WAN Technologies (to interconnect IP routers) Mario Baldi

Transcription

1 WAN Technologies (to interconnect IP routers) Mario Baldi WAN_Technologies - 1 Copyright: see page 2

2 Copyright Notice This set of transparencies, hereinafter referred to as slides, is protected by copyright laws and provisions of International Treaties. The title and copyright regarding the slides (including, but not limited to, each and every image, photography, animation, video, audio, music and text) are property of the authors specified on page 1. The slides may be reproduced and used freely by research institutes, schools and Universities for non-profit, institutional purposes. In such cases, no authorization is requested. Any total or partial use or reproduction (including, but not limited to, reproduction on magnetic media, computer networks, and printed reproduction) is forbidden, unless explicitly authorized by the authors by means of written license. Information included in these slides is deemed as accurate at the date of publication. Such information is supplied for merely educational purposes and may not be used in designing systems, products, networks, etc. In any case, these slides are subject to changes without any previous notice. The authors do not assume any responsibility for the contents of these slides (including, but not limited to, accuracy, completeness, enforceability, updated-ness of information hereinafter provided). In any case, accordance with information hereinafter included must not be declared. In any case, this copyright notice must never be removed and must be reported even in partial uses. WAN_Technologies - 2 Copyright: see page 2

3 The Context IP host IP network Wide Area IP router WAN_Technologies - 3 Copyright: see page 2

4 Why Not Just Cables? Expensive! To lay Time consuming To modify WAN_Technologies - 4 Copyright: see page 2

5 Use a Network Cables are laid once Interconnectivity can be configured Resources (and their costs) shared Interconnecting a new site implies just laying a short cable New virtual interconnections can be easily and quickly created WAN_Technologies - 5 Copyright: see page 2

6 And before building new ones Reuse existing technologies Specifically, existing networks They are Dead : there is no new development Old: designed tens of years ago with various purposes in mind Not for interconnecting IP routers With one exception (frame relay) but huge investments WAN_Technologies - 6 Copyright: see page 2

7 Commonly Deployed Technologies Circuit switching ISDN PDH SONET/SDH Frame Relay ATM Dead and old, but still heavily used relevant! [also optical networks, which are a (relatively) new technology] WAN_Technologies - 7 Copyright: see page 2

8 Circuit Switching Technologies WAN_Technologies - 8 Copyright: see page 2

9 TDM: Time Division Multiplexing Switch Switch BANDWIDTH WAN_Technologies - 9 Copyright: see page 2

10 Interconnections based on TDM TDM (Time Division Multiplexer) divide the total bandwidth in sub-bands Each network user (e.g., router) can see only its assigned sub-band as a synchronous channel with fixed bit rate Routers can use a channel as the equivalent of a physical link In reality at any given time the link carries traffic of only one user WAN_Technologies - 10 Copyright: see page 2

11 TDM: Time Division Multiplexing Take turns Switch Switch BANDWIDTH at predefined, recurring time instants time rules WAN_Technologies - 11 Copyright: see page 2

12 Good service without flexibility (by design) Deterministic performance Delay Jitter Bandwidth Fixed rate Bandwidth not actually used by a user (in a certain interval of time) cannot be used by other services and it is wasted Higher costs Particularly for bursty traffic E.g., data traffic Designed for voice traffic WAN_Technologies - 12 Copyright: see page 2

13 Standard Channel Hierarchies Standardized channel speeds Standardized transmission speeds And corresponding equipment Transmitters Receivers Cables Copper Fibers How to combine multiple low speed channels into a high speed signal transmitted on a link Multiplexing and demultiplexing WAN_Technologies - 13 Copyright: see page 2

14 PDH: Plesiochronous Digital Hierarchy Looser synchronization requirements Europe USA 32 x 64 kb/s E Mbps T1 - DS Mbps 24 x 64 kb/s E Mbps T3 - DS Mbps 4 E Mbps Limited transmission speeds High overhead WAN_Technologies - 14 Copyright: see page 2

15 Why a hierarchy? Hierarchy: how to combine multiple lower rate frames into higher rate frame Higher capacity links in the backbone, lower capacity at the access Grooming and degrooming WAN_Technologies - 15 Copyright: see page 2

