Giovane C M Moura

Aiko Pras
email: a.pras@utwente.nl

Tiago Fioreze
email: t.fioreze@utwente.nl

Pieter-Tjerk De Boer
email: p.t.deboer@utwente.nl

Self-management of Hybrid Networks -Hidden Costs due to TCP Performance Problems

Self-management is one of the most popular research topics in network and systems management. Little is known, however, regarding the costs, in particular with respect to performance, of self-management solutions. The goal of this paper is therefore to analyze such hidden performance costs. Our analysis will be performed within the context of a specific example, namely automatically moving elephant flows from the routed IP layer to optical light-paths (lambdas) in hybrid networks. The advantage of moving elephant flows to light-paths is that such flows will experience lower delays, lower jitter and lower loss, thus better Quality of Service (QoS), while reducing the load at the IP-level, which means that the remaining flows will also experience better QoS. The lower delay at the optical level may cause temporary reordering of packets, however, since the first packet over the light-path may arrive at the receiver side before the last routed IP packet has arrived. Such reordering may lead to short but severe performance problems at the TCP level. We systematically analyze under which conditions such TCP performance problems occur, and how severe these problems are. Although our conclusions are specific to self-management of hybrid networks, it demonstrates by means of an example that self-management solutions may also introduce new problems, which must further be investigated before conclusions can be drawn regarding the pros and cons of self-management.

Introduction

One of the most popular research topics within the network management community is self-management [START_REF] Pras | Key Research Challenges in Network Management[END_REF][START_REF] Jennings | Towards Autonomic Management of Communications Networks[END_REF][START_REF] Lupu | AMUSE: Autonomic Management of Ubiquitous e-Health Systems[END_REF][START_REF] Cheng | Self-organising Management Overlays for Future Internet Services[END_REF][START_REF] Derbel | ANEMA: Autonomic Network Management Architecture to Support Self-configuration and Self-optimization in IP networks[END_REF]. The key idea behind self-management is to develop computer systems that are able to manage their own operation without (or with little) human intervention. Although self-management is often seen as a solution for many problems, little is known about the hidden costs in terms of potential new problems that may result from self-management. Such problems may vary from case to case, and therefore need to be investigated within the context of specific examples.

To get a better understanding of such hidden problems, this paper tackles the example of hybrid networks in which routed flows at the IP level can be moved to the optical level. In such networks, IP packets can be forwarded either through a chain of IP routers, or through an end-to-end lightpath. Such a "lightpath" uses optical switching technology, either at the level of entire fibers, a wavelength within a fiber (lambda), or a TDM-based channel (SONET/SDH) within a wavelength; in any case, switching delays will be smaller, and data rates may well be higher than at the IP level. Moving large flows from the routed IP level to a direct optical lightpath thus enables these flows to experience a faster and more reliable service, while at the same time reducing the load on the IP level equipment, which is typically much more expensive than lightpath equipment.

Current approaches to manage such hybrid networks mostly rely on human operators in order to: (i ) select the flows to be moved to the optical level, and (ii ) create and release the necessary lightpaths. Since these decisions can be slow and error prone, we envision a move towards self-management approaches, which automatically move IP flows to lightpaths on the fly [START_REF] Fioreze | A Statistical Analysis of Network Parameters for the Self-management of Lambda-Connections[END_REF][START_REF] Fioreze | Self-management of Lambda-connections in Optical Networks[END_REF][START_REF] Fioreze | An Architecture for the Self-management of Lambda-Connections in Hybrid Networks[END_REF]. Network operators would only be required to initially configure the self-management process with decision policies, such as setting thresholds and priorities. After this initial setup, the self-management process runs by itself. For more details, see [START_REF] Fioreze | Self-Management of Hybrid Optical and Packet Switching Networks[END_REF]. Self-management of hybrid networks can result in performance problems at the TCP level, however. In a manual process, a lightpath is established a-priori, before the start of the flow (note that within this paper the term "flow" relates to a single TCP connection). Since our self-management process cannot rely on human intelligence to identify a-priori which flows should be transferred over a lightpath, it should analyze existing flows at the IP level to find those flows that are worthwhile to be moved to the optical level. Flows are thus moved on the fly, which means that the first packets of a flow may be forwarded at the IP level, whereas later packets can be moved to the lightpath. The lower delay at the optical level may cause temporary reordering of packets however, since the first packet over the lightpath may arrive at the receiver side before the last packet has arrived via the IP level. Under certain conditions, such reordering may lead to short, but severe performance problems at the TCP level.

The goal of this paper is to investigate the potential performance problems at the TCP level, to gain a better understanding of the potential hidden costs of selfmanaging hybrid networks. With 'cost', we do not necessarily mean monetary costs, but more generally problems and disadvantages (although those may well translate into monetary costs for a commercial network operator). Also, we will not look at the direct costs such as the costs of (re)configuring the equipment when moving a flow.

The approach taken in this paper is to first identify the factors that may limit the throughput of a TCP flow, and define four scenarios to cover these factors, thus extending a previous paper [START_REF] Moreira Moura | Optical switching impact on TCP throughput limited by TCP buffers[END_REF] in which we analyzed only one scenario. We will then use the ns-2 network simulator [START_REF]The Network Simulator NS-2[END_REF] to investigate, for each scenario, the effect of moving TCP flows on the fly.

As noted above, the essence of the problem is the reordering of packets and TCP's reaction to it. Of course, packet reordering is not limited to moving flows to the optical domain, or to hybrid networks in general. It can also have many other causes, such as multipath routing, load balancing, and route changes. In fact, [START_REF] Bennett | Packet reordering is not pathological network behavior[END_REF] shows that packet reordering is a very common occurrence in the Internet, and there have been many studies on its impact and potential countermeasures, such as [START_REF] Zhang | RR-TCP: a reordering-robust TCP with DSACK[END_REF][START_REF] Karlsson | Impact of multipath routing on TCP performance[END_REF]. Our study is different in that the reordering affects a single very high rate flow, making the impact much larger than when the same amount of reordering is spread out over many smaller or lower rate flows. Also, in our case the reordering is intentional, and if its consequences are found to be too severe, it would be an argument against the use of the self-management system.

The paper structure is as follows. Section 2 discusses the factors that limit the TCP throughput, defines the four scenarios that cover these factors, and introduces the ns-2 simulation setup used. Following that, Section 3 presents the simulation results for all four scenarios. In Section 4, the insights gained for the four scenarios are generalized to other scenarios and transport protocols. Finally, Section 5 presents our conclusions.

Simulation Setup

This section discusses the simulation setup: we discuss the topology, the relevant thoughput limiting factors, the TCP variant to be used, and the simulator.

Network Topology Figure 2 shows our simulation topology. It consists of three routers (r1, r2, and r3) and two nodes (Sender and Receiver) connected by two different paths: the IP path (r1-r2-r3) and the optical path (r1-r3). The simulation starts with the sender opening a single TCP connection to the receiver and sending data, forwarded via the IP path. After reaching a predefined throughput value, the decision is made to move that flow to the optical path: from that moment on, router r1 will forward all subsequent data to the receiver via the optical path. Note that this only affects the data direction (sender → receiver), while the acknowledgment packets continue to use the IP path. For a short period of time after the switch -the transient phase -there will be data packets on both the IP and optical paths; after this phase, all data packets are on the optical path.

Simulation Scenarios Although many factors can limit the throughput of TCP [START_REF] Timmer | How to Identify the Speed Limiting Factor of a TCP Flow[END_REF], since the scope of this paper is on self-management of network configurations, we focus on those factors that relate to the configuration of the network, namely the capacity of network links and the size of the TCP buffers. Thus, we have identified the following scenarios:

-Scenario A: the size of the TCP buffers (α in Figure 2) are the limiting factors for the TCP throughput. -Scenario B: the capacity of the sender's local link (β in Figure 2) is the limiting factor for the TCP throughput. -Scenario C: the capacity of the core links (φ 1 and φ 2 in Figure 2) acts as the limiting factor. We distinguish between the cases where the capacity of IP links is equal to that of the optical links (φ 1 = φ 2 ) and where the capacity of the optical links is larger than that of the IP links (φ 2 > φ 1 ). -Scenario D: the receiver local link is the limiting factor (ξ in Figure 2).

For each scenario we simulate three limiting data rates: 100 Mbps, 1 Gbps, and 10 Gbps. In each simulation, the flow is moved to the optical path once the actual throughput reaches the limiting rate. We simulate three base RTT values, namely 10, 100 and 1000 ms, with corresponding optical path RTTs of 6, 60 and 600 ms, respectively. Table 1 summarizes the values of the parameters used in our simulation scenarios for RTT=10 ms; an equal number of simulations was conducted for 100 ms and 1000 ms RTT, with α in Scenario A scaled accordingly. TCP version and simulator For this study, we decided to use TCP CUBIC (version 2.1) [START_REF] Ha | CUBIC: a new TCP-friendly high-speed TCP variant[END_REF], since it is adapted to links with a large bandwidth-delay product (as is the case in our scenarios), and nowadays widely used because it is the default in Linux. For the simulations we use the ns-2 network simulator, version 2.33, which can run the actual TCP CUBIC code from Linux [START_REF] Wei | NS-2 TCP-Linux: an NS-2 TCP Implementation with Congestion Control Algorithms from Linux[END_REF].

