AVT Working Group Mooi C. Chuah
Internet Draft Enrique J. Hernandez-Valencia
Expires June 2001 Lucent Technologies Bell Laboratories
December 2000
A LightWeight IP Encapsulation (LIPE) Scheme
<draft-chuah-avt-lipe-02.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This document is submitted to the Audio/Video Transport Working Group
of the Internet Engineering Task Force (IETF). Comments should be
submitted to the rem-conf@es.net mailing list.
Distribution of this memo is unlimited.
Abstract
Several application level multiplexing/compression schemes have been
proposed in the IETF Audio/Video Transport (AVT) Working Group
[1][2][9] to improve the transport efficiency of packet-voice traffic
over IP-based networks. These approaches generally assume voice
packets are encapsulated in RTP/UDP/IP by the communicating end-
points (e.g., IP phones, mobile terminal, media gateways, etc.). In
some transport scenarios, e.g., CDMA/GSM cellular networks, using RTP
for voice packet is unnecessary as only the data transfer services
provided by the IP/UDP layer, not the media control functions of RTP,
are required.
This document describes a lightweight IP encapsulation scheme to
multiplex low bit rate audio (or multimedia) packets into a single
UDP/IP session. This document is the product of the AVT Working
Chuah, et al. expires June 2001 [Page 1]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the ietf-avt@merit.edu mailing list.
Chuah, et al. expires June 2001 [Page 2]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
Applicability
These extensions are intended for those implementations which desire
to multiplex small data packets together into one IP/UDP protocol
data unit (PDU).
Table of Contents
Chuah, et al. expires June 2001 [Page 3]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
1. Introduction
As the Internet evolves into a ubiquitous communication infrastruc-
ture, IP based technologies have also become more sophisticated. As
a consequence of the maturing of the IP technology, it is now evident
that the previously separate data and voice networks are converging
to provide integrated communications services, including data, voice
and video. While data packets can often be quite large, voice pack-
ets are in general rather small. Codecs in IP phones or IP telephony
gateways compress the incoming speech samples and generate speech
frames with sizes ranging from 5 to 20 bytes per speech sample. For
example, G723.1 generates a 20-byte speech frame at 30 ms intervals
[3]. Many codecs used in cellular environments generate speech frames
of size less than 10 bytes per speech sample.
Such small speech frame sizes are subject to a large transport over-
head when transferred in individual IP packets. For example a 10-byte
voice packet transmitted using UDP/IP encapsulation incurs an over-
head of 28 bytes (20 byte IP header, plus possibly 8 bytes UDP
header), or 280%. In addition, if each audio stream uses one UDP
media session, the large number of packets will create heavy packet
processing load for the intermediate media gateway devices that
operate above the IP-layer, even if no processing of the user flow is
actually required. The available UDP port numbers may also become a
limiting factor on the maximum number of voice flows as media gate-
ways are expected to handle tens of thousand voice flows.
Although the relatively high transport overhead may not constitute a
critical traffic engineering factor in transport scenarios where net-
work resources are plentiful, the situation is undiserable for most
wireless access networks. For instance, a T1/E1 link to a wireless
base station would only be able to support a third of the voice
traffic currently supported by their native packet-voice transport
schemes. The idea of pooling multiple user flows into a more effi-
ciently multiplexed channel is highly appealing.
Fortunately, for many applications, it is possible to multiplex
traffic from a large number of flows into a single IP packet to
improve efficiency and scalability without incurring much multiplex-
ing delay. For example, when long distance telephony is offered over
the Internet, the IP telephony gateways or the mobile switching
centers in a cellular network provide an interface between the exist-
ing circuit switched telephone networks (such as PSTN and cellular
networks like CDMA/GSM/TDMA network) and the packet switched IP data
networks. The voice calls between a pair of IP telephony gateways or
the mobile switching centers can be multiplexed into a single UDP
session. As another example, in a CDMA based cellular network, an IP
network may be used as the access network by the wireless service
Chuah, et al. expires June 2001 [Page 4]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
provider to connect the base stations to the mobile switching
centers, part of whose function is to select the reverse direction
radio frames and duplicate the forward direction radio frames for
mobiles in soft handoff. In this case, the radio frames from dif-
ferent mobiles handled by the same base station, which can be either
voice or data, can also be multiplexed into a single UDP session.
