CMPE 150: Introduction to Computer Networks FINAL REVIEW. Venkatesh Rajendran. Spring 2003 UCSC CMPE150 1

Size: px
Start display at page:

Download "CMPE 150: Introduction to Computer Networks FINAL REVIEW. Venkatesh Rajendran. Spring 2003 UCSC CMPE150 1"

Transcription

1 CMPE 150: Introduction to Computer Networks FINAL REVIEW Venkatesh Rajendran Spring 2003 UCSC CMPE150 1

2 Class Final Exam Final exam Three hours questions -- comprehensive Multiple choice as the midterm Scantron bring your sheet and pencils Wednesday June 11 th Six short days.. Tick, tick, tick 8:00 11:00am Spring 2003 UCSC CMPE150 2

3 Principles of Computer Communication Protocol specification: The description of the protocol is complete and accurate. Safety: A protocol does what it is supposed to do, all the time. Liveness: A protocol does not leave any deadlocks. Efficiency: A protocol makes efficient use of available resources. Fairness: Fair or contractual use of resources Simplicity is desirable, but not necessary. Spring 2003 UCSC CMPE150 3

4 Layering Model Purpose is to divide and conquer complex software and hardware needed to implement services Partition services and functions needed in system into layers Each layer of service is provided by peer protocol entities Communication can be point-to-point or multipoint Layer N packets NODE A Layer-N Protocol Entity interface (virtual communication) protocol Layer-N Protocol Entity NODE B Layer-(N - 1) Protocol Entity Layer-(N - 1) Protocol Entity Spring 2003 UCSC CMPE150 4

5 Protocol Correctness A protocol must be safe and live Safety: Protocol provides the desired service all the time Liveness: Protocol has no deadlocks (no process waits forever for an event to occur) Proving one may depend on the other Spring 2003 UCSC CMPE150 5

6 Protocol Performance Average delay Time between transmission of an information bit and reception of the bit at the receiver Throughput or capacity Number of information bits sent divided by the time between transmission of first bit and delivery of the last bit Computations will make strong assumptions; in most cases, results of analytical model provide only a rough approximation Most effective for comparative analysis Spring 2003 UCSC CMPE150 6

7 Basic Network Services S 1, ,2 D Data may take different paths to destination 1 1 Shared network resources Connection-oriented service: Reliable data transfer: In-order delivery, no duplicates or missing data. Flow control: Do not congest the receiver(s). Congestion control: Do not congest the network(s). Spring 2003 UCSC CMPE150 7

8 Basic Network Services S 1,2,3 2,1,3 D Connectionless service: Shared network resources No delivery guarantees needed from the network. Any connection-oriented service to application is provided by end-to-end protocol. Spring 2003 UCSC CMPE150 8

9 Circuit Switching S D call request call accept DATA call termination termination ack Portion of physical resource is assigned to a single connection. Delay and signaling overhead in establishing and ending connections. Spring 2003 UCSC CMPE150 9

10 S Message Switching D message Message from sender is sent on a store-and-forward basis. Message has a header used for forwarding. Resources shared among different calls. Spring 2003 UCSC CMPE150 10

11 Statistical Multiplexing Share the same communication channel among multiple connections without fixed allocations of the resource to those connections. S1 m2 m1 m2 m2 m1 m1 m2 m1 D1 m2 m1 S2 m2 m1 Link is shared based on the statistics of each connection or flow. D2 Limitation: Entire message must be received at a switch before it can be forwarded Spring 2003 UCSC CMPE150 11

12 S Packet Switching D packet 1 packet 2 packet 3 packet 4 Resources are shared among connections Packets from the same connection can be processed concurrently Connection setup delay can be avoided using datagrams Spring 2003 UCSC CMPE150 12

13 Packet Switching Information is organized into packets A packet consists of a header and a payload Header specifies the control information needed to transport the packet from origin to destination Packets are forwarded from source to destination using routing tables There are two basic approaches to packet switching: datagrams virtual circuits Spring 2003 UCSC CMPE150 13

14 Datagrams a c 1 a->b c->d a->e 2 3 a->e a->b 5 c->d a->e 6 a->b a->e 4 d 7 e b To b go to 2 next To d go to 3 next To e go to 2 next To 4 go to 3 next. Routing table specifies next hop to each destination Packets are forwarded based on the routing table Each packet is routed independently Spring 2003 UCSC CMPE150 14

15 Virtual Circuits 2 VC1 6 e a c 1 3 VC3 5 VC2 4 d 7 b Virtual circuits are established and terminated much like circuits in circuit switching. Statistical multiplexing using packets, rather than FDM or TDM is used to share links among connections. Spring 2003 UCSC CMPE150 15

16 Transmission Media We consider the physical layer as a black box We are interested in the characteristics and services provided by the transmission media that impact the link layer and higher layers. Parameters: Bandwidth Delay or latency: average and variance (aka jitter) Storage capacity (bandwidth-delay product) Reliability and security Order of delivery Type of sharing or access Spring 2003 UCSC CMPE150 16

17 Bandwidth We think of the bandwidth of a network or link as the number of information bits that can be transmitted over it in a certain period of time (e.g., bits per second). The bandwidth of a link is really the frequency range tolerated by the channel without major attenuation. Telephone line is 3000 Hz (300Hz to 3300 Hz) Available bandwidth depends on the rate at which channel can change stored energy. We can model waveforms as sums of sine waves of different frequencies. Channel attenuates and delays each frequency component differently, causing distortion. Spring 2003 UCSC CMPE150 17

18 Sources of Packet Delay A transmission time of packet over each link B nodal processing queueing delay nodal processing queueing delay propagation delay of each link Spring 2003 UCSC CMPE150 18

19 Sources of Packet Delay Nodal processing: Checking for bit errors. Determining output link. Queueing delay: Time waiting at output link for transmission. Depends on congestion level of router. Transmission delay: Time to send bits into link: L/R, where R = link bandwidth (bps) and L = packet length (bits) Propagation delay: Time for each bit to traverse a link: d/s, where d = length of physical link and s = propagation speed in medium (~2x10 8 m/sec) Spring 2003 UCSC CMPE150 19

20 Bandwidth-Delay Product The amount of data stored in the link. Think of a link as a pipe; the latency is the length of the pipe and the bandwidth is its diameter. The BD product gives the volume of the pipe. Example: A channel of 50 ms latency and just 45 Mbps bandwidth can hold 2.25 million bits (the same as the memory of a PC of early 80s!). We are moving to Gigabit networks... Big bandwidth and big distances require: Big aggregation and big memories at hosts New reliable transmission algorithms Migration from client-server to client-content models. Spring 2003 UCSC CMPE150 20

21 Other Parameters Reliability: We will assume that information is transmitted correctly across a link or network with a given likelihood. Security: We will likely not cover this aspect in much detail :( Order of delivery: We will assume FIFO and non- FIFO delivery of packets or messages, depending on the protocol and transmission media. Access: We will consider point-to-point and broadcast links. Spring 2003 UCSC CMPE150 21

22 Functions at The Link Layer MAC: (Medium Access Control) Framing and synchronization Error checking Naming within LANs (with MAC addresses) Sharing of medium Flow control (in some cases) LLC: (Logical Link Control) Retransmission strategy Link management (deciding when a link exists or does not) Flow control (in some cases) Spring 2003 UCSC CMPE150 22

23 Framing of Bits The objective is for the receiver to understand the packets (frames) sent by the sender when bits may get corrupted over the channel. Three approaches: Character- or byte-oriented framing: BISYNC, IMP-IMP, SLIP, and PPP Bit-oriented framing: HDLC Clock-based framing: SONET Spring 2003 UCSC CMPE150 23

24 Character-Oriented Framing A frame starts and ends with a predefined sequence of control bytes or characters, and the occurrence of such sequence in the packet payload is avoided by byte stuffing. Consider the ARPANET IMP-IMP protocol: SYN SYN DLE STX packet payload (header and data) DLE ETX CRC CRC CRC SYN = synchronization DLE = data link escape STX = packet start Character stuffing: If DLE occurs in packet data, sender substitutes DLE with DLE DLE Receiver substitutes DLE DLE in packet payload with DLE In PPP, flag is and such pattern in payload is preceded by Read Section 5.8 in textbook summarizing PPP Spring 2003 UCSC CMPE150 24

25 Bit-Oriented Framing The same procedure is used with bits, bits are stuffed to break the occurrence of control flags. Bit stuffing consists of adding a bit after the occurrence of a bit pattern equal to the control flag used to frame the packet. Assume the control flag is If flag pattern occurs in payload, sender must transmit something different and receiver must be able to get original data. HOW?...Sender inserts a 0 after 5 1 s, and receiver deletes any 0 received after five 1 s in a bit sequence, and the frame is ended if after 5 1 s 10 is detected. Original data: flag payload with bit stuffing flag Receiver then deletes stuffed 0 in any sequence and obtains original data: Spring 2003 UCSC CMPE150 25

26 CRC CRC codes detect errors by adding a few bits (redundancy bits or CRC bits) to each packet. The attractive features of CRC are that only a few redundancy bits are needed to protect many bits of information, and it can be implemented with very simple hardware. A message of m bits is transmitted with r redundancy bits as a transmitted string T = M.R With the message bits being the most significant bits transmitted, and given that R occupies r bit positions, we have T M 2 r + R r+m-1 r M r-1 0 bits R Spring 2003 UCSC CMPE150 26

27 CRC The procedure to choose R to protect M is remarkably simple. A string G of r+1 bits called the generator is agreed upon. R is chosen so that T = A xg for some A => If the received string T is not a multiple of G, then an error has been detected! T equals the (modulo 2) addition of T and an error pattern E, such that a 0 in the pattern indicates no error in that bit position. Now we have: R is the remainder of dividing by G the shifted M T M Spring 2003 UCSC CMPE also M r 2 = r + A G T ' M R 2 = + r A G; R + R + E therefore,

28 CRC Therefore, to protect M, the sender: Computes R by dividing M (shifted r bit positions) by G Transmits M. R When the receiver obtains T : It divides T by G Decides that there is an error if the remainder of the division is not 0 The trick is then choosing a G for which the likelihood that T contains an error string E that is divisible by G is very small. Spring 2003 UCSC CMPE150 28

