rfc 3481

• 2.5g ve 3g uzerinden tcp'nin referansı.
  
  network working group h. inamura, ed.
  request for comments: 3481 ntt docomo, inc.
  bcp: 71 g. montenegro, ed.
  category: best current practice sun microsystems laboratories
  europe
  r. ludwig
  ericsson research
  a. gurtov
  sonera
  f. khafizov
  nortel networks
  february 2003
  
  tcp over second (2.5g) and third (3g) generation wireless networks
  
  status of this memo
  
  this document specifies an internet best current practices for the
  internet community, and requests discussion and suggestions for
  improvements. distribution of this memo is unlimited.
  
  copyright notice
  
  copyright (c) the internet society (2003). all rights reserved.
  
  abstract
  
  this document describes a profile for optimizing tcp to adapt so that
  it handles paths including second (2.5g) and third (3g) generation
  wireless networks. it describes the relevant characteristics of 2.5g
  and 3g networks, and specific features of example deployments of such
  networks. it then recommends tcp algorithm choices for nodes known
  to be starting or ending on such paths, and it also discusses open
  issues. the configuration options recommended in this document are
  commonly found in modern tcp stacks, and are widely available
  standards-track mechanisms that the community considers safe for use
  on the general internet.
  
  inamura, et al. best current practice [page 1]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  table of contents
  
  1. introduction. . . . . . . . . . . . . . . . . . . . . . . . . 3
  2. 2.5g and 3g link characteristics. . . . . . . . . . . . . . . 4
  2.1 latency. . . . . . . . . . . . . . . . . . . . . . . . . 4
  2.2 data rates . . . . . . . . . . . . . . . . . . . . . . . 5
  2.3 asymmetry . . . . . . . . . . . . . . . . . . . . . . . 6
  2.4 delay spikes . . . . . . . . . . . . . . . . . . . . . . 6
  2.5 packet loss due to corruption. . . . . . . . . . . . . . 7
  2.6 intersystem handovers. . . . . . . . . . . . . . . . . . 7
  2.7 bandwidth oscillation. . . . . . . . . . . . . . . . . . 7
  3. example 2.5g and 3g deployments . . . . . . . . . . . . . . . 8
  3.1 2.5g technologies: gprs, hscsd and cdma2000 1xrtt. . . . 8
  3.2 a 3g technology: w-cdma. . . . . . . . . . . . . . . . . 8
  3.3 a 3g technology: cdma2000 1x-ev. . . . . . . . . . . . . 10
  4. tcp over 2.5g and 3g. . . . . . . . . . . . . . . . . . . . . 10
  4.1 appropriate window size (sender & receiver). . . . . . . 11
  4.2 increased initial window (sender). . . . . . . . . . . . 11
  4.3 limited transmit (sender). . . . . . . . . . . . . . . . 12
  4.4 ip mtu larger than default . . . . . . . . . . . . . . . 12
  4.5 path mtu discovery (sender & intermediate routers) . . . 13
  4.6 selective acknowledgments (sender & receiver). . . . . . 13
  4.7 explicit congestion notification (sender, receiver &
  intermediate routers). . . . . . . . . . . . . . . . . . 13
  4.8 tcp timestamps option (sender & receiver). . . . . . . . 13
  4.9 disabling rfc 1144 tcp/ip header compression (wireless
  host) . . . . . . . . . . . . . . . . . . . . . . . . . 15
  4.10 summary . . . . . . . . . . . . . . . . . . . . . . . . . 16
  5. open issues . . . . . . . . . . . . . . . . . . . . . . . . . 16
  6. security considerations . . . . . . . . . . . . . . . . . . . 18
  7. iana considerations . . . . . . . . . . . . . . . . . . . . . 18
  8. acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
  9. normative references . . . . . . . . . . . . . . . . . . . . . 19
  10. informative references . . . . . . . . . . . . . . . . . . . . 21
  11. authors' addresses . . . . . . . . . . . . . . . . . . . . . . 25
  12. full copyright statement . . . . . . . . . . . . . . . . . . . 26
  
  inamura, et al. best current practice [page 2]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  1. introduction
  
  the second generation cellular systems are commonly referred to as
  2g. the 2g phase began in the 1990s when digital voice encoding had
  replaced analog systems (1g). 2g systems are based on various radio
  technologies including frequency-, code- and time- division multiple
  access. examples of 2g systems include gsm (europe), pdc (japan),
  and is-95 (usa). data links provided by 2g systems are mostly
  circuit-switched and have transmission speeds of 10-20 kbps uplink
  and downlink. demand for higher data rates, instant availability and
  data volume-based charging, as well as lack of radio spectrum
  allocated for 2g led to the introduction of 2.5g (for example, gprs
  and pdc-p) and 3g (for example, wideband cdma and cdma2000) systems.
  
  radio technology for both wideband cdma (w-cdma) (adopted, for
  example, in europe, japan, etc) and cdma2000 (adopted, for example,
  in us, south korea, etc) is based on code division multiple access
  allowing for higher data rates and more efficient spectrum
  utilization than 2g systems. 3g systems provide both packet-switched
  and circuit-switched connectivity in order to address the quality of
  service requirements of conversational, interactive, streaming, and
  bulk transfer applications. the transition to 3g is expected to be a
  gradual process. initially, 3g will be deployed to introduce high
  capacity and high speed access in densely populated areas. mobile
  users with multimode terminals will be able to utilize existing
  coverage of 2.5g systems on the rest of territory.
  
  much development and deployment activity has centered around 2.5g and
  3g technologies. along with objectives like increased capacity for
  voice channels, a primary motivation for these is data communication,
  and, in particular, internet access. accordingly, key issues are tcp
  performance and the several techniques which can be applied to
  optimize it over different wireless environments [19].
  
  this document proposes a profile of such techniques, (particularly
  effective for use with 2.5g and 3g wireless networks). the
  configuration options in this document are commonly found in modern
  tcp stacks, and are widely available ietf standards-track mechanisms
  that the community has judged to be safe on the general internet
  (that is, even in predominantly non-wireless scenarios).
  furthermore, this document makes one set of recommendations that
  covers both 2.5g and 3g networks. since both generations of wireless
  technologies exhibit similar challenges to tcp performance (see
  section 2), one common set is warranted.
  
