Download Core network components - Charles Sturt University

ITC242 – Introduction to
Data Communications
Internet Operation
1
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
2
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.
3
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.
4
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
application
transport
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
network
data link
data link
physical
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
application
transport
network
data link
physical
5
Two Key Network-Layer Functions
• forwarding: move
packets from router’s
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
6
Interplay between routing and forwarding
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
value in arriving
packet’s header
0111
1
3 2
7
The Internet Network layer
Host, router network layer functions:
Transport layer: TCP, UDP
Network
layer
IP protocol
•addressing conventions
•datagram format
•packet handling conventions
Routing protocols
•path selection
•RIP, OSPF, BGP
forwarding
table
ICMP protocol
•error reporting
•router “signaling”
Link layer
physical layer
8
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
9
IP protocol: IP Addresses
223.1.1.1
• Interface: connection
between host/router and
223.1.2.1
physical link
223.1.1.2
223.1.1.4 223.1.2.9
– router’s typically have
multiple interfaces
223.1.2.2
223.1.3.27
223.1.1.3
– host typically has one
interface
– IP addresses associated
with each interface
223.1.3.2
223.1.3.1
• Every interface has a unique
IP address:
– A computer might have
two or more IP
223.1.1.1 = 11011111 00000001 00000001 00000001
addresses
223
1
1
1
– A router has many IP
10
addresses
IP Address Classes
Originally there were 5 classes:
1
CLASS “A”
Host-ID
0 Net ID
00000000-01111111(127): 1126
CLASS “B”
100000000-10111111: 128-191
2^14=16,384 Class B addresses
CLASS “C”
2
10
3
110
11000000-11011111: 192-223
2^21=2,097,152
CLASS “D”
CLASS “E”
0
24
7
A
16
14
Host-ID
Net ID
8
21
Host-ID
Net ID
4
28
1110
Multicast Group ID
5
27
11110
Reserved
B
C
D
232-1
11
IP Addresses
Examples
Class “A” address: www.mit.edu
18.181.0.31
(18<128 => Class A)
Class “B” address: mekong.stanford.edu
171.64.74.155
(128<171<128+64 => Class B)
12
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.
13
Solution ?
Subnetting within an organization to
subdivide the organization’s network
ID.
14
Subnets
CLASS “B”
e.g. Company
e.g. Site
2
10
2
10
Net ID
0000
Subnet ID (20)
e.g. Dept
2
10
Subnet ID (22)
2
Host-ID
10
16
000000
2
Host-ID
Subnet
Host ID (10)
16
14
Net ID
1111
Subnet ID (20)
Subnet
Host ID (12)
14
Net ID
Host-ID
Net ID
16
14
16
14
10
Subnet
Host ID (12)
16
14
Net ID
Subnet ID (26)
Host-ID
1111011011
Host-ID
Subnet
Host ID (6)
15
Subnets
• IP address:
– subnet part (high
order bits)
– host part (low order
bits)
223.1.1.1
223.1.2.1
223.1.1.2
223.1.1.4
223.1.1.3
223.1.3.27
223.1.2.2
subnet
• What’s a subnet ?
– device interfaces
with same subnet
part of IP address
– can physically reach
each other without
intervening router
223.1.2.9
223.1.3.1
223.1.3.2
network consisting of 3 subnets
16
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.
223.1.1.0/24
223.1.2.0/24
223.1.3.0/24
Subnet mask: /24
17
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
18
Subnet Mask Calculations
19
Example of Subnetworking
20
Subnet masks
21
Source: http://zdnetasia.com/insight/network/0,39044847,39372217,00.htm
IP addresses: how to get one?
Q: How does network get subnet part of IP
addr?
A: gets allocated portion of its provider
ISP’s address space
ISP's block
11001000 00010111 00010000 00000000
200.23.16.0/20
Organization 0
Organization 1
Organization 2
...
11001000 00010111 00010000 00000000
11001000 00010111 00010010 00000000
11001000 00010111 00010100 00000000
…..
….
200.23.16.0/23
200.23.18.0/23
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
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IP addresses: how to get one?
Q: How does host get IP address?
• hard-coded by system admin in a file
– Wintel: control-panel->network->configuration->tcp/ip>properties
• 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
23
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
24
The Internet Network layer
Host, router network layer functions:
Transport layer: TCP, UDP
Network
layer
IP protocol
•addressing conventions
•datagram format
•packet handling conventions
Routing protocols
•path selection
•RIP, OSPF, BGP
forwarding
table
ICMP protocol
•error reporting
•router “signaling”
Link layer
physical layer
25
“A”
The Problem
“B”
R2
R1
How does R1
choose a route
to host B?
