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Review of networking concepts Prof. Malathi Veeraraghavan University of Virginia M. Veeraraghavan 1 Polytechnic Review of networking concepts Prof. Malathi Veeraraghavan University of Virginia M. Veeraraghavan 1 Polytechnic University

Outline • Review of basic concepts in networking – Prerequisite: A first course on 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) M. Veeraraghavan 2 Polytechnic University

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

What is needed to send data on communication links? • Error control – Error 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 re. Quest) • 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 M. Veeraraghavan 4 Polytechnic University

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

Why use a switch? • If there are N endpoints (end-user equipment), then how 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? M. Veeraraghavan 6 Polytechnic University

Answers • Number of direct links needed to connect N nodes is • N 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 M. Veeraraghavan 7 Polytechnic University

Cost of using a switch? • Switch cost • Can all endpoints have full 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 M. Veeraraghavan 8 Polytechnic University

Concept of multiplexing • Time division multiplexing – Allows data from different sessions to Concept of multiplexing • Time division multiplexing – Allows data from different sessions to be combined at different times on to the same line – How many DS 0 s in a T 1? • Wavelength division multiplexing – Difference between FDM (Frequency Division Multiplexing) and WDM? – Relation between frequency and wavelength M. Veeraraghavan 9 Polytechnic University

Answers • 24 DS 0 s in a T 1 • Term WDM is Answers • 24 DS 0 s in a T 1 • Term WDM is the same as FDM at optical frequencies – see EM spectrum chart • Speed of light c = f • : wavelength; f: frequency M. Veeraraghavan 10 Polytechnic University

Transceiver rate • Rate of transmission and reception at endpoints and the switch – 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 DS 0 s used between endpoints in full mesh network, then T 1 s can be used in 25 endpoint network with a switch for full mesh connectivity M. Veeraraghavan 11 Polytechnic University

Types of switches • Circuit switches: Position-based switching – Switch consults a table to 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 M. Veeraraghavan 12 Polytechnic University

Switch designs • See lectures on circuit switching and packet switching in Course on Switch designs • See lectures on circuit switching and packet switching in Course on Data Networks • Compare unfolded view of a CS with that of a PS • See relevance of queueing theory to delays of calls or packets through switches M. Veeraraghavan 13 Polytechnic University

Network of switches • Expand 1 -switch network to a multi-switch network • Why Network of switches • Expand 1 -switch network to a multi-switch network • Why not build one gigantic switch? – Scalability limitations Switch End-user equipment M. Veeraraghavan End-user equipment Switch 14 Polytechnic University

Different types of networks • • A network is defined by its “switching mode” 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 Switching modes Networking modes Connectionless Packet-switching IP, SS 7 Circuit-switching M. Veeraraghavan 15 Connection-oriented MPLS IP + RSVP ATM, X. 25 Telephone network, SONET/SDH, WDM Polytechnic University

Types of data transfers An application could consist of different types of data transfers Types of data 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 Consuming end Live Sending end Live Stored M. Veeraraghavan Stored Interactive/ Live streaming Recording Stored streaming File transfers 16 Polytechnic University

Types of data transfers An application could consist of different types of data transfers Types of data 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 Consuming end Live Sending end Live Stored M. Veeraraghavan Stored Interactive/ Live streaming Recording Stored streaming File transfers 17 Polytechnic University

Matching applications & networks Data transfers Non-real-time (stored at sender and receiver ends) Real-time 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 M. Veeraraghavan Packet-switched CO networks Short transfers (e. g. short email) Connectionless networks 18 Ideal networks Long transfers (e. g. large image, audio, video or data) Circuit-switched networks Polytechnic University

Congestion control • What is it? – The purpose of a network is to 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) M. Veeraraghavan 19 Polytechnic University

Congestion control • In CO networks – Congestion control: mostly preventive – Connection Admission 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 M. Veeraraghavan 20 Polytechnic University

Congestion control • In CL networks – Have packet switches detect congestion and send Congestion control • In CL networks – Have packet switches detect congestion and send reactive messages asking sender to slow down – e. g. , datagram routers in SS 7 networks send such messages; SRP (Spatial Reuse Protocol) switches in 802. 17 MANs send such messages – IP routers implement Explicit Congestion Notification (ECN) procedures M. Veeraraghavan 21 Polytechnic University