Simulation results

In this section, we show some simulation results for all four scenarios, illustrating the various problems that may occur.

Scenario A: TCP Buffers as the Limiting Factor

In this scenario we configured the TCP buffers to act as the limiting factor of the TCP throughput, as discussed earlier in [START_REF] Moreira Moura | Optical switching impact on TCP throughput limited by TCP buffers[END_REF]. This is done by setting the other potentially limiting factors (link capacities β, φ, and ξ) high enough, as presented in Table 1. The TCP buffers were set equal to the bandwidth-delay product, calculated from the limiting flow rate (100 Mbps, 1 Gbps or 10 Gbps) and the RTT before the switchover. For all cases of Scenario A, only one type of behavior was seen, independent of RTT and buffer sizes: after the switchover, the TCP throughput increases without any packet loss. Figures 3(a) and 3(b) show the throughput as a function of time for the 1 Gbps case, before and after the switch at t = 0 (vertical line).

These graphs differ in their "granularity", i.e., the time interval over which the data rate is averaged. This is a compromise between cluttering the picture at too small granularity, and masking interesting effects at coarse granularity. We henceforth show only graphs for a granularity of 1000 ms; if this hides any interesting effects, these are discussed in the text.

As can be seen, before switchover the flows present a stable rate of 1 Gbps, limited only by the TCP buffers. After the switchover, CUBIC's throughput increases quickly to the expected new theoretical value of 1.667 Gbps (i.e., the buffer size divided by the new RTT).

Scenario B -Sender's Local Link as the Limiting Factor

In Scenario B, the sender's local link is the limiting factor for TCP throughput. Intuitively, one might expect that in this case, the optical switch has no influence, since the bottleneck does not change. However, this is not true; Figure 4 shows that there is a brief decrease of the throughput immediately after the switch (solid line), compared to the case without switching (dotted line). With a finer granularity, one can also see a peak of 1.3 Gbps in the first 0.1 s after the switch. This is due to packets arriving from both the IP and optical paths during this transient phase. The packets arriving via the optical path have a higher sequence number than the ones coming from the IP path, because of the optical path's lower delay. This causes the receiver to perform reordering and ask for retransmissions (through a total of 14186 duplicate ACKs), resulting in the reduction of the congestion window and thus a throughput reduction. This can be seen at t = 102 s, where the throughput reaches 803 Mbps.

Scenario C -Core link as the Limiting Factor

In this scenario, the core link is the limiting factor, and we distinguish two cases: C1 with the IP and optical links having the same capacity (φ 1 = φ 2 ), and C2 with the optical link being faster (φ 2 > φ 1 ). In scenario C1, the behaviour turns out essentially the same as in scenario B, so we focus on scenario C2.

In scenario C2, similar behavior was seen as in scenarios C1 and B during the transient phase: throughput oscillation. However, after this oscillation, the throughput increases significantly, using the optical path's higher capacity. This is shown in Figure 5 for a 10 Gbps IP link and a 39.813 Gbps optical link, at RTTs of 10 and 100 ms. In either case, we see a mostly linear 1 growth of the throughput until the IP link is fully utilized; then the switch to the optical domain is made, and mostly linear growth resumes until the optical link speed is reached. Fig. 5. Throughput of TCP flows in Scenario C2 (1000 ms granularity)

1 One might expect cubic rather than linear growth; however, version 2.1 of TCP CUBIC had an upper bound on the growth rate. This was removed in version 2.2 [START_REF] Ha | CUBIC: a new TCP-friendly high-speed TCP variant[END_REF].

Scenario D -Receiver's Local Link as the Limiting Factor

Finally, we consider the case where the receiver's local link is the bottleneck and all other links are overdimensioned. Results for the 10 Gbps case are shown in Figure 6. As can be seen, there is a severe reduction in the throughput after the switchover.

Like in the other scenarios, after the switchover router r3 temporarily receives data via both the IP and the optical links simultaneously, for a total of 20 Gbps. However, unlike in the other scenarios, the link from this router to the destination was already fully loaded at 10 Gbps, and cannot cope with this temporary double data flow. Queueing all these packets is not possible either (in our simulation, r3 has a 500 packet buffer), causing many packets to be dropped (335107 packets in the first 200 ms after the switchover in the 10ms RTT case). This in turn causes the receiver to send a massive number of duplicate ACKs, which leads the sender to reduce its congestion window, causing the throughput to drop to a minimum value of 1.6 Gbps.

Figure 7 shows how r3's queue size changes in time. Since TCP CUBIC (like most other TCP versions) measures the available bandwidth on the path by increasing its congestion window until packet loss occurs, the queue also builds up at other moments than the switchover, for example at t = 46s. When the optical switchover occurs at t = 55 s, the queue already contains 343 packets due to TCP CUBIC probing for bandwidth. After the switchover, packets arrive from both paths, causing the queue to fill up very quickly and resulting in a massive discarding of packets, as discussed above. The queue increases at later times are again due to CUBIC's normal bandwidth probing.

Note that the problem seen here is fundamentally different from that seen in scenarios B and C. In either case, temporarily two streams of packets (namely via the IP path and via the optical path with less delay) are merged, causing reordering. However, in scenarios B and C, no packets were dropped, whereas in the current scenario many packets are dropped. This causes a much larger reduction in throughput, and recovery from this also takes much more time.

Discussion and generalization

In the previous section, we have seen three types of behaviour when switching a TCP flow from the IP to the optical path:

-When the TCP buffers were the limiting factor (scenario A), nothing untoward happens: the system converges quickly to the new higher throughput made possible by the lower RTT. -When the sender's link or the IP and optical paths are the bottleneck (scenarios B and C), temporarily packets from both paths arrive at the receiver, causing reordering but no loss. We have seen that TCP reacts to this rather benignly, with only a small (< 20%) and short-lived reduction in throughput. -When the receiver's link is the bottleneck (scenario D), it gets overloaded due to the temporary simultaneous arrival of packets via both paths. This causes much packet loss and a severe (> 80%) reduction of throughput, from which recovery takes longer (thousands of RTTs).

These conclusions can easily be generalized to other situations, as follows.

Other TCP variants The choice for TCP CUBIC was already motivated in Section 2. Still, we have done similar experiments with three other TCP variants (Reno, Vegas, Compound). The results for Compound were similar to those for CUBIC reported here, sometimes recovering even faster.

Reno and Vegas performed far worse: due to their at most linear growth of the congestion window, they need much more time to recover. In fact, for the same reason they need much time to fully utilize link with a large delay bandwidth product even before the changeover, making them unsuitable for the kind of elephant flows considered here. Therefore, their problems with recovering from the optical switchover can be safely ignored.

Other protocols Although TCP is the dominant transport protocol in the internet, there are others, such as UDP, SCTP and DCCP. Clearly, after the switchover they will experience the same packet reordering and loss as TCP.

UDP does not by itself have a congestion control mechanism, so the reordering and loss will not directly affect its throughput. However, the reordering and loss will be passed on to the application, so detailed knowledge of the application would be needed to predict the effects for the user.

New transport protocols such as SCTP (Stream Control Transmission Protocol) [START_REF]Stream Control Transmission Protocol (SCTP)[END_REF]) and DCCP (Datagram Congestion Control Protocol) [START_REF] Kohler | Datagram Congestion Control Protocol (DCCP)[END_REF] have congestion control mechanisms that are directly based on TCP variants [START_REF] Floyd | Profile for Datagram Congestion Control Protocol (DCCP) Congestion Control ID 2: TCP-like Congestion Control[END_REF]. Therefore we can expect them to behave similarly to TCP, with possibly additional application layer effects like with UDP.

Other scenarios In the scenarios considered so far, the same parameter was the limiting factor before and after the switchover. Of course, in reality after the switchover a different parameter can be the limiting factor. What happens in those cases will generally be a mixture of the "pure" behaviours studied here.

Also the numerical values of parameters (link speeds etc.) can be different. Clearly, such changes will change the outcomes quantitatively (e.g., recovery will take longer or shorter), but no qualitative differences are to be expected.

One might hope that installing a large buffer at the output router would prevent the massive packet loss in scenario D, but this is not true. TCP's congestion control algorithm would have filled such a buffer (because TCP needs to detect loss to know when to back off), so there would not be space to temporarily accept the extra packets when the flow is moved to the lightpath.

Conclusions

In this paper we investigated hidden costs of self-management within the specific context of hybrid networks. In particular we analyzed the performance problems that may result if an elephant TCP flow at the IP level is moved on the fly to the optical level using ns-2 simulations for four different scenarios. During such move, a temporary but massive reordering of packets occurs since the first packets transferred over the optical level will arrive before the last packets arrive at the IP level.

