Signaling Transport Options in GMPLS Networks: In-band or Out-of-band Malathi Veeraraghavan & Tao Li Charles L. Brown Dept. of Electrical and Computer Engineering University of Virginia Charlottesville, VA 22904, USA

ICCCN 2007 Aug. 14, Outline Background and problem statement Assumptions and delay models Numerical results Conclusions 2

ICCCN 2007 Aug. 14, Background Signaling: needed in connection-oriented (CO) networks, e.g., PSTN, ATM, GMPLS Functions of signaling: ◦ Call setup:  route selection  bandwidth reservation on each link of end-to-end path  switch fabric configuration of each switch ◦ Call release  release bandwidth for use by others

ICCCN 2007 Aug. 14, Examples of signaling protocols ISDN User Part of the SS7 (Signaling System No. 7) protocol stack ◦ to set up and release DS0 (64kbps) circuits in a telephone (circuit-switched) network Resource reSerVation Protocol with Traffic Engineering (RSVP-TE) ◦ used in CO packet-switched networks, such as MPLS and ATM ◦ used in circuit-switched networks, such as SONET/SDH and WDM

ICCCN 2007 Aug. 14, Example: Signaling for call setup 5 Host I- A Host III- B I IV V III II Call setup (Dest: III-B; BW: OC1) Routing table Connection setup actions at each switch on the path: 1.Parse message to extract parameter values 2.Lookup routing table for next hop to reach destination 3.Read and update CAC (Connection Admission Control) table 4.Select timeslots on output port 5.Configure switch fabric: write entry into timeslot mapping table 6.Construct setup message to send to next hop call setup confirm Next hop Interface (Port); Capacity; Avail timeslots IV c; OC12; 1, 4, 5 CAC table INPUT Port /Timeslot OUTPUT Port/Timeslot a/1 c/4 Timeslot mapping table Dest.Next hop III-* IV

ICCCN 2007 Aug. 14, Motivation Call setup delay is an overhead in CO networks ◦ Reserved bandwidth is idle during call setup  Setup message processing delay measured at 91ms on an off-the-shelf SONET switch  If 10 hops, call setup delay > 91x10 =910ms  Transmission time of a 100Mbyte file over a 1Gbps-rate circuit is just 800ms  To use circuits for file transfers, need to reduce call setup delay Why is this not a major concern for others? ◦ Signaling is used to reduce turn-around time for leased lines, which will be held for hours/days 6

ICCCN 2007 Aug. 14, Our solution for reducing call setup delay Components of call setup delay ◦ message processing delay + message transport delay Message processing delay reduction ◦ Past work: We implemented a hardware-accelerated signaling processor  Result: 3  s processing delay for a RSVP PATH message; total of 5  s per call  Processing of the PATH message takes 91ms on an off-the- shelf switch, and RESV message takes 8ms. We focus on message transport delay reduction in this study 7

ICCCN 2007 Aug. 14, Transport options of signaling messages In-band: e.g., DCC channels in SONET ◦ Typical rate: Line DCC - 576kbps for a single OC1 ◦ Low rate may lead to queueing delays at high message loads Out-of-band: e.g., Internet ◦ Typical rate: 10Mbps/100Mbps Ethernet ◦ Queueing delays for the transmitter unlikely ◦ But, can suffer from longer path and delay variations across IP network 8

ICCCN 2007 Aug. 14, Problem statement Which one, in-band or out-of-band transport, is the better option? And, under what circumstances? 9

ICCCN 2007 Aug. 14, Outline Background and problem statement Assumptions and delay models Numerical results Conclusion 10

ICCCN 2007 Aug. 14, Assumptions Signaling protocol processorTransmitter Two stages of servers: protocol processor and transmitter Protocol processor: can be software-based or hardware-based Transmitter: In-band option: several neighbors/transmitters Out-of-band option: one control-plane link to the Internet Message arrival: Poisson process with rate λ Message processing delay: fixed at 1/µ proc Message transmission delay: fixed at 1/µ tx

ICCCN 2007 Aug. 14, Delay models The first server, i.e., protocol processor, can be analyzed with the classical M/D/1 model ◦ Problem: output process of the first stage (input to the second stage) is not Poisson ◦ Our solution approach: simplify the two-stage models by taking into account practical considerations 12

