Transcript Chapter 5 : The Internet: Addressing & Services

Topic 6: Network Layer
- Chapter 5 : The Internet: Addressing &
Services
Business Data Communications,
4e
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Internet Addressing
 32-bit global internet address
 Includes network and host identifiers
 Dotted decimal notation


11000000 11100100 00010001 00111001
(binary)
192.228.17.57 (decimal)
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Types of addresses
Address
Example Software
Application Layer
Network Layer
Data Link Layer
Web browser
TCP/IP
Ethernet
Example Address
ike.ba.ttu.edu
129.118.49.189
00-A0-C9-96-1D-90
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Addressing
The network layer determines the best
route through the network to the final
destination.
Based on this routing, the network layer
identifies the data link layer address of
the next computer to which the
message should be sent.
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Assigning Addresses
In general, the data link layer address is
permanently encoded in each network card,
and as part of the hardware that cannot be
changed.
Network layer addresses are generally assigned
by software. Every network layer software
package usually has a configuration file that
specifies the network layer address for that
computer.
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Assigning Addresses
Application layer addresses (or server
addresses) are also assigned by a software
configuration file. Virtually all servers have
an application layer address, but most client
computers do not.
Network layer addresses and application layer
addresses go hand in hand.
(ruby.bus.utexas.edu - means 146.6.44.95 at
the network layer.)
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*How IP Addresses
Distributed
 Internet Corporation for Assigned Names and
Numbers (ICANN) oversees the Internet Assigned
Numbers Authority (IANA) and controls how the
Net's 4.29 billion IP addresses are used.
 IANA distributes address space to three
geographically diverse Regional Internet Registries
(RIRs) and encourage three RIRs to operate so that
addresses remain unique, are mapped efficiently, and
are treated as a precious resource.
 Three RIRs dole out available pools of IP based on a
shared criteria. All deploy numerical address space to
ISPs, local registries, and in some cases small users.
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IP Address Allocation
IANA
InterNIC
America
RIPE
Europe
APNIC
Asia
National
Regional
Consumer
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Three RIRs
 American Registry for Internet Numbers (ARIN)
 Reseaux IP Europeen (RIPE)
 Asia Pacific Network Information Centre (APNIC)
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Internet Addresses
InterNIC is responsible for network layer
addresses (IP addresses) and application
layer addresses or domain names
(www.ttu.edu).
There are five classes of Internet addresses.
Classes A, B, and C are available to
organizations
Class D and E are reserved for special purposes
and are not assigned to organizations.
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Internet Address Classes
 Class A (/8 address)


The first digit is fixed, ranging 1-126 (01-7E), 16 million addresses
127.x.x.x is reserved for loopback
 Class B (/16 address)

First two bytes are fixed with the first digit ranging 128-191 (80BF), 65,000 addresses.
 Class C (/24 address)

First 3 bytes are fixed, with the first digit ranging 192-223 (C0-DF),
254 addresses.
 Class D & E


The first digit is 224-239 (E0-EF) and 240-255 (F0-FF) respectively.
Reserved for special purposes and not available to organizations.
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Internet Address Classes
Ranges of the first byte for different classes:
224 239
126 128
1
191 192 223
1/2
Class A
1/4
Class B
Class A: 0xxxxxxx
Class B: 10xxxxxx.xxxxxxxx
Class C: 110xxxxx.xxxxxxxx.xxxxxxxx
Class D: 1110xxxx.xxxxxxxx.xxxxxxxx
Class E: 1111xxxx.xxxxxxxx.xxxxxxxx
1/8
240 255
1/16 1/16
Class C Class D Class E
Note:
The IP addresses with the first
byte as 0 and 127 are reserved
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Internet Address Classes
# of Addresses
Class
Available
Addr-Structure
Example Available #
Class A
16 million
50.x.x.x
126
Class B
65k
128.192.x.x
16k
Class C
254
First byte fixed
Organization assigns
last three bytes
First two bytes fixed
Organization assigns
last two bytes
First three bytes fixed
Organization assigns
last byte
192.1.56.x
2 millions
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Internet Addresses
The Internet is quickly running out of
addresses. Although there are more than 1
billion possible addresses, the fact that they
are assigned in sets (or groups) significantly
restricts the number of usable addresses.
The IP address shortage was one of the
reasons behind the IPv6, providing in theory,
3.2 x 1038 possible addresses.
How to apply for IP address?
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Subnets
Assign IP addresses to specific computers so that all
computers on the same local area network have a
similar address.
Each LAN that is logically grouped together by IP
number is called a TCP/IP subnet.
Benefit:



