1. Polytechnic University  M. Veeraraghavan 1 Wireless & Mobile Networking Prof. Malathi Veeraraghavan Elec. & Comp. Engg. Dept/CATT Polytechnic University mv@poly.edu Welcome to the first class of EL604: Wireless & Mobile Networking

2. Polytechnic University  M. Veeraraghavan 2 Outline Review of basic concepts in networking –Prerequisite: A first course on networking –Communication links and switches –Types of networks –Shared links: media access control (MAC) How does the “wireless” dimension change the networking problem? How does the “mobile” dimension change the networking problem? “Mobile” vs. “Portable”

3. Polytechnic University  M. Veeraraghavan 3 What is a communication network? Simplest “network” –Single link between two pieces of end-user equipment (e.g., PC, telephone) End-user equipment End-user equipment –Types of communication links Twisted pair Coaxial cable Optical fiber Wireless links –Radio frequencies –Infra-red frequencies

4. Polytechnic University  M. Veeraraghavan 4 What is needed to send data on communication links? Error control –Error detection: Parity checks, Checksum, Cyclic Redundancy Code (CRC) –Error correction: ARQ (Automatic Repeat reQuest) FEC (Forward Error Correction) Flow control: handles rate mismatch between sender and receiver –x-ON/x-OFF –Window based flow control –Rate based flow control

5. Polytechnic University  M. Veeraraghavan 5 Switches Connect multiple links and route traffic from one link to another End-user equipment End-user equipment End-user equipment End-user equipment Switch

6. Polytechnic University  M. Veeraraghavan 6 Why use a switch? If there are N endpoints (end-user equipment), then how many links are needed for full mesh connectivity? How many physical links are needed if these endpoints are connected through a switch?

7. Polytechnic University  M. Veeraraghavan 7 Answers Number of direct links needed to connect N nodes is N links – since we only need one link from an endpoint to a switch

8. Polytechnic University  M. Veeraraghavan 8 Cost of using a switch? Switch cost Can all endpoints have full connectivity at all times to all other endpoints? –Yes, with multiplexing on the links

9. Polytechnic University  M. Veeraraghavan 9 Concept of multiplexing Time division multiplexing –Allows data from different sessions to be combined at different times on to the same line –How many DS0s in a T1? Wavelength division multiplexing –Difference between FDM (Frequency Division Multiplexing) and WDM? –Relation between frequency and wavelength

10. Polytechnic University  M. Veeraraghavan 10 Answers 24 DS0s in a T1 Term WDM is the same as FDM at optical frequencies – see EM spectrum chart Speed of light c = f : wavelength; f: frequency

11. Polytechnic University  M. Veeraraghavan 11 Transceiver rate Rate of transmission and reception at endpoints and the switch –Needs to be sufficient for “full mesh” connectivity “all the time” –e.g., if DS0s used between endpoints in full mesh network, then T1s can be used in 25 endpoint network with a switch for full mesh connectivity

12. Polytechnic University  M. Veeraraghavan 12 Types of switches Circuit switches: Position-based switching –Switch consults a table to determine output port on which to send data bits based on their arriving position “Position”: Interface (space), time slot and/or wavelength –Space division switch: switch based on input interface –Time division switching: interface + time slot –Wavelength division switching: interface + wavelength –No buffers Packet switches: Label-based switching –Switch consults a table to determine output port on which to send the packet based on value of label (in packet header) –Label could be changed on outgoing port or could stay the same –Have buffers to hold packets

13. Polytechnic University  M. Veeraraghavan 13 Network of switches Expand 1-switch network to a multi-switch network Why not build one gigantic switch? –Scalability limitations End-user equipment End-user equipment Switch End-user equipment Switch

14. Polytechnic University  M. Veeraraghavan 14 Different types of networks A network is defined by its “switching mode” and its “networking mode” Circuit switching vs. packet switching –Circuit-switching: switching based on position (space, time, ) of arriving bits –Packet-switching: switching based on information in packet headers Connectionless vs. connection-oriented networking: –CL: Packets routed based on address information in headers –CO: Connection set up (resources reserved) prior to data transfer Packet-switching Circuit-switching Switching modes Connectionless Connection-oriented Networking modes ATM, X.25 IP, SS7 MPLS IP + RSVP Telephone network, SONET/SDH, WDM

15. Polytechnic University  M. Veeraraghavan 15 Types of data transfers Sending end Consuming end Live Stored Live Stored Interactive/ Live streaming Recording Stored streamingFile transfers An application could consist of different types of data transfers —An http session has an interactive component, but could also have a non-real-time transfer

16. Polytechnic University  M. Veeraraghavan 16 Types of data transfers Sending end Consuming end Live Stored Live Stored Interactive/ Live streaming Recording Stored streamingFile transfers An application could consist of different types of data transfers —An http session has an interactive component, but could also have a non-real-time transfer

