Types of network

1
Chapter 3 Networking and Internetworking

• Introduction
• Types of network
• Network principles
• Internet protocols
• Network case studies
• Ethernet, wireless LAN and ATM
• Summary

2
Concepts

• Why should we study network technology?
• Network is the basis of distributed system
• The performance, reliability, scalability, of
  the underlying networks impact the behavior of DS
  and therefore affect their design
• Some concepts
• transmission media wire, cable, fiber and
  wireless channels
• hardware devices router, switch, bridge, hub,
  repeater and network interface
• software components protocol stacks,
  communication handler and driver
• communication subsystem the collection of
  hardware and software components that provide the
  communication facilities for a distributed
  system.
• host computers and devices that use the network
  for communication purpose
• node computer or switching device attached to a
  network
• subnet a unit of routing (delivering data from
  one part of Internet to another) its a
  collection of nodes that can be reached on the
  same physical network.

3
Networking issues for distributed systems

• Performance
• latency the delay that occurs after a send
  operation is executed before data starts to
  arrive at the destination computer. It can be
  measured as the time the time to transfer an
  empty message. It forms a part of
  process-to-process latency.
• data transfer rate the speed at which data can
  be transferred between two computers in the
  network once transmission has begun, bits/s
• Message transmission time latency length /
  data transfer rate
• data transfer rate is determined primarily by
  network physical characteristics, whereas the
  latency is determined primarily by software
  overheads, routing delays and delay of accessing
  to transmission channels
• In distributed systems, messages are always small
  in size, so the latency is more significant than
  data transfer rate
• total system bandwidth the total volume of
  traffic that can be transferred across the
  network in a given time.
• Ethernet system bandwidth is as same as data
  transfer rate
• WAN multiple channels, deteriorates when there
  are too many messages
• Comparison of different communication channel
• local network a null message transmission time
  is under a millisecond
• local memory - 1000 or more times faster than
  local network
• local hard disk - 500 times slower than fast
  local network
• Internet - round-trip latencies are in 300-600ms
  due to switching and contention

4
Networking issues for distributed systems
continued

• Scalability
• WWW world wide wait ?
• future Internet several billion nodes and
  hundreds of millions of active hosts, new
  addressing and routing mechanisms
• Reliability
• Networks are highly reliable, whereas client and
  server computers and their software often aren't,
  so error detection and recovery is best performed
  end-to-end at the highest feasible level.
• Errors e.g. failures in software of sender or
  receiver, or buffer overflow
• Security
• Firewall to protect the resources in all of the
  computers inside the organization from access by
  external users or processes and to control the
  use of resources outside the firewall by users
  inside the organization, always runs on a gateway
• Secure network environment, e.g. VPN
• Mobility
• Although the current mechanisms have been adapted
  and extended to support them, the expected future
  growth in the use of mobile devices will require
  further extension
• QoS
• require guaranteed bandwidth and bounded
  latencies
• Multicasting
• Need for one-to-many communication

5
Chapter 3 Networking and Internetworking

• Introduction
• Types of network
• Network principles
• Internet protocols
• Network case studies Ethernet, wireless LAN and
  ATM
• Summary

6
Types of network

• Local area networks (LANs)
• high speed, connected to a single communication
  medium, no routing of messages, may have switches
  or hubs
• Ethernet, Token rings and (1970s),
• 10M -gt 100M -gt 1000M (G)
• Wide area networks (WAN)
• lower speeds, links between different cities,
  countries or continents
• communication medium is a set of communication
  circuits linking a set of dedicated computers
  called routers
• Metropolitan area networks (MANs)
• Ethernet, ATM, DSL(digital subscriber line)
• Wireless networks
• IEEE 802.11(WaveLAN) 2-11mbps over 150 meters
• WPANs (wireless personal area networks)
  infra-red links, BlueTooth (1-2 mbps over 10
  meters)
• digital mobile phone network European GSM/USA
  CDPD (up to 2 mbps)
• WAP (Wireless Application Protocol)

7
Types of networks continued

• Internetworks
• several networks are linked together to provide
  common data communication facilities that conceal
  the technology differences.
• They are interconnected by routers and gateways
• e.g. Internet
• Network comparisons
• different failure model TCP vs. UDP

8
Chapter 3 Networking and Internetworking

• Introduction
• Types of network
• Network principles
• Internet protocols
• Network case studies Ethernet, wireless LAN and
  ATM
• Summary