We found three qualitatively different behaviours. In case the TCP throughput of the elephant flow was limited by the size of the TCP send and receive buffers, the throughput increases substantially due to the lower RTT of the optical path. In case the throughput was limited by the sender's local link or by the backbone links, TCP reacts benignly to the reordering, with only a small and short-lived reduction of throughput. On the other hand, if the throughput was limited by the receiver's local link, a significant drop in the throughput occurs for a relatively long period. In this case, the router at the receiver side needs to drop a large number of packets when they arrive simultaneously via both links, because its outgoing link was already fully used.

The significant throughput drop and long recovery period observed in the last scenario can be very noticable to the end user, and thus is something the operator of the network might want to avoid. However, whether or not this problem is going to occur depends on the bottleneck in the receiver's network, which may well be out of sight of the operator of the hybrid network, making this truly a hidden cost of implementing self-management.

The conclusion that can be drawn from the hybrid networks case presented in this paper, is that self-management mechanisms may introduce unexpected side-effects, which require further analysis before such self-management mechanisms can be widely adopted. Research on self-management mechanisms should therefore not be performed in isolation, but always consider the context in which these mechanisms will be applied, to fully understand their pros and cons.

Fig. 1 .

 1 Fig. 1. Self-management of lightpaths in hybrid optical and packet networks: in step 1, the elephant flows are identified; in step 2 the optical switches are informed about the decision to move a flow; and in step 3, the optical switches establish the lightpath.

Fig. 2 .

 2 Fig. 2. Topology used in the simulations and limiting factors (Greek letters)

(Fig. 3 .

 3 Fig. 3. Throughput of TCP flows in Scenario A (1 Gbps limiting rate)

Fig. 4 .

 4 Fig. 4. Throughput of TCP flows in scenario B for RTT=100 ms, β = 1 Gbps and granularity equal to 1000 ms

Fig. 6 .Fig. 7 .

 67 Fig. 6. Throughput of TCP flows for Scenario D (1000 ms granularity)

Table 1 .

 1 Scenarios and values used for the limiting factors for RTT equal to 10 ms

	Scenario Limiting Rate α (rtt=10ms)	β	φ1	φ2	ξ
		100 Mbps	0.125 MB	622.08 Mbps 622.08 Mbps 622.08 Mbps 622.08 Mbps
	A	1 Gbps	1.25 MB	2.488 Gbps 2.488 Gbps 2.488 Gbps 2.488 Gbps
		10 Gbps	12.5 MB	39.813 Gbps 39.813 Gbps 39.813 Gbps 39.813 Gbps
		100 Mbps	1.16 GB	100 Mbps 622.08 Mbps 622.08 Mbps 622.08 Mbps
	B	1 Gbps	1.16 GB	1 Gbps	2.488 Gbps 2.488 Gbps 2.488 Gbps
		10 Gbps	1.16 GB	10 Gbps	39.813 Gbps 39.813 Gbps 39.813 Gbps
		100 Mpbs	1.16 GB	622.08 Mbps 100Mbps	100Mbps	622.08Mbps
	C1	1 Gbps	1.16 GB	2.488 Gbps	1 Gbps	1 Gbps	2.488 Gbps
		10 Gbps	1.16 GB	39.813 Gbps	10 Gbps	10 Gbps	39.813 Gbps
		100 Mbps	1.16 GB	622.08 Mbps 100 Mbps 622.08 Mbps 622.08 Mbps
	C2	1 Gbps	1.16 GB	2.488 Gbps	1 Gbps	2.488 Gbps 2.488 Gbps
		10 Gbps	1.16 GB	39.813 Gbps	10 Gbps	39.813 Gbps 39.813 Gbps
		100 Mbps	1.16 GB	622.08 Mbps 622.08 Mbps 622.08 Mbps 100 Mbps
	D	1 Gbps	1.16 GB	2.488 Gbps 2.488 Gbps 2.488 Gbps	1 Gbps
		10 Gbps	1.16 GB	39.813 Gbps 39.813 Gbps 39.813 Gbps	10 Gbps

Acknowledgments The research reported in this paper is supported by the FP7 ICT UniverSelf project (#257513). The authors would like to thank Wouter Kooij for his work on extending the simulations presented in this paper to other TCP flavors -Vegas, Reno, and Compound.


Substrate influence on the emergence of the TMA systems of the Surinamese Creoles

Keywords: Suriname Creoles, Gbe, substrate influence, TMA

Although the Surinamese Creoles have figured prominently in discussions about Creole genesis, little is still known about the origin of their TMA system, a central area of grammar that has received much attention in this debate. In this paper we assess the relative contribution of the primary substrate input, varieties of Gbe, to the TMA system. Drawing on both contemporary data from several Surinamese Creoles and varieties of Gbe, and historical data from Sranan Tongo, we show that the substrate was clearly responsible for the emergence of some aspect and tense categories. However, in itself, substrate influence cannot explain the emergence of the entire Creole tense and aspect system. Other processes such as internal change, superstrate influence etc. also played an important role.

Introduction.

A variety of different explanations have been offered for the origins of Creole TMA systems, and for those of the Surinamese Creoles in particular. On the one hand, [START_REF] Bickerton | Roots of language[END_REF][START_REF] Bickerton | The language bioprogram hypothesis[END_REF] used Sranan Tongo to illustrate his claim that the core categories shared among Atlantic Creoles, an "Anterior" Tense, an "Irrealis" mood and a "Non-punctual Aspect", were ab ovo creations by children appealing to innate linguistic knowledge. More recently, [START_REF] Bally | On the origin of the Saramaccan TMA system: Relexification and reanalysis[END_REF] claimed that the relexification hypothesis of Creole origins, which [START_REF] Lefebvre | The tense, mood and aspect system of Haitian Creole and the problem of transmission of grammar in creole genesis[END_REF] used to explain the emergence of the Haitian Creole (HC) TMA system, could also be extended to Sa(r)amaka, a sister language of Sranan Tongo. This view is diametrically opposed to that of the so-called "superstratist" view of French-lexicon creole formation, which maintains that most of creole grammar can be traced to the lexifier language, which was available as a target in the earlier stages of contact [START_REF] Chaudenson | Des îsles des hommes, des langues[END_REF][START_REF] Chaudenson | Creolization of language and culture[END_REF]. To add to the disagreement, [START_REF] Mcwhorter | A Creole by any other name: streamlining the terminology. Spreading the word: The issue of diffusion among the Atlantic creoles[END_REF]McWhorter ( :8, 2004) apparently claims that internal factors played the primary role in the emergence of the TMA system of Sranan Tongo. He specifically rejects any significant role for the substrate languages.

The present paper is, in part, an attempt to assess these conflicting views, with particular reference to the Surinamese creoles. Most of our focus here will be on Sranan Tongo and the Eastern Maroon Creoles, particularly Pamaka and Ndyuka, with some reference to Saramaccan where appropriate.

Our approach here, like that of superstratists and substratists alike, is based on the assumption that Creole formation involved a process of second language acquisition. This process was shaped by three complementary factors: the nature and extent of superstrate input, the type and degree of substrate influence, and internally-motivated developments. We assume that the roles played by these factors were guided by universals of language learning and restructuring.

Differences among Creoles depend crucially on the extent to which one or the other of these factors prevailed in the contact situation. This in turn depends on a range of socio-demographic factors that have been discussed in great detail in the literature [START_REF] Arends | Demographic factors in the formation of Sranan. The early stages of creolization[END_REF][START_REF] Chaudenson | Creolization of language and culture[END_REF][START_REF] Mufwene | The ecology of language evolution[END_REF], Singler 1995 etc.). 17 th century Suriname, the unavailability of English as a continuing target meant that the creators of these Creoles relied far more heavily on their L1 grammars to develop the Creole's resources. This is supported by ample evidence of strong substrate influence on various aspects of their grammar (see the Introductin to this volume). We will argue that the TMA systems of the Surinamese Creoles also provide evidence of such substrate influence. Yet we do not claim that such influence by itself explains the emergence of these TMA systems. There is also evidence of some influence from the European languages, as well as internal developments. Those TMA categories that show similarity to their Gbe counterparts are the main focus of this paper.

2. Establishing substrate influence on Creole TMA systems.

A full account of substrate influnce requires that we consider all of those substrate languages that had a primary role to play in Creole formation. In this paper, however, we focus our attention on the influence of the Gbe languages since both sociohistorical and linguistic evidence suggest that speakers of Gbe were most numerous in the formation of the early plantation varieties from which all modern creoles of Suriname descend. Other languages such as Kikongo and Akan were represented in the contact situation to a lesser extent. We leave the role of these languages for later research.

