3 Networking and Internetworking

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3 Networking and Internetworking

• As an infrastructure for DS
• Distributed computing rely on existing networks
  LANs, MANs, WANs (including internetworks) that
  use wired and/or wireless technologies
• Hence such characteristics as performance,
  reliability, scalability, mobility, and QoS of DS
  are impacted by the underlying network technology
  and the OS
• Principles of computer networking
• Every network has
• An architecture or layers of protocols
• Packet switching for communication
• Route selection and data streaming

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Networking and Internetworking 3.1 Intro

• Comm Subsystems (network technologies rest on)
• Transmission media wires, cables, fiber,
  wireless (sat, IR, RF, mwave)
• Hardware devices routers, switches, bridges,
  hubs, repeaters, network interfaces/card/transceiv
  ers
• Software components protocol stacks, comm
  handlers/drivers, OS primitives, network-focus
  APIs
• Hosts
• The computers and end-devices that use the comm
  subsystem
• Subnet A single cluster or collection of nodes,
  which reach each other on the same physical
  medium and capable of routing outgoing and
  incoming messages
• The Internet is a collection of several subnets
  (or intranets)

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Networking and Internetworking 3.1 Intro

• Networking issues for distributed systems
• Initial requirements for DS applications ftp,
  rlogin, email, newsgroup
• Subsequent generation of DS applics. on-line
  shared resources
• Current requirements performance, reliability,
  scalability, mobility, security, QoS,
  multicasting
• Performance
• Key time to deliver unit(s) of messages between
  a pair of interconnected computers/devices
  point-to-point latency (delay) from sending out
  of outgoing-buffer and receiving into
  incoming-buffer. Usually due to software
  overheads, traffic load, and path selection
• Data transfer/bit rate speed of data transfer
  between 2 computers (bps). Usually due to
  physical properties of the medium.
• Message trans time latency length/bit-rate

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Networking and Internetworking 3.1 Intro

• Bandwidth vs. bit-rate
• The total system bandwidth (volume of data sent
  and received in a unit time, e.g., per sec.) is a
  measure of its throughput
• Bit rate or transfer rate is restricted to the
  mediums ability to propagate individual
  bits/signals in a unit time
• In most LANs, e.g., Ethernets, when full
  transmission capacity is devoted to messaging
  (with little or no latency), then bandwidth and
  bit-rate are same in measure
• Local memory vs network resources
• Applications access to shared resources on same
  network usually under msec
• Applications access to local memory usually under
  msec (1000x faster)
• However, for high speed network web-server, with
  caches, the access time is much faster (than
  local disk access due to hard disk latency)

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Networking and Internetworking 3.1 Intro

• Scalability (Internet and DSs)
• Future growth of computing nodes of Internet
  (hosts, switches) in 109s (100s of 106 hosts
  alone)
• Requires substantial changes to routing and
  addressing schemes (more later!)
• Current traffic (load) on Internet approx.
  measured by the latencies (see www.mids.org),
  which seem to have reduced (with advances in
  medium and protocol types).
• Future growth and sustainability depend on
  economies of use, charge rate, locality/placement
  of shared resource
• Reliability
• Failures are typically, not due to the physical
  medium, but at the end-end (at host levels)
  software (application-level), therefore, error
  detection/correction is at the level
• Suggesting that the communication subsystem need
  not be error-free (made transparent/hidden to
  user) because reliability is somewhat guaranteed
  at the send/receiver ends (where errors may be
  caused by, e.g., buffer overflow, clock drifts
  causing premature timeouts)

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Networking and Internetworking 3.1 Intro

• Security
• Most intranets are protected from external
  (Internet-wide) DSs by firewall
• A firewall protects all the resources of an
  organized from unlawful/malicious access by
  external users, and control/monitoring of use of
  resources outside the firewall
• A firewall (bundle of security software and
  network hardware) runs on a gateway the
  entry/exit point of the corporate intranet
• A firewall is usually configured based on
  corporate security policy, and filters incoming
  and outgoing messages
• To go beyond firewalls, and grant access to
  world- or Internet-wide resources, end-to-end
  authentication, privacy, and security (Standards)
  are needed to allow DSs to function
• E.g., techniques are Cryptographic and
  Authentication usually implemented at a level
  above the communication subsystem
• Virtual Private Network (VPN) security concept
  allows intranet-level protection of such
  features/devices as local routers and secure
  links to mobile devices

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Networking and Internetworking 3.1 Intro

