1. Ch 3: Underlying Technologies
Exam 2 on Monday, March 5th
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. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. An ATM cell
Dr. Clincy
Lecture

11. 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

12. 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

13. 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

14. 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

15. Mixed ATM LAN Architecture
Dr. Clincy
Lecture

16. 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

17. CONNECTING DEVICES
Dr. Clincy
Lecture

18. 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

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

20. 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

21. 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

22. 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

23. 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

24. 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