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ITC242 Introduction to Data Communications Internet Operation

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Title: ITC242 Introduction to Data Communications Internet Operation


1
ITC242 Introduction to Data Communications
Internet Operation
2
Last Week
  • SMTP - transmits messages to appropriate hosts
    via TCP, attempts to provide error-free
    transmission.
  • MIME - Intended to resolve problems with SMTP,
    provides info about body of message, defines
    multiple content formats, and encodings
  • HTTP - Stateless protocol, flexible format
    handling, Proxy, Gateway, Tunnel, Cache
  • SIP - Manages real-time sessions over IP, enable
    Internet telephony/VoIP, HTTP-like
    request/response transaction model

3
Last Week
  • Client/server - user-friendly client
    applications, centralized databases, open and
    modular applications, the network is fundamental
  • Intranet - internet-based client/server
    technology within an organization, immensely
    successful
  • Extranets Extend intranet concept to outside
    community, e.g customers and suppliers, enables
    sharing of information between companies, TCP/IP
    enabled form of EDI.

4
Topic 8 Internet Operation
  • Learning Objectives
  • Describe the characteristics of an Internet
    Address
  • Describe the different classes of IP addresses
  • Explain the purpose of subnet masks.

5
Network Layer
  • transport segment from sending to receiving host
  • on sending side encapsulates segments into
    datagrams
  • on rcving side, delivers segments to transport
    layer
  • network layer protocols in every host, router
  • router examines header fields in all IP datagrams
    passing through it

6
Two Key Network-Layer Functions
  • forwarding move packets from routers input to
    appropriate router output( within a single
    router)
  • routing determine route taken by packets from
    source to dest.
  • routing algorithms
  • analogy
  • routing process of planning trip from source to
    dest
  • forwarding process of getting through single
    interchange

7
Interplay between routing and forwarding
8
The Internet Network layer
  • Host, router network layer functions

Transport layer TCP, UDP
Network layer
Link layer
physical layer
9
IP protocol IP Addresses
  • IP (Version 4) addresses are 32 bits long
  • IP addresses are hierarchical
  • They contain a network ID and a host ID
  • IP addresses are assigned statically or
    dynamically (e.g. DHCP)
  • IP (Version 6) addresses are 128 bits long

10
IP protocol IP Addresses
  • Interface connection between host/router and
    physical link
  • routers typically have multiple interfaces
  • host typically has one interface
  • IP addresses associated with each interface
  • Every interface has a unique IP address
  • A computer might have two or more IP addresses
  • A router has many IP addresses

223.1.1.1
223.1.2.9
223.1.1.4
223.1.1.3
223.1.1.1 11011111 00000001 00000001 00000001
223
1
1
1
11
IP Address Classes
Originally there were 5 classes
24
1
7
CLASS A 00000000-01111111(127) 1-126
Host-ID
0
Net ID
16
2
14
CLASS B 100000000-10111111 128-191 21416,384
Class B addresses
Host-ID
10
Net ID
8
3
21
CLASS C 11000000-11011111 192-223 2212,097,1
52
110
Net ID
Host-ID
4
28
CLASS D
1110
Multicast Group ID
5
27
CLASS E
11110
Reserved
A
B
C
D
0
232-1
12
IP AddressesExamples
Class A address www.mit.edu 18.181.0.31
(18lt128 gt Class
A) Class B address mekong.stanford.edu 171.
64.74.155
(128lt171lt12864 gt Class B)
13
IP Address
  • Some Problems
  • Address classes were too rigid. For most
    organizations, Class C were too small and Class B
    too big. Led to inefficient use of address space,
    and a shortage of addresses.
  • Small organizations wanted Class B in case they
    grew to more than 255 hosts. But there were only
    about 16,000 Class B network IDs.

14
Solution ?
  • Subnetting within an organization to subdivide
    the organizations network ID.

15
Subnets
16
2
14
CLASS B e.g. Company
Host-ID
10
Net ID
16
16
2
14
2
14
e.g. Site
Host-ID
0000
Host-ID
1111
10
Net ID
10
Net ID
Subnet ID (20)
Subnet Host ID (12)
Subnet ID (20)
Subnet Host ID (12)
16
16
2
14
2
14
e.g. Dept
10
Net ID
Host-ID
Host-ID
1111011011
10
Net ID
000000
Subnet ID (26)
Subnet Host ID (6)
Subnet ID (22)
Subnet Host ID (10)
16
Subnets
223.1.1.1
  • IP address
  • subnet part (high order bits)
  • host part (low order bits)
  • Whats a subnet ?
  • device interfaces with same subnet part of IP
    address
  • can physically reach each other without
    intervening router

223.1.2.1
223.1.1.2
223.1.2.9
223.1.1.4
223.1.2.2
223.1.1.3
223.1.3.27
subnet
223.1.3.2
223.1.3.1
network consisting of 3 subnets
17
Subnets
  • Recipe
  • To determine the subnets, detach each interface
    from its host or router, creating islands of
    isolated networks. Each isolated network is
    called a subnet.