• Mobility
• Need wireless to support portable computers and
  hand-held devices
• Wireless links are susceptible to, e.g.,
  eavesdropping, distortions in medium,
  out-of-sight/range transmitters/receivers
• Current addressing and routing schemes are based
  on wired technologies, which have been adapted
  and, therefore, not perfect and need extensions
• QoS (Quality of Service)
• Meeting deadlines and user requirements in
  transmitting/processing streams of real-time
  multimedia data
• E.g., QoS requirements guaranteed bandwidth,
  timely delivery or bounded latencies, or dynamic
  readjustments to requirements (more later in Chp
  15)

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Networking and Internetworking 3.1 Intro

• Multicasting
• Most transmissions are point-to-point, but
  several involve one-to-many (either one-to-all
  broadcast or selective broadcast multicast)
• Simply sending the same message from one node to
  several destinations is inefficient
• Multicasting technique allows single transmission
  to multiple destination (simultaneously) by using
  special addressing scheme

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Networking and Internetworking 3.2 Type of
Networks

• 3.2 Types of Networks
• LANs (confined to smaller, typically, 2.5km
  diameter spread)
• higher speed, single medium for interconnection
  (twisted pair, coax, opt), no routing within
  segments all point-to-point (from hub),
  inter-segment connections via switches/hubs, low
  latency, low error rate
• E.g., Ethernet, token ring, slotted ring
  protocols, wired. (1) Ethernet 1970 with
  bandwidth of 10Mbps, with extended versions of
  100/1000Mbps, lacking latency and bandwidth QoS
  for DSs (2) ATM using frame cells and optical
  fills the gap but expensive for LAN, newer
  high-speed Ethernets offer improvement and
  cost-effective
• MANs (confined to extended, regional area,
  typically, up to 50km spread)
• Based on high-bandwidth copper and fiber optics
  for multimedia (audio/video/voice),
• E.g., technologies ATM, high-speed Ethernet
  (IEEE 802.6 protocols for MANs), DSL (digital
  subscriber line) using ATM switches to switch
  digitized voice over twisted pair _at_ 0.25-6Mbps
  within 1.5km, cable modem uses coax _at_ 1.5Mpbs
  using analog signaling on TV networks and longer
  distances than DSL

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Networking and Internetworking 3.2 Type of
Networks

• WANs (worldwide, lower speeds over sets of
  varying types of circuits with routers)
• High latency (due to switching and route
  searching) between 0.1-0.5s, signaling speed
  around 3x105km/s (bounds latency) plus
  propagation delay (round-trip) of about 0.2s if
  using satellite/geostationary dishes generally
  slower at 10-100kbps or best 1-2Mbps
• Wireless (connecting portable, wearable devices
  using access points)
• Common protocol IEEE 802.11 (a, b, and now g)
  (WaveLAN) _at_ 2-11Mbps (11gs bandwidth near
  54Mbps) over 150m creating a WLANs, some mobiles
  connected to fixed devices printers, servers,
  palmtops to create a WPANs (wireless personal
  area networks) using IR links or low-powered
  Bluetooth radio network tech _at_ 1-2Mbps over 10m.
• Most mobile cell phones use Bluetooth tech. e.g.,
  European GSM standard and US, mostly,
  analog-based AMP cellular radio network, atop by
  CDPD cellular digital packet data communication
  system, operating over wider areas at lower speed
  9.6-19.2kbps.
• Tiny screens of mobiles and wearables require a
  new WAP protocol
• Internetworks
• Building open, extendible system for DSs,
  supporting network heterogeneity, multi-protocol
  system involving LANs, MANs, WLANs, connected by
  routers and gateways with layers of software for
  data and protocol conversions creating a
  virtual network using underlying physical
  networks
• E.g., the Internet using TCP/IP (over several
  other physical protocols)

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Networking and Internetworking 3.2 Type of
Networks

• Comparisons
• Range of performance characteristics
• Frequency and types of failures, when used for
  DS applics
• Packet delivery/loss, duplicates (masked at TCP
  level to guarantee some reliability and
  transparency to DSs but may use UDP faster but
  less reliable and DS applics responsibility to
  guarantee reliability)

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Networking and Internetworking 3.3 Network
Principles

• 3.3 Network Principles
• Packet Transmission
• Packet transmission superseded
  telephone/telegraph switched network
• Messages are packetized and packets are queued,
  buffered (in local storage), and transmitted when
  lines are available using asynchronous
  transmission protocol
• Data Streaming
• Multimedia data cant be packetized due to
  unpredicted delays. AV data are streamed at
  higher frequency and bandwidth at continuous flow
  rate
• Delivery of multimedia data to its destination
  is time-critical / low latency requiring
  end-to-end predefined route
• E.g. networks ATM, IPv6 (next generation will
  separate steamed IP packets at network layer
  and use RSVP (resource reserv. protocol)
  resource/bandwidth prealloc and RTP
  play-time/time-reqs (real-time transp protocol)
  at layers 3 1, respectively) to work