16 SDH: Synchronous Digital Hierarchy SONET: Syncronous Optical Network More stringent synchronization USA: SONET OC-1c / STS-1c Mbps OC-3c / STS-3c Mbps OC-12c / STS-12c Mbps OC-48c / STS-48c 2.4 Gbps Europe: SDH STM Mbps STM Mbps STM Gbps Higher transmission speeds Lower overhead WAN_Technologies - 16 Copyright: see page 2 Higher complexity costs

17 Interoperability PDH hierarchies SDH hierarchies Europe USA USA: SONET Europe: SDH E Mbps T1 - DS Mbps OC-1c / STS-1c Mbps E Mbps T3 - DS Mbps OC-3c / STS-3c Mbps STM Mbps E Mbps OC-12c / STS-12c Mbps STM Mbps OC-48c / STS-48c 2.4 Gbps STM Gbps WAN_Technologies - 17 Copyright: see page 2

18 Physical architecture Section: fiber optic between repeaters Line: sequence of sections between devices oeprating at line level Path: end-to-end connection T T T SONET/SDH MUX Repeater Add/Drop MUX Repeater SONET/SDH MUX T T T Section Section Section Section Line Line Path WAN_Technologies - 18 Copyright: see page 2

19 Protocol architecture Multiple layers Complex protocol architecture Monitoring functionalites Fast fault recovery 50 ms Ring topology Terminal Repeater Multiplexer Terminal Higher Layer Higher Layer Path Layer Envelope Path Layer Line Layer STS-N / STM-N Block Line Layer Line Layer Section Layer Frame Section Layer Section Layer Section Layer Photonic Layer Photonic Layer Photonic Layer Photonic Layer Light WAN_Technologies - 19 Copyright: see page 2

20 Frame format STS-1: 810 bytes transmitted in 125 s Mbps s 3 octets 90 octets Synchronous Payload Environment (SPE) 87 octets A1 A2 C1 J1 B1 E1 F1 B3 D1 D2 D3 C2 9 octets H1 B2 D4 H2 K1 D5 H3 K2 D6 Payload G1 F2 H4 Payload D7 D8 D9 Z3 D10 D11 D12 Z4 Z1 Z2 E2 Z5 Section Overhead Line Overhead Path Overhead s WAN_Technologies - 20 Copyright: see page 2

21 Frames In packet switching Frame contains bytes of a single communication Destination (source) identified in the header Frames are transmitted asynchronously Whenever there is data to transmit Whenever a link is free Statistical multiplexing In circuit switching Frame contains bytes of multiple communications Destination (source) identified by the position Frames are transmitted synchronously Back-to-back Independently of whether there is data to transmit WAN_Technologies - 21 Copyright: see page 2

22 What do we do with them? Same duration (125 µs) at any bit rate 1 byte carries one 64kb/s channel More bytes per frame at higher rates Hierarchy: how to combine multiple lower rate frames into higher rate frame Higher capacity links in the backbone, lower capacity at the access Grooming and degrooming WAN_Technologies - 22 Copyright: see page 2

23 How do we connect routers? One channel between two routers All bytes in a frame A fraction of a channel Multiple bytes in a frame WAN_Technologies - 23 Copyright: see page 2

24 But this is not the way it was meant to be used Voice Integrated services WAN_Technologies - 24 Copyright: see page 2

25 ISDN - Integrated Service Digital Network TELEPHONE TERMINAL/ TELEX ISDN COMPUTER FACSIMILE GROUP 4 MULTISERVICE TERMINAL So what? VIDEOTELEPHONE Now it is normal, but back then it was a big step forward WAN_Technologies - 25 Copyright: see page 2

26 ISDN Access Interface ISDN phone Videoconference Bus S NT1 ISDN Exchange (Multiplexer) PC with ISDN Fax G.4 Customer Premises Operator WAN_Technologies - 26 Copyright: see page 2

27 ISDN Access Interface Data + voice The user terminal becomes digital 2B + D or base access 2 data channels at 64 kbps 1 signaling channel at 16 kbps total 144 kbps up to user's premises 30B + D or primary access 30 data channels at 64 kbps 1 signaling channel at 64 kbps total 2 Mbps up to user's premises WAN_Technologies - 27 Copyright: see page 2

