G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) C o m p u t e r N e t w o r k s - X a r x e s d e C o m p u t a d o r s Outline Course Syllabus Unit 1: Introduction Unit 2. IP Networks Unit 3. LANs Unit 4. TCP Unit 5. Network applications L l o r e n ç C e r d à - A l a b e r n 1
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs Outline Introduction IEEE LAN Architecture Ethernet Ethernet Switches Wireless LANs L l o r e n ç C e r d à - A l a b e r n 2
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs Introduction – WAN and LAN differences WANs: Main goal: scalability. Switched network with mesh topology. LANs: Multy-access network with shared media. A Medium Access Control (MAC) protocol is needed. WA N ( P S T N ) L A N s l o c a l l o o p s w i t c h e s Tx Rx Rx ( C e n t r a l O ffj c e ) BUS m o d e m m o d e m Rx Rx Tx Wireless Tx Rx Rx Rx Ring Tx Tx m u l t i p l e x e d l i n e s S w i t c h e d m e d i a S h a r e d m e d i a L l o r e n ç C e r d à - A l a b e r n 3
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs Outline Introduction IEEE LAN Architecture Ethernet Ethernet Switches Wireless LANs L l o r e n ç C e r d à - A l a b e r n 4
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs IEEE LAN Architecture O S I R e f e r e n c e m o d e l : 7 application 6 presentation 5 session I E E E L A N R e f e r e n c e m o d e l 4 transport 3 network L o g i c a l L i n k C o n t r o l ( L L C ) 2 data link I E E E L A N s t a n d a r d s Me d i u m A c c e s s C o n t r o l ( MA C ) 1 physical ( 8 0 2 . x ) P h y s i c a l LLC sublayer (802.2): Common to all 802.x MAC standards. Define the interface with the upper layer and specifies several services (operational modes): (i) unacknowledged connectionless, (ii) connection oriented, (iii) acknowledged connectionless. MAC sublayer: Define the medium access protocol. It is different for each LAN technology. L l o r e n ç C e r d à - A l a b e r n 5
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs IEEE LAN Architecture – IEEE 802 standards (some) 802.1: LAN/MAN architecture. 802.2 Logical Link Control (LLC) 802.3 Ethernet 802.4 Token Bus 802.5 Token Ring 802.8 FDDI 802.11 WiFi: Wireless LANs. 802.15 Personal Area Networks or short distance wireless networks (WPAN) 802.15.1 Bluetooth 802.15.4 low data rate and low cost sensor devices 802.16 WiMAX: broadband Wireless Metropolitan Area Networks. See: http://grouper.ieee.org/groups/802/1, 2, … L l o r e n ç C e r d à - A l a b e r n 6
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs IEEE LAN Architecture – LAN encapsulation h i g h e r l a y e r P D U L L C h e a d e r MA C C R C h e a d e r ... physical layer L l o r e n ç C e r d à - A l a b e r n 7
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs IEEE LAN Architecture – LLC header 3 / 4 b y t e s 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 bits +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Destination SAP| Source SAP | Control / | | | 8 or 16 bits / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ S e r v i c e A c c e s s P o i n t ( S A P ) : I d e n t i fj e s t h e u p p e r l a y e r p r o t o c o l . C o n t r o l : I d e n t i fj e s t h e f r a m e t y p e . I t c a n b e 8 o r 1 6 b i t s l o n g , 8 b i t s f o r u n n u m b e r e d f r a m e s ( u s e d i n c o n n e c t i o n l e s s m o d e s ) . SAP (hex) Protocol 06 ARPANET Internet Protocol (IP) 08 SNA 42 3IEEE 802.1 Bridge Spanning Tree Protocol 98 ARPANET Address Resolution Protocol (ARP) AA SubNetwork Access Protocol (SNAP) S N A P : u s e d i n T C P / I P Novell Netware E0 F0 IBM NetBIOS FF Global LSAP Example of some IEEE SAP values. L l o r e n ç C e r d à - A l a b e r n 8
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs Outline Introduction IEEE LAN Architecture Ethernet Ethernet Switches Wireless LANs L l o r e n ç C e r d à - A l a b e r n 9
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs Ethernet – Introduction Designed by Bob Metcalfe at Xerox in mid-70s. Initially was commercialized by Digital, Intel and Xerox consortium (DIX). Ethernet was standardized by IEEE (802.3) in 1983. Nowadays Ethernet is the leading LAN technology. There are numerous Ethernet standards with different transmission mediums, and line bitrates. There are several active Ethernet working groups inside IEEE 802.3. L l o r e n ç C e r d à - A l a b e r n 1 0
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs Types of MACs Token Passing: Only the station having the token can transmit. After transmission the token is passed to another station. Examples: FDDI and Token-Ring Random: There is no token. Instead, there is a non null collision probability. In case of collision, the frame is retransmitted after a random backoff time. Examples: Ethernet L l o r e n ç C e r d à - A l a b e r n 1 1
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs Carrier Sense Multiple Access/Collision Detection (CSMA/CD) Is a random MAC where the stations “listen” the medium ( carrier sense ) before transmission. When the medium is becomes free the frame is transmitted immediately, and the medium is listened to detect collisions. In case of collision, the frame is retransmitted after a random backoff time. L l o r e n ç C e r d à - A l a b e r n 1 2
G r a u e n e n g i n y e r i a i n f o r m à t i c a - X a r x e s d e C o m p u t a d o r s ( X C - g r a u ) Unit 3. Local Area Networks, LANs Ethernet – CSMA/CD Ethernet protocol (simplified) init Tx discard the frame Legend: y e s m e d i u m InterPacket Gap (IPG): 96 bits. b u s y ? wait backoff n o JAM: 32 bits that produce an erroneus n o wait IPG CRC. y e s r e t r i e s > 1 6 ? transmit the preamble backoff = n T 512 Transmit the JAM T 512 : SlotTime (51,2 s at 10 Mbps) y e s c o l l i s i o n ? n o n = random{0, 2 min{ N , 10} -1}, transmit 1 bit N : number of retransmission of the same frame (1, 2…) y e s c o l l i s i o n ? n o The transmitting station must detect the n o collision (no ack is sent). e n d T x ? y e s L l o r e n ç C e r d à - A l a b e r n 1 3
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