BBR' source code and test scripts for ns-3 (version 3.27).

See the WNS3 Workshop paper (CCL18b) for a peer-reviewed overview.

See the Technical Report (CCL18a) for details.

-- Mark Claypool [email protected]

Directories | Install | Misc | ToDo | Referenes

tests/ - test scripts for BBR'.

src/ - BBR' source code and ns-3 source files that need changes.

patch/ - directory with patchfile for ns-3 allinone tree.

These instructions are to install BBR' to the ns-allinone package (version 3.27). Mileage may vary for alternate uses.

ROOT = ns-3 all-in-one directory

e.g., /home/claypool/ns-allinone-3.27

REPO = this git repository

To install, either see Applying Repository Patch or Linking to Repository.

0. Download the latest "all in one" zip file from:

   https://www.nsnam.org/releases/

1. Extract:

   tar xvjf *.tar.bz2

2. Apply patch:

   patch -p0 < REPO/patch/*.patch

3. Go to ROOT and build:

   cd ROOT/

   ./build.py --enable-examples --enable-tests

4. Run and analyze. Example:

   cd ROOT/ns-3.27/

   ./waf --run bulk

0. Download the latest "all in one" zip file from:

   https://www.nsnam.org/releases/

1. Extract:

   tar xvjf *.tar.bz2

2. Go to ROOT and build:

   cd ROOT/

   ./build.py --enable-examples --enable-tests

3. Go to ROOT source(s) and link in BBR' and supporting files:

   cd ROOT/ns-3.27/src/internet/model

   ln -s REPO/src/bbr/*.cc .

   ln -s REPO/src/bbr/*.h .

   ln -sf REPO/src/internet/*.cc .

   ln -sf REPO/src/internet/*.h .

   ln -sf REPO/src/internet/*.h .

(If using APP_PACING config, do below):

cd ROOT/ns-3.27/src/applications/model

ln -sf REPO/src/applications/*.cc .

ln -sf REPO/src/applications/*.h .

4. Edit script file to build BBR':

   edit ROOT/ns-3.27/src/internet/wscript

Add (line 152):

    'model/tcp-bbr.cc',

    'model/tcp-bbr-state.cc',

Add (line 380):

      'model/tcp-bbr.h',

      'model/tcp-bbr-state.h',

5. Link BBR' script test:

   cd ROOT/ns-3.27/examples/

   ln -s REPOSITORY/bbr-tests .

6. Run and analyze. Example:

   cd ROOT/ns-3.27/

   ./waf --run bulk

There are three possible pacing configurations for BBR':

1. TCP_PACING. Packet pacing is done in TCP, as per the BBR' Technical Report CCL18a. This is the default configuration.

2. APP_PACING. Packet pacing is NOT done in TCP. BBR changes the pacing rate and still expects packets to be paced, but in this configuration, the application layer must do the pacing. The application directory provides a BulkSendApplication that does pacing.

3. NO_PACING. Pacing is not done at all. In this configuration, the BBR' code changes slightly. Instead of having a larger cwnd and having the pacing rate control the bandwidth, the cwnd itself is used to control the bandwidth. Thus, the cwnd is set to the BDP (with any needed gain adjustments) as the sole way of controlling the rate.

Configurations are controlled via PACING_CONFIG in:

ROOT/ns-3.27/src/internet/model/tcp-socket-base.h

e.g.,

const enum_pacing_config PACING_CONFIG = NO_PACING;

There are two possible configurations for the round-trip time used in culling the bandwidth window.

1. PACKET_TIME. Bandwidth window culling is done with a count of "packet-timed" round-trips, as described in CCYJ17. This is the default configuration.

2. WALLCLOCK_TIME. Bandwidth window culling is done using the wall-clock for timing. In this configuration, bandwidth estimates that are older than the minimum round-trip time are removed from the bandwidth window.

Time configurations for bandwidth culling are controlled via TIMING_CONFIG, defined in tcp-bbr.h. e.g.,

const enum_time_config TIME_CONFIG = PACKET_TIME;

Note, the fixed limits TCP receive and send buffers can restrict throughput for some ns-3 simulations (and real TCP connections). In order to have the congestion window (i.e., the bottleneck bandwidth) be the limit instead, the send/receive buffers can be increased from their defaults (128k in ns-3).

To do so, change the ns-3 attributes "SndBufSize" and "RcvBufSize" via script parameters. For example, to double the default size (131072 bytes):

Config::SetDefault("ns3::TcpSocket::RcvBufSize", UintegerValue(131072*2));

Config::SetDefault("ns3::TcpSocket::SndBufSize", UintegerValue(131072*2));

For reference, the source file that sets these values is:

ROOT/ns-3.27/src/internet/model/tcp-socket.cc

Below are BBR features not currently supported by BBR' (section numbers below refer to CCYJ17):

• BBR' assumes that the application always has data to send, thus the transmission rate is limited by the congestion control algorithm, not the application. BBR includes features to handle transmissions that are application-limited. See Section 4.1.1.4. This also means BBR' does not support restarting a flow from idle, a special case in BBR. See Section 4.3.4.4.

• BBR' only transitions to/from PROBE_RTT from PROBE_BW, while BBR has additional transitions for PROBE_RTT. See Section 4.3.5.

• BBR' does not include the "send quantum" in BBR which is used to amortize per-packet host overheads involved in the sending process. The send quantum parameter can be helpful at low rates with small packets. See Section 4.2.2.

[CCG+17] N. Cardwell, Y. Cheng, C.S. Gunn, S.H. Yeganeh, and V. Jacobson. BBR: Congestion-Based Congestion Control, Communications of the ACM, 60(2), February 2017.

[CCL18a] M. Claypool, J.W. Chung, and F. Li. "BBR' - An Implementation of Bottleneck Bandwidth and Round-trip Time Congestion Control for ns-3", Technical Report WPI-CS-TR-18-01, Computer Science, Worcester Polytechnic Institute, January 2018. Online: ftp://ftp.cs.wpi.edu/pub/techreports/pdf/18-01.pdf

[CCL18b] M. Claypool, J.W. Chung, and F. Li. BBR' - An Implementation of Bottleneck Bandwidth and Round-trip Time Congestion Control for ns-3, In Proceedings of the Workshop on ns-3 (WNS3), Mangalore, India, June 2018.

"BBR' - An Implementation of Bottleneck Bandwidth and Round-trip Time Congestion Control for ns-3", Technical Report WPI-CS-TR-18-01, Computer Science, Worcester Polytechnic Institute, January 2018. Online: ftp://ftp.cs.wpi.edu/pub/techreports/pdf/18-01.pdf

[CCYJ17] N. Cardwell, Y. Cheng, S. H. Yeganeh, and V. Jacobson. BBR Congestion Control, IETF Draft draft-cardwell-iccrg-bbr-congestion-control-00, July 2017.

Directories | Install | Misc | ToDo | Referenes