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INTERNET-DRAFT L. Coene
Internet Engineering Task Force Siemens
Issued: 8 may 2000 J. Loughney
Expires: 30 October 2000 Nokia
I. Rytina
Ericsson
L. Ong
Nortel Networks
Stream Control Transmission Protocol Applicability Statement
<draft-ietf-sigtran-sctp-applicability-01.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
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Abstract
This document describes the applicability of the Stream Control
Transmission Protocol for general usage. A few general applications
are described such as the transport of signalling information (SS7,
DSS1/2 ...) over IP infrastructure. The use and specification of
adaptation layers in conjunction with SCTP is described.
1 Introduction
This document covers subject terminology and makes a overview of the
solutions for transporting information over Internet Protocol
infrastructure. The transport medium used is the Stream Control
Transmission Protocol (SCTP). However some of the issues may also
relate to the transport of information via TCP.
SCTP provides the following services to its users:
- acknowledged error-free non-duplicated transfer of user data
- transport-level segmentation to conform to discovered MTU size
- sequenced delivery of user datagrams within multiple streams, with
an option for order-of-arrival delivery of individual datagrams
- optional multiplexing of user datagrams into SCTP datagrams,
subject to MTU size restrictions
- enhanced reliability through support of multi-homing at either
or both ends of the association.
- Explicit indication in the message of the application protocol SCTP
is carrying.
1.1 Terminology
The following terms are commonly identified in related work:
Port Number: Indicates on the transport level which application
needs to be reached in the layer above. Transport Address: An IP
address and a port number forms a transport address which identifies
a SCTP association. Protocol Identifier: Indicates the upper layer
protocol that is using SCTP for the transport of its data. Chunk: a
unit of information within an SCTP datagram, consisting of a chunk
header and chunk-specific content. Each chunk can contain user or
data information about the particular SCTP association. Multihoming:
Endpoint which uses more than one IP address for receiving SCTP
datagrams on the same association. NAT: Network Address Translation
SACK: Selective Acknowledgement message, this is a response on the
data msg acknowledging the receipt of it at the remote side. TSN:
Transaction Sequence Number, this is a number assigned by SCTP to
assure reliable delivery of user data within an association.
2 Stream Control Transmission Protocol -- SCTP
2.1 Introduction
The Stream Control Transmission Protocol (SCTP) provides a high
reliable, redundant transport between two endpoints. The interface
between SCTP and its applications is handled via adaptation layers
which provide a intermediate layer so that the existing upper layer
protocols do not have to change their interface towards the transport
medium and internal functionality when they start using SCTP instead
of an other transport protocol.
The following function are provided by SCTP: - Initialization of
transport association - Synchronization of association state -
Synchronization of sequence numbering - Reliable Data Transfer -
Forward and backward sequence numbering - Timers for transmission and
acknowledgement - Notification of out-of-sequence - Retransmission of
lost messages - Support of multiple control streams - Separate
sequence control and delivery of each stream - Congestion control -
Window flow control - Congestion avoidance based on TCP methods, e.g.
using
retransmission backoff, window reduction, etc. - Detection of
session failure by active means, e.g. heartbeat - Termination of
association SCTP does support a number of functions that are not
provided by current TCP: - no head-of-line blocking, i.e. multiple
streams - multilink failover for added reliability - keep-alive
function for active rapid failure detection - message verses byte
sequence numbering - tighter timer control (than standard TCP
implementations)
By defining the appropriate User adaptation module, a reliable
transport mechanism can be provided: - reliable transmission of
packets with end-to-end congestion control provided using methods
similar to TCP - choice between sequenced and unsequenced, reliable
message delivery - keep-alive message
Within a association between the two endpoints, 1 or more stream(s)
may be available. These streams are visible to the adaptation layers
but are invisible to any layer above the adaptation layer.
2.2 Issues affecting deployment of SCTP
2.2.1 SCTP Multihoming
Redundant communication between 2 SCTP endpoints is achieved by using
multihoming where the endpoint is able to send/receive over more than
one IP address.
