The Internet

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					The Internet
The Internet
 History
    Originates from the ARPANET, a project of the US
    Advanced Research Projects Agency in the 1970s
    First two networks of the ARPANET were
    interconnected in 1969 and other state-funded networks
    (e.g., Universities and Agencies) were rapidly added in
    the following years
    The network was opened for commercial interests in
    1988 (e.g., commercial MCI Mail system)
    The term Internet nowadays refers to the worldwide
    interconnection of packet networks which all use the
    same collection of protocols
The Internet: Routing
 Topology
    Routers are attached to physical links by
    their interfaces
    Multipoint links (e.g., LAN) can have many
    routers attached to them
    Devices attached to a link are each others
    neighbors
The Internet: Routing
   Topology (cont.)
                                                             R
                                Host


                                                                                 Host
                 Router
                                                  Multipoint
                                               link (e.g., LAN)
  Host                          R
                                                                                 R


         Point-to-point link
                                                               Host
                                          Host                                                 R


Figure 2.28, [K] Kumar, Manjunath, Kuri: "Communication Networking: An Analytical Approach",
Morgan Kaufmann Publishers, 2004
The Internet: Routing
 Routing protocols
    Routing protocols allow routers to identify
    good paths on which to forward packets
    Shortest paths are calculated with a
    distributed algorithm
           » Metrics, assigned to the network links
             are used as input
    Being an application running on the
    network, a routing protocol still needs to use
    the packet transport services of the network
The Internet: Routing
 Routing protocols (cont.)
    Common routing algorithms allow nodes to
    learn shortest paths through the network by
    only exchanging packets with their
    neighbors
          » Using a simple protocol (i.e., the ‘Hello’ protocol)
            routers can discover their neighbors
          » After discovery, the routing protocol packets (i.e.,
            the status of links the router is attached to) are
            exchanged
          » These link state advertisements (LSAs) are
            flooded through the network and each router can
            create a full topology view to compute the shortest
            path to other routers
The Internet: Routing
 Open Shortest Path First (OSPF)
    Most popular adaptive routing protocol
    Instead of using the transport protocol, it is
    running directly on the network/internet
    layer in routers
    Utilizes the Dijkstra algorithm to calculate
    the shortest paths
    Defined in RFC 2740
WH: The OSI Model
   The OSI Model (cont.)
           end system                                                        end system
      7. Application layer                                               7. Application layer
      6. Presentation layer                                              6. Presentation layer
      5. Session layer                                                   5. Session layer
      4. Transport layer                                                 4. Transport layer
      3. Network layer                                                   3. Network layer
      2. Link layer                                                      2. Link layer
      1. Physical layer                                                  1. Physical layer

                                           packet switch
                                          3. Network layer
                                          2. Link layer
                                          1. Physical layer


Figure 2.21, [K] Kumar, Manjunath, Kuri: "Communication Networking: An Analytical Approach",
Morgan Kaufmann Publishers, 2004
The Internet
 Protocol Suite
    The development of the ARPANET resulted in
    a set of protocols which are now widely used:
     – The Internet Protocol (IP)
            » i.e., a network layer protocol
              (i.e., layer 3 of the OSI model)
     – The Transmission Control Protocol (TCP)
            » i.e., a transport layer protocol
              (i.e., layer 4 of the OSI model)
     – The User Datagram Protocol (UDP)
            » i.e., a transport layer protocol
              (i.e., layer 4 of the OSI model)
The Internet
 Wireshark - network protocol analyzer
The Internet: IP
 The Internet Protocol (IP)
    Primary protocol in the Internet layer
    Does not see devices working on the physical
    layer (e.g. modems, ..)
    Delivers datagrams from the source to the
    destination over routers
    Devices identified by IP addresses
     – Statically vs. dynamically assigned
The Internet: IP
 The Internet Protocol (IP)
    IPv4 is the most widely deployed version of
    the protocol
     – 32-bit (4B) address
     – e.g. 131.130.1.78 (decimal)
    IPv6 successor
    due to long-anticipated IPv4 address exhaustion
     – 128-bit (16B) address
     – 2007:0db8:0230:0420:0182:1020:1337:57ab
       (hexadecimal)
The Internet: IP
 The Internet Protocol (IP) (cont.)
    Both protocols support addresses to be
    hierarchically assigned into networks and
    sub networks
             » The high-order bits that identify the sub network
               are called the network prefix
    e.g., a sub network in IPv4:
                            32 bits