R4
R3
26
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
27
Technique 1: Naïve Approach
Flood! -- Routers forward packets to all ports
except the ingress port.
R1
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.
28
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
R1
1
R2
R4
2
2
R3
4
4
R6
3
R5
2
R7
3
2
R8
29
Example network
In this simple case, solution is clear from inspection
A
1
R1
1
R2
R4
2
2
R3
4
4
R6
3
R5
2
R7
3
2
R8
B
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So what about this network...!?
The public Internet in 1999
Learn more at
http://www.lumeta.com
31
Technique 3:
Dijkstra’s 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.
32
The problem
• How to route in the Internet?
33
Internet Routing Protocols
• Responsible for receiving and
forwarding packets between
interconnected networks
• Must dynamically adapt to changing
network conditions
34
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
35
Autonomous System Example
36
Directed Graph of Example
37
Routing in the Internet
The Internet uses hierarchical routing
• The Internet is split into Autonomous Systems (AS’s)
• Within an AS, the administrator chooses an Interior
Gateway Protocol (IGP)
 Examples of IGPs: RIP (rfc 1058), OSPF (rfc 1247).
• Between AS’s, the Internet uses an Exterior Gateway
Protocol
 AS’s today use the Border Gateway Protocol, BGP-4
(rfc 1771)
38
Routing in the Internet
The Internet uses hierarchical
Gateway router
routing
•
• Direct link to router in
The Internet is split into
Autonomous Systems (AS)
another 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
39
Interconnected ASes
3c
3a
3b
AS3
1a
2a
1c
1d
1b
Intra-AS
Routing
algorithm
2c
AS2
AS1
Inter-AS
Routing
algorithm
Forwarding
table
2b
• 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 40
external dests
Inter-AS tasks
AS1 must:
1. learn which dests
reachable through
AS2, which through
AS3
2. 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?
3c
3b
3a
AS3
1a
2a
1c
1d
1b
2c
AS2
2b
AS1
41
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
3c
3a
3b
AS3
1a
2a
1c
1d
1b AS1
2c
2b
AS2
42
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
3c
3a
3b
AS3
1a
2a
1c
1d
1b
2c
AS2
2b
AS1
43
44
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:
1. Obtain subnet reachability information from neighboring
ASs.
2. Propagate reachability information to all AS-internal
routers.
3. Determine “good” routes to subnets based on
reachability information and policy.
• allows subnet to advertise its existence to
rest of Internet: “I am here”
45
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
3c
3a
3b
AS3
1a
AS1
iBGP session
2a
1c
1d
1b
2c
AS2
2b
46
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
3c
3a
3b
AS3
1a
AS1
iBGP session
2a
1c
1d
1b
2c
AS2
2b
47
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 Dijkstra’s 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
48
Hierarchical OSPF
49
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.
50
• boundary routers: connect to other AS’s.
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.
51
Backend &
Storage Area Networks
•
•
•
•
•
•
“Computer room networks”
High data rate
High-speed interface
Distributed access
Limited distance
Limited number of devices
52
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
53
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
54
Backbone Local Networks
•
•
•
•
Used instead of single-LAN strategy
Better reliability
Higher capacity
Lower cost
55
Factory Networks
•
•
•
•
•
High capacity
Ability to handle a variety of data traffic
Large geographic extent
High reliability
Ability to specify and control transmission
delays
56
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
57
Tiered LAN Diagram
58
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
59
Guided Media
• Twisted Pair Wires
• Coaxial Cable
• Fibre Optic Cable
60
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
61
Types of Twisted Pair
• STP (shielded
twisted pair)
– the pair is
wrapped with
metallic foil or
braid to insulate
the pair from
electromagnetic
interference
62
Types of Twisted Pair
• UTP
(unshielded
twisted pair)
– each wire is
insulated
with plastic
wrap, but
the pair is
encased in
an outer
covering
63
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
64
Twisted Pair Advantages
• Inexpensive and readily available
• Flexible and light weight
• Easy to work with and install
65
Twisted Pair Disadvantages
• Susceptibility to interference and noise
• Attenuation problem
– For analog, repeaters needed every 5-6km
– For digital, repeaters needed every 2-3km
66
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 “coaxial”
• Traditionally used for
LANs, but growth of
twisted pair for local
nets and optical fiber
for larger nets has
reduced coax use
67
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)
68
Fiber Optic Layers
• consists of three concentric sections
plastic jacket
glass or plastic
fiber core
cladding
69
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.
70
Fiber Optic Signals
fiber optic multimode
step-index
fiber optic single mode
71
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 wirebased 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.
72