Voice Over Packet-Switched Networks: The Future of Internetworking

1. Internetworking: Voice over packet-switched networks and IP over X Malathi Veeraraghavan Associate Professor, Dept. of Elec. Engg. Polytechnic University mv@poly.edu Outline • “Theory” • Practice

2. Outline • “Theory” • Problem statement • Why internetwork? (Slides 4, 29-34) • Is internetworking needed only in the short-term? • Yes, if we can achieve ONE integrated multimedia network • But can we? • My answer: No; Why? (Slides 5-28) • Conclusion: Internetworking will be needed in the long run • Next problem: How to internetwork? (Slides 35-59)

3. Outline • Practice (Slides 60-63) • PSTN/ATM internetworking (Slides 64-111) • PSTN/IP internetworking (Slides 112-155) • IP/ATM internetworking (Slides 156-182) • IP/SONET and IP/WDM internetworking • Provisioned mode (Slides 183-191) • Switched mode (Slides 192-197) • Endpoints choose network (Slides 198-203) • Background, acronyms, references (Rem. slides)

4. e.g. Internet phone and a telephone Why this? Explained later Network 1 Network 2 Network 3 Case 1 Endpoint Endpoint Case 2 Case 3 Why internetwork?

5. Will these cases exist in the long term? • All three cases shown on previous slide could occur only if “different” networks continue to exist • What are “different” networks? • There are many classes of the Network Layer, defined as the one in which switching or routing is performed • There are different classes of network nodes (nodes that perform switching/routing actions) • A “class” of networks can have many “instances”

6. Networking modes Switching modes Connection-oriented Connectionless Packet-switching Circuit-switching Different classes and instances 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 MPLS IP switch ATM, X.25 IP, SS7 Telephone network, SONET/SDH, WDM

7. Long run • In the long run, can we do away with all these different classes of networks and create just ONE integrated network that will serve all applications?

8. Attempts to create the ONE integrated network • ATM networking • Connectionless IP networking • MPLS networking

9. Non-real-time (stored at sender and receiver ends) Real-time (consumed or sent live) To evaluate these options, first classify applications Applications

10. Applications Consuming end Stored Live Sending end Live Interactive/Streaming Recording Stored Streaming Non-real-time

11. Non-real-time (stored at sender and receiver ends) Real-time (consumed or sent live) Streaming (one-way) (consumed live; sent from live or stored source) e.g. radio/TV broadcasts Interactive (two-way) (consumed and sent live) e.g. telephony, telnet, ftp, http Short transfers (e.g. DNS query) Long transfers (e.g. large image, audio, video or data) Recording (one-way) (stored at receiver end; sent from live source); e.g. Replay Connectionless networks Circuit-switched networks Packet-switched CO networks Communication applications Applications Ideal networks

12. Use of circuit switching for long data transfers • Scanned from “Fundamentals of Digital Switching,” by J. MacDonald (article written by Miyahara et al. in 1975); Also in Mischa Schwartz’s old book

13. Answer the long run question • With this understanding of applications, now answer the question: • In the long run, can we do away with all these different classes of networks and create just ONE integrated network that will serve all applications? • Assess the three attempts to create ONE integrated network: • ATM, CL IP, MPLS

14. ATM as an integrated networking solution • Well suited for: • real-time applications that generate bursty traffic in long-lived sessions, where the traffic arrival/departure processes may or may not be easy to model a priori (use ATM VBR or ABR, respectively) • Not ideal for: • short transfers, pay the penalty of setting up a connection • large transfers, pay both penalties of signaling overhead and packet header overhead

15. Connectionless IP as anintegrated networking solution • Well suited for: • short data transfers • bursty data sent in long sessions, where the traffic is not readily modeled, when combined with a connection-oriented transport-layer protocol, i.e. TCP • Not ideal for: • real-time transfers (interactive, streaming or recording) • large transfers, where per-packet header overhead and acknowledgment overhead is incurred because of the unreliability of CL networking

16. MPLS as an integratednetworking solution • What’s MPLS?

17. IPRouter Line cards (e.g., SONET) Line cards (e.g., SONET ) Line cards (e.g., ethernet, T1) Line cards (e.g., ethernet, T1) MPLS NetworkNode ATMSwitch MPLS network node IP routing protocols (e.g., OSPF, BGP) IP packet forwarding engine ATM cell switch OR shim header label switch

18. MPLS as an integratednetworking solution • Solution is not truly integrated in the old sense of using a single user-plane network-layer protocol for all applications • It uses CL (IP) and PS CO (ATM or shim headers) • An MPLS network node consists of an IP router and an ATM switch (or shim header label switch) • Is it an integrated solution if there are different user-plane NL protocols, but an integrated routing protocol, signaling protocol, addressing scheme?