ICCCN 2007 Aug. 14, Software-based signaling engine Assume processing rate µ proc ≤ trans. rate µ tx ◦ Msg processing time of an off-the-shelf switch: 91ms ◦ 1000-bit msg emission time: 1.7ms over 576Kbps DCC channel; even smaller over 10/100Mbps Ethernet Implication: no queueing delay at the 2 nd server ◦ Two-stage model can be approximated with an M/D/1 queue plus constant delay 13 M/D/1

ICCCN 2007 Aug. 14, Hardware-based signaling engine Call arrival rate, λ, determined by data-plane considerations: ◦ Minimum call holding time needed (given call setup delay) due to utilization considerations ◦ Link capacity in channels, which determines traffic load ◦ Number of data-plane links on the switch We estimate λ in 10 3 calls/s region for a 200Gbps switch µ proc =20000 >> λ ◦ Call proc. time in a hardware-accelerated signaling processor: 5 µs ◦ Implication: approximate the first server with a delay line 14 M/D/1

ICCCN 2007 Aug. 14, Consider retransmissions 15 f(T 0 ) Transmitter λ (1-p) p p: packet loss probability T 0 : time-out limit - 3T n, where T n is one-way network delay Combine M/D/1 results, the simplified queueing models with delay line, and the retransmission model, we obtain: ◦ E[T sw ] – average per-switch delay for software-based signaling engine ◦ E[T hw ] – average per-switch delay for hardware-based signaling engine

ICCCN 2007 Aug. 14, Outline Background and problem statement Assumptions and delay models Numerical results Conclusion 16

ICCCN 2007 Aug. 14, Parameter values Change λ so that offered load varies between 0.05 and 0.95 µ proc : 200k msg/sec for h/w; 20 or 50 msg/sec for s/w µ tx : 500 msg/sec for in-band transport; 10k msg/sec for out-of-band transport : 0.2ms in metro area; 25ms in wide-area for s/w; 5ms in wide-area for h/w : 1ms in metro area; 40ms in wide-area for s/w; 10ms in wide-area for h/w 17

ICCCN 2007 Aug. 14, Main delay components Message processing delay: ◦ Queueing delay + service time: software implementation ◦ Negligible: Hardware implementation Message transport delay: ◦ Message transmission delay:  Queueing delay possible with in-band (e.g., 576kbps)  if number of in-band channels is insufficient relative to signaling message load  Negligible: Out-of-band signaling (e.g., 10Mbps) ◦ Network delay:  Propagation delay only: in-band  Propagation delay + queueing delay at IP routers: out-of-band

ICCCN 2007 Aug. 14, Results with software signaling Software signaling processor; plots show the effect of metro-area vs. wide-area, in-band (IB) vs. out-of-band (OOB) transport, with two values of message processing service rate, µ proc 19

ICCCN 2007 Aug. 14, Results with hardware signaling Hardware signaling: plots show the effect of metro-area vs. wide-area, and in-band vs. out-of-band transport 20

ICCCN 2007 Aug. 14, Conclusion: Use in-band transport Software signaling engine  Message processing delay on the same order as network delay  So both message processing delay + message transport delay matter  Preferred transport option: IN-BAND  Why?  Message transmission delay is low (10Mbps transmitter); no queueing  Network delay is higher in out-of-band Hardware signaling engine  Message processing delay negligible, which makes message transport delay even more important than with software signaling  Preferred transport option: IN-BAND  Given that higher call loads can be handled (based on data-plane considerations), a larger number of in-band channels are needed to keep load to the transmitters low to avoid transmitter queueing delays. 21

ICCCN 2007 Aug. 14, Conclusions from a delay perspective Metro area ◦ Choice of transport scheme depending on parameter values Wide area ◦ Software signaling engine  Difference in transmitter rates does not matter much since no queueing delay buildup at the transmitter  In-band transport is better because of lower network delay ◦ Hardware signaling engine  In-band signaling is preferred if message load can be kept low  Using multiple parallel DCC channels or a fat pipe as signaling channel  Network delay through IP routers can be significant, making out-of- band transport a less preferable option in spite of higher transmitter rate 22

ICCCN 2007 Aug. 14, Questions, comments? Thanks! 23