allows it to be connected to the Internet with a
single shared network address
an necessary use of the limited number of
network numbers
Overload Internet routing tables on gateways
outside the organization
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Gateway
146.7.11.1
128.192.254.2
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Subnet Mask
Subnet mask enables a computer to determine
which computers are on the same subnet.
This is very important for message routing.
E.g.
IP address:
129.118.49.189
Subnet mask: 255.255.255.0
IP address:
129.118.49.x is for the
computers in the same subnet
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Subnet
Subnet with partial bytes addresses.
E.g. 129.118.49.1 to 129.118.49.126
Subnet mask: 255.255.255.128
Subnet address: 129.118.49.0
Subnet broadcast address: 129.118.49.127
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Subnet
IP address:
129.118.49.111
Subnet mask:
255.255.192.0
The IP prefix
1000 0001.0111 0110.0011 0001.0110 1111
1111 1111.1111 1111.1100 0000.0000 0000
1000 0001.0111 0110.00
Destination IP:
129.118.51.254
1000 0001.0111 0110.0011 0011.0110 1111
Destination IP:
128.83.127.1
1000 0000.0101 0011.0111 1111.0000 0001
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Subnet Mask Template
150.1.0.0
150
10010110
1
00000001
Broadcast Address
255
255
0
0
Host Address
128 64 32 16 8 4 2 1
000 00000 00000000
Network ID–Class B
128
128
192
192
224
224
240
240
248
248
252
252
254
255 Mask Numbers
Possible Subnet Address
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Dynamic Addressing
An address assignment problem:
Each time the computer is moved, or its
network is assigned a new address, the
software on each individual computer must
be updated.
Solution: dynamic addressing
With this approach, a server is designated to supply a
network layer address to a computer each time the
computer connects to the network.
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Dynamic Addressing
Two standards for dynamic addressing are
commonly used in TCP/IP networks:


Bootstrap Protocol (bootp) for dial-up
networks (1985)
Dynamic Host Control Protocol
(DHCP) for non-dial-up networks (1993)
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Dynamic Addressing
The Bootp or DHCP server can be configured to
assign the same network layer address to the
computer each time it requests an address or
it can lease the address to the computer by
picking the “next available” network layer
address from a list of authorized addresses.
Dynamic addressing greatly simplifies network
management in non-dial-up networks too.
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Address Resolution
Address resolution:
The sender translates the application layer
address (or server name) of the destination
into a network layer address; and in turn
translates that into a data link layer address.
Two approaches used in TCP/IP:

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Server address resolution
Data link layer address resolution.
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Domain
 A domain refers to a group of
networks that are under the
administrative control of a single entity,
such as a company.
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Server Name Resolution
Domain Name Service (DNS)
Used for translating application layer
addresses into network layer addresses.
InterNIC
Keeps the name and IP addresses of the
name server that will provide DNS
information for your address classes.
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Domain Name System
 32-bit IP addresses have two drawbacks


Routers can’t keep track of every network path
Users can’t remember dotted decimals easily
 Domain names address these problems by
providing a name for each network domain
(hosts under the control of a given entity)
 See Figure 5.6 for example of a domain name
tree
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DNS Database
 Hierarchical database containing name, IP
address, and related information for hosts
 Provides name-to-address directory services
 Key features:



Variable-depth hierarchy. Unlimited levels
Distributed database. Scattered throughout the
Internet and private intranet.
Distribution controlled by the database.
Thousands of separately managed zones managed
by separate administrators
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Server Name Resolution
Server address resolution process:


TCP/IP sends a special TCP-level packet to the nearest DNS server
asking for the requesting computer the IP address that matches
the Internet address provided.
If the DNS does not have the answer for the request, it will forward
the request to another DNS.
This is why it sometimes takes a long time to access certain
sites.
IP addresses are then temporarily stored in a server address
table.
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Data Link Layer
Address Resolution
In order to actually send a message, the
network layer software must know the data
link layer of the destination computer.
In the case of a distant computer, the network
layer would route the message by selecting a
path through the network that would
ultimately lead to the destination.
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Data Link Layer
Address Resolution
The process:

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
TCP/IP software sends a broadcast message
(using Address-Resolution-Protocol or ARP) to all
computers in its subnet requesting the data link
layer address.
The computer with the right IP address responds
with its data link layer address
The message is sent to the destination computer
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Routing
There are many possible routes or paths a message can
take to get from one computer to another.
Routing
The process of determining the route or path through
the network that a message will travel from the
sender to the receiver.
Routing table
The routing information on each router, which
specifies how message will travel through the
network.
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Dynamic Routing
There are three commonly used dynamic
routing protocols



Routing Information Protocol (RIP) - used by the
network manager to develop the routing table.
Used by both TCP/IP and IPX/SPX.
Internet Control Message Protocol (ICMP) - used
on the internet with TCP/IP.
Open Shortest Path First (OSPF) uses the number
of computers in a route as well as network traffic
and error rates to select the best route.
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Connectionless vs.
Connection-Oriented Routing
Two ways a group of packets can be routed:

Connectionless routing
 Each packet is treated separately and makes its own way
through the network.