9
Network Switching technology

• Packet switching
• Store and forward, share communication link,
  asynchronous
• Packet transmission
• Messages arbitrary length
• Packet restricted length
• Sufficient buffer storage at each node, avoid
  undue delays
• Data streaming
• Video stream bandwidth requirement, continues
  flow e.g. frame N arrives no more than N/24
  seconds after the first frame arrives
• Bandwidth, latency and reliability must be
  guaranteed predefined route, e.g. ATM and IPv6
• Switching schemes
• Broadcast no switching, Ethernet
• Circuit switching telephone system
• Packet switching
• Frame relay combination of circuit switching and
  packet switching
• Delay Internet -200 milliseconds, telephone - 50
  milliseconds, ATM - a few tens of microseconds

10
Network Protocols

• Protocol
• A specification of the sequence of messages that
  must be exchanged
• A specification of the format of the data in the
  messages
• Protocol layers
• Each layer presents an interface to the layers
  above it that extends the properties of the
  underlying communication system
• Layer encapsulations (n1)
• Protocol suits ( protocol stack)
• Seven-layer Reference Model for OSI adopted by
  ISO
• Simplify and generalize the communication
  interface, but bring significant cost, e.g., N
  copies

11
Encapsulation of a packet
12
Other important concepts in network protocol

• Packet assembly
• Networklayer protocol packets MTU (Maximum
  transfer unit), 1500Bytes in Ethernet, 64K in IP
• Ports
• Software definable destination points for
  communication within a host computer
• Transport address network address port
  number,
• Port numbers above 1023 are available for general
  use
• Packet delivery
• Datagram packet delivery, e.g. IP, Ethernet, and
  most wired and wireless LAN
• Virtual circuit packet delivery, e.g., ATM
• Different to the concepts of Connection oriented
  (TCP)/Connectionless (UDP) in transport layer
  protocol

13
Routing

• Routing algorithm
• Determine the route taken by each packet.
• Predetermined for circuit switching (e.g. X.25)
  and frame relay switching (e.g. ATM) determine
  on the fly for packet switching
• Dynamically update its knowledge of the network
• Distance vector
• Bellman-Ford protocol1957
• RIP (router information protocol)
• Periodically, and whenever the local routing
  table changes, send the router table to all
  accessible neighbours
• When a table is received from a neighbouring
  router, make necessary update
• Convergence problem
• Improvement link cost include bandwidth
  information, speed convergence, etc

14
Routing continued

• Link state algorithm
• Each node maintains all knowledge of the network
• Each node can compute appropriate routes based on
  the knowledge
• Avoid slow convergence and undesirable
  intermediate states
• E.g. OSPF

15
Congestion control

• A rule of thumb
• when the load on a network exceeds 80 of its
  capacity, the total throughput tends to drop as a
  result of packet losses
• Congestion control
• instead of allowing packets to travel through the
  network until they reach over-congested nodes,
  hold them at earlier nodes
• Control approaches
• Informing nodes along the congested route to
  reduce packet transmission rate, i.e buffering
  for long time at intermediate nodes or queue
  packets at source host
• In the Internet, congestion control rely on the
  end-to-end traffic control, e.g. choke packets
  requesting a reduction in transmission rate in TCP

16
Internetworking

• Internetwork
• integrate many subnets that use different network
  technologies
• Requirements
• Unified internetwork addressing scheme that
  enables packets to be addressed to any host
  connected to any subnet
• A protocol defining the format of internetwork
  packets and giving rules according to which they
  are handled
• Interconnecting components that route packets to
  their destinations in terms of internetwork
  addresses, transmitting the packets using subnets
  with a variety of network technologies
• Example

17
Internetworking components

• Router
• Conduct routing, additionally link networks of
  different types
• Bridge
• link networks of different types, but not conduct
  routing
• Hub
• Connect hosts and extend segments of Ethernet and
  other broadcast local network
• Switch
• Perform similar function to router, but for LANs
  only
• Tunnel
• A software layer that transmits packets through
  an alien network environment

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Chapter 3 Networking and Internetworking

• Introduction
• Types of network
• Network principles
• Internet protocols
• Network case studies Ethernet, wireless LAN and
  ATM
• Summary