29 Contention-Based MAC Protocols No coordination: Stations transmit at will when they have data to send (e.g., ALOHA) Carrier sensing (listen before transmit): Stations sense the channel before transmitting a data packet (e.g., CSMA). Listen before and during transmission: Stations listen before transmitting and stop if noise is heard while transmitting (CSMA/CD). Collision avoidance (floor acquisition): Stations carry out a handshake to determine which one can send a data packet (e.g., MACA, FAMA, IEEE802.11, RIMA). Collision resolution: Stations determine which one should try again after a collision. Spring 2003 UCSC CMPE150 29

30 ALOHA Protocol The first protocol for multiple access channels; the first analysis of such protocols (Norm Abramson, Univ. of Hawaii, 1970). Originally planned for systems with a central base station or a satellite transponder. Two frequency bands; Up link and down link (413MHz, 407MH at 9600bps) Central node retransmits every packet it receives! Spring 2003 UCSC CMPE150 30

31 ALOHA Protocol Population is a large number of bursty stations. Each station transmits a packet whenever it receives it from its user; no coordination with other stations! Central node retransmits all packets (good or bad) on down link. Stations decide to retransmit based on the information they hear from central node Spring 2003 UCSC CMPE150 31

32 Throughput of ALOHA Protocol packet overlaps with start of packet from node i packet overlaps with end of packet from node i interfering frame node i frame interfering frame time t0-1 t0 t0 + 1 N nodes in the system The probability of a station starting a packet in a given time slot is p. Node i transmits in time slot starting at t0, i.e., time slot 2. The packet from node i is successful if no other station transmits in the time slots 1 and 2. Spring 2003 UCSC CMPE150 32

33 Throughput of ALOHA Protocol packet overlaps with start of packet from node i packet overlaps with end of packet from node i interfering frame node i frame interfering frame time t0-1 t0 t0 + 1 Node i s frame is vulnerable from any arrival in the time interval (t0-1, t0+1] Highest throughput when we have one packet for each 2-packet time period Spring 2003 UCSC CMPE150 33

34 Slotted ALOHA The throughput of ALOHA can be improved by reducing the time a packet is vulnerable to interference from other packets. Slotted ALOHA works in a slotted channel providing discrete time slots. Stations can start transmitting only at the beginning of time slots. The time synchronization needed for slotting is accomplished at the physical layer, and some synchronization is required in many cases anyway. Spring 2003 UCSC CMPE150 34

35 Throughput of Slotted ALOHA The vulnerability period of a packet is a slot time: arrivals i time Any arrivals in prior slot collide with packet i We double the capacity of the channel (to about 36%)because we reduce in half the vulnerability period of a packet. Spring 2003 UCSC CMPE150 35

36 CSMA: Carrier Sense Multiple Access The capacity of ALOHA or slotted ALOHA is limited by the large vulnerability period of a packet. By listening before transmitting, stations try to reduce the vulnerability period to one propagation delay. This is the basis of CSMA (Kleinrock and Tobagi, UCLA, 1975) Same assumptions made for ALOHA are made now for CSMA. Spring 2003 UCSC CMPE150 36

37 CSMA Protocol no Packet ready Channel Busy? yes Assume non-persistent carrier sensing. Requires a maximum propagation delay much smaller than packet lengths! transmit wait for a round-trip time delay packet transmission k times yes positive ack? no compute random backoff integer k Spring 2003 UCSC CMPE150 37

38 CSMA Throughput Because prop. delay is much smaller than packet length, slotted and pure CSMA have very similar performance. When MAC protocol requires small prop delays, we can use slotted version to predict performance of unslotted version. 1 Analytical Results Reminder: These results are only an upper bound on performance, because we did not take into account the effect of ACKs sent from receivers! S (Throughput) Slotted Aloha Pure CSMA Slotted CSMA Pure Aloha Spring 2003 UCSC CMPE150 Offered Load: G 38

39 CSMA/CD: CSMA with Collision Detection CSMA improves on the performance of ALOHA tremendously. The remaining limitation is that, once a packet is sent, feedback occurs a roundtrip time after the entire packet is transmitted. The solution to improve on the performance of CSMA is to listen to the channel while a packet is being sent. This is called collision detection. R.M Metcalfe and D.R. Boggs, Ethernet: Distributed Packet Switching for Local Computer Networks, Comm. ACM, Vol. 19, 1976 (Xerox PARC). Spring 2003 UCSC CMPE150 39

40 CSMA/CD Protocol Packet ready Non-persistent transmission strategy Collision detection serves as a NACK! Channel busy? no yes delay packet transmission k times Assumption are: All stations hear one another Propagation delay is much smaller than packets transmit no Collision detected? yes abort transmission compute random backoff integer k send jamming signal Station listens to channel while transmitting; Collision is detected when signals sent and heard differ. Jamming signal sent to ensure all stations know of the collision. Spring 2003 UCSC CMPE150 40

41 CSMA/CD collision detection Spring 2003 UCSC CMPE150 41

42 Persistence after Carrier Sensing After detecting carrier, a station can persist trying to transmit after the channel is idle again. Persistence can be done with some probability; in which case we have a p-persistent strategy (Ethernet uses a 1-persistent strategy) Persistence can be limited, in which case a station persists trying to transmit only if the channel becomes idle within a given timeout that is much smaller than the duration of a data packet. Can you think why these approaches are desirable? Spring 2003 UCSC CMPE150 42

43 Collision Avoidance Collision avoidance emulates collision detection in networks where stations are half duplex. First protocol was proposed by Kleinrock and Tobagi (Split Reservation Multiple Access). Many protocols have been proposed since then: MACA, MACAW, FAMA, RIMA. The objective of collision avoidance protocols is to eliminate the hidden-terminal problem of CSMA: R S, R, and N hear one another, and R, N, and H hear one another S N H N hears S s transmission However, S and H cannot hear each other s transmissions to R, and cause interference at the receiver R. Spring 2003 UCSC CMPE150 43

44 Collision Avoidance Because of hidden terminals, the vulnerability of a data packet is just as in pure ALOHA, twice its length. With collision avoidance, stations exchange small control packets to determine which sender can transmit to a receiver. The collision avoidance dialogue can be controlled by the sender or the receiver. In sender-initiated collision avoidance we have: RTS (S to R) -> CTS (R to S) -> DATA (S to R) -> ACK (R to S) In receiver-initiated collision avoidance we can have: RTR (R to S) -> DATA (S to R) -> ACK (R to S) Spring 2003 UCSC CMPE150 44

45 Example of CSMA/CA: Floor Acquisition Multiple Access Stations use carrier sensing to send any packet. The CTS lasts much longer than an RTS (CTS Dominance) to force the interfering sources to detect carrier (from the receiver) and back off. S to R RTS 2τ R to S RTS CTS H to R noise is heard RTS S R H CTS RTS CTS time RTS from S arrives at R with no collisions. RTS from H must start within one prop. delay from CTS from R to S. H must hear noise from CTS and backs off! Spring 2003 UCSC CMPE150 45

46 Collision Resolution and Backoff Strategies Used to stabilize the system by preventing traffic loads that exceed its capacity. Collision resolution: Let packet that collide resolve when each is transmitted and block new traffic from entering the system. Backoff strategies: Increase the time between retransmissions when traffic load (that creates collisions) increases. Spring 2003 UCSC CMPE150 46

47 Collision Resolution and Backoff Strategies Backoff strategy in Ethernet: After experiencing the n th collision of a frame, pick a value, K, randomly from the set {0, 1, 2,, 2^m -1 } with m= min{n, 10}. Wait K * 512 bit times before attempting a retransmission. Goal is to reduce offered load to the channel; however, it provides no assurance that a retransmission will be sent ahead of another new transmission from other nodes. Spring 2003 UCSC CMPE150 47

48 TDMA TDMA: time division multiple access access to channel in "rounds" each station gets fixed length slot (length = pkt trans time) in each round unused slots go idle example: 6-station LAN, 1,3,4 have pkt, slots 2,5,6 idle Spring 2003 UCSC CMPE150 48

49 FDMA FDMA: frequency division multiple access channel spectrum divided into frequency bands each station assigned fixed frequency band unused transmission time in frequency bands go idle example: 6-station LAN, 1,3,4 have pkt, frequency bands 2,5,6 idle. time frequency bands Spring 2003 UCSC CMPE150 49

50 Channel Partitioning (CDMA) CDMA (Code Division Multiple Access) unique code assigned to each user; i.e., code set partitioning used mostly in wireless broadcast channels (cellular, satellite, etc) all users share same frequency, but each user has own chipping sequence (i.e., code) to encode data encoded signal = (original data) X (chipping sequence) decoding: inner-product of encoded signal and chipping sequence allows multiple users to coexist and transmit simultaneously with minimal interference (if codes are orthogonal ) Spring 2003 UCSC CMPE150 50

51 CDMA Encode/Decode Spring 2003 UCSC CMPE150 51

52 Basic Scheme: Token Passing A token granting the right to transmit is circulated among stations. Station with something to send receiving token changes the token into a start of packet and sends its packet. The token is sent back to the system when the sender is done. Two transmission strategies: Release after transmission (RAT): Sender releases the token immediately after transmitting its packet. Release after reception (RAR): Sender waits until it hears the last bit of its own transmission before releasing the token. Token Passing protocols can be used in any network topology; however, token management is simpler in rings. Spring 2003 UCSC CMPE150 52

53 Ethernet Frame Structure Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame Preamble: 7 bytes with pattern followed by one byte with pattern Used to synchronize receiver, sender clock rates Spring 2003 UCSC CMPE150 53

54 Unreliable, Connectionless Service Connectionless: No handshaking between sending and receiving adapter. Unreliable: receiving adapter doesn t send acks or nacks to sending adapter. Stream of datagrams passed to network layer can have gaps. Gaps will be filled if app is using TCP. Otherwise, app will see the gaps. Spring 2003 UCSC CMPE150 54

55 Ethernet uses CSMA/CD No slots Adapter doesn t transmit if it senses that some other adapter is transmitting, that is, carrier sense Transmitting adapter aborts when it senses that another adapter is transmitting, that is, collision detection Before attempting a retransmission, adapter waits a random time, that is, random access Spring 2003 UCSC CMPE150 55