Connection-Oriented routing
 Sets up a virtual circuit between the sender and receiver.
Appears to use point-to-point circuit-switching, but
actually uses store-and-forward.
 Has greater overhead than connectionless, due to the
routing information.
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Connectionless vs.
Connection-Oriented
Virtual Circuit
 Appears to the application software
to use a point-to-point circuit
 The network layer makes one
routing decision and all packets
follow the same route
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Connectionless vs.
Connection-Oriented
TCP vs. UPD
 TCP is used for connection-oriented routing

TCP establishes the virtual circuit and IP routes
the messages.
 UDP is used for connectionless routing
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Multicast
Unicasting
The usual transmission between two computers.
Broadcasting
Sending messages to all computers on a LAN or subnet.
Multicasting
Sending the same message to a group of computers temporarily
in a class D IP address. IGMP is used for multicast.
Anycasting
An IPv6 transmission method allowing messages to be sent to
any one of the host in a sub-network.
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Quality of Service
Quality of Service (QoS):
 The idea that transmission quality (rates,
error rates, bandwidth and jitter) can be
measured, improved, and, to some extent,
guaranteed in advance.
QoS routing:
 A special type of connection-oriented dynamic
routing in which different messages or
packets are assigned different priorities.
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Categories of Traffic
 Elastic traffic, such as FTP, email, etc


Allow fluctuating bandwidth, the total transmission
time is important
The data must correctly transmitted
 Real-time traffic, such as videoconferencing.
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Demands certain bandwidth with isochronous
features
Tolerates some level of errors.
Service quality includes: Throughput, Delay, Delay
variation, and Packet loss.
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Routing at Routers
 Bandwidth schedule

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
First in first out
Round robin
Prioritization
 Queue management
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Packet discard policy
Congestion control
Packet arrival
Packet forward
Packet Drop
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Network Congestion
 What is traffic congestion?

The buffer in a forwarding device
overflows. This results packet losses and
incur retransmission. The transmission will
worsen the situation.
 Network congestion control is very
important in flow management
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Internet Flow Control
 Internet flow control algorithm

Slow start, congestion avoidance
 Router queue management

Random early detection (RED) for packet dropping
 Data flow scheduling
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FIFO, round robin, priority queueing, weighted fair
queueing
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Internet Flow Control
 Slow Start algorithm (RFC2001). To avoid router running out of space

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Two windows: advertised window by receiver and congestion window by
sender. The congestion window is flow control imposed by the sender, while
the advertised window is flow control imposed by the receiver.
The congestion window is initialized to one segment. Each time an ACK is
received, the congestion window is increased by one segment. The sender
can transmit up to the minimum of the congestion window and the
advertised window.
The sender starts by transmitting one segment and waiting for its ACK.
When that ACK is received, the congestion window is incremented from one
to two, and two segments can be sent.
When each of those two segments is acknowledged, the congestion window
is increased to four. This provides an exponential growth.
At some point the capacity of the internet can be reached, and an
intermediate router will start discarding packets. This tells the sender that its
congestion window has gotten too large.
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Internet Flow Control
 Congestion Avoidance (RFC2001)
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Sets congestion window to one segment.
When congestion occurs (indicated by a timeout or the reception of
duplicate ACKs), one-half of the current window size (the minimum of
congestion window and the receiver's advertised window, but at least two
segments) is saved as X.
When new data is acknowledged by the other end, increase congestion
window, but the way it increases depends on whether TCP is performing
slow start or congestion avoidance. If congestion window is less than or
equal to X, TCP is in slow start; otherwise TCP is performing congestion
avoidance.
Slow start continues until TCP is halfway to where it was when congestion
occurred (since it recorded half of the window size that caused the problem
in step 2), and then congestion avoidance takes over.
Congestion avoidance dictates that congestion window be incremented a
linear growth of congestion window, compared to slow start's exponential
growth.
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Internet transmission services
 Best-effort services

The Internet treats all packet equally.
 Integrated services (IntServ)

IntServ refers to mechanisms that enable users to
request a particular QoS for a flow of data.
 Differentiated Services (DiffServ)

