10/21/2015CST 415 - Computer Networks1 Underlying Technologies CST 415

04/20/23 CST 415 - Computer Networks 1

Underlying Technologies

CST 415


Topics• Definitions

• Network Communications

• Ethernet

• FDDI

• ATM

• ARPANET

• NSFNET


DefinitionsConnection Oriented Services

– Also called “circuit-switched” services.– In this scheme, a dedicated circuit is created between

endpoints. An example of this is the current telephone system.

– In this scheme, a physical communication circuit is established between endpoints through intermediate switching stations.

Advantage: Only the endpoint to endpoint traffic will traverse the communication circuit. This guarantees a certain quality of service.

Disadvantage: Cost is fixed regardless of traffic. Also, any failure of an intermediate connection will fail the entire connection.


DefinitionsConnectionless Services

– Also called “packet-switched” services.

– There is no dedicated circuit between endpoints.

– Communication is split up into small digitized chunks (packets).

– End-to-end communication is potentially performed through many different routes depending on network load.

Advantage: Communication redundancy provides a higher level of throughput depending on system load.

Disadvantage: Reconstruction of packets is timely and data rate cannot be guaranteed.


DefinitionsFull Duplex

– The communication media will allow concurrent transfer of information in both directions.

– From the application point of view, it appears as though there is a communication line for sending and a line for receiving.

Half Duplex– The communication media will only transfer in

one direction at a time such as a serial cable.


Network CommunicationsLAN – Local Area Network

– Privately owned networks within a single building or campus, typically spanning a few kilometers as a maximum.

– Bandwidth can be high because of low distance restrictions.

– Security internal to a LAN can be closely monitored.


Network CommunicationsLAN – Topologies

– Ring Topology (Token Ring)

– Bus Topology (Typically Ethernet)

A LAN can deploy any topology that the local system administrator wishes.

Q: What will always be required if a LAN whishes to interoperate with other LAN installations?


Network Communications

Two network topologies(a) Bus

(b) Ring

from Computer Networksby Andrew S. Tanenbaum


Network CommunicationsWAN – Wide Area Network

– Data networks that span large geographical distances.

– Typical speeds are 1.5 Mbps to 155 Mbps.– WAN data rates are usually slower that LAN

data rates.


Network Communications

Wide Area Network


Subnet - a collection of routers and communication lines.


Network Communications from Computer Networksby Andrew S. Tanenbaum

Relative network types and their typical area coverage.


Network Communications• The Internet is not made up of homogeneous

networks.• Ethernet is one type of physical transmission

standard/data link standard used for LAN communications.

• Other packet switching technologies are used for WAN and Internet.– Frame Relay– FDDI– ATM


EthernetThe term Ethernet comes from the

luminiferous ether, the medium through which electromagnetic radiation was thought to propagate.

This was before it was discovered that electromagnetic radiation could propagate in a vacuum.


Ethernet• Developed at Xerox PARC in the early 70’s.• IEEE Standard Number is 802.3• Transceiver taps into the Ethernet cable

– Senses signals (CS)– Sends signals

• NIC (Network Interface Card) adapts the host computer to the transceiver.

• Multiple computers are connected to a single cable to form a bus topology (MA).


Ethernet (CSMA/CD)• A computer decides to send a packet.• The carrier is active and there are no packets

currently being transmitted. (Carrier Sense – CS)• There are multiple computers on the network bus

(Multiple Access – MA)• It is possible and highly probable that more than

one machine will send at the same time.• The collision will be detected (Collision

Detection – CD)• The computers will back off for a random

amount of time and try again.


Ethernet (CSMA/CD)

The amount of time the computer will “back-off” for is determined by a technique known as “binary exponential backoff”.

1. For the first 10 attempts, the mean value of the random delay is doubled.

2. For the next 6 attempts, the mean value is maintained.

3. After 16 unsuccessful attempts, the computer will give up and report a link error.


Ethernet (CSMA/CD)

See 802.3

• Figure 4–3 Relationship among CSMA/CD procedures

• Figure 4–4a—Control flow summary send frame• Figure 4–4b—Control flow summary receive

frame


Ethernet (CSMA/CD)

Thicknet– 10Base5 : The physical signal is carried over a coaxial

cable approximately ½ inch in diameter and up to 500 meters long. Theoretical transmission rate is 10 Mbps

– Transceivers are directly connected to the coaxial cable.