56 Ethernet Technologies: 10Base2 10: 10Mbps; 2: under 200 meters max cable length. Thin coaxial cable in a bus topology. Repeaters used to connect up to multiple segments. Repeater repeats bits it hears on one interface to its other interfaces: physical layer device only! Has become a legacy technology. Spring 2003 UCSC CMPE150 56

57 10BaseT and 100BaseT 10/100 Mbps rate; latter called fast ethernet T stands for Twisted Pair Nodes connect to a hub: star topology ; 100 m max distance between nodes and hub nodes Hubs are essentially physical-layer repeaters: bits coming in one link go out all other links no frame buffering no CSMA/CD at hub: adapters detect collisions provides net management functionality hub Spring 2003 UCSC CMPE150 57

58 Gbit Ethernet Use standard Ethernet frame format Allows for point-to-point links and shared broadcast channels In shared mode, CSMA/CD is used; short distances between nodes to be efficient Uses hubs, called here Buffered Distributors Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now! Spring 2003 UCSC CMPE150 58

59 CSMA/CD Technology Issues IEEE802.3 and Ethernet are based on CSMA/CD. CSMA/CD is used over buses and star topologies. The most popular topology now (more than 80% of installed base) is the star topology with hubs or switches. A hub acts just like a station executing CSMA/CD, and only one transmission can succeed. A switch is different! and is the future. CPU RT Switch stores concurrently transmitted packets. No collisions. Higher throughput Limited by the switch architecture. Spring 2003 UCSC CMPE150 59

60 IEEE Wireless LAN b GHz unlicensed radio spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code widely deployed, using base stations a 5-6 GHz range up to 54 Mbps g GHz range up to 54 Mbps All use CSMA/CA for multiple access All have base-station and ad-hoc network versions Spring 2003 UCSC CMPE150 60

61 Base-Station Approach Wireless host communicates with a base station base station = access point (AP) Basic Service Set (BSS) (a.k.a. cell ) contains: Wireless hosts Access point (AP): base station BSS s combined to form distribution system (DS) Spring 2003 UCSC CMPE150 61

62 Ad Hoc Network approach No AP (i.e., base station) wireless hosts communicate with each other to get packet from wireless host A to B may need to route through wireless hosts X,Y,Z Applications: laptop meeting in conference room, car interconnection of personal devices battlefield IETF MANET (Mobile Ad hoc Networks) working group Spring 2003 UCSC CMPE150 62

63 Summary of Bluetooth Low-power, small radius, wireless networking technology meters omnidirectional not line-of-sight infared Interconnects gadgets GHz unlicensed radio band up to 721 kbps Interference from wireless LANs, digital cordless phones, microwave ovens: frequency hopping helps MAC protocol supports: error correction ARQ Each node has a 12-bit address Spring 2003 UCSC CMPE150 63

64 Logical Link Control MAC protocol provides best effort service. Even when ACKs are used in the MAC, the LLC layer can decide when to retransmit. LLC bridges the gap between service expected by network layer and service provided by MAC layer. LLC uses the header information in MAC frames. Example: PPP (LLC) over Ethernet (MAC) Spring 2003 UCSC CMPE150 64

65 Types of Service LLC Can Provide Unacknowledged connectionless service: Datagram transmission, no connection exists, no error checking, framing is the only service provided (e.g., SLIP). Acknowledged connectionless service: No connections, each frame is ACKed individually. This service can be provided as part of the MAC itself (e.g., CSMA/CA protocols) Connection-Oriented Service: Data exchanged within a connection, provides net layer with a virtual reliable packet stream (e.g., HDLC, PPP) Spring 2003 UCSC CMPE150 65

66 Generic ARQ Scheme SENDER INITIATED SENDER SEQ. # PACKET CRC RECEIVER TIMEOUT acknowledge packet if no errors ACK retransmit if no ACK time time Spring 2003 UCSC CMPE150 66

67 Requirements in ARQ Sender labels each packet it sends using a linear sequence-number space. Receiver ACKs each packet it receives without errors and numbers each ACK with the sequence number of the corresponding packet. Sender times out after not receiving an ACK for the packet within some finite amount of time, and retransmits the packet then. Sender sends up to a certain number of un-acked packets. Spring 2003 UCSC CMPE150 67

68 Stop-and-Wait ARQ Sender transmits packets labeled 1, 2,.. Receiver ACKs every packet received correctly and ACK specified the packet being acknowledged (or next expected packet). Receiver passes copy of packet correctly received to the network layer and drops packets with errors. Sender retransmits copy of packet if no ACK arrives within a timeout interval. Sender and receiver are initialized to start sending and receiving packet 1. Spring 2003 UCSC CMPE150 68

69 Selective Repeat ARQ Motivation: SWP leaves sender idle for long periods of time waiting for ACKs. Solution: Allow sender to transmit multiple packets while waiting for the ACK of a given packet. Have a pipeline of packets! Requirements: Sender and receiver can buffer a number (W ) of packets Sender labels packets using consecutive numbers 1, 2,. Receiver buffers packets received without error, ACKs them, and delivers packets to network layer in the correct order (e.g., if packet P1 is in error and P2 and P3 are received correctly, the receiver buffers them until it receives P1 correctly) Sender buffers copies of transmitted packet until it receives the corresponding ACK. Sender retransmits a packet when its timeout expires with no ACK. ACK refers to the sequence number of the packet it acknowledges. Spring 2003 UCSC CMPE150 69

70 Sequence Numbering in SRP Assume that window is W and packets are numbered modulo 2W (from 0 to 2W -1) Assume that, at time T, packet labeled n is passed to network layer at the receiver (and is the packet with the highest number that can be passed to net layer). R time sender sent packet n <= => sender received all ACKs up to ACK(n-W), because window is W => Smallest sequence number pending an ACK at the sender is n-w+1 n T => n+1 has not been received! (o.w., it would have been sent to network layer) => ACK(n+1) not sent to sender => Largest sequence number sent by sender is n+w Given n, the possible range of sequence numbers of packets at the sender is {n-w+1, n+w} and using modulo 2W sequence number space works correctly Spring 2003 UCSC CMPE150 70

71 Go-Back-N (GBN) ARQ SRP requires sender and receiver to have a buffer, which is not an issue today. With GBN, the receiver discards any packet it receives out of order; therefore, it does not need a buffer. Receiver accepts only those packets received in order. Receiver ACKs a packet received correctly with the sequence number of the last packet received in sequence. The sender starts a timer for each packet it transmits, and after the timeout of a packet expires, it retransmits the packet and all the packets sent after that packet. Sender can have up to W packets waiting for ACKs. Spring 2003 UCSC CMPE150 71

72 Interconnecting with hubs Backbone hub interconnects LAN segments Extends maximum distance between nodes Individual segment collision domains become one large collision domain! If a node in CS and a node EE transmit at same time: collision Cannot interconnect 10BaseT & 100BaseT Spring 2003 UCSC CMPE150 72

73 Internetworking with Bridges Bridges are used to interconnect LANs at the link layer. Frame forwarding from one LAN to another is based on the destination s link-level address (MAC address) without making any changes to the frame. A MAC address is a name, and for a bridge the address of the destination is the adjacent LAN over which the frames to the destination should be forwarded. Plug-and-play, self-learning bridges do not need to be configured. Spring 2003 UCSC CMPE150 73

74 Traffic Isolation with Bridges Bridge installation breaks LAN into LAN segments Bridges filter packets: Same-LAN-segment frames not usually forwarded onto other LAN segments LAN segments become separate collision domains collision domain bridge collision domain = hub = host LAN segment LAN segment LAN (IP network) Spring 2003 UCSC CMPE150 74

75 Internetworking with Bridges To which LAN segment should the bridge forward a frame? A routing problem! There are two types of bridges that have been used: Transparent Source routing Spring 2003 UCSC CMPE150 75

76 Transparent Bridges: Summary The purpose of transparent bridges is to keep the packet forwarding functionality transparent to the hosts. Transparent bridges establish and manage a spanning tree of the network to eliminate packet looping. The address of a station is always the LAN over which packets from that station came last; this is a dynamic process. If no address is known, a bridge broadcasts packets for a station over all its ports (or those in the spanning tree). Spring 2003 UCSC CMPE150 76

77 Bridges in Mesh Topologies Alternative paths from source to destination LANs are desirable for increased reliability. Disabled Spring 2003 UCSC CMPE150 77

78 Spanning Tree Algorithm (STA) The objective is to define a single spanning tree in the internet over which packets flow without looping. Basis of operation (Perlman 1992, part of IEEE standard): Elect distributedly a single bridge as the root of the tree Calculate distance (in hops) on a shortest path to root Elect a designated bridge for each LAN (e.g., closest to the root in the LAN) Allow only designated bridge to forward packets to and from its LAN root A distributed election process is used to build the spanning tree! Spring 2003 UCSC CMPE150 78

79 STA Operation Each bridge has multiple MAC addresses (one per port) A bridge has a bridge-wide ID (one of the MAC addresses) HELLOs: messages used to build tree, sent to all bridges of a LAN HELLO specifies: Root ID: The MAC address of the bridge assumed to be the root Transmitting bridge ID: MAC address of bridge sending HELLO Cost: Length (in hops) of path from bridge to root A bridge starts by considering itself the proposed root Bridge starts election process by sending HELLO = own ID, 0, own ID Spring 2003 UCSC CMPE150 79

80 STA Operation Bridges adopt the smallest HELLO they hear: Minimum root ID Smallest distance to root Minimum reporting bridge ID Bridge compares its own HELLO with its neighbors HELLOs, and chooses the smallest Its root port becomes the port to neighbor bridge with smallest HELLO Bridge composes a new HELLO, adding 1 to the distance to adopted root Bridge 20 must adopt HELLO from neighbor 94 over port x: smallest root ID and smallest distance to root! x 20 y [10,4,94] z [10,20,15] [10,5,20] [21,2,30] [10,5,20] Spring 2003 UCSC CMPE150 80

81 STA Operation Bridge sends new HELLO over all ports from which larger HELLOs were received. Bridge knows if it is the designated bridge for a LAN if it does not hear a smaller HELLO than its own. Its root port is the port from which the smallest HELLO was received. Bridge puts its root port and all ports for which it is the designated bridge in forwarding state. Bridge puts all other ports in blocking state. Data packets, control packets, and learning of addresses take place only over ports in forwarding state (over the spanning tree). Spring 2003 UCSC CMPE150 81

