Networking Essentials
Peer-to-Peer Network:
- fewer than 10 users
- same location
- security is not an issue
Server-based Network: Security is most often the primary reason for choosing a server
based approach to networking.
3 basic network topologies:
- bus
- linear bus
- single cable - truck
- communicate by addressing data to a particular computer
- sending the signal
- passive topology
- only 1 computer at a time can send message
- address matching
- signal bounce - signal has to be stopped then others can send again otherwise bouncing
- the terminators - to stop signal from bouncing
- LAN expansion
- barrel connector - connect two cables together to make a longer one
- repeater - boosts the signal before it sends the signal on its way
- star
- connect to a centralized component, hub
- centralized resources & management
- central point fails, entire network goes down
- ring
- connect computers on a single circle of cable
- active topology
- each computer acts like a repeater to boost the signal & send it on to the next
computer
- the fail of 1 computer can impact the entire network
- token passing
- the token is passed from computer to computer until it gets to a computer has data to
send
- After verification the sending computer creates a new token & releases it on the
network
Hubs
- is the central component in a star topology
- active hubs - regenerate and retransmit the signals like a repeater - multiport repeater
- passive hubs
- wiring panels or punchdown blocks
- connection point and do not regenerate the signal
- not required electrical power
Hybrid Hubs - advanced hubs that will accommodate several different types of cables
Benefits of hub-based topologies
- easy to expand
- different type of cables can be used
- centralized monitoring of network activity and traffic
Star Bus - combination of bus and star topologies
- 1 computer goes down, no affect to the network
- 1 hub goes down, all the computers connected to that hub are unable to communicate, all
others ok.
Star Ring - combination of star and ring topologies
| Topology |
Advantages |
Disadvantages |
| Bus |
- cable is cheap
- media is easy to work with
- simple, reliable
- easy to extend
|
- slow in heavy traffic
- problems are hard to isolate
- cable break can affect the network
|
| Ring |
- equal access for all computers
- even performance despite many users
|
- 1 machine down, affect the network
- problem hard to isolate
|
| Star |
- easy to expand/modify
- centralized monitoring & management
- 1 machine fails doesn't affect network
|
- centralized point goes down, the whole network is down
|
Connecting Network Components
Network Cabling - 3 types:
- Coaxial
- relatively inexpensive
- solid copper surrounded by insulation, a braided metal shielding
- dual shielded - 1 layer of foil insulation + 1 layer of braided metal shielding
- quad shielded - 2 layers of foil insulation + 2 layers of braided metal shielding
- for environments that are subject to higher interference
- shielding protects transmitted data by absorbing stray electronics signals, called noise
- insulating layer protects the core from electrical noise & crosstalk - signal
overflow from an adjacent wire
- the conducting core and the wire mesh must always be separated from each other
(insulation in between) otherwise the cable will experience a short and noise or stray
signal.
- thin (thinnet)
- approx. 180 meters then attenuation
- RG-58 family
- 50-ohm impedance
- RG-58 A/U - stranded wire core
- RG-58/U - solid copper core
- thick (thicknet)
- standard Ethernet
- thicker copper core
- approx. 500 meters
- sometimes used as a backbone
- transceiver connects the thinnet coaxial to the larger thicknet coaxial cable
- 2 grades
- polyvinyl cable (PVC) - when it burns, it gives poisonous gas
- plenum - fine resistance and produce a minimum amount of smoke
| Cable |
Description |
| RG-58/U |
solid copper core, 50-ohm |
| RG-58 A/U |
stranded wire core, thinnet, 50-ohm |
| RG-59 |
cable TV, 75-ohm |
| RG-6 |
larger in diameter and rated higher frequencies than RG-59, used for boardcase as well |
| RG-62 |
ArcNet network, 93-ohm |
- Twisted-pair cable
- two insulated strands of copper wire twisted around each other
- the twisting cancels out electrical noise from adjacent pairs and from each other
sources such as motors, relays and transformers
- 2 types
- unshielded twisted-pair (UTP)
- two insulated copper wires
- category 3 - up to 10 Mbps, four twisted-pairs with three twists per foot