19
Internet protocols

• Protocol layers (n1)
• TCP(UDP)/IP,(n2) web HTTP, Email SMTP,POP,
  news NNTP, FTP, SSL, etc
• Exceptions to the universal adoption of TCP/IP
• The use of WAP for wireless applications on
  portable devices
• Special protocols to support multimedia streaming
  applications
• Heterogeneous underlying networks support
• The success of TCP/IP independence of the
  underlying transmission technology (n3)
• E.g., IP over ATM, IP over Ethernet, IP over PPP,
  etc

20
Internet protocol layers
21
Encapsulation in a message transmitted via TCP
over an Ethernet
22
The programmers conceptual view of a TCP/IP
Internet
23
IP addressing

• Schemes for naming and addressing hosts and for
  routing IP packets to their destination is
  challenging.
• Requirement
• It must be universal
• It must be efficient
• The addressing scheme must lend itself to the
  development of routing scheme
• The scheme
• A 32-bit numeric identifier containing a network
  identifier and a host identifier
• There are four allocated classed of Internet
  address-A,B,C,D

24
Internet address structure
28
25
Decimal representation of Internet addresses
Two steps were taken IPv6, Classless interdomain
routing (CIDR)
26
IP protocol

• Transmits datagrams from one host to another, if
  necessary via intermediate routers
• Unreliable (best-effort) delivery semantics
• packets can be lost, duplicated, delayed or
  delivered out of order
• Address resolution Address Resolution
  Module(ARP)
• IP address -gt Ethernet address mapping, (IP
  address, Ethernet address) pairs cache on each
  host

27
IP routing

• Routs packets from source to destination
• Internet topology Autonomous System, Areas(n1)
• Routing algorithms
• RIP -1
• RIP-2
• Open Short Path First (OSPF)
• Default routes trade routing efficiency for
  table size
• Classless interdomain routing (CIDR) create
  subnet by means of subdividing address or
  aggregating addresses by mask field, e.g.
  162.105.203.0/24

28
Internet topology
29
Future of IP

• IPv6(n1)
• 2128 (31038) addresses, 1000 IP addresses per
  square meter of the Earths surface
• Routing speed no checksum, no fragmentation
• Real time priority and flow label which is used
  to reserve resources
• Extension header ( information of router,
  authentication, etc),
• multicast and anycast
• Security through extension header type
• Migration from IPv4
• IPv6 router island,
• depend on economics

30
IPv6 header layout
31
The MobileIP routing mechanism
32
TCP and UDP

• Use of ports
• Provide process-to-process communication
• UDP features
• TCP features

33
UDP features

• Connectionless
• Datagram delivery
• A UDP datagram is encapsulated inside an IP
  packet, up to 64kb in size
• Con
• unreliable delivery due to unreliable IP
• Pro
• minimal additional cost and transmission delays

34
TCP

• Connection oriented
• two side must shake hands to establish a
  bi-directional communication channel
• Message delivery
• Deliver arbitrary long sequences of bytes via
  stream-based programming abstraction
• Sequencing divide stream into data segments,
  sequence number on each segment
• Checksum cover the header and the data in the
  segment
• Flow control
• Receiver send the highest number of received
  segment and window size to sender by acknowledge
  message
• Buffering receiver buffer and sender buffer used
  for flow control
• In interactive application, receiver inform
  sender when timeout or the buffer reaches the MTU
  limit
• Retransmission retransmit the segment when no
  acknowledgement within a specified timeout

35
Domain names

• Symbolic names for hosts and networks
• pku.edu.cn
• The DNS would not workable without the extensive
  use of caching.

36
Firewall

• The purpose of a firewall is to monitor and
  control all communication into and out of an
  intranet
• including service control,
• behavior control
• and user control
• Filter approaches (n1)
• IP packet filtering, e.g. router/filter
• TCP gateway, e.g. bastion
• Application level gateway, e.g. telnet proxy
  process
• Virtual private networks (VPN)
• Secure connections located at different sites
  using public Internet links
• By the use of cryptographically protected secure
  channels at the IP level

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Firewall configurations
38
Chapter 3 Networking and Internetworking

• Introduction
• Types of network
• Network principles
• Internet protocols
• Network case studies Ethernet, wireless LAN and
  ATM
• Summary

39
Ethernet

• IEEE 802.3Xerox 1973
• Carrier sensing, multiple access with collision
  detection
• Frame broadcasting
• Bandwidth 3m -gt 10m -gt 100m -gt 1000m
• Ethernet packet layout (n1)
• 248 different addresses
• Packet collisions
• Carrier sensing
• wait until no signal is present then transmit
• Collision detection
• When transmit through output port, also listen on
  the input port, and compare the two signals, If
  differ, send jamming signal
• Back-off
• wait a time n? before retransmitting, n a random
  integer