The approach we take here is summed up as follows. First, our arguments are based on a comparison across several representative Gbe languages and Surinamese creoles. (footnote 1 here) The Gbe languages include Ajagbe, Gengbe, Maxigbe, Wacigbe, Xwelagbe, and Xwlagbe. They are representative of the five major sub-groups identified by [START_REF] Capo | Renaissance du Gbe: Réflexions critiques et constructives sur l'Eve, le Fongbe, le Gengbe[END_REF]. For the Surinamese Creoles we focus on Sranan Tongo and the Eastern Maroon Creoles, Pamaka and Ndyuka.

Where appropriate we also include data from Saamaka. Second, our comparison is based on well-known frameworks for the investigation of TMA systems crosslinguistically (see below). Moreover, our analysis of Gbe Tense/Aspect benefits from the intuitions and judgments of linguists who are themselves native speakers of Gbe languages.

A framework for comparing tense-aspect systems

The framework we use to investigate the TA system of the Creoles of Suriname and Gbe is modeled after typological studies of TMA systems such as [START_REF] Dahl | Tense and aspect systems[END_REF], [START_REF] Comrie | Aspect: An introduction to the study of verbal aspect and related problems[END_REF][START_REF] Comrie | Tense[END_REF] and [START_REF] Bybee | The evolution of grammar: Tense, aspect, and modality in the languages of the world[END_REF] and has been discussed more fully in other studies (e.g., Winford 2000aWinford , 2000b)). The basic assumptions of the framework can be outlined as follows. First, our analysis is based on the actual TMA categories themselves. Second, it is crucial for our purposes to distinguish between the TMA categories which are grammaticized in a language, and the notional or semantic categories that may be expressed in various ways by different TMA categories, as well as by other means such as adverbials. Third, we assume, with Dahl, that every TMA category has a dominant meaning and often has other secondary meanings as well. In general, the dominant meaning of a category is represented in its primary or prototypical uses, while secondary meanings are contextually determined interpretations that arise from more peripheral uses of the category.

The distinctions outlined here are crucial to our comparison, for the simple reason that a close match between languages with respect to both meaning and uses of a TMA category is a powerful argument for similarity between them. If we can demonstrate such close similarity between Gbe and Surinamese TMA systems, this would be strong evidence of continuity from the former to the latter.

We must therefore emphasize the crucial role of the discourse context in deciding the interpretation of TMA categories. For these reasons, we employed methods of data collection designed to capture as much discourse context as possible for the use of each tense/aspect category.

Data collection

The data for the Surinamese Creoles were collected from relatively conservative native speakers, e.g. Afro-Surinamese working-class groups in the capital, Paramaribo, and rural groups in Coronie in the case of Sranan Tongo and monolingual subsistence farmers living in the interior villages, or monolinguals and bilinguals from coastal settlements in French Guiana in which maroons are clearly dominant. The Gbe data were collected in Benin from speakers of each of the five major subgroups of Gbe in [START_REF] Capo | Renaissance du Gbe: Réflexions critiques et constructives sur l'Eve, le Fongbe, le Gengbe[END_REF] classification. They are monolingual and bilingual speakers who grew up in the rural villages and have lived there for most of their lives.

The data consist of two types: tape recordings of free conversation among native speakers of the languages in question, and (b) elicitations from selected informants employing a modified version of [START_REF] Dahl | Tense and aspect systems[END_REF] questionnaire. The questionnaire consisted of a number of sentences and short connected texts in English (for Sranan) and French (for Gbe and Pamaka, Ndjuka), which were offered for translation to informants. They were given clear indications, with additional explanation where necessary, of the contexts in which they were to envisage the sentences being uttered. In addition to providing equivalents of the English and French sample sentences, the informants were also encouraged to supply additional examples of their own, to evaluate differences in meaning between similar constructions, and to assess sample sentences constructed by the fieldworkers/authors. The elicited data were also evaluated and discussed in some detail by linguists who are native speakers of Gbe varieties.

2. Substrate influence and SLA

Researchers in second language acquisition (SLA) and creole formation generally agree that learners' L1s exert varying degrees of influence on the acquisition of the target language (TL), or L2. Such influence has been referred to as either "substratum influence" or "transfer" [START_REF] Siegel | Mixing, leveling and pidgin/creole development. The structure and status of pidgins and creoles[END_REF][START_REF] Siegel | Transfer constraints and substrate influence in Melanesian Pidgin[END_REF][START_REF] Siegel | Substrate influence in Creoles and the role of transfer in second language acquisition[END_REF]DeGraff 1999, etc.). On the other hand, researchers such as [START_REF] Lefebvre | The tense, mood and aspect system of Haitian Creole and the problem of transmission of grammar in creole genesis[END_REF]Lefebvre ( , 1998) ) and [START_REF] Lumsden | Language acquisition and creolization[END_REF] argue that the process underlying substratum influence is relexification, a mental process that builds new lexical entries by combining superstrate phonological forms with the syntactic and semantic information of substrate lexical categories (Lumsden 1999: 129). These two approaches in fact share much in common. Lefebvre (1998:376) points out that "the type of data claimed to be associated with the notion of transfer in creole genesis corresponds to the result of the process of relexification." In both scenarios, learners reinterpret lexical items in the available target input as equivalents of L1 forms.

There is also general consensus that such reinterpretation is subject to certain constraints. [START_REF] Siegel | Mixing, leveling and pidgin/creole development. The structure and status of pidgins and creoles[END_REF][START_REF] Siegel | Substrate influence in Hawai'i Creole English[END_REF][START_REF] Siegel | Substrate influence in Creoles and the role of transfer in second language acquisition[END_REF] argues that such constraints fall into two broad categories. One consists of "availability" constraints, among them perceptual salience and congruence, which determine the likelihood that a substrate feature may be transferred to a creole (Siegel 2000:83). Advocates of the relexification hypothesis also recognize these constraints (Lumsden (1999:140).

Siegel further suggests that "reinforcement principles", including frequency, operate to determine "which of the transferred features will actually be retained in the creole" (2000:83). Thus, features or structures that are common to the substrates are particularly likely to be retained, and that the greater the typological similarity among the substrates, the more likely it is that similar kinds of substrate influence will occur in learners' various interlanguages.

Following on the assumptions of the two approaches just discussed, we would hypothesize, first, that superstrate-derived forms whose semantics (partly) match those of substrate functional heads would be selected to express the functional categories of the Creole. We would also expect that grammatical categories and their means of expression (preverbal, periphrastic) that are shared across the (dominant) substrates are also most likely to be retained in the Creole.

4. Tense and aspect in the Surinamese creoles.

Table 1 provides an overview of the tense and aspect categories in four comtemporary Surinamese creoles. Sources include Winford (2000a) for Sranan, [START_REF] Huttar | Ndyuka[END_REF] for Ndyuka and [START_REF] Rountree | Saramaccan Grammar Sketch[END_REF] for Saramaccan, but Table 1 is based primarily on our own analysis.

(Table 1 about here) The expression of tense and aspect in the early texts (van Dyk 1765, Schumann 1783 and others) has been studied in some detail by van den Berg (to appear), who provides a summary of the forms and their primary meanings, reproduced here in amended form as Table 2.

(table 2 about here)

The categories and forms used in early Saramaccan as described by Riemer (1779) and Schumann (1778) are identical, except that imperfective is marked by tan (< tan 'stand, stay') and the future form is consequently realized as tan go.

A comparison of the two tables reveals that all of the tense/aspect categories of the modern creoles, with the exception of Future (g)o, are already well established in the early texts. Moreover, the forms expressing these categories are the same (with some phonological variation), while their positioning and interpretation match. In the case of future time reference, however, there are some differences between the early texts and the modern creoles, which will be discussed further below (cf. Section 5.5.2). It should also be obvious that none of the forms used to express tense/aspect categories in the Surinamese creoles has any counterpart with similar function morphemes in English, and hence could not have been modeled on the latter. We will now provide an overview of the tense/aspect categories of Gbe.

Tense and Aspect in Gbe

As Table 3 shows, the six Gbe varieties chosen for this paper share the same inventory of Tense and Aspect categories and make use of similar strategies to express them. These findings confirm those of other researchers such as [START_REF] Essegbey | Inherent complements revisited: towards understanding of argument structure in Ewe[END_REF], 2004), Fabb (1992), [START_REF] Jondoh | Some Aspects of the predicate phrase in Ge(n)gbe[END_REF], [START_REF] Kinyalolo | A Note on Word Order in the Progressive and Prospective in Fongbe[END_REF], and [START_REF] Lefebvre | A grammar of Frongbe[END_REF]. Table 3 only includes what could be called the core categories of the Gbe tense and aspect system.

(table 3 about here) Table 3 shows that the main difference among the varieties of Gbe emerge in the expression of the aspectual categories. All Gbe varieties have a Perfect, Progressive and Habitual category and several varieties also have a Prospective category but they employ partially different means to encode them. Habitual and Perfect aspect, for instance, are expressed by a preverbal marker in some varieties and by a postverbal marker in others.