Many such applications have stringent delay requirements. In the
first example above, the usual transfer delay and delay jitter
requirements for voice application apply. In the second example, the
duplicate radio frames in the reverse direction must be received by
the mobile switching center within a small time window for the frame
selection.
RTP [4] is a protocol designed to provide various real time services
to the application layer with no assumption on the underlying network
providing timely delivery or quality-of-service commitments. It can
be used when the network is not heavily loaded and the application it
supports can adapt to the varying network conditions to some extent.
To improve the transport efficiency, some multiplexing schemes have
been proposed within the framework of RTP [1,2].
Many of the features of RTP are designed to provide media control
information to cope with the unavailability of QoS guarantees from
the underlying network at the application layer. As such guarantees
become available in modern/future IP networks, some of these features
become unnecessary. These features are also of limited value to non-
RTP applications (e.g., most commercial wireless voice traffic). In
this document, we propose to use a lightweight encapsulation scheme
based on UDP/IP for multiplexing application sessions. LIPE is
designed to support multimedia traffic including both voice and data.
We also include some discussions on how UDP/IP header compression can
be incorporated within LIPE to further improve encapsulation effi-
ciency.
2. The LIPE Encapsulation Scheme
The Lightweight IP Encapsulation (LIPE) uses UDP/IP as the transport
layer. Each LIPE encapsulated payload consists of a variable number
of multimedia data packet (MDP). For each MDP, there is a multiplex-
ing header (MH) that conveys transport and media specific informa-
tion.
The format of the IP packet conveying multiple MDPs over UDP using a
minimum size MH is shown in Figure 1 .
Chuah, et al. expires June 2001 [Page 5]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + + + + + + + |
| IP + UDP + MH1 + MDP1 + MH2 + MDP2 + ~ + MHn + MDPn |
| (20) + (8) + (1) + + (1) + + + (1) + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MH: Multiplexing Header
MDP: Multimedia Data Packet
Figure 1 : Lightweight IP/UDP Encapsulation Scheme (Field lengths expressed in bytes)
The generic protocol stack for LIPE, assuming PPP in HDLC-like fram-
ing [RFC 1662], is as shown in Figure 2:
------------
| LIPE |
------------
| UDP |
------------
| IP |
------------
| HDLC/PPP |
------------
Figure 2: Protocol Stack for LIPE
All LIPE packets on the same PPP link MUST use the LIPE/IP encapsula-
tion depicted in Figure 1. Section 6 explains how IPCP is used to
negotiate for LIPE.
2.1. Basic LIPE Frame Format
The Multiplexing Header (MH) comprises of two components: the MDP
Header Extension bit (the E bit) and the MDP length field. Optional
Extension Headers can be supported via the E bit. The MH format is
shown in Figure 3.
1 2
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + |
|E+ MDP + Extended Headers |
| + Length + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Multiplexing Header Format
E bit: The Header Extension bit is the least significant bit of the
MH header. It is set to one/zero to indicate the presence/absence of
Chuah, et al. expires June 2001 [Page 6]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
an extension header longer than 2 bytes. If the E bit is set to zero,
the multiplexed header contains a 7 bit MDP length and a 2 bytes
extended header identifier. If the E bit is set to one, it means
there are more fields after the EHI.
MDP Length: a 7 bit MDP length field. This field indicates the size
of the entire MDP packet in bytes including the E bit, Length field
and optional Extension Headers (if present). For Type 0 Extended
Header, the actual length is as indicated in the 7 bit field. For
Type 1 Extended Header, the actual length is 4 times the number
expressed in the 7 bit field.
2.2. Extension Headers
Extension Headers are used to convey application specific informa-
tion. They also facilitate customization of LIPE to incorporate addi-
tional transport/session level control functionality such as sequence
number, voice/video quality estimator.
2.2.1. Type 0 Extended Header
The 16-bit Type 0 Extended Header (EH0) is the first field in any
Extension Header. It is used to identify MDPs belonging to specific
small voice/video flows. The format of an LIPE encapsulated payload
with a EH0 Extension Header is shown in Figure 4(a).
