CS4500CS4500 Dr. ClincyLecture1 Ch3: Underlying Technologies (3 of 3) Exam 1 Study Guide and...

Dr. Clincy Lecture 1

CS 4500

Ch3: Underlying Technologies (3 of 3)

Exam 1 Study Guide and Instructions - scheduled for January31st (75 minute exam) – cover chapters 1-3, lectures 1-5 - open book (closed notes) - M/C, FIB, Short Problems, Problems - Can use a calculator – no laptop and no PDA

Lecture #5

If we don’t complete this lecture in class, I will place a recording of the remainder of the lecture online right after class

Pick up project 1 and Project 2 will be posted

Finish Pt-to-Pt WANs and Start and finish Switch WANs


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P-to-P: T1/T3 Service• Transport carriers originally designed for voice (672

circuits ???).

• Typical “long haul” or “back bone” network – also used to interconnect WANs we mentioned

• T1 line can send 8000 193-bit frames in one second

• T3 line can send 224,000 193-bit frames in one second or be treated as 28 T1 lines (we called this a channel T1)

• Fractional T lines – several customers sharing a T1 line – their data is multiplexed onto a single T1.


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P-to-P: SONET• SONET means Synchronous Optical Networks – it’s a

standard that defines a high-speed fiber-optic data carrier.

• Electrical signals (called STSs – synchronous transport signals) are converted to light or optical signals (called optical carriers)

• Comes in different rates, OC-1, OC-3, OC-9 ….. OC-48 ….OC-192

• The lowest data rate for SONET (OC-1) is greater than a T3’s data rate – Wow !


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PPP frame• To make a point-to-point connection, a protocol is needed at the data link layer

(there are multiple protocols)

• Well known protocol called PPP (point-to-point protocol) is used

• PPP is the protocol of choice when connecting IP networks over telephone lines

• Flag – bounds the PPP frame

• Address – broadcast address (recall a point-to-point connection)

• Control – frame sequencing info could go here – although most LANS don’t need a sequence number on frames (no routing)

• Protocol – tells what type of data is in the data field

• Data field – actual data

• FCS – frame check sequence – used for error detection

We also have LCP and NCP. Link Control Protocol – the PPP’s data field carry info regarding the mgmt of the link itself. Network Control Protocol – provides PPP the ability to carry actual IP packets in it’s data field.


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Completing coverage of Pt-to-Pt WAN technologies


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Internet – Underlying Technologies• Internet is comprised of LANs, Point-to-Point WANs and Switched

WANs

• We have covered LANS: Ethernet, Token Ring (not in book), Wireless and FDDI Ring (not in book)

• We have covered Pt-to-Pt WANs: Telephony Modem, DSL, Cable/Modem, T-Lines and SONET

• We will cover Switched WANs: X.25, Frame Relay and ATM


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SWITCHED WANS• Switched WAN - a mesh of point-to-point networks connected via

switches

• Unlike LANS – multiple paths are needed between locations

• Unlike LANS – no direct relationship between Tx and Rx

• Paths are determined upfront and theses paths are used to send and receive (multiple paths for reliability and restoration) – recall that LANS uses Tx/Rx addresses to make the connection

• Uses Virtual Circuit concept

• 3 well known Switch WANs: X.25, Frame Relay and ATM


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X.25• Developed in 1970 – the first switch WAN – becoming

more and more obsolete

• X.25 standard describes all of the functions necessary for communicating with a packet switching network

• Divided into 3 levels:

• (1) physical level – describes the actual interfaces

• (2) frame level – describes the error detection and correction

• (3) Packet level – provides network-level addressing(constant BW efficiency problem – but it worked)

Because X.25 was developed before the Internet, the IP packets are encapsulated in the X.25 packet when you have an IP network on each side of a X.25 backbone


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Frame Relay Network• Designed to replace X.25

• Have higher data rates than X.25

• Can handle “bursty data” by allocating BW as needed versus dedicating constant chucks of BW

• Less error checking and overhead needed – more reliable and efficient

• DTE – data terminating equipment – devices connecting users to the network (ie routers)

• DCE – data circuit-terminating equipment – switches routing the frames through the network

Frame Relay Switches in the yellow cloud


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Switched WANs - ATM• ATM – Asynchronous Transfer Mode – is a cell relay protocol

• Objectives of ATM (upfront initiative):

1. Make better use of high data rate transmission (ie. fiber optics)

2. WAN between various types of packet-switch networks that will not drive a change in the packet-switch networks

3. Must be inexpensive (no barrier to use) – want it to be the international backbone

4. Must be able to support the existing network hierarchies – local loops, long-distance carriers, etc..)

5. Must be connection-oriented (high reliability)

6. Make more hardware oriented versus software oriented in speeding up rates (explain this – circuit vs software)

• Cell – small unit of data of fixed size – basic unit of data exchange

• Different types of data is loaded into identical cells

• Cells are multiplexed with other cells and routed

• By having a static size, the delivery is more predictable and uniform


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ATM multiplexing• ATM uses asynchronous time-division multiplexing –

cells from different channels are multiplexed

• Fills a slot with a cell from any channel that has a cell


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Architecture of an ATM network

• User access devices (called end points) are through a user-to-network interface (UNI) to switches in the network

• The switches are connected through network-to-network interfaces (NNI)


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Virtual circuits• Connections between points are accomplished using transmission

paths (TP), virtual paths (VP) and virtual circuits (VC).