A comparison of Table 3 (Gbe) with Tables 1 and2 above (Surinamese Creoles) reveals several differences between the two language groups. As far as tense is concerned, the Gbe varieties only have one category (Future) while the Surinamese Creoles have two. In Gbe, the basic temporal opposition is between Future and non-future; in the Creoles, there is an opposition between Future and Past. In the area of aspect, the Gbe varieties have distinct Habitual and Progressive categories while the Creoles of Suriname have only an Imperfective category that covers both habitual and progressive meanings. Finally, most Gbe varieties have a Prospective aspect category but the Creoles of Suriname do not.

However, there are still strong similarities between the two language groups in several tense/aspect categories which we discuss in more detail below.

5.

Gbe influence on tense and aspect in the Creoles of Suriname

In this section we investigate the sources of the tense and aspect categories of the creoles of Suriname with particular reference to Gbe influence.

5.1. Comparing Perfective in Gbe and the Surinamese Creoles.

Perfective aspect, expressed by the unmarked verb in both Gbe and Surinamese creoles, presents a situation as an unanalyzed whole, without regard to its internal structure (Comrie 1976:16). Hence, as Winford (2000a:394) points out, the unmarked verb "can lend itself to various interpretations in discourse, depending on the context and the predicate involved."

Table 4 shows that in both Gbe and the Surinamese creoles, the unmarked verb is used in a more or less identical range of meanings and uses.

(table 4 about here)

In both language groups, the unmarked verb generally conveys the sense of 'present' time reference with state-denoting verbs (1) and property items (2) and 'simple past' with non-stative verbs (3) in the default cases, where the point of reference is speech time.

( In Gbe, the unmarked state-denoting verb may also have past time reference (5a).

In the Surinamese Creoles, they may have past time reference in the appropriate discourse context, but normally require the past time marker to express this meaning (5b).

( 1995). It seems that the use of kaba with all types of situation represent a further stage of grammaticalization, most likely due to internal developments (see Detgers 2000, Stolz 1987 on the grammaticalization of completive markers in various creoles). There seems to be a cline of grammaticalization from the more verbal status of vOŸ in Eastern Gbe, to its somewhat more adverbial character in Western Gbe, to the fully adverbial status of kaba "already" in the Surinamese creoles. We conclude then that the use of VP-final kaba to convey Completive aspect in the creoles of Suriname was due in part to influence from a similar structure in the Gbe languages.

5.3. The expression of 'imperfective' meaning in Gbe and the Surinamese creoles.

Imperfective aspect in the Surinamese creoles.

Imperfective aspect covers notions such as 'progressive,' 'continuous', and 'habitual.' All of these meanings are conveyed by the marker e (< de) in contemporary Sranan and the Eastern Maroon Creoles, and by ta (< tan) in Saramaccan. In all the Creoles tan also means 'to stay, to wait' and de functions primarily as a locational copula (Migge 2002). In the early texts, de in Sranan and tan in Saramaccan function primarily as markers of progressive aspect ( 14) and only rarely as habitual markers (15). (footnote 5 here).

( He IMPFV sweep office 'He cleans offices.'

In short, the Progressive uses of e and ta in the modern creoles seem to date from the time of Creole formation while the habitual function appears to have emerged later.

By contrast, the Gbe languages have no Imperfective category. Rather, they distinguish between a Habitual and a Progressive. Our task here is to explain why the Surinamese creoles do not follow Gbe in distinguishing between 'habitual' and 'progressive,' but subsume these meanings under a single category.

The Progressive in Gbe

The progressive construction in Gbe follows three general patterns, as shown in (18) (cf. Fabb 1992).

(18) A: 'Be-at' VV PART B: 'Be-at' (NP/XP)V PART C: 'Be-at' V (XP)

Pattern A is generally used with intransitive verbs (19a) and pattern B with transitive verbs (19b). (footnote 6 here)

(19) Gengbe a.

koŸ fi⁄ leŸ Ÿ yiŸ yiŸ m⁄

Kofi be-at RED-go-PART 'Kofi is leaving.' (Jondoh 1980: 39) b. ´l´Ÿ xO⁄ m´Ÿ tutu-N. he be-at room clean-PART 'He is cleaning the room.' There seems to be agreement that the verb 'be-at' in these constructions selects a following nominalized clause (VV or XP V), and also requires the presence of the sentence-final morpheme, much as auxiliary be requires the verbal suffix -ing in English progressive constructions (Aboh 2004:208;Fabb 1992:11).

The form of the final particle varies across the Gbe languages. It has been argued, for instance, that at least some of the final particles (e.g, wE, wO, N, in Fongbe, Gengbe, and Wacigbe respectively) are either locational nouns or may have derived historically from locational nouns meaning 'in(side)' (see Fabb 1992:5,13 for discussion). In Gungbe, according to Aboh (2004:208), "the sentence-final morpheme undergoes partial deletion, leaving only a low tone that attaches to the preceding syllable."

In addition to Patterns A and B, Gengbe also employs a third pattern (C) in which the copula directly precedes an unredublicated verb (20) (footnote 7 here) Our informant clearly preferred this construction, which is similar to the one found in the Surinamese creoles.

(20) Gengbe meŸ le‹ ∂uŸ nu⁄ .

I be-at eat thing 'I'm eating. ' Fabb (1992 :5) In Xwelagbe, the progressive is expressed by a form homophonous with the verb 'to stay,' directly preceding an unreduplicated verb in both transitive (21a) and intransitive (21b) sentences.

( This construction is clearly parallel to the one found in Saramaccan.

In Western Gbe varieties, including Ajagbe, Gengbe, Wacigbe and other Ewe varieties, when a tense marker is present, nO (< 'stay') replaces the copula 'be-at' in both copular and progressive constructions.

(22) a. Gengbe aŸ wuŸ dZE¤ A⁄ leŸ drO⁄ meŸ dress red DET be-at closet in 'The red dress is in the closet.' (Jondoh 1980: 132) b.

AŸ fi⁄ nOŸ nAŸ gAŸ li⁄ pleŸ wOŸ Afi PROG HAB gari buy make 'Afi is generally buying gali.' (Jondoh 1980: 40) Xwelagbe employs nO in all tense/ aspect specifications.

2. Comparing progressive constructions in Gbe and Suriname.

In their progressive use, Imperfective e and ta convey the sense of an event or activity in progress (17). In this, they mirror the Gbe Progressive. In addition, e and ta in the Surinamese Creoles also express secondary meanings similar to those expressed by the progressive construction in Gbe. For instance, when they precede property items and certain psychological state-denoting verbs such as 'know', they convey an inchoative or 'in-process' meaning.

(23) a. Gungbe sin lO⁄ toŸ fi⁄ faŸ . (Aboh, pc 2004) Water DET be-at RED-cold Hertoch IMPFV know DET way 'Hertoch is getting to know the way.' [START_REF] Essegbey | Inherent complements revisited: towards understanding of argument structure in Ewe[END_REF] has argued that the progressive construction yields an inchoative meaning with property-denoting predicates and verbs like 'know' because they are, in fact, process items in the Gbe languages (but see Aboh (2004:227) for a different view). [START_REF] Winford | Property items and predication in Sranan[END_REF] and [START_REF] Migge | The origin of property items in the Surinamese Plantation Creole. Language Change and Language Contact in Pidgins and Creoles[END_REF] make a similar case for the processual nature of these verbs in Sranan and other Surinamese creoles.

Finally, in both Gbe and Surinamese creoles the progressive construction may also convey an imminent future meaning when the main verb expresses motion.

(25) a. Ewe e⁄ gbe ya la me-le asime yi-m⁄ today as-for TOP 1sg-be.at market go-PROG 'As for today, I'm going to the market' b. Pamaka A tamaa a e gwe kaba.

FOC tomorrow she IMPFV leave already 'It's tomorrow she will/is going to leave.' (lit. '..she is leaving already..)'

Perhaps the most striking thing about the progressive construction in the Surinamese Creoles is that their progressive marker is derived from a copula meaning 'to be at', which also functions as a main verb. In the Gbe languages, the copula used in the progressive construction also functions as a main verb in its own right.

(26) a. Sranan A pikin de a oso.

DET child COP LOC house 'The child's at home.' b. Gengbe e⁄ le⁄ eŸ kplO¤ AŸ dZi ⁄ (Jondoh 1980:46) it be-at table-the on 'It's on the table.'

Further important evidence in favor of Gbe influence on the progressive category of the Surinamese creoles is the fact, noted earlier, that in several Gbe varieties, 'be-at' in both copular and progressive constructions is replaced by nO 'to stay' when combined with a tense/aspect or negative marker (21b, 22b). This may also have contributed to the fact that Saramaccan chose ta(n) 'stay' to express progressive meaning. This choice may have been also influenced by the use of ta (< Portuguese estar 'to be') functioning as an Imperfective marker in the Portuguese-lexicon contact variety that was part of the input to Saramaccan.

Based on this evidence, we argue that the emergence of de as a locational copula in the early plantation creole (cf. Migge 2002) was the trigger for its extension to the marking of progressive meaning. The model for this extension was the fact that the locative copula is also used in progressive constructions in a number of Gbe languages. This was most likely a gradual development. The early texts include many cases where a progressive meaning is attributed to an unmarked verb form, as in the following examples.