1 2
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + + + |
|0+ Length +X+ Seq + FlowId |
| + + + No + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MDPn Payload |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4(a) : A MH with a Type 0 EH
When X bit is clear, the following 3 bits are used as the Sequence
Number. This means the FlowId field is 12 bits. This version is used
mostly for applications that generate small packets e.g. voice. The
12-bit FlowId allows up to 4096 flows to be multiplexed into a single
UDP/IP session.
Chuah, et al. expires June 2001 [Page 7]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
2.2.2. Type 1 Extended Header
The 16-bit Type 1 Extended Header (EH1) is used to identify flows
that generate large data packets. The format of an LIPE encapsulated
payload with a Type 1 Extension Header is shown in Figure 4(b). The
least significant bit of the 1st byte of EH1 is the X bit. When X is
set to one, it indicates that a EOF bit and a 3-bit Seq Number fields
exist. This means when X bit is set, the FlowId field is 11-bit.
The EOF bit is set when there are more fragments to be transmitted.
For the non-fragment case, this bit is clear.
1 2
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +E+Seq + |
|0+ Length +X+O+ No + FlowId |
| + + +F+ + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MDPn Payload |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4(b) : A MH with a Type 1 EHI field
2.2.3. Payload Identifier (PID)
If the E-bit is set, it means there is a Paylaod Identifier (PID)
extension header following the Multiplexed Header Identifier field.
The Payload Identifier field starts with a 4-bit Payload Type Iden-
tifier (PTI) , a 4-bit PID Length and any additional payload specific
data. The format of the PID field is illustrated in Figure 6.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + PID + |
| PTI + LNGTH + PID Payload |
| + + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 : Format of the PID field
Thus, a MH with a Type 0 Multiplexed Header and the PID extended
header will look like Figure 6.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + + + |
|1+ Length +0+ Seq + FlowId |
Chuah, et al. expires June 2001 [Page 8]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
| + + + No + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PID + PID + PID + Data |
| Type + LnG=3 + Payload + Payload |
| 1 + + + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: A MH with a FlowId field and a PID field
Note that one can use the PID Type to indicate different wireless
access technologies e.g. PID Type = 1 indicates IS95 network, PID
Type = 2indicates UMTS network.
2.3. Examples of LIPE Encapsulated Payloads
In this section, we show some specific LIPE examples:
2.3.1. Carrying raw IS95 voice packets
In this scenario, the E bit of the first MH header is set to zero to
indicate that there is no PID field. Type 0 extended header is used.
1 2
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + + + |
|0+ Length +0+Seq + FlowId |
| + + +No + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User |
| Payload |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7(a) : Carrying raw IS95 voice packets
2.3.2. carrying UMTS Interactive Data packets.
1 2
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + + + Seq + |
|0+ Length +1+0+ No + FlowId |
| + + + + + |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| FP PDU |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chuah, et al. expires June 2001 [Page 9]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
Figure 7(b): Carrying UMTS Interactive Data packets
In this scenario, Type 1 Extended Header is used where the E bit is
set to one and the X bit is set to one. The FlowId is used to iden-
tify different user flows. The payload is the frame protocol (FP)
PDU described in [TS25.413].
Note that in our encapsulation scheme, no field is provided in the
header for error checking purposes. We rely on the link layer error
detection capability (e.g., CRC field in HDLC or ATM/AAL5) and possi-
bly the additional UDP checksum on LIPE/UDP/IP to provide for the
overall LIPE payload error detection. We believe this level of pro-
tection is sufficient.
2.4. LIPE Signaling Channel
LIPE end-points need a mechanism to specify UDP destination port
numbers for data transfer and negotiate FlowId. The LIPE signaling
channel is designed to serve such purposes.
A specified Destination Port number is used to indicate the LIPE Sig-
naling Channel. The format of the LIPE signaling message over this
channel is illustrated in Figure 8.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+
| + + + + |
| IP + UDP + Type + LNG + Control Msg Payload |
| (20B) + (8B) +(4bits)+(4bits)+ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+
Figure 8: LIPE Signaling Channel Message Format for IP/UDP Encapsulation
Here, the UDP Port Number xxx (TBD) identifies the LIPE Signaling
Channel, the 4-bit LIPE Signaling Channel Type field is used to iden-
tify the LIPE Control Message Type, and the 4-bit Length (LNG) field
identifies the length of Control Msg Payload expressed in bytes.
