1. Ch 3: Underlying Technologies
Exam 2 on Tuesday, June 26th
75 minutes and opened book
FIB, MC, Short Questions and Short Problems
Covers lectures 9 through 13 and associated book chapters and sections
Dr. Clincy
Lecture

2. WIRELESS LANS
Wireless communication is one of the fastest growing technologies. The demand for connecting devices without the use of cables is increasing everywhere. Wireless LANs can be found on college campuses, in office buildings, and in many public areas.
In this section, we concentrate on two wireless technologies for LANs:
IEEE wireless LANs, sometimes called wireless Ethernet,
and Bluetooth, a technology for small wireless LANs.
Dr. Clincy
Lecture

3. Wireless Transmission (not in book)
Wireless devices can transmit signals using radio frequency narrow band, infrared waves and radio frequency spread spectrum.
The frequency spread spectrum technique is typically used for internet applications
Two types of frequency spread spectrum techniques: (1) FHSS- Frequency Hopping Spread Spectrum and (2) DSSS – Direct Sequence Spread Spectrum
Dr. Clincy
Lecture

4. FHSS- Frequency Hopping Spread Spectrum (not in book)
Tx transmits at different carrier frequencies for the same period of time (rotates between a set of frequencies)
The required bandwidth must be N times the original bandwidth, where N is the number of different carrier frequencies
Tx and Rx must agree to the hopping pattern. In this case, the first bit signal is transmitted in spectrum Ghz, 2nd bit transmitted in the Ghz spectrum, 3rd bit transmitted in the GHz spectrum, etc..
Good technique for security reasons – if someone tunes to one of the 5 frequency spectrums below, they would only get 1/5 of the info being transmitted.
Dr. Clincy
Lecture

5. DSSS – Direct Sequence Spread Spectrum (not in book)
Each bit sent by the Tx is replaced with a set of bits called a “chip code”
For the time it takes to send the original single bit, it now will take more time to send the chip code
Therefore, the data rate must be N times the original data rate, where N is the # of bits of the chip code
Also, the bandwidth for the chip code should N times greater than the original bit stream’s BW
Example of original bits being transmitted as 6-bit chip codes
Dr. Clincy
Lecture

6. ISM bands (not in book)
In 1985, the FCC modified the radio spectrum to allow unlicensed devices (operating at 1 watt or less) to ISM bands – Industrial, Scientific and Medical bands
Stimulated growth in wireless technology
Dr. Clincy
Lecture

7. Wireless LANs Architecture
IEEE covers 2 services – (1) BSS - Basic service set and (2) ESS – Extended service set
BSS – is the base architecture for a wireless LAN – it contains a stationary or mobile stations and a central access point (optional)
Without central access point, the BSS can’t transmit to other BSS’s
example ? example ?
Dr. Clincy
Lecture

8. Wireless LANs Architecture - ESS
Contains 2 or more BSS’s with central access points
The BBS’s central access points are connected via a distribution system (could be a wired LAN) – this network is called an Infrastructure network
BBS’s within reach of one another can communicate
BBS’s not within reach have to communicate via the central access points
Dr. Clincy
Lecture

9. Wireless LANs Access Method
Wireless LANs use an access method similar to CSMA/CD access method discussed last lecture
The access method is called CSMA/CA (vs CSMA/CD) and stands for carrier sense multiple access with collision avoidance
With CSMA/CA, all nodes have equal access and the medium is sensed before data is sent
However, collision detection is not applicable because the environment is wireless – THEREFORE, COLLISIONS MUST BE AVOIDED.
CSMA/CA Process
Each station determines how long it needs the medium and all other stations refrain from using it
After the Tx detects the medium is free, it sends a RTS (request to send) and it contains the amount of time
The Rx acknowledges the request by issuing a CTS (clear to send) to all stations
Tx sends data
Rx acknowledges the receipt of data
Dr. Clincy
Lecture
Example

10. CSMA/CA and NAV
After Rx receive RTS, it waits amount of time called short interframe space (SIFS), before send a CTS
If free, Tx waits amount of time called distributed interframe space (DIFS)
2CTS
The way collisions are prevented is: when the Tx issues a RTS, a timer called Network Allocation Vector (NAV) is created for the duration of time for (1) to (4) above – all stations affected by this transmission uses the NAV in letting it know when it can check the channel for idleness
Dr. Clincy
Lecture

11. Frame format Carries the NAV value or ID of the frame
Defines sequence # of frame for flow control
CRC-32 error detection
Defines the frame type and some control info
Depends on To DS and From DS fields
Can carry up to 2312 bytes
DS- Distribution System
For wireless, some time the protocol recommends “fragmentation” due to corrupted frames (the smaller the better) or frames being too large
Dr. Clincy
Lecture

12. Frame Types
Wireless LANs have three categories of frames: (1) Management Frames, (2) Control Frames, and (3) Data frames
Mgmt frames – used for the initial communications between stations and access points
Data Frames – used for carrying data and control info
Control Frames – used for accessing the channel and acknowledging frames
Dr. Clincy
Lecture

13. Bluetooth Wireless LAN technology designed to:
connect devices of different functions (ie phone, camera, printer, etc)
spontaneously form (devices find each other)
connect to the Internet
be small by nature – large size will cause chaos
Handle data rate of 1 Mbps with 2.4 GHz of bandwidth
Can be interference between b wireless LAN and Bluetooth LANS (802.15)
The networks are called “Piconet”
Defined by standard (PAN)
Dr. Clincy
Lecture

14. Bluetooth Architectures (2 types)
Can have up to 8 stations
One station is the primary and the rest are secondary stations
all secondary stations synch their clock to the primary station.
The communications with the primary can be 1-to-1 or 1-to-many
Can have an unused 8th secondary – must be activated to use and some existing secondary must be deactivated
Multiple piconets combined is a Scatternet
A secondary station in one piconet can be a primary station in a 2nd Piconet
Dr. Clincy
Lecture