Under the assumption that every IP address will have a different path
towards the remote endpoint, (this is the responsibility of the
routing protocols or of manual configuration), if the transport to
one of the IP address (= 1 particular path) fails then the traffic
can migrate to the other remaining IP address (= other paths) within
the SCTP association.
As a practical matter, it is recommended that IP addresses in a
multihomed endpoint be assigned IP endpoints from different TLV's to
ensure against network failure.
Multihoming provides redundant communication in SCTP by allowing
communication between two endpoints to continue in the event of
failure along a path between the endpoints.
SCTP will always send its traffic to a certain transport address (=
destination address + port number combination) for as long as the
transmission is uninterrupted (= primary). The other transport
addresses (secondary paths) will act as a backup in case the primary
path goes out of service. The changeover between primary are backup
will occur without packet loss and is completely transparent to the
application.
The port number is the same for all transport addresses of that
specific association.
Applications directly using SCTP may choose to control the
multihoming service themselves. The applications have then to supply
the specific IP address to SCTP for each datagram. This might be done
for reasons of load-sharing and load-balancing across the different
paths. This might not be advisable as the throughput of any of the
paths is not known in advance and constantly changes due to the
actions of other associations and transport protocols along that
particular path, would require very tight feedback of each of the
paths to the loadsharing functions of the user.
Applications using adaptation layers to run over SCTP do not have
that kind of control. The adaptation layers will have to take care of
this.
By sending a keep alive message on all the multiple paths that are
not used for active transmission of messages across the association,
it is possible for SCTP to detect whether one or more paths have
failed. SCTP will not use these failed paths when a changeover is
required.
The transmission rate of sending keep alive message should be
modifiable and the possible loss of keep alive message could be used
for the monitoring and measurements of the concerned paths.
2.2.2 Fast retransmit of chunks
The retransmission of a message is basically governed by the
retransmission timer. So if no acknowledgement is received after a
certain time, then the message is retransmitted. However there is a
faster way for retransmitting which is not dependant on that timer.
Every second message that a node received will be acknowledge to the
remote peer. If gaps occur in the acknowledge message at the remote
side, then the remote side will wait 3 further gap
reports(acknowledgements) before it retransmit the message. As the
gap occurs, the node must transmit a SACK on every datagram until
there are no more gap. This retransmission will happen far sooner
than with a timer. Especially if the traffic volume increases in
SCTP, those retransmissions of the chunks would happen faster and
faster (and hopefully, they would also be faster acknowledged). In
any case if gaps occur, the node will certainly try to acknowledge
them faster(irespective of the fact if the SACKs will get to the
remote node, where, if received, they would speed up the
retransmission of the chunks)
See also the paragraph on congestion control and avoidance.
2.2.3 Use of SCTP in Network Address Translator (NAT) Networks
When a NAT is present between two endpoints, the endpoint that is
behind the NAT, i.e., one that does not have a publicly available
network address, shall take one of the following options:
A) Indicate that only one address can be used by including no
transport addresses in the INIT message. This will make the endpoint
that receives this Initiation message to consider the sender as only
having that one address. This method can be used for a dynamic NAT,
but any multi-homing configuration at the endpoint that is behind the
NAT will not be visible to its peer, and thus not be taken advantage
of.
B) Indicate all of its networks in the Initiation by specifying all
the actual IP addresses and ports that the NAT will substitute for
the endpoint. This method requires that the endpoint behind the NAT
must have pre-knowledge of all the IP addresses and ports that the
NAT will assign.
This requires the adaptation of NAT boxes to search within SCTP
outgoing INIT and incoming INIT_ACK mesages for the addresses and
replace them with the NAT internal address in addition to replacing
the addresses in the IP header.
C) Use RSIP [RFCRSIP] where the connection is tunneled from host
until the NAT border and the host layers above IP network layer have
no knowledge of the NAT internal addresses.