28 Packet Switching Technologies WAN_Technologies - 28 Copyright: see page 2

29 Packet-based multiplexing/switching If a source has no traffic, bandwidth is not wasted Statistical multiplexing The same network infrastructure can statistically accommodate more communications Cost of communicating is lower Service is not deterministic WAN_Technologies - 29 Copyright: see page 2

30 Statistical Multiplexing Switch Switch BANDWIDTH WAN_Technologies - 30 Copyright: see page 2

31 Statistical Multiplexing Take turns Switch Switch BANDWIDTH opportunistically, i.e., as soon as link is available WAN_Technologies - 31 Copyright: see page 2

32 Statistical Multiplexing If one is using less, others can use more Switch Switch BANDWIDTH WAN_Technologies - 32 Copyright: see page 2

33 Building packet switching on top of circuit switching Use circuits through a circuit network to interconnect packet/frame switches/routers X.25 Frame Relay ATM Packet switching PDH Cell switching SDH WAN_Technologies - 33 Copyright: see page 2

34 Frame Relay WAN_Technologies - 34 Copyright: see page 2

35 Frame Relay Network Architecture Data Communication Equipment DTE DCE DTE DCE Frame Relay Network DCE DTE DCE Virtual Circuits DTE Data Terminal Equipment WAN_Technologies - 35 Copyright: see page 2

36 Frame Relay standard Standard for DCE-DTE interfaces Multiple logical connections through a single access link Similarly to X.25 Layer 2 only Switches do not need to process 2 headers (layer 2 and layer 3) like in the previous X.25 X.25 does have a layer 3 WAN_Technologies - 36 Copyright: see page 2

37 Core-Edge Approach Error correction: re-transmission only at the network edge, not in the intermediate nodes (core) X.25 corrects errors at each hop Requires reliable links Takes advantage of fast links Small latency: 2 ms per frame relay node from 5 to 20 ms per X.25 node WAN_Technologies - 37 Copyright: see page 2

38 Frame Relay applications Interconnection of Intermediate Systems (router, bridge, gateway) through WANs All commercial devices offer FR interfaces Physical layer is common (PDH) Data-link layer is implemented in software It is possible to specify the bandwidth required by/provided to the customer Variable transit times Problematic with voice/video transmission WAN_Technologies - 38 Copyright: see page 2

39 CIR: Committed Information Rate B c : committed burst size Maximum burstiness T c =B c /CIR Interval of time where CIR is applied It is possible to transmit up to B c bitatwirespeed of the access link in each time interval T c Wire speed Non guaranteed service B c CIR Guaranteed service T c WAN_Technologies - 39 Copyright: see page 2

40 Asynchronous Transfer Mode (ATM) WAN_Technologies - 40 Copyright: see page 2

41 Relationships among different technologies analog telephony Digital conversion leased analog Switching digital telephony leased digital frame packet voice + data ISDN wideband B-ISDN DQDB cells SMDS cells ATM TDM cells + + core-edge Frame Relay core-edge X.25 WAN_Technologies - 41 Copyright: see page 2

42 Distinguishing Factors Protocol Architecture Core & Edge Cells System design choices Asynchronous interconnection servces ATM Enabling technlogies Optical fibers VLSI (CMOS) WAN_Technologies - 42 Copyright: see page 2

43 General features Switching of small, fixed length data units: cells 53 bytes Fast links (with low bit error rate) 150 Mb/s Low latency Good for data, voice and video For deployment in both LAN and WAN Selected for implementing the B-ISDN WAN_Technologies - 43 Copyright: see page 2

44 General features Sophisticated signaling: Multiparty or point-to-point connections Sophisticated mechanisms for flow control Sliding window is not efficient on long, fat pipes Dynamic bandwidth allocation Bandwidth management Fine granularity in bandwidth allocation Support for bursty traffic Adaptability for applications that are sensible to time or data loss Anything else?!?! WAN_Technologies - 44 Copyright: see page 2

45 Virtual channels ATM net 4 Mbps (3 party conference) 50 Mbps (Image transfer) ATM Switch WAN_Technologies - 45 Copyright: see page 2

