Service Providers & Data Link & Physical layers

1. Service Providers &Data Link & Physical layers Week 4 Lecture 2

2. To-day we will look at the WAN and who provides it. AT&T Telstra NTT Optus

3. IP Links are router to router Router Switch

4. Some background • The National and International telephone networks were built for voice and circuit switching • Connections to customers were analogue although inter-exchange links were being converted to digital • Demand for data communications started in the seventies • Data traffic now exceeds voice • Privatisation of old monopolies started with the AT&T break-up in 1986

5. Background continued • Telco’s started to bring WAN to large buildings – Fibre • Telco’s expanded capacity dramatically in the late 90s – 5 times the fibre X 100 time efficiency = 500 times the capacity • But usage is only doubling each year • Hence the Telecom shakeout we are seeing

6. The larger Telcos 1. AT&T US $66 2. Verizon US $65 3. NTT Japan $58 4. SBC US $51 5. Worldcom (UUNet)US $39 6. Deutsche Telekom Germany $39 7. France Telecom France $32 8. BT UK $30 19. Telstra Australia $12 Source : Year 2000 company reports in US$bn

7. International Carriers • Each of these have International “Hubs” in the countries in which they operate • They own or lease a share of the intercontinental cables • Many of them “own” the last mile and much of the national networks • They either provide ISP services direct to users (Telsta’s Bigpond or UUNet’s Ozemail), or • To smaller ISP that service geographical areas

8. The major carriers share cables such as: • PacRim East & PacRim West • Telstra has a share • 1 gbps transmission rate • Europe to Asia link • Southern Cross Cable between Australasia and the US • 600 communication satellites

9. Some characteristics of the Southern Cross Cable • Owned by: • Telecom NZ (50%) • Cable & Wireless Optus (40%) • WorldCom (UUNet) (10%) • Went live in November 2000 • Currently 240gbps and 480gbps eventually – that is the data on a 3km stack of paper or in 8 full length films, every second • Reduced TransPacific costs to 1/10 and transmission time from 300ms to 70ms

10. Southern Cross Cable cont. • 30,500 km of cable in 2 separate cables • Optical repeaters every 40-70km • Designed to provide 99.999% reliability – that is 50 minutes downtime in 10 years, but it went down early in 2001 as mods were being done to one link and the other was cut by a ship • Managed out of Auckland • Connection points in Alexandria & Brookvale

11. Southern Cross Cable cont. • The cable consists of: • Six strands of fibre • Set in jelly & hydrogen • Within a steel tube • Protected by high strength steel wire • Surrounded by seam welded copper • Insulated by high density polyethelene • To form a cable 18mm thick

12. Southern Cross cable

13. We tend to think the public Internet and the Web are dominant.But most large organisations have their own WAN.

14. More than 30 companies offer Frame Relay or ATM services in Australia • AAPT has Optic fibre in most capital cities with fibre direct to 250 buildings. They have 50 FR/ATM POPs • Cable & Wireless Optus have 38 FR/ATM POPs • CITEC a business unit of the Queensland State Gov. • Telstra has 300 FR/ATM POPs and 2,200 customers Figures as at September 2000, Telsyte report

15. An Organisation’s network can be: • Leased channels • VPN Virtual Private Network • VPN on Public network • Public Network • Combination of some or all or these

16. Data link & Physical Layers • Function is to move frame over individual link • Services can include • Point-to Point or Multicast • Reliable service • Flow control • Error detection & correction • Half or Full duplex • Data link and Physical often implemented in the adaptor or NIC

17. Wide variety of Protocols • Many changes taking place • Level at which services are sold thus as a DIS architect you may need to negotiate for these services • Different LAN and WAN Protocols • Earlier protocol families are being used at this level

18. The main WAN protocols are • PPP – Point-to-Point Protocol • HDLC – High level Data Link Control • FDDI – Fibre Distributed Data Interface • ATM – Asynchronous Transfer Mode • X.25 & Frame Relay • SONET – Synchronous Optical Network • ISDN – Integrated Services Data Network

19. Point-to-Point Protocol • Typical protocol for link from home to ISP • Used over any medium – digital or analogue • Encapsulates datagram in a PPP frame • Has a link establishment & termination procedure • Detects errors but the protocol does not require it to fix them

20. Asynchronous Transfer Mode • Developed in 1980s by ATM Forum and ITU • Can provide a full solution for a broadband, packet switched virtual circuit network • Widely used in telephone and Internet backbones • With ascendance of TCP/IP likely to remain at Data link level • Carries IP using special interface called AAL5

21. ATM Continued • Investment has resulted in very high performance switches • Fixed length 53 byte packet carrying 48 bytes of data • Fixed length allows fast hardware switching • Bit level error detection & correction • Some link level congestion control • Different levels of Quality of Service (QoS) • At PMD (Physical Medium Dependent) Layer it operates over copper, microwave & fibre

22. ATM over SONET • In multiples of 51.84mbps • Examples are: • OC-1 51.84mbps • OC-3 155.52mbps • OC-12 622.08mbps • OC-192 10gbps • But these are multiplexed • 160 channels of OC-192 gives 1.6tbps • 82 channels of OC-768 gives 3.28tbps (under test)

