Connection( less & oriented)
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Transcript of Connection( less & oriented)
6/1/99 1
Internetworking connectionless and connection-oriented networks
Malathi Veeraraghavan Mark Karol
Polytechnic University Bell Laboratories
[email protected] [email protected]
Outline:» Why internetwork?» Prior work» Our proposal
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Why internetwork?
Router
Switch
Endpoint
Endpoint
Connection-Oriented (CO)Network
Connectionless (CL) Network CL Network
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Problem Statement
• Applications at endpoints start sending 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?
Connectionless Connection-oriented
Packet-switching
Circuit-switching
Switching modesNetworking modes
ATM
Telephony network,SONET/SDH, WDM
IP
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Use provisioned connections
• Use provisioned connections through CO network– Suitable for some cases
Provisioned connections: set up a priori based on anticipated trafficSwitched connections: set up on demand as traffic arrives
CO Network
CL Network CL Network
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Switched connections
• Need switched connections for some cases– CL applications have an application-level handshake 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 NetworkSwitch
CL NetworkRouter
Endpoint
Endpoint
Gateway
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Prior work
• Interesting case - Case 3– A choice exists of which network to use
• Existing solutions:– MPOA (Multi-Protocol Over ATM)
– MPLS (Multi-Protocol Label Switching)
CO Network
CL Network
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Solutions - MPOA
• MPOA:– Overlay model
– Routing data not shared
– Good solution if choice to use CO network made based on application needs (e.g., interactive sessions with long holding times)
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5710
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CO Network
CL Network
SETUP
Interactive application(long-lived flow;if flow classifier is set to use CO network forthis flow type)
IP packet
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Solutions - MPOA
• MPOA:– Not a good solution if either CL or CO network can be used for a given
application (e.g., large bulk-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
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5710
11
CO Network
CL NetworkIP packet
IP packet IP packet
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Solutions - MPLS
• MPLS:– Peer model– Routing data is shared– Requires every CO switch to also be a CL router– Same example as last slide - large bulk-data transfer that could go either way
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CO/CL Network
CL NetworkIP packet
Gateway will selectCO network becausepath is shorter
IP packetSETUP
IP packet SETUPIP packet
SETUP
IP packetSETUP
Packets will be forwarded in CL mode while
connection is being set up
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Proposed solution
• Peer model
• Routing data is shared
– 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
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Routing related actions
• Gateways running OSPF connected by a CO network (non-broadcast network) announce point-to-point links between gateways
R1S1
R2
R4R7
R5
R3R6
S4
S5
S3
S2
CL NetworkCO Network
GW1
GW2
GW3
Note: switches have no CL capability
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Routing related actions
• Topological view of each router and gateway
R1
R2
R4R7
R5
R3R6
CL Network
GW1
GW2
GW3
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1 2
4
1
5
2
1
2
1
1
1
1
1
Shortest path fromR4 to R7 is viaGW3 and GW2
User data packets from R4 to R7 arrive at GW3 even before connection is set up
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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 segment– 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
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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 time-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
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For flows for which the CO 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
Applications
Bulk-datae.g. ftp, smtp, http
Interactivee.g., telnet, rlogin,
telephonyPacket-switched CO networks
CL (packet-switched) networks
Small amounts ofdata transfer
Large amounts ofdata transfer
Circuit-switched or CL networks
Streaminge.g., live or stored
audio or videoCircuit-switched (CO) networks
Peer model needed for this case
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Comparison of 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 bandwidth and buffer for specific flow (hard state)
– No additional overhead IP (network-layer) rides over DLL
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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 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?”
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Options
• Option 1:– Use protocol conversion not protocol encapsulation
• Avoids having to carry TCP ACKs in CO network
• Much simpler 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
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Option 1: Protocol conversion
• Drawback: TCP state information about many connections needs to be held at the gateways
• Feasibility as yet untested.
DLL
IP
TCP/UDP
APP
PHY
Endpoint
DLL
IP
TCP/UDP
APP
PHY
Endpoint
DLL
ATM
AAL5
APP
PHY
TCP/UDP
IP
DLL
DLL
Gateway
DLL
IP
TCP/UDP
APP
PHY
AAL5
ATM
DLL
DLL
GatewayRouter
IP
DLL
PHY PHY
DLL
ATM
ATM Switch
DLL
PHY PHY
DLL
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Option 2: Download software to endpoints
Web browser
TCP/IP
Link-layer module
CO Network
CL Network
Web server
TCP/IP
Link-layer module
CO device driver
CO interfaceprogram
CO device driver
CO interfaceprogram CGI
Link-layermux/demux
Link-layermux/demux
Both Windowsand Solaris allowfor device driver
addition
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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