Subnet mask /24
18
Subnets Subnet Masks
  • Allows for subdivision of internets within an
    organization
  • Each LAN can have a subnet number, allowing
    routing among networks
  • Host portion is partitioned into subnet and host
    numbers

19
Subnet Mask Calculations
20
Example of Subnetworking
21
Subnet masks
Source http//zdnetasia.com/insight/network/0,390
44847,39372217,00.htm
22
IP addresses how to get one?
  • Q How does network get subnet part of IP addr?
  • A gets allocated portion of its provider ISPs
    address space

ISP's block 11001000 00010111 00010000
00000000 200.23.16.0/20 Organization 0
11001000 00010111 00010000 00000000
200.23.16.0/23 Organization 1 11001000
00010111 00010010 00000000 200.23.18.0/23
Organization 2 11001000 00010111 00010100
00000000 200.23.20.0/23 ...
..
. . Organization 7
11001000 00010111 00011110 00000000
200.23.30.0/23 a.b.c.d/x
where x bits constitute the network portion
of The IP address, and often referred to as the
prefix of the address
23
IP addresses how to get one?
  • Q How does host get IP address?
  • hard-coded by system admin in a file
  • Wintel control-panel-gtnetwork-gtconfiguration-gttcp
    /ip-gtproperties
  • DHCP Dynamic Host Configuration Protocol
    dynamically get address from a server
  • plug-and-play
  • Goal allow host to dynamically obtain its IP
    address from network server when it joins network
  • Can renew its lease on address in use
  • Allows reuse of addresses (only hold address
    while connected an on
  • Support for mobile users who want to join
    network

24
IP addressing the last word...
  • Q How does an ISP get block of addresses?
  • A ICANN Internet Corporation for Assigned
  • Names and Numbers
  • allocates addresses
  • manages DNS
  • assigns domain names, resolves disputes

25
The Internet Network layer
  • Host, router network layer functions

Transport layer TCP, UDP
Network layer
Link layer
physical layer
26
The Problem
A
B
R2
R1
R4
R3
How does R1 choose a route to host B?
27
Routing Metrics
  • Metrics
  • Delay to send an average size packet (Make high
    speed links attractive, but closeness counts)
  • Bandwidth
  • Link utilization
  • Stability Is a link (or path) up or down?
  • Today about 1/3 of Internet routes are
    asymmetric

28
Technique 1 Naïve Approach
Flood! -- Routers forward packets to all
ports except the ingress port.
  • Advantages
  • Simple.
  • Every destination in the network is reachable.
  • Disadvantages
  • Some routers receive a packet multiple times.
  • Packets can go round in loops forever.
  • Inefficient.

29
Technique 2 Bellman-Ford Algorithm
Objective Determine the route from (R1, , R7)
to R8 that minimizes the cost.
Examples of link cost Distance, data rate,
price, congestion/delay,
1
1
4
R1
R6
R4
R2
2
3
2
2
R7
3
R5
2
R3
4
R8
30
Example network
In this simple case, solution is clear from
inspection
A
1
1
4
R1
R6
R4
R2
2
3
2
2
R7
3
R5
2
R3
4
R8
B
31
So what about this network...!?The public
Internet in 1999
Learn more at http//www.lumeta.com
32
Technique 3 Dijkstras Shortest Path First
Algorithm
  • The algorithm identifies the least costly paths
    between source and destination, given that costs
    are assigned to the edges.
  • Routers send out update messages whenever the
    state of a link changes. Hence the name Link
    State algorithm.
  • Each router calculates lowest cost path to all
    others, starting from itself.

33
The problem
  • How to route in the Internet?

34
Internet Routing Protocols
  • Responsible for receiving and forwarding packets
    between interconnected networks
  • Must dynamically adapt to changing network
    conditions

35
Autonomous Systems (AS)
  • Key characteristics
  • Set of routers and networks managed by single
    organization
  • group of routers exchanging information via a
    common routing protocol
  • connected (in a graph-theoretic sense) that is,
    there is a path between any pair of nodes

36
Autonomous System Example
37
Directed Graph of Example
38
Routing in the Internet
  • The Internet uses hierarchical routing
  • The Internet is split into Autonomous Systems
    (ASs)
  • Within an AS, the administrator chooses an
    Interior Gateway Protocol (IGP)
  • Examples of IGPs RIP (rfc 1058), OSPF (rfc
    1247).
  • Between ASs, the Internet uses an Exterior
    Gateway Protocol
  • ASs today use the Border Gateway Protocol, BGP-4
    (rfc 1771)