Seven types of control messages are currently defined:
Type = 0 Tunnel Set Up Request Type = 1 Tunnel Set Up Response Type =
2 Tunnel Teardown Request Type = 3 Flow Set Up Request Type = 4 Flow
Set Up Response Type = 5 Flow Teardown Request Type = 6 Flow Handoff
Request Type = 7 Flow Handoff Response
Chuah, et al. expires June 2001 [Page 10]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
All LIPE signaling messages are UDP/IP messages. We also assume that
all LIPE signaling messages are retransmitted for a maximum of MAX_RETRY
times. LIPE peers which send a LIPE signaling message will wait for a
response and times out after MAX_Response_Time. When time out occurs,
the LIPE sending peer will retransmit the LIPE signaling message for a
maximum of MAX_RETRY times before giving up.
2.4.1. LIPE Signaling Message Exchange
2.4.1.1. LIPE Tunnel SetUp/Teardown Procedure
LIPE Peer 1 LIPE Peer 2
| |
| Tunnel Set Up Request |
| -----------------------> |
| Tunnel Set Up Response |
| <----------------------- |
| |
| |
Figure 9: Tunnel/Flow Set Up Procedures
Two LIPE peers will first exchange tunnel set up request/response
messages.
After this exchange, the LIPE peers know which UDP port number to use
for transporting LIPE data packets.
2.4.1.1.1. Tunnel Set Up Request Message
1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +
|Typ=0 + Trid + Lngth +
| + + +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Port No +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10 (a): Tunnel Set Up Request Message
For Tunnel Set Up Request message, there is a 4 bit transaction iden-
tifier. This field is not incremented when a request is retransmit-
ted. If necessary, later we can add QoS Parameter as an extension to
this message to do QoS negotiation for the tunnel. When the tunnel
is no longer needed, the LIPE peer sends a Tunnel Teardown message.
This message can only be sent when there is no more active flow being
Chuah, et al. expires June 2001 [Page 11]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
supported in the tunnel.
2.4.1.1.2. Tunnel Set Up Response Message
1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +
|Typ=1 + Trid + Lngth +
| + + +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10 (b): Tunnel Set Up Response Message
The Tunnel Set Up Response Message will contain the error codes.
Error Code = 0 means the tunnel set up is successful.
2.4.1.1.3. Tunnel TearDown Message
1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +
|Typ=2 + Trid + Lngth +
| + + +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Destination Port No +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10 (c): Tunnel Teardown Message
The tunnel teardown message can only be sent when no more flows exist
in the tunnel.
2.4.1.2. LIPE Flow SetUp/Teardown Procedure
LIPE Peer 1 LIPE Peer 2
| |
| Flow Set Up Request |
| -----------------------> |
| Flow Set Up Response |
| <-------------------- |
| |
Figure 11: Flow Set Up Request Procedure
Chuah, et al. expires June 2001 [Page 12]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
The Flow Set Up Request message can only be sent after the sending
peer is sured that there exists at least a tunnel between itself and
the receiving peer. The LIPE peer which receives a Flow Setup Request
message will respond with a FlowSetup Response Message.
To teardown a flow and reclaim a flow identifier, a LIPE peer will
send a Flow Teardown message.
2.4.1.2.1. Flow Set Up Request Message
1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +
|Typ=3 + Trid + Lngth +
| + + +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RAB Id +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dnlink FlowId +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12 (a): Flow Set Up Request Message
2.4.1.2.2. Flow Set Up Response Message
1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +
|Typ=4 + Trid + Lngth +
| + + +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RABId +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Uplink FlowId +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12 (b): Flow Set Up Response Message
Note that only if the Flow Set Up is successful will the Flow Set Up
Response message contains RABId and a corresponding Uplink FlowId.