D) Use the hostname feature and the DNS to resolve the addresses.
(Ed note: have to figure out hows this precisely works)
2.2.4 MTU path discovery
SCTP discovers the maximal length of the message that can be
transported through the network to the final destination without
having to fragment(=chop something in pieces) the message in IP
network layer. This avoids using IP fragmenting. SCTP level
segmentation is beneficial because if a packet is lost during network
transmission, only that packet will need to be retransmitted.
Contrasted with IP-level segmentation, where the whole unsegmented
message will have to be retransmitted, this is a much more effective
scheme [RFC1981].
2.2.5 Use of multiple streams
A stream in a one-directional stream of bytes between 2 endpoints
within a SCTP association. A association can have one or more streams
in its association and the number of streams in one direction does
NOT need to be the same as the number of streams in the opposite
direction. The number of streams in both directions is thus
assymmetrical.
The application can choose on which stream it can send it data.
Streams may specify order of deliver or sequenced delivery. Some
application level protocols may reserve certain streams for certain
media, for example sending graphical content (jpeg, gif, etc.) of a
web page through a certain stream while text through others, and
streaming content through others. Any packet loss on one stream will
not block packet transmission on others.
Each stream within a association should be looked upon as a link
between two points. If multiple streams are used then the application
is dealing with multiple links towards the destination. Some
applications require the use of sequenced delivery, which would
require for them to select a certain link to send their message on.
2.2.6 Congestion control & avoidance
Congestion control and/or avoidance is of primordial importance in
any connectionless network. Congestion is the result of approaching
or exceeding the processing capacity of the link, network,
application and/or transport layers. If the processing capacity is
exceeded, then the congestion can be avoided (example taking a other
non-congested path towards the destination) or controlled (for
example, reducing the rate of messages to that destination).
The reaction of SCTP to congestion is detailed in the next
paragraphs.
Congestion can be controlled and/or avoided on different levels: -
Transport: congestion control/avoidance within SCTP, TCP(fig 2.1.2) -
Network : Congestion control/avoidance present in the network layers(
example: SCCP, MTP ...) - Link layer: flow control
SCTP conforms to the model of end-to-end congestion control (Fig
2.2.6.2) [RFCSALLY] while ISUP and SCCP model themselves on a link
and network based congestion control/overload mechanism (Fig
2.2.6.3).
| |
| Application and/or transport layer |
+---------------------------------------------------+
| A
| |
| +-------------------------------------+ |
---->| |----
| Network layer |
---->| |----
| +-------------------------------------+ |
| |
| V
+---------------------------------------------------+
| |
| Link layer |
Fig 2.2.6.1 General Congestion model
| |
|transport layer| Congestion control present based on
| SCTP | windows
+---------------+
| A
V |
+---------------+
| |
| Network layer | No congestion control present
| IP(v4/v6) | in the IP layer
+---------------+
| A
V |
+---------------+
| Ethernet | No congestion control present
| Link layer | in the Ethernet link layer
Fig 2.2.6.2 End-to-End congestion control
| |
|Application layer| Congestion control present for
| TC + MAP, IN... | specific applications
+-----------------+ - MAP: No congestion control
| A - IN: Call gapping
V |
+-----------------+
| |
| Network layer | Congestion control present in the
| SCCP & MTP | in MTP and SCCP based on link and
+-----------------+ destination status
| A
V |
+-----------------+
| MTP lvl 2 | Congestion control present
| Link layer | in the link layer
Fig 2.2.6.3 Distributed congestion control
By default, SCTP associations do not have a fixed capacity assigned
to them unless other QoS mechanisms are employed. Thus congestion
within SCTP association can and will be affected by all traffic using
the same links including other SCTP, TCP, RTP, UDP ... traffic
traveling on the same path followed by the SCTP association.
2.2.6.1 3-SACK rule in SCTP.