(27) Early SN a. Mastra bille hatti mi kwetti.

Master belly hurt me quite 'My stomach hurts very bad, master.' (Arends & Perl 1995:167).

b. joe jam te moesi.

you eat too much 'You're eating too much.' (Arends & Perl 1995:135).

This suggests that de may have still been in process of becoming the required marker of progressive meaning during the early 18 th century.

Habitual meanings

As we noted earlier, an important difference between the Gbe languages and the Surinamese Creoles is the fact that e and ta in the latter are regularly used to express habitual and generic meanings (see 16).

By contrast, in the Gbe languages, habitual and generic meanings are typically conveyed by a separate habitual marker that either occurs preverbally (28a) or postverbally (28b). In Xwelagbe habitual aspect is marked by a high tone on the verb.

[ (Jondoh 1980:39) The extension of a progressive marker to an imperfective is well-attested crosslinguistically, so that universal tendencies to change may also have played a role. Another possible contributing factor may have been the fact that the creators of the creole did not find a suitable English form in the English constructions available to them, which could have been reinterpreted as a habitual aspect marker on the model of the Gbe habitual marker.

Comparing Tense in Gbe and Suriname

Past time reference

As we noted earlier, Gbe languages have no Past tense category, hence we cannot claim any influence from that source on the Relative Past category of the Surinamese creoles. We will therefore say nothing further about it here. However, we do find some similarities between the two language groups as far as future time reference is concerned.

5.5.2. Future time reference.

The modern creoles employ two markers of futurity: o, which expresses a predictive or relatively certain future, and sa (< Dutch zal), which has more modal overtones, and expresses a more uncertain or potential future.

( In all these cases, both in western Gbe and the maroon creoles, what seems to be expressed by the modal auxiliary is the sense of something that is possible, or a potential situation -a sense which may be interpreted in the various ways described above. These similarities suggest that sa in the maroon creoles might have been modelled, in part, after the Potential future marker of Western Gbe varieties.

Conclusion.

Our comparison of tense/aspect in Gbe and the creoles of Suriname shows that substrate influence must have played an important role in the emergence of the creole tense/aspect systems. Several of the tense/aspect categories and strategies/lexical forms used to express them in the creoles have close counterparts in varieties of Gbe. Our analysis, however, also revealed several differences between the creoles and the varieties of Gbe suggesting that other linguistic sources and mechanisms must have also contributed to the formation of the creoles of Suriname. It seems clear that, in addition to English varieties, European languages such as Portuguese and Dutch also had an impact on the early plantation creole during the formative process and on its descendants in later periods. Language-internal change also played a role in the emergence of the plantation creole and particularly in the development of certain TMA categories found in the modern varieties.

We hypothesized that categories that were shared across the (dominant)

substrates were most likely to be retained in the Creole. Our findings show that this is true of Perfective, Completive, Progressive/Imperfective and Potential Future. However, shared substrate categories such as Habitual and Prospective have no counterparts in the creoles -perhaps due to the fact that there were no forms in the superstrate input that they could 'transfer to'. It should also follow from this hypothesis that categories not found in the substrates would not be found in the creoles. But this is belied by the fact that the creoles developed two tense categories, Predictive Future and Relative Past, which had no models in the substrates. It would appear that these were purely internal developments.

We also hypothesized that surface structures or means of expression (preverbal, periphrastic, etc.) shared among the substrates would be retained in the creoles. The Gbe languages generally employ pre-verbal markers of tense and aspect as well as modality. Given the relatively unmarked character of analytic as opposed to synthetic expression of morphological categories, it is not surprising that the Surinamese (and other New World) creoles should have adopted the same pattern of periphrastic preverbal expression of TMA categories. The only exception to the use of pre-verbal markers in the creoles is the choice of a VPfinal marker of Completive/Perfect, but again this has a model in the dominant Gbe substrates.

Finally, following Siegel's "availability" constraints and the assumptions of the relexification hypothesis, we hypothesized that superstrate-derived lexical items whose semantics (partly) matched those of substrate functional heads would be selected to express the functional categories of the Creole. This process of selection would be guided by interlingual identifications between forms in the L2 varieties of English that slaves were targeting, and forms in their L1s which matched the former in meaning and position, and thus lent themselves to transfer.

Table 5 provides an overview of the actual sources of the Sranan tense/aspect markers.

(table 5 about here)

All of these forms, except for the Relative Past and Predictive Future markers, were a close match in function and/or meaning to the respective Gbe tense/aspect markers that provided models for them. Thus, the creoles chose the unmarked verb to convey perfective aspect; a form homophonous with a locative copula to express progressive or imperfective meanings; a form homophonous with a verb is adjoined to le and, therefore, causes the vowel to be lengthened and the tone to be rising. This tone is dropped when the complement is preposed.

8. This use of progressive + go is common in modern Sranan (Winford 2000a:418). 9. It still isn't clear from examples like (33) that go has been fully grammaticized as a future marker, rather than retaining its status as a verb. In the latter case, examples like these may be better interpreted as serial verb structures (Aboh, pc 2005).

  meaning 'finish' to mark Completive aspect; and a form sa, probably derived from Dutch zal, as a marker of Potential Mood. Note also that the selection of the superstrate forms conforms to the "availability" constraints proposed by Siegel, in particular, perceptual salience and congruence. The forms chosen are generally invariant in form, are isolatable, and have a single function or meaning. All of these factors strongly favor transfer, as Siegel has argued.Finally, as we noted earlier, Gbe influence by itself cannot fully explain the emergence of the tense/aspect categories of the Surinamese creoles. The roles of other substrate languages, internal developments, and influence from Dutch, are matters for future research.

  Comparing the Completive in Gbe and the Surinamese creolesThe category of completive aspect is conveyed by a marker that is formally similar to a main verb meaning 'finish' kaba (< Portuguese acabar 'finish') in the Surinamese creoles. It is often shortened to kba and kaa in modern There are differences among the Gbe languages in the ways they express the sense of completive aspect. Fongbe varieties use preverbal kò, whichAboh (2004:174) analyzes as an Anterior marker (9a), while the Phla-Phera varieties Xwelagbe and Xwlagbe use preverbal mOŸ and nOŸ respectively (9b).The Fongbe construction is a serial verb construction in which fó or vOŸ retain their full verbal status. In Aja and Waci, however, vOŸ seems to have been grammaticized to a more adverbial marker of aspect (see Da Cruz 1995 for further discussion). (footnote 4 here) By contrast, the Gbe completive marker is compatible only with non-static situations and "punctual occurrences" (eg. arrive) (Ameka to appear; Da Cruz

	It would appear, then, that the Completive in the Surinamese creoles
	5) a. Xwlagbe E⁄ e⁄ , uŸ n nyO⁄ EŸ n. yes I know-him 'Yes, I knew him.' b. Pamaka Iya, mi be sabi en, mi be Yes I PAST know him I PAST see him one time si en wan leisi. they kill king DET 'They've killed the king.' b. SN Den kiri a kownu. they kill DET king 'They've killed the king.' The close similarities in meaning and use of the unmarked verb strongly suggest that Gbe influence played a primary role in the emergence of the Perfective category in the Surinamese creoles. final position, and indicates that a situation is completed, yielding the sense of a perfect of result with non-statives, including activities, accomplishments and achievements (7a,b) and the sense of a state beginning in the past and continuing to the reference point with statives (7c). In all these cases, kaba etc. can be interpreted as a relational adverb conveying the sense of "already." (7) SN a. yu ben pai en kaba? (8) Early SN a. Mastra we doore kaba. Master we arrive COMPL (Van Dyk, quoted in Arends & Perl, p. 127) b. Mi memree wie abi piekienwan kaba 1sg remember 2pl have little-one COMPL Western Gbe varieties such as Ajagbe, Wacigbe and some varieties of Gengbe use VP-final vOŸ , which also derives from a main verb meaning 'finish', to convey the sense of the completion of the situation expressed by the main verb (10). (9) a. Fongbe. Kòfí kó sà aŸ sO⁄ n Kofi ANT sell crab 'Kofi has already sold the crab.' b. Xwlagbe OŸ , e⁄ nOŸ ku⁄ . no he COM die 'No, he is already dead.' (10) Ajagbe AŸ xOŸ su lO aŸ , e va⁄ Ío⁄ vOŸ . king the TOP he come arrive COM (11) Fongbe kOŸ Ÿ ku⁄ ∂uŸ mOŸ liŸ nku⁄ n O⁄ ⁄ vOŸ Koku eat rice DET finish Koku finished eating the rice. patterns after these two constructions where the form used to express the completive meaning also appears in VP-final position and is derived from a verb meaning 'finish' (12). (12) a. Gengbe gaŸ li⁄ -a⁄ vO (Jondoh 1980:50) gali-DET finish 'There's no more gali.' b. Pamaka Moni kaba. money finish (13) a. A famiri fu mi disi, a abi achttien yaar kaba? DET family of 1sg DET 3sg have eighteen year COM "This relative of mine, is she already eighteen years old?' b. Oom N. firgiti a boi kaba 5.2. Sranan and Saamaka respectively. Unlike other TMA markers, it occurs in VP-'I remember we have a little bit already.' Uncle N. forget DET boy COM
	(Weygandt, quoted in Arends & Perl, p. 118) "Uncle N. has already forgotten the boy.'