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Networking and Internetworking 3.3 Network
Principles

• Switching Schemes 4 Kinds of switching methods
  typically used
• Broadcast no switching logic, all nodes see
  signals on circuits/cells (e.g., Ethernet,
  wireless networks)
• Circuit Switching Interconnected segments of
  circuits via switches/exchange boxes, e.g., POTS
  (Plain Old Telephone System)
• Packet Switching Developed as computing tech
  advanced with processors and storage spaces using
  store-and-forward algorithms and computers as
  switches. Packets are not sent instantaneously,
  routed on different links, reordered, may be
  lost, high latency (few msec msecs). Extension
  to switch audio/video data brought integration of
  digitized data for computer comm., telephone
  services, TV, and radio broadcasting,
  teleconferencing
• Frame Relay PS (not instantaneous, just an
  illusion!), but FR, which integrates CS and PS
  techniques, streams smaller packets (53
  byte-cells called frames) as bits at processing
  nodes. E.g., ATM

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Networking and Internetworking 3.3 Network
Principles

• Protocols
• Protocols implemented as pairs of software
  modules in send/receive nodes,
• Specify the sequence of messages for
  transmission
• Specify the format of the data in the messages
• Protocols Layers layered architecture,
  following the OSI suite
• packets are communicated as peer-to-peer
  transmission but effected vertically across
  layers by encapsulation method over a physical
  medium

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Networking and Internetworking 3.3 Network
Principles

• Protocols Layers layered architecture,
  following the OSI suite
• each protocol type is included in headers to
  help protocol stack at receiver end to unpack the
  encapsulated packets

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Networking and Internetworking 3.3 Network
Principles

• Protocols Suites The 7-layered architecture of
  the ISO-OSI
• Each layer provides service to the layer above
  it and extends the service provided by the layer
  below it
• A complete set of protocol layers constitute a
  suite or stack
• Layering simplifies and generalizes the software
  interface definitions, but costly overhead due to
  encapsulations and protocol conversions

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Networking and Internetworking 3.3 Network
Principles
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Networking and Internetworking 3.3 Network
Principles
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Networking and Internetworking 3.3 Network
Principles

• Protocols
• Packet Assembly
• Decomposing messages (packetizing) into packets,
  transmitting, and reassembling using sequence s
  at delivery-switch to receiving host in the
  transport layer. Applied to messages that exceed
  MTU (Max. transfer unit) of the switch. E.g.,
  Ethernet MTU is 1518 bytes and Internet MTU is
  8kbyes (min) to 64kbytes (max).
• Ports
• Software-defined transmission/delivery points for
  network-independent transport service on a host
  computer. Processes are typically attached to
  ports for pair-wise communication

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Networking and Internetworking 3.3 Network
Principles

• Protocols
• Addressing
• Transport layer addressing scheme, composed of
  network address (of host), I.e., the IP address,
  and the port number. The combined address is
  typically called a socket or transport address of
  the Transport Layer. Each host may have several
  port s for different kinds of protocols (e.g.,
  for HTTP, FTP) or services. Hosts send port
  numbers to clients to establish, e.g., TCP,
  connection. Finding port on server hosts in DS
  for arbitrary services requires RMI/RPC type of
  schemes
• Packet Delivery (at network layer)
• Datagram one-at-a-time, hop-by-hop transmission
  of packets with no storing of copies at switches,
  no setup of paths, unreliable and failures are
  handled by hosts, each packet contains full
  network address of source-to-destination, e.g.,
  Internet IP datagram in network layer and some
  wireless networks
• Virtual circuits set up of end-to-end
  path/address held in switch tables, no network
  address in packets except VC , switching at
  intermediate nodes, more reliable, latency
  depends on time to use the links/path segments,
  unlike POTS voice-links VC links can be shared
  and used/entered in multiple tables, e.g., ATM
• Note At transport layer, connection-oriented
  TCP is like virtual circuits, and connection-less
  UDP is like datagram

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Networking and Internetworking 3.3 Network
Principles