82 Example of STA Operation [10,4,94] [10,4,50] root port x 20 z v [21,2,30] [10,5,20] y forwarding mode forwarding mode [10,20,15] [10,5,20] Spring 2003 UCSC CMPE150 82

83 Example root Spring 2003 UCSC CMPE150 83

84 Bridges vs. Routers Both store-and-forward devices Routers: network layer devices (examine network layer headers) Bridges are link layer devices Routers maintain routing tables, implement routing algorithms Bridges maintain bridge tables, implement filtering, learning and spanning tree algorithms Spring 2003 UCSC CMPE150 84

85 Routers vs. Bridges Bridges + and - + Bridge operation is simpler requiring less packet processing. + Bridge tables are self learning. - All traffic confined to spanning tree, even when alternative bandwidth is available. Spring 2003 UCSC CMPE150 85

86 Routers vs. Bridges Routers + and - + arbitrary topologies can be supported, cycling is limited by TTL counters (and good routing protocols) + provide protection against broadcast storms - require IP address configuration (not plug and play) - require higher packet processing bridges do well in small (few hundred hosts) while routers used in large networks (thousands of hosts) Spring 2003 UCSC CMPE150 86

87 Ethernet Switches Essentially a multi-interface bridge layer 2 (frame) forwarding, filtering using LAN addresses Switching: A-to-A and B-to- B simultaneously, no collisions large number of interfaces often: individual hosts, starconnected into switch Ethernet, but no collisions! Spring 2003 UCSC CMPE150 87

88 Network Layer The main functions at the network layer are addressing, routing, congestion control, and admission control. Addressing consists of identifying where a destination is with respect to the network topology. Routing consists of (a) computing paths from sources to destinations and (b) forwarding packets along such paths. Congestion control consists of limiting the amount of data a source can sent into the network. Admission control consists of limiting the number of sources allowed to send data into the network, and in a way is part of system-wide congestion control. Spring 2003 UCSC CMPE150 88

89 Routing Algorithms Most books and papers classify routing algorithms into distance-vector and link-state algorithms. Distance-Vector Algorithm: Routers exchange their distances to known destinations; a router uses the distance vectors received from its neighbors to compute its own distances. Computation is distributed. Link-State Algorithm: Routers exchange information about the state of the links in the network; a router uses this information to compute its distances to destinations. Computation is local. This is a very limiting view! Spring 2003 UCSC CMPE150 89

90 Shortest-Path Routing Problem: Compute the path of minimum length from each router to each destination Notation: G(N, E) is the network of N nodes and E links i P j N i q i (i, k) p i l k k D i j h2 = l i hop h P i. ( h i, h + 1 i j hx ) j Spring 2003 UCSC CMPE150 90

91 Bellman-Ford Algorithm BF iterates on the number of hops away from a node. Step 1: Initialize source node S with a 0 distance to itself and all other nodes with an infinite distance. Step 2: Set H = 1 Step 3: Label all nodes H hops away from S with the smallest distance from S to the nodes. Step 4: Stop if all nodes have been covered and no label can be reduced by increasing H. Else, set H = H+1 and repeat Step 3 0 S 1 5 Spring 2003 UCSC CMPE A 2 B C D 10 Link costs are the same in both link directions 2 2 E

92 Bellman-Ford Algorithm H = 4: 1 5 A 10 C S E B 1 D 3 4 No more nodes can be reached and no label can be reduced Spring 2003 UCSC CMPE150 92

93 Distributed Bellman-Ford Algorithm (DBF) The objective of DBF is to have a distributed implementation of BF, so that routers can compute distances to destinations distributedly. To accomplish this, the computation of a distance to a destination starts at the destination itself. The iteration of DBF is on the number of hops away from a destination. DBF operates independently for each destination. Destination starts by stating the distance to itself is 0 The neighbors of the destination receive this information, process it and send their own updates. Distances propagate throughout the network. Spring 2003 UCSC CMPE150 93

94 DBF Information maintained at each router: Distance Table: Distance to each destination reported by each neighbor Link-Cost Table: Cost of link to each adjacent node Routing Table: Distance and successor (next hop) to each destination Information exchanged among routers: Vector of one or more entries, each entry stating the distance to a destination Services assumed: Update messages are exchanged reliably, a node knows who its neighbors are Spring 2003 UCSC CMPE150 94

95 Example of DBF Operation For simplicity, we will assume synchronous operation in all cases! d c b a j time Spring 2003 UCSC CMPE150 95

96 Counting to Infinity in DBF The problem with DBF is that it does not have a termination detection mechanism! d c b a j 3 = 2+1 X 4 4 = etc time Spring 2003 UCSC CMPE150 96

97 Ad Hoc Solutions (do not work) Counting to N takes too long! Alternatives include: Split horizon: Does not report routes through a successor to the successor itself. Hold-down timer: After distance to destination increases, send update stating new distance through current successor, wait for a long period of time before computing new successor and shortest distance and then act as in DBF. Poisoned reverse: After distance increase, report an infinite distance and then correct the distance. (Or in general, reporting infinity to the successor of destinations routed through it). Next-hop information: Communicate the distance and next hop to each destination (used in RIP v2) Spring 2003 UCSC CMPE150 97

98 Looping in DBF 5, B A 10 2, j C 1 2 6, A S X0, j j 5 2 B 1 D 3, D 2, j Spring 2003 UCSC CMPE150 98

99 Looping in DBF 5, B A 10 5,B C 5 1 6, A S B 1 D 4 3, D 4, B Spring 2003 UCSC CMPE150 99

100 Looping in DBF 5, B A 10 5,B C Erroneous paths persist as long as they appear to be the shortest paths. 6, A S Similar looping could occur if the cost of the links to j increased drastically (e.g., to 20). DBF cannot be used with link costs that have a large variance! 5 5 B D etc 1 3, D 4, B Spring 2003 UCSC CMPE

101 Traditional Link-State Algorithm (LSA) Developed as a result of DBF s looping and nontermination problems. Two components: Topology map distribution Local shortest path computation Each router runs a local shortest-path algorithm (Dijkstra s) using the topology stored locally. Flooding is used to replicate the topology map at every router. Each router is responsible for reporting the state of outgoing links to the rest of the network. Two link-state updates per link reach every router. Spring 2003 UCSC CMPE

102 Shortest-Path First (SPF) Algorithm Step 1: Initialize Set SPF = { root }, where root is router running SPF Distance to root = 0 and distance to other nodes = cost of link or infinity Step 2: Find next node for SPF set: Find a node x not in SPF set such that: distance to/from root = Min{distance to node outside of SPF set} Augment SPF set with x Stop if SPF set contains all nodes Step 3: Change minimum distance: For each node y outside SPF set do: dist. to y = Min{ dist. to y, dist. to z in SPF + cost of (z, y) } Repeat Step 2 Spring 2003 UCSC CMPE

103 SPF Example SPF ={S, A, B, D} Labels do not change as we continue to expand SPF set 1 1 A 10 5 C 2 SPF ={S, A, B, D, C} SPF ={S, A, B, D, C, E} Stop after covering E since all nodes are covered by SPF set. 0 S 5 2 B 2 1 D 10 2 E Note that iteration is on the next node that can be covered with the next shortest path; hence complete topology must be known by router. Spring 2003 UCSC CMPE

104 Flooding of Link States Information Stored at Routers: Each router maintains all the nodes and all the links in the network in a topology graph. Each link in the graph has a cost, a sequence number, and an age. Spring 2003 UCSC CMPE

105 Flooding of Link States Information Exchanged: Each router is responsible for communicating the latest state of each adjacent outgoing link. The router sends a link state update (LSU) to report changes on an adjacent outgoing link. A sequence number is used to identify the latest LSU. An LSU also specified the age of the LSU, and the age of an LSU is decremented each time it is forwarded and while it is in storage. We assume that LSUs are exchanged reliably between any two routers and that a router knows who its neighbors are! Spring 2003 UCSC CMPE

106 IP Internetworking Based on Cerf s catenet model V.G. Cerf, The Catenet Model for Internetworking, IEN 48, July Basic premises: Heterogeneous transmission media Heterogeneous hardware and OS in hosts and gateways Common protocol for network interconnection runs in all gateways and hosts! Common protocol used for data transfer and signaling Common address space used to identify where a host or router is in the internetwork An address states at which network a node attaches to the internetwork Spring 2003 UCSC CMPE

107 Service Model: Theory and Practice The Internet Protocol (IP) evolved from the catenet model. Theory: Datagram Delivery is assumed, so that packets can get lost, out of order, and multiple copies can be delivered. Practice: TCP needs in-order delivery of packets to work efficiently, and (as we will see) Internet routing protocols provide a single path for each destination and do not adapt very rapidly. Too many destinations! Spring 2003 UCSC CMPE

108 IPv4 Datagram Format IP protocol version number header length (words) type of data max number remaining hops (decremented at each router) upper layer protocol to deliver payload to how much overhead with TCP? 20 bytes of TCP 20 bytes of IP = 40 bytes + app layer overhead ver head. len 16-bit identifier time to live type of service upper layer 32 bits flgs length fragment offset Internet checksum 32 bit source IP address 32 bit destination IP address Options (if any) data (variable length, typically a TCP or UDP segment) total datagram length (bytes) for fragmentation and reassembly e.g. timestamp, record route taken, specify list of routers to visit. Spring 2003 UCSC CMPE

109 IPv4 Addresses IP addresses are global and, unlike MAC addresses, they are hierarchical. IP address has a network part and a host part and specifies host@network A host has an address for each network to which it attaches. IP addresses are denoted using the dotted-decimal notation: Each byte of the address is written in its decimal form and is separated by a dot from the other bytes, e.g., => Spring 2003 UCSC CMPE

110 IPv4 Addresses (past) Class A 0 network host million Class B 10 network host 16,382 65,534 Class C 110 network host 2 million 254 Class D 1110 multicast address Class E reserved address Spring 2003 UCSC CMPE

111 IPv4 Addressing Problems There were too few networks left due to the class structure used in IP address assignments! There are many more IP devices and appliances coming. Routing tables cannot have millions of entries. Solutions: Aggregation of addresses without classes (subnetting, and now CIDR) New and bigger global address space (IPv6) Locally unique addresses (NAT and other techniques) Spring 2003 UCSC CMPE

