables
• The routing algorithm determines the values that
  are inserted into the routers forwarding tables
• It can be decentralized or centralized
• Can a human configure a forwarding table?

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Connection Setup

• Besides forwarding and routing functions, some
  computer networks have an additional function a
  connection setup
• Example of computer networks that use a
  connection setup service
• ATM (Asynchronous Transfer Mode)
• Frame Relay
• X.25

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Network Service Models

• Some questions related to a network service model
• Will a packet arrive at a receiving host?
• Will a network layer inform about congestion in
  the network?
• Will packets arrive in the same order as they
  were sent?
• Answer It depends on a network service model.

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Network Service Models

• When a packet is passed from the transport layer
  to the network layer, specific services that
  could be provided by the network layer include
• A guaranteed delivery service
• A guaranteed delivery with bounded delay service

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Network Service Models

• Other services provided by the network layer
• Inorder packet delivery
• Guaranteed minimal bandwidth
• The network service emulates the behavior of a
  transmission link of a specified bit rate between
  a sending host and a receiving host
• Ensure a packet to arrive within a specified
  host-to-host delay bound

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Network Service Models

• Other services provided by the network layer
• Guaranteed maximum jitter
• The amount of time between the transmission of
  two successive packets at a sending host is
  equal to the amount time between their receipt at
  a receiving host

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Network Service Models

• What is a network service model provided by the
  Internet?
• Best-known Effort service (no service at all)
• Packets are not guaranteed to be delivered
• Packets are not guaranteed to be received in the
  order in which they are sent

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Virtual Circuit Networks Vs Datagram Networks

• Virtual-Circuit Networks provide a connection
  service at the network layer
• Datagram Networks provide only a connectionless
  service at the network layer
• Note The implementation of a connection-oriented
  service in the transport layer and a connection
  service in the network are fundamentally
  different
• Both use different information in making their
  forwarding decisions

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Virtual-Circuit and Datagram Networks

• Examples of Virtual-Circuit Networks
• ATM, Frame Relay and X.25
• An example of Datagram networks
• Internet

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Virtual Circuit Networks

• A Virtual Circuit network consists of
• A path a series of links and routers
• Entries in a forwarding table in each router
• VC numbers/ids, one number/id for each link along
  the path

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Suppose a path from A to B is A-R1-R2-B and
assigns VC numbers 12, 22, 32
12
22
32
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Virtual Circuit Networks

• Why a packet does not keep the same VC number/id?
• Replacing the number from a link to a link
  reduces the length of the VC field in the packet
  header
• If a common VC number/id is used along the path,
  routers would have to have to agree on a common
  VC number/id this will increase communication
  messages between routers

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Virtual Circuit Networks

• A virtual circuit network must maintain
  connection state information
• If a connection is established, entries must be
  added into a forwarding table
• If the connection is released, the entries must
  be removed from the table

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Virtual Circuit Network

• Three identifiable phases in a virtual circuit
• VC setup
• Data Transfer
• VC teardown can be initiated by either a sending
  host or receiving host

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Virtual Circuit Network

• VC setup
• Transport Layer (TL) contacts Network Layer (NL),
  specifies a receivers address
• TL then waits the NL to set up a VC
• NL determines a path
• NL determines VC numbers/ids
• NL adds entries into forwarding tables

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