       10100100.01011001.0110xxxx.xxxxxxxx
        E.g., 20 bits as network prefix   Remaining 12 bits to identify
        to identify the sub network       each device in the sub network
                                          uniquely
The Internet: IP packet
 Version (IPv4 vs. IPv6)
 Type of Service, also referred to as Quality of Service
 length of the packet in bytes,
 identification tag to help reconstruct the packet from several
 fragments,
 Time to live (TTL), which is the number of hops (router, computer
 or device along a network) the packet is allowed to pass before it
 dies
 protocol (TCP, UDP, ICMP, etc.)
 Header Checksum, a number used in error detection,
 source IP address,
 destination address.
The Internet: IP
 The Internet Protocol (IP) (cont.)
    No fix paths for packet flows are defined
    Each packet carries the full network address of its
    designated destination end point
    After consulting the routing table, packet switches
    decide for each arriving packet, which outgoing link
    the packet should be forwarded to
    The routing table stores network prefixes and
    corresponding outgoing links
     – Routing protocols deal with the identification of good paths to
       forward packets
    IP packets are transferred independently
The Internet: IP
 The Internet Protocol (IP) (cont.)
    The per-packet, hop-by-hop, best-effort
    routing scheme of the Internet Protocol
    allows:
           » Quick delivery of small amounts of data
           » Automatic resilience to link failures
           » Ease of multicast
                   (i.e., the transmission of a packet to multiple
                   destinations by replicating it at appropriate
                   points in the network)
The Internet: IP
 The Internet Protocol (IP) (cont.)
    Each packet is routed as a single entity and
    consecutive packets of the same session
    may follow different routes
    This leads to:
        – Different delays of the arriving packets
            » Packets arrive out of order
        – Packets that may not be successfully transferred
            » They are discarded on the link layer (e.g.,
               because of reaching the maximum tries to send
               the packet) or physical layer (e.g., because of
               exhaustion of buffer space) of a packet switch
The Internet: IP
 The Internet Protocol (IP) (cont.)
    Being unreliable and nonsequential, the
    packet delivery service provided by the
    Internet Protocol transport layer, is known
    as a datagram delivery service
    Connection-less protocol
    It does not provide any substantial QoS to
    the traffic streams it handles
    Reliability might be assured on the higher
    layers (transport layer)
The Internet: TCP
 Transmission Control Protocol (TCP)
    Transport layer protocol (layer 4)
    Transfers data between two applications
     – IP protocol used for communication between two devices
       (computers)
 Source/destination identified by port number
    IP address = Street + house number, port = name of person
    Client/private ports (>1023) vs. server/well-known (SSH 22,
    SMTP 25, HTTP 80)
 Used for WWW, email, file transfer, etc. but not
 suitable for real-time applications (waiting for
 retransmissions)
The Internet: TCP segment
 Source port
 Destination port
 Window size - the number of bytes that the
 receiver is currently willing to receive
 Checksum
 Flags – reset connection, no more data etc.
The Internet: TCP
 Connection-oriented
   Fully-duplex connection
   Ordered delivery
   Retransmission of lost packets
   Flow control
   Congestion control
 Can detect data damaged due to technical problems
 Cannot detect data modified by an attacker/intruder
     – Cryptographic protocols needed (TLS/SSL, S/MIME)
The Internet: TCP
 Reliable transmission
   Sequence number to identify each byte of data
   Discarding duplicate packets, retransmission of lost
   packets, ordered-data transfer
 Error detection
   Checksum
 Flow and congestion control
   Avoiding sender sending the data too fast
   Sliding window – recipient defines the number of
   bytes that is willing to buffer; the size changes
   depending on the situation
                               Example: Modeling TCP
  Evolution of expected window size: no loss
                               no−loss
   W                          0


 Avrg Window size [packets]




                                   Time (number of RTTs)