End-to-end path • Transport protocols – Ensure reliable transfer across a communication path consisting 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 M. Veeraraghavan 22 Polytechnic University

Applications • Most Internet applications are client-server based End-user equipment Web server (Usually runs Applications • Most Internet applications are client-server based End-user equipment Web server (Usually runs on fixed hosts) Network Web clients Network End-user equipment Email-sending clients (outlook, messenger) M. Veeraraghavan Outgoing email servers (pop, imap) Network Incoming email servers (smtp) 23 End-user equipment Polytechnic University Email-receiving clients (outlook, messenger)

Protocol Stacks AL AL TL TCP/UDP NL NL NL IP DLL DLL DLL PHY Protocol Stacks AL AL TL TCP/UDP NL NL NL IP DLL DLL DLL PHY PHY PHY Switch Endpoint • 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 M. Veeraraghavan 24 Polytechnic University

Example protocols • • • AL protocols: http, smtp, ftp, PCM voice TL protocols: Example protocols • • • AL protocols: http, smtp, ftp, PCM voice TL protocols: TCP, UDP, RTP, AAL NL protocols: IP, ATM DLL protocols: PPP, HDLC PHY protocols: DS 0, DS 1 Ethernet: PHY+DLL+NL M. Veeraraghavan 25 Polytechnic University

Functions of protocol layers • PHY: sends bits across a link • DLL: error 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 M. Veeraraghavan 26 Polytechnic University

Congestion control and connection control in TCP • IP routers did not implement ECN 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 M. Veeraraghavan 27 Polytechnic University

User plane, control plane, and management plane • Management plane: consists of all the 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 M. Veeraraghavan 28 Polytechnic University

Routing protocol in all three types of networks - Phase 1 Dest. B II Routing protocol in all three types of networks - Phase 1 Dest. B II Host A I Dest. Next hop III-* IV Routing protocol IV Dest. Next hop III-* III Next hop B Host B III Routing protocol V Routing tables • Routing protocols exchange topology/loading/reachability information • Routes to destinations are precomputed and stored in M. Veeraraghavan 29 Polytechnic University routing tables

Signaling protocol for NL connection setup in a PS CO network - Phase 2 Signaling protocol for NL connection setup in a PS CO network - Phase 2 Connection setup (B) a Host A IN Port /Label a/L 1 IN Port /Label II d/L 1 b I c OUT Port/Label c/L 2 b/L 3 a Connection setup b a Connection setup IV III d c IN Port /Label b Host B c V d OUT Port/Label a/L 2 • OUT Port/Label c/L 1 Connection setup Virtual circuit 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 M. Veeraraghavan 30 Polytechnic University

Signaling protocol for NL connection setup in a CS CO network - Phase 2 Signaling protocol for NL connection setup in a CS CO network - Phase 2 Connection setup (B) Host A a I II d/2 b c IN OUT Port /Timeslot Port/Timeslot c/2 b/1 a Connection setup b a a/1 IN OUT Port /Timeslot Port/Timeslot IV Connection setup III d c b Host B c V d Connection setup IN OUT Port /Timeslot Port/Timeslot a/2 c/2 Circuit • 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) – M. Veeraraghavan. Writing the port/timeslot/ mapping table 31 Polytechnic University

TL connection setup in a CL PS network - Phase 2 • Notion of 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 re. Quest) based error correction, i. e. , retransmissions in case of errors Dest. B II Host A I Dest. II SYN ACK Host B SYN V IV Dest. Next hop B M. Veeraraghavan B III Next hop B Next hop III 32 Routing tables Polytechnic University

User-plane packet forwarding in a PS CO network - Phase 3 II L 1 User-plane packet forwarding in a PS CO network - Phase 3 II L 1 b Host A IN Port /Label a/L 1 a I L 1 c III c d b a OUT Port/Label c/L 2 L 3 a IV d b Host B c V L 2 • Labels are VPI/VCIs in ATM • Labels are translated from link-to-link M. Veeraraghavan 33 Polytechnic University

