Chapter 6 -

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Chapter 6

Networking Protocols


Look at:

Protocol Basics(6.1)

A Brief Protocol Prospectus(6.2)

Transmission Control Protocol/Internet
Protocol (TCP/IP)(6.3)

TCP/IP Network Access Layer


Look at:

TCP/IP Internet Layer Protocols(6.5)

TCP/IP Transport Layer Protocols(6.6)

TCP/IP Application Layer Protocols(6.7)

Protocol Basics

A protocol is a set of rules and conventions
that determines how computers exchange
information over a network medium

A wide variety of communication protocols
exist, and many of them rely on others for

Groups of related protocols are often called


protocol stacks

A Brief Protocol Prospectus

Data packets can be sent over the medium
using any one of a number of protocols

Protocols can be either standard or

standard protocol is one where users can
purchase equipment from any manufacturer
because it is programmed to communicate

A Brief Protocol Prospectus

A proprietary protocol is usually protected by
patents or other legal stipulation

Proprietary protocols include






A Brief Protocol Prospectus

XNS stands for the Xerox Network

This is a suite of protocols created by
Xerox in the late 1970s and early 1980s
for use in Ethernet networks

XNS is used in very few new networks

A Brief Protocol Prospectus

The Network Basic Input/Output
System (NetBIOS) interface was
developed in 1983 for IBM

The intention was to allow applications
on different computers to communicate
within a local area network

NetBIOS was not designed for large

A Brief Protocol Prospectus

In the early 1980s, Novell introduced its own
network protocol stack called Internetwork
Packet Exchange/Sequenced Packet
Exchange (IPX/SPX)

This stack was based on the XNS network
protocol family

IPX is the Network layer protocol

SPX is the Transport layer protocol

A Brief Protocol Prospectus

AppleTalk is Macintosh’s networking protocol

It is designed to be a flexible, simple, and
inexpensive network means for connecting
computers, peripherals, and servers

Newer versions of Macintosh operating
systems use TCP/IP and SMB as default
protocols rather than AppleTalk

AppleTalk is a protocol and LocalTalk is a
media type

A Brief Protocol Prospectus


is a proprietary network protocol
designed by Digital Equipment Corporation

Currently two versions of DECnet are in use:

DECnet Phase IV which is based on the
Phase IV Digital Network Architecture

DECnet/OSI also called DECnet Phase V
is a layered model

Transmission Control
Protocol/Internet Protocol

TCP/IP is considered the language of the

It is the most widely used protocol today

It is a suite, or stack, of small, specialized

Because of its routing ability, TCP/IP has
become the protocol of choice for many
LANs, as well as the basis for the Internet,
making it the standard

Transmission Control
Protocol/Internet Protocol

In the early 1970s, the Department of
Defense funded ARPA to design a new set of
computer communication protocols that
would allow multiple networks to be
interconnected in a flexible and dynamic way

The protocol developed was originally called
Network Control Protocol

This success led to the implementation of the
two main Internet protocols

These are Transmission Control Protocol and
Internet Protocol (TCP/IP)

Transmission Control
Protocol/Internet Protocol

TCP/IP’s implementation of the OSI
model makes functionality simpler

It maps the same seven layers of
the OSI model to a four
TCP/IP model instead

The TCP/IP model focuses more on
delivering interconnectivity than on
functional layers

Transmission Control
Protocol/Internet Protocol

Since TCP/IP is the language of the Internet,
you may also hear this model referred to as
the Internet reference model

The Layers are:

Network Access




TCP/IP Network Access Layer

The Network Access layer is the lowest
layer in the model

It Maps to Layers 1 (Physical) and 2
(Data Link) of the OSI model

It is responsible for the delivery of
datagrams by creating a frame for the
network type and then sending the data
to the wire

TCP/IP Network Access Layer

This layer contains the protocols that are
used to deliver data to computers and
devices on the network

These include Serial Line Interface Protocol
(SLIP) and Point
Point Protocol (PPP)

These are communication protocols for serial
data transmission by which IP packets can be
sent over a modem

TCP/IP Network Access Layer

Other protocols that are used at this layer
include a means to relate different types of
addresses to each other:

the Address Resolution Protocol (ARP)

the Reverse Address Resolution Protocol

This layer defines the logical network layout
so routers can determine where to forward

TCP/IP Internet Layer Protocols

The layer above the Network Access
layer is called the Internet layer

It manages the routing of packets that
are to be forwarded on to different

It relies on routable protocols for

TCP/IP Internet Layer Protocols

The Internet Protocol (IP) is responsible for
making data packets routable

It is a forwarding protocol that uses routing
tables that are created by routing protocols

It is a simple, connectionless internetworking

The basis of IP is how it uses routing tables to
make decisions about routing an IP packet

TCP/IP Internet Layer Protocols

Every host on the network needs
an IP address

TCP/IP uses a 32
bit Layer 3 address in
the format to identify the
network and the host compute

Each set of xxx is called an octet

TCP/IP Internet Layer Protocols

There are five classes of IP addresses
their corresponding numbers are:

Class A
: Has a first octet number between
1 and 126 and can support a network with
16,777,216 hosts.