- category 5 - up to 100Mbps, four twisted-pairs of copper wire
- problem - crosstalk - STP to reduce crosstalk
- shielded twisted-pair (STP)
- woven copper braid jacket which is higher quality, more protective jacket than UTP has
- foil wrap between the wire pairs and internal twisting of the pairs
- less susceptible to electrical interference - higher transmission over long distance
- can travels 100 meters
- connection hardware - RJ45 similar to RJ-11 (telephone connector)
- expandable patch panels
| category |
for |
speed |
| 1 |
voice |
|
| 2 |
voice |
4Mbps |
| * 3 |
data |
10Mbps |
| 4 |
data |
16Mbps |
| * 5 |
data |
100Mbps |
- Fiber-optic cable
- digital data signal, 100Mbps
- safe method - no electrical impulses are carried
- high speed, high capacity
- extremely thin cylinder of glass, called the core surrounded by a concentric layer of
glass called cladding
- each glass strand passes signals in only one direction - so, a cable consists of two
strands in separate jackets
- not subject to electrical interference and are extremely fast (now 100 Mpbs) signal
can't be tapped
- signals travel 2km
| Factor |
UTP |
STP |
Coaxial |
Fiber-Optic |
| Cost |
Lowest |
Moderate |
Moderate |
Highest |
| Capacity |
1 to 100 Mbps (typically 10 Mbps) |
1 to 155Mbps (typically 16Mbps) |
typically 10Mbps |
2Gpbs (typically 100Mbps) |
| Attenuation |
High (range of hundreds of meters) |
High (range of hundreds of meters) |
Lower (range of a few kms) |
Lowest (range of tens of kms) |
| Electromagnetic interference |
Most sensitive to EMI and eavesdropping |
Less sensitive than UTP but still sensitive to EMI and eavesdropping |
Less sensitive than UTP but still sensitive to EMI and eavesdropping |
Not affected by EMI or eavesdropping |
Baseband Transmission
- use digital signaling over a single frequency
- digital signal uses the complete bandwidth of the cable - 1 channel
- bi-directional
- use repeater to regenerate signal
Broadband Transmission
- analog signaling and a range of frequencies
- uni-directional, solutions:
- mid-split broadband - divide the bandwidth into two channels - 2 different frequencies
- in dual-cable broadband - two cables physically, one for send and one for receive
- use amplifiers to regenerate signal
Cabling considerations
- installation logistics - how easy is the cable to install and work with
- shielding - added cost, noisier the area, more shielding the cables need
- crosstalk - security is crucial, generated by power lime, motors, relays....
- transmission speed - measured in Mbps
- attenuation - the reason for cable specification that recommend certain length limits on
different types of cabling
- costs
Wireless - 3 categories
- local area network
- the transceiver (access point) broadcase and receives signals to and from the
surrounding computers
- use small wall-mounted transceivers to the wired network
- establish radio contact with portable networked devices
- transmission techniques
- infrared
- 10Mbps, =<100 feet, no strong ambient light
- line-of-sight networks - only clear line of sight
- scatter infrared networks - limit to 100 feet, slow because signals bounce off wall and
ceilings
- reflective networks - optical transmit toward a common location which redirects the
transmissions to the appropriate PC
- broadbrand optical telepoint - can handled high quality multimedia
requirements, provide
broadbrand services like wired
- laser - like infrared, but requires a direct line of sight, person or things can block
the transmission
- narrow-band (single frequency) radio
- like radio broadcasting - PC tunes the frequency
- 5000 square meters
- can't go through steel or load-bearing walls
- 4.8Mbps, slow!
- spread-spectrum radio
- broadcasts over a range of frequencies
- frequencies divided into channels or hops
- security - sender and receiver both use a code
- 250kbps
- truly wireless
- extended local area network
- multipoint wireless connectivity
- wireless bridge to link buildings w/o using cables
- the long-range wireless bridge
- use also spread-spectrum radio
- up to 25 miles
- eliminates the need for T1 line or microwave connection
- T1 transmission rates of 1.544Mbps (voice and data)
- mobile computing
- involves telephone carries and public services to transmit and receive signals
- slow 8kbps to 19.2kbps
- packet-radio communication - breaks a transmission into packets
- source address
- destination address
- error-correction info.
