Computer Networking From LANs to WANs: Hardware, Software, and Security

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Oct 27, 2013 (3 years and 11 months ago)

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Computer Networking From LANs
to WANs: Hardware, Software, and
Security

Chapter 7

Low
-
Level Protocols

Computer Networking From LANs to WANs: Hardware, Software, and Security

2

Objectives


Describe the format of a serial data transmission


List the differences between SLIP and PPP


Explain the operation of the Logical Link Control
sublayer


Discuss the role of NetBEUI, NetBIOS, and
NetBIOS over TCP/IP in a Windows network

Serial Data Communication


Communication over single communication line


One bit at a time (least significant bit first)


11
-
bit transmission waveform standard


Used for transmitting 7
-
bit ASCII characters


First bit: start bit (always low)


Identifies beginning of new transmission


Next seven bits: ASCII code


Last data bit: parity bit


Last two transmission frame bits: stop bits (always
high)


May be one, one and one
-
half, two stop bits

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Computer Networking From LANs to WANs: Hardware, Software, and Security

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Serial Data Communication (cont’d.)


Parity bits


Determine error in the received character


Odd parity


Occurs if odd number of 1s


Even parity


Occurs if even number of 1s


Transmission error:


Received parity not in line with expected parity

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Serial Data Communication (cont’d.)


Example: ASCII character lower case I


ASCII code is 69 hexadecimal (1101001 binary)

Figure 7
-
1

11
-
bit transmission code

Serial Data Communication (cont’d.)


Each waveform bit takes same amount of time


Related to baud rate of the serial transmission


Baud rate


Generally: number of bits per second in a transmission


Actually: number of transitions per second


Advantages


Simple connection requirements


Single transmit wire, single receive wire (plus ground)


Asynchronous communication not possible


Start bit used to synchronize transmitter and receiver

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Computer Networking From LANs to WANs: Hardware, Software, and Security

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Serial Data Communication (cont’d.)


UARTs (universal asynchronous receiver
transmitter)


Digital devices handling serial data transmission


Parallel input data converted to serial output data


Serial input data converted into parallel output data

Figure 7
-
2

The UART

SLIP


First protocol to transmit TCP/IP over dial
-
up lines


Provides basic method to encapsulate TCP/IP data


Not provided


Error detection


Internet Protocol (IP) address assignments


Link testing


Synchronous communication


Transmission protocols other than TCP/IP


Compressed SLIP (CSLIP) available


Replaced Point
-
to
-
Point Protocol (PPP)

Computer Networking From LANs to WANs: Hardware, Software, and Security

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PPP


Provides serial connection encapsulation


TCP/IP, IPX, NetBEUI, AppleTalk, other protocols


PPP frame provides:


Error detection


Checksum value tests data validity


Ability to assign IP addresses


As needed during session duration


Link testing


Mechanism to periodically test PPP link operation
status

Computer Networking From LANs to WANs: Hardware, Software, and Security

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PPP (cont’d.)


PPP frame provides: (cont’d.)


Synchronous, asynchronous communication modes


Security (user name, password authentication)


Password Authentication Protocol (PAP)


Challenge Handshake Authentication Protocol (CHAP)


Compression


Operates on layers 1 (Physical) and 2 (Data
-
Link)

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Figure 7
-
3

PPP frame format

Computer Networking From LANs to WANs: Hardware, Software, and Security

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PPP (cont’d.)

Table 7
-
1

Comparing SLIP and PPP

Computer Networking From LANs to WANs: Hardware, Software, and Security

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PPPoE


Allows multiple LAN users to share a single Internet
connection


Encapsulates PPP within an Ethernet frame


User establishes PPPoE session through the single
ISP Internet connection


Each PPPoE user session can be monitored (billing)

Computer Networking From LANs to WANs: Hardware, Software, and Security

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PPPoE (cont’d.)


Code field: PPPoE frame type (discovery, session)


Session ID, Ethernet frame’s source and destination
MAC addresses


Uniquely identify PPPoE session


Length field: payload size or user data, sent


Figure 7
-
4

PPPoE frame format

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Logical Link Control


Data
-
Link layer contains two parts

Figure 7
-
5

Data
-
Link layer details

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Logical Link Control (cont’d.)