17. Polytechnic University  M. Veeraraghavan 17 Matching applications & networks Data transfers Non-real-time (stored at sender and receiver ends) Real-time (consumed or sent live) Interactive (two-way) (consumed and sent live) e.g. telephony, telnet, ftp, http Streaming (one-way) (consumed live; sent from live or stored source) e.g. radio/TV broadcasts Recording (one-way) (stored at receiver end; sent from live source); e.g. Replay Short transfers (e.g. short email) Long transfers (e.g. large image, audio, video or data) Ideal networks Connectionless networks Circuit-switched networks Packet-switched CO networks

18. Polytechnic University  M. Veeraraghavan 18 Congestion control What is it? –The purpose of a network is to allow sharing of resources –This means if demand is high, there could be competition for resources from multiple users –What are network resources: Link capacity (bandwidth) Switch buffer space (only in packet switches)

19. Polytechnic University  M. Veeraraghavan 19 Congestion control In CO networks –Congestion control: mostly preventive –Connection Admission Control (CAC) Check availability of bandwidth and buffer resources before admitting a connection CS CO networks: congestion will not occur once circuits are admitted PS CO networks: congestion can occur after connection is admitted if connection admission is based on statistical multiplexing –Have some supplemental reactive congestion control scheme

20. Polytechnic University  M. Veeraraghavan 20 Congestion control In CL networks –Have packet switches detect congestion and send reactive messages asking sender to slow down –e.g., datagram routers in SS7 networks send such messages; SRP (Spatial Reuse Protocol) switches in 802.17 MANs send such messages –IP routers implement Explicit Congestion Notification (ECN) procedures

21. Polytechnic University  M. Veeraraghavan 21 End-to-end path Transport protocols –Ensure reliable transfer across a communication path consisting of many links (“zero” loss) –OR ensure delay-controlled path across a communication path consisting of many links –Error control and flow control –Delay control (e.g., RTP) –Congestion control and connection control – special in TCP

22. Polytechnic University  M. Veeraraghavan 22 Applications Most Internet applications are client-server based Web server End-user equipment Network Web clients (Usually runs on fixed hosts) Network End-user equipment Email-sending clients (outlook, messenger) Outgoing email servers (pop, imap) Network End-user equipment Email-receiving clients (outlook, messenger) Incoming email servers (smtp)

23. Polytechnic University  M. Veeraraghavan 23 Protocol Stacks OSI model: two more layers between AL and TL –Session layer and presentation layer PHY: Physical; DLL: Data Link Layer; NL: Network Layer; TL: Transport Layer; AL: Application Layer DLL NL TL AL PHY Endpoint Switch NL DLL PHY DLL IP TCP/UDP AL PHY Endpoint Switch NL DLL PHY DLL

24. Polytechnic University  M. Veeraraghavan 24 Example protocols AL protocols: http, smtp, ftp, PCM voice TL protocols: TCP, UDP, RTP NL protocols: IP, ATM DLL protocols: PPP, HDLC PHY protocols: DS0, DS1 Ethernet: PHY+DLL+NL

25. Polytechnic University  M. Veeraraghavan 25 Functions of protocol layers PHY: sends bits across a link DLL: error control and flow control on a link NL: switching (routing), multiplexing, congestion control TL: error control and flow control on an end-to-end basis AL: Functions specific to the application

26. Polytechnic University  M. Veeraraghavan 26 Congestion control and connection control in TCP IP routers did not implement ECN until recently –TCP performs congestion control –Senses whether network switches (routers) are congested or not –Adjusts rate accordingly –Slow start and congestion avoidance Concept of a “connection” at the TL –End hosts maintain state information regarding a TCP connection to track sequence numbers and ACKs –Connection open (SYN) and close (FIN) procedures –Contrast with a “connection” at the NL, where each switch maintains state about the connection

27. Polytechnic University  M. Veeraraghavan 27 User plane, control plane, and management plane Management plane: consists of all the protocols needed to “configure” data tables for the operation of the network –For example, protocols for routing data dissemination (distributed or centralized) –Other functions: performance, fault mgmt., accounting, security Control plane: –Connection control protocols in CO networks, this includes connection setup at each switch (connections at the network layer) in CL networks, this includes connection setup only at the endpoints (connections at the transport layer, if the TL protocol is reliable) –Call control protocols User plane: protocols for the actual flow of data

28. Polytechnic University  M. Veeraraghavan 28 Routing protocol in all three types of networks - Phase 1 Host A Host B I IV V III II Routing protocol Dest. Next hop III-* IV Dest. Next hop III-* III Dest. Next hop B B Routing tables Routing protocols exchange topology/loading/reachability information Routes to destinations are precomputed and stored in routing tables