19. MPLS as an “integrated”networking solution • Well suited for: • Interactive, streaming, recording applications • Short data transfers • Not ideal for: • Large bulk-data transfers • Finally, if ONE user-plane NL protocol not ideal for all applications, then why should one expect the same of ONE routing protocol or ONE addressing scheme?

20. My answer to the long run question We will continue to need/have heterogeneous networks

21. Reasons • Different applications are served best by different networking modes • Domains of operation • Different types of end equipment • Can use a “non-ideal” networking mode to support an application with engineering

22. First reason • Different applications are served best by different networking modes: • Need different “classes” of network layer protocols • Define a networking solution to carry multimedia traffic (audio, video, data) generated by interactive, bulk-data, streaming, recording applications: • Answer: An internetwork of heterogeneous networks • Including all three networking modes: • Connectionless • Packet-switched connection-oriented • Circuit switched

23. Second reason: domains of operation • Reason for having different “instances” of the same class of networks • Example: Use of circuit switched backbone networks • Example: Use of CL switches (routers) in LANs

24. Domains of operation example • TDM and WDM circuit-switched networks • For e.g., backbone networks with heavy volumes of aggregated traffic • it may not be feasible to build TDM electronic switches with multiple Tb/s switching capacity • best option with existing technology: WDM circuit switches (both circuit-switched)

25. Domains of operation example • Second example: LANs • Ethernet switches that perform MAC frame forwarding rather than IP routers - both of the CL class • IP header more complex than ethernet MAC header: ethernet switches cheaper than IP routers • Ethernet: started as shared medium networks • Hence MAC headers needed an address field to identify destination • Presence of addresses in MAC headers enabled creation of ethernet switches

26. Third reason: Different types of end equipment • End equipment (existing and new) • telephones generate data for a circuit-switched network (when traffic is best handled by a PS CO network) • telephones are simple to use • legacy • long file/web page transfers are implemented for CL networks (when traffic best served by a CS network) • “legacy” computers with TCP/IP stack • wireless end devices require light-weight protocols

27. Fourth reason: “engineering” in non-ideal networks • Circuit-switched TDM network can be used to carry interactive (bursty) telephony traffic • Large bulk-data transfers can be carried on CL IP networks in spite of per-packet header and ACK overheads • Streaming applications are being implemented on CL IP networks - jitter problem addressed with adaptive playout buffers at the receiver • In all cases, user sees no degradation of service

28. Observations & Implications • Observations • Ideal networking solutions for different application classes are different • Different domains of operation dictate need for different networking solutions • Legacy end equipment/software generate traffic in non-ideal modes likely to exist for a while + new end equipment • Non-ideal networks can be used with engineering solutions • Implications • Integrated homogeneous network for all applications and domains will remain a pipe dream! • Heterogeneous networks should be accepted as reality • HENCE INTERNETWORK!

29. Network 1 Network 2 Network 3 Case 1 Endpoint Endpoint Case 2 Case 3 Map internetworking scenarios to reasons for needing heterogeneous networks Different domains of operation Ideal networking modes Engineering in non-ideal networks Different types of endpoints

30. An explanation of the case 3 internetworking scenario • Reasons for the case 3 internetworking scenario: • reroute traffic generated by endpoints working in a “non-ideal” mode on to a network that is “ideal” for the application subject to route availability • if ideal network route is overloaded using non-ideal network with “engineering” solutions

31. PSTN Endpoint Endpoint GW GW Gateway ATM Example 1 • Example 1 • Endpoints  telephones • Network 1  PSTN; Network 2  ATM • Redirect interactive telephony traffic to PS CO network

32. IP Endpoint Endpoint GW GW Gateway ATM Example 2 • Example 2 • Network 1: IP network; Network 2: ATM • Redirect interactive, streaming and recording traffic to PS CO network

33. IP Endpoint Endpoint GW GW Gateway SONET Example 3 • Example 3 • Network 1: IP network; Network 2: SONET • Redirect large bulk-data traffic to circuit-switched network

34. Take stock • Done so far: • Why internetwork? What are internetworking scenarios? • Will internetworking be needed in the long run? • Why are heterogeneous networks needed? • Now on to: • How to internetwork?