- cellular network - CDPD - fast, only suffers subsecond delays
- satellite stations
- microwave system
- most common in Us
- 2 radio transceiver 1 receive and 1 send
- 2 directional antennas points at each other to implement communication of the signals
broadcast by the transceivers
Network Adapter Card
- prepare data from the computer for the network cable
- send the data to another computer
- control the flow of data between the computer and the cabling system
- contain firmware programming that implements the logical link control and media access
control functions (data link layer)
- on the network cable, data must travel in a single bit stream
- serial transmission - one bit follows another, one-lane highway
- one way at a time - either send or receive
- take data in group to serial
- translate the computer's digital signals into electrical and optical signals for the
network cable = transceiver
- network addresses are determined by the IEEE committee
- has a unique address on a network
-
- move the data from computer requesting the computer's data
- signals the computer requesting the computer's data
- bus moves data from memory to the card
- has buffer (RAM) - faster
- select IRO, commonly IRQ5 is free, IRQ 3,4 are for com 2,1
- select base I/O port - info follows between computer's hardware and it's CPU. The port
appears to the CPU as an address
- select base memory address - identifies a location in RAM as a buffer area
- select the transceiver - 10Base2, 10BaseT, external
- ISA - 8 or 16 bits
- EISA - 32 bits
- Micro Channel Architecture - IBM - 16 or 32 buts
- PCI - 32 bits
- BNC connector - round - thinnet
- AUI connector - 15 pint - link joystick port - thicknet
- RJ-45 - like telephone plug - 10BaseT
- speed up the movement of data
- DMA - data moves directly from network card to computer's memory
- shared adapter memory - computer uses network card's memory
- shared system memory - network card uses computer's memory
- bus mastering- card takes temporary controls of the computer's bus - EISA and Micro
Channel Architecture
- buffering RAM
- onboard microprocessor - doesn't need the computer's processor
How A Network Functions
The OSI and 802 Networking models:
- protocol - rules of behaviors - a set of procedures in performing each task before
sending data from one computer.
- OSI standard
- 7 layers
- the functions of each layer communicate and work with the functions of the layers
immediately above and below it.
- layers separated from each other by boundaries called interfaces
- the purpose of each layer is to provide service to the next higher layer
- data is passed from one layer to another it's broken down into packets
- layer 7 - application layer
- represents the services that directly support user application , such as software for
file transfer, database
- handle general network access, flow control, error recovery
- layer 6 - presentation layer
- determines the format used to exchange data among networked computers - network's
translator
- protocol conversion
- encrypting the data
- data compression
- utility known as redirector operates at this layer
- layer 5 - session layer
- allows two applications on different computers to establish, use and end a connection
called a session
- performs name recognition like security
- placing checkpoints in the data stream
- dialog control between communicating processes
- layer 4 - transport layer
- ensure that packet are delivered error free
- break long message into several packet and repackage it when in receive mode
- send an acknowledgement of receive
- flow control, error handling
- layer 3 - network layer
- addressing messages and translation logical addresses to physical addresses
- determine the route from the source to the destination computer
- packet switching, routing, controlling the congestion of data
- if the network card on the router can't transmit a data chuck as large as the
source PC sends, the network layer on the router compensates by breaking the data into
smaller units
- layer 2 - data link layer
- sends data frames from the network layer to the physical layer
- receive end - it packages raw bits from the physical layer into data frames
- provide the error-free transfer of these frames
- sends a frame, it waits for an acknowledgment from the recipient
- layer 1 - physical layer
- transmits the unstructured raw bit stream over a physical medium (cable)
- defines how the cable is attached to the network adapter
- responsible for transmitting bits (1 & 0)
- easier way to remember the above: All People Seems To Need
Data Processing
- 802 project model
- define the network standards for the physical components of a network - the interface
card and cabling - physical and data link layer of the OSI model
- 802.3 - CSMA/CD LAN Ethernet
- 802.5 - token ring LAN
- data link layer - divided into two sublayer
