H.248 Gateway Control Protocol Signaling
Traffic Related Protocol Analysis
Antti Miettinen
S-38.310 Thesis Seminar on Networking Technology
Helsinki University of Technology
07.12.2004
Rev A
07.12.2004
1
Antti Miettinen
Basic Information
• Thesis written at Oy L M Ericsson Ab, Finland
• Supervisor: Professor Jorma Jormakka
• Instructors: M.Sc. Juha Eloranta
Rev A
07.12.2004
2
Antti Miettinen
Contents
•
•
•
•
•
•
•
•
•
Background
Problem Description
Objectives
Scope
UMTS Release 5 Network
H.248 Gateway Control Protocol
H.248 Protocol Traffic Analysis
Protocol Traffic Analyzers
Conclusion and Future Work
Rev A
07.12.2004
3
Antti Miettinen
Background (1/3)
• The Universal Mobile Telecommunications System
(UMTS) is a third generation mobile network standard
specified by the 3rd Generation Partnership Project (3GPP)
• UMTS network is developed from the GSM and GPRS
• UMTS specifications and features grouped into releases
• Each release contains specific functionalities and
advancements
• Releases enable vendors to make interoperable networks
Rev A
07.12.2004
4
Antti Miettinen
Background (2/3)
• The UMTS Release 4 network architecture introduced the
layered network architecture
– Call control is separated from the media and bearer control
• H.248 Gateway Control Protocol framework (GCP) is used
in the UMTS core network between the Media Gateway
Controller (MGC) and the Media Gateway (MGW) and
between the Media Resource Function Controller (MRFC)
and Media Resource Function Processor (MRFP).
Rev A
07.12.2004
5
Antti Miettinen
Background (3/3)
• This means:
– The MGC and the MRFC handles the call control while the MGW
and the MRFP handles the media and the bearer control.
– The MGC and MRFC steer and control the calls through the MGW
and the MRFP with help of the GCP
Rev A
07.12.2004
6
Antti Miettinen
Problem Description
• The GCP traffic analysis has an essential role in
troubleshooting the network anomalies
• By analyzing the GCP traffic, the past status and the
prevailing operations of the network node can be revealed
• However, the GCP messages are big and frequent. Thus,
the protocol traffic analysis is a heavy process.
• The research problem of this thesis is to find out an
efficient method to analyze the GCP protocol traffic to
troubleshoot the network nodes
Rev A
07.12.2004
7
Antti Miettinen
Objectives
• The objective of this study is to find out efficient methods
to analyze the H.248 Gateway Control Protocol signaling
traffic to be able to troubleshoot the network nodes
efficiently.
Rev A
07.12.2004
8
Antti Miettinen
Scope
• Different methods to efficiently analyze the H.248 protocol
traffic are explored. Those methods are mapped to
protocol traffic analyzer requirements.
