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Topic 6: Network Layer - Chapter 5 : The Internet: Addressing & Services Business Data Communications, 4e Internet Addressing 32-bit global internet address Includes network and host identifiers Dotted decimal notation 11000000 11100100 00010001 00111001 (binary) (decimal)

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Topic 6: Network Layer - Chapter 5 : The Internet: Addressing & Services

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topic 6 network layer chapter 5 the internet addressing services

Topic 6: Network Layer- Chapter 5 : The Internet: Addressing & Services

Business Data Communications, 4e

internet addressing
Internet Addressing
  • 32-bit global internet address
  • Includes network and host identifiers
  • Dotted decimal notation
    • 11000000 11100100 00010001 00111001 (binary)
    • (decimal)
types of addresses
Types of addresses

Address Example Software Example Address

Application Layer Web browser

Network Layer TCP/IP

Data Link Layer Ethernet 00-A0-C9-96-1D-90


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.

assigning addresses
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.

assigning addresses6
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. ( - means at the network layer.)

how ip addresses distributed
*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.

IP Address Allocation











three rirs
Three RIRs
  • American Registry for Internet Numbers (ARIN)
  • Reseaux IP Europeen (RIPE)
  • Asia Pacific Network Information Centre (APNIC)
internet addresses
Internet Addresses

InterNIC is responsible for network layer addresses (IP addresses) and application layer addresses or domain names (

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.

internet address classes
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 (80-BF), 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.
internet address classes12
Internet Address Classes

Ranges of the first byte for different classes:

224 239




192 223


240 255






Class A

Class B

Class D Class E

Class C

Class A: 0xxxxxxx

Class B: 10xxxxxx.xxxxxxxx

Class C: 110xxxxx.xxxxxxxx.xxxxxxxx

Class D: 1110xxxx.xxxxxxxx.xxxxxxxx

Class E: 1111xxxx.xxxxxxxx.xxxxxxxx


The IP addresses with the first

byte as 0 and 127 are reserved

internet address classes13
Internet Address Classes

# of Addresses

Class Available Addr-Structure Example Available#

Class A 16 million First byte fixed 50.x.x.x 126

Organization assigns

last three bytes

Class B 65k First two bytes fixed 128.192.x.x 16k

Organization assigns

last two bytes

Class C 254 First three bytes fixed 192.1.56.x 2 millions

Organization assigns

last byte

internet addresses14
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?


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.


  • 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


subnet mask
Subnet Mask

Subnet mask enables a computer to determine which computers are on the same subnet. This is very important for message routing.


IP address:

Subnet mask:

IP address: 129.118.49.x is for the computers in the same subnet


Subnet with partial bytes addresses.

E.g. to

Subnet mask:

Subnet address:

Subnet broadcast address:


IP address: 1000 0001.0111 0110.0011 0001.0110 1111

Subnet mask: 1111 1111.1111 1111.1100 0000.0000 0000

The IP prefix 1000 0001.0111 0110.00

Destination IP: 1000 0001.0111 0110.0011 0011.0110 1111

Destination IP: 1000 0000.0101 0011.0111 1111.0000 0001















Subnet Mask Template

Broadcast Address





Host Address



128 64 32 16 8 4 2 1

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

1 0 0 1 0 1 1 0

0 0 0 0 0 0 0 1

Network ID–Class B


Mask Numbers

Possible Subnet Address

dynamic addressing
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.

dynamic addressing22
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)
dynamic addressing23
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.

address resolution
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:

  • Server address resolution
  • Data link layer address resolution.
  • A domain refers to a group of networks that are under the administrative control of a single entity, such as a company.
server name resolution
Server Name Resolution

Domain Name Service (DNS)

Used for translating application layer addresses into network layer addresses.


Keeps the name and IP addresses of the name server that will provide DNS information for your address classes.

domain name system
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
dns database
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
server name resolution29
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.

data link layer address resolution
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.

data link layer address resolution31
Data Link Layer Address Resolution

The process:

  • 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

There are many possible routes or paths a message can take to get from one computer to another.


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.

dynamic routing
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.
connectionless vs connection oriented routing
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.
connectionless vs connection oriented
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
connectionless vs connection oriented36
Connectionless vs. Connection-Oriented


  • TCP is used for connection-oriented routing
    • TCP establishes the virtual circuit and IP routes the messages.
  • UDP is used for connectionless routing


The usual transmission between two computers.


Sending messages to all computers on a LAN or subnet.


Sending the same message to a group of computers temporarily in a class D IP address. IGMP is used for multicast.


An IPv6 transmission method allowing messages to be sent to any one of the host in a sub-network.

quality of service
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.
categories of traffic
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.
    • Demands certain bandwidth with isochronous features
    • Tolerates some level of errors.
    • Service quality includes: Throughput, Delay, Delay variation, and Packet loss.
routing at routers
Routing at Routers
  • Bandwidth schedule
    • First in first out
    • Round robin
    • Prioritization
  • Queue management
    • Packet discard policy
    • Congestion control

Packet arrival

Packet forward

Packet Drop

network congestion
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
internet flow control
Internet Flow Control
  • Internet flow control algorithm
    • Slow start, congestion avoidance
  • Router queue management
    • Random early detection (RED) for packet dropping
  • Data flow scheduling
    • FIFO, round robin, priority queueing, weighted fair queueing
internet flow control43
Internet Flow Control
  • Slow Start algorithm (RFC2001). To avoid router running out of space
    • 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.
internet flow control44
Internet Flow Control
  • Congestion Avoidance (RFC2001)
    • 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.
internet transmission services
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.
integrated services
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
    • Integrated Services Architecture (ISA): To enable the provision of QoS support over IP-based Internet.
    • Resource ReSerVation Protocol (RSVP)
integrated services architecture
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
resource reservation protocol rsvp
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
differentiated services diffserv
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
ipv4 type of service field
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












diffserv domains
DiffServ Domains

Border component



Interior component

diffserv operation
DiffServ Operation
  • Routers are either boundary nodes or interior nodes
  • Interior nodes use per-hop behavior (PHB) rules
  • Boundary nodes have PHB & traffic conditioning
token bucket scheme
Token Bucket Scheme

Max Burstiness:

RT + B

R: Token replenishment rate

B: Bucket size

tcp ip configuration information
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
some network commands
*Some Network Commands
  • Some useful network commands
    • ping
    • finger
    • nslookup
    • tracert
    • ipconfig
port addresses
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.
application layer port addresses
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.
application layer port addresses58
Application Layer Port Addresses
  • Default port number assignments
    • 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.
  • 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.
news about ipv6
*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 IPv6-capable products in preparation for the third wave in early 2003.