DiffServ Use type-of-service in IPv4 header to
indicate the required service quality.
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Integrated Services
 Routers require additional functionality to
handle QoS-based service
 IETF is developing suite of standards to
support this
 Two standards have received widespread
support
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
Integrated Services Architecture (ISA): To enable
the provision of QoS support over IP-based
Internet.
Resource ReSerVation Protocol (RSVP)
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Integrated Services
Architecture
 Enables provision of QoS over IP-networks
 Features include




Admission Control: A new flow needs a reservation
for QoS
Routing Algorithm: more parameters are
considered other than just delay
Queuing Discipline: Queuing policy takes into
account of different requirements
Discard Policy: Particularly for congestion
management
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Resource Reservation Protocol
(RSVP)
 A tool for prevention of congestion through
reservation of network resources
 Can be used in unicast or multicast transmissions
 Receivers (not senders) initiate resource reservations
 Operation:


Complexity is in multicast transmission
RSVP uses two basic messages: Resv and Path. In multicast,
Resv messages generated by one of the multicast group
receivers propagate upstream through distribution tree and
create soft state in routers. Once it reaches the sender,
hosts are enabled to set parameters for the first hop. Path is
used to provide upstream routing information and sent from
senders via the down stream tree to all receivers
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Differentiated Services
(DiffServ)
 Provides QoS based on user group
needs rather than traffic flows
 Can use current IPv4 octets
 Service-Level Agreements (SLA) govern
DiffServ, eliminating need for
application-based assignment
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IPv4 Type of Service Field
 Allows user to provide guidance on individual
datagrams
 3-bit precedence subfield


Indicates degree of urgency or priority
Queue Service & Congestion Control
 4-bit TOS subfield


Provides guidance on selecting next hop
Route selection, Network Service, & Queuing Discipline
0
1
Precedence
2
3
4
5
TOS
6
7
0
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DiffServ Domains
Border component
Host
Host
Interior component
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DiffServ Operation
 Routers are either boundary nodes or interior
nodes
 Interior nodes use per-hop behavior (PHB)
rules
 Boundary nodes have PHB & traffic
conditioning
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Token Bucket Scheme
Max Burstiness:
RT + B
R: Token replenishment rate
B: Bucket size
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TCP/IP Configuration
Information
At least four pieces of information needed
for a client computer TCP/IP
configuration




IP address
Subnet mask
Gateway IP address
Domain name Server IP address
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*Some Network Commands
 Some useful network commands
ping
 finger
 nslookup
 tracert
 ipconfig

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Port Addresses
What is a port address?
 A unique number assigned to a network application
as an address to receive or send data.
Why need port addresses?
 A single host may run several servers, such as Web,
FTP, Telnet, Email, etc. When the network layer
receives a message, it needs to know which
application layer software package should receive the
message.
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Application Layer Port
Addresses
 Port numbers are divided in three
ranges:



Well-known ports: 0-1023, controlled by
IANA
Registered ports: 1024-49151
Dynamic or private ports: 49152-65535.
We also call them ephemeral ports.
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Application Layer Port
Addresses
 Default port number assignments




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Web: 80 (or 8080)
FTP: 21
News group: 119 (or 8119)
Telnet: 23
SMTP: 25
 IANA (Internet Assigned Numbers
Authority) is taking care this issue.
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*WINS
 WINS (Windows Internet Naming Service) manages the
association of workstation names and locations with IP
addresses without the user or an administrator having to be
involved in each configuration change.
 WINS automatically creates a computer name-IP address
mapping entry in a table. When a computer is moved to another
geographic location, the new subnet information will be updated
automatically in the WINS table.
 WINS complements the NT Server's DHCP.
 WINS have been submitted to IETF as proposed open
standards. New features are included in the follow-on to
Windows NT, Windows 2000.
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*News about IPv6
 "IPv6 Internet Protocol Comes of Age“, AsiaBizTech
(07/16/01)
IP version 6 (IPv6) will be unrolled in three waves extending from
mid-2001 through 2003:



The arrival of home gateways and IPv6-compliant PCs will comprise the first
phase;
the second wave will be marked by the advent of networked household
appliances;
the third wave will be the release of IPv6-enabled mobile phones.
ISPs and manufacturers of equipment such as routers and switches
expect to benefit by accelerating their own IPv6 development
initiatives. The first wave is expected to hit at the same time Microsoft
introduces Windows XP in October of this year, thus changing over its
PC line to IPv6. The first manifestations of the second wave will be
home gateways and IPv6-enabled game consoles, followed by AV gear
such as DVD players and camera-equipped VCRs. NTT DoCoMo and
the J-Phone Group are among the cellular carriers readying IPv6capable products in preparation for the third wave in early 2003.
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