• Only open source analyzers are explored
– The source code is available => modifications to the analyzer can
be done to meet the requirements better
– No license fees
– Commercial products do not distribute fully functional demo
versions => no real evaluation can be done
• An protocol traffic analyzer is selected as a
recommendation for the H.248 protocol traffic analysis
Rev A
07.12.2004
9
Antti Miettinen
UMTS
Release 5
Network
AuC
BSC
BSS
BTS
CN
CS
EIR
GGSN
GMSC
HLR
ME
MGW
MS
MSC
PS
PSTN
RNC
RNS
SGSN
SIM
USIM
VLR
Authentication Centre
Base Station Controller
Base Station System
Base Transceiver Station
Core Network
Circuit Switched
Equipment Identity Register
Gateway GPRS Support Node
Gateway Mobile Switching Centre
Home Location Register
Mobile Equipment
Media Gateway
Mobile Station
Mobile Switching Centre
Packet Switched
Public Switched Telephone Network
Radio Network Controller
Radio Network Subsystem
Serving GPRS Support Node
Subscriber Identity Module
User Services Identity Module
Visitor Location Register
Rev A
07.12.2004
10
Antti Miettinen
H.248 Gateway Control Protocol (1/5)
• Connection model
– The most important abstractions are the Contexts, Terminations
and Streams
= the direction of a media flow
= a stream
Tx
= termination x
MGW
Context1
Context2
T2
T1
Rev A
Context3
T2
T3
T1
07.12.2004
T2
T3
11
T1
T3
Antti Miettinen
H.248 Gateway Control Protocol (2/5)
• Message structure
– GCP message has a
modular structure
GCP message
Transaction1
Action1
Command1
Action2
TopologyDescriptor
Action3
Command1
Command2
Command3
Command4
Command2
Transaction2
Action1
Rev A
07.12.2004
12
Command1
MediaDescriptor
Antti Miettinen
H.248 Gateway Control Protocol (3/5)
• Messages
– Large when presented in human readable form
– Transaction request (easily >100 lines) bigger than transaction
replies
• Replies do not usually contain descriptors
• Signaling traffic asymmetric
– Treelike hierarchy
• Transactions
• Actions
• Commands
• Descriptors
Rev A
07.12.2004
13
Antti Miettinen
H.248 Gateway Control Protocol (4/5)
•
Possible errors situations
1. H.248.8 packet defines 60 different error descriptor
• e.g. “Unknown TerminationID”, error code 430 or “insufficient
bandwidth”, error code 526.
• Network node might end up to an unspecified state (the failed
command remains half executed)
• Must be taken into account when searching reasons for
network node anomalies
Rev A
07.12.2004
14
Antti Miettinen
H.248 Gateway Control Protocol (5/5)
•
Possible errors situations (cont.)
2. Unclosed transactions
• May realize in case of unreliable signaling connection
• GCP specifies the three timers to prevent this but they are not
100% sure
Rev A
07.12.2004
15
Antti Miettinen
H.248 Protocol Traffic Analysis (1/3)
• Data Presentation Format
– “Overview first, zoom and filter, then details-on-demand”, Ben
Shneiderman
– The call related parameters should be shown in their own columns
in the overview part:
• transactionId, contextId, command type, terminationID and
wildcard
– Scroll bars, colored messages (e.g. error messages), colored
barplots and tool tips
Rev A
07.12.2004
16
Antti Miettinen
H.248 Protocol Traffic Analysis (2/3)
• Filtering Functions
– One of the most important features needed in troubleshooting
• Sorting Functions
– Basic function
– Implemented in every analyzer
• Monitoring Functions
– Error descriptors in messages
– Unclosed transactions
Rev A
07.12.2004
17
Antti Miettinen
H.248 Protocol Traffic Analysis (3/3)
• Summary Function
– Shows the key information about the traffic, e.g.
• The number of transaction requests, replies and pendings
• The number of errored messages
• The number of completed and uncompleted transactions
Rev A
07.12.2004
18
Antti Miettinen
H.248 Protocol Traffic Analyzers (1/2)
• Only open source analyzers explored
• Examined analyzers:
–
–
–
–
TcpDump & WinDump
Ethereal
Analyzer
Packetyzer
Rev A
07.12.2004
19
Antti Miettinen
H.248 Protocol Traffic Analyzers (2/2)
• Recommendation:
– Ethereal
• Meets the requirements of the H.248 protocol traffic analysis
best
• Actively developed
• Missing features: H.248 specific columns, monitoring functions,
summary function, colored barplots
Rev A
07.12.2004
20
Antti Miettinen
Rev A
07.12.2004
21
Antti Miettinen
Conclusion and Future Work
• Topics for future work:
– Implement the missing requirements to Ethereal
– Explore the commercial analyzers if they are even more suitable
for the H.248 traffic analysis
Rev A
07.12.2004
22
Antti Miettinen
Thank you!
Questions or comments?
Rev A
07.12.2004
23
Antti Miettinen