  inamura, et al. best current practice [page 3]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  two example applications of the recommendations in this document are:
  
  o the wap forum [25] (part of the open mobile alliance [26] as of
  june 2002) is an industry association that has developed standards
  for wireless information and telephony services on digital mobile
  phones. in order to address wap functionality for higher speed
  networks such as 2.5g and 3g networks, and to aim at convergence
  with internet standards, the wap forum thoroughly revised its
  specifications. the resultant version 2.0 [31] adopts tcp as its
  transport protocol, and recommends tcp optimization mechanisms
  closely aligned with those described in this document.
  
  o i-mode [33] is a wireless internet service deployed on handsets in
  japan. the newer version of i-mode runs on foma [34], an
  implementation of w-cdma. i-mode over foma deploys the profile of
  tcp described in this document.
  
  this document is structured as follows: section 2 reviews the link
  layer characteristics of 2.5g/3g networks; section 3 gives a brief
  overview of some representative 2.5g/3g technologies like w-cdma,
  cdma2000 and gprs; section 4 recommends mechanisms and configuration
  options for tcp implementations used in 2.5g/3g networks, including a
  summary in chart form at the end of the section; finally, section 5
  discusses some open issues.
  
  2. 2.5g and 3g link characteristics
  
  link layer characteristics of 2.5g/3g networks have significant
  effects on tcp performance. in this section we present various
  aspects of link characteristics unique to the 2.5g/3g networks.
  
  2.1 latency
  
  the latency of 2.5g/3g links is high mostly due to the extensive
  processing required at the physical layer of those networks, e.g.,
  for fec and interleaving, and due to transmission delays in the radio
  access network [58] (including link-level retransmissions). a
  typical rtt varies between a few hundred milliseconds and one second.
  the associated radio channels suffer from difficult propagation
  environments. hence, powerful but complex physical layer techniques
  need to be applied to provide high capacity in a wide coverage area
  in a resource efficient way. hopefully, rapid improvements in all
  areas of wireless networks ranging from radio layer techniques over
  signal processing to system architecture will ultimately also lead to
  reduced delays in 3g wireless systems.
  
  inamura, et al. best current practice [page 4]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  2.2 data rates
  
  the main incentives for transition from 2g to 2.5g to 3g are the
  increase in voice capacity and in data rates for the users. 2.5g
  systems have data rates of 10-20 kbps in uplink and 10-40 kbps in
  downlink. initial 3g systems are expected to have bit rates around
  64 kbps in uplink and 384 kbps in downlink. considering the
  resulting bandwidth-delay product (bdp) of around 1-5 kb for 2.5g and
  8-50 kb for 3g, 2.5g links can be considered ltns (long thin networks
  [19]), and 3g links approach lfns (long fat networks [2], as
  exemplified by some satellite networks [48]). accordingly,
  interested readers might find related and potentially relevant issues
  discussed in rfc 2488 [49]. for good tcp performance both lfns and
  ltns require maintaining a large enough window of outstanding data.
  for lfns, utilizing the available network bandwidth is of particular
  concern. ltns need a sufficiently large window for efficient loss
  recovery. in particular, the fast retransmit algorithm cannot be
  triggered if the window is less than four segments. this leads to a
  lengthy recovery through retransmission timeouts. the limited
  transmit algorithm rfc 3042 [10] helps avoid the deleterious effects
  of timeouts on connections with small windows. nevertheless, making
  full use of the sack rfc 2018 [3] information for loss recovery in
  both lfns and ltns may require twice the window otherwise sufficient
  to utilize the available bandwidth.
  
  this document recommends only standard mechanisms suitable both for
  ltns and lfns, and to any network in general. however, experimental
  mechanisms suggested in section 5 can be targeted either for ltns
  [19] or lfns [48].
  
  data rates are dynamic due to effects from other users and from
  mobility. arriving and departing users can reduce or increase the
  available bandwidth in a cell. increasing the distance from the base
  station decreases the link bandwidth due to reduced link quality.
  finally, by simply moving into another cell the user can experience a
  sudden change in available bandwidth. for example, if upon changing
  cells a connection experiences a sudden increase in available
  bandwidth, it can underutilize it, because during congestion
  avoidance tcp increases the sending rate slowly. changing from a
  fast to a slow cell normally is handled well by tcp due to the self-
  clocking property. however, a sudden increase in rtt in this case
  can cause a spurious tcp timeout as described in section 2.7. in
  addition, a large tcp window used in the fast cell can create
  congestion resulting in overbuffering in the slow cell.
  
  inamura, et al. best current practice [page 5]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  2.3 asymmetry
  
  2.5g/3g systems may run asymmetric uplink and downlink data rates.
  the uplink data rate is limited by battery power consumption and
  complexity limitations of mobile terminals. however, the asymmetry
  does not exceed 3-6 times, and can be tolerated by tcp without the
  need for techniques like ack congestion control or ack filtering
  [50]. accordingly, this document does not include recommendations
  meant for such highly asymmetric networks.
  
  2.4 delay spikes
  
  a delay spike is a sudden increase in the latency of the
  communication path. 2.5g/3g links are likely to experience delay
  spikes exceeding the typical rtt by several times due to the
  following reasons.
  
  1. a long delay spike can occur during link layer recovery from a
  link outage due to temporal loss of radio coverage, for example,
  while driving into a tunnel or within an elevator.
  
  2. during a handover the mobile terminal and the new base station
  must exchange messages and perform some other time-consuming
  actions before data can be transmitted in a new cell.
  
  3. many wide area wireless networks provide seamless mobility by
  internally re-routing packets from the old to the new base station
  which may cause extra delay.
  
  4. blocking by high-priority traffic may occur when an arriving
  circuit-switched call or higher priority data temporarily preempts
  the radio channel. this happens because most current terminals
  are not able to handle a voice call and a data connection
  simultaneously and suspend the data connection in this case.
  
  5. additionally, a scheduler in the radio network can suspend a low-
  priority data transfer to give the radio channel to higher
  priority users.
  
  delay spikes can cause spurious tcp timeouts, unnecessary
  retransmissions and a multiplicative decrease in the congestion
  window size.
  
  inamura, et al. best current practice [page 6]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  2.5 packet loss due to corruption
  
  even in the face of a high probability of physical layer frame
  errors, 2.5g/3g systems have a low rate of packet losses thanks to
  link-level retransmissions. justification for link layer arq is
  discussed in [23], [22], [44]. in general, link layer arq and fec
  can provide a packet service with a negligibly small probability of
  undetected errors (failures of the link crc), and a low level of loss
  (non-delivery) for the upper layer traffic, e.g., ip. the loss rate
  of ip packets is low due to the arq, but the recovery at the link
  layer appears as delay jitter to the higher layers lengthening the
  computed rto value.
  