The Selective Acknowledgement (SACK) is one of the cornerstones of
SCTP. It selectively Acknowledges datagrams that have been
successfully received by the remote node. It serves 2 purposes: - it
indicates until a certain datagram that all previous datagrams have
been received (without any holes in the sequence) and - it indicates
the datagrams sequence ranges which have been received (and so does
indicate the holes/gaps between them). It provides us with a form of
gap/hole report on messages that have been lost or delayed. A hole
can consist of one or more messages.
sender Receiver
- |----- | -
Emission I | | I Link delay
time - |---- | I time
| ----------->| -
- |--- |
I | ------------>|
Round I |-- |
trip I | ------------->|
time I | /----|<-------- acknowledge sent
I | -------- / --->| after 3 data's
I | / |
- |<------------/ |
Round trip Time = RTT
Windowsize = Cwnd
Fig 2.2.6.4 Influence of Window Size/ Link Speed/ Round Trip Delay
Fig 2.2.6.4 is given here as a example where after receiving 3
messages an advisory acknowledgement (SACK) is sent (in this case
window = 6). Therefore the sender could be kept busy. The
acknowledgement opens the window again. The total time (from first
emission till the receiving of the acknowledgement) calculates as:
(max. windowsize * emission time)/2 + round trip delay. If the round
trip time(RTT) is large, the advisory acknowledgments (SACK) will
enhance the throughput.
The SACK is always generated and send back to the sender either -
after every second message received (delayed ack). - after at most
200ms after receiving the last message.
The reason for the holes may be diverse: - simple message loss -
different round trip times of messages being transmitted on different
interfaces
At the sender end, whenever the sender notices a hole in a SACK, it
should wait for 3 further SACKs (identifying the same hole) before
taking action. This is 3 strikes besides the first one, so that means
4. Thus after 4 SACK, the datagrams belonging to the hole should be
retransmitted(and only those).
If gaps occur, the receiver end will send SACKs on every data message
received instead on being send on every second data message received.
As the sender is waiting for the 3 SACK strikes and the receiver is
increasing the SACK rate, that would mean that retransmission would
be happening faster. Also the window should be opening up more than
in the normal case (= transmission without gaps).
The 3 SACKs rule might be relaxed in certain networks provided
certain condition are met:
- private IP network - closed networks - only a single type of
application traffic is running on that network (the message in the
network exhibit the same characteristics:
example: signalling messages).
The SACK rule might be configurable in such a networks, if the
network operator felt confident in the correctness of the network.
This would mean that in case of packet loss, retransmission could be
"immediate".
SACK will also report duplicate message arrival. See paragraph
2.2.6.4.
2.2.6.2 Congestion Control
The number of messages in flight is determined by the Congestion
window (Cwnd). Every time a message is SACK, a new message might be
send to the remote side(up till the Cwnd), even if gaps exists which
might ultimately lead to retransmissions.
The value of the Cwnd is dependant on the slow start and/or
congestion avoidance/control.
If messages are getting lost, then it is assumed by SCTP that they
are lost according to congestion, not that they are lost due to error
on the link(such as cable cutthrough ...).
When messages are lost then the rate of messages sending is reduced,
till no messages are lost.
2.2.6.3 Use of Explicit Congestion notification (ECN)
Explicit Congestion control is a experimental method for
communicating congestion back to the end node. SCTP does not support
the use of ECN, but specific recommendations for using ECN with SCTP
might be forthcoming.
2.2.6.4 Duplicated messages
SACKs can get lost. The receiving node would then received duplicated
packets. A reason for such a behavior is imbalance between the 2
traffic direction, use of different up and down path.
(Ed note: something more has to be put here, still thinking on the
right words and reading a couple of RFCs on the subject :-)
2.2.6.5 SCTP in high throughput delivery networks
The TSN is associated with a message, not with the number of bytes(as
is the sequence number of TCP) in the message. So the TSN will wrap
around less frequently but has a dependency on the length of each
message. Use of short messages will lead to a faster wrapping around
of the TSN. So in high throughput networks, it is advised to make the
messages as long as possible so that the wrap around will be less
frequent.
