CTCP (Circuit TCP) v1.0

Transcription

1 Outline C (Circuit ) v1.0 Helali Bhuiyan and Malathi Veeraraghavan {helali,mv5g}@virginia.edu Purpose of C Requirements to run C code C Components C Operation C details C Usage Usage of C across an Internet path 1 2 Introduction Purpose of C What is C? It is a transport protocol for dedicated end to end circuits. Implemented by disabling congestion control. Why C? Bandwidth is reserved for an end to end circuit in a call setup phase. Therefore there is no contention for resources (no congestion) in the data plane. C maintains a constant sending rate matched with the reserved bandwidth of the circuit. What does it do? Converts a socket into a C socket disabling congestion control algorithm. What it does not do Setup a circuit between end hosts. routers routers Host1 Host2 I GbE GbE I CHEETAH Network Circuit Network (dynamically setup and Sycamore SN16000 SONET Sycamore SN16000 released) Atlanta, GA MCNC, NC C was developed for use in the CHEETAH ( network. Each host in CHEETAH is equipped with two NIC cards. The primary NIC is connected to the internet; it is used to carry control-plane messages. The secondary NIC (data plane) is connected to the CHEETAH network. connections set up between two Is that are connected via a circuit are configured to operate in C mode 3 4 1

2 Requirements for C C Components Kernel ed with the corresponding ( Plans are underway to upgrade C to Kernel Space C that modifies regular inside the kernel disabling the congestion control algorithm. User Space This is a user-space application which runs as a daemon. It communicates with the kernel via. Tester A users space application to submit a request for a C connection configuration. 5 6 C Modifies both kernel code and Web100 code Details of the C will be provided later Usage: Compile kernel with this This application runs as a daemon on both sending and receiving hosts. Listens on a UNIX socket for messages carrying the following parameters: Source address Destination address Sending Rate polls the code in a loop awaiting the creation of connections between the specified source address and destination address. Upon detection of a new connection between the specified source and destination addresses, it sets parameters related to the sending rate

3 This application has two parts: Front End () Back End () forks creates three sockets A Unix socket to listen for a C connection configuration request from an external application like tester. A Unix socket to communicate with the. An Inet socket to communicate with the on the remote end of the C connection. Then it starts listening on these sockets When receives a C connection configuration request from tester, it does two things Tell its to look for a connection that matches the connection specification (source and destination addresses) received from the tester. Sends the connection specification to the remote host s s Tester The remote then tells its to look for the same tcp connection. Both the s check periodically in / directory for the appearance of any connection that matches the specification. If a matching connection exists: does the following Disables the congestion control algorithm for that socket by setting a new parameter called WAD_Cheetah Extracts the rtt (round trip time) measurement (in milliseconds) from for the specified source-destination pair Calculates required bdp (bandwidth-delay product) in packets to maintain the sending rate (in Mbps). bdp = (cktrate * rtt * 1000)/(8 * PKT_SIZE) + 1) Set computed bdp in a second new parameter, WAD_Bdp. Congestion window (cwnd) variable is ignored and WAD_Bdp is used to maintain the sending rate. On the receiver side, advertised window (rwnd) is clamped to the WAD_Bdp value. This is a simple application that tells the which socket to configure for operation as a C socket. Passes source address and destination address and sending rate (in Mbps) to. All connections between this source and destination addresses will be configured as C sockets

4 Outline C Operation Purpose of C Requirements to run C code C Components C Operation C Patch details C Usage Usage of C across an Internet path I I Setup a circuit Initiate I I I I

5 {Source & Destination addresses, Send rate} tester Run tester with connection specification sends connection specification to remote host I I I I provides connection specification for which to monitor socket creations Run user application I I I I

6 User application creates a socket finds the socket and configures it into a C connection I I I I Outline C Patch for Purpose of C Requirements to run C code C Components C Operation C Patch details C Usage Usage of C across an Internet path 23 uses to disable the congestion control algorithm from being executed on a particular connection. Two new writable variables are added to the to modify a connection s behavior WAD_Bdp Denotes the sending rate. WAD_Cheetah A boolean variable to identify whether this a socket or a C socket. 24 6

7 C Patch for Kernel Outline Modifications are made to to disable the congestion control algorithm. tcp.h, tcp_input.c and tcp_output.c files are modified for this purpose. If WAD_Cheetah == 1 Before sending each packet, sender bypasses the comparison of the current in_flight_packets with cwnd value Instead it compares the WAD_Bdp value with current in_flight_packets New packets are allowed to be sent if in_flight_packets <= WAD_Bdp Hence slow start and other congestion avoidance algorithms are disabled and a constant sending rate is maintained. Purpose of C Requirements to run C code C Components C Operation C Patch details C Usage Usage of C across an Internet path C Usage: Overview C Usage: Ensure that kernel v modified by and C is running. Run on both end hosts as a daemon. Start tester on either host Start application that creates a connection Run on both end hosts as a daemon. <Control_Plane_> & Control_Plane_: address of the primary NIC - see Slide 4 For example, if control-plane addresses of the sender and receiver are and , respectively, run as follows Sending Host: & Receiving Host: &

8 C Usage: tester Tester is invoked as tester <Data_Plane_> <Remote_Data_Plane_> <sending_rate(in Mbps)> <Remote_Control_Plane_> Data_Plane_: address of the secondary NIC (see Slide 4) of the host on which tester is executed Remote_Data_Plane_: address of the secondary NIC of the remote host If a sending rate of 512 Mbps is required, tester can be invoked as./tester : secondary NIC address of host on which tester is executed : secondary NIC address of remote host : primary NIC address of remote host C Usage: Application Run your application which needs a C connection. For example, if you want to use iperf for data transmission, invoke iperf as follows On server side iperf -s On client side iperf -c This will create a pair of connected sockets between these two hosts s running on both machines will detect the creation of these sockets and configure them into C sockets The receiver side will always advertise a fixed receive window (rwnd). The sender side will always keep WAD_Bdp amount of data outstanding on the network C Usage: Rate specification configures all connections created between the sender and destination whose addresses are provided by the tester If there are multiple connections between two end hosts, all of them will be configured as C connections with the same sending rate. This will cause packet loss if the aggregate sending rate is higher than the reserved bandwidth. To use multiple C connections, one should ensure that Aggregate sending rate <= circuit rate. For example, two C connections with rate 300Mbps can be used over a 600Mbps circuit. Here invoke tester as tester Usage of C across an Internet path Since C was designed for usage on dedicated circuits, using it across a connectionless path could result in buffer overflows at routers since the sender persists in sending at a fixed (usually high) rate. As Internet hosts typically have only one NIC card (which means there are no separate data-plane and control-plane addresses), to use C across the Internet Invoke on sender as & Invoke on receiver as & Invoke tester as - tester Where x is the corresponding host NIC's address and 100 is the sending rate in Mbps. Tip: Measure available bandwidth using tools such as iperf or pathload and then use this value as the sending rate