  2.6 intersystem handovers
  
  in the initial phase of deployment, 3g systems will be used as a 'hot
  spot' technology in high population areas, while 2.5g systems will
  provide lower speed data service elsewhere. this creates an
  environment where a mobile user can roam between 2.5g and 3g networks
  while keeping ongoing tcp connections. the inter-system handover is
  likely to trigger a high delay spike (section 2.4), and can result in
  data loss. additional problems arise because of context transfer,
  which is out of scope of this document, but is being addressed
  elsewhere in the ietf in activities addressing seamless mobility
  [51].
  
  intersystem handovers can adversely affect ongoing tcp connections
  since features may only be negotiated at connection establishment and
  cannot be changed later. after an intersystem handover, the network
  characteristics may be radically different, and, in fact, may be
  negatively affected by the initial configuration. this point argues
  against premature optimization by the tcp implementation.
  
  2.7 bandwidth oscillation
  
  given the limited rf spectrum, satisfying the high data rate needs of
  2.5g/3g wireless systems requires dynamic resource sharing among
  concurrent data users. various scheduling mechanisms can be deployed
  in order to maximize resource utilization. if multiple users wish to
  transfer large amounts of data at the same time, the scheduler may
  have to repeatedly allocate and de-allocate resources for each user.
  we refer to periodic allocation and release of high-speed channels as
  bandwidth oscillation. bandwidth oscillation effects such as
  spurious retransmissions were identified elsewhere (e.g., [30]) as
  factors that degrade throughput. there are research studies [52],
  [54], which show that in some cases bandwidth oscillation can be the
  single most important factor in reducing throughput. for fixed tcp
  parameters the achievable throughput depends on the pattern of
  
  inamura, et al. best current practice [page 7]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  resource allocation. when the frequency of resource allocation and
  de-allocation is sufficiently high, there is no throughput
  degradation. however, increasing the frequency of resource
  allocation/de-allocation may come at the expense of increased
  signaling, and, therefore, may not be desirable. standards for 3g
  wireless technologies provide mechanisms that can be used to combat
  the adverse effects of bandwidth oscillation. it is the consensus of
  the pilc working group that the best approach for avoiding adverse
  effects of bandwidth oscillation is proper wireless sub-network
  design [23].
  
  3. example 2.5g and 3g deployments
  
  this section provides further details on a few example 2.5g/3g
  technologies. the objective is not completeness, but merely to
  discuss some representative technologies and the issues that may
  arise with tcp performance. other documents discuss the underlying
  technologies in more detail. for example, arq and fec are discussed
  in [23], while further justification for link layer arq is discussed
  in [22], [44].
  
  3.1 2.5g technologies: gprs, hscsd and cdma2000 1xrtt
  
  high speed circuit-switched data (hscsd) and general packet radio
  service (gprs) are extensions of gsm providing high data rates for a
  user. both extensions were developed first by etsi and later by
  3gpp. in gsm, a user is assigned one timeslot downlink and one
  uplink. hscsd allocates multiple timeslots to a user creating a fast
  circuit-switched link. gprs is based on packet-switched technology
  that allows efficient sharing of radio resources among users and
  always-on capability. several terminals can share timeslots. a gprs
  network uses an updated base station subsystem of gsm as the access
  network; the gprs core network includes serving gprs support nodes
  (sgsn) and gateway gprs support nodes (ggsn). the rlc protocol
  operating between a base station controller and a terminal provides
  arq capability over the radio link. the logical link control (llc)
  protocol between the sgsn and the terminal also has an arq capability
  utilized during handovers.
  
  3.2 a 3g technology: w-cdma
  
  the international telecommunication union (itu) has selected wideband
  code division multiple access (w-cdma) as one of the global telecom
  systems for the imt-2000 3g mobile communications standard. w-cdma
  specifications are created in the 3rd generation partnership project
  (3gpp).
  
  inamura, et al. best current practice [page 8]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  the link layer characteristics of the 3g network which have the
  largest effect on tcp performance over the link are error controlling
  schemes such as layer two arq (l2 arq) and fec (forward error
  correction).
  
  w-cdma uses rlc (radio link control) [20], a selective repeat and
  sliding window arq. rlc uses protocol data units (pdus) with a 16
  bit rlc header. the size of the pdus may vary. typically, 336 bit
  pdus are implemented [34]. this is the unit for link layer
  retransmission. the ip packet is fragmented into pdus for
  transmission by rlc. (for more fragmentation discussion, see section
  4.4.)
  
  in w-cdma, one to twelve pdus (rlc frames) constitute one fec frame,
  the actual size of which depends on link conditions and bandwidth
  allocation. the fec frame is the unit of interleaving. this
  accumulation of pdus for fec adds part of the latency mentioned in
  section 2.1.
  
  for reliable transfer, rlc has an acknowledged mode for pdu
  retransmission. rlc uses checkpoint arq [20] with "status report"
  type acknowledgments; the poll bit in the header explicitly solicits
  the peer for a status report containing the sequence number that the
  peer acknowledges. the use of the poll bit is controlled by timers
  and by the size of available buffer space in rlc. also, when the
  peer detects a gap between sequence numbers in received frames, it
  can issue a status report to invoke retransmission. rlc preserves
  the order of packet delivery.
  
  the maximum number of retransmissions is a configurable rlc parameter
  that is specified by rrc [39] (radio resource controller) through rlc
  connection initialization. the rrc can set the maximum number of
  retransmissions (up to a maximum of 40). therefore, rlc can be
  described as an arq that can be configured for either high-
  persistence or low-persistence, not perfect-persistence, according to
  the terminology in [22].
  
  since the rrc manages rlc connection state, bandwidth oscillation
  (section 2.7) can be eliminated by the rrc's keeping rf resource on
  an rlc connection with data in its queue. this avoids resource de-
  allocation in the middle of transferring data.
  
  in summary, the link layer arq and fec can provide a packet service
  with a negligibly small probability of undetected error (failure of
  the link crc), and a low level of loss (non-delivery) for the upper
  layer traffic, i.e., ip. retransmission of pdus by arq introduces
  latency and delay jitter to the ip flow. this is why the transport
  layer sees the underlying w-cdma network as a network with a
  
  inamura, et al. best current practice [page 9]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  relatively large bdp (bandwidth-delay product) of up to 50 kb for the
  384 kbps radio bearer.
  