23. An ATM network can look like one logical link to IP with the AAL layer only at the edges of the ATM network IP IP AAL AAL ATM ATM ATM ATM Physical Physical Physical Physical ATM Switch ATM Switch

24. X.25 • X.25 introduced in Europe in the early 1980s as the first packet switched network • Because of high error rates on copper links it provided for error recovery on a link-by-link basis • Still in use in Europe

25. Frame Relay • Introduced in the early 1990s as a second generation X.25 network • Designed for lower bit error rates & has no error recovery & no flow control • Lower overhead and thus higher transmission rates and low latency • Virtual circuit based, packet switching service provided by Telcos • Sold to corporate users as VPNs

26. Frame Relay (Cont.) • TCP/IP and other protocols can be carried over Frame Relay • Variable length packets mean no hardware switching thus slower than ATM • Services up to 20mbps • Sometimes numbers of FR circuits aggregated onto ATM circuits and then back to FR • Uses statistical multiplexing to provide: • Permanent Virtual Circuits, or • Switched Virtual Circuits • Like ATM, Frame Relay networks can look like single links to TCP/IP

27. CIR (Committed Information Rate) • VPN purchaser contracts for say 256kbps • Supplier commits to supply that rate • User can burst above that rate if unused capacity available • If capacity not available packets over the CIR may be dropped • This provides the guaranteed service level that TCP/IP is unable to provide • Users port access devices typically can deliver higher rates than the CIR

28. SONET (Synchronous Optical Network) • Standard interface for transporting digital signals over optic fibre • Allows multiplexing of circuits from different vendors over the same fibre • High speed rates as discussed before • Circuit switched • Usually only part of a carrier’s network

29. Rationalising the backbone links IP IP IP IP ATM ATM SONET SONET WDM WDM WDM WDM WDM is Wave Division Multiplexing Voice over IP will replace PBX and thus voice will be carried over data networks

30. Evolution of private networks • Based on leased lines/circuits • ATM or Frame relay using permanent virtual circuits • Internet based VPNs or IP based VPNs

31. VPN (Virtual Private Network) • Replacing private networks based on leased circuits. • A VPN is • A WAN • Providing what appears to be dedicated lines to the organisation • But are actually network facilities shared by multiple customers

32. VPN (Virtual Private Network) • Frame Relay service is the leading VPN service • Now can be implemented as secure “tunnels” over the Public Internet at the IP layer, between edge routers or firewalls • IP based VPNs are • Encapsulated data paths • Using one of a number of strategies e.g. IPSec (Internet Protocol Security) to provide • content encryption, and • Packet authentication (prevent spoofing)

33. IP based VPN • Because IP is layer 3, it gains the benefit of the high up time service from ATM • It is becoming popular because • Low cost • Simple to establish • Widespread connectivity • Access for mobile users • ATM could allow service providers to offer the SLAs required for corporate use.

34. IP based VPN (Cont.) • Mobile users can dial into an ISP POP for a local call and tunnel through to the corporate network for e-Mail, Web and our corporate DIS • IP VPNs can be used to extend Frame Relay VPN for remote offices • They can be used as Extranets – Secure environments for B2B e-Commerce • Extranet segregated from corporate network by a firewall

35. Routing algorithms The main function of IP at the Network layer

36. Routing algorithms • The network layer has to determine the route the message is to take • In a virtual circuit all packets for the connection will follow the same path • In a datagram service like IP, packets may take different routes • In both situations the routing algorithm within the Network layer will determine the routes

37. IP address = Network + Host

38. What does it do? • It finds the best path from source to destination • A good path is usually defined as least cost • Where cost takes into account • The number of hops • The length of the hops and • The congestion on specific hops • But may also be affected by policy – e.g. do not use routers belonging to Optus

39. Routing algorithms can be: • Global – assumes all information about all possible routes is known and the source to destination can be calculated • Decentralised – where routers exchange information with their nearest neighbours and slowly build up least cost information

40. They can also be: • Static – where cost data only changes with human intervention • Dynamic – where the algorithm responds to changes in topology and load on various links • The IP uses a dynamic approach

41. But the Internet has many routers and hosts! • It is broken down into AS (Autonomous Systems) where all of the routers are under the control of a single organisation – like Telstra or UUNet • Routers in an AS use the same algorithm • Protocols such as RIP are used within the AS and • A special protocol called BGP4 is used when passing packets between AS (in gateway routers) • We also know that a service provider may push the IP routers to the edge of its ATM network, which then uses its hardware addresses for quick passing of frames through its network

42. Autonomous regions AS2 AS1 RIP BGP4 AS4 AS3

43. IP Links are router to router Router Switch

44. These algorithms are complex • Of great interest to mathematicians • We do not need to know • See Kuross page 301 for details if it excites you

45. Intranet • Uses Internet & Web technology: TCP/IP, Browsers & Servers, HTML and HTTP • To provide access to an organisation’s information by staff in that organisation • May use a private network or an IP VPN

46. Extranet • Similar to an Internet, but access is given to authorised users from specific organisations • Typically used in B2B commerce • Usually the organisation’s private Intranet protected by a firewall • Uses passwords and Digital certificates to control access.