Evolution of window size
No packet loss
The Internet: UDP
 The User Datagram Protocol
   Transport layer protocol (layer 4)
   Connection-less
   Unreliable, out-of-order or duplicated
   delivery, packet lost
   Checksum is optional
   Used for DNS, time-sensitive applications
   (dropping is preferable to waiting for
   delayed packets), such as streaming media
   and online games
The Internet: UDP
   Supports broadcasting
   Different data flows are distinguished by
   different UDP port numbers
   Offers logical multiplexing of several flows
   originating and terminating at a common IP
   address
    – Data delivered by multicasting, not every client
      needs it separate connection -> sparing capacity
The Internet: Application layer
    Top layer in OSI model
    Makes sure that other party is identified and
    can be reached
    Provides authentication, if needed

    User protocols (file transfer, email, …)
     – HTTP, SMTP, FTP, POP3, TLS/SSL…
    Service protocols (network management)
     – RADIUS, SNMP
 The Internet
QoS Architectures
The Internet: QoS
 The lack of Quality of Service
   The Internet’s packet transport is not
   designed to provide specific QoS
    – rather offers an unreliable, nonsequential packet
      transport service
   TCP with its end-to-end structure tries to
   achieve a reliable and sequential packet
   transport service but still offers only some
   fair sharing of network bandwidth
   Aspects such as loss, response time,
   signal-to-noise ratio …
The Internet: QoS
 Different types of services have different
 needs
 Applications with QoS needed
   Real-time streaming multimedia
   VoIP, videoconferences, online games …
 Issues in Internet
   Large, diverse network
   Many private networks/network service providers
   Unpredictable behavior
 Two approaches to QoS
   IntServ vs DiffServ architecture
The Internet: QoS - IntServ
 Integrated Services Architecture
    The Integrated Services Architecture
    (IntServ) allows each session arriving to the
    network to request QoS guarantees
           » The session has to declare its traffic
             characteristics to the network
           » The network has the choice of rejecting the
             request or accepting it at some lower lever of QoS
    IntServ requires signaling protocols and
    packet-scheduling mechanisms in every
    router in parts of the network over which
    such QoS guarantees are needed
The Internet: QoS - IntServ
    Every application needs to make a
    reservation
    Flow Specs
     – describes what the reservation is for
    RSVP (resource reservation protocol)
     – Signals over the network


    It has to store many states in each router,
    thus, it is not suitable for large scale
    systems
The Internet: QoS - DiffServ
 Differentiated Services Architecture
    In the high-speed core of the network,
    session arrival rates and packet rates are
    too high to permit session-by-session
    analysis and packet-by-packet scheduling
    The Differentiated Services Architecture
    (DiffServ) allows packets to be assigned to
    different QoS classes
          » e.g., low-latency to traffic such as streaming
            media, and best-effort packet transport for other
            packets (web servers, file transfers)
The Internet: QoS - DiffServ
 Differentiated Services Architecture (cont.)
    The scheduling at the links distinguishes
    the different classes of packets

    The class of a packet is identified by the
    contents of its header
           » Either by the DiffServ code (DS code),
             which is part of the IP header, or
           » the source and destination addresses, or
           » the destination transport protocol port numbers
The Internet: QoS - DiffServ
 Differentiated Services Architecture (cont.)
    DiffServ core networks may set limits on the
    amounts of traffic of each class it is willing
    to accept from each customer network that
    transports traffic through it
    If a client network violates such restrictions,
    the DiffServ core can either
     – reject the excess traffic, or
     – handle it at lower levels of service
The Internet: QoS – IntServ vs. DiffServ
 IntServ vs. DiffServ
    The IntServ architecture is suitable in the
    lower-speed edges of the network
    DiffServ is sufficient for the core of the
    network, handling higher session arrival and
    packet rates

    In conjunction, IntServ and DiffServ
    architectures provide an overall end-to-end
    QoS to applications
The Internet: QoS – Traffic Engineering
 Traffic Engineering
    If there is enough sufficient bandwidth the
    best-effort packet transport (e.g., provided
    by the Internet Protocol) fulfills the
    requested QoS
    QoS can therefore be managed by network
    and traffic engineering
           » e.g., by deploying new bandwidth when needed
             (i.e., optical networks and such)
    But traffic engineering alone cannot
    address the problem of congestion in
    access networks

				
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posted:9/20/2012
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