29. Polytechnic University  M. Veeraraghavan 29 Signaling protocol for NL connection setup in a PS CO network - Phase 2 Connection setup consists of each switch on the path –Route lookup for next hop node to reach destination –CAC (Connection Admission Control) for buffer and BW –Writing the input/output label mapping tables and programming the scheduler Host A Host B I IV V III II Connection setup a b c a b c d dc a b IN Port /Label OUT Port/Label a/L1 c/L2 IN Port /Label OUT Port/Label a/L2 c/L1 IN Port /Label OUT Port/Label d/L1 b/L3 Connection setup (B) Connection setup Virtual circuit

30. Polytechnic University  M. Veeraraghavan 30 Signaling protocol for NL connection setup in a CS CO network - Phase 2 Connection setup consists of each switch on the path –Route lookup for next hop node to reach destination –CAC (Connection Admission Control) for BW (note: no buffers) –Writing the port/timeslot/  mapping table Host A Host B I IV V III II Connection setup a b c a b c d dc a b IN Port /Timeslot OUT Port/Timeslot a/1 c/2 IN Port /Timeslot OUT Port/Timeslot a/2 c/2 IN Port /Timeslot OUT Port/Timeslot d/2 b/1 Connection setup (B) Connection setup Circuit

31. Polytechnic University  M. Veeraraghavan 31 TL connection setup in a CL PS network - Phase 2 Notion of transport layer connections –Exchange initial sequence numbers end-to-end to allow for ARQ (Automatic Repeat reQuest) based error correction, i.e., retransmissions in case of errors Host A Host B I IV V III II Dest. Next hop B II Dest. Next hop B III Dest. Next hop B B Routing tables SYN ACK

32. Polytechnic University  M. Veeraraghavan 32 User-plane packet forwarding in a PS CO network - Phase 3 Labels are VPI/VCIs in ATM Labels are translated from link-to-link Host A Host B I IV V III II a b c a b c d dc a b L2 L1 L3 IN Port /Label OUT Port/Label a/L1 c/L2

33. Polytechnic University  M. Veeraraghavan 33 User-plane actions in a circuit-switched network - Phase 3 Bits arriving at switch I on time slot 1 on port a are switched to time slot 2 of port c Host A Host B I IV V III II a b c a b c d dc a b 12 1212 12 OUT Port/Timeslot IN Port /Timeslot a/1 c/2

34. Polytechnic University  M. Veeraraghavan 34 User-plane packet forwarding in a CL PS network - Phase 3 Packet headers carry destination host address (unchanged as it passes hop by hop) Each CL packet switch does a route lookup to determine the outgoing port/next hop node Host A Host B I IV V III II a b c a b c d dc a b B B BB

35. Polytechnic University  M. Veeraraghavan 35 Addressing Where are endpoint addresses used: –In CL PS networks, endpoint addresses are carried in packet headers –In CO networks, be it PS or CS, endpoint addresses are carried in connection setup messages

36. Polytechnic University  M. Veeraraghavan 36 Summarized addresses What are summarized addresses? Why summarize addresses?

37. Polytechnic University  M. Veeraraghavan 37 Summarized addresses What are summarized addresses? –An address that represents a group of endpoint addresses –e.g., all 212 numbers, 128.238 IP addresses Why summarize addresses? –Reduces routing table sizes – hold one entry for a summarized address instead of a large number of individual addresses –Reduces routing message lengths that convey reachability information

38. Polytechnic University  M. Veeraraghavan 38 Examples of signaling protocols SS7 (Signaling System No. 7) network (with its SS7 protocol stack) carries signaling messages to set up and release circuits in a telephone network

39. Polytechnic University  M. Veeraraghavan 39 Examples of routing protocols In the Internet: –Link-state routing protocols, such as Open Path Shortest First (OSPF) –Distance-vector based routing protocols, such as Routing Information Protocol (RIP) In telephone networks: –Real-Time Network Routing (RTNR)

40. Polytechnic University  M. Veeraraghavan 40 Examples of addressing schemes Internet –4-byte IP addresses Telephone networks –8-byte E.164 address (telephone number) ATM networks –20-byte ATM End System Address (AESA)

41. Polytechnic University  M. Veeraraghavan 41 Broadcast links Wireless Copper: ethernet hubs Optical fiber: Passive star couplers Ethernet hub or WDM Passive Star Coupler Blind broadcast Ethernet switch (packet switch) Dest: A A

42. Polytechnic University  M. Veeraraghavan 42 MAC protocols Medium Access Control (MAC) protocols are used in broadcast links to allow a node to access medium and send information As if “switch” is in endpoints Wasteful of resources because all endpoints receive all packets End-user equipment A End-user equipment B End-user equipment C To B B’s MAC layer checks destination address to determine whether the packet should be “switched” to the application or dropped C’s MAC layer checks destination address to determine whether the packet should be “switched” to the application or dropped