SCTP already has a larger window than TCP does even when TCP is using
the "large windows" option.
2.2.6.6 SCTP in long delay/Fat networks (LFN)
Long delay(Fat) Networks consists of network paths which have a high
"bandwidth*delay product"(such as satelite links(high delay) or high
capacity fiber(high bandwith)). There the 3-SACK rule would lead to
enhanced throughput, if the initial windowsize is set higher than
2(which is the default value for non-LFNs).
The initial windowsize should be set to a higher value (4 or 8) as
that would mean that 4 messages would be injected in the network and
the first sack would come back at about the same time as the last
message before the window is full, is injected.
Thus to have the most of the 3 sack rule immediatly, the initial
window size should at least be set at 4 (and possible at 8 if we are
dealing with really very long delays).
The drawback of this is that it makes SCTP more aggressive to begin
with(certainly when faced with TCP).
For a more precise description of the issues associated with this,
refer to [RFC123], [RFC2001] and [RFC2018]
2.2.6.7 SCTP in Long Thin Networks(LTN)
Long thin networks consists of network paths that traverse "very low
bit-rate" links(such as 56 Kbit modem links). This means that a
single host can very easy saturate such a link(= pushing the link
into congestion).
2.2.7 Use of the protocol identifier in SCTP
Indicates the the upper layer protocol that is using the
associations. The protocol identifier is available to the application
and is included in each chunk. 0 is the unknown protocol. This
protocol id can be used by firewalls for filtering out certain
protocols. If firewalls drops certain protocol id then then
association will fail in the end because the TSN will be lost. If the
chunk(without its user data) is simulated with the TSN in it, then
the user data will be dropped, but the association is preserved.
The protocol identifier is administered by IANA[IANA].
2.2.8 Use of QoS methods
SCTP is a end-to-end protocol which cannot guarantee the quality-of-
service along the complete path(s) taken by the messages of that
particular association. If more guarantees are required for improving
the reliability of the transport, some form of QoS mechanism may be
needed.
The possible schemes are as follows.
2.2.8.1 Over-provisioning
Over-provisioning of the links so that the total traffic running over
the link never exceeds the link capacity. In practice, this may be
difficult to ensure reliably.
2.2.8.2 Private Internets
Use of a private network solely for transport purposes. Private
networks may allow better control and monitoring of resources
available.
2.2.8.3 Differentiated services
By providing a certain code point in the Type-of-service field (TOS),
certain Differential services can be selected. [RFC2597, RFC2598]
Setting the code point for transport requires some thought. It is
dependant on the kind of differentiate service selected. Also the use
of traffic is important: example signalling info should have a higher
priority than the user data traffic for which the signalling is
responsible(and that relation does not always exist).
2.2.8.4 Integrated services
By use of integrated services [RFC2208], resources are reserved for
signaling transport.
If resources are unavailable for to initiate a new signaling
transport, that request will be denied. RSVP may not scale well and
this solution may prove to be unfeasible.
An example is Multi Protocol Label Switching.
2.2.9 SCTP Checksum
SCTP uses the Adler-32 checksum algorithm. This algorithm will
perform better than a 16 bit (CRC or not) checksum or even a 32 bit
CRC checksum.
The message can also be protected by IPSEC which is much stronger. In
that case, the checksum should still be computed.
2.2.10 Tunneling of SCTP association over UDP
The basic operation of SCTP is to run directly on top of IP. However,
due to restrictions placed on implementers by Operating Systems, not
all implementations may be able to run over IP directly. Therefore an
alternative is given which might circumvent some or all of the
restrictions.