46 Cell switching ATM Switch 5 48 Cell = 53 bytes WAN_Technologies - 46 Copyright: see page 2

47 Statistical multiplexing A A C B C Multiplex ATM A C B C A WAN_Technologies - 47 Copyright: see page 2

48 ATM technology Switch Switch BANDWIDTH ATM Switch ATM Switch WAN_Technologies - 48 Copyright: see page 2

49 ATM Cell Header Payload GFC VPI VPI VCI VCI VCI PT CLP HEC User Data (48 octets) UNI Cell WAN_Technologies - 49 Copyright: see page 2

50 Header Field Names GFC: General Flow Control VPI: Virtual Path Identifier VCI: Virtual Channel Identifier PT: Payload Type CLP: Congestion Loss Priority HEC: Header Error Control WAN_Technologies - 50 Copyright: see page 2

51 A couple more details Cells are transmitted back-to-back, poossibly inserting empty ones Each cell carries an indentifier of the circuit VCI/VPI: Virtual Channel/Path Identifier Error correction: Core-edge approach as in frame relay Flow control more sophisticated than sliding windows, to take into account: Different types of traffic The memory of the channel WAN_Technologies - 51 Copyright: see page 2

52 Cell Routing Look-up port #2 Port Label i D 1 C B A C n i m D VCI/VPI changes each time an ATM switch is traversed WAN_Technologies - 52 Copyright: see page 2

53 Core-Edge Principle Nodes execute only basic functionalities (switching and multiplexing) ATM Layer (L1-L2 OSI stack) Additional functionalities for the different services are implemented at the edge Upper layer protocols AAL ATM Error control (only for some services and upon request) ATM (core) PHY PHY PHY Upper layer protocols AAL ATM PHY User terminal ATM switch User terminal WAN_Technologies - 53 Copyright: see page 2

54 B-ISDN/ATM Reference Model Management Plane Control Plane User Plane Higher Layer Protocols Higher Layer Protocols ATM Adaption Layer (AAL) ATM Layer Layer Management Pl M t Physical Layer WAN_Technologies - 54 Copyright: see page 2

55 AAL 5 Segmentation and Reassembly L3-PDU USER BITS 0 to 65,000 Bytes PAD Ctrl/Length CRC Bytes SEGMENTATION REASSEMBLY WAN_Technologies - 55 Copyright: see page 2

56 The Vision Bridge / Router Private UNI Private UNI Private ATM Network Private NNI Public UNI Public UNI Public NNI Public UNI Private UNI Bridge / Router Private UNI Public ATM Network Public UNI Public UNI WAN_Technologies - 56 Copyright: see page 2

57 Reality IP host IP network ATM IP router WAN_Technologies - 57 Copyright: see page 2

58 A problematic solution R How can R know that Q is the next hop towards D? How can R know the ATM address of Q? ATM Q D WAN_Technologies - 58 Copyright: see page 2

59 ATM LAN Emulation ATM Workstation ATM SWITCH Access device B Ethernet workstation Higher Layer LLC LAN em AAL ATM PHY Signalling AAL ATM PHY Bridging LAN em AAL MAC ATM PHY PHY Higher Layer LLC MAC PHY Access devices operate as bridges WAN_Technologies - 59 Copyright: see page 2

60 ATM LAN Emulation ATM Workstation SWITCH ATM BUS Access device Server LES Access device WAN_Technologies - 60 Copyright: see page 2

61 IP over ATM: Classical model Direct communication within a subnet Use router across subnets Emulate ARP for address resolution within the subnet Find ATM address of destination or router It does not use ATM potential (performance) IP Subnet A H1 ARP Server A R IP Subnet B ARP Server B H2 H3 WAN_Technologies - 61 Copyright: see page 2

62 Advanced Solutions: Next Hop Resolution Protocol Source finds the ATM address of the best hop to a destination Destination itself if it is on the ATM network A router connected out of the ATM network if the destination is not on the ATM network Complex Logical Address Group A H1 NHRP Server A Logical Address Group B NHRP Server B H2 H3 WAN_Technologies - 62 Copyright: see page 2

63 Only one good way out R Routers and ATM switches speak the same language It s the MPLS solution! Same control plane ATM Q Routers and ATM/MPLS switches exchange routing D information Destinations are identified with IP addresses WAN_Technologies - 63 Copyright: see page 2