Class B
: Has a first octet number between
128 and 191 and can support 65,536 hosts

TCP/IP Internet Layer Protocols

There are five classes of IP addresses
their corresponding numbers are:

Class C
: Has a first octet number between
192 and 223 and can support 254 hosts
per network

Class D
: Begins at 224 and ends at 239.
This address class is reserved for sending
multicast messages

TCP/IP Internet Layer Protocols

A There are five classes of IP
addresses their corresponding numbers

Class E
: Begins with 240 and ends at 255.
This address class is reserved for
experimental use

The IP address is used as the
loopback address

TCP/IP Internet Layer Protocols

A datagram

is the packet format defined by IP

Datagrams are packets that consist of a
header, data, and a trailer

The header contains information that the
network needs to route the datagram

Trailers typically contain a checksum value,
which is used to ensure that the data is not
modified in transit

TCP/IP Internet Layer Protocols

IP delivers the datagram by checking
the destination address in the header

When IP checks the destination address
in the header, if it is the address of a
host on the local network, the datagram
is delivered directly to the destination

If it is not on the local network, the
datagram is passed on for delivery

TCP/IP Internet Layer Protocols

Each router that a datagram passes through
is considered a hop

A system transmits IP datagrams as fast as it
can generate them

IP has two features that can affect throughput

the IP Time to Live (TTL)

IP Fragmentation

TCP/IP Internet Layer Protocols

By interconnecting multiple switches with
redundant paths, you overcome problems
with faulty cables or port failures

Another less well
known side effect of a loop
is the corruption of the forwarding tables on
all the switches

It would take very little time before Layer 2
broadcast loops completely destroy the
functionality of a network

TCP/IP Internet Layer Protocols

The Spanning Tree Protocol (STP) prevents
bridging loops by identifying a preferred path
through a series of looped bridges

Administrators can provide redundancy and
tolerance by wiring a loop, and then
using STP turn off ports that would cause
loops to occur

If a primary link fails, STP will reactivate the
up port allowing normal operation of the
network to continue

TCP/IP Internet Layer Protocols

The TTL field is actually the number of
hops the datagram has made

IP places a limit on how long a
datagram may live in the network

Specifications for higher
layer protocols
usually assume that the maximum time
a datagram can live in the network is
only two minutes

TCP/IP Internet Layer Protocols

Each type of network has a maximum
transmission unit (MTU), which is the largest
packet it can transfer

A datagram received from one network may
be too large to be transmitted in a single
packet on another network

It may be necessary to divide the datagram
into smaller pieces

This division process is called fragmentation

TCP/IP Internet Layer Protocols

Internet Control Message Protocol (ICMP) is
part of the Internet layer and uses IP
datagram delivery to send its messages

ICMP uses the basic support of IP as if it was
level protocol, but it is actually an
integrated part of IP

ICMP is a protocol meant to be used as an
aid for other protocols

It is used to test for connectivity and search
for configuration errors in a network

TCP/IP Internet Layer Protocols

PING uses the ICMP echo function

A small packet containing an ICMP

message is sent through the network to a
particular IP address

The computer that sent the packet then waits
for a return packet

If the connections are good and the target
computer is up, the echo message return
packet will be received

TCP/IP Internet Layer Protocols

PING is one of the most useful network tools
available because it tests the most basic
function of an IP network


was originally developed for the
Unix operating system but is used for many
operating systems and most routers

It is used to track the path a packet takes to
get to its destination

It measures how long it takes to travel
through each hop to get to its target

TCP/IP Internet Layer Protocols

Traceroute uses an ICMP echo request
packet to find the path

Besides assisting in troubleshooting
functions such as PING and Traceroute,
ICMP capabilities include:

Announcing network errors


Timeout notification

TCP/IP Transport Layer

The protocol layer above the Internet
layer is the Transport


It is responsible for providing end
data integrity

It also provides a reliable
communication service so that an
extended two
way conversation may
take place

TCP/IP Transport Layer

This layer accepts and returns
information to be transmitted as a
stream of characters

It uses open and close commands to
initiate and terminate the connection

It consists of two protocols:

Transmission Control Protocol (TCP)

User Datagram Protocol (UDP)

TCP/IP Transport Layer

TCP provides connection
oriented data

It can support multiple data streams

It provides for flow and error control

It uses sequence numbers and
acknowledgements to guarantee

TCP/IP Transport Layer

Sockets make up a TCP connection

The two most typical network
applications that use TCP are:

File Transfer Protocol (FTP)


Telnet uses port 23

FTP uses port 21

TCP/IP Transport Layer

UDP does not provide either
sequencing or acknowledgements

It is a connectionless protocol

It is used a lot in telephony traffic and
the Remote Procedure Call (RPC)

The major difference between TCP and
UDP is reliability

TCP/IP Application Layer

The top layer in the Internet reference
model is the Application layer

This is how applications and certain
services access the network

It provides the services that applications
use to communicate over the network

It serves as a service provider for
workstations and applications.

TCP/IP Application Layer

The most widely known and
implemented TCP/IP Application layer
services are:

File Transfer Protocol (FTP) which allows
files to be uploaded and downloaded on
port 21

Telnet which uses terminal emulation for
access to remote hosts using port 23

TCP/IP Application Layer

The most widely known and
implemented TCP/IP Application layer
services are:

Simple Mail Transfer Protocol (SMTP)
which supports basic message delivery
services between mail servers on port 25

HyperText Transfer Protocol (HTTP) which
is a low
overhead Web browser service
protocol that uses port 80

TCP/IP Application Layer

The most widely known and
implemented TCP/IP Application layer
services are:

Simple Network Management Protocol
(SNMP) which uses UDP port 161 to
collect information from network devices.

Network News Transfer Protocol (NNTP):
handles distribution and posting of news
articles using port 119

TCP/IP Application Layer

The most widely known and
implemented TCP/IP Application
layer services are:

Dynamic Host Configuration Protocol
(DHCP) allows for automatic IP addressing

Domain Name Service (DNS) uses UDP
port 53 for resolving domain names to IP