The STCP messages are transported over UDP instead. The following
issues must be observed: - the port number in the UDP header should
be the port number assigned to SCTP. The port number in the SCTP
common header should be the one assigned to the user adaptation layer
or to the application of SCTP. This means that port numbers
previously used in UDP and/or TCP can be reused for the same
application using SCTP. SCTP DOES NOT change the semantics of the
port number just because the protocol identifier is added to the SCTP
message. - the checksum field might be used as a additional guard
against errors(particular errors in the UDP header). However, the
SCTP checksum employed is far better at catching errors, but does not
take the UDP header into account.
2.2.11 How to define and Use adaptation layers
Many different applications may use SCTP for different purposes. They
go from File transfer over HTTP transport to signalling information
transport.
Some applications might want preserve the existing interface with its
lower layer (in this case SCTP) while for other applications, this
does not pose a problem. A narchitecture has been devised to let the
application choose whether they want to run over SCTP directly (just
a many applications run over TCP) or let application run on top of a
adaptation layer over SCTP.
The basic architecture is as in Figure 2.11.1 :
User/Application level Protocols
| | |
+------------------------------------+
| User Adaptation modules |
+------------------------------------+
|
+------------------------------------+
|Stream Control Transmission protocol|
+------------------------------------+
|
+------------------------------------+
| Standard IP Transport |
+------------------------------------+
|
Network Layer (IP)
Figure 2.11.1: Transport Components
The three components of the transport protocol are : Adaptation
modules that support specific primitives, e.g. management
indications, required by a particular user/ application protocol. The
use of a adaptation protocol is optional. It is only used in case in
which the application protocol does not want to change its interface
with the underlying layer.
the Stream Control Transmission Protocol itself that supports a
common set of reliable transport functions.
a standard IP transport/network protocol provided by the operating
system. In some network scenarios, it has been recognized that TCP
can provide limited (but sufficient) reliable transport functionality
for some applications.
2.2.12 Security considerations
The following aspects of security are :
Authentication:
Information is sent/received from a known and/or trusted partner.
Integrity:
Information may not be modified while in transit. The integrity of a
message in a public network is not guaranteed.
Confidentiality:
Confidentiality of the user data must be ensured. User data can not
be examined by unauthorized users.
Availability:
The communicating endpoint must remain in service in all
circumstances. Some services have very high availability
requirements: for example, all SS7 nodes have to remain active for
the 99.999% of the time.
2.2.12.1 General Considerations
SCTP only tries to increase the availability of a network. SCTP does
not contain any protocol elements in its messages which are directly
related to Authentication, Integrity and Confidentiality functions.
It depends for such a features on the IPSEC protocols and
architecture.
The only function which has some bearing on security of SCTP is the
integrity of message in SCTP, which is guarded by a Checksum. This
checksum is mandatory if IPSEC is NOT used. If IPSEC is used then the
SCTP checksum becomes optional. The use of IPSEC in the SCTP
association must in this case be END-TO-END. The use of IPSEC on a
part of a path of a SCTP association does NOT relieve SCTP from using
the checksum(as this ain't end-to-end transport)
The general rule is that IPSEC should be turned on unconditionally.
The description of the internet security architecture and the use of
it is described in [RFC2401].
2.2.12.2 The cookie mechanism and Denial-of-Service (DOS) attacks
The cookie mechanism in SCTP is a measure against Denial-of-Service
(DOS) attacks. In a DOS attack, a lot of init chunks are send towards
a single terminating node (the source is a bogus node = a invalid
source address in the datagram), so that very quickly all resources
are used up and that normal users are rejected due to resource
shortage.
When a INIT chunk is received, the TCB info is encoded and put into
the cookie and send to the initiating node via the INIT_ACK. No TCB
is allocated at the receiving node as all info is encoded in the
cookie and the cookie will return in the COOKIE_ACK (at that time the
TCB will be really allocated with the info from the cookie and a full
association is set up). As the INIT_ACK will be send back to a bogus
address, no COOKIE_ACK will come back and no resources will be tied
up in the terminating node.
