Download Business Data Communications and Networking

Chapter 5:
Network and Transport
Layers
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1
Outlines
Network Protocols and TCP/IP
Networking Addressing
Routing
Network flow control and QoS
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Network Protocols and TCP/IP
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Transmission Control Protocol/
Internet Protocol (TCP/IP)
The Transmission Control Protocol/
Internet Protocol (TCP/IP) was
developed for the U.S. Dept of
Defense’s Advanced Research Project
Agency Network (ARPANET) in 1974.
TCP/IP allows reasonable efficient and
error-free transmission.
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TCP/IP
TCP/IP has two parts:


TCP - performs packetizing: TCP is only
active at the sender and receiver.
IP - performs routing and addressing.
A typical TCP packet has 192-bit (24byte) header of control information.
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TCP/IP
Two forms of IP are currently in use:
IPv4 also has a 192-bit (24-byte) header.
 IPv6 has a 320-bit (40-byte) header.
The primary reason for the increase in packet size is
an increase in the address size from 32 bits to 128
bits, due to the dramatic growth in the usage of
the Internet.

The size of the message field depends on the
data link layer protocol used. TCP/IP is
commonly combined with Ethernet.
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TCP Packet
1
2
3
4
1
2
3
4
5
6
7
8
9
10
11
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5
6
7
8
9
Source ID
Destination ID
Sequence number
ACK number
Header length
Unused
Flags
Flow control
CRC 16
Urgent pointer
Options
10
11
User Data
16 bits
16 bits
32 bits
32 bits
4 bits
6 bits
6 bits
16 bits
16 bits
16 bits
16 bits
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IP Packet version
IP4
1
1
2
3
4
5
6
7
8
2
3
4
5
Version number
Header length
Type of Service
Total length
Identifiers
Flags
Packet offset
Hop limit
6
7
8
4 bits
4 bits
8 bits
16 bits
16 bits
3 bits
13 bits
8 bits
9
10
11
12
13
14
15
16
9
10
11
12
13
Protocol
CRC 16
Source address
Destination Address
Options
User data
Flow name
Next header
14
8 bits
16 bits
32 bits
32 bits
varies
varies
24 bits
8 bits
IP6
1
15
4
16
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8
11 (128 bits)
12 (128 bits)
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*History of IPng Effort
By the Winter of 1992 the Internet community had developed four
separate proposals for IPng. These were "CNAT", "IP Encaps",
"Nimrod", and "Simple CLNP". By December 1992 three more proposals
followed; "The P Internet Protocol" (PIP), "The Simple Internet
Protocol" (SIP) and "TP/IX". In the Spring of 1992 the "Simple CLNP"
evolved into "TCP and UDP with Bigger Addresses" (TUBA) and "IP
Encaps" evolved into "IP Address Encapsulation" (IPAE).
By the fall of 1993, IPAE merged with SIP while still maintaining the
name SIP. This group later merged with PIP and the resulting working
group called themselves "Simple Internet Protocol Plus" (SIPP). At
about the same time the TP/IX Working Group changed its name to
"Common Architecture for the Internet" (CATNIP).
The IPng area directors made a recommendation for an IPng in July of
1994 [RFC 1752].
The formal name of IPng is IPv6
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Why Need IPv6?
Internet Growth


Network numbers and size
Traffic management
Quality of Services (QoS)
Internet Transition


Routing
Addressing
No question that an IPv6 is needed, but when
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Other Protocols
Internetwork Packet Exchange/Sequenced Packet
Exchange (IPX/SPX)

Developed by Xerox in the 1970s. It is primary network
protocol used by Novell NetWare. Novell has replaced
IPX/SPX with TCP/IP.
X.25

ITU-T’s standard for WAN. Mature standard. Seldom used in
north America.
System Network Architecture (SNA)

IBM developed SNA in 1974. It is used on IBM’s mainframes.
It is hard to integrate SNA with other networks.
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The Message Field Size
Maximum Ethernet packet size = 1492
TCP message field
1492 - 24 (TCP header) - 24 (IPv4 header) =
1444
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Addressing
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Types of addresses
Address
Example Software
Application Layer
Web browser
Example Address
ike.ba.ttu.edu
(also called domain name)
Network Layer
Data Link Layer
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TCP/IP
Ethernet
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. ike.ba.ttu.edu means 129.118.49.189 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
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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
127
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
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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:


Server address resolution
Data link layer address resolution.
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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)
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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:



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
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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.
Types of routing:
Centralized routing
Decentralized routing: Static routing, Dynamic routing
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Routing
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Routing Table for Computer B
Destination
A
C
D
E
F
G
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Route
A
C
A
E
E
C
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Static Routing
Static Routing

