1、6/1/99,1,Internetworking connectionless and connection-oriented networks,Malathi Veeraraghavan Mark KarolPolytechnic University Bell Laboratoriesmvpoly.edu Outline: Why internetwork? Prior work Our proposal,6/1/99,2,Why internetwork?,6/1/99,3,Problem Statement,Applications at endpoints start sending
2、 data without warning in connectionless networks CO networks need a connection setup phase So how do the gateways cope with the traffic arriving from the CL networks without time to set up a connection?,6/1/99,4,Use provisioned connections,Use provisioned connections through CO network Suitable for
3、some cases,Case 1,Provisioned connections: set up a priori based on anticipated traffic Switched connections: set up on demand as traffic arrives,CO Network,CL Network,CL Network,6/1/99,5,Switched connections,Need switched connections for some casesCL applications have an application-level handshake
4、 that can be used to trigger connection setups e.g., interconnecting an Internet telephony PC to a telephone e.g., H.245 signaling to Q.931 signaling through the PSTN phone,CO Network,Case 2,Switch,CL Network,Router,Endpoint,Endpoint,Gateway,6/1/99,6,Prior work,Interesting case - Case 3 A choice exi
5、sts of which network to use Existing solutions: MPOA (Multi-Protocol Over ATM) MPLS (Multi-Protocol Label Switching),CO Network,CL Network,Case 3,6/1/99,7,Solutions - MPOA,MPOA: Overlay model Routing data not shared Good solution if choice to use CO network made based on application needs (e.g., int
6、eractive sessions with long holding times),CO Network,CL Network,Interactive application (long-lived flow; if flow classifier is set to use CO network for this flow type),6/1/99,8,Solutions - MPOA,MPOA: Not a good solution if either CL or CO network can be used for a given application (e.g., large b
7、ulk-data transfers),If flow classification does not detect this as a flow to be handled by the CO network, it will not take advantage of shorter path through the CO network,CO Network,CL Network,6/1/99,9,Solutions - MPLS,MPLS: Peer model Routing data is shared Requires every CO switch to also be a C
8、L router Same example as last slide - large bulk-data transfer that could go either way,CO/CL Network,CL Network,Gateway will select CO network because path is shorter,Packets will be forwarded in CL mode while connection is being set up,6/1/99,10,Proposed solution,Peer model Routing data is shared
9、How is this done: routing-related actions But, not all nodes in the CO network need to have CL capability Problem created: Data arrives from the CL endpoints into the gateway before connections are set up User-plane actions,6/1/99,11,Routing related actions,Gateways running OSPF connected by a CO ne
10、twork (non-broadcast network) announce point-to-point links between gateways,R1,S1,R2,R4,R7,R5,R3,R6,S4,S5,S3,S2,CL Network,CO Network,Note: switches have no CL capability,6/1/99,12,Routing related actions,Topological view of each router and gateway,R1,R2,R4,R7,R5,R3,R6,CL Network,GW1,GW2,GW3,Shorte
11、st path from R4 to R7 is via GW3 and GW2,User data packets from R4 to R7 arrive at GW3 even before connection is set up,6/1/99,13,User-plane actions,IP datagrams arrive at the gateway to be carried through the CO network when no connection exists through it. IP datagram could be carrying a TCP segme
12、nt IP datagram could be carrying a UDP datagram CO network used only for flows classified as needing connections or those that can be handled on either network,6/1/99,14,For flows for which the CO network is to be used,TCP segment If it is a SYN segment, hold it up, set up connection SYN-related tim
13、e-outs are large (5 sec) If it is a data segment, then send zero-window-size acknowledgment to halt data if persist timers get routed through some other path and new data packets arrive before the connection is set up, send another zero-window-size acknowledgment,6/1/99,15,For flows for which the CO
14、 network is to be used,UDP datagram For applications with user-level message exchange, hold up such messages and set up connection (e.g., H.245 open logical channel) For applications without such exchanges use source routing to override default routes use small-bandwidth provisioned pipes,Applicatio
15、ns,Bulk-data e.g. ftp, smtp, http,Interactive e.g., telnet, rlogin, telephony,Packet-switched CO networks,CL (packet-switched) networks,Circuit-switched or CL networks,Streaming e.g., live or stored audio or video,Circuit-switched (CO) networks,Peer model needed for this case,6/1/99,17,Comparison of
16、 CO network options,Circuit switches IP traffic is bursty by the time it reaches gateway owing to TCP congestion control Circuit switching not efficient for bursty traffic ATM switches 20% overhead due to 10% cell header overhead + TCP acks not fitting in one cell Switched IP connections: Reserve ba
17、ndwidth and buffer for specific flow (hard state) No additional overhead IP (network-layer) rides over DLL,6/1/99,18,Switched IP connections,New IP routers capable of performing multi-tuple route lookups/scheduling at wire-speed destination and source addresses destination and source ports protocol
18、type and TOS (Type of Service) Question: Are there any conditions under which a network of ATM switches or circuit switches can perform better than these “IP switches?”,6/1/99,19,Options,Option 1: Use protocol conversion not protocol encapsulation Avoids having to carry TCP ACKs in CO network Much s
19、impler transport-layer protocol can be used in CO network since the network nodes now maintain state and perform congestion control (instead of state information being maintained at endpoints) Option 2: Generate traffic at endpoints in mode appropriate for network used,6/1/99,20,Option 1: Protocol c
20、onversion,Drawback: TCP state information about many connections needs to be held at the gateways Feasibility as yet untested.,6/1/99,21,Option 2: Download software to endpoints,Web browser,TCP/IP,Link-layer module,Web server,TCP/IP,Link-layer module,Link-layer mux/demux,Link-layer mux/demux,Both Wi
21、ndows and Solaris allow for device driver addition,6/1/99,22,Conclusions,For applications whose data can be carried in either the CL network or CO network, internetworking should allow for the exchange of routing information (peer model) Requiring all CO nodes to have CL capability seems too constraining (an MPLS requirement) Hence, our proposed solution: Share routing data “Halt” or “turn back traffic” while setting up connections To overcome overheads of protocol encapsulation Perform protocol conversion, or Download software to endpoints for CO service,