  3.3 a 3g technology: cdma2000 1x-ev
  
  one of the terrestrial radio interface standards for 3g wireless
  systems, proposed under the international mobile telecommunications-
  2000 umbrella, is cdma2000 [55]. it employs multi-carrier code
  division multiple access (cdma) technology with a single-carrier rf
  bandwidth of 1.25 mhz. cdma2000 evolved from is-95 [56], a 2g
  standard based on cdma technology. the first phase of cdma2000
  utilizes a single carrier and is designed to double the voice
  capacity of existing cdma (is-95) networks and to support always-on
  data transmission speeds of up to 316.8 kbps. as mentioned above,
  these enhanced capabilities are delivered by cdma2000 1xrtt. 3g
  speeds of 2 mbps are offered by cdma2000 1x-ev. at the physical
  layer, the standard allows transmission in 5,10,20,40 or 80 ms time
  frames. various orthogonal (walsh) codes are used for channel
  identification and to achieve higher data rates.
  
  radio link protocol type 3 (rlp) [57] is used with a cdma2000 traffic
  channel to support cdma data services. rlp provides an octet stream
  transport service and is unaware of higher layer framing. there are
  several rlp frame formats. rlp frame formats with higher payload
  were designed for higher data rates. depending on the channel speed,
  one or more rlp frames can be transmitted in a single physical layer
  frame.
  
  rlp can substantially decrease the error rate exhibited by cdma
  traffic channels [53]. when transferring data, rlp is a pure nak-
  based finite selective repeat protocol. the receiver does not
  acknowledge successfully received data frames. if one or more rlp
  data frames are missing, the receiving rlp makes several attempts
  (called nak rounds) to recover them by sending one or more nak
  control frames to the transmitter. each nak frame must be sent in a
  separate physical layer frame. when rlp supplies the last nak
  control frame of a particular nak round, a retransmission timer is
  set. if the missing frame is not received when the timer expires,
  rlp may try another nak round. rlp may not recover all missing
  frames. if after all rlp rounds, a frame is still missing, rlp
  supplies data with a missing frame to the higher layer protocols.
  
  4. tcp over 2.5g and 3g
  
  what follows is a set of recommendations for configuration parameters
  for protocol stacks which will be used to support tcp connections
  over 2.5g and 3g wireless networks. some of these recommendations
  imply special configuration:
  
  inamura, et al. best current practice [page 10]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  o at the data receiver (frequently a stack at or near the wireless
  device),
  
  o at the data sender (frequently a host in the internet or possibly
  a gateway or proxy at the edge of a wireless network), or
  
  o at both.
  
  these configuration options are commonly available ietf standards-
  track mechanisms considered safe on the general internet. system
  administrators are cautioned, however, that increasing the mtu size
  (section 4.4) and disabling rfc 1144 header compression (section 4.9)
  could affect host efficiency, and that changing such parameters
  should be done with care.
  
  4.1 appropriate window size (sender & receiver)
  
  tcp over 2.5g/3g should support appropriate window sizes based on the
  bandwidth delay product (bdp) of the end-to-end path (see section
  2.2). the tcp specification [14] limits the receiver window size to
  64 kb. if the end-to-end bdp is expected to be larger than 64 kb,
  the window scale option [2] can be used to overcome that limitation.
  many operating systems by default use small tcp receive and send
  buffers around 16kb. therefore, even for a bdp below 64 kb, the
  default buffer size setting should be increased at the sender and at
  the receiver to allow a large enough window.
  
  4.2 increased initial window (sender)
  
  tcp controls its transmit rate using the congestion window mechanism.
  the traditional initial window value of one segment, coupled with the
  delayed ack mechanism [17] implies unnecessary idle times in the
  initial phase of the connection, including the delayed ack timeout
  (typically 200 ms, but potentially as much as 500 ms) [4]. senders
  can avoid this by using a larger initial window of up to four
  segments (not to exceed roughly 4 kb) [4]. experiments with
  increased initial windows and related measurements have shown (1)
  that it is safe to deploy this mechanism (i.e., it does not lead to
  congestion collapse), and (2) that it is especially effective for the
  transmission of a few tcp segments' worth of data (which is the
  behavior commonly seen in such applications as internet-enabled
  mobile wireless devices). for large data transfers, on the other
  hand, the effect of this mechanism is negligible.
  
  tcp over 2.5g/3g should set the initial cwnd (congestion window)
  according to equation 1 in [4]:
  
  min (4*mss, max (2*mss, 4380 bytes))
  
  inamura, et al. best current practice [page 11]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  this increases the permitted initial window from one to between two
  and four segments (not to exceed approximately 4 kb).
  
  4.3 limited transmit (sender)
  
  rfc 3042 [10], limited transmit, extends fast retransmit/fast
  recovery for tcp connections with small congestion windows that are
  not likely to generate the three duplicate acknowledgements required
  to trigger fast retransmit [1]. if a sender has previously unsent
  data queued for transmission, the limited transmit mechanism calls
  for sending a new data segment in response to each of the first two
  duplicate acknowledgments that arrive at the sender. this mechanism
  is effective when the congestion window size is small or if a large
  number of segments in a window are lost. this may avoid some
  retransmissions due to tcp timeouts. in particular, some studies
  [10] have shown that over half of a busy server's retransmissions
  were due to rto expiration (as opposed to fast retransmit), and that
  roughly 25% of those could have been avoided using limited transmit.
  similar to the discussion in section 4.2, this mechanism is useful
  for small amounts of data to be transmitted. tcp over 2.5g/3g
  implementations should implement limited transmit.
  