'Yes, I knew him, I saw him once.'

The unmarked verb is also used in all the languages to convey the sense of current relevance, in much the same way as the English Perfect does. The following examples illustrate: (6) a. Ajagbe. woŸ wu aŸ xOŸ su lO. 'Have you already paid him?' b. Oom N. firgiti a boi kaba. 'Uncle N. has already forgotten the boy.' c. A famiri fu mi disi, a abi achttien jaar kaba? 'This relative of mine, is she already eighteen years old?' Uses of the completive marker with both non-statives and statives are well established in the early Sranan texts: 'As for the king, he has already come.' Fongbe varieties also have a construction with a VP-final verb, fó or vOŸ both meaning 'finish" (See (12), from Da Cruz (1995:361).

'There is no more money.'

We argue therefore that Completive kaba in the Surinamese creoles is modeled after the VP-final marker of completion common to both Eastern and Western Gbe languages. This is not to say that kaba and its Gbe counterpart are identical in status or function. For instance, kaba is compatible with both stative (13a) and non-stative situations, including all types of achievement (13b).

  Migge to appear). While sa in Sranan clearly owes much of its meaning to Dutch zal, we suggest that its functions in the maroon creoles are also modelled on the potential future marker in Western Gbe languages.In Gbe future time reference is expressed by the preverbal marker lá, ná or

	FUT b. Jan sa come (41) Ajagbe nO⁄ e PM se⁄ seŸ	tear go a	faansi taa toŸ nu,	wiki. a	yi
	(33) Early SM In short, the reanalysis of go appears to have been a purely language internal mi sa kotti di pau. 'If you put a stone in this bad, it'll tear.' John POT go LOC France other week if you hear-PROG ear thing FUT go
	I development in the Surinamese creoles. Unlike (g)o, however, sa does show FUT cut DET tree mumu le etO tu dru⁄ .
	'Ich werde, od. will den Baum umhauen. evidence of substrate influence. 'John may go to France next week.' play LOC river side possibility
	[I am going to or want to fell that tree.]' In other Gbe varieties, e.g. Gengbe, Ajagbe and Ewegbe varieties such as 'If you listen to me, you'll be able to go to the river to play.'
	(Riemer 1779: in Arends & Perl 1995: 341) 5.5.3. Comparing sa with the Gbe future marker. Wacigbe and Anlogbe, lá, á seem to express a wider range of future meanings, The Gbe Potential marker can also be used to indicate that it is possible for
	and has strong overtones of potentiality. In fact, Essegbey (to appear, 14) argues someone to do something: The maroon creoles also use sa in this function.
	In the early texts, future time reference is also conveyed by a combination of the In contemporary Sranan, sa expresses primarily modal meanings related to that à in Anlogbe (Ewe variety) is a potential rather than a future marker, which
	progressive marker and the movement verb go, de+go (Sranan) and tan+go epistemic necessity or probability. In the maroon creoles, however, it can express expresses hypothetical meanings that include epistemic and deontic-type (root) (39) Anlogbe aŸ -xle ‡ agbale ‡ ‡ ma⁄ bObOe (Essegby to appear p. 10) (42) PM Efu i teki mi taki, i sa go pee a liba.
	(Saramaccan). The construction expresses the sense of a prospective future or an a wider range of meanings associated with potentiality of various types (Winford possibility, and can refer to situations that are not in the future. Thus, à can be you.POT-read book that easily if you take my talk, you POT go play LOC river
	30) SM intention. (footnote 8 here) Te when I mi ko come old gaandi, nou mi o now I FUT make mbei wan gaan wosu u mi. one big house for me. 'When I've become old, I will build myself a big house.' (34) a. Early SN mi de go gi ju tetei, va nai mi klossi. I PROG go give you thread for seam my clothing 'I am going to give you thread to seam my clothing.' used with stative predicates to refer to a possible state of affairs in the present (37a), and to refer to a possible state of affairs that is past (37b): (37) Anlogbe a. john a› -nO a˙e⁄ me fi⁄ fi⁄ a⁄ 'You can read that book easily.' In this case, Essegbey(to appear, p. 11) comments: "this sentence does not make predictions about a state of affairs to come. Instead, it suggests that the addressee & Migge 2003; á. In Eastern Gbe varieties such as Fongbe (Maxigbe, Gungbe) as well as Phla-John POT-be_located home now is in a position to read the book without difficulty". This more deontic-type use of
	(31) Ndyuka Phera (Xwlagbe and Xwelagbe) these markers represent a future tense category, J. sa go a Faansi taa wiki. (Schuman 1783: 50 cited in van den Berg to appear) 'John may be at home now' the Gbe Potential has counterparts in the maroon creoles, but apparently not in
	J. b. Early SM mi tann go worko. may go LOC France other week expressing meanings such as later time reference (36a), intention (36b) and (= It's possible that John is at home now). Sranan.
	'J. may go to France next week/it is possible that J. will go to I PROG go work b. kofi prediction (36c). a› -yi gE xo⁄ xo⁄
	(40) PM	France next week.' 'I will work.' Kofi POT-go Accra already A sama de abi	dobu bon,
	(36) Ajagbe	(Riemer 1779, in Arends & Perl 1995: 374) va⁄ esO 'Kofi may have gone to Accra already.' a. a DET person there have double bone,
	This situation contrasts with that in the early texts, where sa (also spelt zal, sal, he-FUT come tomorrow a sa opo 100 kilo.
	etc.) appears to be the usual means of expressing both predictive and potential Constructions in which go appears to function as a future marker in its 'He'll come tomorrow.' This epistemic use of the Gbe Potential marker has parallels in the similar use of he MOD lift 100 kilo
	future. own right only emerge towards the end of the 18 th century. (footnote 9 here) Xwlagbe b. nE⁄ uŸ n kpoŸ OŸ ma⁄ xOŸ OŸ xwe⁄ gbo⁄ lo⁄ kpo sa in all of the Surinamese creoles, as in the following examples: 'That guy is really strong. He can lift a hundred kilos.'
		if I	old PART I-FUT buy house big one
	(32) Early SN (35) Early SN mi go teh 'When I am old, I'll buy a big house.' ju sa oure, ju skin sa hebbi tu. selli da-sanni bakka. (38) Sranan a. Jan sa de na oso nownow. Finally, in western Gbe varieties, the Potential marker (in conjunction with an
	when you FUT old FUT? sell that-thing you body FUT heavy too again Wacigbe c. N´Ÿ y´⁄ cO I ´Ÿ kp´⁄ l´⁄ akpoŸ ya⁄ mEŸ John MOD be-there LOC house now appropriate adverbial) can be used to express notions such as permissibility.
		'when you grow old, your body will also be burdensome.' 'I am going to sell that again.' if you put stone LOC bag this in 'John should be at home now.'
		(Schumann 1783: 128 cited in van den Berg to appear.) (Schuman 1783: 50 cited in van den Berg to appear) a⁄ ya⁄ vun.

'If you obey me, you will be able to go and play by the river.'

Table 1 :

 1 Tense/aspect in contemporary Sranan, Pamaka and Saramaccan.(All forms are preverbal, except for Perfect kaba, which is VP-final.)

	Forms				Category	Meanings
	SN	PM ND SM
	Tense
	ben	be	be bi	Relative Past	Past events 'distanced' from S.
						Background past or 'framepast'
						especially in narratives. Past in
						relation to another reference
						point in the past.
	o	o	o	o	Future	Later time reference; Intention or
						prediction. Predictability.
	Aspect
	ø	ø	ø	ø	Perfective	States or events seen as
						unanalyzed wholes.
	e	e	e	ta	Imperfective	Situations (both states and
						occurrences) seen as 'unbounded'
						and ongoing at reference time,
						which encompasses situations
						that are repeated, habitual, in
						progress or continuous.
	k(a)ba kaba kaba kaa	Completive	Situations seen as completed.
	(footnote 2 after 'completive')	Conveys the meaning
						'already.' Expresses the sense of a
						'perfect of result' with non-
						statives, and the sense of a state
						beginning in the past and
						continuing to the reference point
						with statives.

Table 2 .

 2 The tense and aspect categories in the early Sranan texts

	TENSE		ASPECT
	CATEGORY Past	Future	Imperfectiv	Completive Perfective
			e
	Early Sranan ben	sa, go (?), de go de	kaba	Ø

Table 5 .