2.2.12.3 Initiate Tag considerations
As the tag is fixed during the whole lifetime of the association, the
initiate Tag values should be selected as random as possible to help
protect against "man in the middle" and "sequence number" attacks. It
is suggested that RFC 1750 [RFC1750] be used for the Tag
randomization. A new tag is only assigned if a new association is set
up.
2.2.12.4 Fingerprinting of SCTP
Different implementations may show a certain fingerprint in their
messages when they have to answer to certain messages send to them.
It is advisabel to send only the basic required information back
according to the SCTP protocol.
2.2.12.5 The ACK-Splitting attack
(Ed note : something need to be provided here)
3 Recommendations
To be provided.
4 Adaptation Layers
Currently, there are four adaptation layers, to support carrying of
SS7 application protocols over IP. These adaptation layers are being
developed for different purposes, and there is no assumption that
they should interwork - i.e. - M2UA carries M3UA. They should be
thought of as individual protocols for specific uses.
4.1 IUA
There is a need for Switched Circuit Network (SCN) signaling protocol
delivery from an ISDN Signaling Gateway (SG) to a Media Gateway
Controller (MGC). The delivery mechanism should meet the following
criteria
* Support for transport of the Q.921 / Q.931 boundary primitives *
Support for communication between Layer Management modules on SG and
MGC * Support for management of active associations between SG and
MGC
This draft supports both ISDN Primary Rate Access (PRA) as well as
Basic Rate Access (BRA) including the support for both point-to-point
mode and point-to-multipoint modes of communication. QSIG adaptation
layer requirements do not differ from Q.931 adaptation layer, hence
the procedures described in this draft are also applicable to QSIG
adaptation layer.
4.2 M2UA
There is a need for SCN signaling protocol delivery from an Signaling
Gateway (SG) to a Media Gateway Controller (MGC) or IP Signaling
Point (IPSP). The delivery mechanism should meet the following
criteria:
* Support for MTP Level 2 / MTP Level 3 interface boundary *
Support for communication between Layer Management modules on SG and
MGC * Support for management of active associations between the SG
and MGC
In other words, the Signaling Gateway will transport MTP Level 3
messages to a Media Gateway Controller (MGC) or IP Signaling Point
(IPSP). In the case of delivery from an SG to an IPSP, the SG and
IPSP function as traditional SS7 nodes using the IP network as a new
type of SS7 link. This allows for full MTP Level 3 message handling
and network management capabilities.
4.3 M3UA
There is a need for SCN signaling protocol delivery from an SS7
Signaling Gateway (SG) to a Media Gateway Controller (MGC) or IP-
resident Database as described in the Framework Architecture for
Signalling Transport [11]. The delivery mechanism should meet the
following criteria:
* Support for transfer of all SS7 MTP3-User Part messages (e.g.,
ISUP, SCCP, TUP, etc.) * Support for the seamless operation of
MTP3-User protocol peers * Support for the management of SCTP
transport associations and traffic between an SG and one or more MGCs
or IP-resident Databases * Support for MGC or IP-resident Database
failover and loadsharing * Support for the asynchronous reporting of
status changes to management
In simplistic terms, the SG will terminate SS7 MTP2 and MTP3
protocols and deliver ISUP, SCCP and/or any other MTP3-User protocol
messages over SCTP transport associations to MTP3-User peers in MGCs
or IP-resident Databases.
4.4 SUA
This document details the delivery of SCCP-user messages (MAP & CAP
over TCAP, RANAP, etc.) over IP. The architecture may be from from
an SS7 Signaling Gateway (SG) to an IP-based signaling node (such as
an IP-resident Database) as described in the Framework Architecture
for Signaling Transport [RFC2719], or between two endpoints located
completely within an IP network. The delivery mechanism SHOULD meet
the following criteria:
* Support for transfer of SS7 SCCP-User Part messages (e.g., TCAP,
RANAP, etc.) * Support for SCCP connectionless service. * Support
for SCCP connection oriented service. * Support for the seamless
operation of SCCP-User protocol peers * Support for the management
of SCTP transport associations between an SG and one or more IP-based
signaling nodes). * Support for distributed IP-based signaling
nodes. * Support for the asynchronous reporting of status changes
to management
5 References and related work
[SCTP] Stewart, R. R., Xie, Q., Morneault, K., Sharp, C. , ,
Schwarzbauer, H. J., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and
Paxson, V."Stream Control Transmission Protocol", <draft-ietf-
sigtran-sctp-09.txt>, April 2000. Work In Progress.