39
Routing in the Internet
  • The Internet uses hierarchical routing
  • The Internet is split into Autonomous Systems
    (AS)
  • aggregate routers into regions, AS
  • routers in same AS run same routing protocol
  • intra-AS routing protocol
  • routers in different AS can run different
    intra-AS routing protocol
  • Gateway router
  • Direct link to router in another AS

40
Interconnected ASes
  • forwarding table configured by both intra- and
    inter-AS routing algorithm
  • intra-AS sets entries for internal dests
  • inter-AS Intra-As sets entries for external
    dests

41
Inter-AS tasks
  • AS1 must
  • learn which dests reachable through AS2, which
    through AS3
  • propagate this reachability info to all routers
    in AS1
  • Job of inter-AS routing!
  • suppose router in AS1 receives datagram dest
    outside of AS1
  • router should forward packet to gateway router,
    but which one?

42
Example Setting forwarding table in router 1d
  • suppose AS1 learns (via inter-AS protocol) that
    subnet x reachable via AS3 (gateway 1c) but not
    via AS2.
  • inter-AS protocol propagates reachability info to
    all internal routers.
  • router 1d determines from intra-AS routing info
    that its interface I is on the least cost path
    to 1c.
  • installs forwarding table entry (x,I)


x
3a
3b
2a
AS3
AS2
1a
AS1
43
Example Choosing among multiple ASs
  • now suppose AS1 learns from inter-AS protocol
    that subnet x is reachable from AS3 and from AS2.
  • to configure forwarding table, router 1d must
    determine towards which gateway it should forward
    packets for dest x.
  • this is also job of inter-AS routing protocol!



x
44
(No Transcript)
45
Internet inter-AS routing BGP
  • BGP (Border Gateway Protocol) the de facto
    standard
  • maintain a table of IP networks or 'prefixes'
    which designate network reachability among AS.
  • BGP provides each AS a means to
  • Obtain subnet reachability information from
    neighboring ASs.
  • Propagate reachability information to all
    AS-internal routers.
  • Determine good routes to subnets based on
    reachability information and policy.
  • allows subnet to advertise its existence to rest
    of Internet I am here

46
BGP basics
  • pairs of routers (BGP peers) exchange routing
    info over TCP connections BGP sessions
  • when AS2 advertises prefix to AS1
  • AS2 promises it will forward any addresses
    datagrams towards that prefix.
  • AS2 can aggregate prefixes in its advertisement

eBGP session
iBGP session
3a
3b
2a
AS3
AS2
1a
AS1
47
Distributing reachability info
  • using eBGP session between 3a and 1c, AS3 sends
    prefix reachability info to AS1.
  • 1c can then use iBGP do distribute new prefix
    info to all routers in AS1
  • 1b can then re-advertise new reachability info to
    AS2 over 1b-to-2a eBGP session
  • when router learns of new prefix, creates entry
    for prefix in its forwarding table.

eBGP session
iBGP session
3a
3b
2a
AS3
AS2
1a
AS1
48
Intra-AS Routing Protocols
  • OSPF(Open Shortest Path First) A link-state
    protocal
  • Link-state updates sent (using flooding) as and
    when required. A router broadcasts routing
    information to all other routers in the AS, not
    just to its neighboring routers.
  • Every router locally runs Dijkstras algorithm to
    determine a shortest-path tree to all subnets.
  • Authenticated updates all OSPF messages
    authenticated (to prevent malicious intrusion)
  • Autonomous system may be partitioned into
    areas.
  • hierarchical OSPF in large domains

49
Hierarchical OSPF
50
Hierarchical OSPF
  • two-level hierarchy local area, backbone.
  • Link-state advertisements only in area
  • each nodes has detailed area topology only know
    direction (shortest path) to nets in other areas.
  • area border routers summarize distances to
    nets in own area, advertise to other Area Border
    routers.
  • backbone routers run OSPF routing limited to
    backbone.
  • boundary routers connect to other ASs.

51
Topic 9 LAN architecture and protocols
  • Learning Objectives
  • Define the various types of Local Area Networks
    (LANs)
  • Discuss the different types of transmission media
    commonly used in LANs.

