Wireless Communications Networks - University of …

1 E&EC 710 (2) Wireless Communications NetworksXuemin (Sherman) ShenOffice: EIT 4155 Phone: x 32691 Email: Notes: #1 Dept. Electrical and Computer Engineering , University of Waterloo, X. understand the way network operations areorganized; (how network works) understand how to predict performance of anetwork before implementing it. (when designing anew network )Dept. Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast21. Introduction to CommunicationNetworksWhat are Communications Networks ? communication Networks are arrangements of hardwareand software that allow users to exchange other words, a communication network is a meshconnection of links and switches, which permits theexchange of copper wire, fiber optics, radio microwaves, Electrical and Computer Engineering , University of Waterloo, X.

2 ShenFirstPreviousNextLast3 Switches circuit switching, packet switching, switch (routers/ nodes) is a box with input andoutput links. When a traffic arrives, the switch or routerfigures out the output link. After some delay, the switchsends the traffic on the output Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast4 Wireline NetworkFHMHBSMSCSMHW ireless NetworkMobile Switching CentreBase Station/Bluetooth card/IEEE HostFixed HostRadio LinkSwitch (Router)(Copper wire, etc) Wired LinkWireline NetworkFHMHBSMSCSMHW ireless NetworkMobile Switching CentreBase Station/Bluetooth card/IEEE HostFixed HostRadio LinkSwitch (Router)(Copper wire, etc) Wired LinkDept.

3 Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast5 Mobile Swithcing Center (MSC) or Mobile Telephone Switching Office (MTSO)BS1BS2BS3 PSTNP ublic Switched Telephone network (Backbone) ATM InternetVoice and data links (landline or microwave links)Radio link(air interface)Dept. Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast6 Radio Access network (RAN)Wireline Backbone NetworkRANL aptopLaptopLaptopCell phoneCell phoneCell phoneCameraGatewayfor PANG atewayfor pointsBluetooth enabled productsRAN: Radio Access network PAN: Personal Area network BT: BluetoothDept.

4 Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast7 Circuit Switching: a circuit is set up between the twotelephone terminals for the duration of the conversationand release the circuit when the call terminates(Telephone network )Virtual Circuit Switching: a message is broken intosmaller units (packets1) for transmission and the packets that belong to a given connection allfollow the same path. The resource of the circuit can beshared by other connection. (ATM network )1 Each packet is marked with its destination Electrical and Computer Engineering , University of Waterloo, X.

5 ShenFirstPreviousNextLast8 Packet Switching: packets2can be transmitted followingdifferent paths in the network , and the resources can beshared by other connections. (Internet)Details of packet switchingA message is segmented into blocks of data calledpackets. A packet is a group of bits, typically from a fewhundreds to packet is marked with its destination Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast9A packet consists of a header, user information, and atrailer. The header usually contains the addresses of thedestination and of the source of the packet; it may alsoinclude a sequence number that the destination users toverify that all the packets were received or to reorderthem.

6 The trailer contains error control bits that thenodes use to verify that they received the are transmitted without prior reservation of linkcapacity. When a packet is received at a switch, it isinspected to determine the appropriate output link. If theDept. Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast10output link is available, it is transmitted. Otherwise, it isstored and then forward to the next switch on its way tothe destination (store & forward network )The transmission of messages as small packets iscalled store-and-forward packet store-and-forward packet switching can reduce themessage delivery time.

7 The reduction in the delivery timeis called thepipelining :Transmission a message on a direct link Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast11 SourceintermediatedestinationABIf the message is decomposed into60packets that takes1second each to be transmitted on a direct link, thenduring the first second packet1is sent fromAtoB,during the next second packet2is sent fromAtoBandpacket1is sent fromBtoC, and so on. After1minuteand1second, the complete message is received Electrical and Computer Engineering , University of Waterloo, X.

8 ShenFirstPreviousNextLast12 TimeAB1122113322If there areNintermediate nodes, the transmission ofDept. Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast13the undivided message takesN+ 1minutes while that ofthe60packets takes only1minute Telephone network is designed for Internet is a network of computer Networks thatcovers most of the world and allows millions of users toexchange messages and computer files and some limitedvideo and audio Asynchronous Transfer Mode (ATM) network isdesigned to offer from best effort delivery of packets toDept.

9 Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast14transmission with guaranteed small delays and high other words, ATM network is designed for of the three types of network is less well suited to data and othernonconversational transmissions tend to be bursty, meaning thatdata come in spurts with idle gaps between are required to interconnect a variety of digitaldevices (different data rate).Dept. Electrical and Computer Engineering , University of Waterloo, X. ShenFirstPreviousNextLast15 Circuit switching is inflexible.

10 Circuit switching sees alltransmissions as equal (no priority).The Internet is suited to data transmission only. Itprovides best-effort services, with no guarantee on thedelays or even the loss rate of the transmissions. Thenetwork is not reliable and offers no security. The mostastonishing aspect of the Internet is itsself-organizing mechanisms. The packets find their wayto their destination even a link or a router breaks is an excellent link and switching technology. TheDept. Electrical and Computer Engineering , University of Waterloo, X.