User-plane actions in a circuit-switched network - Phase 3 II 1 Host A 2 User-plane actions in a circuit-switched network - Phase 3 II 1 Host A 2 a b I 1 c b a IN OUT Port /Timeslot Port/Timeslot a/1 c/2 1 a 1 2 d c IV III d 2 b Host B c V 2 • Bits arriving at switch I on time slot 1 on port a are switched to time slot 2 of port c M. Veeraraghavan 34 Polytechnic University

User-plane packet forwarding in a CL PS network - Phase 3 II b Host User-plane packet forwarding in a CL PS network - Phase 3 II b Host A a I B c B B a c b a IV III d d b Host B c V B • 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 M. Veeraraghavan 35 Polytechnic University

Addressing • Where are endpoint addresses used: – In CL PS networks, endpoint addresses 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 M. Veeraraghavan 36 Polytechnic University

Summarized addresses • What are summarized addresses? • Why summarize addresses? M. Veeraraghavan 37 Summarized addresses • What are summarized addresses? • Why summarize addresses? M. Veeraraghavan 37 Polytechnic University

Summarized addresses • What are summarized addresses? – An address that represents a group 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 M. Veeraraghavan 38 Polytechnic University

Examples of signaling protocols • SS 7 (Signaling System No. 7) network (with its Examples of signaling protocols • SS 7 (Signaling System No. 7) network (with its SS 7 protocol stack) carries signaling messages to set up and release circuits in a telephone network M. Veeraraghavan 39 Polytechnic University

Examples of routing protocols • In an Ethernet network – Spanning tree algorithm and Examples of routing protocols • In an Ethernet network – Spanning tree algorithm and address learning • 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) M. Veeraraghavan 40 Polytechnic University

Examples of addressing schemes • Internet – 4 -byte IP addresses • Telephone networks 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) M. Veeraraghavan 41 Polytechnic University

Broadcast links • Wireless • Copper: ethernet hubs • Optical fiber: Passive star couplers Broadcast links • Wireless • Copper: ethernet hubs • Optical fiber: Passive star couplers Dest: A Ethernet hub or WDM Passive Star Coupler A Ethernet switch (packet switch) Blind broadcast M. Veeraraghavan 42 Polytechnic University

MAC protocols • Medium Access Control (MAC) protocols are used in broadcast links to 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 B’s MAC layer checks destination address to determine whether the packet should be “switched” to the application or dropped End-user equipment A To B M. Veeraraghavan C’s MAC layer checks destination address to determine whether the packet should be “switched” to the application or dropped End-user equipment B To B End-user equipment C 43 Polytechnic University

Consider wireless links • Naturally broadcast medium – One transmitter sends data; multiple receivers Consider wireless links • Naturally broadcast medium – One transmitter sends data; multiple receivers can receive the signal and obtain the data – Need a MAC (Medium Access Control) protocol to share the “naturally broadcast” wireless medium Endpoint M. Veeraraghavan Endpoint 44 Polytechnic University

Shared links in wired domain outbound Hub or optical passive star coupler inbound Host Shared links in wired domain outbound Hub or optical passive star coupler inbound Host Multipoint drops: potential interference on inbound line – polling; e. g. multidrop telephone lines Host Hubs/Optical passive star couplers: any data received on one line is broadcast to all other lines • Distance limitation between farthest hosts – Shannon’s capacity; SNR; attenuation M. Veeraraghavan 45 Polytechnic University

Classification of MAC protocols Fixed-assignment schemes Random-access schemes Circuit-switched (e. g. , FDMA, TDMA) Classification of MAC protocols Fixed-assignment schemes Random-access schemes Circuit-switched (e. g. , FDMA, TDMA) Connectionless packet-switched (e. g. , Ethernet, 802. 11) Channelization M. Veeraraghavan 46 Demand assignment schemes Connection-oriented packet-switched (e. g. , CDMA, polling) Polytechnic University

Shared link as a LAN: relation between MAC protocols and LANs • A shared Shared link as a LAN: relation between MAC protocols and LANs • A shared link allows multiple end stations to hear a transmission from any station • No node is serving as a “forwarding engine” for packets in a controlled fashion – hubs, passive star couplers, ring adapters, taps blindly send data UNLIKE switches, routers, bridges • This shared link concept works well as a local area network – if too large a network – with many hosts – each host will get a small percentage of bandwidth M. Veeraraghavan 47 Polytechnic University

