1. Internetworking connectionless
and connection-oriented networks
Malathi Veeraraghavan Mark Karol
Polytechnic University Bell Laboratories
mv@poly.edu mk@lucent.com
Outline:
» Why internetwork?
» Prior work
» Our proposal
6/1/99 1

2. Why internetwork?
Connectionless (CL) Network CL Network
Connection-Oriented (CO)
Network
Router
Endpoint
Switch
Endpoint
6/1/99 2

3. 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?
Networking modes
Switching modes
Connectionless Connection-oriented
Packet-switching IP ATM
Telephony network,
Circuit-switching
SONET/SDH, WDM
6/1/99 3

4. Use provisioned connections
• Use provisioned connections through CO network
– Suitable for some cases
CL Network CL Network
CO Network
Provisioned connections: set up a priori based on anticipated traffic
Switched connections: set up on demand as traffic arrives
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5. 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
Router CL Network
Endpoint
Gateway
Switch
CO Network
Endpoint
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6. 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)
CL Network
CO Network
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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., interactive sessions with long holding times)
CL Network
IP packet 10 7
5
1 1
Interactive application 1 1
(long-lived flow;
SETUP
if flow classifier is set
to use CO network for CO Network
this flow type)
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8. 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)
CL Network
IP packet 10 7
5
1 1
1 6
1 IP packet IP packet 1
CO Network
1 1
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
6/1/99 8

9. 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
CL Network
IP packet 10 7
5
1 1
1 6
Gateway will select IP packet IP packet
1 1
CO network because SETUP SETUP
path is shorter CO /CL Network
Packets will be forwarded in 1 1
CL mode while IP packet IP packet
SETUP SETUP
connection is being set up
6/1/99 9

10. 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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11. Routing related actions
• Gateways running OSPF connected by a CO network
(non-broadcast network) announce point-to-point links
between gateways
GW1 S4
R6 S2
R3
R1 GW2
S1 S5
R5
R2
R7 GW3
R4 S3
CO Network
CL Network
Note: switches have no CL capability
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12. Routing related actions
• Topological view of each router and gateway
2 GW1 1
5 R6
R3 1
1 2 GW2 1
R1
Shortest path from 3
1 1 1
R4 to R7 is via 1 R5
GW3 and GW2 R2 2
4 R7 GW3
R4
1
CL Network
User data packets from R4 to R7 arrive at GW3 even before connection is set up
6/1/99 12

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 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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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 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
6/1/99 14

15. 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
6/1/99 15

16. Applications
Interactive Streaming
Bulk-data e.g., live or stored
e.g., telnet, rlogin, e.g. ftp, smtp, http audio or video
telephony
Packet-switched CO networks Circuit-switched (CO) networks
Small amounts of Large amounts of
data transfer data transfer
CL (packet-switched) networks Circuit-switched or CL networks
Peer model needed for this case

17. 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
6/1/99 17

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 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 18

19. 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
6/1/99 19

20. Option 1: Protocol conversion
APP APP APP APP
TCP/UDP TCP/UDP AAL5 AAL5 TCP/UDP TCP/UDP
IP IP IP ATM ATM ATM IP IP
DLL DLL DLL DLL DLL DLL DLL DLL DLL DLL
PHY PHY PHY PHY DLL PHY PHY PHY DLL PHY
Endpoint Router Gateway ATM Switch Gateway Endpoint
• Drawback: TCP state information about many
connections needs to be held at the gateways
• Feasibility as yet untested.
6/1/99 20

21. Option 2: Download software
to endpoints
CO interface Web browser
CO interface Web server
program Both Windows
program CGI
and Solaris allow
for device driver
addition
CO device driver TCP/IP
CO device driver TCP/IP
Link-layer module
Link-layer module
CL Network
Link-layer Link-layer
mux/demux mux/demux
CO Network
6/1/99 21

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
6/1/99 22