112 IP Addressing: CIDR Classful addressing: Inefficient use of address space, address space exhaustion. A class B address has enough addresses for 65K hosts, even if only a few more than 256 hosts are located in that network CIDR: Classless InterDomain Routing Eliminate the strict assignment of address portion in class-full addressing. Enable a network portion of address of arbitrary length. CIDR Address Format: a.b.c.d/x, where x is # bits in network portion of address network part host part /23 Spring 2003 UCSC CMPE

113 Assigning Blocks of Addresses to ISPs ICANN: Internet Corporation for Assigned Names and Numbers Allocates IP address space Manages DNS (domain name system) Assigns domain names and resolves disputes Spring 2003 UCSC CMPE

114 Internet Control Protocols In addition to packet forwarding and keeping routing tables correct, sending IP packets requires a number of control protocols: Application has the name of an intended destination. An IP address has to be found for that name; The application typically calls a resolver in the Domain Name System (DNS) or uses a static hosts file (e.g., /etc/hosts) Host determines if destination IP address is the same or different. If different, packet is sent to an attached (default) router. If same subnet, the IP address must be converted to a MAC address using a protocol (ARP). Destination router must also map IP address to MAC address using ARP. Errors may have to be reported to the source of an IP packet using a protocol (ICMP). Spring 2003 UCSC CMPE

115 Fragmentation Packet length is in bytes and includes header; maximum length is then 65,535 bytes MAC protocol my not support such long packets, and an IP packet may have to be fragmented. Ethernet accepts frames of up to 1500 bytes and FDDI of up to 4500 bytes Each fragment is a self-contained datagram. Fragmentation is handled with: The packet ID, which is the same for all fragments The offset, which states the byte (position) of the fragment A flag indicating that there a more fragments for the same ID coming. Spring 2003 UCSC CMPE

116 IPv4 Header TTL (time to live indicates how long the packet can stay in the network; it is specified in hops and is decremented each time the packet is forwarded. Default is 64 hops; nodes can play with the field to limit the scope Protocol specifies the type of payload Checksum is computed considering the entire header as a sequence of 16-bit words, adding them up with 1 s complement arithmetic and taking the 1 s complement of the result. This checksum is NOT as powerful as a CRC but is simple to do in software. Why this way? Because it is done at each hop (software) What if we process headers in hardware? Spring 2003 UCSC CMPE

117 Error Reporting In general, errors can be reported to the origin of a packet or to intermediate relays or both. In the IP Internet, errors are reported to the source using ICMP (internet control message protocol). The choice stems from using IP for all signaling and user data transfer in the Internet. ICMP messages are encapsulated in IP. An IP packet specifies the source and destination and not the relays (options are not supported in general) Spring 2003 UCSC CMPE

118 Address Resolution Protocol Goal: Enable a host to build a table of mappings between IP addresses and MAC addresses in a dynamic manner. Mappings are called ARP cache or ARP table. Approach: ARP is designed assuming a fully connected, broadcast link layer (LAN) and the requestor is responsible for persisting. Hosts and routers broadcast requests and responses and listen to requests and responses from any other node in the LAN. Different approach would be needed in a multihop LAN. Spring 2003 UCSC CMPE

119 Dynamic Host Configuration Host must be assigned an IP address, because it is not committed to hardware as a MAC address. Configuring hosts with proper IP addresses is involved. DHCP (dynamic host configuration protocol) is a solution to this configuration and management problem. DHCP is intended to support manual, automatic and dynamic configurations DHCP is designed to work with no pre-configured addresses of servers and across networks. Spring 2003 UCSC CMPE

120 DHCP: Dynamic Host Configuration Protocol Goal: Allow host to dynamically obtain its IP address from network server when it joins network. Can renew its lease on address in use Allows reuse of addresses only hold address while connected and on Support for mobile users who want to join network (more shortly) DHCP overview: host broadcasts DHCP discover msg DHCP server responds with DHCP offer msg host requests IP address: DHCP request msg DHCP server sends address: DHCP ack msg Spring 2003 UCSC CMPE

121 NAT: Network Address Translation rest of Internet local network (e.g., home network) / All datagrams leaving local network have same single source NAT IP address: , different source port numbers Datagrams with source or destination in this network have /24 address for source, destination (as usual) Spring 2003 UCSC CMPE

Based on Computer Networking, 4 th Edition by Kurose and Ross

Based on Computer Networking, 4 th Edition by Kurose and Ross Computer Networks Ethernet Hubs and Switches Based on Computer Networking, 4 th Edition by Kurose and Ross Ethernet dominant wired LAN technology: cheap $20 for NIC first widely used LAN technology Simpler,

More information

EECS 122: Introduction to Computer Networks Multiaccess Protocols. ISO OSI Reference Model for Layers

EECS 122: Introduction to Computer Networks Multiaccess Protocols. ISO OSI Reference Model for Layers EECS 122: Introduction to Computer Networks Multiaccess Protocols Computer Science Division Department of Electrical Engineering and Computer Sciences University of California, Berkeley Berkeley, CA 94720-1776

More information

LAN Switching. 15-441 Computer Networking. Switched Network Advantages. Hubs (more) Hubs. Bridges/Switches, 802.11, PPP. Interconnecting LANs

LAN Switching. 15-441 Computer Networking. Switched Network Advantages. Hubs (more) Hubs. Bridges/Switches, 802.11, PPP. Interconnecting LANs LAN Switching 15-441 Computer Networking Bridges/Switches, 802.11, PPP Extend reach of a single shared medium Connect two or more segments by copying data frames between them Switches only copy data when

More information

Ethernet. Ethernet Frame Structure. Ethernet Frame Structure (more) Ethernet: uses CSMA/CD

Ethernet. Ethernet Frame Structure. Ethernet Frame Structure (more) Ethernet: uses CSMA/CD Ethernet dominant LAN technology: cheap -- $20 for 100Mbs! first widely used LAN technology Simpler, cheaper than token rings and ATM Kept up with speed race: 10, 100, 1000 Mbps Metcalfe s Etheret sketch

More information

Lecture 7 Multiple Access Protocols and Wireless

Lecture 7 Multiple Access Protocols and Wireless Lecture 7 Multiple Access Protocols and Wireless Networks and Security Jacob Aae Mikkelsen IMADA November 11, 2013 November 11, 2013 1 / 57 Lecture 6 Review What is the responsibility of the link layer?

More information

Local Area Networks transmission system private speedy and secure kilometres shared transmission medium hardware & software

Local Area Networks transmission system private speedy and secure kilometres shared transmission medium hardware & software Local Area What s a LAN? A transmission system, usually private owned, very speedy and secure, covering a geographical area in the range of kilometres, comprising a shared transmission medium and a set

More information

CSE331: Introduction to Networks and Security. Lecture 6 Fall 2006

CSE331: Introduction to Networks and Security. Lecture 6 Fall 2006 CSE331: Introduction to Networks and Security Lecture 6 Fall 2006 Open Systems Interconnection (OSI) End Host Application Reference model not actual implementation. Transmits messages (e.g. FTP or HTTP)

More information

CSE 123A Computer Networks

CSE 123A Computer Networks CSE 123A Computer Networks Winter 2005 Lecture 5: Data-Link II: Media Access Some portions courtesy Srini Seshan or David Wetherall Last Time Framing: How to translate a bitstream into separate packets

More information

CS263: Wireless Communications and Sensor Networks

CS263: Wireless Communications and Sensor Networks CS263: Wireless Communications and Sensor Networks Matt Welsh Lecture 4: Medium Access Control October 5, 2004 2004 Matt Welsh Harvard University 1 Today's Lecture Medium Access Control Schemes: FDMA TDMA

More information

EPL 657 Wireless Networks

EPL 657 Wireless Networks EPL 657 Wireless Networks Some fundamentals: Multiplexing / Multiple Access / Duplex Infrastructure vs Infrastructureless Panayiotis Kolios Recall: The big picture... Modulations: some basics 2 Multiplexing

More information

Random Access Protocols

Random Access Protocols Lecture Today slotted vs unslotted ALOHA Carrier sensing multiple access Ethernet DataLink Layer 1 Random Access Protocols When node has packet to send transmit at full channel data rate R. no a priori

More information

Attenuation (amplitude of the wave loses strength thereby the signal power) Refraction Reflection Shadowing Scattering Diffraction

Attenuation (amplitude of the wave loses strength thereby the signal power) Refraction Reflection Shadowing Scattering Diffraction Wireless Physical Layer Q1. Is it possible to transmit a digital signal, e.g., coded as square wave as used inside a computer, using radio transmission without any loss? Why? It is not possible to transmit

More information

ESSENTIALS. Understanding Ethernet Switches and Routers. April 2011 VOLUME 3 ISSUE 1 A TECHNICAL SUPPLEMENT TO CONTROL NETWORK

ESSENTIALS. Understanding Ethernet Switches and Routers. April 2011 VOLUME 3 ISSUE 1 A TECHNICAL SUPPLEMENT TO CONTROL NETWORK VOLUME 3 ISSUE 1 A TECHNICAL SUPPLEMENT TO CONTROL NETWORK Contemporary Control Systems, Inc. Understanding Ethernet Switches and Routers This extended article was based on a two-part article that was

More information

10. Wireless Networks

10. Wireless Networks Computernetzwerke und Sicherheit (CS221) 10. Wireless Networks 1. April 2011 omas Meyer Departement Mathematik und Informatik, Universität Basel Chapter 6 Wireless and Mobile Networks (with changes CS221

More information

LANs. Local Area Networks. via the Media Access Control (MAC) SubLayer. Networks: Local Area Networks

LANs. Local Area Networks. via the Media Access Control (MAC) SubLayer. Networks: Local Area Networks LANs Local Area Networks via the Media Access Control (MAC) SubLayer 1 Local Area Networks Aloha Slotted Aloha CSMA (non-persistent, 1-persistent, p-persistent) CSMA/CD Ethernet Token Ring 2 Network Layer

More information

How To Make A Multi-User Communication Efficient

How To Make A Multi-User Communication Efficient Multiple Access Techniques PROF. MICHAEL TSAI 2011/12/8 Multiple Access Scheme Allow many users to share simultaneously a finite amount of radio spectrum Need to be done without severe degradation of the

More information

Introduction to LAN/WAN. Network Layer

Introduction to LAN/WAN. Network Layer Introduction to LAN/WAN Network Layer Topics Introduction (5-5.1) Routing (5.2) (The core) Internetworking (5.5) Congestion Control (5.3) Network Layer Design Isues Store-and-Forward Packet Switching Services

More information

Collision of wireless signals. The MAC layer in wireless networks. Wireless MAC protocols classification. Evolutionary perspective of distributed MAC

Collision of wireless signals. The MAC layer in wireless networks. Wireless MAC protocols classification. Evolutionary perspective of distributed MAC The MAC layer in wireless networks The wireless MAC layer roles Access control to shared channel(s) Natural broadcast of wireless transmission Collision of signal: a /space problem Who transmits when?

