Investigating Stream ControlTransmission Protocol

Author: Nie SenNokia Networks/Mobile Packet Core

Supervisor: Professor Timo Korhonen

Content

■ Framework of SIGTRAN■ Introduction of SCTP

– Multi-homing Feature– Multi-streaming Feature

■ Introduction of IPv6■ Introduction of Linux kernel implemtation of SCTP

– OpenSS7– lksctp

■ Test network configuration■ Test Result Analysis■ Conclusion

Framework of SIGTRAN

SG

MGC

MG

SG

MGC

MG

SIGTRAN

SIGTRAN SIGTRAN

SCN Signal

SCN Signal

MediaStream

MediaStream

■ SG : Signaling Gateway

■ MGC : Media Gateway Controller■ MG : Media Gateway

■ SCN : Switched Circuit Network

Where is the SCTP?

Standard IP transport (IPv4 or IPv6)

Stream Control Transmission Protocol

SCN Adaptation Module

Examples of SIGTRAN Protocol Stack

7 & $ 3

6 & & 3

0 7 3 �

0 7 3 �

0 7 3 �

0 7 3 �

0 7 3 �

0 7 3 �

0 � 8 $

6 & 7 3

,3

7 & $ 3

6 & & 3

0 � 8 $

6 & 7 3

,3

,: ) �6 & & 3

S G /S T P M G CS E P

S S 7 IP

Examples of SIGTRAN Protocol Stack

6 � 8 3

0 7 3 �

0 7 3�

0 7 3�

0 � 8 $

6 & 7 3

,3

6 � 8 3

0 7 3 �

0 � 8 $

6 & 7 3

,3

,: )

S G /S T P M G CS E P

S S 7 IP

0 7 3 �

0 7 3 �

Multi-homing Feature of SCTP

IP path 1

IP path 2

IP path N

… ...

An Association

Host AHost B

■ Both peers of an SCTP association support multiple IP address

■ A client informs the server about all its IP addresses with the INITchunk’s address parameters.

■ One of the IP paths is set as primary path, others are backup path■ The path state can be probed by sending HEARTBEAT message.

Multi-streaming Feature of SCTP

Stream 0

Stream N

Stream 1

… ...

An Association

Data 1/1Data 2/1

Data 3/1Data 4/1

Data 5/1Data 6/1

SCTP user

Data 1/1

Data 2/1

Data 3/1

Data 4/1

Data 5/1

Data 6/1

Stream 0 Stream 1 Stream N

Buffered Buffered Buffered

SCTP user

Multi-streaming Feature of SCTP (continue)

■ Within an association the reliable transfer of datagrams is assured byusing a checksum, a sequence number and a selective retransmissionmechanism. Without taking the initial sequence into account, everycorrectly received data chunk is delivered to a second, independentlevel. The sequence number is called TSN, Transport SequenceNumber

■ The second level realizes a flexible delivery mechanism which is basedon the notion of several independent streams of datagrams within anassociation, by giving each chunk a SSN, Stream Sequence Number.The SSN numbers are used at the receiver to determine the sequenceof delivery. SCTP performs in-sequence delivery per stream (for alldatagrams which are not marked for out-of-order delivery). Thismechanism avoids head-of-line blocking between independent streamsof datagrams within one association.

Functions of SCTP

Association

startup

and

takedown

Sequenced deliverywithin streams

User Data Fragmentation

Acknowledgementand

Congestion Avoidance

Chunk Bundling

Packet Validation

Path Management

SCTP User Adaptation

IP Network Service

SCTPLayer

Introduction of IPv6

■ Larger address space. IPv6 has 128-bit address space, which is 4times wider in bits in compared to IPv4’s 32-bit address space.

■ Better performance. IPv6 has simplified header , which can reduce theprocessing effort on hosts or routers.

■ Better security . IPv6 includes security in the basic spec. It includesencryption of packets (ESP: Encapsulated Security Payload) andauthentication of the sender of packets (AH: Authentication Header).

■ Better support for real time traffic . IPv6 includes flowlabel in the spec,with which routers can recognize to which end-to-end flow the packetsbelongs.

IPv6 Address AllocationAllocation Prefix (binary)

Reserved 0000 0000 Unassigned 0000 0001 Reserved for NSAP Allocation 0000 001 Reserved for IPX Allocation 0000 010 Unassigned 0000 011 Unassigned 0000 1 Unassigned 1 Aggregatable Global Unicast Addresses 1 Unassigned 10 Unassigned 11 Unassigned 100 Unassigned 101 Unassigned 110 Unassigned 1110 Unassigned 1111 0 Unassigned 1111 10 Unassigned 1111 110 Unassigned 1111 1110 0 Link-Local Unicast Addresses 1111 1110 10 Site-Local Unicast Addresses 1111 1110 11 Multicast Addresses 1111 1111

IPv6 Address Allocation

■ The IPv6 address has 128 bits, usually written in 8 16bits’ hexadecimalformat. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are thehexadecimal values of the eight 16-bit pieces of the address.

– Unicast: An identifier for a single interface. A packet sent to aunicast address is delivered to the interface identified by thataddress.

– Anycast: An identifier for a set of interfaces (typically belonging todifferent nodes). A packet sent to an anycast address is deliveredto one of the interfaces identified by that address (the "nearest"one, according to the routing protocols' measure of distance).

– Multicast: An identifier for a set of interfaces (typicallybelonging to different nodes). A packet sent to a multicastaddress is delivered to all interfaces identified by thataddress.