  4.4 ip mtu larger than default
  
  the maximum size of an ip datagram supported by a link layer is the
  mtu (maximum transfer unit). the link layer may, in turn, fragment
  ip datagrams into pdus. for example, on links with high error rates,
  a smaller link pdu size increases the chance of successful
  transmission. with layer two arq and transparent link layer
  fragmentation, the network layer can enjoy a larger mtu even in a
  relatively high ber (bit error rate) condition. without these
  features in the link, a smaller mtu is suggested.
  
  tcp over 2.5g/3g should allow freedom for designers to choose mtu
  values ranging from small values (such as 576 bytes) to a large value
  that is supported by the type of link in use (such as 1500 bytes for
  ip packets on ethernet). given that the window is counted in units
  of segments, a larger mtu allows tcp to increase the congestion
  window faster [5]. hence, designers are generally encouraged to
  choose larger values. these may exceed the default ip mtu values of
  576 bytes for ipv4 rfc 1191 [6] and 1280 bytes for ipv6 [18]. while
  this recommendation is applicable to 3g networks, operation over 2.5g
  networks should exercise caution as per the recommendations in rfc
  3150 [5].
  
  inamura, et al. best current practice [page 12]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  4.5 path mtu discovery (sender & intermediate routers)
  
  path mtu discovery allows a sender to determine the maximum end-to-
  end transmission unit (without ip fragmentation) for a given routing
  path. rfc 1191 [6] and rfc 1981 [8] describe the mtu discovery
  procedure for ipv4 and ipv6, respectively. this allows tcp senders
  to employ larger segment sizes (without causing ip layer
  fragmentation) instead of assuming the small default mtu. tcp over
  2.5g/3g implementations should implement path mtu discovery. path
  mtu discovery requires intermediate routers to support the generation
  of the necessary icmp messages. rfc 1435 [7] provides
  recommendations that may be relevant for some router implementations.
  
  4.6 selective acknowledgments (sender & receiver)
  
  the selective acknowledgment option (sack), rfc 2018 [3], is
  effective when multiple tcp segments are lost in a single tcp window
  [24]. in particular, if the end-to-end path has a large bdp and a
  high packet loss rate, the probability of multiple segment losses in
  a single window of data increases. in such cases, sack provides
  robustness beyond tcp-tahoe and tcp-reno [21]. tcp over 2.5g/3g
  should support sack.
  
  in the absence of sack feature, the tcp should use newreno rfc 2582
  [15].
  
  4.7 explicit congestion notification (sender, receiver & intermediate
  routers)
  
  explicit congestion notification, rfc 3168 [9], allows a tcp receiver
  to inform the sender of congestion in the network by setting the
  ecn-echo flag upon receiving an ip packet marked with the ce bit(s).
  the tcp sender will then reduce its congestion window. thus, the use
  of ecn is believed to provide performance benefits [32], [43]. rfc
  3168 [9] also places requirements on intermediate routers (e.g.,
  active queue management and setting of the ce bit(s) in the ip header
  to indicate congestion). therefore, the potential improvement in
  performance can only be achieved when ecn capable routers are
  deployed along the path. tcp over 2.5g/3g should support ecn.
  
  4.8 tcp timestamps option (sender & receiver)
  
  traditionally, tcps collect one rtt sample per window of data [14],
  [17]. this can lead to an underestimation of the rtt, and spurious
  timeouts on paths in which the packet transmission delay dominates
  the rtt. this holds despite a conservative retransmit timer such as
  the one specified in rfc 2988 [11]. tcp connections with large
  windows may benefit from more frequent rtt samples provided with
  
  inamura, et al. best current practice [page 13]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  timestamps by adapting quicker to changing network conditions [2].
  however, there is some empirical evidence that for tcps with an rfc
  2988 timer [11], timestamps provide little or no benefits on backbone
  internet paths [59]. using the tcp timestamps option has the
  advantage that retransmitted segments can be used for rtt
  measurement, which is otherwise forbidden by karn's algorithm [17],
  [11]. furthermore, the tcp timestamps option is the basis for
  detecting spurious retransmits using the eifel algorithm [30].
  
  a 2.5/3g link (layer) is dedicated to a single host. it therefore
  only experiences a low degree of statistical multiplexing between
  different flows. also, the packet transmission and queuing delays of
  a 2.5/3g link often dominate the path's rtt. this already results in
  large rtt variations as packets fill the queue while a tcp sender
  probes for more bandwidth, or as packets drain from the queue while a
  tcp sender reduces its load in response to a packet loss. in
  addition, the delay spikes across a 2.5/3g link (see section 2.4) may
  often exceed the end-to-end rtt. the thus resulting large variations
  in the path's rtt may often cause spurious timeouts.
  
  when running tcp in such an environment, it is therefore advantageous
  to sample the path's rtt more often than only once per rtt. this
  allows the tcp sender to track changes in the rtt more closely. in
  particular, a tcp sender can react more quickly to sudden increases
  of the rtt by sooner updating the rto to a more conservative value.
  the tcp timestamps option [2] provides this capability, allowing the
  tcp sender to sample the rtt from every segment that is acknowledged.
  using timestamps in the mentioned scenario leads to a more
  conservative tcp retransmission timer and reduces the risk of
  triggering spurious timeouts [45], [52], [54], [60].
  
  there are two problematic issues with using timestamps:
  
  o 12 bytes of overhead are introduced by carrying the tcp timestamps
  option and padding in the tcp header. for a small mtu size, it
  can present a considerable overhead. for example, for an mtu of
  296 bytes the added overhead is 4%. for an mtu of 1500 bytes, the
  added overhead is only 0.8%.
  
  o current tcp header compression schemes are limited in their
  handling of the tcp options field. for rfc 2507 [13], any change
  in the options field (caused by timestamps or sack, for example)
  renders the entire field uncompressible (leaving the tcp/ip header
  itself compressible, however). even worse, for rfc 1144 [40] such
  a change in the options field effectively disables tcp/ip header
  compression altogether. this is the case when a connection uses
  the tcp timestamps option. that option field is used both in the
  data and the ack path, and its value typically changes from one
  
  inamura, et al. best current practice [page 14]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  packet to the next. the ietf is currently specifying a robust
  tcp/ip header compression scheme with better support for tcp
  options [29].
  
  the original definition of the timestamps option [2] specifies that
  duplicate segments below cumulative ack do not update the cached
  timestamp value at the receiver. this may lead to overestimating of
  rtt for retransmitted segments. a possible solution [47] allows the
  receiver to use a more recent timestamp from a duplicate segment.
  however, this suggestion allows for spoofing attacks against the tcp
  receiver. therefore, careful consideration is needed in
  implementing this solution.
  
  recommendation: tcp should use the tcp timestamps option. it allows
  for better rtt estimation and reduces the risk of spurious timeouts.
  