Three types of service:


Type 1: Connectionless communication (unreliable)


Type 2: Connection
-
oriented communication (reliable)


Type 3: Acknowledged connectionless
communication


LLC protocol:


Based on HDLC (High
-
Level Data
-
Link Control)


Provides mechanism for sending commands and
responses over a communication link

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Logical Link Control (cont’d.)


DSAP and SSAP fields


Indicate how payload interpreted


SNAP (subnetwork access protocol) payload use


When high
-
level protocol handled by LLC sublayer

Figure 7
-
6

Logical Link Control PDU

Logical Link Control (cont’d.)


MAC sublayer


Interfaces LLC sublayer with different network
technologies


LLC sublayer does not know details


Allows the same LLC sublayer to work with different
network technologies


Additional responsibilities


Controlling access to network media


Recovering from errors


Addressing (working with MAC addresses)


Computer Networking From LANs to WANs: Hardware, Software, and Security

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NetBIOS


Provides all functionality to share resources
between networked computers


Utilizes three types of services:


Name: Finding and naming machines


Session: Connection
-
oriented reliable transfer of
messages


Datagram: Connectionless non
-
reliable datagram
transfer


NetBIOS message main component


SMB (server message block)


Provide all functionality possible under NetBIOS

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Computer Networking From LANs to WANs: Hardware, Software, and Security

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NetBIOS (cont’d.)

Table 7
-
2

Sample NetBIOS commands

Computer Networking From LANs to WANs: Hardware, Software, and Security

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NetBIOS (cont’d.)


Machine names


NetBIOS names that identify each machine


Up to 15 characters (letters, numbers, limited set of
symbols)

Figure 7
-
7

Windows 9x Network Identification display

Figure 7
-
8

Invalid NetBIOS computer

name error message

Computer Networking From LANs to WANs: Hardware, Software, and Security

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NetBEUI


Transport mechanism to deliver NetBIOS messages
over a LAN


Does not conform to OSI model


Uses Transport, Network, LLC part of Data
-
Link


Not a routable protocol


Uses MAC addresses to specify source, destination
computers


Only used on small networks


Windows Internet Name Service (WINS)


Maps NetBIOS names to IP addresses

Computer Networking From LANs to WANs: Hardware, Software, and Security

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NetBEUI (cont’d.)


NetBIOS over TCP/IP


NetBIOS messages transported using TCP


Used to share resources over a WAN


View Network properties window


NETSTAT displays active NetBIOS ports


Some may cause computer vulnerability

Table 7
-
3

NetBIOS over TCP/IP port assignments

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Figure 7
-
9

Active network connections on a Windows system

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Figure 7
-
10(a)

Network Properties showing

protocol bindings on a Windows 9x computer

Computer Networking From LANs to WANs: Hardware, Software, and Security

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NetBEUI (cont’d.)


Communication channel


Formed between protocol and adapter


When protocol bound to network adapter


Protocol cannot use an adapter until it is bound to it


Multiple protocols


May be bound to single adapter or multiple adapters


NetBEUI originally used by IBM LAN Manager
network



Now adapted by Microsoft for use in Windows

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Figure 7
-
10(b)

Windows 9x NetBEUI Properties window

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Figure 7
-
10(c
) Windows 9x NetBEUI Properties window

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Figure 7
-
11

NetBEUI Properties windows

on Windows 2003 server

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Troubleshooting Techniques


Protocol information sources


http://www.protocols.com


http://www.whatis.com

Computer Networking From LANs to WANs: Hardware, Software, and Security

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Summary


Low
-
level protocols


Establish serial communication


Exchange data over different hardware technologies


Provide peer
-
to
-
peer communication


Serial data communication


One bit at a time over a single communication line


Parity bits help determine errors in the received
waveform


Many protocols available


SLIP, PPP, PPPoE, NetBIOS, NetBEUI