[Q1400] SG11, ITU-T Recommendation Q.1400, " architecture framework
for the development of signaling and OA&M protocols using OSI
concepts ",1993
[HUITEM] Huitema, C., "Routing in the Internet", Prentice-Hall, 1995.
[RFC2373] Hinden, R. and Deering, S., "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[RFC2460] Hinden, R. and Deering, S., "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC814] Clark, D.D., "Names, addresses, ports and routes", RFC 0814,
July 1982.
[RFC2401] Kent, S., and Atkinson, R., "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[RFC1981] McCann, J., Deering, S., and Mogul, J., "Path MTU Discovery
for IP version 6", RFC 1981, August 1996.
[RFC2208] Mankin, A. Ed., Baker, F., , Braden, B., Bradner, S.,
O`Dell, M., Romanow, A., Weinrib, A. and Zhang, L., "Resource
ReSerVation Protocol (RSVP) -- Version 1 Applicability Statement Some
Guidelines on Deployment" , RFC 2208, September 1997.
[RFC2597] Heinanen, J., Baker, F., Weiss, W. and Wroclawski, J.,
"Assured Forwarding PHB Group", RFC2597, June 1999
[RFC2598] Jacobson, V., Nichols, K. and Poduri, K., "An Expedited
Forwarding PHB", RFC2598, June 1999
[RFC2719] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene,
L., Lin, H., Juhasz, I., Holdrege, M., Sharp, C., "Framework
Architecture for Signaling Transport", RFC2719, October 1999
[IANA] Internet Assigned Numbers Authority, http://www.iana.org/,
April 2000
[RFCRSIP] Borella, M., Grabelsky, D., Lo, J., Tuniguchi, K. "Realm
specific IP",RFCxxxx, xxxx 2000
[RFCSALLY] Floyd, S. Ed., "Congestion Control Principles", <draft-
floyd-cong-02.txt> RFCxxxx, April 2000
[RFC1750] Eastlake, 3rd, D., Crocker, S., Schiller, J., "Randomness
Recommendations for Security", RFC1750, December 1994
[RFC1323] Jacobson, V., Braden, R., Borman, D., "TCP Extensions for
High Performance", RFC1323, May 1992
[RFC2001] Stevens, W., "TCP Slow Start, Congestion Avoidance, Fast
Retransmit, and Fast Recovery Algorithms ", RFC2001, Januarey 1997
[RFC2018] Mathis, M., Mahdavi, J., Floyd, S., Romanow, A., "TCP
Selective Acknowledgement Options ", RFC2018, October 1996
6 Acknowledgments
The authors wish to thank Renee Revis, R.R. Stewart, Q. Xie, H.J.
Schwarzbauer, M. Tuexen, J.P. Martin-Flatin and many others for their
invaluable comments.
7 Author's Address
Lode Coene
Siemens Atea
Atealaan 34
B-2200 Herentals
Belgium
Phone: +32-14-252081
EMail: [email protected]
John Loughney
Nokia Research Center
Itamerenkatu 11-13
FIN-00180 Helsinki
Finland
Phone: +358-9-43761
EMail: [email protected]
Ian Rytina
Ericsson Australia
37/360 Elizabeth Street
Melbourne, Victoria 3000
Australia
Phone : -
EMail:[email protected]
Lyndon Ong
Nortel Networks
4401 Great America Parkway
Santa Clara, CA 95054
USA
Phone: -
EMail: [email protected]
Expires: October 30, 2000
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