- logical link control sublayer (LLC) - manager data-link communication and defines the
use of logical interface points - service access point (SAPs) defined
by 802.2
- media access control sublayer (MAC) - communicate directly with the network card &
is responsible for delivering error-free data between 2 computers on the network &
provide share access from network card to physical layer
- Drivers
- network drivers provide communication between adapter card and the network redirector
running in the PC
- redirector is part of the networking software that accepts I/O request over the network
- network card drivers reside in the media control sublayer
- Sending data
- large amounts of data sent as one large unit ties up the network
- smaller packages - in case of error in transmission
- in order for many users at once to transmit data quickly and easily across the network,
the data must be broken into smaller, manageable chucks - packers or frames
- packet components
- source address
- data
- destination address
- instructions that for network components how to pass the data along
- info that tells the receiving Pc how to connect the packet to other packet to reassemble
the complete data
- error checking info
- packet - 3 parts
- header
- alert signal to indicate that the packet is being transmitted
- source address
- destination address
- clock info
- data - actual data : 0.5k to 4k
- trailer - protocol and CRC
- this is a packet:
- at the transport layer, the original block of data get broken into the actual packets
- at the transport layer, sequence information is address which will guide the receiving
computer in reassembling the data from packet
- broadcast type address - can get the simultaneous attention of many computers on the
network
- 2 ways for directing packets
- packet forwarding - PC can send a packet onto the next appropriate
network component based on the address in the packet's header
- packet filtering - using criteria such as an address to select specific packet packets
- Protocols
- 3 points to keep in mind
- there are many protocols
- some protocols work at various OSI layer
- several protocols may work together - protocol stack
- The sending PC
- breaks the data into smaller sections
- adds addressing info
- prepares the data for actual transmission
- The receiving PC
- takes the data off the cable
- brings the data packets into the computer via network card
- strip the data packets of all of the transmission info added to the sending PC
- copies the data from packet to buffer for reassembly
- passes the reassembled data for the application
- routable vs nonroutable protocols
- data being sent from one LAN to another along any of several available paths is routed
- the protocols that support multipath LAN-to-LAN communication are known as routable
protocols
- protocol stacks
- application layer - initiates a request or accepts a request
- presentation layer - adds formatting, display & encryption info to the packet
- session layer - traffic flow info is added - packet sent?
- transport layer - add error-free handling info
- network layer - sequencing and address info is added
- datalink layer - add error-check info (CRC) and prepare data to physical layer
- physical layer - packet sent as a bit stream
- binding - e.g. if TCP/IP is bound as the first protocol, TCP/IP will be used to attempt
to make a network connection, if this network connection fails, your computer will
transparently attempt to make a connection using the next protocol in the binding order
- 3 protocol types
- application protocol
- work at the first 3 OSI layer
- application-to-application interaction & data exchange
- SMTP, FTP, SMB (ms)
- transport protocol
- work at transport layer
- provide for communication session between computers and ensure the data is able to move
reliably
- TCP, SPX, NetBEUI
- network protocol
- work at the lower 3 OSI payers
- provide link services
- handling addressing and routing info, error-checking and retransmission request
- IP, IPX, NWLink, NetBEUI
- TCP/IP - internetworking protocol
- NetBEUI - NetBIOS extended user interface - not routable
- IPX/SPX - Novell - support routing
- Access Methods
- Carrier-Sense Multiple Access with Collision Detection (CSMA/CD)
- a computer 'sense' that the cable is free
- the computer can send data
- if there's data on the cable, no other computer may transmit until the data has reached
its destination and the cable is free again
- data collision - stop transmitting for a random period of time and then attempt to
retransmit
- attempt to transmit and listen to see if any collision occur at the same time
- not effective beyond 2,500 meters
- contention method - computers complete to send data
- can be a slow method if too many computers on the network
- Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA)
- each computer signals its intent to transmit before it actually transmit data