43. Polytechnic University  M. Veeraraghavan 43 Outline Review of basic concepts in networking –Prerequisite: A first course on networking –Communication links and switches –Types of networks –Shared links: media access control (MAC)  How does the “wireless” dimension change the networking problem? How does the “mobile” dimension change the networking problem? “Mobile” vs. “Portable”

44. Polytechnic University  M. Veeraraghavan 44 The “wireless” dimension Naturally broadcast medium Poor link quality Low power

45. Polytechnic University  M. Veeraraghavan 45 Protocol impact Need a MAC protocol to share the “naturally broadcast” wireless medium High error rate because of the poor link quality –Need link-level error correction Low power causes high error rate

46. Polytechnic University  M. Veeraraghavan 46 Outline Review of basic concepts in networking –Prerequisite: A first course on networking –Communication links and switches –Types of networks –Shared links: media access control (MAC) How does the “wireless” dimension change the networking problem?  How does the “mobile” dimension change the networking problem? “Mobile” vs. “Portable”

47. Polytechnic University  M. Veeraraghavan 47 Portable vs. mobile A portable end user device is one that can be removed easily from its network point of attachment and connected to a different point in the network –usually nodes that run “client” software not server A mobile end user device is one that can be moved while engaged in a communication session

48. Polytechnic University  M. Veeraraghavan 48 Impact of “portable” nodes When a node connects to some switch (router) of a network, it should be assigned an endpoint address derived from the network address of switch –Allows for routing information in the rest of the network to not require an update –e.g., DHCP (Dynamic Host Configuraion Protocol) @Home Poly network R My laptop 24.3 R get address address: 24.3.5.10 yahoo web server Dest: yahoo; Src: 24.3.5.10 My laptop Dest: 24.3.5.10; Src: yahoo 128.238 get address address: 128.238.24.5 Dest: yahoo; Src: 128.238.24.5 Dest: 128.238.24.5; Src: yahoo

49. Polytechnic University  M. Veeraraghavan 49 Node: client or a server If the node that is portable is a client, i.e., no other host tries to reach this node, then this solution of it obtaining a temporary address works. But in cellular telephone network, this is not applicable because all endpoints can be “called” “Server” receives calls/session requests “Client” only makes calls, initiate sessions

50. Polytechnic University  M. Veeraraghavan 50 What happens if the server (called end) moves? The server is known to all nodes in the network by some address If the server changes its point of connection to the network, its location should be “managed” This is the problem of location management. Any ideas for how to solve this problem?

51. Polytechnic University  M. Veeraraghavan 51 Location management problem in IP networks 128.238.42 Host A.110 R1 R2 R4 Host B 110.54.66.11 Host C DestNext-hop 128.238.42 110.54.66 R2 R4 R3 R5 Host A 128.238.42.110 To A How is the IP packet destined to A delivered?

52. Polytechnic University  M. Veeraraghavan 52 Location management in cellular telephone networks How is a call delivered to A? S1 S2 S4 415-555 DestNext-hop 718-261 415-555 S2 S4 S3 S5 718-261-5678 415-555-1234 setup(718-261-5678) 718-261

53. Polytechnic University  M. Veeraraghavan 53 A user moves while in a connection If a user moves while communicating –how does the network reroute data destined to the user? –this is called handoff management Examples –In cellular networks, a user traveling in a car while communicating keeps changing his connection point to the network (base station)

54. Polytechnic University  M. Veeraraghavan 54 Cellular network handoffs S1 S2 S4 S3 S5 718-261-5678 718-261 718-261-5678 Have to preserve the connection as the user moves

55. Polytechnic University  M. Veeraraghavan 55 Handoffs in a data network In an IP network, there is a similar need for a handoff if a mobile wireless user moves while the user’s laptop is engaged in a TCP connection (say for email download or web file download)

56. Polytechnic University  M. Veeraraghavan 56 Big difference between these two types of handoffs In CO networks, every switch on the path has been configured with translation tables specifying how to route bits arriving on each connection –Handoff involves a rewriting of this data In CL networks such as IP, with TCP as a CO transport protocol, state information is only held at the end hosts –Handoff is a lot simpler

57. Polytechnic University  M. Veeraraghavan 57 Mobility management Mobility management includes both –Handoff management –Location management

58. Polytechnic University  M. Veeraraghavan 58 Summary Reviewed networking concepts To support wireless links, need –MAC protocols –Location management –Handoff management To support mobile servers on wireless links, need –Location management –Handoff management To support mobile clients on wired or wireless links (portables), need support for dynamically allocated addresses