• Routing
• Routing is necessary in MANs and WANs, rarely in
  LANs since point-to-point is typically used in
  LANs. Adaptive/dynamic routing is usually used
  adapting to traffic patterns, topological
  changes, etc. Switching is done by multiple
  switches/routers in the subnet for host-to-host
  delivery using available routing algorithm.
• Algorithms depends on 1) Either using VC or
  datagram - depends on network type, e.g., ATM
  uses VC connection-oriented and Internet uses
  datagram connectionless packet-switching and 2)
  dynamics of the network topologically, traffic
  patterns
• Routing decision is made hop-by-hop, with period
  update and distribution of traffic data, e.g.,
  the distance-vector, dynamic, distributed
  algorithm

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Networking and Internetworking 3.3 Network
Principles
The Routing Table matrix/graph construction,
reflecting topology of network
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Networking and Internetworking 3.3 Network
Principles

• The RIP algorithm for dynamic update and
  distribution of routing table info
• Prepare RIP packets containing change-info and
  send to active links and update table if the new
  cost to a neighboring node is lower/better

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Networking and Internetworking 3.3 Network
Principles

• Congestion Control
• Link overload and queue overflows
• Packet dropping manageable at network layer
  using retransmission up to a threshold/limit
  (when throughput starts to decline)
• Congestion control methods arrest overload
  problem early (at higher nodes closer to hosts)
  or buffering of packets for longer times at
  intermediate nodes, or hosts throttle application
  programs and/or queue packets in hard-drives
• Example
• In datagram/IP/Internet connectionless networks,
  where host is responsible for network problems,
  choke packets are used to throttle senders
• In ATM, using connection-oriented protocol,
  congestion control schemes depend on the QoS
  specified in the service

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Networking and Internetworking 3.3 Network
Principles

• Internetworking
• Network technologies (or subnets)
• LANs Ethernet, ATM networks using different
  physical, data link, and network layers
• WANs Internet, using analog and digital POTS
  switched technologies, satellite links and
  wide-area ATM networks, and relying on underlying
  LANs and MANs
• Internetworking
• Integrated network of subnets using
• 1) unified internetworking addressing scheme for
  communication between host and any subnet
• 2) PDU (protocol data unit) format and
  conversion/handling protocols
• 3) standards/protocols and devices/switches for
  interconnecting and addressing component subnets
  and hosts
• Network (hardware) components routers, bridges,
  hubs, switches
• Tunneling Internetworking protocol, e.g., IPv6,
  for bridging a variety of physical subnets using
  packet encapsulation techniques. E.g., IPv6
  protocol packets encapsulated inside IPv4, IP,
  ATM PDUs and transported across a sea of IPv4,
  IP, ATM networks. Another, e.g., MobileIP
  transmits IP packets to other mobiles by
  encapsulating IP packets over other networks,
  Another, e.g., PPP for transmitting IP packets.

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Networking and Internetworking 3.3 Network
Principles
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Networking and Internetworking 3.3 Network
Principles
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Networking and Internetworking 3.4 Internet
Protocols
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Networking and Internetworking 3.4 Internet
Protocols

• Internet Protocols
• History 1970s research results. TCP Transport
  control protocol, IP Internet protocol
• Forms a single internetworking protocol (using
  IP datagram encapsulation methods)
• Many existing application-specific/layer
  protocols are based on / using TCP/IP i.e., built
  on top of TCP/IP (e.g., Web (HTTP), SMTP, POP,
  FTP, Telnet)
• When TCP is not enough additional higher-level
  protocol, e.g., SSL (secure socket protocol) for
  security, can be built atop TCP
• Internet protocols were initially developed for
  simple ftp and e-mails
• Exceptional networks not using TCP/IP WAP and
  protocols for multimedia
• Internet protocols usually layered over existing
  physical networks, e.g., over Ethernets and
  over telephone serial lines via PPP for modem
  connection

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Networking and Internetworking 3.4 Internet
Protocols

• Encapsulation
• Tags in the encapsulation help in determining
  and conversion (packing / unpacking packets)
  among protocol types

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Networking and Internetworking 3.4 Internet
Protocols
Conceptual (user view) architecture of TCP/IP
over transmission networks
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Networking and Internetworking 3.4 Internet
Protocols
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Networking and Internetworking 3.4 Internet
Protocols
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Networking and Internetworking 3.4 Internet
Protocols
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Networking and Internetworking 3.4 Internet
Protocols
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Networking and Internetworking 3.4 Internet
Protocols
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Networking and Internetworking 3.4 Internet
Protocols
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Networking and Internetworking 3.5 Network case
studies
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Networking and Internetworking 3.5 Network case
studies
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Networking and Internetworking 3.5 Network case
studies
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Networking and Internetworking 3.5 Network case
studies
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Networking and Internetworking 3.5 Network case
studies