More information

Note! The problem set consists of two parts: Part I: The problem specifications pages Part II: The answer pages

Note! The problem set consists of two parts: Part I: The problem specifications pages Part II: The answer pages Part I: The problem specifications NTNU The Norwegian University of Science and Technology Department of Telematics Note! The problem set consists of two parts: Part I: The problem specifications pages

More information

Ethernet, VLAN, Ethernet Carrier Grade

Ethernet, VLAN, Ethernet Carrier Grade Ethernet, VLAN, Ethernet Carrier Grade Dr. Rami Langar LIP6/PHARE UPMC - University of Paris 6 Rami.langar@lip6.fr www-phare.lip6.fr/~langar RTEL 1 Point-to-Point vs. Broadcast Media Point-to-point PPP

More information

Technical Support Information Belkin internal use only

Technical Support Information Belkin internal use only The fundamentals of TCP/IP networking TCP/IP (Transmission Control Protocol / Internet Protocols) is a set of networking protocols that is used for communication on the Internet and on many other networks.

More information

TCOM 370 NOTES 99-12 LOCAL AREA NETWORKS AND THE ALOHA PROTOCOL

TCOM 370 NOTES 99-12 LOCAL AREA NETWORKS AND THE ALOHA PROTOCOL 1. Local Area Networks TCOM 370 NOTES 99-12 LOCAL AREA NETWORKS AND THE ALOHA PROTOCOL These are networks spanning relatively short distances (e.g. within one building) for local point-to-point and point-to-multipoint

More information

Wireless Networks. Reading: Sec5on 2.8. COS 461: Computer Networks Spring 2011. Mike Freedman

Wireless Networks. Reading: Sec5on 2.8. COS 461: Computer Networks Spring 2011. Mike Freedman 1 Wireless Networks Reading: Sec5on 2.8 COS 461: Computer Networks Spring 2011 Mike Freedman hep://www.cs.princeton.edu/courses/archive/spring11/cos461/ 2 Widespread Deployment Worldwide cellular subscribers

More information

Route Discovery Protocols

Route Discovery Protocols Route Discovery Protocols Columbus, OH 43210 Jain@cse.ohio-State.Edu http://www.cse.ohio-state.edu/~jain/ 1 Overview Building Routing Tables Routing Information Protocol Version 1 (RIP V1) RIP V2 OSPF

More information

CS6956: Wireless and Mobile Networks Lecture Notes: 2/11/2015. IEEE 802.11 Wireless Local Area Networks (WLANs)

CS6956: Wireless and Mobile Networks Lecture Notes: 2/11/2015. IEEE 802.11 Wireless Local Area Networks (WLANs) CS6956: Wireless and Mobile Networks Lecture Notes: //05 IEEE 80. Wireless Local Area Networks (WLANs) CSMA/CD Carrier Sense Multi Access/Collision Detection detects collision and retransmits, no acknowledgement,

More information

Networking Test 4 Study Guide

Networking Test 4 Study Guide Networking Test 4 Study Guide True/False Indicate whether the statement is true or false. 1. IPX/SPX is considered the protocol suite of the Internet, and it is the most widely used protocol suite in LANs.

More information

IP Networking. Overview. Networks Impact Daily Life. IP Networking - Part 1. How Networks Impact Daily Life. How Networks Impact Daily Life

IP Networking. Overview. Networks Impact Daily Life. IP Networking - Part 1. How Networks Impact Daily Life. How Networks Impact Daily Life Overview Dipl.-Ing. Peter Schrotter Institute of Communication Networks and Satellite Communications Graz University of Technology, Austria Fundamentals of Communicating over the Network Application Layer

More information

Computer Network. Interconnected collection of autonomous computers that are able to exchange information

Computer Network. Interconnected collection of autonomous computers that are able to exchange information Introduction Computer Network. Interconnected collection of autonomous computers that are able to exchange information No master/slave relationship between the computers in the network Data Communications.

More information

Network layer: Overview. Network layer functions IP Routing and forwarding

Network layer: Overview. Network layer functions IP Routing and forwarding Network layer: Overview Network layer functions IP Routing and forwarding 1 Network layer functions Transport packet from sending to receiving hosts Network layer protocols in every host, router application

More information

Ethernet. Ethernet. Network Devices

Ethernet. Ethernet. Network Devices Ethernet Babak Kia Adjunct Professor Boston University College of Engineering ENG SC757 - Advanced Microprocessor Design Ethernet Ethernet is a term used to refer to a diverse set of frame based networking

More information

8.2 The Internet Protocol

8.2 The Internet Protocol TCP/IP Protocol Suite HTTP SMTP DNS RTP Distributed applications Reliable stream service TCP UDP User datagram service Best-effort connectionless packet transfer Network Interface 1 IP Network Interface

More information

Transport and Network Layer

Transport and Network Layer Transport and Network Layer 1 Introduction Responsible for moving messages from end-to-end in a network Closely tied together TCP/IP: most commonly used protocol o Used in Internet o Compatible with a

More information

COMP 3331/9331: Computer Networks and Applications

COMP 3331/9331: Computer Networks and Applications COMP 3331/9331: Computer Networks and Applications Week 10 Wireless Networks Reading Guide: Chapter 6: 6.1 6.3 Wireless Networks + Security 1 Wireless and Mobile Networks Background: # wireless (mobile)

More information

IP address format: Dotted decimal notation: 10000000 00001011 00000011 00011111 128.11.3.31

IP address format: Dotted decimal notation: 10000000 00001011 00000011 00011111 128.11.3.31 IP address format: 7 24 Class A 0 Network ID Host ID 14 16 Class B 1 0 Network ID Host ID 21 8 Class C 1 1 0 Network ID Host ID 28 Class D 1 1 1 0 Multicast Address Dotted decimal notation: 10000000 00001011

More information

Chapter 4 Network Layer

Chapter 4 Network Layer Chapter 4 Network Layer A note on the use of these ppt slides: We re making these slides freely available to all (faculty, students, readers). They re in PowerPoint form so you can add, modify, and delete

More information

What is CSG150 about? Fundamentals of Computer Networking. Course Outline. Lecture 1 Outline. Guevara Noubir noubir@ccs.neu.

What is CSG150 about? Fundamentals of Computer Networking. Course Outline. Lecture 1 Outline. Guevara Noubir noubir@ccs.neu. What is CSG150 about? Fundamentals of Computer Networking Guevara Noubir noubir@ccs.neu.edu CSG150 Understand the basic principles of networking: Description of existing networks, and networking mechanisms

More information

Introduction to LAN/WAN. Network Layer (part II)

Introduction to LAN/WAN. Network Layer (part II) Introduction to LAN/WAN Network Layer (part II) Topics The Network Layer Introduction Routing (5.2) The Internet (5.5) IP, IP addresses ARP (5.5.4) OSPF (5.5.5) BGP (5.5.6) Congestion Control (5.3) Internetworking

More information

Note! The problem set consists of two parts: Part I: The problem specifications pages Part II: The answer pages

Note! The problem set consists of two parts: Part I: The problem specifications pages Part II: The answer pages Part I: The problem specifications NTNU The Norwegian University of Science and Technology Department of Telematics Note! The problem set consists of two parts: Part I: The problem specifications pages

More information

How To Understand And Understand Network Theory

How To Understand And Understand Network Theory University of Southern California Course Title: EE450: Computer Networks Semester: Fall Semester 2014 Instructor: Professor A. Zahid, azahid@usc.edu Office: PHE 418, 213-740-9058 Office Hours: TTH 9:00

More information

RTT 60.5 msec receiver window size: 32 KB

RTT 60.5 msec receiver window size: 32 KB Real-World ARQ Performance: TCP Ex.: Purdue UCSD Purdue (NSL): web server UCSD: web client traceroute to planetlab3.ucsd.edu (132.239.17.226), 30 hops max, 40 byte packets 1 switch-lwsn2133-z1r11 (128.10.27.250)

More information

Network layer" 1DT066! Distributed Information Systems!! Chapter 4" Network Layer!! goals: "

Network layer 1DT066! Distributed Information Systems!! Chapter 4 Network Layer!! goals: 1DT066! Distributed Information Systems!! Chapter 4" Network Layer!! Network layer" goals: "! understand principles behind layer services:" " layer service models" " forwarding versus routing" " how a

More information

Faculty of Engineering Computer Engineering Department Islamic University of Gaza 2012. Network Chapter# 19 INTERNETWORK OPERATION

Faculty of Engineering Computer Engineering Department Islamic University of Gaza 2012. Network Chapter# 19 INTERNETWORK OPERATION Faculty of Engineering Computer Engineering Department Islamic University of Gaza 2012 Network Chapter# 19 INTERNETWORK OPERATION Review Questions ٢ Network Chapter# 19 INTERNETWORK OPERATION 19.1 List

More information

Architecture and Performance of the Internet

Architecture and Performance of the Internet SC250 Computer Networking I Architecture and Performance of the Internet Prof. Matthias Grossglauser School of Computer and Communication Sciences EPFL http://lcawww.epfl.ch 1 Today's Objectives Understanding

More information

IP addressing and forwarding Network layer

IP addressing and forwarding Network layer The Internet Network layer Host, router network layer functions: IP addressing and forwarding Network layer Routing protocols path selection RIP, OSPF, BGP Transport layer: TCP, UDP forwarding table IP

More information

R2. The word protocol is often used to describe diplomatic relations. How does Wikipedia describe diplomatic protocol?