• TP – all physical connections between two points

• VP – set of connections (a subset of TP) (ie. Highway)

• VC – all cells belonging to a single message follow the same VC and remain in original order until reaching Rx (ie. Lane)

• The virtual connection is defined by the VP and VC identifiers


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An ATM cell


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ATM layers• ATM Standard defines 3 layers: Application Adaptation Layer, ATM Layer and Physical

Layer

• Application Adaptation Layer – facilitates communications between ATM networks and other Packet-Switched Networks by taking the packets and fitting them into fixed-sized CELLS.

• At the Rx, cells are re-assembled back into packets

• Keep in mind that any type of transmission signal can be packaged into an ATM cell: data, voice, audio and video - makes ATM very powerful

Application Adaptation Layer is divided into 4 parts:

• AAL1- handles the constant bit rate cases (ie. voice, real-video)

• AAL2- handles variable bit rate cases (ie. compressed voice, non-real-time video, data)

• AAL3/4 – handles connection-oriented data services (ie VoIP)

• AAL5 – handles connectionless-oriented protocols (ie. TCP/IP)


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ATM layers

• ATM Layer in general – routing, flow control switching & multiplexing

• ATM Layer – going down – accepts bytes segments and translate to cells

• ATM Layer – going up – translate cells back into byte segments – keep in mind that a node can be acting as both an intermediate and Rx node (and Tx)

• ATM Physical Layer – translate cells into a flow of bits (or signals) and vice versa


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ATM LAN architecture• ATM LAN speeds: 155 Mbps and 622 Mbps

• 3 design approaches: (1) pure ATM LAN, (2) legacy ATM LAN and (3) combo of (2) and (3)

• Pure ATM LAN: ATM switch is used to connect the stations in a LAN (uses VPI/VCI versus destination/source addresses)


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Legacy ATM LAN architecture

• Use an ATM LAN as a backbone – frames staying with in a certain network need not be converted

• Frames needing to cross to another LAN must be converted and ride the ATM LAN


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Mixed ATM LAN Architecture


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Internet – Underlying Technologies• Recall that the Internet is comprised of LANs, Point-to-Point WANs and

Switched WANs• We covered LANS: Ethernet, Token Ring, Wireless and FDDI Ring• We covered Switched WANs: X.25, Frame Relay and ATM• We covered Pt-to-Pt WANs: Telephony Modem, DSL, Cable/Modem, T-

Lines and SONET

How are these networks connected ?


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CONNECTING DEVICES


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Repeater

Operates at the physical layer – layer 1

Receives the signal and regenerates the signal in it’s original pattern

Is there a difference between a regen or repeater and an amp ??

A repeater forwards every bit; it has no filtering capability


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Repeaters

d

For the architecture above, will a signal ever traverse through more than 2 repeaters ?


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HubsHub – multi-port repeater

Typically used to create a physical star topology

Also used to create multiple levels of hierarchy

For bus technology type networks, hubs can be used to increase the collision domain


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Bridge• Operates at both the physical and data link layers

• At layer 1, it regenerates the signal. At layer 2, it checks the Tx/Rx physical address (using a bridge table)

• Example Below:

• If packet arrives to bridge-interface #1 for either of the 71….. stations, the packet is dropped because the 71…. Stations will see the packet

• If packet arrives to bridge-interface #2 for either of the 71….. stations, the packet is forwarded to bridge-interface #1

With such an approach, the “bridged” network segments will acted as a single larger network

What is a “smart” bridge ??


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Routers• Is a 3-layer device: (1) at layer 1, regen the signals, (2) at layer 2, check physical address and (3) at layer 3,

check network addresses• Routers are internetworking devices• Routers contain a physical and logical/IP address for it’s interfaces (repeaters/bridges don’t)• Routers only act on the packets needing to pass through• Routers change the physical address of the packets needing to pass through (repeaters/bridges don’t change

physical addresses)

d

d

Show example where a decision is needed


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Routing example

LAN 1 LAN2

• Routers can change the physical address of a packet

• Example: as a packet flow from LAN 1 to LAN 2

• In LAN 1, the source address is the Tx’s address and the destination address is the Router’s interface address

• In LAN 2, the source address is the Router’s interface address and the destination address is the Rx’s address


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You are a High Priced Network Consultant

dThey want all departments to communicate with one another; you want the network to maintain top performance – which design would you recommend ? Which devices would you recommend for empty circles ? – the least cost solution is the best solution

Marketing Dept

Engineering Dept

(Super Computer)

Manufacturing Dept (Robots)


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Reminder• If lecture is over before end-of-class:

– Quickly illustrate going from LAN-to-LAN via WAN

CS4500CS4500 Dr. ClincyLecture1 Ch3: Underlying Technologies (3 of 3) Exam 1 Study Guide and...

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