  4.9 disabling rfc 1144 tcp/ip header compression (wireless host)
  
  it is well known (and has been shown with experimental data) that rfc
  1144 [40] tcp header compression does not perform well in the
  presence of packet losses [43], [52]. if a wireless link error is
  not recovered, it will cause tcp segment loss between the compressor
  and decompressor, and then rfc 1144 header compression does not allow
  tcp to take advantage of fast retransmit fast recovery mechanism.
  the rfc 1144 header compression algorithm does not transmit the
  entire tcp/ip headers, but only the changes in the headers of
  consecutive segments. therefore, loss of a single tcp segment on the
  link causes the transmitting and receiving tcp sequence numbers to
  fall out of synchronization. hence, when a tcp segment is lost
  after the compressor, the decompressor will generate false tcp
  headers. consequently, the tcp receiver will discard all remaining
  packets in the current window because of a checksum error. this
  continues until the compressor receives the first retransmission
  which is forwarded uncompressed to synchronize the decompressor [40].
  
  as previously recommended in rfc 3150 [5], rfc 1144 header
  compression should not be enabled unless the packet loss probability
  between the compressor and decompressor is very low. actually,
  enabling the timestamps option effectively accomplishes the same
  thing (see section 4.8). other header compression schemes like rfc
  2507 [13] and robust header compression [12] are meant to address
  deficiencies in rfc 1144 header compression. at the time of this
  writing, the ietf was working on multiple extensions to robust header
  compression (negotiating robust header compression over ppp,
  compressing tcp options, etc) [16].
  
  inamura, et al. best current practice [page 15]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  4.10 summary
  
  items comments
  ----------------------------------------------------------------
  appropriate window size (sender & receiver)
  based on end-to-end bdp
  
  window scale option (sender & receiver)
  [rfc1323] window size > 64kb
  
  increased initial window (sender)
  [rfc3390] cwnd = min (4*mss,
  max (2*mss, 4380 bytes))
  
  limited transmit (sender)
  [rfc3042]
  
  ip mtu larger than more applicable to 3g
  default
  
  path mtu discovery (sender & intermediate routers)
  [rfc1191,rfc1981]
  
  selective acknowledgment
  option (sack)
  [rfc2018] (sender & receiver)
  
  explicit congestion
  notification(ecn)
  [rfc3168] (sender, receiver &
  intermediate routers)
  
  timestamps option (sender & receiver)
  [rfc1323, r.t.braden's id]
  
  disabling rfc1144
  tcp/ip header compression
  [rfc1144] (wireless host)
  
  5. open issues
  
  this section outlines additional mechanisms and parameter settings
  that may increase end-to-end performance when running tcp across
  2.5g/3g networks. note, that apart from the discussion of the rto's
  initial value, those mechanisms and parameter settings are not part
  of any standards track rfc at the time of this writing. therefore,
  they cannot be recommended for the internet in general.
  
  inamura, et al. best current practice [page 16]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  other mechanisms for increasing tcp performance include enhanced tcp/
  ip header compression schemes [29], active queue management rfc 2309
  [28], link layer retransmission schemes [23], and caching packets
  during transient link outages to retransmit them locally when the
  link is restored to operation [23].
  
  shortcomings of existing tcp/ip header compression schemes (rfc 1144
  [40], rfc 2507 [13]) are that they do not compress headers of
  handshaking packets (syns and fins), and that they lack proper
  handling of tcp option fields (e.g., sack or timestamps) (see section
  4.8). although rfc 3095 [12] does not yet address this issue, the
  ietf is developing improved tcp/ip header compression schemes,
  including better handling of tcp options such as timestamps and
  selective acknowledgements. especially, if many short-lived tcp
  connections run across the link, the compression of the handshaking
  packets may greatly improve the overall header compression ratio.
  
  implementing active queue management is attractive for a number of
  reasons as outlined in rfc 2309 [28]. one important benefit for
  2.5g/ 3g networks, is that it minimizes the amount of potentially
  stale data that may be queued in the network ("clicking from page to
  page" before the download of the previous page is complete).
  avoiding the transmission of stale data across the 2.5g/3g radio link
  saves transmission (battery) power, and increases the ratio of useful
  data over total data transmitted. another important benefit of
  active queue management for 2.5g/3g networks, is that it reduces the
  risk of a spurious timeout for the first data segment as outlined
  below.
  
  since 2.5g/3g networks are commonly characterized by high delays,
  avoiding unecessary round-trip times is particularly attractive.
  this is specially beneficial for short-lived, transactional (request/
  response-style) tcp sessions that typically result from browsing the
  web from a smart phone. however, existing solutions such as t/tcp
  rfc 1644 [27], have not been adopted due to known security concerns
  [38].
  
  spurious timeouts, packet re-ordering, and packet duplication may
  reduce tcp's performance. thus, making tcp more robust against those
  events is desirable. solutions to this problem have been proposed
  [30], [35], [41], and standardization work within the ietf is ongoing
  at the time of writing. those solutions include reverting congestion
  control state after such an event has been detected, and adapting the
  retransmission timer and duplicate acknowledgement threshold. the
  deployment of such solutions may be particularly beneficial when
  running tcp across wireless networks because wireless access links
  may often be subject to handovers and resource preemption, or the
  mobile transmitter may traverse through a radio coverage hole. such
  
  inamura, et al. best current practice [page 17]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  disrupting events may easily trigger a spurious timeout despite a
  conservative retransmission timer. also, the mobility mechanisms of
  some wireless networks may cause packet duplication.
  
  the algorithm for computing tcp's retransmission timer is specified
  in rfc 2988 [11]. the standard specifies that the initial setting of
  the retransmission timeout value (rto) should not be less than 3
  seconds. this value might be too low when running tcp across 2.5g/3g
  networks. in addition to its high latencies, those networks may be
  run at bit rates of as low as about 10 kb/s which results in large
  packet transmission delays. in this case, the rtt for the first data
  segment may easily exceed the initial tcp retransmission timer
  setting of 3 seconds. this would then cause a spurious timeout for
  that segment. hence, in such situations it may be advisable to set
  tcp's initial rto to a value larger than 3 seconds. furthermore, due
  to the potentially large packet transmission delays, a tcp sender
  might choose to refrain from initializing its rto from the rtt
  measured for the syn, but instead take the rtt measured for the first
  data segment.
  
  some of the recommendations in rfc 2988 [11] are optional, and are
  not followed by all tcp implementations. specifically, some tcp
  stacks allow a minimum rto less than the recommended value of 1
  second (section 2.4 of [11]), and some implementations do not
  implement the recommended restart of the rto timer when an ack is
  received (section 5.3 of [11]). some experiments [52], [54], have
  shown that in the face of bandwidth oscillation, using the
  recommended minimum rto value of 1 sec (along with the also
  recommended initial rto of 3 sec) reduces the number of spurious
  retransmissions as compared to using small minimum rto values of 200
  or 400 ms. furthermore, tcp stacks that restart the retransmission
  timer when an ack is received experience far less spurious
  retransmissions than implementations that do not restart the rto
  timer when an ack is received. therefore, at the time of this
  writing, it seems preferable for tcp implementations used in 3g
  wireless data transmission to comply with all recommendations of rfc
  2988.
  
