ch. 7 Telecommunications & Network

Protocols: FTP, TFTP, SNMP, SMTP, Telnet, HTTP

• Translation into standard formats
• Deals with Encryption and Compression
• No protocols in this layer - just services and standards:

• ASCII
• EBCDIC
• TIFF
• JPEG
• MPEG
• MIDI

• Set up connection Between applications
• NFS
• NetBIOS
• SQL
• RPC

• Simplex - Communication takes place in one direction
• Half duplex - Communication takes place in both directions but only one at a time
• Full duplax - both directions, communicate at the same time

Handle end-to-end transmission and segmentation

Responsible for handling computer to computer communication

Describes the data transfer between the applications, flow control, and error detection and correction

• TCP
• UDP
• SSL
• SPX

Two computers agree on communication and hand shake process

Include internetworking service, addressing, routing

• Describes the data transfer between networks i.e. moves data between two hosts that are not physically connected
• Uses Internet Protocol from TCP/IP suite for addressingRouters read information on layer 3 packet and use their routing table to determine the next hop on the network

• IP
• ICMP
• IGMP
• RIP
• OSPF
• IPX

Convert data into LAN or WAN frames for transmissions - converts messages to bits

Devided into two:

• LLC (logical Link control) - Error detection
• MAC (Media Access Control) - Transmits and receives frames from peers that are physically connected

• Protocols:
• ARP - address resolution protocol
• RARP - reverse address resolution protocol
• PPP - Point-to-Point Protocol
• SLIP - Serial Line Internet Protocol

• Converts bits into electrical signals - controls the physical aspects of the data transmission.
• HSSI - High speed serrial interface
• X.21
• EIA/TIA-232 & EIA/TIA-449

Analog Transmission Signals - Electromagnetic waves - through a process of modulation and a pre-determined frequency for the carrier

• Amplitude - height of signal
• Frequency - number of waves for a period of time

• Digital Signals - represent binary digits with electrical pulses
• Bandwidth - The maximum number of pulses that can be transmitted over a link

• Asynchrounous Communication - communication is not synchronized. Sender can send anytime and receiver must be ready
• Synchrounous Communication - communication between two devices that are synchronized usually through clocking mechanism

• Broadband - splits communication channel into individual channels so that different data types can be communicated simultaneously
• Baseband - Uses entire communication for transmission

• Copper Cable
• Coax – bulky, heavy, but relatively immune to noise
• Twisted pair – thinner, lighter, cheaper, and okay about noise

• Fiber Optic Cable
• Multi-mode – good for relatively short distances (a couple of km) and moderate speeds (< 10 Gbps)
• Single-mode – good for short and long distances (100+ km) and virtually any speed

Radio, Microwaves, Satellite, others

• Ethernet
• Token Ring
• FDDI
• ATM
• SLIP/PPP
• Frame Relay
• SONET
• Waxed String

• Ethernet
• Ethernet has a very simple transmission control protocol

802.3

• Listen to the network
• If someone is talking, wait your turn
• If no one is talking, send your data
• If someone starts talking while you are talking, stop talking and scream at them!

Ethernet uses CSMA/CD - Carrier Sense Multiple Access with Collision Detection

• Transmission Control Protocol
• Connection-oriented
• Stream based
• Reliable - In order, Once and only once
• “Heavy weight” - 3-way handshake

• Common uses:Remote login (Telnet, RSH/Rlogin, SSH)
• File Transfer (FTP, SCP, HTTP)Newer NFS

• UDP – The User Datagram Protocol
• Connectionless
• Datagram based
• Unreliable“Quick & Dirty”

Common uses:Domain Name System (DNS)Simple Network Management Protocol (SNMP)Older Network File System (NFS)

Unicast transmission - Occurs when a packet is sent from one source computer to one destination computer

Broadcast transmission - occurs when a packet is sent from one source computer to all computers on a certain network segment

Multicast Cattransmission - Occurs when a packet is sent from one source computer to several specific computers

Uses linear, single cable for all computers. All traffic travels the full cable. All data can be viewed by users.

Problems - if one segment goes down it can negitavely affect computers on the same line

ETHERNET

All computers are connected in a unidirectional communication link.

The cable is a closed loop

PRoblem - one station goes down it can affect other computers on same ring

FDDI

All computers are connected to a central hub

PROBLEM - the central device is a single point of failure

Logical bus (Ethernet) and ring topolgies (Token Ring)

A bus topology that does not have one linear cable but instead uses branches of cables

PROBLEM - none

ETHERNET

Computers are connected to each other - more redundancy

PROBLEM - Expensive

Internet

10Base2 - ThinNet - Coax Cable - maximum cable length of 185 meters, requires BNC connectors

Speed 10bps

• Thicker cable than 10Base2
• Coax cables
• BNC connectors
• Usually used as network backbone
• * more resistent to electric interference

• twisted pair copper wiring
• RJ-45 Connector
• usually implemented in a star topology
• 10 Mbps

• uses CSMA/CD
• 100 Mbps

• IEEE Standard 802.5
• Uses token passing technology
• Uses star-configured topology - ring - how the signal travels

Each computer is connected to cenral hub - MAU - Multi-Station-Unit

Token-passing technology - Cannot communicate unless a machine has a token ( a control frame) that travels in a logical circle.