35. How to internetwork? User-plane protocols • To internetwork, simply interwork: • user-plane protocols: for user data • routing protocols: to create routing information for packet forwarding or call routing • addressing schemes: addresses carried in CL packet headers or in signaling messages in CO networks • signaling protocols: used to set up/release connections [VEERARAGHAVAN & KAROL] Routing protocols CL networks CO networks Addressing schemes Signaling protocols

36. Schemes for interworking user-plane protocols • Protocol encapsulation • Stack transport-layer/network-layer protocols of the first network on top of those of the second network • Protocol conversion • Convert transport-layer/network-layer protocols from those of one network to those of the second network

37. Protocol Encapsulation (typical) Protocol Conversion (possible) Depends on internetworking scenarios Endpoint Endpoint Protocol Conversion

38. Schemes for interworking routing protocols • Asymmetric: Gateways (nodes in the first network) do not participate in the routing protocol of the second network - appear as end hosts to the second network • Separate: Gateways participate in both routing protocols, but do not routing propagate information about links passing through one network into the other network • Integrated: Gateways participate in both routing protocols and propagate information about links passing through one network into the other network • NO interworking: when internetworks are such that gateways do not have a choice of networks

39. Applicability • Integrated scheme applicable if the two networks being interworked offer a similar set of services • Advantage: Total throughput of the internetwork will be best • Disadvantage: Increased routing protocol exchanges • Separate scheme best if for most services one network is ideal, and for a small subset of applications both networks can be used • Asymmetric scheme best used if the two networks offer different services: clear-cut separation of which network to use for each application

40. Schemes for interworking addresses • Use address translation messages: • Send messages, broadcast or unicast, when a datagram or call setup request arrives • Use encapsulated addresses: • Use address encapsulation, address registrations and routing protocol reachability updates • Hybrid • Use of administered data tables

41. Applicability • Address translation approach: • Suitable if address space of network is small and cannot afford space for encapsulated addresses • Suitable for LANs • Routing protocol approach: • Suitable if address space of network is large and can afford space for encapsulated addresses • Suitable for WANs

42. Schemes for interworking signaling protocols • Map signaling messages, parameters, procedures

43. Different cases • Consider various combinations: • CL to CL • Circuit switched CO to circuit-switched CO • Packet-switched CO to packet-switched CO • CL to CO (circuit- or packet-switched) • Packet-switched CO to circuit-switched CO • CO networks can be operated in provisioned or switched mode

44. Provisioned vs. switched • Provisioned: Connections are set up (resources reserved) a priori • e.g., leased T1 lines, SONET OC3, ATM PVCs • Switched: Connections are set up (resources reserved) on demand • e.g., telephone calls (DS0 circuits), ATM SVCs • how about SONET OC1/OC3 circuits on-demand for large file transfers

45. Connectionless; route determined when each packet arrives; COMPLETE SHARING CL; routes predetermined; SPACE DIMENSION OF SWITCHING REMOVED CL + Resource reservation; Partial partitioning DIFFSERV EQUAL Connection-oriented route determined + resources reserved when each call arrives; Switched mode CO; Resources reserved for “pipes” - pairwise provisioned connections CO; Resources reserved for a destination - provisioned trees Shades of gray between provisioned and switched

46. Resource allocation on a tree basis Provisioned trees vs. pairwise connections Resource allocation on pairwise basis Resources: Bandwidth and buffer resources

47. CL network-to-CL network internetworking • User-plane protocol interworking • Protocol encapsulation (scenarios 1 and 3) • Routing protocol interworking • Integrated (since both networks provide “same” type of service) • Addressing scheme interworking • Any of the three • Signaling protocol interworking: Not applicable

48. Example: IP-ethernet internetworking • View a network of ethernet switches as a CL network - ethernet layer serves as NL • Internetwork this network of ethernet switches with a CL network of IP routers IP Router IP Router PPP link PPP link Host IP Router IP Router Host Ethernet switch Case 3 Ethernet switch Ethernet switch

49. IP-ethernet internetworking • User-plane protocol: • Protocol encapsulation; hence IP over ethernet • Ethernet frame forwarding at switches till egress gateway is reached at which point IP datagram forwarding is performed • Routing: • Integrated interworking: GW IP routers send routing information of their connectivity through the ethernet to the remaining IP routers • Addressing scheme: • Both - address resolution and encapsulated addresses

50. ARP (125.25.16.11) ARP reply (0x01:98:ef:ab:87:12) IP to ethernet address mapping: address translation messages • ARP (Address Resolution Protocol) • Message broadcast with an IP address and an ethernet address returned in a reply IP Router IP Router PPP link PPP link Host IP Router IP Router Host 125.25.16.11 0x01:98:ef:ab:87:12 Ethernet switch Ethernet switch Ethernet switch