  6. security considerations
  
  in 2.5g/3g wireless networks, data is transmitted as ciphertext over
  the air and as cleartext between the radio access network (ran) and
  the core network. ip security rfc 2401 [37] or tls rfc 2246 [36] can
  be deployed by user devices for end-to-end security.
  
  7. iana considerations
  
  this specification requires no iana actions.
  
  inamura, et al. best current practice [page 18]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  8. acknowledgements
  
  the authors would like to acknowledge contributions to the text from
  the following individuals:
  
  max hata, ntt docomo, inc. (hata@mml.yrp.nttdocomo.co.jp)
  
  masahiro hara, fujitsu, inc. (mhara@flab.fujitsu.co.jp)
  
  joby james, motorola, inc. (joby@miel.mot.com)
  
  william gilliam, hewlett-packard company (wag@cup.hp.com)
  
  alan hameed, fujitsu fnc, inc. (alan.hameed@fnc.fujitsu.com)
  
  rodrigo garces, mobility network systems
  (rodrigo.garces@mobilitynetworks.com)
  
  peter ford, microsoft (peterf@exchange.microsoft.com)
  
  fergus wills, openwave (fergus.wills@openwave.com)
  
  michael meyer (michael.meyer@eed.ericsson.se)
  
  the authors gratefully acknowledge the valuable advice from the
  following individuals:
  
  gorry fairhurst (gorry@erg.abdn.ac.uk)
  
  mark allman (mallman@grc.nasa.gov)
  
  aaron falk (falk@isi.edu)
  
  9. normative references
  
  [1] allman, m., paxson, v. and w. stevens, "tcp congestion control",
  rfc 2581, april 1999.
  
  [2] jacobson, v., braden, r. and d. borman, "tcp extensions for high
  performance", rfc 1323, may 1992.
  
  [3] mathis, m., mahdavi, j., floyd, s. and r. romanow, "tcp
  selective acknowledgment options", rfc 2018, october 1996.
  
  [4] allman, m., floyd, s. and c. partridge, "increasing tcp's
  initial window", rfc 3390, october 2002.
  
  inamura, et al. best current practice [page 19]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  [5] dawkins, s., montenegro, g., kojo, m. and v. magret, "end-to-end
  performance implications of slow links", bcp 48, rfc 3150, july
  2001.
  
  [6] mogul, j. and s. deering, "path mtu discovery", rfc 1191,
  november 1990.
  
  [7] knowles, s., "iesg advice from experience with path mtu
  discovery", rfc 1435, march 1993.
  
  [8] mccann, j., deering, s. and j. mogul, "path mtu discovery for ip
  version 6", rfc 1981, august 1996.
  
  [9] ramakrishnan, k., floyd, s. and d. black, "the addition of
  explicit congestion notification (ecn) to ip", rfc 3168,
  september 2001.
  
  [10] allman, m., balakrishnan, h. and s. floyd, "enhancing tcp's loss
  recovery using limited transmit", rfc 3042, january 2001.
  
  [11] paxson, v. and m. allman, "computing tcp's retransmission
  timer", rfc 2988, november 2000.
  
  [12] bormann, c., burmeister, c., degermark, m., fukushima, h.,
  hannu, h., jonsson, l-e., hakenberg, r., koren, t., le, k., liu,
  z., martensson, a., miyazaki, a., svanbro, k., wiebke, t.,
  yoshimura, t. and h. zheng, "robust header compression (rohc):
  framework and four profiles: rtp, udp, esp, and uncompressed",
  rfc 3095, july 2001.
  
  [13] degermark, m., nordgren, b. and s. pink, "ip header
  compression", rfc 2507, february 1999.
  
  [14] postel, j., "transmission control protocol - darpa internet
  program protocol specification", std 7, rfc 793, september 1981.
  
  [15] floyd, s. and t. henderson, "the newreno modification to tcp's
  fast recovery algorithm", rfc 2582, april 1999.
  
  [16] bormann, c., "robust header compression (rohc) over ppp", rfc
  3241, april 2002.
  
  [17] braden, r., "requirements for internet hosts - communication
  layers", std 3, rfc 1122, october 1989.
  
  [18] deering, s. and r. hinden, "internet protocol, version 6 (ipv6)
  specification", rfc 2460, december 1998.
  
  inamura, et al. best current practice [page 20]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  10. informative references
  
  [19] montenegro, g., dawkins, s., kojo, m., magret, v. and n.
  vaidya, "long thin networks", rfc 2757, january 2000.
  
  [20] third generation partnership project, "rlc protocol
  specification (3g ts 25.322:)", 1999.
  
  [21] fall, k. and s. floyd, "simulation-based comparisons of tahoe,
  reno, and sack tcp", computer communication review, 26(3) , july
  1996.
  
  [22] fairhurst, g. and l. wood, "advice to link designers on link
  automatic repeat request (arq)", bcp 62, rfc 3366, august 2002.
  
  [23] karn, p., "advice for internet subnetwork designers", work in
  progress.
  
  [24] dawkins, s., montenegro, g., magret, v., vaidya, n. and m.
  kojo, "end-to-end performance implications of links with
  errors", bcp 50, rfc 3135, august 2001.
  
  [25] wireless application protocol, "wap specifications", 2002,
  <http://www.wapforum.org/>.
  
  [26] open mobile alliance, "open mobile alliance", 2002,
  <http://www.openmobilealliance.org/>.
  
  [27] braden, r., "t/tcp -- tcp extensions for transactions", rfc
  1644, july 1994.
  
  [28] braden, r., clark, d., crowcroft, j., davie, b., deering, s.,
  estrin, d., floyd, s., jacobson, v., minshall, g., partridge,
  c., peterson, l., ramakrishnan, k., shenker, s., wroclawski, j.
  and l. zhang, "recommendations on queue management and
  congestion avoidance in the internet", rfc 2309, april 1998.
  
  [29] ietf, "robust header compression", 2001,
  <http://www.ietf.org/…tml.charters/rohc-charter.html>.
  
  [30] ludwig, r. and r. h. katz, "the eifel algorithm: making tcp
  robust against spurious retransmissions", acm computer
  communication review 30(1), january 2000.
  