– Drop cables connect the cable to the Ethernet controller.


Ethernet (CSMA/CD)

Thinnet– 10Base2 : The physical signal is carried over a coaxial

cable that is pliable and easy to run through ceilings, floors and walls.

– Span is up to 200 meters long.

– Theoretical transmission rate is 10 Mbps

– Transceivers are resident on controller cards resident in host computers.


Ethernet (CSMA/CD)

Twisted Pair Ethernet– 10BaseT : The physical signal is carried 4 unshielded

twisted pair wires that are resident in standard telephone equipment (Category 5 or Cat5).

– The cable is connected up to a hub that provides the Bus topology.

– Length of wire is limited to 100 meters.

– Theoretical transmission rate is 10 Mbps


Ethernet (CSMA/CD)

Fast Ethernet– 100BaseT : The physical signal is carried 4

unshielded twisted pair wires that are resident in standard telephone equipment (Category 5 or Cat5).



– Theoretical transmission rate is 100 Mbps.

– The increase in rate is provided by clever use of the provided 4 twisted pairs to increase data rate.


Ethernet (CSMA/CD)

Gigabit Ethernet– 1000BaseT : The physical signal is carried 4

unshielded twisted pair wires that are resident in standard telephone equipment (Category 5 or Cat5).



– Theoretical transmission rate is 1000 Mbps.


Ethernet (CSMA/CD)

• Each of the Ethernet standards has a relatively short physical limitation.

• To extend the distance of a single network, an administrator can employ:

– Repeater : simply amplify and propagate packet signal.

– Bridges : repeat the packets with the intelligence of receiving a good packet before passing it on.

– Smart Bridges: only propagate those packets within a certain address range.

– Transport Bridge: perform a protocol conversion into a protocol running over a “long-haul” network (e.g. ATM).


Ethernet (CSMA/CD)Standards –

10BASE2: IEEE 802.3 Physical Layer specification for a 10 Mb/s CSMA/CD local area network over RG 58 coaxial cable. (See IEEE 802.3 Clause 10)

10BASE5: IEEE 802.3 Physical Layer specification for a 10 Mb/s CSMA/CD local area network over coaxial cable (i.e., thicknet). (See IEEE 802.3 Clause 8.)

10BASE-F: IEEE 802.3 Physical Layer specification for a 10 Mb/s CSMA/CD local area network over fiber optic cable. (See IEEE 802.3 Clause 15.)

10BASE-FB port: A port on a repeater that contains an internal 10BASE-FB Medium Attachment Unit (MAU) that can connect to a similar port on another repeater. (See IEEE 802.3 Clause 9, Figure 15-1b and Figure 17.3.) 9ITU-T publications are vailable from the International Telecommunications Union, Place des Nations, CH-1211Geneva 20, Switzerland (www.itu.int/). 10For information on MatLab contact: The MathWorks, 24 Park Way, Natick, MA, (www.mathworks.com). IEEE Std 802.3-2002, Section One LOCAL AND METROPOLITAN AREA NETWORKS: 12 Copyright © 2002 IEEE. All rights reserved.

http://www.itu.int/

http://www.mathworks.com/


Ethernet (CSMA/CD)Standards –

10BASE-FB segment: A fiber optic link segment providing a point-to-point connection between two 10BASE-FB ports on repeaters. (See link segment IEEE 802.3 Figure 15-1b and Figure 15–2.)

10BASE-FL segment: A fiber optic link segment providing point-to-point connection between two 10BASE-FL Medium Attachment Units (MAUs). (See link segment IEEE 802.3 Figure 15-1c and Figure 15–2.)

10BASE-FP segment: A fiber optic mixing segment, including one 10BASE-FP Star and all of the attached fiber pairs. (See IEEE 802.3 Figure 15–1a, Figure 1–3, and mixing segment.)