40
Ethernet frame layout
41
Ethernet continued

• Ethernet efficiency
• Efficiency number of packets transmitted
  successfully / theoretical maximum number without
  collision
• Affected by
• A finite time for a signal inserted at a point in
  the media to reach all other points
• number of stations on the network
• stations level of activity

42
Wireless LAN

• Wireless LAN types
• Infrastructure network, e.g. IEEE 802.11 (n1)
• Ad hoc network network built on the fly
• Collision detection failures in 802.11
• Hidden stations carrier sensing fail to detect
  that another station on the network is
  transmitting, lead to collision at base station
• Fading the strength of radio signals diminishes
  rapidly with the distance from the transmitter,
  so that defeating both carrier sensing and
  collision detection
• Collision masking

43
Wireless LAN configuration
44
802.11 introduction

• Slot reservation added to the MAC protocol in
  802.11
• Firstly, sense the medium, if no carrier signal,
  then
• medium is available
• an out-of-range station is in the process of
  requesting a slot
• an out-of-range station is using a slot
• Sender send a RTS (Request To Send) frame to
  receiver Receiver reply a CTS (Clear To Send)
  frame to sender. The effect of the exchange is
• the station within range of sender will pick up
  the RTS frame and take note of the duration
• the station within range of receiver will pick up
  the CTS frame and take note of the duration
• Begin to transmit

45
802.11 introduction continued

• 802.11 avoid collisions in ways
• CTS frames avoid the hidden station and fading
  problem
• If RTS/CTS is corrupted, then a back-off period
  is used
• When RTS/CTS exchange correctly, there is no
  collisions in the following communication except
  intermittent fading prevents a third party from
  receiving either of them
• Security in 802.11
• Shared-key authentication mechanism
• XOR operation on the base of shared key to
  prevent from eavesdropping

46
Asynchronous Transfer Mode networks (ATM)

• Deploy ATM on top of other networks
• Can be implemented over existing digital
  telephony networks, Bandwidth from 32 kbps
  (voice) to 622mbps
• Native mode Over optical fiber, copper and other
  transmission media, bandwidth up to several
  gigabits per seconds
• ATM layers (n1)
• Adaptation layer
• end-to-end layer implemented at the sending and
  receiving host
• ATM layer
• connection-oriented service that transmits fixed
  length packets called cells, avoid flow control
  and error checking at the switching, provide
  bandwidth and latency guarantees
• VC (virtual channel) a logical unidirectional
  association between two endpoints of a link in
  the physical path from source to destination
• VP (virtual path) a bundle of virtual channel
  that are associated with a physical path between
  two switching nodes

47
ATM protocol layers
48
ATM continued

• The nodes in a ATM network can play three
  distinct roles (n1)
• Hosts send and receive messages
• VP switches hold tables showing the
  correspondence information between incoming and
  outgoing VPs
• VP/VC switches correspondence information for
  both VPs and VCs
• ATM cell 5-bytes header and a 48-byte data field

49
Switching virtual paths in an ATM network
50
Chapter 3 Networking and Internetworking

• Introduction
• Types of network
• Network principles
• Internet protocols
• Network case studies Ethernet, wireless LAN and
  ATM
• Summary

51
Summary

• Layered protocols
• 7 layers in OSI model / 5 layers in the Internet
• Delivery approach
• Packet switch, frame relay
• Routing mechanism
• distance vector / link state
• Congestion control
• The Internet
• TCP/IP
• Network cases
• Ethernet, WLAN, ATM

52
OSI protocol summary
53
Distance-Vector Routing table for the network
54
Psudo-code for RIP routing algorithm
Send Each t seconds or when Tl changes, send Tl
on each non-faulty outgoing link. Receive
Whenever a routing table Tr is received on link
n for all rows Rr in Tr if (Rr.link ltgt n)
Rr.cost Rr.cost 1 Rr.link n if
(Rr.destination is not in Tl) add Rr to Tl
// add new destination to Tl else for all rows Rl
in Tl if (Rr.destination Rl.destination and
(Rr.cost lt Rl.cost or Rl.link n)) Rl Rr //
Rr.cost lt Rl.cost remote node has better
route // Rl.link n remote node is more
authoritative
55
Simplified view of the QMW Computer Science
network
56
Tunnelling
57
ATM cell layout