Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Network tap wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Computer network wikipedia , lookup
Airborne Networking wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Internet protocol suite wikipedia , lookup
Deep packet inspection wikipedia , lookup
Piggybacking (Internet access) wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Southern Methodist University Fall 2003 EETS 8316/NTU CC745-N Wireless Networks Lecture 7: Mobile Data, Part II Instructor: Jila Seraj email: [email protected] http://www.engr.smu.edu/~jseraj/ tel: 214-505-6303 EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #1 Session Outline Review of last week More GPRS LAN Primer IP Primer EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #2 Review, Aloha Aloha is a wireless network designed in Hawaii and thus the name Aloha It was experimented in many way to find a good solution for wireless communication The system consisted of wireless devices communicating together using a communication satellite EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #3 Review, Aloha Aloha —Stations starts sending when they have something to send —Pure Aloha, no contention resolution, relies on timed-out acks, max throughput approximately 18% —Slotted Aloha, no contention resolution, relies on timed-out acks, only can start sending in the beginning of a slot, max through put approximately 36% EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #4 Review, Pure ALOHA Throughput — In equilibrium, throughput (rate of successfully transmitted frames) = rate of new transmissions, S S = GP0 where P0 = probability of successful transmission (no collision) — P0 depends on “vulnerable interval” for frame, 2T - transmission attempt at time 0 frame A - collision if starts in interval (-T,0) frame B frame C -T 0 EETS 8316/NTU TC 745, Fall 2003 - collision if starts in interval (0,T) time T SMU ENGINEERING #5 Review, Pure ALOHA P0 = Pr(no other frame in 2T interval) — Assume total number of frames in any interval t is also Poisson distributed, with average G: Pr(k transmissions in t) = (Gt)ke-Gt/k! then P0 = e-2G — By substitution, throughput is S = GP0 = Ge-2G — This is maximum at G = 0.5, where S = 1/2e = 0.184 (frames per interval T) • Pure ALOHA achieves low throughput EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #6 Review, Slotted ALOHA Slotted ALOHA is a modification to increase efficiency — Time is divided into time slots = transmission time of a frame, T — All stations are synchronized (e.g., by periodic synchronization pulse) — Any station with data must wait until next time slot to transmit — Any time slot with two or more frames results in a collision and loss of all frames – retransmitted after a random time EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #7 Review, Slotted ALOHA “Vulnerable interval” is reduced by factor of 2 to just T -T frame A - transmission attempt at time 0 frame B - collision if frame B was ready in interval (-T,0) 0 EETS 8316/NTU TC 745, Fall 2003 time T SMU ENGINEERING #8 Review, Slotted ALOHA Throughput P0 = Pr(no frames ready in previous time slot) = e-G — Now throughput is S = GP0 = Ge-G — This is maximum at G = 1, where S = 1/e = 0.368 (frames per interval T) • Slotted ALOHA doubles throughput of pure ALOHA EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #9 Primer: Slotted ALOHA Note that throughput is never very high Also, at high loads, throughput goes to 0 – a general characteristic of networks with shared resources — Number of empty time slots and successful slots decrease, number of collisions increase — Average number of retransmissions per frame increases — Average delay (from first transmission attempt to successful transmission) increases EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #10 Review, CSMA Carrier Sense Multiple Access = CSMA Sense the presence of carrier, sense the channel is free, send data, wait for Ack, resend if timed-out, if busy back off and try again. Max throughput 60% EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #11 Review, CSMA Family of CSMA protocols defined by rules for backing off with varying degrees of persistence — 1-persistent CSMA: stations are most persistent — P-persistent CSMA: persistence increases with value of p — Non-persistent CSMA: stations are not that persistent EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #12 Review, CSMA (Cont) Carrier Sense Multiple Access-Collision Detection (CSMA-CD) — Send when carrier is free, listen to detect collision. — CSMA-CA is the method of choice Carrier Sense Multiple Access-Collision Avoidance (CSMA-CA) — Uses two messages before transmission, RequestTo-Send (RTS) and Clear-To-Send (CTS) . — Method of choice for wireless LAN EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #13 Review, Mobile Data 2 main options for wireless packet data: —High speed wireless LANs (e.g., 802.11) —Low speed wide area services • Mobitex/RAM Mobile Data • CDPD (cellular digital packet data) • GPRS (general packet radio service) • ARDIS (advanced radio data information services) EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #14 Review, Mobile Data , Cont... ERMES (European Radio Message System) was standardized by ETSI early 1980. Originated by Swedish Telecom (now Telia Mobitel) as private mobile alarm system for field personnel Development Continued by MOA (Mobitex Operators Association) and Ericsson Mobile Communications http://www.ericsson.com/wireless/products/ mobsys/mobitex/mobitex.shtml) EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #15 Review, Mobitex/RAM Mobile Data Mobitex - widely accepted de facto standard for wireless packet data —Developed by Swedish Telecom (now Telia Mobitel) as private mobile alarm system for field personnel —Development Continued by MOA (Mobitex Operators Association) and Ericsson —1986 Commercial operation in Sweden —Now widely deployed in Europe, US, Australia EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #16 Review, Mobitex , Cont... 1986 Commercial operation in Sweden Now widely deployed in Europe, US, Australia In US, RAM Mobile Data, a joint venture between RAM broadcasting and Cingular. http://www.cingular.com/business/mobitex_ map EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #17 Review, Mobitex, Major features, Cont... Major features —Seamless roaming —Store and forward of messages —Dependability above 99.99% —Interoperability and many connectivity options —Capacity to support millions of subscribers —Security against eavesdropping EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #18 Review, Mobitex, Major features, Cont... Major features —Packet switching occurs at lowest level of system hierarchy - relieves backbone traffic —Packet multicasting (to multiple recipients) is handled by network —Closed User Group (CUG) feature —Frequency depends of the country, 900 MHZ in US and 450 in most others. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #19 Review, Mobitex - Architecture NCC NCC: network Control center Main exchange Regional switch Local switch Regional switch Local switch Base stations use 1-4 frequencies each 8 kb/s FEP EETS 8316/NTU TC 745, Fall 2003 Local switch covers a service area, each with 10-30 frequency pairs SMU ENGINEERING #20 Review, Mobitex - Architecture , Cont... Network Control Center (NCC), provides network management functions Main Exchange and Regional Switch have basically the same function, but they reside on different level of network hierarchy. —Packet switching —Protocol handling (X.25 and HDLC) —Subscriber data for nodes below —Multiple connection to other switches —Alternate routing EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #21 Review, Mobitex - Architecture , Cont... Local Switches, similar to regional switches. Also handles —Communication with base stations —Connection to host computers via FEP (Front-End-Processor) FEP provides —Protocol conversion to hosts supporting X.25, TCP/IP, and SNA —Convert connectionless protocol to connection oriented protocol. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #22 Review, Mobitex, protocol architecture Applications 4-7 Applications 3 2 1 MPAK MPAK MPAK MASC MASC RS232 RS232 GMSK Mobile EETS 8316/NTU TC 745, Fall 2003 ROSI ROSI HDLC GMSK X.21 Base Station Radio modem SMU ENGINEERING MPAK HDLC X.25 X.21 X.21 Local switch MPAK X.25 X.21 Server #23 Review, Mobitex - Network Layer Network layer packet = MPAK (Mobitex PAcKet) —User data, segmented into packets of maximum 512 bytes —Alert messages (high priority) —Network layer signaling, e.g., login/logout requests EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #24 Review, Mobitex - Network Layer , Cont... MPAK header Contains —Identification of application that generated packet —Class (significance) —Type (priority) —Whether can be stored in recipient’s mailbox (temporary storage) if cannot be delivered immediately EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #25 Review, Mobitex - Data Link Layer Data link layer protocol is MASC (Mobitex Asynchronous Communication) MPAK delivers user packets plus addressing and network data to MASC Data link layer functions —Selection of most suitable base station —Retransmissions of frames lost on the radio channel (stop-and-wait ARQ) —Channel access procedure - variation of slotted ALOHA EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #26 Review, Mobitex - Data Link Layer , Cont... —Base station initiates a Contention cycle by sending a FREE frame downlink —Mobile stations can Contend for number of free timeslots by choosing a random slot and transmitting during that slot —If mobile has more data than fits in a time slot, it can start by sending a short access request message —Base station grants access to requesting mobile stations after a free cycle EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #27 Review, Mobitex - Data Link Layer , Cont... ROSI (Radio Signaling), takes care of transmission towards Mobitex infrastructure GMSK (Gaussian Minimum Shift Keying) X.21 and X.25 are the packet data communication protocols used for many years. Good for connectionless short bursts of data. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #28 Review, Mobitex - Radio Interface , Cont... —Data link also handles channel access procedure - variation of slotted ALOHA • Base station broadcasts a FREE frame indicating a free cycle, including number and length of time slots in the free cycle • Mobile terminal chooses a random timeslot in next free cycle and transmits its frame then EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #29 Review, Mobitex - common functions Requires subscription —individual —groups of terminals —host computer —groups of host computers Security —Password based —ESN —CUG (Closed User Group) EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #30 Review, Mobitex - Mobility Mobiles monitor and evaluate signals from other base stations At power-up, mobile tries to register with the last base station in its memory, if possible Base station provides necessary information, such as acceptable signal strength, neighbor list,etc periodically. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #31 Review, CDPD Cellular digital packet data (CDPD): connectionless packet-switched data designed to work with an analog cellular system (e.g., AMPS) —Originated by IBM as packet-switching overlay to analog cellular system, early 1990s developed by CDPD Forum, now developed by Wireless Data Forum —Overlay system uses unused bandwidth in cellular system and existing AMPS functions and capabilities EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #32 Review, CDPD , Cont... CDPD is a value added system. Other users do not need to be aware of its presence in the network. This has implications: CDPD transmission must not interfere with transmission of other services No dedicated bandwidth, uses only idle time between users, channel-hop No dedicated Control channel, all Control is in-band. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #33 Review, CDPD , Cont... CDPD is transparent to voice system —To avoid collisions with voice calls, CDPD uses channel hopping when antenna detects a power ramp-up (indicating initiation of voice traffic) —Base station closes current transmission channel within 40 msec and new idle channel is chosen to hop to EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #34 Review, CDPD , Cont... CDPD is transparent to voice system —New channel may or may not be announced before old channel closed • If not announced, mobile terminal must hunt around set of potential CDPD channels to find new one EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #35 Review, CDPD - Network Architecture Internet or other networks IS IS MD-IS Intermediate systems = generic packet switches in backbone network IS Mobile data intermediate systems = packet switches with mobility management capabilities MD-IS Mobile data base station = base station EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #36 Review, CDPD - Network Architecture , Cont... Mobile end system (MES): may be handheld PDA to laptop to terminal —Stationary or mobile, but treated as potentially mobile —Network Continually tracks location to ensure that packets are delivered even if physical location changes —May sleep - messages are then queued in network EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #37 Review, CDPD - Network Architecture , Cont... Mobile data base station (MDBS): mobile data link relay —Supports CDPD MAC and data link protocols across radio interface —Handles radio channel allocation, interoperation of channels between CDPD and voice calls, tracks busy/idle status of channels —Often co-located with AMPS base stations (shares AMPS antenna) EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #38 Review, CDPD - Network Architecture , Cont... Mobile data intermediate system (MD-IS) —Mobility management: location tracking, registration, authentication, encryption • Exchange location information by CDPDspecific mobile network location protocol (MNLP) • “Mobile home function” (MHF) in home network maintains current location info for a mobile end system and forwards packets EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #39 Review, CDPD - Network Architecture , Cont... Mobile data intermediate system (MD-IS) • “Mobile serving function” (MSF) in visited network maintains info for visiting mobile end systems in its area (through registration process) —Accounting and billing (based on usage) EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #40 Review, CDPD , Cont... CDPD network layer —Internet protocol (IP and mobile IP) and connectionless network protocol (CLNP, OSI’s equivalent of IP) are supported —Backbone network of intermediate systems (IS) provides connectionless packet routing • IS can be off-the-shelf IP or CLNP routers EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #41 GPRS - Network Architecture Internet or other networks HLR SGSN MSC/ VLR GGSN Gateway GSN = packet switch interworks with other networks SGSN Serving GPRS support node = packet switch with mobility management capabilities BSC/PCU GPRS makes use of existing GSM base stations EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #42 GPRS , Cont... GSM Release’97 introduced general packet radio service (GPRS) for bursty data Make use of existing GSM network equipment and functions In Contrast to CDPD, it is integrated into GSM, i.e. dedicated Control channel and data channel. Requires two new network element, GGSN and SGSN EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #43 GPRS , Cont... SGSN = Serving GPRS Support Node —Ciphering —Authentication, IMEI check —Mobility Management —Logical Link Management towards mobile station —Packet routing and transfer —Connection to HLR, MSC, BSC and SMSMC EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #44 GPRS , Cont... GGSN = Gateway GPRS Support Node — External interfaces — Routing GPRS register maintains GPRS subscriber data and routing information. Normally it is integrated in GSM HLR PCU (Packet Control Until) is collocated with BSC. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #45 GPRS , Cont... Three class of mobile terminals —Class A: Operates GPRS and Circuit switched service simultaneously —Class B: Monitors the Control channels of GPRS and GSM simultaneously but can operate one set of services at a time —Class C: Only CS or GPRS capable. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #46 GPRS , Cont... For mobility management a new concept is defined, Routing Area RAI = MCC +MNC + LAC + RAC EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #47 GPRS Features Packet data can use up to 8 timeslots to provide 115.2 kb/s Suitable for bursty data such as web browsing EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #48 GPRS Interfaces EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #49 GPRS – Data Connection GPRS data connection starts with Attach and ends with Detach. Attach is the phase when the mobile informs the network of its intention to create a data connection At conclusion of Attach, SGSN is ready to set up data services on behalf of the mobile user. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #50 GPRS – Data Connection, Cont… Detach is the phase when mobile terminates the connection. GPRS requires subscription EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #51 GPRS Attach Scenario BTS BSS SGSN HLR IMSI, P_TMSI+OLD RAI… Update Location Insert Subs. Data Insert Data Ack Update Location GPRS Attach Accepted EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #52 GPRS – Mobile Attach Scenario Mobile sends Attach message. This message contains P-TMSI or TMSI. It also contains NSAPI (Network Service Point Identifier) SGSN contacts HLR to verify if the user is permitted to use the service After authentication, SGSN send back Attach Accepted together with a TLLI (Temporary Logical Link Identity) EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #53 GPRS – Mobile Attach Scenario A database in SGSN is now populated with mobile identity and TLLI. TLLI is used by logical link controller in the SGSN. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #54 GPRS – Setting Up Packet Data Session After attach the mobile is known by SGSN and have an identity there, but it is not known to the external network. First it needs to create an identity for itself by performing a procedure called PDP Context Activation. PDP is Packet Data Protocol, which could be IP or x.25 protocol. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #55 PDP Context Activation BTS BSS SGSN Activate PDP Context Create PDP Context Request NASPI, PDP type PDP, QoS,APN Activate PDP Context Accepted PDP Type, PDP Address, QoS EETS 8316/NTU TC 745, Fall 2003 GGSN SMU Create PDP Context Response PDP Address, QoS ENGINEERING #56 PDP Context Activation, Cont.. Mobile requests PDP Context Activation Based on the information provided, SGSN determines which GGSN to connect to. The GGSN should be capable to support the PDP requested by mobile GGSN updates its data base and assign a TID to the mobile and SGSN SGSN updates its data base with the GGSN address and TID. It then send PDP Context Activation Accepted message to mobile EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #57 Actually Sending Data After PDP Context Activation the mobile is known to the external packet network (PDN) When SGSN receives data from mobile, it looks up its database and relate the TLLI to NSAPI. SGSN and SNDPC pad the IP packet and replace the destination address with GGSN IP address and sets GTP header to TID EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #58 Actually Sending Data, Cont… Packets are then sent to GGSN with SGSN as sender At GGSN, the additional information is removed to get the original packet . The packet can now be routed to its intended destination. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #59 GPRS Terminology APN = Access Point Name PDP = Packet Data Protocol NSAPI = Network Service Area Point Identifier TLLI = Temporary Logical Link Identifier LLC = Logical Link Control TID = Tunnel Identifier EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #60 GPRS Terminology PDN = Packet Data Network SNDCP = Sub network Dependent Convergence Protocol GTP = GPRS Tunneling Protocol EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #61 Local Area Networks Primer General characteristics —Small number of stations (e.g., tens hundreds) —Diameter of a few kilometers (e.g., building) —High bandwidth of several Mb/s or more —Single (private) ownership —Homogeneous user community —Random contention for a shared medium (radio) follows a medium access control (MAC) protocol EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #62 LAN Primer, Cont —Why not fixed-assignment multiple access? • Each station could use separate frequency bands (FDMA), time slots (TDMA), or codes (CDMA) • No contention but inefficient because LAN data is typically bursty —Topology is usually bus or dual bus, ring or dual ring, star • Logical topology can be different from physical topology EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #63 LAN Primer, Cont Ring Bus Star Dual bus EETS 8316/NTU TC 745, Fall 2003 Dual ring SMU ENGINEERING #64 LAN Primer, MAC Protocols MAC protocol is a sub layer in data link layer For LANs, data link layer = logical link control (LLC) sub layer + MAC sub layer network LLC data link MAC physical EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING - defines how stations access the shared medium #65 LAN Primer, Cont MAC Protocol, Cont.. —LLC sub layer builds on MAC sub layer to provide medium-independent communication service to higher layers (makes MAC sub layer transparent) —LLC can provide appearance of connectionless or connection-oriented service EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #66 LAN Primer, MAC Protocol, Cont.. • Connectionless service treats each message independently –No connection setup and no sequential order • Connection-oriented service requires connection setup and preserves sequential order of messages EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #67 LAN Primer, Token Passing Token ring and token bus — Every station connected to the bus is given a token — The token is passed according to order — When a station has something to send, it keeps the token until it is done, before sending it to the next station. It is fair and has no contention The system encounters delays for sending the token. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #68 LAN Primer, Token Passing, Cont… Token passing is another technique to eliminate contention (collisions) Token is short packet representing permission to transmit — Token is passed from station to station according to an arranged order defining a logical token ring topology — A station with the token can transmit for a limited time — After transmission, token is sent to next station in ring EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #69 LAN Primer, Polling Objective to eliminate random contention (collisions) which reduces throughput of system Polling is centralized control — One station will periodically poll other stations to see if they have data to transmit — A polled station may transmit data, otherwise controller will poll next station in a list Polling involves exchange of control messages between stations and controller EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #70 LAN Primer, Polling, Cont)… —Efficient only if (1) roundtrip propagation delay is small (2) overhead due to control messages is small (3) user population is not large and bursty —As population increases with more bursty users, performance of polling degrades Polling is used widely in wired network environments but not popular in wireless networks EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #71 LAN Primer, Token passing, Cont Commonly used in wired LANs (IEEE 802.4 token bus and 802.5 token ring), token passing has not found much adoption in wireless networks Overhead is increased to improve throughput under heavy load — Issue is efficiency EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #72 Internet Primer Internet is a set of rules that helps different network to connect to each other. Thus the name internet. Any network connected to a internet capable router can be connected to other internet capable routers. A host is a hardware and software entity connected to a local loop and served by a router. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #73 Internet Primer (cont) Every host has an IP address. A node with multiple connection to the internet has multiple IP addresses. The IP address is used for sending information to the host. IP address consists of 32 bits and is normally shown as a doted decimal notation. Every decimal indicates one octet, for example C013F112 is shown as 192.19.241.18 EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #74 Internet Primer (cont) Internet can be seen as collection of network with diverse physical layer and application connected to each other by routers. Nodes can join and leave the network at anytime. The service provided in the internet is “best effort”, in other words, no quality of service is guaranteed. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #75 Internet Primer, TCP/IP Reference Model Termial Emulator Application TELNET Web Browser FTP HTTP Remoter File Access User Interfaces RIP Application protocols TCP NFS UDP Operating System ICMP Network prorocols Internet Protocol (IP) 802.3 UTP PPP RS-232 Transport Protocols FDDI Fiber Link prorocols Device Driver and Hardware Network EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #76 Internet Primer, Abbreviations TCP Transmission Control Protocol IP Internet Protocol FTP File Transfer Protocol UDP User Datagram Protocol RIP Routing Information Protocol EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #77 Internet Primer, Abbreviations DNS Domain Name Server ICMP Internet Control Message Protocol PPP Point-to-Point Protocol EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #78 Internet Primer, Components of IP Header Vers IHL Type of Total length Service Identification Flags Fragment Offset Time to Live Protocol Header Checksum Source Address Destination Address IP Options Transport Layer (eg TCP) Header Application Layer (eg HTTP) Header Application Layer Data (eg Web Page) EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #79 Internet Primer, IP Address Every node connected to the IP has an IP address. An address is 32 bits and contains a prefix and a host number In most cases, host numbers are assigned dynamically. Each router maintains a routing table. Addressing in the internet is not hierarchical. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #80 Internet Primer, Routing Routing in Internet is distributed. Routing table in a router is used for forwarding a packet towards its destination. Three types of entry in a routing table • Host specific. 32 bits specifies an IP Destination Address. • Network specific, 1< prefix length<31. Defines the network address • Default route, prefix =0, only if no matches are found in the table, this route is used. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #81 Internet Primer, Routing If no routes matches, the node sends ICMP Unreachable message error to the source packet. Every node on the same link must have identical network prefix. DNS (Domain Name Server) are used to translate alphanumeric address to 32 bits IP address. Entries in the DNS can be manual or dynamic, almost the same way a host gets IP address. EETS 8316/NTU TC 745, Fall 2003 SMU ENGINEERING #82