  [31] wireless application protocol, "wap wireless profiled tcp",
  wap-225-tcp-20010331-a, april 2001,
  <http://www.wapforum.com/what/technical.htm>.
  
  inamura, et al. best current practice [page 21]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  [32] hadi salim, j. and u. ahmed, "performance evaluation of explicit
  congestion notification (ecn) in ip networks", rfc 2884, july
  2000.
  
  [33] ntt docomo technical journal, "special issue on i-mode service",
  october 1999.
  
  [34] ntt docomo technical journal, "special article on imt-2000
  services", september 2001.
  
  [35] floyd, s., mahdavi, j., mathis, m. and m. podolsky, "an
  extension to the selective acknowledgement (sack) option for
  tcp", rfc 2883, july 2000.
  
  [36] dierks, t. and c. allen, "the tls protocol version 1.0", rfc
  2246, january 1999.
  
  [37] kent, s. and r. atkinson, "security architecture for the
  internet protocol", rfc 2401, november 1998.
  
  [38] de vivo, m., o. de vivo, g., koeneke, r. and g. isern, "internet
  vulnerabilities related to tcp/ip and t/tcp", acm computer
  communication review 29(1), january 1999.
  
  [39] third generation partnership project, "rrc protocol
  specification (3gpp ts 25.331:)", september 2001.
  
  [40] jacobson, v., "compressing tcp/ip headers for low-speed serial
  links", rfc 1144, february 1990.
  
  [41] blanton, e. and m. allman, "on making tcp more robust to packet
  reordering", acm computer communication review 32(1), january
  2002, <http://roland.grc.nasa.gov/…man/papers/tcp-reorder-
  ccr.ps>.
  
  [42] karn, p. and c. partridge, "improving round-trip time estimates
  in reliable transport protocols", acm sigcomm 87, 1987.
  
  [43] ludwig, r., rathonyi, b., konrad, a. and a. joseph, "multi-layer
  tracing of tcp over a reliable wireless link", acm sigmetrics
  99, may 1999.
  
  [44] ludwig, r., konrad, a., joseph, a. and r. katz, "optimizing the
  end-to-end performance of reliable flows over wireless links",
  kluwer/acm wireless networks journal vol. 8, nos. 2/3, pp. 289-
  299, march-may 2002.
  
  inamura, et al. best current practice [page 22]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  [45] gurtov, a., "making tcp robust against delay spikes", university
  of helsinki, department of computer science, series of
  publications c, c-2001-53, nov 2001,
  <http://www.cs.helsinki.fi/…tov/papers/report01.html>.
  
  [46] stevens, w., "tcp/ip illustrated, volume 1; the protocols",
  addison wesley, 1995.
  
  [47] braden, r., "tcp extensions for high performance: an update",
  work in progress.
  
  [48] allman, m., dawkins, s., glover, d., griner, j., tran, d.,
  henderson, t., heidemann, j., touch, j., kruse, h., ostermann,
  s., scott, k. and j. semke, "ongoing tcp research related to
  satellites", rfc 2760, february 2000.
  
  [49] allman, m., glover, d. and l. sanchez, "enhancing tcp over
  satellite channels using standard mechanisms", bcp 28, rfc 2488,
  january 1999.
  
  [50] balakrishnan, h., padmanabhan, v., fairhurst, g. and m.
  sooriyabandara, "tcp performance implications of network
  asymmetry", rfc 3449, december 2002.
  
  [51] kempf, j., "problem description: reasons for performing context
  transfers between nodes in an ip access network", rfc 3374,
  september 2002.
  
  [52] khafizov, f. and m. yavuz, "running tcp over is-2000", proc. of
  ieee icc, 2002.
  
  [53] khafizov, f. and m. yavuz, "analytical model of rlp in is-2000
  cdma networks", proc. of ieee vehicular technology conference,
  september 2002.
  
  [54] yavuz, m. and f. khafizov, "tcp over wireless links with
  variable bandwidth", proc. of ieee vehicular technology
  conference, september 2002.
  
  [55] tia/eia/cdma2000, "mobile station - base station compatibility
  standard for dual-mode wideband spread spectrum cellular
  systems", washington: telecommunication industry association,
  1999.
  
  [56] tia/eia/is-95 rev a, "mobile station - base station
  compatibility standard for dual-mode wideband spread spectrum
  cellular systems", washington: telecommunication industry
  association, 1995.
  
  inamura, et al. best current practice [page 23]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  [57] tia/eia/is-707-a-2.10, "data service options for spread spectrum
  systems: radio link protocol type 3", january 2000.
  
  [58] dahlman, e., beming, p., knutsson, j., ovesjo, f., persson, m.
  and c. roobol, "wcdma - the radio interface for future mobile
  multimedia communications", ieee trans. on vehicular technology,
  vol. 47, no. 4, pp. 1105-1118, november 1998.
  
  [59] allman, m. and v. paxson, "on estimating end-to-end network path
  properties", acm sigcomm 99, september 1999.
  
  [60] gurtov, a. and r. ludwig, "responding to spurious timeouts in
  tcp", ieee infocom'03, march 2003.
  
  inamura, et al. best current practice [page 24]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  11. authors' addresses
  
  hiroshi inamura
  ntt docomo, inc.
  3-5 hikarinooka
  yokosuka shi, kanagawa ken 239-8536
  japan
  
  email: inamura@mml.yrp.nttdocomo.co.jp
  uri: http://www.nttdocomo.co.jp/
  
  gabriel montenegro
  sun microsystems laboratories, europe
  avenue de l'europe
  zirst de montbonnot
  38334 saint ismier cedex
  france
  
  email: gab@sun.com
  
  reiner ludwig
  ericsson research
  ericsson allee 1
  52134 herzogenrath
  germany
  
  email: reiner.ludwig@ericsson.com
  
  andrei gurtov
  sonera
  p.o. box 970, fin-00051
  helsinki,
  finland
  
  email: andrei.gurtov@sonera.com
  uri: http://www.cs.helsinki.fi/u/gurtov/
  
  farid khafizov
  nortel networks
  2201 lakeside blvd
  richardson, tx 75082,
  usa
  
  email: faridk@nortelnetworks.com
  
  inamura, et al. best current practice [page 25]
  
  rfc 3481 tcp over 2.5g/3g february 2003
  
  12. full copyright statement
  
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  inamura, et al. best current practice [page 26]