Chuah, et al. expires June 2001 [Page 13]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
2.4.1.2.3. Flow TearDown Message
1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +
|Typ=5 + Trid + Lngth +
| + + +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RAB Id +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dnlink FlowId +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Uplink FlowId +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12 (c): Flow Teardown Message
2.4.1.3. LIPE Soft Handoff Procedure
LIPE1 LIPE 2
Peer Peer
Flow ^ | Flow
Handoff | | Handoff
Response | v Request
LIPE4 LIPE 3
Peer Peer
Figure 13: Soft Handoff scenario
For some scenarios where a flow needs to be extended to another LIPE
pairs, one LIPE peer can send a soft handoff request message to a new
LIPE peer to initiate soft handoff. The soft handoff request message
will contain the existing RABID. In response, the new LIPE peer
allocates a new flow identifier. The new LIPE peer (LIPE 3 Peer) can
then initiate a flow set up request to LIPE4 peer (provided a LIPE
tunnel already exists between LIPE 3 and LIPE 4).
2.4.1.3.1. Soft Handoff Request Message
1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +
|Typ=6 + Trid + Lngth +
Chuah, et al. expires June 2001 [Page 14]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
| + + +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RAB Id +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14 (a): Soft Handoff Request Message
2.4.1.3.2. Soft Handoff Response Message
1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| + + +
|Typ=7 + Trid + Lngth +
| + + +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RAB Id +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New FlowId +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14 (b): Soft Handoff Response Message
3. QoS
Besides the traditional best-effort service, other services such as
integrated service (including controlled load service and guaranteed
service) and differentiated service have been defined. These ser-
vices, by reserving certain network resources such as bandwidth, can
provide the traffic with certain guarantees such as delay and loss.
LIPE is compatible with both the DifServ and IntServ QoS models. To
support multiple QoS classes, the DSCP bits of the IP header can be
used to request a particular PHB e.g., for high quality voice the IP
packet with multiplexed audio frames can be marked with the EF code
point; for low quality voice, the IP packet can be marked with one of
the appropriate AF code points.
LIPE specific QoS requirements may also be conveyed on an end-point
specific basis via the TunnelID or FlowId field.
4. Multiplexing Policy
Given the link MTU L_max, a UDP/IP packet can carry payload of up to
Chuah, et al. expires June 2001 [Page 15]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
L_max - H_ip - H_udp, where H_ip is the IP header length (20 bytes
without option) and H_udp is the UDP header length (8 bytes). To
limit the multiplexing delay, a multiplexing timer with a lifetime of
T_mux is used. H_mh is the multiplexing header length. The encapsula-
tion policy is as follows:
a) If the total size of the received radio frames plus that of that
of their H_mh exceeds L_max - H_ip - H_udp, send all the MDP frames
except the most recently received one (no fragmentation of MDP) in
one UDP packet, and restart the multiplexing timer. The newly
received MDP is held for multiplexing with upcoming MDPs.
b) If the multiplexing timer expires, send the accumulated MDPs in
one UDP packet and restart the encapsulation timer.
5. UDP/IP Header Compression
Note that if IP headers are not required to do routing (say the
underlying network is either ATM or MPLS), one can either remove or
compress the UDP/IP header. That will increase further the bandwidth
efficiency of using the LIPE scheme in a radio access network where
the BSs have IP interfaces that run over ATM/MPLS networks.
When we map a certain IP tunnel into a particular MPLS/ATM connec-
tion, we need to ensure that the quality of service provided by the
MPLS/ATM connection matches with the DSCP indicated in the IP header.
6. Security
This draft does not impose additional security considerations beyond
those that apply to PPP and header-compression schemes over PPP.
7. Summary
LIPE is designed to support multimedia traffic when certain resource
guarantees are available from the underlying network. It is based on
UDP/IP or IP; hence is lightweight compared with other proposals
based on RTP [1,2]. As IP based networks become more and more sophis-
ticated and offer various levels of resource guarantees [5], this
scheme is more suitable to the modern/future IP architecture compared
with RTP based schemes.
A multiplexing policy is also outlined for LIPE.