1.4.8 10BASE-FP Star: A passive device that is used to couple fiber pairs together to form a 10BASE-FP segment. Optical signals received at any input port of the 10BASE-FP Star are distributed to all of its output ports (including the output port of the optical interface from which it was received). A 10BASE-FP Star is typically comprised of a passive-star coupler, fiber optic connectors, and a suitable mechanical housing. (See IEEE 802.3, 16.5.)


Ethernet (CSMA/CD)10BASE-T: IEEE 802.3 Physical Layer specification for a 10 Mb/s CSMA/CD local

area network over two pairs of twisted-pair telephone wire. (See IEEE 802.3 Clause 14.)

100BASE-FX: IEEE 802.3 Physical Layer specification for a 100 Mb/s CSMA/CD local area network over two optical fibers. (See IEEE 802.3 Clauses 24 and 26.)

100BASE-T: IEEE 802.3 Physical Layer specification for a 100 Mb/s CSMA/CD local area network. (See IEEE 802.3 Clauses 22 and 28.)

100BASE-T2: IEEE 802.3 specification for a 100 Mb/s CSMA/CD local area network over two pairs of Category 3 or better balanced cabling. (See IEEE 802.3 Clause 32.)

100BASE-T4: IEEE 802.3 Physical Layer specification for a 100 Mb/s CSMA/CD local area network over four pairs of Category 3, 4, and 5 unshielded twisted-pair (UTP) wire. (See IEEE 802.3 Clause 23.)


Ethernet (CSMA/CD)100BASE-TX: IEEE 802.3 Physical Layer specification for a 100 Mb/s CSMA/CD

local area network over two pairs of Category 5 unshielded twisted-pair (UTP) or shielded twisted-pair (STP) wire. (SeeIEEE 802.3 Clauses 24 and 25.)

100BASE-X: IEEE 802.3 Physical Layer specification for a 100 Mb/s CSMA/CD local area network that uses the Physical Medium Dependent (PMD) sublayer and Medium Dependent Interface (MDI) of the ISO/IEC 9314 group of standards developed by ASC X3T12 (FDDI). (See IEEE 802.3 Clause 24.)

1000BASE-CX: 1000BASE-X over specialty shielded balanced copper jumper cable assemblies. (See IEEE 802.3 Clause 39.)

1000BASE-LX: 1000BASE-X using long wavelength laser devices over multimode and single-mode fiber. (See EEE 802.3 Clause 38.)


Ethernet (CSMA/CD)1000BASE-SX: 1000BASE-X using short wavelength laser devices over

multimode fiber. (See IEEE802.3 Clause 38.)

1000BASE-T: IEEE 802.3 Physical Layer specification for a 1000 Mb/s CSMA/CD LAN using four pairs of Category 5 balanced copper cabling. (See IEEE 802.3 Clause 40.)

1000BASE-X: IEEE 802.3 Physical Layer specification for a 1000 Mb/s CSMA/CD LAN that uses a Physical Layer derived from ANSI X3.230-1994 (FC-PH) [B20]11. (See IEEE 802.3 Clause 36.) CSMA/CD IEEE Std 802.3-2002, Section One

10BROAD36: IEEE 802.3 Physical Layer specification for a 10 Mb/s CSMA/CD local area network over single broadband cable. (See IEEE 802.3 Clause 11.)

1BASE5: IEEE 802.3 Physical Layer specification for a 1 Mb/s CSMA/CD local area network over two pairs of twisted-pair telephone wire. (See IEEE 802.3 Clause 12.)


Ethernet (CSMA/CD) – Frame



Preamble:

– 56 bits of alternating 1’s and 0’s– Provided to help receiving interfaces

synchronize.



SFD (Start Frame Delimiter):

• The SFD field is the sequence 10101011.

• It immediately follows the preamble pattern and indicates the start of a frame.



Source and Destination Address:• 48 bits

• I/G – Address belongs to an individual Enet controller or a group of controllers (multicast). Set to 0 in the source address.

• U/L – Universal is typical for all addresses encoded into the Ethernet controller at time of manufacture. Local is typical for broadcast and can potentially be used for multicast.