IPv6 Address Allocation

■ A host is required to recognize the following addresses as identifyingitself:

• Its Link-Local Address for each interface

• Assigned Unicast Address• Loopback Address• All-Nodes Multicast Addresses

• Solicited-Node Multicast Address for each of its assigned unicast andanycast addresses

• Multicast Addresses of all other groups to which the host belongs.

■ The procedure of enabling IPv6 support in Linux Kernel is introduced inmy thesis, based on the instructions of http://linuxdoc.org/HOWTO/Linux+IPv6-HOWTO/

Linux Kernel Implementation of SCTP

■ OpenSS7– Download from www.openss7.org

– Red Hat Linux kernel 2.2.12-2

■ lksctp– Download from http://sourceforge.net/projects/lksctp/

– Linux kernel 2.4.1 and 2.4.17

■ Both of them are based on :– RFC2960 Stream Control Transmission Protocol– Internet Draft : draft-ietf-tsvwg-sctpsocket-02.txt

Linux Kernel Implementation of SCTP

socket ( )

sendmsg ( )

recvmsg ( )

listen ( )

bind ( )

socket ( )

close ( )

close ( )

Connection Setup

( SCTP four way handshake)

Data 1

Data N

ConnectionShutdown

repeat

repeat

sendmsg ( )

sendmsg ( )

recvmsg ( )recvmsg ( )

recvmsg ( )

recvmsg ( )Get COMMUNICATION_UP

notification

Get COMMUNICATION_UP

notification

Get the NthData

Get SHUTDOWN_COMPLETE

notification

Data N

recvmsg ( ) Get the First Data

Get the NthData

Process on Host 1 Process on Host 2

bind ( )

Linux Kernel Implementation of SCTP

■ socket() :– sd = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP); /*

for IPv4 */

– sd = socket(PF_INET6, SOCK_SEQPACKET, IPPROTO_SCTP);/* for IPv6*/

■ sendmsg() and recvmsg()– ssize_t sendmsg(int socket, const struct msghdr *message, int

flags);

– ssize_t recvmsg(int socket, struct msghdr *message, int flags);

– The structure msghdr is introduced in detail in my thesis.

Test Network Configuration

■ Host1,host2 and the router are PCs running Linuxwith SCTP patch

■ Three connections shown in above figure areconfigured to different network segments.

Test Network Configuration

Performance Test Plan

start

test

0 12

1

i

Initiate remote addressInitiate local address

Creat socket sk1Bind sk1 to local address

Initiate outmessageInitiate inmessage

sendmsg

If inmessageis notification

If notification isSCTP_ASSOC_CHANGE

printf printf

repeat =1 repeat =0loopbreak = 1

repeat = 0

Get ending timeCalculate RTT

If repeat ==1

Save RTT into file

shutdown=0loopbreak=0

exit

=SHUTDOWN_COMPLETE=COMMUNICATION_UP

T

F

TF

Initiate messagesize array

SCTP Process

on Host 1

i

1 REPEAT

1

Get start time

recvmsg

If sac_state is

printf

repeat =1

If loopbreak ==1

close socket sk1

test

T

F

start

test

0 12

1

test

Initiate remote addressInitiate local address

Creat socket sk2Bind sk2 to local address

Initiate outmessageInitiate inmessage

recvmsg

If inmessageis notification

If sac_state is

printf printf

shutdown=0 shutdown=1

sendmsg

outmessage = inmessage

If shutdown==0

close socket sk2

shutdown=0

exit

=SHUTDOWN_COMPLETE=COMMUNICATION_UP

T

F

TF

If notification isSCTP_ASSOC_CHANGE

shutdown=0

printf

T F

SCTP Process

on Host 2

Listen sk2

Result Analysis - lksctp

SCTP IPv6 Performance Test Result

802900 931

993 10291088 1134 1170 1202 1242 1286

1355 1393

0

200

400

600

800

1000

1200

1400

1600

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Package Size (in bytes)

Mea

n R

ound

Trip

Tim

e (in

mic

rose

cond

s)

Mean RTT

Result Analysis - lksctp

SCTP IPv4 PerformanceTest Result

810

911961

10031047

1109 11331176 1208

12621312 1345

1402

0

200

400

600

800

1000

1200

1400

1600

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Packet Size (in bytes)

Mea

n R

ound

Trip

Tim

e (in

mic

rose

cond

s)

Mean RTT

Result Analysis - lksctp

TCP IPv6 Performance Test Result

225259

298335

373411

447486

523560

599635

674

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Packet Size (in Bytes)

Mea

n R

ou

nd

Tri

p T

ime

(in

mic

rose

con

ds)

MEAN RTT

Result Analysis - lksctpTCP IPv4 Performance Test Result

227259

297333

368406

442482

515551

589625

660

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Packet Size (in Bytes)

Me

an

Ro

un

d T

rip

Tim

e

(in

mic

rose

con

ds)

MEAN RTT

Conclusion

■ Both of two implementations are not stable. TheOpenSS7 version is too unstable to work, test failed.

■ Both of two implementations are not completed.Some of important features , such as multi-homing,are still missing.

■ The performance of SCTP is far lower than TCP, butstill matches the need for SS7 signalling.

■ IPv6 gives more performance than IPv4.■ As the packet size increases towards the MTU size,

the performance gap of the SCTP and TCP begins tobe narrower.