The routing table is developed by
the network manager, and changes
are made only when computers are
added or removed from network.
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Dynamic Routing
Dynamic Routing (adaptive routing)
An initial routing table is developed by the network
manager, but is continuously updated by the
computers themselves to reflect changing network
conditions, such as network traffic.
Used when there are multiple routes through a
network and it is important to select the best (or
fastest) route, in order to route messages away
from traffic on busy circuits.
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Dynamic Routing
Commonly used dynamic routing protocols





Routing Information Protocol (RIP) - used by the network
manager to develop the routing table.
Border Gateway Protocol (BGP). A dynamic exterior routing
protocol for the Internet.
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.
Enhanced Interior Gateway Routing Protocol (EIGRP) – a
dynamic link state interior routing protocol and commonly
used inside an organization.
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Dynamic Routing
Routing Information Protocol (RIP)
When new computers are added, it counts
the number of computers in the possible
routes to the destination and selects the rout
with the least number.
Computers using RIP send broadcast
messages every minute or so to announce
routing state.
It is used by TCP/IP and IPX/SPX.
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Dynamic routing
Border Gateway Protocol (BGP)


A dynamic routing protocol used on the
Internet to exchange routing information
between autonomous systems – the large
sections of the Internet. It is seldom used
inside companies
Large, complex and hard to administer
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Dynamic Routing
Internet Control Message Protocol
(ICMP)
Uses both broadcast messages and
the messages to specific computers
to exchange routing information
Only used by TPC/IP
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Dynamic Routing
Open Shortest Path First (OSPF)
More efficient than RIP because it
normally doesn’t use broadcast
messages. Instead it selectively sends
status update messages directly to
selected computers
Used by TCP/IP
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Dynamic routing
Enhanced Interior Gateway Routing
Protocol (EIGRP)



A dynamic link state interior routing
protocol developed by CISCO
Commonly used inside an organization
Computers/routers store their own routing
table and their neighbors’ routing tables
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Dynamic Routing
Two drawbacks to Dynamic Routing.
It requires more processing by each
computer in the network than
centralized or static routing.
 The transmission of status
information “wastes” network
capacity.

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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. ConnectionOriented Routing
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. ConnectionOriented Routing
TCP/IP vs. UPD/IP
TCP/IP is used for connection-oriented
routing

TCP establishes the virtual circuit and IP routes
the messages.
UDP/IP is used for connectionless routing

The TCP packet is replaced with a User Datagram
Protocol (UDP) packet.
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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.
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Broadcast
Individual
transfers
Host
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Clients
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Multicast
Could be one packet that all receive or
replicated by routers in the network
Data replicated
by the network
Clients
Host
Multicast
Infrastructure
One transfer
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Multicast
Computers wishing to participate in a multicast send
a message to the sending computer or some other
computer performing routing along the way using
a special type of TCP-level packet called Internet
Group Management Protocol (IGMP).
Each multicast group is temporarily assigned a
special Class D IP address to identify the group,
thus allowing a restricted broadcast of messages
to this specific group.
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*TCP/IP
Application
Presentation
Session
Transport
TELNET
FTP
SMTP
DNS
SNMP
DHCP
RIP
RTP
RTCP
Transmission
Control Protocol
User Datagram
Protocol
ICMP
IGMP
Network
OSPF
Internet Protocol
ARP
Data link
Ethernet
Physical
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Token Bus
Token Ring
FDDI
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Flow control and QoS
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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
Service quality concerns mainly in transmission delay and
error control.
Real-time traffic, such as videoconferencing.



Demands certain bandwidth with isochronous features
Tolerates some level of errors.
Service quality criteria include: Throughput, Delay, Delay
variation (jitter), and Packet loss.
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Routing at Routers
Bandwidth schedule



First in first out
Round robin
Prioritization
Queue management


Packet discard policy
Congestion control
Packet arrival
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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

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





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)





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


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
1
0
Precedence
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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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A TCP/IP Example
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A TCP/IP Example
How a client access a web server in the
same subnet with a known address?
How a client access a web server in a
different subnet with a known
address?
How a client access a web server in the
same subnet with an unknown
address?
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Sender
Application
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Receiver
HTTP
Request
TCP HTTP
Request
IP
TCP HTTP
Ethernet IP
Physical
Layer
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Application
Layer
Transport
Layer
Request
TCP HTTP
Request
Network
Layer
Data Link
Layer
HTTP
Request
TCP HTTP
Request
IP
TCP HTTP
Ethernet IP
Request
TCP HTTP
Request
Physical
Layer
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Data transmission using
TCP/IP and Ethernet
Ethernet
packet header
IP
packet
TCP
packet
HTTP
packet
User Data
Ethernet
packet trailer
IP address
Data link layer address
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