Chuah, et al. expires June 2001 [Page 16]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
8. References
[1] J. Rosenberg, An RTP Payload Format for User Multiplexing
work in progress, draft-ietf-avt-aggregation-00.txt
[2] B. Subbiah, S. Sengodan, User Multiplexing in RTP payload between
IP Telephony Gateway, work in progress, draft-ietf-avt-mux-rtp-00.txt,
Aug, 1998
[3] ITU-T Recommendation G.723.1 "Dual Rate Speech Coder for
Multimedia Communications Transmitting At 5.3 and 6.3 Kbps", 1995
[4] H. Schulzrinne, R. Frederick, V. Jacobson,
RTP: A Transport Protocol for Real-Time Applications, RFC 1889
[5] K. El-Khatib, G. Luo, G. Bochmann, P. Feng,
Multiplexing Scheme for RTP flows between access routers, work
in progress, draft-ietf-avg-multiplexing-rtp-01.txt Oct 22, 1999
[6] 3G TS 25.413 v3.1.0, 3rd Generation Partnership Project: UTRAN Iu
Interface RANAP
Signaling, March 2000
[7] W. Simpson, Ed.,"PPP in HDLC-like Framing", STD 5X, RFC 1662, July
1994
[8] M. Engan etc, "IP header compression over PPP", RFC 2509, Feb 1999
[9] T. Koren etc, Enhancements to IP/UDP/RTP Header Compression, work
in progress, draft-koren-avt-crtp-enhance-01.txt
[10] Simpson, W., Ed., "The Point-To-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
9. Intellectual Property Considerations
Lucent Technologies Inc. may own intellectual property in some on
some of the technologies disclosed in this document. The patent
licensing policy of Lucent Technologies Inc. with respect to any
patents or patent applications relating to this submission is stated
in the March 1, 1999, letter to the IETF from Dr Roger E. Stricker,
Intellectual Property Vice President, Lucent Technologies, Inc. This
letter is on file in the offices of the IETF Secretariat.
Chuah, et al. expires June 2001 [Page 17]
INTERNET DRAFLightweight Internet Protocol Encapsulation SchemDecember 2000
10. Acknowledgements
The authors wish to thank S. Abraham for useful discussions.
11. Authors' Addresses
Mooi C. Chuah
Bell Laboratories
Lucent Technologies
101, Crawfords Corner Road,
Holmdel, NJ 07733
chuah@bell-labs.com
(732)-949-7206
Enrique J. Hernandez-Valencia
Bell Laboratories
Lucent Technologies
101, Crawfords Corner Road,
Holmdel, NJ 07733
enrique@bell-labs.com
(732)-949-6153
0 1
.ti 0 INSERT-THIS
Chuah, et al. expires June 2001 [Page 18]
Table of Contents
1. Introduction .................................................. 4
2. The LIPE Encapsulation Scheme ................................. 5
2.1. Basic LIPE Frame Format ..................................... 6
2.2. Extension Headers ........................................... 7
2.2.1. Type 0 Extended Header .................................... 7
2.2.2. Type 1 Extended Header .................................... 8
2.2.3. Payload Identifier (PID) .................................. 8
2.3. Examples of LIPE Encapsulated Payloads ...................... 9
2.3.1. Carrying raw IS95 voice packets ........................... 9
2.3.2. carrying UMTS Interactive Data packets. .................. 9
2.4. LIPE Signaling Channel ...................................... 10
2.4.1. LIPE Signaling Message Exchange ........................... 11
2.4.1.1. LIPE Tunnel SetUp/Teardown Procedure .................... 11
2.4.1.1.1. Tunnel Set Up Request Message ......................... 11
2.4.1.1.2. Tunnel Set Up Response Message ........................ 12
2.4.1.1.3. Tunnel TearDown Message ............................... 12
2.4.1.2. LIPE Flow SetUp/Teardown Procedure ...................... 12
2.4.1.2.1. Flow Set Up Request Message ........................... 13
2.4.1.2.2. Flow Set Up Response Message .......................... 13
2.4.1.2.3. Flow TearDown Message ................................. 14
2.4.1.3. LIPE Soft Handoff Procedure ............................ 14
2.4.1.3.1. Soft Handoff Request Message .......................... 14
2.4.1.3.2. Soft Handoff Response Message ......................... 15
3. QoS ........................................................... 15
4. Multiplexing Policy ........................................... 15
5. UDP/IP Header Compression ..................................... 16
6. Security ...................................................... 16
7. Summary ....................................................... 16
8. References .................................................... 17
9. Intellectual Property Considerations .......................... 17
10. Acknowledgements ............................................. 18
11. Authors' Addresses ........................................... 18
TO-HERE
Chuah, et al. expires June 2001 [Page 1]