Source and Destination Address:

• A MAC sublayer address is one of two types:– Individual Address. The address associated with a particular

station on the network.

– Group Address. A multidestination address, associated with one or more stations on a given network.

• There are two kinds of multicast address:– Multicast-Group Address. An address associated by higher-level

convention with a group of logically related stations.

– Broadcast Address. A distinguished, predefined multicast address that always denotes the set of all stations on a given LAN.



Length/Type:

• Identifies the type of data being carried in the frame (e.g. ARP, IP, etc. ).

• Allows for Ethernet frames to be self identifying.



General Comments:maxValidFrame = maxUntaggedFrameSize –

(2 x addressSize + lengthOrTypeSize + crcSize) / 8;

addressSize = 48 bits (6 octets)lengthOrTypeSize = 16 bits (2 octets)crcSize = 32 bits (4 octets)maxUntaggedFrameSize = 1518 octets for 10, and 100

Mbps.

maxValidFrame = 1506 octets for an IP payload



General Comments:

• Each octet of a MAC frame is transmitted least significant bit first.

• The FCS is transmitted lowest order bit first.• minFrameSize is dependent on underlying

transmission (e.g. 64 octets for 100 Mbps)• If the data being sent is not large enough for the

fill the minimum frame, the frame will be padded.


FDDI Fiber Distributed Data Interconnect

– Provides a data rate of 100 Mbps– Designed to use Fiber optical cable where data

is encoded in a pulse of light.– Based on a ring topology– Uses token passing to control access to the

information transmission media.


FDDI • Initially, there will be two rings with

traffic rotating in opposite directions.• Each node in the ring has the ability to

perform a loop back. This allows a FDDI network to be a “self-healing” network transport media.

• When a node failure occurs, the faulty node will be removed from the network by neighbor nodes looping away from the faulty node.


FDDI


FDDI

• FDDI never caught on as a LAN technology.

• Station management was too complicated

• Hardware prices were too high


ATM (Asynchronous Transfer Mode)

• A Fiber-Optic based technology.

• Designed to operate in LAN and WAN environments.

• Permits extremely high level of bandwidth (gigabit speeds).

• Must use a high-speed ATM switch.

• ATM is a connection oriented service– This allows service providers to charge based

on connection time.



An ATM virtual circuit.



• To establish a connection in a ATM network, connection initiation requires the sending of a connection setup packet.

• As the connection packet is routed through the network, it establishes a “virtual circuit”.

• To increase efficiency, the ATM network transmits small, fixed sized packets.

– 53 bytes– 5 header octets– 48 “payload” octets– The ATM packet is called a “cell”



• Since the protocol defines a fixed sized packet, fragmentation never needs to be performed.

• Initial route setup can be done in hardware because no packet fragmentation and re-assembly needs to be done.

• Broadcast can also be done in hardware because of fixed packet size.

• Like Ethernet, ATM does not guarantee cell delivery.


ARPANET

Advanced Research Projects Agency

• Awarded a contract to develop network based technologies (contract awarded to BBN Technologies).

• Served as a major test bed for the major packet switched networking technologies.

• Tied major universities, military bases, and government laboratories together.


ARPANET

The original ARPANET design.



ARPANETfrom Computer Networksby Andrew S. Tanenbaum

Growth of the ARPANET (a) December 1969. (b) July 1970.

(c) March 1971. (d) April 1972. (e) September 1972.


NSFNETNational Science Foundation

• Established to ensure network communications remain available to scientist and engineers.

• Established a US backbone, regional (mid-level) networks, and campus (access) networks.

• Mid-level networks attached to the backbone network.

• Access networks attached to mid-level networks.


NSFNET

The NSFNET backbone in 1988.


NSFNET

• NSFNET tied together several scientific supercomputer centers (housing the then “ultimate” Cray supercomputers).

• NSFNET gained increasing popularity as ARPANET was ramping down.

• As use went up, the government stepped out of the network administration and gave it up to commercial “telcos” (PacBell, Sprint, etc.).

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10/21/2015CST 415 - Computer Networks1 Underlying Technologies CST 415