Active Monitor- Removes tokens that are endlessly circling the network

• high-speed token passing media access technology
• 100 mbps - typically backbone network using fiber optic cable

Fault tolerance - counter rotating fiber ring - if one goes down, the othe ring will be activated

• 10Base2
• 10Base5

• Higher bandwidth
• resistent to electromagnetic interference (EMI)

baseband (one channel) and broadband (multi-channel) methods

• Shielded Twisted Pair - add resistents to radio frequency and EMI
• Unshielded Twisted Pair - Less resistence to radio frequency and EMI

The more twisted the wire, the more resistent the cable is interference and attenuation

Cross-Talk - UTP can electrical signals spill from one wire to another

• Glass that carries light waves
• More resistent to attenuation and EMI than copper wires
• Does not radiate signals
• higher speeds and longer distances

Used as backbone to networks

• ARP - knows IP and broadcasts to find MAC - ARP table poisoning masquerading
• RARP - knows MAC broadcasts to find IP
• DHCP
• ICMP - Loki Attack - send data within ICMP packet to compromised system - backdoor

• Dynamic - Router updates routing table and makes decision of routing path
• Static - Admin has to update
• Distance Vector - dicsion based on number of hops and vector (direction)
• Link-state - database of network topology - look at packet size, speed, delay, ... etc.

• Routing Information Protocol - How routers share information
• - not in use - no authentication, slow performance

• Open Shortest Path
• link-state algorithms to send out routing table information - smaller more frequent routing table updates
• requires more memory and CPU

Authentication in clear text or hashed

Interior Gateway Routing Protocol - distance vector routing protocol - Cisco systems - 5 criteria to determine best route.

Border Gateway Protocol - How border routers share information with other networks. Uses link-state and distance-vector routing algorithms.

An attacker can capture a packet at one end of a network and tunnel it to another location on the network

two attackers

countermeasure - leash - data on on header of packet - restricts packet distance

• Repeaters - physical
• Bridge - data link
• Switch - data link - network
• Router - network

Multi-Level Protocol Switching - Used to address service requiremest for different kinds of packets - VOIP or video conferencing

• Metropolitan Area Network
• SONET or FDDI - provided by telecommunication providers .

SONET - Synchronous Optical Networks - dual rings - redundancy

Channel Service Unit/Data Service Unit - required to connect a LAN to a WAN

Circuit Switching - Acts like a dedicated link

Packet Switching - traffice can pass through a various number of hops

• Works on Data-Link layer
• Cost based on amount of bandwidth - Commited information rate (CIR)
• DTE - Data Terminal Equipment - Company owned router
• DCE - Data Circuit-Terminating Equipmentd - Service Provider network equipment - performes the traffic movement
• Costs less than leased line

Combining multiple channels of data over a single transmission path.

• Statistical time-division multiplexing (STDM)
• Uses statistics for the workload of each inputdevice and determines the real time how much each device should be allocated for data transmission

• Frequency-division multiplexing
• - each frequency in a wireless spectrum is used to move data

Channel Service Unit/Data Service Unit - Requried when digital equpment will be used to connect a LAN to a WAN.

• PVC - Permanent Virtual Circuit - works like a privite line - agreed upon badwidth adn availalbility. Path established
• SVC - Switched virtual Circuit - Circuit must be built - required bandwidth

• Older WAN protocol - how devicesa dn entworks establish and maintain conenctions.
• data devided into 128 bytes and enca;uslated in High-level Data Link Control (HDLC) frames
• Not very efficient

• Asynchronous Transfer Mode (ATM) -
• Uses cell-switching instead of packet switching. Data segmented int fixed size cells of 53 bytes. (instead of variable size packets).
• Uses virtual circuits
• Good for voice and video

Quality of Service - protocol can distinguish between different classes of messages - priority level

CBR - Constant Bit Rate - Connection oriented channel - provides a consistent data through put of rtiem-sensitive applciations. customers specify bandwidth

VBR - Connection oriented channel - customers specify requried peak and sustatied rate of data throughput - variable bandwidth and speed

UBR - A connectionless channel that does not promise data through put

ABR- Connection oriented channel - allows the bit rate to be adjusted. Customers are given the bandwidth remaining

• Best Effort
• Differentiated service - less drops, more bandwidth, shorter delays
• guaranteed servcie - time sensitive data - voice and video

• Switched Multimegabit Data Service - High speed packet-switched thecnology used to enable customers to extend their LANs acros MANs and WANs.
• Connectionless -- REPLACED by FRAME RELAY

Synchronouse Data Link Control protocol - networks that use didicated, leased, or permanent physical connections. Used mainly for IBM hosts and mainframes to communicate to remote locations.

HDLC (High-Level Data Link Control) - protocol - extension of SDLC - high throughput, full-duplex .. point to point or multipoint networks

• High-Speed Serial Interface - interface used to connect multiplexers and routers to high-speed communication servcies - such as ATM and frame relay
• Physical Layer

Multiservice Access Technologies - combine several types of communication categories over one transmission line

Integrated Services Digital Network - Communication protocol provided by telephone companies and IPSs - uses equipment to transport digital data over phone lines.

• BRI - two channels that enable data to be transfeered adn one D channel tha provides for call setup ... ID .. etc
• PRI - 23 B channels and 1 D channel - used in corporations as a backup communication solution

Digital Subscriber Line - 6 to 30 times faster than ISDN - 52 MBPS

• 802.11b - most common
• 802.11a - in 'dirty range of frequency' - must be close to AP, may not work in other countries
• 802.11e - implemented QoS
• 802.11f - Allows users to roam - APs can talk to each other and make sure a user is authenticated
• 802.11g - higher transfer rates - up to 54 MBPS
• 802.11h - builds upon 802.11a - adapts type of data transmission for European wireless rules

• 802.11i - use of EAP (Extensible Authentication Protocol) and 802.11x to enforce user authentication and mutual authentication.
• TKIP - Temperal Key Integrity Protocol