- broadcasting generate traffic on cable and slows down network performance, slower
method
- Token Passing - special type of packet called a token circulates around a cable ring
from PC to PC
- Demand Priority
- for 100mbps, 100VG-AnyLAN, IEEE 802.12
- computers can receive and transmit at the same time - four pairs of wires are used
- only communication between sending PC, the hub (repeater) and the destination PC - more
efficient
- each hub knows only about the end nodes and repeaters directly connected to it
- transmit through the hub only
Network Architectures
Ethernet
- perform the same functions as the OSI physical and data link layers of data
communication
- IEEE 802.3 standard
- baseband transmission
- 10Mbps to 100Mbps
- passive hub - draw power form the computer
- thinnet, thicknet, UTP
- breaks down data into frames - a package of info transmitted as a single unit
- Ethernet frames is between 64 and 1,518 bytes long, 18 is needed, so, data in
Ethernet is
between 46 & 1,500 bytes long
- CSMA/CD access method
- 10BaseT (10Mbps, Baseband, over twisted-pair cable)
- 802.3 IEEE specification
- UTP, STP, category 3,4,5
- max. cable segment = 100m
- repeater can be used to extended
- 10BaseT LAN server 1,024 computers
- RJ-45 connectors
- backbone for hubs - coaxial or fiber-optics
- 10Base2 (10Mbps, Baseband, roughly two times 100 meters)
- coaxial cable, thinnet
- max. 185 meters
- 30 computers per 185 segment
- BNC barrel connectors, BNC T-connectors, BNC terminators
- 5-4-3 rule in thinnet: 5 cable segments connected by 4 repeaters but only 3 segments can
have stations attached
- max. total network length: 925m
- 10Base5 (10Mbps, Baseband, 500 meters)
- thicknet, bus topology support 100 nodes per backbone segment
- 802.3 IEEE specification
- DIX or AUI connector
- N-serise connectors including N-series barrel connectors and N-series terminators
- 5-4-3 rule in thicknet: 5 backbone segments, 4 repeaters, 3 segments that can have
stations
- min. 2.5 meters thicknet cable between segments
- 10BaseFL (10Mbps, Baseband, fiber-optic cable) - max. segment 2000 meters
- 100VG-AnyLAN
- 100VG (Voice grade)
- IEEE 802.12 = 802.3 + 802.5
- 100Mbps
- category 5 TP & fiber optic cable
- demand priority access method
- support both Ethernet frames and token ring packet
- star topology
- child hubs act as computers to their parent hubs
- 100BaseT hub to a computer cannot exceed 250 meters
- 100BaseX
- fast Ethernet
- UTP category 5
- CSMA/CD access method
- 100BaseT4 (4-pair, category 5)
- 100BaseTX (2-pair category 5 UTP or STP)
- 100BaseFX (2-strand fiber-optic cable)
Token Ring
- IEEE 802.5 specification
- token passing access method
- logical ring, but actual wiring scheme passes through the hub
- STP (IBM type 1,2,3)
- 4 or 16 Mbps
- star wired ring topology
- baseband transmission
- in the frame, the media access control field indicates whether the frame is a token
frame or a data frame
- when the first token ring computer comes online, the network generates a token
- only 1 computer which has the token can send data over the network
- finished sending - the computer removes the frame from the ring and transmit a new token
back on the ring
- each PC acts as a unidirectional repeater
- hub - MAU, MSAU, SMAU
- MSAU
- 10 connection port
- 72 computers - UTP
- 260 PCs - STP
- 19 MSAU can connect to each other
- can sense if a PC is down then discount it from the ring
- STP or UTP to a hub, IBM type 1,2,3 cable
- 101m from MSAU to PC for type 1
- 100m from MSAU to PC for STP
- 45m from MSAU to PC for UTP
- 150 feet from MSAU to PC for type 3
ArcNet and AppleTalk
- local talk
- CSMA/CA access method
- 3 things happen when devices attached
- device assigns itself an address randomly
- device broadcast the address to see if it's used
- if not, the device will use it the next time it's online again
- bus or tree
- STP
- max. 32 devices
- Apple share
- file server on an AppleTalk network
- divided into zones
- EtherTalk
- 802.3
- allows protocols to run on Ethernet coaxial cable
- TokenTalk
- 802.5
- allows Macintosh to connect to token ring network
ArcNet
- 802.4
- token-passing
- broadband
- 2.5Mbps
- ArcNet plus - 20Mbps
- connected by cable to hub
- 93-ohm RG-62 A/U - 610m max., star
- 93-ohm RG-62 A/U - 305m max., bus
- RJ-11, RJ-45 UTP - max. 244m on star or bus
Network Operations
Network O/S setup
- 2 major types of multitasking
- preemptive - O/S can take control of the processor without the task's cooperation
- non-preemptive (cooperation) - the task itself decides when to give up the processor. no
other program can run until the non-preemptive program gives up the control of the
processor
- a network O/S
- ties together all the PCs and peripheral in the network
- coordinates the functions of all PCs and peripherals in a network
- provide security for and access to database and peripherals in a network