R2. The word protocol is often used to describe diplomatic relations. How does Wikipedia describe diplomatic protocol? Chapter 1 Review Questions R1. What is the difference between a host and an end system? List several different types of end systems. Is a Web server an end system? 1. There is no difference. Throughout

More information

Datagram-based network layer: forwarding; routing. Additional function of VCbased network layer: call setup.

Datagram-based network layer: forwarding; routing. Additional function of VCbased network layer: call setup. CEN 007C Computer Networks Fundamentals Instructor: Prof. A. Helmy Homework : Network Layer Assigned: Nov. 28 th, 2011. Due Date: Dec 8 th, 2011 (to the TA) 1. ( points) What are the 2 most important network-layer

More information

DATA COMMUNICATION AND NETWORKS

DATA COMMUNICATION AND NETWORKS DATA COMMUNICATION AND NETWORKS 1. Define the term Computer Networks. A Computer network is a number if computers interconnected by one or more transmission paths. The transmission path often is the telephone

More information

IT4405 Computer Networks (Compulsory)

IT4405 Computer Networks (Compulsory) IT4405 Computer Networks (Compulsory) INTRODUCTION This course provides a comprehensive insight into the fundamental concepts in data communications, computer network systems and protocols both fixed and

More information

Lecture 17: 802.11 Wireless Networking"

Lecture 17: 802.11 Wireless Networking Lecture 17: 802.11 Wireless Networking" CSE 222A: Computer Communication Networks Alex C. Snoeren Thanks: Lili Qiu, Nitin Vaidya Lecture 17 Overview" Project discussion Intro to 802.11 WiFi Jigsaw discussion

More information

Internet Protocols Fall 2005. Lectures 7-8 Andreas Terzis

Internet Protocols Fall 2005. Lectures 7-8 Andreas Terzis Internet Protocols Fall 2005 Lectures 7-8 Andreas Terzis Outline Internet Protocol Service Model Fragmentation Addressing Original addressing scheme Subnetting CIDR Forwarding ICMP ARP Address Shortage

More information

CS 5480/6480: Computer Networks Spring 2012 Homework 4 Solutions Due by 1:25 PM on April 11 th 2012

CS 5480/6480: Computer Networks Spring 2012 Homework 4 Solutions Due by 1:25 PM on April 11 th 2012 CS 5480/6480: Computer Networks Spring 2012 Homework 4 Solutions Due by 1:25 PM on April 11 th 2012 Important: The solutions to the homework problems from the course book have been provided by the authors.

More information

Link Layer. 5.6 Hubs and switches 5.7 PPP 5.8 Link Virtualization: ATM and MPLS

Link Layer. 5.6 Hubs and switches 5.7 PPP 5.8 Link Virtualization: ATM and MPLS Link Layer 5.1 Introduction and services 5.2 Error detection and correction 5.3Multiple access protocols 5.4 Link-Layer Addressing 5.5 Ethernet 5.6 Hubs and switches 5.7 PPP 5.8 Link Virtualization: and

More information

Internetworking. Problem: There is more than one network (heterogeneity & scale)

Internetworking. Problem: There is more than one network (heterogeneity & scale) Internetworking Problem: There is more than one network (heterogeneity & scale) Hongwei Zhang http://www.cs.wayne.edu/~hzhang Internetworking: Internet Protocol (IP) Routing and scalability Group Communication

More information

Computer Networks. Main Functions

Computer Networks. Main Functions Computer Networks The Network Layer 1 Routing. Forwarding. Main Functions 2 Design Issues Services provided to transport layer. How to design network-layer protocols. 3 Store-and-Forward Packet Switching

More information

Internet Firewall CSIS 4222. Packet Filtering. Internet Firewall. Examples. Spring 2011 CSIS 4222. net15 1. Routers can implement packet filtering

Internet Firewall CSIS 4222. Packet Filtering. Internet Firewall. Examples. Spring 2011 CSIS 4222. net15 1. Routers can implement packet filtering Internet Firewall CSIS 4222 A combination of hardware and software that isolates an organization s internal network from the Internet at large Ch 27: Internet Routing Ch 30: Packet filtering & firewalls

More information

Data Link Protocols. Link Layer Services. Framing, Addressing, link access: Error Detection:

Data Link Protocols. Link Layer Services. Framing, Addressing, link access: Error Detection: Data Link Protocols Link Layer Services Framing, Addressing, link access: encapsulate datagram into frame, adding header, trailer channel access if shared medium MAC addresses used in frame headers to

More information

Network Simulation Traffic, Paths and Impairment

Network Simulation Traffic, Paths and Impairment Network Simulation Traffic, Paths and Impairment Summary Network simulation software and hardware appliances can emulate networks and network hardware. Wide Area Network (WAN) emulation, by simulating

More information

Names & Addresses. Names & Addresses. Hop-by-Hop Packet Forwarding. Longest-Prefix-Match Forwarding. Longest-Prefix-Match Forwarding

Names & Addresses. Names & Addresses. Hop-by-Hop Packet Forwarding. Longest-Prefix-Match Forwarding. Longest-Prefix-Match Forwarding Names & Addresses EE 122: IP Forwarding and Transport Protocols Scott Shenker http://inst.eecs.berkeley.edu/~ee122/ (Materials with thanks to Vern Paxson, Jennifer Rexford, and colleagues at UC Berkeley)

More information

Operating System Concepts. Operating System 資 訊 工 程 學 系 袁 賢 銘 老 師

Operating System Concepts. Operating System 資 訊 工 程 學 系 袁 賢 銘 老 師 Lecture 7: Distributed Operating Systems A Distributed System 7.2 Resource sharing Motivation sharing and printing files at remote sites processing information in a distributed database using remote specialized

More information

Communication Systems Internetworking (Bridges & Co)

Communication Systems Internetworking (Bridges & Co) Communication Systems Internetworking (Bridges & Co) Prof. Dr.-Ing. Lars Wolf TU Braunschweig Institut für Betriebssysteme und Rechnerverbund Mühlenpfordtstraße 23, 38106 Braunschweig, Germany Email: wolf@ibr.cs.tu-bs.de

More information

CSMA/CA. Information Networks p. 1

CSMA/CA. Information Networks p. 1 Information Networks p. 1 CSMA/CA IEEE 802.11 standard for WLAN defines a distributed coordination function (DCF) for sharing access to the medium based on the CSMA/CA protocol Collision detection is not

More information

DSR: The Dynamic Source Routing Protocol for Multi-Hop Wireless Ad Hoc Networks

DSR: The Dynamic Source Routing Protocol for Multi-Hop Wireless Ad Hoc Networks DSR: The Dynamic Source Routing Protocol for Multi-Hop Wireless Ad Hoc Networks David B. Johnson David A. Maltz Josh Broch Computer Science Department Carnegie Mellon University Pittsburgh, PA 15213-3891

More information

Network-Oriented Software Development. Course: CSc4360/CSc6360 Instructor: Dr. Beyah Sessions: M-W, 3:00 4:40pm Lecture 2

Network-Oriented Software Development. Course: CSc4360/CSc6360 Instructor: Dr. Beyah Sessions: M-W, 3:00 4:40pm Lecture 2 Network-Oriented Software Development Course: CSc4360/CSc6360 Instructor: Dr. Beyah Sessions: M-W, 3:00 4:40pm Lecture 2 Topics Layering TCP/IP Layering Internet addresses and port numbers Encapsulation

More information

BCS THE CHARTERED INSTITUTE FOR IT. BCS HIGHER EDUCATION QUALIFICATIONS BCS Level 5 Diploma in IT COMPUTER NETWORKS

BCS THE CHARTERED INSTITUTE FOR IT. BCS HIGHER EDUCATION QUALIFICATIONS BCS Level 5 Diploma in IT COMPUTER NETWORKS BCS THE CHARTERED INSTITUTE FOR IT BCS HIGHER EDUCATION QUALIFICATIONS BCS Level 5 Diploma in IT COMPUTER NETWORKS Friday 2 nd October 2015 Morning Answer any FOUR questions out of SIX. All questions carry

More information

DATA COMMUNICATIONS AND NETWORKING. Solved Examples

DATA COMMUNICATIONS AND NETWORKING. Solved Examples Page 1 of 10 DATA COMMUNICATIONS AND NETWORKING Solved Examples References: STA: Stallings, Data and Computer Communications, 6 th ed. TAN: Tannenbaum, Computer Networks, 4 th ed.) 1. Given the following

More information

Computer Networks and the Internet

Computer Networks and the Internet ? Computer the IMT2431 - Data Communication and Network Security January 7, 2008 ? Teachers are Lasse Øverlier and http://www.hig.no/~erikh Lectures and Lab in A126/A115 Course webpage http://www.hig.no/imt/in/emnesider/imt2431

More information

ECE/CS 372 introduction to computer networks. Lecture 13

ECE/CS 372 introduction to computer networks. Lecture 13 ECE/CS 372 introduction to computer networks Lecture 13 Announcements: HW #4 hard copy due today Lab #5 posted is due Tuesday June 4 th HW #5 posted is due Thursday June 6 th Pickup midterms Acknowledgement:

More information

:-------------------------------------------------------Instructor---------------------

:-------------------------------------------------------Instructor--------------------- Yarmouk University Hijjawi Faculty for Engineering Technology Computer Engineering Department CPE-462 Digital Data Communications Final Exam: A Date: 20/05/09 Student Name :-------------------------------------------------------Instructor---------------------

More information

Unit of Learning # 2 The Physical Layer. Sergio Guíñez Molinos sguinez@utalca.cl 2-2009

Unit of Learning # 2 The Physical Layer. Sergio Guíñez Molinos sguinez@utalca.cl 2-2009 Unit of Learning # 2 The Physical Layer Sergio Guíñez Molinos sguinez@utalca.cl 2-2009 Local Area Network (LAN) Redes de Computadores 2 Historic topologies more used in LAN Ethernet Logical Bus and Physical

More information

Chapter 3. TCP/IP Networks. 3.1 Internet Protocol version 4 (IPv4)

Chapter 3. TCP/IP Networks. 3.1 Internet Protocol version 4 (IPv4) Chapter 3 TCP/IP Networks 3.1 Internet Protocol version 4 (IPv4) Internet Protocol version 4 is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely

More information

CS 43: Computer Networks IP. Kevin Webb Swarthmore College November 5, 2013

CS 43: Computer Networks IP. Kevin Webb Swarthmore College November 5, 2013 CS 43: Computer Networks IP Kevin Webb Swarthmore College November 5, 2013 Reading Quiz IP datagram format IP protocol version number header length (bytes) type of data max number remaining hops (decremented

More information

Real-Time (Paradigms) (51)

Real-Time (Paradigms) (51) Real-Time (Paradigms) (51) 5. Real-Time Communication Data flow (communication) in embedded systems : Sensor --> Controller Controller --> Actor Controller --> Display Controller Controller Major

More information

TCP over Multi-hop Wireless Networks * Overview of Transmission Control Protocol / Internet Protocol (TCP/IP) Internet Protocol (IP)

TCP over Multi-hop Wireless Networks * Overview of Transmission Control Protocol / Internet Protocol (TCP/IP) Internet Protocol (IP) TCP over Multi-hop Wireless Networks * Overview of Transmission Control Protocol / Internet Protocol (TCP/IP) *Slides adapted from a talk given by Nitin Vaidya. Wireless Computing and Network Systems Page

More information

Data Link Protocols. TCP/IP Suite and OSI Reference Model

Data Link Protocols. TCP/IP Suite and OSI Reference Model Data Link Protocols Relates to Lab. This module covers data link layer issues, such as local area networks (LANs) and point-to-point links, Ethernet, and the Point-to-Point Protocol (PPP). 1 TCP/IP Suite

More information

Chapter 5: Sample Questions, Problems and Solutions Bölüm 5: Örnek Sorular, Problemler ve Çözümleri Örnek Sorular (Sample Questions):

Chapter 5: Sample Questions, Problems and Solutions Bölüm 5: Örnek Sorular, Problemler ve Çözümleri Örnek Sorular (Sample Questions): Chapter 5: Sample Questions, Problems and Solutions Bölüm 5: Örnek Sorular, Problemler ve Çözümleri Örnek Sorular (Sample Questions): What is Store-and-Forward packet switching? What is a connectionless

More information

Controlled Random Access Methods

Controlled Random Access Methods Helsinki University of Technology S-72.333 Postgraduate Seminar on Radio Communications Controlled Random Access Methods Er Liu liuer@cc.hut.fi Communications Laboratory 09.03.2004 Content of Presentation

More information

Transport Layer Protocols

Transport Layer Protocols Transport Layer Protocols Version. Transport layer performs two main tasks for the application layer by using the network layer. It provides end to end communication between two applications, and implements

More information

Objectives. The Role of Redundancy in a Switched Network. Layer 2 Loops. Broadcast Storms. More problems with Layer 2 loops

Objectives. The Role of Redundancy in a Switched Network. Layer 2 Loops. Broadcast Storms. More problems with Layer 2 loops ITE I Chapter 6 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 1 Objectives Implement Spanning Tree Protocols LAN Switching and Wireless Chapter 5 Explain the role of redundancy in a converged

More information

Data Center Networks, Link Layer Wireless (802.11)

Data Center Networks, Link Layer Wireless (802.11) Internet-Technologien (CS262) Data Center Networks, Link Layer Wireless (802.11) 1.4.2015 Christian Tschudin Departement Mathematik und Informatik, Universität Basel 6 Wiederholung Warum «multiple access»?

More information

802.11 standard. Acknowledgement: Slides borrowed from Richard Y. Yang @ Yale

802.11 standard. Acknowledgement: Slides borrowed from Richard Y. Yang @ Yale 802.11 standard Acknowledgement: Slides borrowed from Richard Y. Yang @ Yale IEEE 802.11 Requirements Design for small coverage (e.g. office, home) Low/no mobility High data-rate applications Ability to

More information

Computer Networks. Chapter 5 Transport Protocols

Computer Networks. Chapter 5 Transport Protocols Computer Networks Chapter 5 Transport Protocols Transport Protocol Provides end-to-end transport Hides the network details Transport protocol or service (TS) offers: Different types of services QoS Data

More information

Computer Networks. Definition of LAN. Connection of Network. Key Points of LAN. Lecture 06 Connecting Networks

Computer Networks. Definition of LAN. Connection of Network. Key Points of LAN. Lecture 06 Connecting Networks Computer Networks Lecture 06 Connecting Networks Kuang-hua Chen Department of Library and Information Science National Taiwan University Local Area Networks (LAN) 5 kilometer IEEE 802.3 Ethernet IEEE 802.4

More information

Future Internet Technologies

Future Internet Technologies Future Internet Technologies Traditional Internet Dr. Dennis Pfisterer Institut für Telematik, Universität zu Lübeck http://www.itm.uni-luebeck.de/people/pfisterer Internet Protocol v4 (IPv4) IPv4 Model

More information

Internetworking and Internet-1. Global Addresses

Internetworking and Internet-1. Global Addresses Internetworking and Internet Global Addresses IP servcie model has two parts Datagram (connectionless) packet delivery model Global addressing scheme awaytoidentifyall H in the internetwork Properties

More information

CSCI 491-01 Topics: Internet Programming Fall 2008

CSCI 491-01 Topics: Internet Programming Fall 2008 CSCI 491-01 Topics: Internet Programming Fall 2008 Introduction Derek Leonard Hendrix College September 3, 2008 Original slides copyright 1996-2007 J.F Kurose and K.W. Ross 1 Chapter 1: Introduction Our

More information

CS 457 Lecture 19 Global Internet - BGP. Fall 2011

CS 457 Lecture 19 Global Internet - BGP. Fall 2011 CS 457 Lecture 19 Global Internet - BGP Fall 2011 Decision Process Calculate degree of preference for each route in Adj-RIB-In as follows (apply following steps until one route is left): select route with

More information

Level 2 Routing: LAN Bridges and Switches

Level 2 Routing: LAN Bridges and Switches Level 2 Routing: LAN Bridges and Switches Norman Matloff University of California at Davis c 2001, N. Matloff September 6, 2001 1 Overview In a large LAN with consistently heavy traffic, it may make sense

More information

Guide to TCP/IP, Third Edition. Chapter 3: Data Link and Network Layer TCP/IP Protocols

Guide to TCP/IP, Third Edition. Chapter 3: Data Link and Network Layer TCP/IP Protocols Guide to TCP/IP, Third Edition Chapter 3: Data Link and Network Layer TCP/IP Protocols Objectives Understand the role that data link protocols, such as SLIP and PPP, play for TCP/IP Distinguish among various

More information

CCNA R&S: Introduction to Networks. Chapter 5: Ethernet

CCNA R&S: Introduction to Networks. Chapter 5: Ethernet CCNA R&S: Introduction to Networks Chapter 5: Ethernet 5.0.1.1 Introduction The OSI physical layer provides the means to transport the bits that make up a data link layer frame across the network media.

More information

Internetworking and IP Address

Internetworking and IP Address Lecture 8 Internetworking and IP Address Motivation of Internetworking Internet Architecture and Router Internet TCP/IP Reference Model and Protocols IP Addresses - Binary and Dotted Decimal IP Address

More information

Lecture Computer Networks

Lecture Computer Networks Prof. Dr. H. P. Großmann mit M. Rabel sowie H. Hutschenreiter und T. Nau Sommersemester 2012 Institut für Organisation und Management von Informationssystemen Thomas Nau, kiz Lecture Computer Networks

More information

RARP: Reverse Address Resolution Protocol

RARP: Reverse Address Resolution Protocol SFWR 4C03: Computer Networks and Computer Security January 19-22 2004 Lecturer: Kartik Krishnan Lectures 7-9 RARP: Reverse Address Resolution Protocol When a system with a local disk is bootstrapped it

More information

Network Security TCP/IP Refresher

Network Security TCP/IP Refresher Network Security TCP/IP Refresher What you (at least) need to know about networking! Dr. David Barrera Network Security HS 2014 Outline Network Reference Models Local Area Networks Internet Protocol (IP)

More information

Module 15: Network Structures

Module 15: Network Structures Module 15: Network Structures Background Topology Network Types Communication Communication Protocol Robustness Design Strategies 15.1 A Distributed System 15.2 Motivation Resource sharing sharing and

More information

Data Link Layer Overview

Data Link Layer Overview Data Link Layer Overview Date link layer deals with two basic issues: Part I How data frames can be reliably transmitted, and Part II How a shared communication medium can be accessed In many networks,

More information

TCP/IP Fundamentals. OSI Seven Layer Model & Seminar Outline

TCP/IP Fundamentals. OSI Seven Layer Model & Seminar Outline OSI Seven Layer Model & Seminar Outline TCP/IP Fundamentals This seminar will present TCP/IP communications starting from Layer 2 up to Layer 4 (TCP/IP applications cover Layers 5-7) IP Addresses Data

More information

Agenda. Distributed System Structures. Why Distributed Systems? Motivation

Agenda. Distributed System Structures. Why Distributed Systems? Motivation Agenda Distributed System Structures CSCI 444/544 Operating Systems Fall 2008 Motivation Network structure Fundamental network services Sockets and ports Client/server model Remote Procedure Call (RPC)

More information

Data Networking and Architecture. Delegates should have some basic knowledge of Internet Protocol and Data Networking principles.

Data Networking and Architecture. Delegates should have some basic knowledge of Internet Protocol and Data Networking principles. Data Networking and Architecture The course focuses on theoretical principles and practical implementation of selected Data Networking protocols and standards. Physical network architecture is described

More information

Module 2 Overview of Computer Networks

Module 2 Overview of Computer Networks Module 2 Overview of Computer Networks Networks and Communication Give me names of all employees Who earn more than $100,000 % ISP intranet % % % backbone satellite link desktop computer: server: network

More information

COMPUTER NETWORKS HANDOUTS LECTURERS # 01 45 PREPARED BY: HAMMAD KHALID KHAN. Copyright Virtual University of Pakistan

COMPUTER NETWORKS HANDOUTS LECTURERS # 01 45 PREPARED BY: HAMMAD KHALID KHAN. Copyright Virtual University of Pakistan COMPUTER NETWORKS (CS610) HANDOUTS LECTURERS # 01 45 PREPARED BY: HAMMAD KHALID KHAN 1 Table of contents Lecture No. 1...4 INTRODUCTION...4 Lecture No. 2...9 Motivation and Tools...9 Lecture No. 3...13

More information