15. Internet – Underlying Technologies
Recall the various types of interconnected networks comprising the Internet: LANs, Point-to-Point WANs and Switched WANs
We have covered LANS: Ethernet, Token Ring, Wireless and FDDI Ring
Let’s cover the Point-to-Point WANs
Point-to-Point WANS
Connect devices via a public network line (ie. telephone company)
Telephone company – physical layer
Point-to-Point WAN – data link layer and up
Company services provided to make the connection:
Modem (modem to switching station to ISP)
DSL
Cable Modem
T Lines (ie. T1, T3)
SONET (optical carriers)
Dr. Clincy
Lecture

16. Telephony/56K Modem Digital Signal Analog Signal Digital Data
Sampled 8000 times per sec with 8 bits per sample (1 bit for control) = 56 kps
Dr. Clincy
Lecture

17. P-to-P: DSL – Digital Subscriber Line
DSL – a set of technologies used to provide high-speed data service over copper wires that connect between the central office and local residences/businesses without expensive repeaters.
How is DSL implemented ? – high-speed DIGITAL WAN between COs – link between subscriber and the network is analog (becoming more and more digital though)
How does DSL work ? – divides the given bandwidth into 3 bands and offer phone service on one band and up and down stream traffic on the other 2 – phone service can occur with NO interruptions.
What does POTS stands for ??
Ranges changed for 4th Book Ed
Dr. Clincy
Lecture

18. P-to-P: Other DSL Services
RADSL – rate adaptive asymmetric DSL – scales back the speed of ADSL based on the quality of the wire and distance between the CO and user.
Side Note: A newer version of ADSL called Universal ADSL (or UADSL) is being deployed in an attempt to standardize ADSL to a set of standard speeds – speeds vary across the Country
HDSL – high bit rate DSL – an digital alternative to T-1 analog service (T-1 contains multiple high-speed analog lines)
SDSL – symmetric DSL – same as HDSL however only 1 line is provided (is full-duplex)
VDSL – very high bit rate DSL – similar to ADSL however, in addition to using twisted-pair, coaxial and fiber-optic can be used in getting a much higher bit rate
Dr. Clincy
Lecture

19. P-to-P: Cable Modem Still talking about point-to-point WANS
Uses the cable TV network
How does it work ?. some of the bandwidth dedicated to television signals is used for data traffic.
How does it work ?. The data signals are modulated into sine waves and placed on analog channels
How does it work ?. Typically, the BW in a neighborhood (or certain proximity) is shared (like a LAN in an office). Therefore, you never know if you have access to all of the BW. The more people using cable modems the worst the performance.
Some cable companies can dedicate some BW for phone service therefore offering voice, video/TV and data services on one cable
Cable modems are faster than computer modems because they are not limited by the 3000 Hz BW of the telephone line
The newer cable systems uses digital cable boxes and digital networks can send/receive data on separate digital channels
(draw picture of typical cable/video network – briefly explain history)
Dr. Clincy
Lecture

20. 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 bit frames in one second
T3 line can send 224, 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.
Dr. Clincy
Lecture

21. 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 !
Dr. Clincy
Lecture

22. 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
Protocol – tells what type of data is in the data field
Data field – actual data
FCS – frame check sequence – used for error detection
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)
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.
Dr. Clincy
Lecture

23. 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
Dr. Clincy
Lecture

24. Ch 3: Underlying Technologies
Dr. Clincy
Lecture

25. 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
Dr. Clincy
Lecture

26. 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
Dr. Clincy
Lecture

27. 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
Dr. Clincy
Lecture

28. 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
Dr. Clincy
Lecture

29. Switched WANs - ATM
ATM – Asynchronous Transfer Mode – is a cell relay protocol
Objectives of ATM (upfront initiative):
Make better use of high data rate transmission (ie. fiber optics)
WAN between various types of packet-switch networks that will not drive a change in the packet-switch networks
Must be inexpensive (no barrier to use) – want it to be the international backbone
Must be able to support the existing network hierarchies – local loops, long-distance carriers, etc..)
Must be connection-oriented (high reliability)
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
Dr. Clincy
Lecture

30. 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
Dr. Clincy
Lecture

31. 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)
Dr. Clincy
Lecture

32. 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
Dr. Clincy
Lecture

33. An ATM cell
Dr. Clincy
Lecture

34. 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)
Dr. Clincy
Lecture

35. 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
Dr. Clincy
Lecture

36. 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)
Dr. Clincy
Lecture

37. 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
Dr. Clincy
Lecture

38. Mixed ATM LAN Architecture
Dr. Clincy
Lecture

39. 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 ?
Dr. Clincy
Lecture

40. CONNECTING DEVICES
Dr. Clincy
Lecture

41. Repeater Operates at the physical layer – layer 1
Receives the signal and regenerates the signal in it’s original pattern
A repeater forwards every bit; it has no filtering capability
Is there a difference between a regen or repeater and an amp ??
Dr. Clincy
Lecture

42. Repeaters d
For the architecture above, will a signal ever traverse through more than 2 repeaters ?
Dr. Clincy
Lecture

43. Hubs Hub – 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
Dr. Clincy
Lecture

44. 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 ??
Dr. Clincy
Lecture

45. Routers Show example where a decision is needed d d
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)
Show example where a decision is needed d d
Dr. Clincy
Lecture

46. 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
LAN LAN2
Dr. Clincy
Lecture

47. You are a High Priced Network Consultant
Marketing Dept
Engineering Dept
(Super Computer)
Manufacturing Dept (Robots) d
They 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
Dr. Clincy
Lecture