- client software
- redirector - process of forwarding requests is done by a redirector
- intercepts requests in the PC
- determines if they should be left alone to continue in the local PC's bus or redirected
out to the network to another server
- designates - e.g. share drive in other PC, alphabet as a designator, such as G:
- peripherals - redirectors can send requests to either computers or peripherals
- server software
- resources sharing - security as well
- managing users - create, privileges, remove
- windows NT server
- server naming - domain, workgroup
- divided into domain
- the 1st server installed in a domain must be installed as the primary domain controller
(PDC), every domain is required to have one and only one PDC
- a backup domain controller partitioning
- configuring the network adapter card - default protocol for NT server is TCP/IP
- TCP/IP installation
- IP address - logical 32-bit address to identity a TCP/IP host, two parts: network ID and
host ID
- subnet mask - is used to mask a portion of the IP address so that TCP/IP can distinguish
the network ID from the host ID - 255.255.0.0
- default gateway - for communication with a host on another network, an IP host must be
configured with a route to the destination network otherwise only local communication
- manual install - assign IP address, subnet mask and the default gateway
- automatic install - dynamic host configuration protocol (DHCP) server service, when a
DHCP server is configured on the network, clients that support DHCP (NT W/S & NT
Server) can request TCP/IP configuration info (IP address, subnet mask, default gateway
and so forth) from the DHCP server
Networking printing
- process -
- the PC's redirector put the print job onto the network cable
- print server's network software takes the print job from the cable and send it into a
queue with other items waiting from access to the shared printer
- network uses a spool (simultaneous peripheral operation on line)
- a spooler is a memory buffer in the print server's ram that holds print jobs
- PDL - page description language - the printer uses the PDL to construct text and
graphics to create the page image, PDLs are like blueprint
- can manage the printer remotely
Network Application
- e-mail
- mailboxes - a mailbox for each user on the system. A mailbox is the delivery location
for all incoming e-mail for a designated user
- activities at layer 7 (application layer) of the OSI model
- X.400 - hardware and software independence
UA - user agent
MTA - message transfer agent
MTS - message transfer system - X.500 - to other network, distributed network
- SMTP - part of the TCP/IP protocol stack
- gateway to translate incoming message from other e-mail language to its own that can be
understood
Network in multivendor environment
- server's O/S, the client's O/S & the redirector have to be compatible
- the client solution - implement the appropriate redirector, the redirector forwards your
request to the appropriate destination
- the server solution - install a service on the service
Client/Server
- centralized computing - when a client requests data from a database, the system moves
all the data across the network to the client
- client/server computing - the client computer makes a request and a computer acting as
the server fulfills the request
- the client software uses the structured query language (SQL) to translate what the user
sees into a request that the database can understand
Network Administration & Support
Managing Network Account
- five management area
- user administration
- resource management
- configuration management
- performance management
- maintenance
Managing Network Performance
- bottlenecks
- one device uses noticeable more CPU time than the others
- these devices tend to become bottlenecks: CPU, memory, network card, disk controllers,
network media
- windows NT performance monitor
- view operations in both real time and recorded time for: processors, HDD, memory,
network utilization, network as a whole
- can record the performance data
- send an alert to the network manager
- run utility that can adjust the system back into acceptable ranges
- establish a baseline of system management
- simple network management protocol (SNMP) - in a SNMP environment, program called agents
are loaded onto each managed device. The agents monitor network traffic and behavior
in
these key network components in order to gather statistical data. This data is stored in a
management information base (MB)
- SNMP components include: hubs, servers, interface cards, routers and bridges
Total System Management
- Microsoft system management server (SMS)
- centralized administration of computers in a WAN
- inventory management - collects and maintains an inventory of hardware and software for
each computer and stored in a SQL server database, info. like RAM, CPU, HDD size...