52
Backend Storage Area Networks
  • Computer room networks
  • High data rate
  • High-speed interface
  • Distributed access
  • Limited distance
  • Limited number of devices

53
Storage Area Network (SAN)
  • A separate network to handle storage needs
  • Decouples storage tasks from specific servers
  • Creates a shared storage facility across a
    high-speed network

54
High-Speed Office Networks
  • Increased processing and transfer requirements in
    many graphics-intensive applications now require
    significantly higher transfer rates
  • Decreased cost of storage space leads to program
    and file bloat, increased need for transfer
    capacity
  • Typical office LAN runs at 10Mbps, high-speed
    alternatives run at 100Mbps, 1 Gbps, 10Gbps

55
Backbone Local Networks
  • Used instead of single-LAN strategy
  • Better reliability
  • Higher capacity
  • Lower cost

56
Factory Networks
  • High capacity
  • Ability to handle a variety of data traffic
  • Large geographic extent
  • High reliability
  • Ability to specify and control transmission delays

57
Tiered LANs
  • Cost of attachment to a LAN tends to increase
    with data rate
  • Alternative to connecting all devices is to have
    multiple tiers
  • Multiple advantages
  • Higher reliability
  • Greater capacity (less saturation)
  • Better distribution of costs based on need

58
Tiered LAN Diagram
59
The Media
  • The Transmission Media is the physical path
    between transmitter and receiver
  • Can be classified as guided or unguided
  • For both transmission is with electromagnetic
    waves.
  • Guided Media waves are guided along a solid
    medium, e.g. cables
  • Unguided Media wireless transmission

60
Guided Media
  • Twisted Pair Wires
  • Coaxial Cable
  • Fibre Optic Cable

61
Twisted Pair Wires
  • Consists of two insulated copper wires arranged
    in a regular spiral pattern to minimize the
    electromagnetic interference between adjacent
    pairs
  • Often used at customer facilities and also over
    distances to carry voice as well as data
    communications
  • Low frequency transmission medium

62
Types of Twisted Pair
  • STP (shielded twisted pair)
  • the pair is wrapped with metallic foil or braid
    to insulate the pair from electromagnetic
    interference

63
Types of Twisted Pair
  • UTP (unshielded twisted pair)
  • each wire is insulated with plastic wrap, but the
    pair is encased in an outer covering

64
Ratings of Twisted Pair
  • Category 3 UTP
  • data rates of up to 16mbps are achievable
  • Category 5 UTP
  • data rates of up to 100mbps are achievable
  • more tightly twisted than Category 3 cables
  • more expensive, but better performance
  • Category 5e UTP 1Gbps
  • Category 6 UTP- Up to 10 Gbps
  • STP
  • More expensive, harder to work with

65
Twisted Pair Advantages
  • Inexpensive and readily available
  • Flexible and light weight
  • Easy to work with and install

66
Twisted Pair Disadvantages
  • Susceptibility to interference and noise
  • Attenuation problem
  • For analog, repeaters needed every 5-6km
  • For digital, repeaters needed every 2-3km

67
Coaxial Cable (or Coax)
  • Used for cable television, LANs, telephony
  • Has an inner conductor surrounded by a braided
    mesh
  • Both conductors share a common center axial,
    hence the term co-axial
  • Traditionally used for LANs, but growth of
    twisted pair for local nets and optical fiber for
    larger nets has reduced coax use

68
Fiber Optic Cable
  • Fiber optic cable is used for modular light
    transmission. Instead of transmitting electrical
    signals, it transmits pulses of light that
    represent bits.
  • Advantages
  • Greater capacity
  • Smaller size/lighter weight
  • Lower attenuation
  • Electromagnetic isolation
  • Operate in the range of about 1014 to 1015 Hz
    (portions of the infrared and visible spectrums)

69
Fiber Optic Layers
  • consists of three concentric sections

70
Fiber Optic Types
  • single-mode fiber
  • A single-mode cable uses lasers to generate
    light. It allows just one mode of light to pass
    through it at a time, but is capable of greater
    bandwidth and greater distances than multimode
    cable. It is more expensive than multimode cable,
    and has a maximum cable length of 60 kilometers
  • multimode fiber
  • Multimode cable allows multiple light modes to
    pass along its fibers. Favored in workgroup
    applications, multimode cable uses light emitting
    diodes (LEDs) to generate light. A multimode
    fiber optic cable cannot exceed 2 kilometers.

71
Fiber Optic Signals
fiber optic multimode step-index
fiber optic single mode
72
Comparison of Media
  • Twisted pair cable is a common cable type - it is
    available as shielded twisted pair (STP) or
    unshielded twisted pair (UTP). STP cable combines
    the techniques of twisting wires and shielding.
    UTP cable is a copper wire-based cable used in a
    variety of networks. Coaxial cable operates
    over relatively large distances, and transmits
    data at speeds of up to 100 Mbps. Installing
    coaxial cable is more expensive than installing
    twisted pair cable.Fiber optic cable transmits
    bits in the form of modulated light data. Light
    is refracted along the cable and can go around
    bends. Fiber optic cables are available as
    single-mode or multimode cable.Wireless signals
    are radio frequencies and infrared waves that can
    travel through air. They are a growth area in
    network communications and represent the future
    of communication media.
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