Shared links as “access” links • Two reasons for using shared links on the Shared links as “access” links • Two reasons for using shared links on the access segment – individual endpoints (hosts/phones) generate small quantities of data traffic – Costs should be kept low for end users • Consequence: access links are often shared • MAC protocols in the upstream direction M. Veeraraghavan 48 Polytechnic University

Shared link in the presence of basestations/APs? • Is it still one shared link Shared link in the presence of basestations/APs? • Is it still one shared link if basestations/APs forward data between two endpoints that cannot “hear” each other – No, basestations/APs become forwarding engines, i. e. , switches – If a cell phone under one basestation calls another cell phone under the same basestation and the basestation allocates frequencies for both ends and forwards data bits • Not different from a circuit switch forwarding bits received on one DS 0 to another DS 0 – Same thing when an AP uses destination addresses to rebroadcast data – it acts as a packet switch M. Veeraraghavan 49 Polytechnic University

Compare TDMA on an access link with TDM on an inter-switch link Basestation Circuit Compare TDMA on an access link with TDM on an inter-switch link Basestation Circuit switch Endpoint Timeslot 1 Timeslot 2 Timeslot 3 Circuit switch T 1 line carrying 24 different DS 0 s (phone calls) • Similar in concept: sharing resources on one link among many users • Difference: – Multiple senders on access link – One sender in each direction on inter-switch link M. Veeraraghavan 50 Polytechnic University

Internetworking • An internet – A path that traverses multiple networks possibly ones using Internetworking • An internet – A path that traverses multiple networks possibly ones using different networking techniques M. Veeraraghavan 51 Polytechnic University

Single networks A shared link: often used to create a LAN Simplest network – Single networks A shared link: often used to create a LAN Simplest network – one link Endpoint Endpoint One network – same type of switches – link rates can be different Endpoint Switch Endpoint M. Veeraraghavan 52 Polytechnic University

The Internet approach to internetworking An internetwork Endpoint Switch Endpoint Network 1 • • The Internet approach to internetworking An internetwork Endpoint Switch Endpoint Network 1 • • Switch IP router Network 3 Switch Endpoint Network 2 Have all endpoints speak the IP (Internet Protocol) in addition to their own network protocols For loss-sensitive applications: run TCP, an end-to-end transport protocol, irrespective of whether – both ends are within the same network – the two ends are on different networks • IP routers are connectionless packet switches M. Veeraraghavan 53 Polytechnic University – they forward IP packets from one network to another based on the destination IP address carried in the IP header and information stored in their routing tables

Protocol stacks in the Internet M. Veeraraghavan 54 Polytechnic University Protocol stacks in the Internet M. Veeraraghavan 54 Polytechnic University

Today’s most common networks in the Internet • Ethernet within enterprises using a combination Today’s most common networks in the Internet • Ethernet within enterprises using a combination of – shared-medium Ethernet LANs with hubs, or – with Ethernet switches – which are connectionless packet switches • PDH/SONET networks in the MAN and WAN domains – Routers are interconnected by T 1, T 3, OC 3 connections that are set up through a PDH/SONET circuit-switched network – PPP, Point-to-Point Protocol, is executed on these circuits M. Veeraraghavan 55 Polytechnic University

Need Internet address and Network address Internetwork IP router Host A Switch 1 Switch Need Internet address and Network address Internetwork IP router Host A Switch 1 Switch 2 1 Host B 2 Switch 3 Switch 4 Host D 3 Ethernet 1 Host A sends a packet to Host C: - Places Host C’s IP address in IP header - To get through Ethernet 1, it needs Ethernet address of IP router’s interface 1 - Switch 1 and Switch 2 forward packets based on destination Ethernet address of IP router’s interface 1 - IP router forwards packet to port 2 to reach Host C (based on IP level routing data using destination IP address of host C) - IP router needs Ethernet address of Host C to send the packet through Ethernet 2 M. and 4 forward packets based on destination Ethernet address 56 - Switch 3 Veeraraghavan of Host C Ethernet 2 Host E Switch Host F Ethernet 3 Polytechnic University

Summary • Reviewed networking concepts M. Veeraraghavan 57 Polytechnic University Summary • Reviewed networking concepts M. Veeraraghavan 57 Polytechnic University