- shared application management - shared application can also distributed to a server for
clients access
- software distribution - SMS can install and configure new software or upgrade
previously installed software
- remote control and network monitor - provide help desk and diagnostics utilities to
control remote client directly and access to remote client
Data security
- audit records show the users that have accessed or attempted to access specific
resources in security log
- diskless computers
- data encryption
- data can't be stolen from the cable. When the data gets to the proper PC, a key, the
code for deciphering encrypted data, decode the bits into understandable info.
- DES data encryption standard
- CCEP commercial COMSEC endorsement program
Avoiding Data Loss
Larger Network
Modem
- telephones use analog signal - a smooth curver can represent any values
- computers use digital signal - synonymous with only 0 and 1
- baud refers to the speed of the oscillation of the sound wave on which a bit of data is
carried over the telephone wire
- the bps can be greater than the baud rate due to compress and encode data so that each
modulation of sound can carry more than one bit of data is carried over the telephone line
- 2 types of modem
- asynchronous communications (Async)
- use common phone lines
- not synchronized, no clocking device
- up to 28,800bps now
- error control - a parity bit which is used in an error checking and correction scheme
called parity checking
- signaling or channel speed - how fast the bits are encoded onto the communication
channel
- throughputs - amount of useful information going across the channel
- v.32bis, v.42, v.42bis
- synchronous communication
- relies on a timing scheme coordinated between two devices to separate
groups of bits and
transmit them in blocks known as frames
- if there's error, re-transmit it
- some synchronous protocol perform the following that asynchronous protocols don't:
- format data into blocks
- add control info
- check the info to provide error control
- the primary protocols in synchronous communication are:
- synchronous data link control (SDLC)
- high-level data link control (HDLC)
- binary synchronous communication protocol
- 2 types of lines:
- public dial network (bisync) lines (dial-up lines) - manually dial up to make a
connection
- leased (dedicated) lines - full time connection that do not go through a series of
switches, 56kbps to 45mbps
Larger Network
- repeaters
- don't translate or filter anything
- both segments must use the same access method e.g.CSMA/CD
- can take an Ethernet packet from a thinnet coax and pass it on to a fiber-optic segment
- pass a broadcast storm along from on segment to the next further and back
- regenerate signals
- work at the Physical layer of OSI
- bridges
- all features that repeaters have
- work at the data link layer of OSI between them
- work at the MAC sublayer and called Media Access Control layer bridges
- as traffic passes through the bridges, info. about the PC's address is stored in the
bridge's RAM. This ram is to build a routing table based on source addresses
- if a bridge knows the location of the destination node, it forwards the packet to it. If
it doesn't know the destination, it forwards the packet to all segments
- re-generate data at the packet level
- packets can travel more than one route
- routers
- determine the best path for sending data and filtering broadcast traffic to the local
segment
- work at the network layer of OSI
- filtering and isolating traffic
- connecting network segments
- routing table contains
- all known network addresses
- how to connect to other networks
- possible paths between those routers
- costs of sending data over those paths
- not only network addresses but also media access control sublayer addresses for each node
- only pass info. if network address is known
- routable protocols: DECnet, IP, IPX, OSI, XNS, DDP(apple)
- non-routable protocols: LAT, NetBEUI
- can choose the best paths
- decides the path the data packet will follow by determining the number of hops between
internetwork segments
- OSPF is a link-state routing algorithm TCP/IP supports OSPF
- RIP uses distance-vector algorithm to determine routes TCP/IP & IPX support RIP
- NLSP is a link-state algorithm for use with IPX
- 2 types of routers
- static - manually setup and config the routing table and to specify each route
- dynamic - automatic discovery of routers
- recognized not only an address, as the bridge did, but also a type of protocol as well,
and it can identify addresses of other router and determine which packets to forward to
which routers
- forwards particular protocols to particular addresses (other routers)
- brouters
- combines the best qualities of bother a bridge and a router
- bridge non-routable protocols
- gateway
- repackage and convert data going from one environment to another so that each
environment can understand the other environment's data
- gateway links two systems don't use the same
- protocols
- data formatting structure
- languages
- architecture
- task-specific
- convert at the application layer of OSI
- takes the datafrom one environment, strips it, and re-packages it in the protocol stack
from the destination system
WAN
- analog
- dial-up line - via public switched telephone network (PSTN)
- dedicated line - fast, reliable, expensive, implement line conditioning
- digital
- digital data service (DDS) provide point-to-point synchronous communications at 2.4,
4.8, 9.6 or 56kbps
- guarantees full-duplex bandwidth by setting up a permanent link from each endpoint
- 99% error free
- doesn't requires modem, requires bridge or router through a device called a CSU/DSU
- T1
- PPP transmission
- uses two-wires pairs (1 pair to send, 1 to receive)
- full-duplex signal at 1.544mbps
- multiplexing - signals from different source are collected into a component called a
multiplexer and fed into one cable 8,000 times a second
- each channel can transmit at 64kbps - DS-0
- 1.544mbps known as DS-1
- T3 - 6mbps to 45mbps
- switched 56
- 56kbps
- used on demand
- equipped CSU/DSU to dial-up another switched 56 sites
- packet switching
- data package is broken into packers and each package is tagged with a destination
address and other info.