 5 Tense/Aspect categories in Sranan and their sources.

	Sranan category	Marker	Source
	Perfective	Unmarked	Bare verb
	Imperfective	e < de	locational copula < English
			there
	Terminative Perfect	kaba (VP-final)	Portuguese acabar "finish"
	Relative Past.	ben	Eng. been
	Predictive Future	o	Eng. go
	Potential Future	sa	Dutch zal

Footnotes

* The research on which this paper is based was funded by NSF grant # SBR -930635 and NSF grant BCS-0113826. We wish to express our sincere thanks to the NSF for making this research possible. We owe a great debt of gratitude to our consultants, Hounkpati Capo in Benin and Robby Morroy in Suriname, and especially to Daniel Gagnon, who worked tirelessly to ensure that our Gbe data were transcribed and translated accurately. We are also indebted to Enoch Aboh and James Essegbey for their meticulous and insightful guidance in this analysis, which would have been poorer without them. We also want to thank Laurence Goury for help with data from the early texts. Above all, we wish to thank our many informants who gave so willingly of their time to provide us with the data for this study.

1. We are of course aware that our data from contemporary Gbe languages may not accurately reflect the way these languages looked some four centuries ago, when they were introduced into Suriname. But, as [START_REF] Thomason | On identifying the sources of creole structures[END_REF] suggests, four hundred years is not a very long time in the history of a language. Also, our data were elicited from speakers of more conservative speakers of contemporary Gbe.

2. The category we have labeled 'Completive" might just as well be labeled "Perfect." In any case, we regard it as a subtype of the cross-linguistic category PERFECT [START_REF] Dahl | Tense and aspect systems[END_REF].


Thomas Pötsch

Nawaz Safdar

Marwat Khan

Yasir Zaki

Carmelita Görg

Poster Abstract: Performance Evaluation of Machine-to-Machine Communication on Future Mobile Networks in Disaster Scenarios

Long Term Evolution (LTE) is the recent standard of wireless communication developed by the Third Generation Partnership Project (3GPP). As the future mobile network, it is currently being rolled out to numerous areas world-wide. Besides other objectives such as enhancing the spectral efficiency and reducing latency for broadband services, LTE has been designed as a pure packet switched system. Hence, it targets the data volume requirements of cellular mobile users by increasing the peak-user data throughput to up to 100 Mbit/s [START_REF]Requirements for Evolved UTRA and UTRAN[END_REF]. However, legacy circuit switched services are no longer supported by this technology. Contrary to the existing, wide-spread GSM network, this implies that the support of voice calls and Short Message Service (SMS) have to be realized by voice and SMS via the IP Multimedia Subsystem (IMS). In other words, voice calls are no longer separated from pure data traffic and hence influence each other.

Along with the "Internet of Things" as a new paradigm for connected devices, Machine-to-Machine (M2M) communication is a world-wide, fast growing field of application. According to [START_REF]Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update[END_REF], the mobile traffic of the variety and number of connected devices will grow significantly within the next decade. Therefore, the multitude of remotely monitored equipment is growing and includes buildings, vending machines, vehicles and other physical equipment. The application fields incorporate for example health monitoring, logistics and shipping, environmental monitoring, or asset tracking. Besides that, the overall mobile network is expected to grow 24-fold from 2012 to 2017 and the number of mobile connected devices will exceed the world's population by the end of 2013 [START_REF]Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update[END_REF].

Looking at the increasing number of mobile connected devices and on one particular scenario where mobile communication is very beneficial in terms of life-saving measures, the capacities of future mobile networks are becoming more and more important. Over the past decades, natural disaster and emergency events have been increasing significantly all over the world [START_REF] Guha-Sapir | Thirty Years of Natural Disasters 1974-2003: The Numbers[END_REF] [START_REF] Cavallo | The Economics of Natural Disasters: A Survey[END_REF]. Although the capabilities of predicting natural disasters have been become more precise and reliable, certain natural disasters are unpredictable. Besides that, other emergency events such as terror attacks or multiple accidents are not predictable at all, and when occurring, mostly numerous people are affected. However, throughout almost any emergency event, mobile communication plays an important role for both, involved persons and rescue activities. Besides the regular and existing network traffic, additional traffic emerges and is indirectly caused by the emergency event itself. However, taking such a scenario as a rather rare and unlikely event, but where mobile communication plays a tremendous and important role, M2M operators have to cope with severe challenges, like for example, how does M2M communication perform in an emergency event when numerous people instantaneously begin to use IP-based services. Although a possible off-time of M2M communicating devices does not play a severe role, an off-time of devices facilitating e-healthcare, etc. might be critical. Figure 1 shows an example of the traffic load in a mobile network during an event of disaster. Shortly after an event of disaster, the traffic load of the mobile network increases significantly by emergency calls. Right after emergency calls, people usually start sending out messages to notify others about their current situation and condition. Those messages could be regular phone calls, text messages and/or status updates in social networks. Nowadays, SMS services have been widely replaced by Instant Messaging (e.g. Whatsapp, iMessage, etc.) and social networking (e.g. Facebook, Google+, etc.) have been become very popular. Therefore, it is very likely that people start sending out numerous messages, pictures and videos to inform others about their current situation and to spread the scale of the disaster to others. To investigate the influence of such a situation, a simulation model was developed using the OPNET simulator [6] with the main focus on end-to-end performance evaluations on the user plane. All nodes in the network contain the full protocol stack implementation that was done following the 3GPP release 8 specification. Further details of the simulation model can be found in [START_REF] Zaki | Long Term Evolution (LTE) Model development within OPNET Simulation Environment[END_REF] and [START_REF] Zaki | Optimized Service Aware LTE MAC Scheduler: Design, Implementation and Performance Evaluation[END_REF].

During the first 1000 seconds of the simulation, the scenario consists of 10 VoIP users, 10 file transfer users and 100 M2M devices. M2M devices and file transfer users share the same QoS class. These terminals are operating continuously with the parameters shown in Table 1 The simulation results of regular LTE traffic users are depicted in Figure 2. The green bars denote the end-to-end delay in the regular scenario (t<1000s), whereas the blue bars indicate the delay after an event of disaster (t>1000s). The best effort traffic experiences the highest impact of the additional users in an emergency event. As illustrated in Figure 2a, these additional users drastically degrade the performance of the file transfer. This is mainly caused by the limited amount of remaining resources within the cell and by the low priority given by the LTE scheduler. This results in an average increase of the upload response time by the factor of 19.6. The simulation results of the M2M users are represented in Figure 2b as a subset of 10 users. These 10 users are randomly chosen and reflect the overall performance of all 100 M2M users. It can be seen, that all user experience a 4.8 fold increase of the upload response time. The voice user results (cf. Figure 2c) do not reveal a considerable effect of the increasing traffic load within the LTE cell. Since voice traffic is delay sensitive traffic, the LTE scheduler gives strict priority to this traffic. Resulting from this, the packet endto-end delay is increased on average by the factor 1.1.

Even though the performance of voice user remains unaffected by the additional users during an emergency event, file upload and M2M traffic experience a considerable delay. In comparison to M2M traffic, file upload traffic experience a ∼4 times higher delay. However, time sensitive M2M application, like e-healthcare, could suffer from this increase.

Fig. 1 :

 1 Fig. 1: Example of Traffic Load in Event of Disaster (adapted from [5])

Fig. 2 :

 2 Fig. 2: (a) Average File Upload Time of File Transfer User (b) Average File Upload Time of M2M User (c) Average Voice User Packet End-to-End Delay

Table 1 :

 1 . After 1000 seconds, an emergency event occurs where additionally 60 emergency VoIP users and 30 Instant Messaging (IM) users start to operate. The emergency VoIP users behave like regular VoIP users whereas the IM user start sending messages, videos and pictures. Simulation Parameters

	Parameter	Setting	Parameter	Setting
	Cell layout	1 eNodeB, 3 Cells	File transfer traffic model
	System bandwidth	5 MHz (∼25 PRBs)	Quantity	10
	Frequency reuse	1	File size	2 MB
	factor		File inter-	Uniform
	Cell radius	375 m	request time	(15s, 25s)
	UE velocity	3 km/h	M2M traffic model
	Max UE power	23 dBm	Quantity	100
	Path loss	128.1+37.6 log10(R),	Message size	6 kB
		R in km	Message inter-	30 s
	Slow fading	Log-normal shadowing,	transmission time
		8 dB standard deviation,	Instant messaging traffic model
		correlation 1	Quantity	30
	Fast fading	Jakes-like method	Message size	Uniform
	Mobility model	Random Way Point		(0.2 kB, 2MB)
	UE buffer size	∞	Message inter-	Uniform
	Power control	Fractional PC, α = 0.6,	request time	(10s, 20s)
		P0 = -58 dBm	Voice traffic model
	Traffic environment	Loaded	Quantity	10 + 60 emergency
	LTE uplink scheduler	BQA [8]	Silence/talk spurt	Exponential
	Simulation time	2000s	length	(3 s)
	Time of disaster	1000s	Encoder scheme	GSM EFR