- relayed through stations in a computer network
- data paths for individual packets depend on the best route at any given instant
- use virtual circuit - logical connection between the sending computer and the receiving
computer
Advanced WAN
- X.25
- a set of protocols incorporated in a packet-switching network
- uses switches circuits and routes as available to provide the best routing at any
particular time
- uses telephone lines - slow - error checking
- synchronous packer-mode host or other device and the public data network (PDN) over a
dedicated or leased-line circuit
- DTC/DCE interface
- frame relay
- fast packet variable-length, digital, packet-switching technology
- point-to-point
- uses PVC to transmit at Data Link Layer
- over digital leased-line
- required frame-relay capable router or bridge
- ATM
- fixed-sized packets over broadband and baseband LANs or WANs
- 155mbps to 622mbps or more
- broadband cell relay method that transmit data in 53-byte cells rather than in
variable-length frames
- cell consists of 48 bytes of application info.
- up to 1.2gigabib per second
- hardware like routers, bridges have to be ATM compatible
- switches are multiport hubs
- router-like devices
- media
- FDDI (100mbps)
- fiber channel (155mbps)
- OC3 SONET (155mbps)
- T3 (45mbps)
- ISDN
- 3 data channels - 2 for 64kbps, 1 for 16kbps
- 64kbps channels are known as B channels, carry voice, data or image
- the 16kbps channel is D channel which carries signaling and link management data
- basic rate = 2B+D
- dial-up service, not dedicated, not bandwidth on-demand
- FDDI
- 100mbps token-passing ring network that uses fiber-optic
- max. ring length of 100km and 500 computers
- different from 802.5
- FDDI network can transmit as many frames as it can produce within a predetermined time
before letting the token go. More than 1 computer at a time can transmit
- the computer detects a fault then sends a'beacon' to its upstream neighbor then so on,
until the computer that originally sends the beacon receives its own beacon, it assumes
the problem is fixed and re-generates the token
- SONET
- synchronous optical network
- > 1Gbps
- fiber-optic
- SMDS
- switched multimegabit data services
- 1mbps to 34mbps
- fixed length cell relay technology same as ATM
Solving Network Problem
Monitoring network behaviors
- network monitoring
- events log - record errors, security audits, and other significant events for problem
diagnosis
- usage statistics - who is accessing resources and how they are accessing them
- performance statistics - indicate such things as processor utilization, memory usage and
server throughput
- windows NT - performance monitor
- establishing a baseline - all network behaviors can be compared to it as part of the
on-going monitoring process
Network Troubleshooting
- digital volt meters (DVM)
- check cable for continuous and can carry network traffic
- check if broken and will bring the network down
- continuity check
- two parts of the same cable are exposed and touching
- part of cable is touching another conductor such as metal surface
- time-domain reflectometers (TDRs)
- can look for any kind of a break, short or imperfection that might affect performance
- can locate a break within a few feet of the actual separation in the cable
- protocol analyzers
- perform real-time network traffic analysis
- packet capture, decoding and transmission
- look inside the packet to identify the problem
- generate statistics based on the network traffic
- built-in time-domain reflectometer
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